l3experimental 2966 (19nov11)

git-svn-id: svn://tug.org/texlive/trunk@24655 c570f23f-e606-0410-a88d-b1316a301751

16 files changed, 3208 insertions, 2226 deletions

diff --git a/Master/texmf-dist/doc/latex/l3experimental/l3str/l3regex.pdf b/Master/texmf-dist/doc/latex/l3experimental/l3str/l3regex.pdf
index 9ee837a7c92..0ddd7169a49 100644
--- a/Master/texmf-dist/doc/latex/l3experimental/l3str/l3regex.pdf
+++ b/Master/texmf-dist/doc/latex/l3experimental/l3str/l3regex.pdf
diff --git a/Master/texmf-dist/doc/latex/l3experimental/l3str/l3str.pdf b/Master/texmf-dist/doc/latex/l3experimental/l3str/l3str.pdf
index f4b06528802..d82842dca5f 100644
--- a/Master/texmf-dist/doc/latex/l3experimental/l3str/l3str.pdf
+++ b/Master/texmf-dist/doc/latex/l3experimental/l3str/l3str.pdf
diff --git a/Master/texmf-dist/doc/latex/l3experimental/xcoffins/xcoffins.pdf b/Master/texmf-dist/doc/latex/l3experimental/xcoffins/xcoffins.pdf
index b20f638d514..796242d76b6 100644
--- a/Master/texmf-dist/doc/latex/l3experimental/xcoffins/xcoffins.pdf
+++ b/Master/texmf-dist/doc/latex/l3experimental/xcoffins/xcoffins.pdf
diff --git a/Master/texmf-dist/doc/latex/l3experimental/xgalley/l3galley.pdf b/Master/texmf-dist/doc/latex/l3experimental/xgalley/l3galley.pdf
index 3cad13a681f..c238f89d86d 100644
--- a/Master/texmf-dist/doc/latex/l3experimental/xgalley/l3galley.pdf
+++ b/Master/texmf-dist/doc/latex/l3experimental/xgalley/l3galley.pdf
diff --git a/Master/texmf-dist/doc/latex/l3experimental/xgalley/xgalley.pdf b/Master/texmf-dist/doc/latex/l3experimental/xgalley/xgalley.pdf
index 38d903ad9fb..8e77fd9b96f 100644
--- a/Master/texmf-dist/doc/latex/l3experimental/xgalley/xgalley.pdf
+++ b/Master/texmf-dist/doc/latex/l3experimental/xgalley/xgalley.pdf
diff --git a/Master/texmf-dist/source/latex/l3experimental/l3str/l3regex.dtx b/Master/texmf-dist/source/latex/l3experimental/l3str/l3regex.dtx
index e2977e2b249..cb0476ac898 100644
--- a/Master/texmf-dist/source/latex/l3experimental/l3str/l3regex.dtx
+++ b/Master/texmf-dist/source/latex/l3experimental/l3str/l3regex.dtx
@@ -35,7 +35,7 @@
 %
 %<*driver|package>
 \RequirePackage{expl3}
-\GetIdInfo$Id: l3regex.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: l3regex.dtx 2943 2011-10-30 15:59:43Z bruno $
   {L3 Experimental Regular Expressions}
 %</driver|package>
 %<*driver>
@@ -68,7 +68,7 @@
 %
 % \begin{documentation}
 % \newenvironment{l3regex-syntax}
-%   {\begin{itemize}\def\makelabel##1{\hss\llap{\ttfamily\string##1}}}
+%   {\begin{itemize}\def\\{\char`\\}\def\makelabel##1{\hss\llap{\ttfamily##1}}}
 %   {\end{itemize}}
 %
 % \section{\pkg{l3regex} documentation}
@@ -91,15 +91,13 @@
 % by \enquote{\texttt{is}}. A more complicated example is
 % a pattern to add a comma at the end of each word:
 % \begin{verbatim}
-%   \regex_replace_all:nnN { (\w+) } { \1 , } \l_my_str
+%   \regex_replace_all:nnN { \w+ } { \0 , } \l_my_str
 % \end{verbatim}
 % The |\w| sequence represents any \enquote{word} character,
-% and |*| indicates that the |\w| sequence should be repeated
-% as many times as possible, hence matching a word in the
-% input string. The parentheses \enquote{capture} what their
-% contents matched in the input string, and this can be used
-% in the replacement text as |\1| (and higher numbers if several
-% groups are used in the regular expression).
+% and |+| indicates that the |\w| sequence should be repeated
+% as many times as possible (at least once), hence matching a word in the
+% input string. In the replacement text, |\0| denotes the full match
+% (here, a word).
 %
 % \subsection{Syntax of regular expressions}
 %
@@ -111,13 +109,11 @@
 % \begin{itemize}
 % \item every alphanumeric character (\texttt{A}--\texttt{Z},
 %   \texttt{a}--\texttt{z}, \texttt{0}--\texttt{9}) matches
-%   exactly itself, none of them should be escaped, because
-%   most of those escape sequences have special meanings;
-% \item non-alphanumeric printable ascii characters can always
-%   be safely escaped, and for highest portability, they should
-%   always be escaped (this avoids problems if some currently
-%   \enquote{normal} characters is given a meaning in later
-%   releases);
+%   exactly itself, and should not be escaped, because
+%   |\A|, |\B|, \ldots{} have special meanings;
+% \item non-alphanumeric printable ascii characters can (and should)
+%   always be escaped: many of them have special meanings (\emph{e.g.},
+%   |(|, |)|, |?|, |.|);
 % \item spaces should always be escaped (even in character
 %   classes);
 % \item any other character may be escaped or not, without any
@@ -138,88 +134,97 @@
 %
 % Characters.
 % \begin{l3regex-syntax}
-% \item[\x\{hh\ldots{}\}]
-%   Character with hex code \texttt{hh\ldots{}}
-% \item[\xhh]
-%   Character with hex code \texttt{hh}.
-% \item[\a] Alarm (hex 07).
-% \item[\e] Escape (hex 1B).
-% \item[\f] Form-feed (hex 0C).
-% \item[\n] New line (hex 0A).
-% \item[\r] Carriage return (hex 0D).
-% \item[\t] Horizontal tab (hex 09).
+%   \item[\\x\{hh\ldots{}\}] Character with hex code \texttt{hh\ldots{}}
+%   \item[\\xhh] Character with hex code \texttt{hh}.
+%   \item[\\a] Alarm (hex 07).
+%   \item[\\e] Escape (hex 1B).
+%   \item[\\f] Form-feed (hex 0C).
+%   \item[\\n] New line (hex 0A).
+%   \item[\\r] Carriage return (hex 0D).
+%   \item[\\t] Horizontal tab (hex 09).
 % \end{l3regex-syntax}
 %
 % Character types.
 % \begin{l3regex-syntax}
-% \item[.] A single period matches any character,
-%   including newlines.\footnote{Should that be changed?}
-% \item[\N] A character that is not
-%   the |\n| character (hex 0A).\footnote{Is that right?}
-% \item[\d] Any decimal digit.
-% \item[\h] Any horizontal space character,
-%   equivalent to |[\^^I\ ]|: space and tab.
-% \item[\s] Any space character,
-%   equivalent to |[\^^I\^^J\^^L\^^M\ ]|.
-% \item[\v] Any vertical space character,
-%   equivalent to |[\^^I-\^^M]|. Note that |\^^K| is a vertical space,
-%   but not a space, for compatibility with perl.
-% \item[\w] Any word character, \emph{i.e.},
-%   alpha-numerics and underscore, equivalent to |[A-Za-z0-9\_]|.
-% \item[\D] Any character not matched by |\d|.
-% \item[\H] Any character not matched by |\h|.
-% \item[\S] Any character not matched by |\s|.
-% \item[\V] Any character not matched by |\v|.
-% \item[\W] Any character not matched by |\w|.
+%   \item[.] A single period matches any character, including newlines.
+%   \item[\\d] Any decimal digit.
+%   \item[\\h] Any horizontal space character,
+%     equivalent to |[\ \^^I]|: space and tab.
+%   \item[\\s] Any space character,
+%     equivalent to |[\ \^^I\^^J\^^L\^^M]|.
+%   \item[\\v] Any vertical space character,
+%     equivalent to |[\^^J\^^K\^^L\^^M]|. Note that |\^^K| is a vertical space,
+%     but not a space, for compatibility with Perl.
+%   \item[\\w] Any word character, \emph{i.e.},
+%     alpha-numerics and underscore, equivalent to |[A-Za-z0-9\_]|.
+%   \item[\\D] Any character not matched by |\d|.
+%   \item[\\H] Any character not matched by |\h|.
+%   \item[\\N] Any character other than the |\n| character (hex 0A).
+%   \item[\\S] Any character not matched by |\s|.
+%   \item[\\V] Any character not matched by |\v|.
+%   \item[\\W] Any character not matched by |\w|.
 % \end{l3regex-syntax}
 %
 % Character classes match exactly one character in the subject string.
 % \begin{l3regex-syntax}
-% \item[{[...]}] Positive character class.
-% \item[{[\string^...]}] Negative character class.
-% \item[{[x-y]}] Range (can be used with escaped characters).
+%   \item[{[\ldots{}]}] Positive character class.
+%     Matches any of the specified characters.
+%   \item[{[\char`\^\ldots{}]}] Negative character class.
+%     Matches any character other than the specified characters.
+%   \item[{[x-y]}] Range (can be used with escaped characters).
 % \end{l3regex-syntax}
 %
-% Quantifiers.
+% Quantifiers (repetition).
 % \begin{l3regex-syntax}
-% \item[?] $0$ or $1$, greedy.
-% \item[??] $0$ or $1$, lazy.
-% \item[*] $0$ or more, greedy.
-% \item[*?] $0$ or more, lazy.
-% \item[+] $1$ or more, greedy.
-% \item[+?] $1$ or more, lazy.
-% \end{l3regex-syntax}
-% Not implemented yet: ^^A !
-% \begin{l3regex-syntax}\def\makelabel#1{\hss\llap{\ttfamily#1}}
-% \item[\{$n$\}] Exactly $n$.
-% \item[\{$n,$\}] $n$ or more, greedy.
-% \item[\{$n,$\}?] $n$ or more, lazy.
-% \item[\{$n,m$\}] At least $n$, no more than $m$, greedy.
-% \item[\{$n,m$\}?] At least $n$, no more than $m$, lazy.
+%   \item[?] $0$ or $1$, greedy.
+%   \item[??] $0$ or $1$, lazy.
+%   \item[*] $0$ or more, greedy.
+%   \item[*?] $0$ or more, lazy.
+%   \item[+] $1$ or more, greedy.
+%   \item[+?] $1$ or more, lazy.
+%   \item[\{$n$\}] Exactly $n$.
+%   \item[\{$n,$\}] $n$ or more, greedy.
+%   \item[\{$n,$\}?] $n$ or more, lazy.
+%   \item[\{$n,m$\}] At least $n$, no more than $m$, greedy.
+%   \item[\{$n,m$\}?] At least $n$, no more than $m$, lazy.
 % \end{l3regex-syntax}
 %
 % Anchors and simple assertions.
 % \begin{l3regex-syntax}
-% \item[\b] Word boundary.
-% \item[\B] Not a word boundary.
-% \item[^\string\A] Start of the subject string.\footnote{The
-%     multiline mode is not implemented yet, so those are currently
-%     identical.}
-% \item[$\string\Z\string\z] End of the subject
-%   string.\footnotemark[\thefootnote]
-% \item[\G] Start of the current match. This is only different from |^|
-%   in the case of multiple matches: for instance
-%   |\regex_count:nnN { \G a } { aaba } \l_tmpa_int| yields $2$, but
-%   replacing |\G| by |^| would result in \cs{l_tmpa_int} holding the
-%   value $1$.
+%   \item[\\b] Word boundary.
+%   \item[\\B] Not a word boundary.
+%   \item[\char`^ \textrm{or} \\A]
+%     Start of the subject string.
+%   \item[\char`$\textrm{,} \\Z \textrm{or} \\z]
+%     End of the subject string.
+%   \item[\\G] Start of the current match. This is only different from |^|
+%     in the case of multiple matches: for instance
+%     |\regex_count:nnN { \G a } { aaba } \l_tmpa_int| yields $2$, but
+%     replacing |\G| by |^| would result in \cs{l_tmpa_int} holding the
+%     value $1$.
 % \end{l3regex-syntax}
 %
 % Alternation and capturing groups.
 % \begin{l3regex-syntax}
-% \item[A\string|B\string|C] Either one of \texttt{A}, \texttt{B},
-%   or \texttt{C}.
-% \item[(\ldots{})] Capturing group.
-% \item[(?:\ldots{})] Non-capturing group.
+%   \item[A\char`|B\char`|C] Either one of \texttt{A}, \texttt{B},
+%     or \texttt{C}.
+%   \item[(\ldots{})] Capturing group.
+%   \item[(?:\ldots{})] Non-capturing group.
+% \end{l3regex-syntax}
+%
+% Options can be set with |(?|\meta{option}|)| and
+% unset with |(?-|\meta{option}|)|. Options are local
+% to the group in which they are set, and revert to their
+% previous setting upon reaching the closing parenthesis.
+% For instance, in \verb"(?i)a(b(?-i)c|d)e", the |i| option
+% applies to the letters |a|, |b| and |e|.
+% \begin{l3regex-syntax}
+%   \item[(?i) \textrm{and} (?-i)] Toggle to a case
+%     insensitive/sensitive mode. This only applies to ascii letters
+%     (mapping \texttt{A}--\texttt{Z} to \texttt{a}--\texttt{z}).
+%     For instance, |(?i)[Y-\\]| matches the characters |Y|, |Z|, |[|,
+%     |\|, and the lower case letters |y| and |z|, while |(?i)[^aeiou]|
+%     matches any character which is not a vowel.
 % \end{l3regex-syntax}
 %
 % In character classes, only |^|, |-|, |]|, |\| and spaces are special,
@@ -235,29 +240,23 @@
 % opening parenthesis, starting at $1$. The contents of those groups
 % corresponding to the \enquote{best} match (leftmost longest)
 % can be extracted and stored in a sequence of strings using for
-% instance \cs{regex_extract:nnNTF}.
+% instance \cs{regex_extract_once:nnNTF}.
 %
 % \subsection{Syntax of in the replacement text}
 %
 % Most of the features described in regular expressions do not make sense
 % within the replacement text. Escaped characters are supported as inside
-% regular expressions. The various submatches are accessed with |\1|, |\2|,
-% \emph{etc.}, and the whole match is accessed using |\0|.
+% regular expressions. The whole match is accessed as |\0|, and the first
+% $9$ submatches are accessed as |\1|, \ldots{}, |\9|. Submatches with
+% numbers higher than $9$ are accessed as |\g{|\meta{number}|}| instead.
 %
 % For instance,
 % \begin{verbatim}
-% \str_set:Nn \l_my_str { Hello,~world! }
-% \regex_replace_all:nnN { ([er]?l|o) . } { \(\0\-\-\1\) } \l_my_str
+%   \str_set:Nn \l_my_str { Hello,~world! }
+%   \regex_replace_all:nnN { ([er]?l|o) . } { \(\0\-\-\1\) } \l_my_str
 % \end{verbatim}
 % results in \cs{l_my_str} holding |H(ell--el)(o,--o) w(or--o)(ld--l)!|
 %
-% Submatches with numbers higher than $10$ are accessed in the same way,
-% namely |\10|, |\11|, \emph{etc}. To insert in the replacement text
-% a submatch followed by a digit, the digit must be entered using the
-% |\x| escape sequence: for instance, to get the first submatch followed
-% by the digit $7$, use |\1\x37|, because $7$ has character code |37|
-% (in hexadecimal).
-%
 % \subsection{Precompiling regular expressions}
 %
 % If a regular expression is to be used several times,
@@ -268,8 +267,7 @@
 % regular expression argument either as an explicit string
 % or as a precompiled regular expression.
 %
-% \begin{function}{\regex_set:Nn}
-% \begin{function}{\regex_gset:Nn}
+% \begin{function}{\regex_set:Nn, \regex_gset:Nn}
 %   \begin{syntax}
 %     \cs{regex_set:Nn} \meta{tl var} \Arg{regex}
 %   \end{syntax}
@@ -280,20 +278,23 @@
 %     \tl_new:N \l_my_regex_tl
 %     \regex_set:Nn \l_my_regex_tl { my\ (simple\ )? reg(ex|ular\ expression) }
 %   \end{verbatim}
-%   The assignment is local for \cs{regex_set:Nn}
-%   and global for \cs{regex_gset:Nn}.
+%   The assignment is local for \cs{regex_set:Nn} and global for
+%   \cs{regex_gset:Nn}.
 %   \begin{texnote}
 %     Precompiled regular expressions can be safely written to a file
 %     and read when the \LaTeX3 syntax is active (as triggered by
 %     \cs{ExplSyntaxOn}).
 %   \end{texnote}
 % \end{function}
-% \end{function}
 %
 % \subsection{String matching}
 %
-% \begin{function}[TF]{\regex_match:nn}
-% \begin{function}[TF]{\regex_match:Nn}
+% All regular expression functions are available in both |:n| and |:N|
+% variants. The former require a \enquote{standard} regular expression,
+% while the later require a precompiled expression as generated by
+% \cs{regex_(g)set:Nn}.
+%
+% \begin{function}[TF]{\regex_match:nn, \regex_match:Nn}
 %   \begin{syntax}
 %     \cs{regex_match:nnTF} \Arg{regex} \Arg{string} \Arg{true code} \Arg{false code}
 %   \end{syntax}
@@ -303,16 +304,15 @@
 %     \regex_match:nnTF { b [cde]* } { abecdcx } { TRUE } { FALSE }
 %     \regex_match:nnTF { [b-dq-w] } { example } { TRUE } { FALSE }
 %   \end{verbatim}
-%   leaves \texttt{TRUE FALSE} in the input stream.
-% \end{function}
+%   leaves \texttt{TRUE} then \texttt{FALSE} in the input stream.
 % \end{function}
 %
-% \begin{function}{\regex_count:nnN}
-% \begin{function}{\regex_count:NnN}
+% \begin{function}{\regex_count:nnN, \regex_count:NnN}
 %   \begin{syntax}
 %     \cs{regex_count:nnN} \Arg{regex} \Arg{string} \meta{int var}
 %   \end{syntax}
-%   Sets \meta{int var} equal to the number of times
+%   Sets \meta{int var} within the current \TeX{} group level
+%   equal to the number of times
 %   \meta{regular expression} appears in \meta{string}.
 %   The search starts by finding the left-most longest match,
 %   respecting greedy and ungreedy operators. Then the search
@@ -325,29 +325,26 @@
 %   \end{verbatim}
 %   results in \cs{l_foo_int} taking the value $5$.
 % \end{function}
-% \end{function}
 %
 % \subsection{Submatch extraction}
 %
-% \begin{function}{\regex_extract:nnN}
-% \begin{function}{\regex_extract:NnN}
-% \begin{function}[TF]{\regex_extract:nnN}
-% \begin{function}[TF]{\regex_extract:NnN}
+% \begin{function}[TF]{\regex_extract_once:nnN, \regex_extract_once:NnN}
 %   \begin{syntax}
-%     \cs{regex_extract:nnNTF} \Arg{regex} \Arg{string} \meta{seq~var} \Arg{true code} \Arg{false code}
+%     \cs{regex_extract_once:nnN} \Arg{regex} \Arg{string} \meta{seq~var}
+%     \cs{regex_extract_once:nnNTF} \Arg{regex} \Arg{string} \meta{seq~var} \Arg{true code} \Arg{false code}
 %   \end{syntax}
 %   Finds the first match of the \meta{regular expression}
 %   in the \meta{string}. If it exists, the match is stored
 %   as the zeroeth item of the \meta{seq~var}, and further
 %   items are the contents of capturing groups, in the order
-%   of their opening left parenthesis. The \meta{seq~var}
+%   of their opening parenthesis. The \meta{seq~var}
 %   is assigned locally. If there is no match,
 %   the \meta{seq~var} is not altered.
-%   The testing versions return \meta{true} if a match was found,
-%   and \meta{false} otherwise.
+%   The testing versions insert the \meta{true code} into the input
+%   stream if a match was found, and the \meta{false code} otherwise.
 %   For instance, assume that you type
 %   \begin{verbatim}
-%     \regex_extract:nnNTF { ^(La)?TeX(!*)$ } { LaTeX!!! }
+%     \regex_extract_once:nnNTF { ^(La)?TeX(!*)$ } { LaTeX!!! }
 %       \l_foo_seq { true } { false }
 %   \end{verbatim}
 %   Then the regular expression (anchored at the start with |^| and
@@ -357,14 +354,26 @@
 %   the items |{LaTeX!!!}|, |{La}|, and |{!!!}|, and the \texttt{true}
 %   branch is left in the input stream.
 % \end{function}
-% \end{function}
-% \end{function}
+%
+% \begin{function}[TF]{\regex_extract_all:nnN, \regex_extract_all:NnN}
+%   \begin{syntax}
+%     \cs{regex_extract_all:nnNTF} \Arg{regex} \Arg{string} \meta{seq~var} \Arg{true code} \Arg{false code}
+%   \end{syntax}
+%   Finds all matches of the \meta{regular expression}
+%   in the \meta{string}, and stores all the submatch information
+%   in a single sequence (concatenating the results of
+%   multiple \cs{regex_extract_once:nnN} calls).
+%   For instance, assume that you type
+%   \begin{verbatim}
+%     \regex_extract_all:nnN { \w+ } { Hello,~world! } \l_foo_seq
+%   \end{verbatim}
+%   Then the regular expression will match twice, and the resulting
+%   sequence contains the two items \texttt{Hello} and \texttt{world}.
 % \end{function}
 %
 % \subsection{String splitting}
 %
-% \begin{function}{\regex_split:nnN}
-% \begin{function}{\regex_split:NnN}
+% \begin{function}{\regex_split:nnN, \regex_split:NnN}
 %   \begin{syntax}
 %     \cs{regex_split:nnN} \Arg{regular expression} \meta{string} \meta{seq~var}
 %   \end{syntax}
@@ -375,15 +384,18 @@
 %   If no match is found the resulting \meta{seq~var} has the \meta{string} as
 %   its sole item. If the \meta{regular expression} matches the empty string,
 %   then the \meta{string} is split into single character substrings.
-% \end{function}
+%   For example, after
+%   \begin{verbatim}
+%     \seq_new:N \l_path_seq
+%     \regex_split:nnN { / } { the/path/for/this/file.tex } \l_path_seq
+%   \end{verbatim}
+%   the sequence |\l_path_seq| contains the items |{the}|, |{path}|,
+%   |{for}|, |{this}|, and |{file.tex}|.
 % \end{function}
 %
 % \subsection{String replacement}
 %
-% \begin{function}{\regex_replace_once:nnN}
-% \begin{function}{\regex_replace_once:NnN}
-% \begin{function}[TF]{\regex_replace_once:nnN}
-% \begin{function}[TF]{\regex_replace_once:NnN}
+% \begin{function}[TF]{\regex_replace_once:nnN,\regex_replace_once:NnN}
 %   \begin{syntax}
 %     \cs{regex_replace_once:nnN} \Arg{regular expression} \Arg{replacement} \meta{str~var}
 %   \end{syntax}
@@ -393,12 +405,8 @@
 %   |\0| represents the full match, |\1| represent the contents
 %   of the first capturing group, |\2| of the second, \emph{etc.}
 % \end{function}
-% \end{function}
-% \end{function}
-% \end{function}
 %
-% \begin{function}{\regex_replace_all:nnN}
-% \begin{function}{\regex_replace_all:NnN}
+% \begin{function}{\regex_replace_all:nnN, \regex_replace_all:NnN}
 %   \begin{syntax}
 %     \cs{regex_replace_all:nnN} \Arg{regular expression} \Arg{replacement} \meta{str~var}
 %   \end{syntax}
@@ -407,53 +415,42 @@
 %   |\0| represents the full match, |\1|
 %   represent the contents of the first capturing group,
 %   |\2| of the second, \emph{etc.} Every match
-%   is treated independently. The result is assigned
-%   locally to \meta{str~var}.
-% \end{function}
+%   is treated independently, and matches cannot overlap.
+%   The result is assigned locally to \meta{str~var}.
 % \end{function}
 %
 % \subsection{Bugs, misfeatures, future work, and other possibilities}
 %
-% The \texttt{\{\}} quantifiers are not implemented.
-%
-% The following need discussion.
+% The following need to be done now.
 % \begin{itemize}
+% \item The \texttt{\{\}} quantifiers are only partially implemented.
+% \item Space's catcode wrong in the result of a replacement!
 % \item Newline conventions are not done.
 %   In particular, |.| should not match newlines.
 %   Also, |\A| should differ from |^|, and |\Z|, |\z| and |$| should
 %   differ.
-% \item Caseless matching and more generally
-%   |(*..)| and |(?..)| sequences to set some options.
-% \item General look-ahead/behind assertions.
-% \item Idea of |#| as a synonym of |.*?|.
-% \item Do we need a facility for balanced groups? (That's non-regular.)
 % \end{itemize}
 %
 % The following features are likely to be implemented at some point
 % in the future.
 % \begin{itemize}
+% \item General look-ahead/behind assertions.
+% \item Regex matching on external files.
+% \item Conditional subpatterns with look ahead/behind: \enquote{if
+%     what follows is [\ldots{}], then [\ldots{}]}.
+% \item \verb"(?|..|..)" to reset the capturing group number at the start
+%   of each alternative.
+% \item |(*..)| and |(?..)| sequences to set some options.
+% \item Reduce the number of epsilon-transitions in alternatives.
 % \item Optimize simple strings: use less states
 %   (|abcade| should give two states, for |abc| and |ade|).
 % \item Optimize groups with no alternative.
 % \item Optimize the use of \cs{prg_stepwise_...} functions.
-% \item Implement regex matching on external files.
-% \item Conditional subpatterns with look ahead/behind: \enquote{if
-%     what follows is [\ldots{}], then [\ldots{}]}.
-% \item "(?|..|..)" to reset the capturing group number at the start
-%   of each alternative.
-% \item Todo: check space's catcode in the result of a replacement.
+% \item |\K| for resetting the beginning of the match.
+% \item UTF-8 mode for pdf\TeX{}.
 % \end{itemize}
 %
-% The following features not present in PCRE nor perl (because they can
-% be done in other ways in those languages) might be added.
-% \begin{itemize}
-% \item |#| as a synonym of |.*?|, in a way similar to macro parameters.
-% \item Facility to match balanced groups: this is non-regular, but quite
-%   useful, and it can be implemented without too much performance loss.
-%   (\emph{cf.} callout?)
-% \end{itemize}
-%
-% The following features of PCRE or perl will probably not be implemented.
+% The following features of PCRE or Perl will probably not be implemented.
 % \begin{itemize}
 % \item Other forms of escapes, and character classes.
 %   |\cx|$\simeq$|\^^x|, |\ddd| (octal \texttt{ddd}).
@@ -465,7 +462,7 @@
 %   or look-behind condition): this is non-regular, isn't it?
 % \end{itemize}
 %
-% The following features of PCRE or perl will not be implemented.
+% The following features of PCRE or perl will definitely not be implemented.
 % \begin{itemize}
 % \item Comments: \TeX{} already has its own system for comments.
 % \item Named subpatterns: \TeX{} programmers have lived so far without
@@ -482,9 +479,9 @@
 % \item Back-references: non-regular feature, this requires backtracking,
 %   which is prohibitively slow.
 % \item Backtracking control verbs: intrinsically tied to backtracking.
-% \item |\K| for resetting the beginning of the match: tied to backtracking.
-% \item |\C| single byte in UTF-8 mode: well, UTF-8 mode is not
-%   implemented, and that seems like a very rarely useful feature anyways.
+% \item |\C| single byte in UTF-8 mode: Xe\TeX{} and Lua\TeX{} serve
+%   us characters directly, and splitting those into bytes is tricky,
+%   encoding dependent, and most likely not useful anyways.
 % \end{itemize}
 %
 % \end{documentation}
@@ -521,9 +518,28 @@
 %
 % \subsection{Constants and variables}
 %
+% \begin{variable}
+%   {
+%     \c_forty_eight, \c_fifty_eight, \c_sixty_five, \c_ninety_one,
+%     \c_ninety_seven, \c_one_hundred_twenty_three,
+%     \c_one_hundred_twenty_seven
+%   }
+%   We declare here some integer values which delimit ranges of
+%   ASCII characters of various types.
+%    \begin{macrocode}
+\int_const:Nn \c_forty_eight  { 48 }
+\int_const:Nn \c_fifty_eight  { 58 }
+\int_const:Nn \c_sixty_five   { 65 }
+\int_const:Nn \c_ninety_one   { 91 }
+\int_const:Nn \c_ninety_seven { 97 }
+\int_const:Nn \c_one_hundred_twenty_three { 123 }
+\int_const:Nn \c_one_hundred_twenty_seven { 127 }
+%    \end{macrocode}
+% \end{variable}
+%
 % \begin{macro}{\regex_tmp:w}
-% \begin{variable}{\g_regex_tmpa_tl,\l_regex_tmpa_tl,\l_regex_tmpb_tl}
-% \begin{variable}{\l_regex_tmpa_int}
+% \begin{variable}{\g_regex_tmpa_tl, \l_regex_tmpa_tl, \l_regex_tmpb_tl}
+% \begin{variable}{\l_regex_tmpa_int, \l_regex_tmpb_int}
 %   Temporary variables.
 %    \begin{macrocode}
 \cs_new:Npn \regex_tmp:w { }
@@ -531,6 +547,7 @@
 \tl_new:N   \l_regex_tmpa_tl
 \tl_new:N   \l_regex_tmpb_tl
 \int_new:N  \l_regex_tmpa_int
+\int_new:N  \l_regex_tmpb_int
 %    \end{macrocode}
 % \end{variable}
 % \end{variable}
@@ -538,16 +555,8 @@
 %
 % \subsubsection{Variables used while building}
 %
-% \begin{variable}{\l_regex_pattern_str}
-%   The \meta{pattern} is stored in a string variable.
-%    \begin{macrocode}
-\tl_new:N  \l_regex_pattern_str
-%    \end{macrocode}
-% \end{variable}
-%
 % \begin{variable}{\l_regex_max_state_int}
-% \begin{variable}{\l_regex_left_state_int,\l_regex_right_state_int}
-% \begin{variable}{\l_regex_left_state_seq,\l_regex_right_state_seq}
+% \begin{variable}{\l_regex_left_state_int, \l_regex_right_state_int}
 %   The last state that was allocated is stored in \cs{l_regex_max_state_int},
 %   and \cs{l_regex_left/right_state_int} point to both end-points of the
 %   last group (which any quantifier would repeat). For simple strings of
@@ -556,21 +565,29 @@
 \int_new:N  \l_regex_max_state_int
 \int_new:N  \l_regex_left_state_int
 \int_new:N  \l_regex_right_state_int
-\seq_new:N  \l_regex_left_state_seq
-\seq_new:N  \l_regex_right_state_seq
 %    \end{macrocode}
 % \end{variable}
 % \end{variable}
+%
+% \begin{variable}{\l_regex_group_begin_seq, \l_regex_group_end_seq}
+%   Alternatives are implemented by branching from a state into the
+%   various choices, then merging those into another state. We store
+%   information about those states in two sequences (several can be
+%   active at the same time when nesting groups).
+%    \begin{macrocode}
+\seq_new:N  \l_regex_group_begin_seq
+\seq_new:N  \l_regex_group_end_seq
+%    \end{macrocode}
 % \end{variable}
 %
 % \begin{variable}{\l_regex_capturing_group_int}
 % \begin{variable}{\l_regex_capturing_group_seq}
-%   \cs{l_regex_capturing_group_int} is the id number of the current
+%   \cs{l_regex_capturing_group_int} is the ID number of the current
 %   capturing group, starting at $0$ for a group enclosing the full
 %   regular expression, and counting in the order of their left parenthesis.
 %   This number is used when a branch of the alternation ends.
 %   Capturing groups can be arbitrarily nested, and we keep track of
-%   the stack of id numbers in \cs{l_regex_capturing_group_seq}.
+%   the stack of ID numbers in \cs{l_regex_capturing_group_seq}.
 %    \begin{macrocode}
 \int_new:N  \l_regex_capturing_group_int
 \seq_new:N  \l_regex_capturing_group_seq
@@ -588,33 +605,17 @@
 %    \end{macrocode}
 % \end{variable}
 %
-% \begin{variable}{l_regex_repetition_int}
-%   Used when to distinguish threads at the same state but with
-%   different repetitions of some quantifiers.
-%    \begin{macrocode}
-\int_new:N  \l_regex_repetition_int
-%    \end{macrocode}
-% \end{variable}
-%
-% \begin{variable}{\l_regex_look_behind_bool}
-% \begin{variable}{\l_regex_look_behind_str}
-%   The boolean \cs{l_regex_look_behind_bool} indicates whether
-%   a look-behind assertion appears within the regular expression
-%   (currently only |\b| or |\B|). When matching, we will keep
-%   track of the part of the string before the current character
-%   in \cs{l_regex_look_behind_str}, stored backwards.
-%    \begin{macrocode}
-\bool_new:N \l_regex_look_behind_bool
-\tl_new:N \l_regex_look_behind_str
-%    \end{macrocode}
-% \end{variable}
-% \end{variable}
-%
 % \subsubsection{Character classes}
 %
 % \begin{macro}{\regex_build_tmp_class:n}
 % \begin{variable}{\l_regex_class_bool,\l_regex_class_tl}
-%   Used when building character classes.
+%   \cs{l_regex_class_bool} is false for negative character classes.
+%   \cs{l_regex_class_tl} holds the tests which should be performed
+%   to decide whether the \cs{l_regex_current_char_int} matches that
+%   character class. Once the class is read completely, the full
+%   instructions are stored in \cs{regex_build_tmp_class:n}, whose
+%   argument is the target state if the test succeeds. It is also used
+%   for all other single-character situations (\emph{e.g.}, |\d|, or |.|).
 %    \begin{macrocode}
 \cs_new_eq:NN \regex_build_tmp_class:n \use_none:n
 \bool_new:N \l_regex_class_bool
@@ -633,73 +634,73 @@
 %   are recognized by |\d|, |\D|, |\w|, \emph{etc.}
 %   in regular expressions. Namely, |\d=[0-9]|,
 %   |\w=[0-9A-Z_a-z]|, |\s=[\ \^^I\^^J\^^L\^^M]|,
-%   |\h=[\ \^^I]|, |\v=[\^^J-\^^M]|, and the upper-case
-%   counterparts match anything that the lowercase
+%   |\h=[\ \^^I]|, |\v=[\^^J-\^^M]|, and the upper case
+%   counterparts match anything that the lower case
 %   does not match.
 %   The order in which the various ranges appear is
-%   optimized for usual mostly lowercase letter text.
+%   optimized for usual mostly lower case letter text.
 %    \begin{macrocode}
 \tl_const:Nn \c_regex_d_tl
   {
-    \regex_item_range:nn {48} {57} % 0--9
+    \regex_item_range:nn { \c_forty_eight } { 57 } % 0--9
   }
 \tl_const:Nn \c_regex_D_tl
   {
-    \regex_item_more:n {57} % 9
-    \regex_item_range:nn {0} {47} % 0
+    \regex_item_geq:n { \c_fifty_eight } % > `9
+    \regex_item_range:nn { \c_zero } { 47 } % 0
   }
 \tl_const:Nn \c_regex_h_tl
   {
-    \regex_item_equal:n {32} % space
-    \regex_item_equal:n {9}  % tab
+    \regex_item_equal:n { \c_thirty_two } % space
+    \regex_item_equal:n { \c_nine } % tab
   }
 \tl_const:Nn \c_regex_H_tl
   {
-    \regex_item_neq:n {32} % space
-    \regex_item_neq:n {9}  % tab
-    \regex_break_true:w
+    \regex_item_geq:n { 33 } % > space
+    \regex_item_range:nn { \c_ten } { 31 } % tab < ... < space
+    \regex_item_range:nn { \c_zero } { \c_eight } % < tab
   }
 \tl_const:Nn \c_regex_s_tl
   {
-    \regex_item_equal:n  {32}     % space
-    \regex_item_neq:n    {11}     % vtab
-    \regex_item_range:nn {9} {13} % tab, lf, vtab, ff, cr
+    \regex_item_equal:n  { \c_thirty_two } % space
+    \regex_item_range:nn { \c_nine } { \c_ten } % tab, lf
+    \regex_item_range:nn { \c_twelve } { \c_thirteen } % ff, cr
   }
 \tl_const:Nn \c_regex_S_tl
   {
-    \regex_item_more:n   {32}      % > space
-    \regex_item_range:nn {14} {31} % tab < ... < space
-    \regex_item_range:nn {0}  {8}  % < tab
-    \regex_item_equal:n  {11}      % vtab
+    \regex_item_geq:n    { 33 } % > space
+    \regex_item_range:nn { \c_fourteen } { 31 } % tab < ... < space
+    \regex_item_range:nn { \c_zero } { \c_eight } % < tab
+    \regex_item_equal:n  { \c_eleven } % vtab
   }
 \tl_const:Nn \c_regex_v_tl
   {
-    \regex_item_range:nn {10} {13} % lf, vtab, ff, cr
+    \regex_item_range:nn { \c_ten } { \c_thirteen } % lf, vtab, ff, cr
   }
 \tl_const:Nn \c_regex_V_tl
   {
-    \regex_item_more:n   {13}    % cr
-    \regex_item_range:nn {0} {9} % < lf
+    \regex_item_geq:n    { \c_fourteen } % >cr
+    \regex_item_range:nn { \c_zero } { \c_nine } % < lf
   }
 \tl_const:Nn \c_regex_w_tl
   {
-    \regex_item_range:nn {97} {122} % a--z
-    \regex_item_range:nn {65}  {90} % A--Z
-    \regex_item_range:nn {48}  {57} % 0--9
-    \regex_item_equal:n  {95}       % _
+    \regex_item_range:nn { \c_ninety_seven } { 122 } % a--z
+    \regex_item_range:nn { \c_sixty_five } { 90 } % A--Z
+    \regex_item_range:nn { \c_forty_eight } { 57 } % 0--9
+    \regex_item_equal:n  { 95 } % _
   }
 \tl_const:Nn \c_regex_W_tl
   {
-    \regex_item_range:nn  {0} {47} % <`0
-    \regex_item_range:nn {58} {64} % (`9+1)--(`A-1)
-    \regex_item_range:nn {91} {94} % (`Z+1)--(`_-1)
-    \regex_item_equal:n  {96}      % `
-    \regex_item_more:n  {122}      % z
+    \regex_item_range:nn { \c_zero } { 47 } % <`0
+    \regex_item_range:nn { \c_fifty_eight } { 64 } % (`9+1)--(`A-1)
+    \regex_item_range:nn { \c_ninety_one } { 94 } % (`Z+1)--(`_-1)
+    \regex_item_equal:n  { 96 } % `
+    \regex_item_geq:n    { \c_one_hundred_twenty_three } % z
   }
 \tl_const:Nn \c_regex_N_tl
   {
-    \regex_item_neq:n {10} % lf
-    \regex_break_true:w
+    \regex_item_geq:n { \c_eleven } % > lf
+    \regex_item_range:nn { \c_zero } { \c_nine } % < lf
   }
 %    \end{macrocode}
 % \end{variable}
@@ -711,43 +712,69 @@
 %
 % \subsubsection{Variables used when matching}
 %
-% \begin{variable}{\l_regex_query_str}
+% \begin{variable}{\l_regex_query_other_str}
 %   The string that is being matched.
+%   In that string, spaces have category code \enquote{other}.
 %    \begin{macrocode}
-\tl_new:N \l_regex_query_str
+\tl_new:N \l_regex_query_other_str
 %    \end{macrocode}
 % \end{variable}
 %
+% \begin{variable}{\l_regex_current_step_int}
 % \begin{variable}{\l_regex_start_step_int}
-%   In the case of multiple matches, \cs{l_regex_start_step_int}
-%   is equal to the position where the current match
-%   attempt began.
+% \begin{variable}{\l_regex_success_step_int}
+%   While reading through the query string, \cs{l_regex_current_step_int}
+%   is the position in the string. Each match begins at the position
+%   given by \cs{l_regex_start_step_int}. Whenever an execution thread
+%   succeeds, the corresponding step is stored into
+%   \cs{l_regex_success_step_int}, which will be the next starting step
+%   (except in the case of empty matches).
 %   \begin{macrocode}
+\int_new:N \l_regex_current_step_int
 \int_new:N \l_regex_start_step_int
+\int_new:N \l_regex_success_step_int
+%    \end{macrocode}
+% \end{variable}
+% \end{variable}
+% \end{variable}
+%
+% \begin{variable}{\l_regex_unique_step_int}
+%   In the case of repeated matches, \cs{l_regex_current_step_int}
+%   is reset to the end-position of the previous match. In contrast,
+%   \cs{l_regex_unique_step_int} is simply incremented to provide
+%   a unique number for each iteration of the matching loop. This
+%   is handy to attach each set of submatch information to a given
+%   iteration (and automatically discard it when it corresponds to
+%   a past iteration).
+%    \begin{macrocode}
+\int_new:N \l_regex_unique_step_int
 %    \end{macrocode}
 % \end{variable}
 %
 % \begin{variable}{\l_regex_current_char_int}
-% \begin{variable}{\l_regex_current_step_int}
-%   The character at the current position in the string,
-%   and the current position.
+% \begin{variable}{\l_regex_last_char_int}
+% \begin{variable}{\l_regex_case_changed_char_int}
+%   The character codes of the character at the current position
+%   in the string, and at the previous position, and the current
+%   character with its case changed (|A-Z|$\leftrightarrow$|a-z|).
+%   The \cs{l_regex_last_char_int} is used to test for word boundaries
+%   (|\b| and |\B|). The \cs{l_regex_case_changed_char_int} is
+%   only computed if the \enquote{case insensitive} option |(?i)|
+%   is used in the regex.
 %    \begin{macrocode}
 \int_new:N \l_regex_current_char_int
-\int_new:N \l_regex_current_step_int
+\int_new:N \l_regex_last_char_int
+\int_new:N \l_regex_case_changed_char_int
 %    \end{macrocode}
 % \end{variable}
 % \end{variable}
+% \end{variable}
 %
-% \begin{variable}{\l_regex_unique_step_int}
-%   This gives a unique identifier to every step in the loop over
-%   characters in the string. In the case of a single match, it is
-%   equal to \cs{l_regex_current_step_int}, but for multiple matches,
-%   it is not reset to the start of the next match, but incremented.
-%   A unique identifier is handy when considering whether a state of
-%   the automaton has been visited at that step or not, and when
-%   tracking submatch information.
+% \begin{variable}{\l_regex_caseless_bool}
+%   True if caseless matching is used within the regular expression.
+%   This controls whether \cs{l_regex_case_changed_char_int} is computed.
 %    \begin{macrocode}
-\int_new:N \l_regex_unique_step_int
+\bool_new:N \l_regex_caseless_bool
 %    \end{macrocode}
 % \end{variable}
 %
@@ -755,17 +782,37 @@
 %   For every character in the string, each of the active states is
 %   considered in turn.
 %   The variable \cs{l_regex_current_state_int} holds the state
-%   of the NFA which is currently considered.
+%   of the NFA which is currently considered: transitions are then
+%   given as shifts relative to the current state.
+%   In the case of groups with quantifiers,
+%   \cs{l_regex_current_state_int} is shifted to a fake value for
+%   transitions to point to the correct states.
 %    \begin{macrocode}
 \int_new:N \l_regex_current_state_int
+%    \end{macrocode}
+% \end{variable}
+%
+% \begin{variable}{\l_regex_current_submatches_prop}
+% \begin{variable}{\l_regex_success_submatches_prop}
+%   The submatches for the thread which lies at the
+%   \cs{l_regex_current_state_int} are stored in a property
+%   list variable. This property list is stored by
+%   \cs{regex_action_cost:n} into the \tn{toks} register
+%   for the target state of the transition. When a thread
+%   succeeds, this property list is copied to
+%   \cs{l_regex_success_submatches_prop} and only the last
+%   sucessful thread will remain there.
+%    \begin{macrocode}
 \prop_new:N \l_regex_current_submatches_prop
+\prop_new:N \l_regex_success_submatches_prop
 %    \end{macrocode}
 % \end{variable}
+% \end{variable}
 %
 % \begin{variable}{\l_regex_max_index_int}
 %   All the currently active states are kept in order of precedence
 %   in the \tn{skip} registers, which for our purpose serve as an array:
-%   the $i$-th item of the array is \tn{skip}$i$. The largest index used
+%   the $i$th item of the array is \tn{skip}$i$. The largest index used
 %   after treating the previous character is \cs{l_regex_max_index_int}.
 %   At the start of every step, the whole array is unpacked, so that the
 %   space can immediately be reused, and \cs{l_regex_max_index_int} reset
@@ -785,11 +832,25 @@
 %    \end{macrocode}
 % \end{macro}
 %
+% \begin{variable}{\l_regex_success_bool}
+%   The boolean \cs{l_regex_success_bool} is true if the current match
+%   attempt was successful.
+%    \begin{macrocode}
+\bool_new:N \l_regex_success_bool
+%    \end{macrocode}
+% \end{variable}
+%
 % \begin{macro}{\regex_last_match_empty:F}
-%   This function is most often \cs{use:n}, unless the current
-%   regular expression can match an empty string at the current
-%   position, and has already done so at the previous match attempt.
-%   The goal is to break infinite loops.
+% \begin{macro}[aux]{\regex_last_match_empty_no:F}
+% \begin{macro}[aux]{\regex_last_match_empty_yes:F}
+%   When doing multiple matches, we need to avoid infinite loops where
+%   each iteration matches the same empty string. When we detect such
+%   a situation, the next match attempt is shifted by one character.
+%   Namely, an empty match is discarded if it follows an empty match
+%   at the same position. If the previous match was non-empty,
+%   \cs{regex_last_match_empty:F} is simply \cs{use:n}, and keeps
+%   the match. If it was empty, then we test whether the new match
+%   has moved or not: if it has not, then the success is discarded.
 %    \begin{macrocode}
 \cs_new_protected:Npn \regex_last_match_empty_no:F #1 {#1}
 \cs_new_protected:Npn \regex_last_match_empty_yes:F
@@ -797,37 +858,25 @@
 \cs_new_eq:NN \regex_last_match_empty:F \regex_last_match_empty_no:F
 %    \end{macrocode}
 % \end{macro}
+% \end{macro}
+% \end{macro}
 %
-% \begin{variable}{\l_regex_success_bool}
-% \begin{variable}{\l_regex_success_step_int}
-% \begin{variable}{\l_regex_success_submatches_prop}
 % \begin{variable}{\l_regex_success_empty_bool}
-%   The booleans \cs{l_regex_success_bool} and
-%   \cs{l_regex_success_empty_bool} are true if the current match
-%   attempt was successful, and if the match was empty, respectively.
-%   The other two variables hold the step number at which the match
-%   was successful and a property list of submatches.
-%    \begin{macrocode}
-\bool_new:N \l_regex_success_bool
-\bool_new:N \l_regex_success_empty_bool
-\int_new:N  \l_regex_success_step_int
-\prop_new:N \l_regex_success_submatches_prop
-%    \end{macrocode}
-% \end{variable}
-% \end{variable}
-% \end{variable}
-% \end{variable}
-%
 % \begin{variable}{\l_regex_fresh_thread_bool}
-%   This boolean marks when the current thread has started from
-%   the beginning of the regular expression at this character,
-%   in other words, it is true if the current thread has matched
-%   an empty string so far (and we only care about this boolean
-%   when a thread succeeds, hence matching an empty string overall).
+%   When a match succeeds, \cs{l_regex_success_empty_bool}
+%   records whether it is empty. This information is used
+%   to initialize \cs{regex_last_match_empty:F} before
+%   starting the next match attempt.
+%   The boolean \cs{l_regex_fresh_thread_bool} is true
+%   when the current thread has started from the beginning of the
+%   regular expression at this character.
+%   This is probably suboptimal. Improvements welcome.
 %    \begin{macrocode}
+\bool_new:N \l_regex_success_empty_bool
 \bool_new:N \l_regex_fresh_thread_bool
 %    \end{macrocode}
 % \end{variable}
+% \end{variable}
 %
 % \subsubsection{Variables used for user functions}
 %
@@ -848,6 +897,15 @@
 %    \end{macrocode}
 % \end{variable}
 %
+% \begin{variable}{\g_regex_extract_all_seq}
+%   The \cs{regex_extract_all:nnN} function stores its result
+%   in that sequence variable before assigning it to the
+%   variable provided by the user.
+%    \begin{macrocode}
+\seq_new:N \g_regex_extract_all_seq
+%    \end{macrocode}
+% \end{variable}
+%
 % \begin{variable}{\g_regex_split_seq}
 %   The \cs{regex_split:nnN} function stores its result
 %   in that sequence variable before assigning it to the
@@ -909,59 +967,66 @@
 % \end{macro}
 % \end{macro}
 %
-% \subsubsection{Interrupting recursions}
+% \subsubsection{Unsafe substring extraction}
 %
-% \begin{macro}[int]{\regex_if_tail_stop:N}
-% \begin{macro}[int]{\regex_if_tail_error:Nn}
-%   Test for the end of the \meta{string}, and either stop
-%   or cause an error if it is reached.
+% \begin{macro}[int]{\regex_query_substr:NN}
+% \begin{macro}[aux]{\regex_query_substr_aux:nnn}
+%   Extracting submatches from the query string is done
+%   in a way similar to \cs{str_substr:Nnn}, but omitting
+%   most checks, hence faster.
 %    \begin{macrocode}
-\cs_new_eq:NN \regex_if_tail_stop:N \quark_if_recursion_tail_stop:N
-\cs_new_protected_nopar:Npn \regex_if_tail_error:Nn #1#2
-  { \quark_if_recursion_tail_stop_do:Nn #1 { \regex_build_error:n {#2} } }
+\cs_new_nopar:Npn \regex_query_substr:NN #1#2
+  {
+    \exp_after:wN \regex_query_substr_aux:NN
+    \exp_after:wN #1
+    \exp_after:wN #2
+    \l_regex_query_other_str
+    \q_stop
+  }
+\cs_new:Npn \regex_query_substr_aux:NN #1#2
+  {
+    \str_skip_do:nn {#1}
+      { \str_collect_do:nn { #2 - #1 } { \use_i_delimit_by_q_stop:nw } }
+  }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 %
-% \begin{macro}[int]{\regex_build_error:n}
-%   This macro is called if anything goes wrong when building
-%   the NFA corresponding to a given regular expression
-%   Negative codes are specific to the \LaTeX3 implementation.
-%   Other error codes match with the PCRE codes (not all of
-%   the PCRE errors can occur, since some constructions are
-%   not supported).
+% \subsubsection{Sequences}
+%
+% \begin{macro}[int]{\regex_seq_pop:N}
+% \begin{macro}[int]{\regex_seq_get:N}
+%   When building the regular expression, some settings are kept
+%   local to capturing groups without any help from \TeX{}'s grouping.
+%   This is done \enquote{by hand}, in sequences whose items contain
+%   instructions such as |\int_set:Nn| \meta{int~var} \Arg{value},
+%   which should be run immediately.
 %    \begin{macrocode}
-\cs_new_protected_nopar:Npn \regex_build_error:n #1
+\cs_new_protected_nopar:Npn \regex_seq_pop:N #1
   {
-    \msg_error:nnxx { regex } { build-error } {\int_eval:n{#1}}
-      {
-        \prg_case_int:nnn {#1}
-          {
-            {-999} {File~not~found}
-            {-998} {Unsupported~construct}
-            {-997} {The~regular~expression~is~too~large~(32768~states).}
-            {1}  {\iow_char:N\\~at~end~of~pattern }
-%           {2}  {\iow_char:N\\c~at~end~of~pattern }
-            {4}  {Numbers~out~of~order~in~\iow_char:N\{\iow_char\}~quantifier.}
-            {6}  {Missing~terminating~\iow_char:N\]~for~character~class }
-            {7}  {Invalid~escape~sequence~in~character~class}
-            {8}  {Range~out~of~order~in~character~class}
-            {22} {Mismatched~parentheses}
-            {34} {Character~value~in~\iow_char:N\\x{...}~sequence~is~too~large}
-%           {44} {Invalid~UTF-8~string}
-%           {46} {Malformed~\iow_char:N\\P~or\iow_char:N\\p~sequence}
-%           {47} {Unknown~property~after~\iow_char:N\\P~or\iow_char:N\\p}
-%           {68} {\iow_char:N\\c~must~be~followed~by~an~ASCII~character}
-          }
-          { Internal~bug. }
-      }
+    \seq_pop:NN #1 \l_regex_tmpa_tl
+    \l_regex_tmpa_tl
+  }
+\cs_new_protected_nopar:Npn \regex_seq_get:N #1
+  {
+    \seq_get:NN #1 \l_regex_tmpa_tl
+    \l_regex_tmpa_tl
   }
-\msg_new:nnn { regex } { build-error } { (error~#1): ~ #2 }
 %    \end{macrocode}
 % \end{macro}
+% \end{macro}
 %
 % \subsubsection{Testing characters}
 %
+% \begin{macro}{\regex_item_dot:T}
+%   The dot meta-character matches any character,
+%   except the end-of-string marker.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_item_dot:T
+  { \int_compare:nNnF \l_regex_current_char_int = \c_minus_one }
+%    \end{macrocode}
+% \end{macro}
+%
 % \begin{macro}[int]{\regex_break_point:TF}
 % \begin{macro}[int]{\regex_break_true:w,\regex_break_false:w}
 %   When testing whether a character of the query string matches
@@ -977,25 +1042,27 @@
 %   Otherwise, \cs{regex_break_point:TF} leaves the \meta{false code}
 %   in the input stream.
 %    \begin{macrocode}
-\cs_new_nopar:Npn \regex_break_true:w #1 \regex_break_point:TF #2 #3 {#2}
-\cs_new_nopar:Npn \regex_break_false:w #1 \regex_break_point:TF #2 #3 {#3}
-\cs_new_eq:NN \regex_break_point:TF \use_ii:nn
+\cs_new_protected_nopar:Npn \regex_break_true:w
+   #1 \regex_break_point:TF #2 #3 {#2}
+\cs_new_protected_nopar:Npn \regex_break_false:w
+   #1 \regex_break_point:TF #2 #3 {#3}
+\cs_new_protected_nopar:Npn \regex_break_point:TF #1 #2 { #2 }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 %
-% \begin{macro}[int]{\regex_item_equal:n,\regex_item_range:nn}
-% \begin{macro}[int]{\regex_item_less:n,\regex_item_more:n}
-% \begin{macro}[int]{\regex_item_neq:n}
+% \begin{macro}[int]{\regex_item_caseful_equal:n}
+% \begin{macro}[int]{\regex_item_caseful_range:nn}
+% \begin{macro}[int]{\regex_item_caseful_geq:n}
 %   Simple comparisons triggering \cs{regex_break_true:w} when true.
 %    \begin{macrocode}
-\cs_new_nopar:Npn \regex_item_equal:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseful_equal:n #1
   {
     \if_num:w #1 = \l_regex_current_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_range:nn #1 #2
+\cs_new_protected_nopar:Npn \regex_item_caseful_range:nn #1 #2
   {
     \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
       \reverse_if:N \if_num:w #2 < \l_regex_current_char_int
@@ -1003,29 +1070,97 @@
       \fi:
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_less:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseful_geq:n #1
   {
-    \if_num:w #1 > \l_regex_current_char_int
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_more:n #1
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[int]{\regex_item_caseless_equal:n}
+% \begin{macro}[int]{\regex_item_caseless_range:nn}
+% \begin{macro}[int]{\regex_item_caseless_geq:n}
+%   For caseless matching, we perform the test both on
+%   \cs{l_regex_current_char_int} and on
+%   \cs{l_regex_case_changed_char_int}.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_item_caseless_equal:n #1
   {
-    \if_num:w #1 < \l_regex_current_char_int
+    \if_num:w #1 = \l_regex_current_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+    \if_num:w #1 = \l_regex_case_changed_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_neq:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseless_range:nn #1 #2
   {
-    \if_num:w #1 = \l_regex_current_char_int
-      \exp_after:wN \regex_break_false:w
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
+      \reverse_if:N \if_num:w #2 < \l_regex_current_char_int
+        \exp_after:wN \exp_after:wN \exp_after:wN \regex_break_true:w
+      \fi:
+    \fi:
+    \reverse_if:N \if_num:w #1 > \l_regex_case_changed_char_int
+      \reverse_if:N \if_num:w #2 < \l_regex_case_changed_char_int
+        \exp_after:wN \exp_after:wN \exp_after:wN \regex_break_true:w
+      \fi:
     \fi:
   }
+\cs_new_protected_nopar:Npn \regex_item_caseless_geq:n #1
+  {
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+    \reverse_if:N \if_num:w #1 > \l_regex_case_changed_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[int]{\regex_item_equal:n}
+% \begin{macro}[int]{\regex_item_range:nn}
+% \begin{macro}[int]{\regex_item_geq:n}
+%   By default, matching takes the letter case into account.
+%   Note that those functions are not protected:
+%   they will expand at the building step, hard-coding which
+%   states take care of caseless versus caseful matching.
+%    \begin{macrocode}
+\cs_new:Npn \regex_item_equal:n  { \regex_item_caseful_equal:n }
+\cs_new:Npn \regex_item_range:nn { \regex_item_caseful_range:nn }
+\cs_new:Npn \regex_item_geq:n    { \regex_item_caseful_geq:n }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}[int]{\regex_build_caseless:,\regex_build_caseful:}
+%   Switch between caseful and caseless matching.
+%   This is only done during the building step.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_build_caseless:
+  {
+    \bool_set_true:N \l_regex_caseless_bool
+    \cs_set:Npn \regex_item_equal:n  { \regex_item_caseless_equal:n }
+    \cs_set:Npn \regex_item_range:nn { \regex_item_caseless_range:nn }
+    \cs_set:Npn \regex_item_geq:n    { \regex_item_caseless_geq:n }
+  }
+\cs_new_protected_nopar:Npn \regex_build_caseful:
+  {
+    \bool_set_false:N \l_regex_caseless_bool
+    \cs_set:Npn \regex_item_equal:n  { \regex_item_caseful_equal:n }
+    \cs_set:Npn \regex_item_range:nn { \regex_item_caseful_range:nn }
+    \cs_set:Npn \regex_item_geq:n    { \regex_item_caseful_geq:n }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
 % \subsubsection{Grabbing digits}
 %
 % \begin{macro}[int]{\regex_get_digits:nw}
@@ -1042,23 +1177,27 @@
       {
         \exp_not:n {#1}
         { \if_false: } } \fi:
-        \regex_get_digits_aux:N
+        \regex_get_digits_aux:NN
   }
-\cs_new_nopar:Npn \regex_get_digits_aux:N #1
+\cs_new_nopar:Npn \regex_get_digits_aux:NN #1#2
   {
-    \if_num:w 9 < 1 \exp_not:N #1 \exp_stop_f:
-    \else:
-      \if_charcode:w \c_space_token \exp_not:N #1
+    \if_meaning:w \regex_build_raw:N #1
+      \if_charcode:w \c_space_token \exp_not:N #2
       \else:
-        \regex_get_digits_end:w
+        \if_num:w 9 < 1 \exp_not:N #2 \exp_stop_f:
+          #2
+        \else:
+          \regex_get_digits_end:w #1 #2
+        \fi:
       \fi:
+    \else:
+      \regex_get_digits_end:w #1 #2
     \fi:
-    #1 \regex_get_digits_aux:N
+    \regex_get_digits_aux:NN
   }
-\cs_new_nopar:Npn \regex_get_digits_end:w
-    \fi: \fi: #1 \regex_get_digits_aux:N
+\cs_new_nopar:Npn \regex_get_digits_end:w #1 \fi: #2 \regex_get_digits_aux:NN
   {
-    \fi: \fi:
+    \fi: #2
     \if_false: { { \fi: } }
     #1
   }
@@ -1066,7 +1205,20 @@
 % \end{macro}
 % \end{macro}
 %
-% \subsubsection{More char testing}
+% \subsubsection{More character testing}
+%
+% \begin{macro}[EXP,pTF]{\regex_token_if_other_digit:N}
+%   In the replacement text, |\g{|\meta{int}|}| denotes the \meta{int}-th
+%   submatch. Parsing this construction robustly requires a test of whether
+%   a token is a digit or not.
+%    \begin{macrocode}
+\prg_new_conditional:Npnn \regex_token_if_other_digit:N #1 { TF }
+  {
+    \if_num:w \c_nine < 1 \exp_not:N #1 \exp_stop_f:
+      \prg_return_true: \else: \prg_return_false: \fi:
+  }
+%    \end{macrocode}
+% \end{macro}
 %
 % \begin{macro}[EXP,aux]{\regex_aux_char_if_alphanumeric:NTF}
 % \begin{macro}[EXP,aux]{\regex_aux_char_if_special:NTF}
@@ -1076,11 +1228,11 @@
 %   ones have special meanings and which should be interpreted
 %   as \enquote{raw} characters. Namely,
 %   \begin{itemize}
-%   \item alphanumerics are \enquote{raw} if they are not escaped,
-%     and may have a special meaning when escaped;
-%   \item non-alphanumeric printable ascii characters are \enquote{raw}
-%     if they are escaped, and may have a special meaning when not escaped;
-%   \item characters other than printable ascii are always \enquote{raw}.
+%     \item alphanumerics are \enquote{raw} if they are not escaped,
+%       and may have a special meaning when escaped;
+%     \item non-alphanumeric printable ascii characters are \enquote{raw}
+%       if they are escaped, and may have a special meaning when not escaped;
+%     \item characters other than printable ascii are always \enquote{raw}.
 %   \end{itemize}
 %   The code is ugly, and highly based on magic numbers and the ascii
 %   codes of characters. This is mostly unavoidable for performance
@@ -1095,43 +1247,40 @@
 %    \begin{macrocode}
 \prg_new_conditional:Npnn \regex_aux_char_if_special:N #1 { TF }
   {
-    \if_num:w `#1 < 97 \exp_stop_f:
-      \if_num:w `#1 < 58 \exp_stop_f:
-        \if_num:w \int_eval:w (`#1 - \c_eight)/\c_sixteen = \c_two
-          \prg_return_true:
-        \else:
-          \prg_return_false:
-        \fi:
+    \if_num:w `#1 < \c_ninety_one
+      \if_num:w `#1 < \c_fifty_eight
+        \if_num:w `#1 < \c_forty_eight
+          \if_num:w `#1 < \c_thirty_two
+            \prg_return_false: \else: \prg_return_true: \fi:
+        \else: \prg_return_false: \fi:
       \else:
-        \if_num:w \int_eval:w `#1 / 26 = \c_three
-          \prg_return_false:
-        \else:
-          \prg_return_true:
-        \fi:
+        \if_num:w `#1 < \c_sixty_five
+          \prg_return_true: \else: \prg_return_false: \fi:
       \fi:
     \else:
-      \if_num:w \int_eval:w `#1 / \c_five = 25 \exp_stop_f:
-        \prg_return_true:
+      \if_num:w `#1 < \c_one_hundred_twenty_three
+        \if_num:w `#1 < \c_ninety_seven
+          \prg_return_true: \else: \prg_return_false: \fi:
       \else:
-        \prg_return_false:
+        \if_num:w `#1 < \c_one_hundred_twenty_seven
+          \prg_return_true: \else: \prg_return_false: \fi:
       \fi:
     \fi:
   }
 \prg_new_conditional:Npnn \regex_aux_char_if_alphanumeric:N #1 { TF }
   {
-    \if_num:w `#1 < 91 \exp_stop_f:
-      \if_num:w `#1 < 65 \exp_stop_f:
-        \if_num:w \c_nine < 1 #1 \exp_stop_f:
-          \prg_return_true:
-        \else:
-          \prg_return_false:
-        \fi:
+    \if_num:w `#1 < \c_ninety_one
+      \if_num:w `#1 < \c_fifty_eight
+        \if_num:w `#1 < \c_forty_eight
+          \prg_return_false: \else: \prg_return_true: \fi:
       \else:
-        \prg_return_true:
+        \if_num:w `#1 < \c_sixty_five
+          \prg_return_false: \else: \prg_return_true: \fi:
       \fi:
     \else:
-      \if_num:w \int_eval:w (`#1-\c_six)/26 = \c_four
-        \prg_return_true:
+      \if_num:w `#1 < \c_one_hundred_twenty_three
+        \if_num:w `#1 < \c_ninety_seven
+          \prg_return_false: \else: \prg_return_true: \fi:
       \else:
         \prg_return_false:
       \fi:
@@ -1153,8 +1302,8 @@
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_new_state:
   {
-    \int_compare:nNnTF \l_regex_max_state_int > {32766}
-      { \regex_build_error:n {-997} }
+    \int_compare:nNnTF \l_regex_max_state_int > { 32766 }
+      { \msg_error:nn { regex } { -997 } }
       {
         \int_incr:N \l_regex_max_state_int
         \tex_toks:D \l_regex_max_state_int { \s_regex_toks }
@@ -1174,15 +1323,15 @@
   {
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      { #1 { \int_use:N #2 } }
+      { #1 { \int_eval:n { #2 - \l_regex_left_state_int } } }
   }
 \cs_new_protected_nopar:Npn \regex_build_transitions_aux:NNNN #1#2#3#4
   {
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
-        #1 { \int_use:N #2 }
-        #3 { \int_use:N #4 }
+        #1 { \int_eval:n { #2 - \l_regex_left_state_int } }
+        #3 { \int_eval:n { #4 - \l_regex_left_state_int } }
       }
   }
 %    \end{macrocode}
@@ -1191,8 +1340,10 @@
 %
 % \subsubsection{From regex to NFA: framework}
 %
-% In order for the construction \texttt{ab\string|cd} to work, we enclose
-% the whole pattern within parentheses. These have the added benefit
+% In order for the construction \verb"ab|cd" to work, we enclose
+% the whole pattern within parentheses (in the code below,
+% \cs{regex_build_open_aux:} and \cs{regex_build_close_aux:}).
+% These have the added benefit
 % to form a capturing group: hence we get the data of the whole match
 % for free.
 %
@@ -1270,28 +1421,20 @@
 %
 % \begin{macro}[int]{\regex_build_setup:}
 %   Hopefully, we didn't forget to initialize anything here.
-%   The search is not anchored: to acheive that, we insert state(s)
+%   The search is not anchored: to achieve that, we insert state(s)
 %   responsible for repeating the match attempt on every character
-%   of the string: the first state has a free transition to the second
-%   state, where the regular expression really begins, and a costly
-%   transition to itself, to try again at the next character.
+%   of the string.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_setup:
   {
     \cs_set_eq:NN \regex_build_control:N \regex_build_default_control:N
     \cs_set_eq:NN \regex_build_raw:N \regex_build_default_raw:N
     \int_set_eq:NN \l_regex_capturing_group_int \c_zero
-    \int_zero:N \l_regex_left_state_int
-    \int_zero:N \l_regex_right_state_int
     \int_zero:N \l_regex_max_state_int
     \regex_build_new_state:
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_action_start_wildcard:nn
-          { \int_use:N \l_regex_left_state_int }
-          { \int_use:N \l_regex_right_state_int }
-      }
+      { \regex_action_start_wildcard:nn {0} {1} }
   }
 %    \end{macrocode}
 % \end{macro}
@@ -1305,9 +1448,9 @@
   {
     \seq_if_empty:NF \l_regex_capturing_group_seq
       {
-        \regex_build_error:n {22}
+        \msg_error:nn { regex } {22}
         \prg_replicate:nn
-          { \seq_length:N \l_regex_capturing_group_seq } % (
+          { \seq_length:N \l_regex_capturing_group_seq }
           { \regex_build_close_aux: \regex_build_group_: }
       }
     \regex_toks_put_right:Nx \l_regex_right_state_int
@@ -1339,7 +1482,13 @@
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \int_compare:nNnT {#1} = \l_regex_current_step_int
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 %    \end{macrocode}
@@ -1360,7 +1509,13 @@
       {
         \exp_not:N \int_compare:nNnT
           \c_minus_one = \l_regex_current_char_int
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_eq:Nc \regex_build_Z: { regex_build_$: } %$
@@ -1374,52 +1529,50 @@
 % \begin{macro}[int]{\regex_build_B:}
 % \begin{macro}[aux]{\regex_if_word_boundary:TF}
 %   Contrarily to |^| and |$|, which could be implemented without
-%   really knowing what preceeds in the string, this requires
-%   more information. We request it by setting
-%   \cs{l_regex_look_behind_bool}. Then the matching code will
-%   keep store the characters that were already read, backwards,
-%   in \cs{l_regex_look_behind_str}, and we can analyse the first
-%   character of that string.
+%   really knowing what precedes in the string, this requires
+%   more information, namely, the knowledge of the last character
+%   code. Case sensitivity does not change word boundaries.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_b:
   {
-    \bool_set_true:N \l_regex_look_behind_bool
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \regex_if_word_boundary:TF
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
           { }
       }
   }
 \cs_new_protected_nopar:Npn \regex_build_B:
   {
-    \bool_set_true:N \l_regex_look_behind_bool
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \regex_if_word_boundary:TF
           { }
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_protected_nopar:Npn \regex_if_word_boundary:TF
   {
-    \tl_if_empty:NTF \l_regex_look_behind_str
-      { \c_regex_w_tl }
-      {
-        \group_begin:
-          \cs_set_nopar:Npx \regex_tmp:w
-            {
-              \int_set:Nn \l_regex_current_char_int
-                { ` \str_head:N \l_regex_look_behind_str }
-            }
-          \regex_tmp:w
-          \c_regex_w_tl
-          \regex_break_point:TF
-            { \group_end: \c_regex_W_tl }
-            { \group_end: \c_regex_w_tl }
-      }
+    \group_begin:
+      \int_set_eq:NN \l_regex_current_char_int \l_regex_last_char_int
+      \c_regex_w_tl
+      \regex_break_point:TF
+        { \group_end: \c_regex_W_tl \regex_item_equal:n { -1 } }
+        { \group_end: \c_regex_w_tl }
     \regex_break_point:TF
   }
 %    \end{macrocode}
@@ -1434,18 +1587,16 @@
 %   (actually, any unknown combination) will match itself
 %   and the thread will fail otherwise. We prepare
 %   \cs{regex_build_tmp_class:n} with the relevant test and
-%   commands. The program steps to be inserted in those
-%   commands will come as |##1| and |##2|: we don't know
-%   yet what those will be before checking for quantifiers.
+%   commands. The state shift to be inserted in those
+%   commands will come as |##1|: we don't know
+%   yet what this will be before checking for quantifiers.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_default_raw:N #1
   {
     \cs_set:Npx \regex_build_tmp_class:n ##1
       {
-        \exp_not:n { \exp_not:N \if_num:w }
-            \int_value:w `#1 = \l_regex_current_char_int
-          \regex_action_cost:n { ##1 }
-        \exp_not:n { \exp_not:N \fi: }
+        \regex_item_equal:n { \int_value:w `#1 }
+        \regex_break_point:TF { \regex_action_cost:n { ##1 } } { }
       }
     \regex_build_one_quantifier:
   }
@@ -1459,11 +1610,7 @@
 \cs_new_protected_nopar:cpn { regex_build_.: }
   {
     \cs_set:Npn \regex_build_tmp_class:n ##1
-      {
-        \exp_not:N \if_num:w \c_minus_one < \l_regex_current_char_int
-          \regex_action_cost:n {##1}
-        \exp_not:N \fi:
-      }
+      { \regex_item_dot:T { \regex_action_cost:n {##1} } }
     \regex_build_one_quantifier:
   }
 %    \end{macrocode}
@@ -1486,9 +1633,7 @@
     \cs_set:Npn \regex_build_tmp_class:n ##1
       {
         \exp_not:N #1
-        \exp_not:N \regex_break_point:TF
-          { \regex_action_cost:n {##1} }
-          { }
+        \regex_break_point:TF { \regex_action_cost:n {##1} } { }
       }
     \regex_build_one_quantifier:
   }
@@ -1557,16 +1702,8 @@
           {
             \exp_not:o \l_regex_class_tl
             \bool_if:NTF \l_regex_class_bool
-              {
-                \exp_not:N \regex_break_point:TF
-                  { \regex_action_cost:n {##1} }
-                  { }
-              }
-              {
-                \exp_not:N \regex_break_point:TF
-                  { }
-                  { \regex_action_cost:n {##1} }
-              }
+              { \regex_break_point:TF { \regex_action_cost:n {##1} } { } }
+              { \regex_break_point:TF { } { \regex_action_cost:n {##1} } }
           }
         \regex_build_one_quantifier:
       }
@@ -1607,7 +1744,7 @@
 \cs_new_protected_nopar:Npn \regex_class_single:N #1
   {
     \tl_put_right:Nx \l_regex_class_tl
-      { \exp_not:N \regex_item_equal:n { \int_value:w `#1 } }
+      { \regex_item_equal:n { \int_value:w `#1 } }
   }
 %    \end{macrocode}
 % \end{macro}
@@ -1641,14 +1778,14 @@
 \cs_new_protected_nopar:Npn \regex_class_range_put:NN #1#2
   {
     \if_num:w `#1 > `#2 \exp_stop_f:
-      \regex_build_error:n {8}
+      \msg_error:nn { regex } {8}
     \else:
       \tl_put_right:Nx \l_regex_class_tl
         {
           \if_num:w `#1 = `#2 \exp_stop_f:
-            \exp_not:N \regex_item_equal:n
+            \regex_item_equal:n
           \else:
-            \exp_not:N \regex_item_range:nn { \int_value:w `#1 }
+            \regex_item_range:nn { \int_value:w `#1 }
           \fi:
           { \int_value:w `#2 }
         }
@@ -1781,26 +1918,29 @@
         \exp_not:N \regex_build_raw:N \c_lbrace_str #1#2
       }
   }
-\cs_new_protected_nopar:Npn \regex_build_quantifier_lbrace:nnw #1#2#3
+\cs_new_protected_nopar:Npn \regex_build_quantifier_lbrace:nnw #1#2#3#4
   {
-    \str_if_eq:xxTF { \exp_not:N #3 } { \c_rbrace_str }
+    \str_if_eq:xxTF
+      { \exp_not:n {#3#4} }
+      { \exp_not:N \regex_build_control:N \c_rbrace_str }
       {
         \tl_if_empty:nTF {#2}
-          { \regex_build_quantifier_aux:nnN { {#1} {\c_max_int} } {nn} }
+          { \regex_build_quantifier_aux:nnNN { {#1} } { n* } }
           {
             \int_compare:nNnT {#1} > {#2}
-              { \regex_build_error:n {4} }
-            \regex_build_quantifier_aux:nnN { {#1} {#2} } {nn}
+              { \msg_error:nn { regex } {4} }
+            \regex_build_quantifier_aux:nnNN { {#1} {#2} } { nn }
           }
       }
       {
         \regex_build_quantifier_end:n { }
         \use:x
           {
-            \exp_not:n { \exp_args:No \tl_map_function:nN }
-              { \c_lbrace_str #1 #2 , }
-            \regex_build_raw:N
+            \exp_args:No \tl_map_function:nN
+              { \c_lbrace_str #1 , #2 }
+              \regex_build_raw:N
           }
+        #3 #4
       }
   }
 %    \end{macrocode}
@@ -1923,83 +2063,49 @@
 %   This function is called in case the syntax is
 %   \texttt{\{\meta{int}\}}. Greedy and lazy operators
 %   are identical, since the number of repetitions is fixed.
+%   Simply repeat |#1| times the effect of \cs{regex_build_one_:}.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_one_n: #1
-  {
-    \int_set_eq:NN \l_regex_tmpa_int \l_regex_right_state_int
-    \regex_build_new_state:
-    \regex_build_new_state:
-    \regex_toks_put_right:Nx \l_regex_tmpa_int
-      { %^^A safe \if nesting?
-        \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \else:
-          \regex_action_no_repeat_move:n
-            { \int_use:N \l_regex_right_state_int }
-        \exp_not:N \fi:
-      }
-    \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_build_tmp_class:n
-          { \int_use:N \l_regex_tmpa_int }
-      }
-  }
+  { \prg_replicate:nn {#1} { \regex_build_one_: } }
 \cs_new_eq:cN { regex_build_one_n?: } \regex_build_one_n:
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 %
-% \begin{macro}[aux]{\regex_build_one_nn:}
-% \begin{macro}[aux]{\regex_build_one_nn?:}
-% \begin{macro}[aux]{\regex_build_one_nn_aux:nn}
-%   This function is called when the syntax is either
-%   \texttt{\{\meta{int},\}} or \texttt{\{\meta{int},\meta{int}\}}.
+% \begin{macro}[aux]{\regex_build_one_n*:}
+% \begin{macro}[aux]{\regex_build_one_n*?:}
+%   This function is called in case the syntax is
+%   \texttt{\{\meta{int},\}}.
 %    \begin{macrocode}
-\cs_new_protected_nopar:Npn \regex_build_one_nn: #1#2
+\cs_new_protected_nopar:cpx { regex_build_one_n*: } #1
   {
-    \regex_build_one_nn_aux:nn {#1}
-      {
-        \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-          \regex_action_repeat_copy:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \fi:
-        \regex_action_no_repeat_move:n
-          { \int_use:N \l_regex_right_state_int }
-      }
+    \exp_not:N \prg_replicate:nn {#1} { \exp_not:N \regex_build_one_: }
+    \exp_not:c { regex_build_one_*: }
   }
-\cs_new_protected_nopar:cpn { regex_build_one_nn?: } #1#2
+\cs_new_protected_nopar:cpx { regex_build_one_n*?: } #1
   {
-    \regex_build_one_nn_aux:nn {#1}
-      {
-        \regex_action_no_repeat_copy:n
-          { \int_use:N \l_regex_right_state_int }
-        \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \fi:
-      }
+    \exp_not:N \prg_replicate:nn {#1} { \exp_not:N \regex_build_one_: }
+    \exp_not:c { regex_build_one_*?: }
   }
-\cs_new_protected_nopar:Npn \regex_build_one_nn_aux:nn #1#2
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[aux]{\regex_build_one_nn:}
+% \begin{macro}[aux]{\regex_build_one_nn?:}
+% \begin{macro}[aux]{\regex_build_one_nn_aux:Nnn}
+%   This function is called when the syntax is
+%   \texttt{\{\meta{int},\meta{int}\}}.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_build_one_nn_aux:Nnn #1#2#3
   {
-    \int_set_eq:NN \l_regex_tmpa_int \l_regex_right_state_int
-    \regex_build_new_state:
-    \regex_build_new_state:
-    \regex_toks_put_right:Nx \l_regex_tmpa_int
-      {
-        \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \else:
-          #2
-        \exp_not:N \fi:
-      }
-    \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_build_tmp_class:n
-          { \int_use:N \l_regex_tmpa_int }
-      }
+    \prg_replicate:nn {#2} { \regex_build_one_: }
+    \prg_replicate:nn {#3-#2} {#1}
   }
+\cs_new_protected_nopar:Npx \regex_build_one_nn:
+  { \regex_build_one_nn_aux:Nnn \exp_not:c { regex_build_one_?: } }
+\cs_new_protected_nopar:cpx { regex_build_one_nn?: }
+  { \regex_build_one_nn_aux:Nnn \exp_not:c { regex_build_one_??: } }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
@@ -2007,8 +2113,8 @@
 %
 % \subsubsection{Groups and alternation}
 %
-% We support the syntax \texttt{(\meta{expr1}|\ldots{}%^^A
-%   |\meta{expr$\sb{n}$})\meta{quantifier}} for alternations.
+% We support the syntax \texttt{\meta{expr1}|\ldots{}%^^A
+%   |\meta{expr$\sb{n}$}} for alternations.
 %
 % \begin{macro}[aux]{\regex_build_(:, \regex_build_):}
 % \begin{macro}[aux]{\regex_build_open_aux:}
@@ -2017,14 +2123,14 @@
 %     \regex_build_end_alternation:}
 %   Grouping and alternation go together.
 %   \begin{itemize}
-%   \item Allocate the next available number for the end vertex
-%     of the alternation/group and store it on a stack (so that nested
-%     alternations work).
-%   \item Put free transitions to separate all cases of the alternation.
-%   \item Build each branch separately, and merge them to the common
-%     end-node.
-%   \item Test for a quantifier, and if needed, transfer the initial
-%     vertex to a new vertex.
+%     \item Allocate the next available number for the end vertex
+%       of the alternation/group and store it on a stack (so that nested
+%       alternations work).
+%     \item Put free transitions to separate all cases of the alternation.
+%     \item Build each branch separately, and merge them to the common
+%       end-node.
+%     \item Test for a quantifier, and if needed, transfer the initial
+%       vertex to a new vertex.
 %   \end{itemize}
 %    \begin{macrocode}
 \cs_new_protected_nopar:cpn { regex_build_(: } #1#2
@@ -2042,10 +2148,19 @@
 \cs_new_protected_nopar:Npn \regex_build_open_aux:
   {
     \regex_build_new_state:
-    \seq_push:Nx \l_regex_left_state_seq
-      { \int_use:N \l_regex_left_state_int }
-    \seq_push:Nx \l_regex_right_state_seq
-      { \int_use:N \l_regex_right_state_int }
+    \seq_push:Nx \l_regex_group_begin_seq
+      {
+        \int_set:Nn \l_regex_left_state_int
+          { \int_use:N \l_regex_left_state_int }
+      }
+    \bool_if:NTF \l_regex_caseless_bool
+      { \seq_push:Nn \l_regex_group_end_seq { \regex_build_caseless: } }
+      { \seq_push:Nn \l_regex_group_end_seq { \regex_build_caseful: } }
+    \seq_push:Nx \l_regex_group_end_seq
+      {
+        \int_set:Nn \l_regex_right_state_int
+          { \int_use:N \l_regex_right_state_int }
+      }
     \regex_build_begin_alternation:
   }
 \cs_new_protected_nopar:cpn { regex_build_|: }
@@ -2056,7 +2171,7 @@
 \cs_new_protected_nopar:cpn { regex_build_): }
   {
     \seq_if_empty:NTF \l_regex_capturing_group_seq
-      { \regex_build_error:n {22} }
+      { \msg_error:nn { regex } { 22 } }
       {
         \regex_build_close_aux:
         \regex_build_group_quantifier:
@@ -2065,10 +2180,9 @@
 \cs_new_protected_nopar:Npn \regex_build_close_aux:
   {
     \regex_build_end_alternation:
-    \seq_pop:NN \l_regex_left_state_seq  \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_left_state_int  \l_regex_tmpa_tl
-    \seq_pop:NN \l_regex_right_state_seq \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_right_state_int \l_regex_tmpa_tl
+    \regex_seq_pop:N \l_regex_group_begin_seq
+    \regex_seq_pop:N \l_regex_group_end_seq
+    \regex_seq_pop:N \l_regex_group_end_seq
   }
 %    \end{macrocode}
 %   Building each branch.
@@ -2076,16 +2190,28 @@
 \cs_new_protected_nopar:Npn \regex_build_begin_alternation:
   {
     \regex_build_new_state:
-    \seq_get:NN \l_regex_left_state_seq \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_left_state_int \l_regex_tmpa_tl
+    \regex_seq_get:N \l_regex_group_begin_seq
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+      {
+        \regex_action_free:n
+          {
+            \int_eval:n
+              { \l_regex_right_state_int - \l_regex_left_state_int }
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_build_end_alternation:
   {
-    \seq_get:NN \l_regex_right_state_seq \l_regex_tmpa_tl
-    \regex_toks_put_right:Nx \l_regex_right_state_int
-      { \regex_action_free:n { \l_regex_tmpa_tl } }
+    \int_set_eq:NN \l_regex_left_state_int \l_regex_right_state_int
+    \regex_seq_get:N \l_regex_group_end_seq
+    \regex_toks_put_right:Nx \l_regex_left_state_int
+      {
+        \regex_action_free:n
+          {
+            \int_eval:n
+              { \l_regex_right_state_int - \l_regex_left_state_int }
+          }
+      }
   }
 %    \end{macrocode}
 % \end{macro}
@@ -2102,7 +2228,7 @@
   {
     \cs_if_exist_use:cF { regex_build_special_group_\token_to_str:N #2 : }
       {
-        \regex_build_error:n { -998 }
+        \msg_error:nn { regex } { -998 }
         \regex_build_control:N ( % )
         \regex_build_raw:N ?
         #1 #2
@@ -2125,6 +2251,55 @@
 %    \end{macrocode}
 % \end{macro}
 %
+% \begin{macro}{\regex_build_special_group_i:}
+% \begin{macro}{\regex_build_special_group_-:}
+% \begin{macro}[aux]{\regex_build_options:NNN}
+% \begin{macro}[aux]{\regex_build_option_+i:}
+% \begin{macro}[aux]{\regex_build_option_-i:}
+%   The match can be made case-insensitive by setting the option
+%   with \texttt{(?i)}.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_build_special_group_i:
+  {
+    \regex_build_options:NNN +
+    \regex_build_raw:N i
+  }
+\cs_new_protected_nopar:cpn { regex_build_special_group_-: }
+  {
+    \regex_build_options:NNN -
+  }
+\cs_new_protected_nopar:Npn \regex_build_options:NNN #1#2#3
+  {
+    \token_if_eq_meaning:NNTF \regex_build_raw:N #2
+      {
+        \cs_if_exist_use:cF { regex_build_option_#1#3: }
+          { \msg_error:nnx { regex } { unknown-option } { #3 } }
+        \regex_build_options:NNN #1
+      }
+      {
+        \prg_case_str:nnn { #3 }
+          { % (
+            { ) } { }
+            { - } { \regex_build_options:NNN - }
+          }
+          { \msg_error:nnx { regex } { invalid-in-option } { #3 } }
+      }
+  }
+\cs_new_protected_nopar:cpn { regex_build_option_+i: }
+  {
+    \regex_build_caseless:
+    \cs_set_eq:NN \regex_match_loop_case_hook:
+      \regex_match_loop_caseless_hook:
+  }
+\cs_new_protected_nopar:cpn { regex_build_option_-i: }
+  { \regex_build_caseful: }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
 % \subsubsection{Quantifiers for groups}
 %
 % \begin{macro}[aux]{\regex_build_group_quantifier:}
@@ -2162,7 +2337,7 @@
 %
 % \begin{macro}[aux]{\regex_build_group_:}
 %   When there is no quantifier, the group is simply inserted as is,
-%   and we only need to track submatches.
+%   and we only need to track submatches, and move to a new state.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_group_:
   {
@@ -2184,14 +2359,22 @@
     \int_set_eq:NN \l_regex_tmpa_int \l_regex_left_state_int
     \regex_build_new_state:
     \tex_toks:D \l_regex_right_state_int = \tex_toks:D \l_regex_tmpa_int
-    \use:x
+    \regex_toks_put_left:Nx \l_regex_right_state_int
+      {
+        \int_set:Nn \l_regex_current_state_int
+          { \int_use:N \l_regex_tmpa_int } % ^^A here we lie!
+      }
+    \cs_set:Npx \regex_tmp:w
       {
         \tex_toks:D \l_regex_tmpa_int
-          { \s_regex_toks #1 { \int_use:N \l_regex_right_state_int } }
+          {
+            \s_regex_toks
+            #1 { \int_eval:n { \l_regex_right_state_int - \l_regex_tmpa_int } }
+          }
       }
+    \regex_tmp:w
     \regex_build_group_submatches:NN
       \l_regex_right_state_int \l_regex_left_state_int
-    \int_set_eq:NN \l_regex_right_state_int \l_regex_left_state_int
   }
 %    \end{macrocode}
 % \end{macro}
@@ -2216,9 +2399,13 @@
 \cs_new_protected_nopar:Npn \regex_build_group_qs_aux:NN #1#2
   {
     \regex_build_group_shift:N \regex_action_free:n
+    \int_set_eq:NN \l_regex_right_state_int \l_regex_left_state_int
     \regex_build_transition_aux:NN \regex_action_free:n #1
     #2 \l_regex_tmpa_int
-      { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+      {
+        \regex_action_free:n
+          { \int_eval:n { \l_regex_right_state_int - \l_regex_tmpa_int } }
+      }
   }
 \cs_new_protected_nopar:cpn { regex_build_group_?: }
   {
@@ -2275,84 +2462,108 @@
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}[aux]{\regex_build_group_n_aux:n}
+%   The braced quantifiers rely on replicating the states
+%   corresponding to the group that has just been built,
+%   and joining the right state of each copy to the left state
+%   of the next copy. Once this function has been run,
+%   \cs{l_regex_tmpa_int} points to the last copy of the initial
+%   left-most state, \cs{l_regex_left_state_int} has its initial
+%   value, and \cs{l_regex_right_state_int} points to the last
+%   copy of the initial right-most state. Furthermore,
+%   \cs{l_regex_max_state_int} is set appropriately to the largest
+%   allocated \tn{toks} register.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_build_group_n_aux:n #1
+  {
+    \regex_toks_put_right:Nx \l_regex_right_state_int
+      {
+        \regex_action_free:n
+          { \int_eval:n { \l_regex_max_state_int - \l_regex_left_state_int } }
+      }
+    \int_set_eq:NN \l_regex_tmpa_int \l_regex_left_state_int
+    \int_set:Nn \l_regex_tmpb_int { \l_regex_max_state_int + \c_one }
+    \int_set:Nn \l_regex_max_state_int
+      {
+        \l_regex_left_state_int - \c_one
+        + #1 * ( \l_regex_max_state_int - \l_regex_left_state_int + \c_one )
+      }
+    \int_until_do:nNnn \l_regex_tmpb_int > \l_regex_max_state_int
+      {
+        \tex_toks:D \l_regex_tmpb_int = \tex_toks:D \l_regex_tmpa_int
+        \int_incr:N \l_regex_tmpa_int
+        \int_incr:N \l_regex_tmpb_int
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
 % \begin{macro}[aux]{\regex_build_group_n:}
 % \begin{macro}[aux]{\regex_build_group_n?:}
 %   These functions are called in case the syntax is
 %   \texttt{\{\meta{int}\}}. Greedy and lazy operators
 %   are identical, since the number of repetitions is fixed.
+%   We only record the submatch information at the last repetition.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_group_n: #1
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
     \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
-      {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \regex_action_no_repeat_move:n
-                { \int_use:N \l_regex_right_state_int }
-            \exp_not:N \fi:
-          }
-      }
+      \regex_action_free:n \l_regex_right_state_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
   }
 \cs_new_eq:cN { regex_build_group_n?: } \regex_build_group_n:
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}[aux]{\regex_build_group_n*:}
+% \begin{macro}[aux]{\regex_build_group_n*?:}
+%   These functions are called in case the syntax is
+%   \texttt{\{\meta{int},\}}. They are somewhat hybrid between
+%   the \texttt{\{\meta{int}\}} and the \texttt{*} quantifiers.
+%   Contrarily to the \texttt{*} quantifier, for which we had
+%   to be careful not to overwrite the submatch information in
+%   case no iteration was made, here, we know that the submatch
+%   information is overwritten in any case.
+%    \begin{macrocode}
+\cs_new_protected_nopar:cpn { regex_build_group_n*: } #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
+    \regex_build_transitions_aux:NNNN
+      \regex_action_free:n \l_regex_tmpa_int
+      \regex_action_free:n \l_regex_right_state_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
+  }
+\cs_new_protected_nopar:cpn { regex_build_group_n*?: } #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
+    \regex_build_transitions_aux:NNNN
+      \regex_action_free:n \l_regex_right_state_int
+      \regex_action_free:n \l_regex_tmpa_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
 % \begin{macro}[aux]{\regex_build_group_nn:}
 % \begin{macro}[aux]{\regex_build_group_nn?:}
 %   These functions are called when the syntax is either
 %   \texttt{\{\meta{int},\}} or \texttt{\{\meta{int},\meta{int}\}}.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_build_group_nn: #1#2
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
-    \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
-      {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-                \tex_the:D \tex_toks:D \l_regex_tmpa_int
-              \exp_not:N \fi:
-              \regex_action_no_repeat_copy:n
-                { \int_use:N \l_regex_right_state_int }
-            \exp_not:N \fi:
-          }
-      }
+  { % ^^A Not Implemented Yet!
+    \msg_expandable_error:n { Quantifier~{m,n}~not~implemented~yet }
+    \use:c { regex_build_group_n*: } {#1}
   }
 \cs_new_protected_nopar:cpn { regex_build_group_nn?: } #1#2
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
-    \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
-      {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \regex_action_no_repeat_copy:n
-                { \int_use:N \l_regex_right_state_int }
-              \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-                \tex_the:D \tex_toks:D \l_regex_tmpa_int
-              \exp_not:N \fi:
-            \exp_not:N \fi:
-          }
-      }
+  { % ^^A Not Implemented Yet!
+    \msg_expandable_error:n { Quantifier~{m,n}~not~implemented~yet }
+    \use:c { regex_build_group_n*?: } {#1}
   }
 %    \end{macrocode}
 % \end{macro}
@@ -2435,22 +2646,6 @@
 %
 % \subsubsection{Helpers for running the NFA}
 %
-% \begin{macro}[aux]{\regex_if_state_free:nT}
-%   A state is free if it is not marker as taken, namely
-%   if the corresponding \tn{dimen} register is $0\mathtt{sp}$
-%   rather than $1\mathtt{sp}$.
-%    \begin{macrocode}
-\cs_new_protected:Npn \regex_if_state_free:nT #1
-  {
-    \if_num:w \tex_dimen:D #1 = \l_regex_unique_step_int
-      \exp_after:wN \use_none:n
-    \else:
-      \exp_after:wN \use:n
-    \fi:
-  }
-%    \end{macrocode}
-% \end{macro}
-%
 % \begin{macro}[aux]{\regex_store_state:n}
 %   Put the given state in the array of \tn{skip} registers.
 %   This is done by increasing the pointer
@@ -2468,27 +2663,33 @@
 % \end{macro}
 %
 % \begin{macro}[int]{\regex_state_use:}
-% \begin{macro}[int]{\regex_state_use_submatches:}
-% \begin{macro}[aux]{\regex_state_use_aux:n}
+% \begin{macro}[int]{\regex_state_use_with_submatches:}
 % \begin{macro}[aux]{\regex_state_use_aux_ii:w}
+% \begin{macro}[aux]{\regex_state_use_aux:n}
 %   Use a given program instruction, unless it has already been
 %   executed at this step. The \tn{toks} registers begin with
 %   some submatch information, ignored by \cs{regex_state_use:},
-%   but not by \cs{regex_state_use_submatches:}.
+%   but not by \cs{regex_state_use_with_submatches:}.
+%   A state is free if it is not marker as taken, namely
+%   if the corresponding \tn{dimen} register is not
+%   \cs{l_regex_unique_step_int} in \texttt{sp}.
+%   The primitive conditional is ended before unpacking
+%   the \tn{toks} register.
 %    \begin{macrocode}
-\cs_new_protected_nopar:Npn \regex_state_use_submatches:
+\cs_new_protected_nopar:Npn \regex_state_use_with_submatches:
   { \regex_state_use_aux:n { } }
 \cs_new_protected_nopar:Npn \regex_state_use:
   { \regex_state_use_aux:n { \exp_after:wN \regex_state_use_aux_ii:w } }
-\cs_new:Npn \regex_state_use_aux_ii:w #1 \s_regex_toks { }
-\cs_new_protected:Npn \regex_state_use_aux:n #1
-  {
-    \regex_if_state_free:nT {  \l_regex_current_state_int }
-      {
-        \tex_dimen:D \l_regex_current_state_int
-          = \l_regex_unique_step_int sp \scan_stop:
-        #1 \tex_the:D \tex_toks:D \l_regex_current_state_int \scan_stop:
-      }
+\cs_new_nopar:Npn \regex_state_use_aux_ii:w #1 \s_regex_toks { }
+\cs_new_protected_nopar:Npn \regex_state_use_aux:n #1
+  {
+    \if_num:w \tex_dimen:D \l_regex_current_state_int
+        < \l_regex_unique_step_int
+      \tex_dimen:D \l_regex_current_state_int
+        = \l_regex_unique_step_int sp \scan_stop:
+      #1 \tex_the:D \tex_toks:D \exp_after:wN \l_regex_current_state_int
+    \fi:
+    \scan_stop:
   }
 %    \end{macrocode}
 % \end{macro}
@@ -2506,7 +2707,7 @@
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_disable_submatches:
   {
-    \cs_set_eq:NN \regex_state_use_submatches: \regex_state_use:
+    \cs_set_eq:NN \regex_state_use_with_submatches: \regex_state_use:
     \cs_set_eq:NN \regex_store_submatches:n
       \regex_protected_use_none:n
     \cs_set_eq:NN \regex_action_submatches:n
@@ -2517,37 +2718,42 @@
 % \end{macro}
 %
 % \begin{macro}[int]{\regex_store_submatches:n}
-% \begin{macro}[aux]{\regex_store_submatches_aux:Nw}
-% \begin{macro}[aux]{\regex_store_submatches_aux_ii:wnnwwn}
+% \begin{macro}[aux]{\regex_store_submatches_aux:w}
+% \begin{macro}[aux]{\regex_store_submatches_aux_ii:Nnnw}
 %   The submatch information pertaining to one given thread is moved
 %   from state to state as we execute the NFA.
+%   We make sure that most of the \tn{toks} register is not read
+%   before being assigned again to that same register.
 %    \begin{macrocode}
 \cs_new_protected:Npn \regex_store_submatches:n #1
   {
-    \exp_after:wN \regex_store_submatches_aux:Nw
-    \exp_after:wN \l_regex_current_submatches_prop
-    \tex_the:D \tex_toks:D #1 \scan_stop: \q_stop
-    { #1 }
+    \tex_toks:D #1 \exp_after:wN
+      {
+        \tex_romannumeral:D
+        \exp_after:wN \regex_store_submatches_aux:w
+        \tex_the:D \tex_toks:D #1
+      }
   }
-\cs_new_protected:Npn \regex_store_submatches_aux:Nw #1 #2 \s_regex_toks
+\cs_new_protected:Npn \regex_store_submatches_aux:w #1 \s_regex_toks
   {
-    \exp_args:No \regex_store_submatches_aux_ii:wnnwwn { #1 }
-      #2
-      \regex_state_submatches:nn { \c_minus_one } { \q_prop }
+    \regex_store_submatches_aux_ii:Nnnw
+      #1
+      \regex_state_submatches:nn \c_minus_one \q_prop
     \s_regex_toks
   }
-\cs_new_protected:Npn \regex_store_submatches_aux_ii:wnnwwn
-    #1 \regex_state_submatches:nn #2#3 #4 \s_regex_toks #5 \q_stop #6
+\cs_new_protected:Npn \regex_store_submatches_aux_ii:Nnnw
+    \regex_state_submatches:nn #1 #2 #3 \s_regex_toks
   {
-    \tex_toks:D #6 \exp_after:wN
+    \exp_after:wN \c_zero
+    \exp_after:wN \regex_state_submatches:nn \exp_after:wN
       {
-        \exp_after:wN \regex_state_submatches:nn \exp_after:wN
-          { \int_value:w \int_eval:w \l_regex_unique_step_int + \c_one }
-          { #1 }
-        \regex_state_submatches:nn {#2} {#3}
-        \s_regex_toks
-        #5
+        \int_value:w \int_eval:w
+          \l_regex_unique_step_int + \c_one
+        \exp_after:wN
       }
+      \exp_after:wN { \l_regex_current_submatches_prop }
+    \regex_state_submatches:nn {#1} {#2}
+    \s_regex_toks
   }
 %    \end{macrocode}
 % \end{macro}
@@ -2562,7 +2768,7 @@
 \cs_new_protected:Npn \regex_state_submatches:nn #1#2
   {
     \if_num:w #1 = \l_regex_unique_step_int
-      \tl_set:Nn \l_regex_current_submatches_prop {#2}
+      \tl_set:Nn \l_regex_current_submatches_prop { #2 }
     \fi:
   }
 %    \end{macrocode}
@@ -2571,7 +2777,7 @@
 % \subsubsection{Matching: framework}
 %
 % \begin{macro}[int]{\regex_match:n}
-%   Store the query string in \cs{l_regex_query_str}.
+%   Store the query string in \cs{l_regex_query_other_str}.
 %   Then reset a few variables which should be set only once,
 %   before the first match, even in the case of multiple matches.
 %   Then run the NFA (\cs{regex_match_once:} matches multiple times
@@ -2579,7 +2785,7 @@
 %    \begin{macrocode}
 \cs_new_protected:Npn \regex_match:n #1
   {
-    \tl_set:Nx \l_regex_query_str { \tl_to_other_str:n {#1} }
+    \tl_set:Nx \l_regex_query_other_str { \tl_to_other_str:n {#1} }
     \regex_match_initial_setup:
     \regex_match_once:
   }
@@ -2588,6 +2794,7 @@
 %
 % \begin{macro}[int]{\regex_match_once:}
 % \begin{macro}[aux]{\regex_match_once_aux:}
+% \begin{macro}[aux]{\regex_match_once_aux_ii:N}
 %   After setting up more variables in \cs{regex_match_setup:},
 %   skip the \cs{l_regex_start_step_int} first characters of the
 %   query string, and loop over it.
@@ -2597,15 +2804,32 @@
 \cs_new_protected_nopar:Npn \regex_match_once:
   {
     \regex_match_setup:
-    \exp_after:wN \regex_match_once_aux: \l_regex_query_str
+    \exp_after:wN \regex_match_once_aux: \l_regex_query_other_str
       \q_recursion_tail \q_recursion_stop
     \bool_if:NT \l_regex_success_bool { \l_regex_every_match_tl }
   }
 \cs_new_protected_nopar:Npn \regex_match_once_aux:
-  { \str_skip_do:nn { \l_regex_start_step_int } { \regex_match_loop:N } }
+  {
+    \int_compare:nNnTF \l_regex_start_step_int = \c_zero
+      {
+        \int_set_eq:NN \l_regex_current_char_int \c_minus_one
+        \regex_match_loop:N
+      }
+      {
+        \str_skip_do:nn
+          { \l_regex_start_step_int - \c_one }
+          { \regex_match_once_aux_ii:N }
+      }
+  }
+\cs_new_protected_nopar:Npn \regex_match_once_aux_ii:N #1
+  {
+    \int_set:Nn \l_regex_current_char_int { `#1 }
+    \regex_match_loop:N
+  }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
+% \end{macro}
 %
 % \begin{macro}[aux]{\regex_match_initial_setup:}
 %   This function holds the setup that should be done
@@ -2613,12 +2837,11 @@
 %   string. It is called only once for the whole string.
 %   On the other hand, \cs{regex_match_setup:}
 %   is called for every match in the string in case of
-%   repeated matches, and \cs{regex_match_loop_setup:}
+%   repeated matches, and \cs{regex_match_loop_setup:N}
 %   is called at every step.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_match_initial_setup:
   {
-    \tl_clear:N \l_regex_look_behind_str
     \prg_stepwise_inline:nnnn {1} {1} { \l_regex_max_state_int }
       { \tex_dimen:D ##1 \c_minus_one sp \scan_stop: }
     \int_set_eq:NN \l_regex_unique_step_int  \c_minus_one
@@ -2650,18 +2873,6 @@
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}[aux]{\regex_match_loop_setup:}
-%   This is called for every character in the string.
-%    \begin{macrocode}
-\cs_new_protected_nopar:Npn \regex_match_loop_setup:
-  {
-    \int_incr:N \l_regex_current_step_int
-    \int_incr:N \l_regex_unique_step_int
-    \bool_set_false:N \l_regex_fresh_thread_bool
-  }
-%    \end{macrocode}
-% \end{macro}
-%
 % \begin{macro}[int]{\s_regex_step}
 % \begin{macro}[aux]{\regex_break_step:w}
 %   When a thread succeeds, all threads with lower precedence
@@ -2677,7 +2888,7 @@
 %
 % \begin{macro}[aux]{\regex_match_loop:N}
 % \begin{macro}[aux]{\regex_match_one_index:n}
-% \begin{macro}[aux]{\regex_match_one_index_aux:nn}
+% \begin{macro}[aux]{\regex_match_one_index_aux:n}
 %   Setup what needs to be reset at every character,
 %   then set \cs{l_regex_current_char_int} to the
 %   character code of the character that is read
@@ -2688,10 +2899,7 @@
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_match_loop:N #1
   {
-    \regex_match_loop_setup:
-    \token_if_eq_meaning:NNTF #1 \q_recursion_tail
-      { \int_set_eq:NN \l_regex_current_char_int \c_minus_one }
-      { \int_set:Nn \l_regex_current_char_int {`#1} }
+    \regex_match_loop_setup:N #1
     \cs_set_nopar:Npx \regex_tmp:w
       {
         \int_zero:N \l_regex_max_index_int
@@ -2705,28 +2913,80 @@
       \exp_after:wN \use_none_delimit_by_q_recursion_stop:w
     \fi:
     \quark_if_recursion_tail_stop:N #1
-    \bool_if:NT \l_regex_look_behind_bool
-      { \tl_put_left:Nx \l_regex_look_behind_str {#1} }
     \regex_match_loop:N
   }
 \cs_new_nopar:Npn \regex_match_one_index:n #1
   {
-    \regex_match_one_index_aux:n { \int_value:w \tex_skip:D #1 }
+    \regex_match_one_index_aux:n
+      { \int_value:w \tex_skip:D #1 }
   }
 \cs_new_protected_nopar:Npn \regex_match_one_index_aux:n #1
   {
     \int_set:Nn \l_regex_current_state_int {#1}
     \prop_clear:N \l_regex_current_submatches_prop
-    \regex_state_use_submatches:
+    \regex_state_use_with_submatches:
   }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}[aux]{\regex_match_loop_setup:N}
+%   This is called for every character in the string.
+%   At every step in reading the query string, we store the character
+%   code of the current character in \cs{l_regex_current_char_int},
+%   unless the end was reached: then we store $-1$.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_match_loop_setup:N #1
+  {
+    \int_incr:N \l_regex_current_step_int
+    \int_incr:N \l_regex_unique_step_int
+    \bool_set_false:N \l_regex_fresh_thread_bool
+    \int_set_eq:NN \l_regex_last_char_int \l_regex_current_char_int
+    \if_meaning:w #1 \q_recursion_tail
+      \int_set_eq:NN \l_regex_current_char_int \c_minus_one
+    \else:
+      \int_set:Nn \l_regex_current_char_int {`#1}
+    \fi:
+    \regex_match_loop_case_hook:
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\regex_match_loop_case_hook:}
+% \begin{macro}{\regex_match_loop_caseless_hook:}
+%   In the case where the regular expression contains caseless matching,
+%   the \cs{regex_match_loop_case_hook:} (normally empty) is redefined
+%   to set \cs{l_regex_case_changed_char_int} properly.
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \regex_match_loop_case_hook: { }
+\cs_new_protected_nopar:Npn \regex_match_loop_caseless_hook:
+  {
+    \int_set_eq:NN \l_regex_case_changed_char_int \l_regex_current_char_int
+    \if_num:w \l_regex_current_char_int < \c_ninety_one
+      \if_num:w \l_regex_current_char_int < \c_sixty_five
+      \else:
+        \int_add:Nn \l_regex_case_changed_char_int { \c_thirty_two }
+      \fi:
+    \else:
+      \if_num:w \l_regex_current_char_int < \c_one_hundred_twenty_three
+        \if_num:w \l_regex_current_char_int < \c_ninety_seven
+        \else:
+          \int_sub:Nn \l_regex_case_changed_char_int { \c_thirty_two }
+        \fi:
+      \fi:
+    \fi:
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
 % \subsubsection{Actions when matching}
 %
 % \begin{macro}[aux]{\regex_action_start_wildcard:nn}
+%: the first state has a free transition to the second
+%   state, where the regular expression really begins, and a costly
+%   transition to itself, to try again at the next character. ^^A ??
 %   The search is made unanchored at the start by putting
 %   a free transition to the real start of the NFA, and a
 %   costly transition to the same state, waiting for the
@@ -2751,7 +3011,10 @@
 %   to state |#1|.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_action_cost:n #1
-  { \regex_store_state:n {#1} }
+  {
+    \exp_args:Nf \regex_store_state:n %^^A optimize!
+      { \int_eval:n { \l_regex_current_state_int + #1 } }
+  }
 %    \end{macrocode}
 % \end{macro}
 %
@@ -2790,41 +3053,32 @@
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_action_free:n #1
   {
-    \regex_if_state_free:nT {#1}
+    \cs_set_nopar:Npx \regex_tmp:w
       {
-        \use:x
-          {
-            \int_set:Nn \l_regex_current_state_int {#1}
-            \regex_store_submatches:n { \l_regex_current_state_int }
-            \regex_state_use:
-            \int_set:Nn \l_regex_current_state_int
-              { \int_use:N \l_regex_current_state_int }
-            \tl_set:Nn \exp_not:N \l_regex_current_submatches_prop
-              { \exp_not:o \l_regex_current_submatches_prop }
-          }
+        \int_add:Nn \l_regex_current_state_int {#1}
+        \regex_state_use:
+        \int_set:Nn \l_regex_current_state_int
+          { \int_use:N \l_regex_current_state_int }
+        \tl_set:Nn \exp_not:N \l_regex_current_submatches_prop
+          { \exp_not:o \l_regex_current_submatches_prop }
       }
+    \regex_tmp:w
   }
 %    \end{macrocode}
 % \end{macro}
 %
 % \begin{macro}[aux]{\regex_action_submatch:n}
+%   Update the current submatches with the information
+%   from the current step.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_action_submatch:n #1
   {
     \prop_put:Nno \l_regex_current_submatches_prop {#1}
       { \int_use:N \l_regex_current_step_int }
-    \regex_store_submatches:n { \l_regex_current_state_int }
   }
 %    \end{macrocode}
 % \end{macro}
 %
-%    \begin{macrocode}
-\cs_new_protected_nopar:Npn \regex_action_repeat_copy:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_repeat_move:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_no_repeat_copy:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_no_repeat_move:n { \ERROR }
-%    \end{macrocode}
-%
 % \subsection{Submatches, once the correct match is found}
 %
 % \begin{macro}[int]{\regex_extract:}
@@ -2839,11 +3093,7 @@
         \regex_extract_aux:nTF { ##1 }
           {
             \seq_gput_right:Nx \g_regex_submatches_seq
-              {
-                \str_from_to:Nnn \l_regex_query_str
-                  { \l_regex_tmpa_tl }
-                  { \l_regex_tmpb_tl }
-              }
+              { \regex_query_substr:NN \l_regex_tmpa_tl \l_regex_tmpb_tl }
           }
           { \seq_gput_right:Nn \g_regex_submatches_seq { } }
       }
@@ -2918,9 +3168,13 @@
             = \int_use:N \l_regex_max_state_int
           \l_regex_capturing_group_int
             = \int_use:N \l_regex_capturing_group_int
-          \bool_if:NTF \l_regex_look_behind_bool
-            { \bool_set_true:N \l_regex_look_behind_bool }
-            { \bool_set_false:N \l_regex_look_behind_bool }
+          \token_if_eq_meaning:NNT
+            \regex_match_loop_case_hook:
+            \regex_match_loop_caseless_hook:
+            {
+              \cs_set_eq:NN \regex_match_loop_case_hook:
+                \regex_match_loop_caseless_hook:
+            }
           \prg_stepwise_function:nnnN
             {1} {1} {\l_regex_max_state_int}
             \regex_set_aux:n
@@ -2946,7 +3200,7 @@
 %   If a token list variable starts with \cs{regex_nfa:Nw},
 %   then it most likely holds the data for a precompiled pattern.
 %    \begin{macrocode}
-\prg_new_protected_conditional:Npnn \regex_check_nfa:N #1 { TF }
+\prg_new_protected_conditional:Npnn \regex_check_nfa:N #1 { T , TF }
   { \exp_after:wN \regex_check_nfa_aux:Nw #1 \q_stop }
 \cs_new:Npn \regex_check_nfa_aux:Nw #1 #2 \q_stop
   {
@@ -2957,11 +3211,6 @@
       \prg_return_false:
     \fi:
   }
-\msg_new:nnn { regex } { not-nfa }
-  {
-    I~was~expecting~a~regular~expression~variable.\\
-    Instead,~I~got~#1.
-  }
 %    \end{macrocode}
 % \end{macro}
 %
@@ -3001,7 +3250,7 @@
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_return_after_group:
   {
-    \if_bool:N \l_regex_success_bool
+    \if_meaning:w \c_true_bool \l_regex_success_bool
       \group_insert_after:N \prg_return_true:
     \else:
       \group_insert_after:N \prg_return_false:
@@ -3016,7 +3265,7 @@
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_extract_after_group:N #1
   {
-    \if_bool:N \l_regex_success_bool
+    \if_meaning:w \c_true_bool \l_regex_success_bool
       \regex_extract:
       \group_insert_after:N \seq_set_eq:NN
       \group_insert_after:N #1
@@ -3100,7 +3349,7 @@
   }
 \cs_new_protected:Npn \regex_count:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -3116,7 +3365,6 @@
             \regex_count_after_group:N #3
           }
       }
-      { }
   }
 %    \end{macrocode}
 % \end{macro}
@@ -3124,12 +3372,12 @@
 %
 % \subsubsection{Submatch extraction}
 %
-% \begin{macro}{\regex_extract:nnN}
-% \begin{macro}{\regex_extract:NnN}
-% \begin{macro}[TF]{\regex_extract:nnN}
-% \begin{macro}[TF]{\regex_extract:NnN}
+% \begin{macro}{\regex_extract_once:nnN}
+% \begin{macro}{\regex_extract_once:NnN}
+% \begin{macro}[TF]{\regex_extract_once:nnN}
+% \begin{macro}[TF]{\regex_extract_once:NnN}
 %    \begin{macrocode}
-\cs_new_protected:Npn \regex_extract:nnN #1#2#3
+\cs_new_protected:Npn \regex_extract_once:nnN #1#2#3
   {
     \regex_user_aux:n
       {
@@ -3138,7 +3386,8 @@
         \regex_extract_after_group:N #3
       }
   }
-\prg_new_protected_conditional:Npnn \regex_extract:nnN #1#2#3 { T , F , TF }
+\prg_new_protected_conditional:Npnn \regex_extract_once:nnN #1#2#3
+  { T , F , TF }
   {
     \regex_user_aux:n
       {
@@ -3148,9 +3397,9 @@
         \regex_return_after_group:
       }
   }
-\cs_new_protected:Npn \regex_extract:NnN #1#2#3
+\cs_new_protected:Npn \regex_extract_once:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -3159,9 +3408,9 @@
             \regex_extract_after_group:N #3
           }
       }
-      { }
   }
-\prg_new_protected_conditional:Npnn \regex_extract:NnN #1#2#3 { T , F , TF }
+\prg_new_protected_conditional:Npnn \regex_extract_once:NnN #1#2#3
+  { T , F , TF }
   {
     \regex_check_nfa:NTF #1
       {
@@ -3181,6 +3430,66 @@
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}{\regex_extract_all:nnN}
+% \begin{macro}{\regex_extract_all:NnN}
+% \begin{macro}[aux]{\regex_extract_all_aux:}
+% \begin{macro}[aux]{\regex_extract_all_after_group:N}
+%   Similarly to \cs{regex_count:nnN} functions,
+%   recurse through matches of the pattern. Then we do
+%   something slightly different, extracting submatches.
+%   Submatches are not extracted if the pattern matched
+%   an empty string at the start of the match attempt
+%   (to avoid adding spurious empty items to the resulting
+%   sequence).
+%    \begin{macrocode}
+\cs_new_protected:Npn \regex_extract_all:nnN #1#2#3
+  {
+    \regex_user_aux:n
+      {
+        \seq_gclear:N \g_regex_extract_all_seq
+        \tl_set:Nn \l_regex_every_match_tl { \regex_extract_all_aux: }
+        \regex_build:n {#1}
+        \regex_match:n {#2}
+        \regex_extract_all_after_group:N #3
+      }
+  }
+\cs_new_protected:Npn \regex_extract_all:NnN #1#2#3
+  {
+    \regex_check_nfa:NT #1
+      {
+        \regex_user_aux:n
+          {
+            \seq_gclear:N \g_regex_extract_all_seq
+            \tl_set:Nn \l_regex_every_match_tl { \regex_extract_all_aux: }
+            \regex_use:N #1
+            \regex_match:n {#2}
+            \regex_extract_all_after_group:N #3
+          }
+      }
+  }
+\cs_new_protected_nopar:Npn \regex_extract_all_aux:
+  {
+    \regex_extract:
+    \seq_gconcat:NNN \g_regex_extract_all_seq
+      \g_regex_extract_all_seq \g_regex_submatches_seq
+    \regex_match_once:
+  }
+\cs_new_protected_nopar:Npn \regex_extract_all_after_group:N #1
+  {
+    \seq_if_empty:NF \g_regex_extract_all_seq
+      {
+        \regex_extract:
+        \group_insert_after:N \seq_set_eq:NN
+        \group_insert_after:N #1
+        \group_insert_after:N \g_regex_extract_all_seq
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
 % \subsubsection{Splitting a string by matches of a regex}
 %
 % \begin{macro}{\regex_split:nnN}
@@ -3208,7 +3517,7 @@
   }
 \cs_new_protected:Npn \regex_split:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -3219,7 +3528,6 @@
             \regex_split_after_group:N #3
           }
       }
-      { }
   }
 \cs_new_protected_nopar:Npn \regex_split_aux:
   {
@@ -3231,9 +3539,8 @@
           {
             \seq_gput_left:Nx \g_regex_submatches_seq
               {
-                \str_from_to:Nnn \l_regex_query_str
-                  { \int_use:N \l_regex_start_step_int }
-                  { \l_regex_tmpa_tl }
+                \regex_query_substr:NN
+                  \l_regex_start_step_int \l_regex_tmpa_tl
               }
           }
           { \msg_error:nn { regex } { internal } }
@@ -3252,9 +3559,8 @@
       {
         \seq_gput_right:Nx \g_regex_split_seq
           {
-            \str_from_to:Nnn \l_regex_query_str
-              { \int_use:N \l_regex_start_step_int }
-              { \int_use:N \l_regex_current_step_int }
+            \regex_query_substr:NN
+              \l_regex_start_step_int \l_regex_current_step_int
           }
       }
     \group_insert_after:N \seq_set_eq:NN
@@ -3270,55 +3576,77 @@
 % \subsubsection{String replacement}
 %
 % \begin{macro}[int]{\regex_replacement:n}
-% \begin{macro}[aux]{\regex_replacement_loop:N}
-% \begin{macro}[aux]{\regex_replacement_normal:N}
+% \begin{macro}[aux]{\regex_replacement_escaped:N}
+% \begin{macro}[aux]{\regex_replacement_submatch:w}
+% \begin{macro}[aux]{\regex_replacement_submatch_aux:nN}
 %    \begin{macrocode}
 \cs_new_protected:Npn \regex_replacement:n #1
   {
     \str_aux_escape:NNNn
       \prg_do_nothing:
       \regex_replacement_escaped:N
-      \regex_replacement_raw:N
+      \prg_do_nothing:
       {#1}
     \tl_set_eq:NN \l_regex_replacement_tl \g_str_result_tl
     \tl_set:Nx \l_regex_replacement_tl
       { \l_regex_replacement_tl \prg_do_nothing: }
   }
-\cs_new_nopar:Npn \regex_replacement_raw:N { \exp_not:N \prg_do_nothing: }
 \cs_new_nopar:Npn \regex_replacement_escaped:N #1
   {
-    \if_num:w 9 < 1 #1 \exp_stop_f:
-      \exp_not:N \regex_replacement_escaped_ii:nN {#1}
-    \else:
-      #1
-    \fi:
+    \regex_token_if_other_digit:NTF #1
+      {
+        \exp_not:n
+          { \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } } {#1}
+      }
+      {
+        \token_if_eq_charcode:NNTF g #1
+          { \exp_not:N \regex_replacement_submatch:w }
+          { #1 }
+      }
   }
-\cs_new_nopar:Npn \regex_replacement_escaped_ii:nN #1#2
+\cs_new_nopar:Npn \regex_replacement_submatch:w #1
   {
-    \regex_token_if_other_digit:NTF #2
-      { \regex_replacement_escaped_ii:nN {#1#2} }
-      { \exp_not:N \seq_item:Nn \exp_not:N \g_regex_submatches_seq {#1} #2 }
+    \exp_after:wN \token_if_eq_meaning:NNTF \c_lbrace_str #1
+      { \regex_replacement_submatch_aux:nN { } }
+      {
+        \regex_token_if_other_digit:NTF #1
+          { \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } }
+          { \msg_expandable_error:n { \g misused~in~replacement~text. } }
+        #1
+      }
   }
-\prg_new_conditional:Npnn \regex_token_if_other_digit:N #1 { TF }
+\cs_new_nopar:Npn \regex_replacement_submatch_aux:nN #1 #2
   {
-    \if_num:w 9 < 1 \exp_not:N #1 \exp_stop_f:
-      \prg_return_true:
-    \else:
-      \prg_return_false:
-    \fi:
+    \regex_token_if_other_digit:NTF #2
+      { \regex_replacement_submatch_aux:nN {#1#2} }
+      {
+        \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } {#1}
+        \exp_after:wN \token_if_eq_meaning:NNF \c_rbrace_str #2
+          {
+            \msg_expandable_error:n { \g misused~in~replacement~text. }
+            #2
+          }
+      }
   }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 % \end{macro}
+% \end{macro}
 %
 % \begin{macro}[aux]{\regex_replace_after_group:N}
+%   I wonder why I implemented things with \tn{aftergroup}
+%   rather than simply placing that code after the explicit
+%   \cs{group_end:} that I have. (General remark.)
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \regex_replace_after_group:N #1
   {
-    \group_insert_after:N \tl_set_eq:NN
+    \group_insert_after:N \tl_set:Nx
     \group_insert_after:N #1
-    \group_insert_after:N \g_regex_replaced_str
+    \group_insert_after:N {
+      \group_insert_after:N \tl_to_str:N
+      \group_insert_after:N \g_regex_replaced_str
+    \group_insert_after:N }
   }
 %    \end{macrocode}
 % \end{macro}
@@ -3339,15 +3667,16 @@
       \regex_extract:
       \regex_extract_aux:nTF {0}
         {
+          \cs_set_nopar:Npn \regex_tmp:w
+            { \str_skip_do:nn { \l_regex_tmpb_tl } { } }
           \tl_gset:Nx \g_regex_replaced_str
             {
-              \str_from_to:Nnn \l_regex_query_str {0} { \l_regex_tmpa_tl }
+              \regex_query_substr:NN \c_zero \l_regex_tmpa_tl
               \l_regex_replacement_tl
-              \str_from_to:Nnn \l_regex_query_str
-                { \l_regex_tmpb_tl } { \c_max_int }
+              \exp_after:wN \regex_tmp:w \l_regex_query_other_str
             }
         }
-        { \tl_gset_eq:NN \g_regex_replaced_str \l_regex_query_str }
+        { \tl_gset_eq:NN \g_regex_replaced_str \l_regex_query_other_str }
     \group_end:
   }
 \cs_new_protected:Npn \regex_replace_once:nnN #1#2#3
@@ -3404,12 +3733,10 @@
       \tl_gclear:N \g_regex_replaced_str
       #2
       \exp_args:No \regex_match:n {#1}
+      \cs_set_nopar:Npn \regex_tmp:w
+        { \str_skip_do:nn { \l_regex_start_step_int } { } }
       \tl_gput_right:Nx \g_regex_replaced_str
-        {
-          \str_from_to:Nnn \l_regex_query_str
-            { \int_use:N \l_regex_start_step_int }
-            { \c_max_int }
-        }
+        { \exp_after:wN \regex_tmp:w \l_regex_query_other_str }
     \group_end:
   }
 \cs_new_protected_nopar:Npn \regex_replace_all_aux:
@@ -3419,9 +3746,8 @@
       {
         \tl_gput_right:Nx \g_regex_replaced_str
           {
-            \str_from_to:Nnn \l_regex_query_str
-              { \int_use:N \l_regex_start_step_int }
-              { \l_regex_tmpa_tl }
+            \regex_query_substr:NN
+              \l_regex_start_step_int \l_regex_tmpa_tl
             \l_regex_replacement_tl
           }
       }
@@ -3450,6 +3776,47 @@
 % \end{macro}
 % \end{macro}
 %
+% \subsection{Messages}
+%
+% Negative codes are specific to the \LaTeX3 implementation.
+% Other error codes match with the PCRE codes (not all of
+% the PCRE errors can occur, since many constructions are
+% not supported).
+%    \begin{macrocode}
+% \msg_new:nnn { regex } { -999 } { File~not~found }
+\msg_new:nnn { regex } { -998 } { Unsupported~construct }
+\msg_new:nnn { regex } { -997 }
+  { The~regular~expression~is~too~large~(32768~states). }
+\msg_new:nnn { regex } { 1 } { \iow_char:N\\~at~end~of~pattern }
+% \msg_new:nnn { regex } { 2 } { \iow_char:N\\c~at~end~of~pattern }
+\msg_new:nnn { regex } { 4 }
+  { Numbers~out~of~order~in~\iow_char:N\{\iow_char\}~quantifier. }
+\msg_new:nnn { regex } { 6 }
+  { Missing~terminating~\iow_char:N\]~for~character~class }
+\msg_new:nnn { regex } { 7 }
+  { Invalid~escape~sequence~in~character~class }
+\msg_new:nnn { regex } { 8 }
+  { Range~out~of~order~in~character~class }
+\msg_new:nnn { regex } { 22 } { Mismatched~parentheses }
+\msg_new:nnn { regex } { 34 }
+  { Character~value~in~\iow_char:N\\x{...}~sequence~is~too~large }
+% \msg_new:nnn { regex } { 44 } { Invalid~UTF-8~string }
+% \msg_new:nnn { regex } { 46 }
+%   { Malformed~\iow_char:N\\P~or\iow_char:N\\p~sequence }
+% \msg_new:nnn { regex } { 47 }
+%   { Unknown~property~after~\iow_char:N\\P~or\iow_char:N\\p }
+% \msg_new:nnn { regex } { 68 }
+%   { \iow_char:N\\c~must~be~followed~by~an~ASCII~character }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\msg_new:nnn { regex } { not-nfa }
+  {
+    LaTeX~was~expecting~a~regular~expression~variable.\\
+    Instead,~LaTeX~found~'#1'.
+  }
+%    \end{macrocode}
+%
 %    \begin{macrocode}
 %</package>
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex/l3experimental/l3str/l3str.dtx b/Master/texmf-dist/source/latex/l3experimental/l3str/l3str.dtx
index a718f986ce7..b3648c57ede 100644
--- a/Master/texmf-dist/source/latex/l3experimental/l3str/l3str.dtx
+++ b/Master/texmf-dist/source/latex/l3experimental/l3str/l3str.dtx
@@ -35,7 +35,7 @@
 %
 %<*driver|package>
 \RequirePackage{expl3}
-\GetIdInfo$Id: l3str.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: l3str.dtx 2921 2011-10-17 13:23:36Z bruno $
   {L3 Experimental Strings}
 %</driver|package>
 %<*driver>
@@ -72,25 +72,23 @@
 % \LaTeX3 provides a set of functions to manipulate token lists
 % as strings of characters, ignoring the category codes of those
 % characters.
-%
-% There is no separate string data type: string variables are simply
-% specialized token lists, conventionally made out only of characters
-% with category code $12$ (other), except spaces, which have category
-% code $10$ (blank space). All the \enquote{safe} functions in this
-% module first convert their argument to a string for internal processing,
+% 
+% String variables are simply specialised token lists, but by convention
+% should be named with the suffix \texttt{\ldots str}. Such variables should
+% contain characters with category code $12$ (other), except spaces, which
+% have category code $10$ (blank space). All the \enquote{safe} functions in
+% this module first convert their argument to a string for internal processing,
 % and will not treat a token list or the corresponding string representation
-% differently. However, it is often better to name token list variables
-% meant to contain string data with a name such as \cs{l_\ldots{}_str}.
-% Those are then manipulated mostly with tools from \pkg{l3tl}.
+% differently.
 %
 % Most functions in this module come in three flavours:
 % \begin{itemize}
-% \item \cs{str_...:N...}, which expect a token list
-%   variable as their argument;
-% \item \cs{str_...:n...}, taking any token list (or string) as an argument;
-% \item \cs{str_..._ignore_spaces:n...}, which ignores any space encountered
-%   during the operation: these functions are slightly faster than those
-%   which take care of escaping spaces appropriately;
+%   \item \cs{str_...:N...}, which expect a token list
+%     variable as their argument;
+%   \item \cs{str_...:n...}, taking any token list (or string) as an argument;
+%   \item \cs{str_..._ignore_spaces:n...}, which ignores any space encountered
+%     during the operation: these functions are slightly faster than those
+%     which take care of escaping spaces appropriately;
 % \end{itemize}
 % When performance is important, the internal \cs{str_..._unsafe:n...}
 % functions, which expect a \enquote{safe} string in which spaces
@@ -98,66 +96,119 @@
 %
 % \subsection{Conversion and input of strings}
 %
-% \begin{variable}{\c_backslash_str,
-%     \c_lbrace_str,\c_rbrace_str,\c_hash_str,\c_percent_str}
+% \begin{variable}
+%   {
+%     \c_backslash_str,
+%     \c_lbrace_str,
+%     \c_rbrace_str,
+%     \c_hash_str,
+%     \c_percent_str
+%   }
 %   Constant strings, containing a single character, with category code $12$.
 % \end{variable}
 %
-% \begin{function}[EXP]{\tl_to_str:N,\tl_to_str:n}
+% \begin{function}[EXP]{\tl_to_str:N, \tl_to_str:n}
 %   \begin{syntax}
 %     \cs{tl_to_str:N} \meta{tl var}
 %     \cs{tl_to_str:n} \Arg{token list}
 %   \end{syntax}
-%   Converts the \meta{token list} to a \meta{string}.
+%   Converts the \meta{token list} to a \meta{string}, leaving the resulting
+%   tokens in the input stream.
+% \end{function}
+%
+% \begin{function}{\str_set:Nn, \str_set:Nx, \str_set:cn, \str_set:cx}
+%   \begin{syntax}
+%     \cs{str_set:Nn} \meta{str var} \Arg{token list}
+%   \end{syntax}
+%   Converts the \meta{token list} to a \meta{string},
+%   and saves the result in \meta{str var}.
+% \end{function}
+%
+% \begin{function}{\str_gset:Nn, \str_gset:Nx, \str_gset:cn, \str_gset:cx}
+%   \begin{syntax}
+%     \cs{str_gset:Nn} \meta{str var} \Arg{token list}
+%   \end{syntax}
+%   Converts the \meta{token list} to a \meta{string},
+%   and saves the result in \meta{str var} globally.
 % \end{function}
 %
 % \begin{function}
 %   {
-%     \str_set:Nn, \str_set:Nx,
-%     \str_set:cn, \str_set:cx,
-%     \str_gset:Nn, \str_gset:Nx,
-%     \str_gset:cn, \str_gset:cx,
+%     \str_put_left:Nn, \str_put_left:Nx,
+%     \str_put_left:cn, \str_put_left:cx
 %   }
+%   \begin{syntax}
+%     \cs{str_put_left:Nn} \meta{str var} \Arg{token list}
+%   \end{syntax}
+%   Converts the \meta{token list} to a \meta{string},
+%   and prepends the result to \meta{str var}.
+%   The current contents of the \meta{str var} are not
+%   automatically converted to a string.
+% \end{function}
+%
 % \begin{function}
 %   {
-%     \str_put_left:Nn, \str_put_left:Nx,
-%     \str_put_left:cn, \str_put_left:cx,
 %     \str_gput_left:Nn, \str_gput_left:Nx,
-%     \str_gput_left:cn, \str_gput_left:cx,
+%     \str_gput_left:cn, \str_gput_left:cx
 %   }
+%   \begin{syntax}
+%     \cs{str_gput_left:Nn} \meta{str var} \Arg{token list}
+%   \end{syntax}
+%   Converts the \meta{token list} to a \meta{string},
+%   and prepends the result to \meta{str var}, globally.
+%   The current contents of the \meta{str var} are not
+%   automatically converted to a string.
+% \end{function}
+%
 % \begin{function}
 %   {
 %     \str_put_right:Nn, \str_put_right:Nx,
-%     \str_put_right:cn, \str_put_right:cx,
-%     \str_gput_right:Nn, \str_gput_right:Nx,
-%     \str_gput_right:cn, \str_gput_right:cx,
+%     \str_put_right:cn, \str_put_right:cx
 %   }
 %   \begin{syntax}
-%     \cs{str_set:Nn} \meta{str var} \Arg{token list}
+%     \cs{str_put_right:Nn} \meta{str var} \Arg{token list}
 %   \end{syntax}
 %   Converts the \meta{token list} to a \meta{string},
-%   and saves the result in \meta{str var}.
-% \end{function}
+%   and appends the result to \meta{str var}.
+%   The current contents of the \meta{str var} are not
+%   automatically converted to a string.
 % \end{function}
+%
+% \begin{function}
+%   {
+%     \str_gput_right:Nn, \str_gput_right:Nx,
+%     \str_gput_right:cn, \str_gput_right:cx
+%   }
+%   \begin{syntax}
+%     \cs{str_gput_right:Nn} \meta{str var} \Arg{token list}
+%   \end{syntax}
+%   Converts the \meta{token list} to a \meta{string},
+%   and appends the result to \meta{str var}, globally.
+%   The current contents of the \meta{str var} are not
+%   automatically converted to a string.
 % \end{function}
 %
-% \begin{function}{\str_input:Nn,\str_ginput:Nn}
+% \begin{function}{\str_input:Nn, \str_ginput:Nn}
 %   \begin{syntax}
 %     \cs{str_input:Nn} \meta{str var} \Arg{token list}
 %   \end{syntax}
 %   Converts the \meta{token list} into a \meta{string}, and stores
-%   it in the \meta{str var}. Special characters can be input by
+%   it in the \meta{str var}, within the current \TeX{} group level
+%   for the \texttt{input} variant and globally for the \texttt{ginput}
+%   version.
+%   Special characters can be input by
 %   escaping them with a backslash.
 %   \begin{itemize}
-%   \item Spaces are ignored unless escaped with a backslash.
-%   \item |\xhh| produces the character with code \texttt{hh}
-%     in hexadecimal: when |\x| is encountered, up to two hexadecimal digits
-%     (\texttt{0}--\texttt{9}, \texttt{a}--\texttt{f}, \texttt{A}--\texttt{F})
-%     are read to give a number between $0$ and $255$.
-%   \item |\x{hh...}| produces the character with code \texttt{hh...}
-%     (an aribtrary number of hexadecimal digits are read):
-%     this is mostly useful for Lua\TeX{} and Xe\TeX{}.
-%   \item |\a|, |\e|, |\f|, |\n|, |\r|, |\t| stand for specific characters:
+%     \item Spaces are ignored unless escaped with a backslash.
+%     \item |\xhh| produces the character with code \texttt{hh}
+%       in hexadecimal: when |\x| is encountered, up to two hexadecimal digits
+%       (\texttt{0}--\texttt{9}, \texttt{a}--\texttt{f},
+%       \texttt{A}--\texttt{F})
+%       are read to give a number between $0$ and $255$.
+%     \item |\x{hh...}| produces the character with code \texttt{hh...}
+%       (an arbitrary number of hexadecimal digits are read):
+%       this is mostly useful for \LuaTeX{} and \XeTeX{}.
+%     \item |\a|, |\e|, |\f|, |\n|, |\r|, |\t| stand for specific characters:
 %     \begin{center}
 %       \begin{tabular}{cccc}
 %         |\a| & |\^^G| & alarm  & hex \texttt{07} \\
@@ -172,26 +223,27 @@
 %   For instance,
 %   \begin{quote}
 %     \cs{tl_new:N} \cs{l_my_str} \\
-%     \cs{str_input:Nn} \cs{l_my_str} |{\x3C \\ \# abc\ def\^}|
+%     \cs{str_input:Nn} \cs{l_my_str} |{\x3C \\ \# abc\ def\^\n}|
 %   \end{quote}
-%   results in \cs{l_my_str} containing the characters |\<#abc def^|,
-%   since |<| has ascii code \texttt{3C} (in hexadecimal).
+%   results in \cs{l_my_str} containing the characters |<\#abc def^|,
+%   followed by a newline character (hex \texttt{0A})
+%   since |<| has \textsc{ascii} code \texttt{3C} (in hexadecimal).
 % \end{function}
 %
 % \subsection{Characters given by their position}
 %
-% \begin{function}[EXP]{\str_length:N}
-% \begin{function}[EXP]{\str_length:n}
-% \begin{function}[EXP]{\str_length_ignore_spaces:n}
+% \begin{function}[EXP]
+%   {\str_length:N, \str_length:n, \str_length_ignore_spaces:n}
 %   \begin{syntax}
 %     \cs{str_length:n} \Arg{token list}
 %   \end{syntax}
 %   Leaves the length of the string representation of \meta{token list}
-%   in the input stream. The functions differ in their treatment of spaces.
+%   in the input stream as an integer denotation. The functions differ in
+%   their treatment of spaces.
 %   In the case of \cs{str_length:N} and \cs{str_length:n},
 %   all characters including spaces are counted.
-%   The \cs{str_length_ignore_spaces:n} returns the number of non-space
-%   characters.
+%   The \cs{str_length_ignore_spaces:n} leaves the number of non-space
+%   characters in the input stream.
 %   \begin{texnote}
 %     The \cs{str_length:n} of a given token list may depend
 %     on the category codes in effect when it is measured,
@@ -200,12 +252,8 @@
 %     on the escape character, and the category code of \texttt{a}.
 %   \end{texnote}
 % \end{function}
-% \end{function}
-% \end{function}
 %
-% \begin{function}[EXP]{\str_head:N}
-% \begin{function}[EXP]{\str_head:n}
-% \begin{function}[EXP]{\str_head_ignore_spaces:n}
+% \begin{function}[EXP]{\str_head:N, \str_head:n, \str_head_ignore_spaces:n}
 %   \begin{syntax}
 %     \cs{str_head:n} \Arg{token list}
 %   \end{syntax}
@@ -215,18 +263,14 @@
 %   The functions differ in their treatment of spaces.
 %   In the case of \cs{str_head:N} and \cs{str_head:n},
 %   a leading space is returned with category code $10$ (blank space).
-%   The \cs{str_head_ignore_spaces:n} function returns the first
-%   non-space character.
+%   The \cs{str_head_ignore_spaces:n} function leaves  the first
+%   non-space character in the input stream.
 %   If the \meta{token list} is empty (or blank in the case of the
 %   \texttt{_ignore_spaces} variant), then nothing is left on the
 %   input stream.
 % \end{function}
-% \end{function}
-% \end{function}
 %
-% \begin{function}[EXP]{\str_tail:N}
-% \begin{function}[EXP]{\str_tail:n}
-% \begin{function}[EXP]{\str_tail_ignore_spaces:n}
+% \begin{function}[EXP]{\str_tail:N, \str_tail:n, \str_tail_ignore_spaces:n}
 %   \begin{syntax}
 %     \cs{str_tail:n} \Arg{token list}
 %   \end{syntax}
@@ -239,12 +283,8 @@
 %   only that space, while \cs{str_tail_ignore_spaces:n} trims
 %   the first non-space character.
 % \end{function}
-% \end{function}
-% \end{function}
 %
-% \begin{function}[EXP]{\str_item:Nn}
-% \begin{function}[EXP]{\str_item:nn}
-% \begin{function}[EXP]{\str_item_ignore_spaces:nn}
+% \begin{function}[EXP]{\str_item:Nn, \str_item:nn, \str_item_ignore_spaces:nn}
 %   \begin{syntax}
 %     \cs{str_item:nn} \Arg{token list} \Arg{integer expression}
 %   \end{syntax}
@@ -260,29 +300,25 @@
 %   the right-most character, \emph{etc.}, while $0$ is the first
 %   (left-most) character.
 % \end{function}
-% \end{function}
-% \end{function}
 %
-% \begin{function}[EXP]{\str_from_to:Nnn}
-% \begin{function}[EXP]{\str_from_to:nnn}
-% \begin{function}[EXP]{\str_from_to_ignore_spaces:nnn}
+% \begin{function}[EXP]
+%   {\str_substr:Nnn, \str_substr:nnn, \str_substr_ignore_spaces:nnn}
 %   \begin{syntax}
-%     \cs{str_from_to:nnn} \Arg{token list} \Arg{start index} \Arg{end index}
+%     \cs{str_substr:nnn} \Arg{token list} \Arg{start index} \Arg{end index}
 %   \end{syntax}
 %   Converts the \meta{token list} to a \meta{string},
 %   and leaves in the input stream the characters
 %   between \meta{start index} (inclusive) and \meta{end index} (exclusive).
 %   If either of \meta{start index} or \meta{end index} is negative,
-%   the it is incremented by the length of the list.
-% \end{function}
-% \end{function}
+%   the it is incremented by the length of the list. Both \meta{start index}
+%   and \meta{end index} count from $0$ for the first (left most) character.
 % \end{function}
 %
 % \subsection{String conditionals}
 %
-% \begin{function}[EXP,pTF]{\str_if_eq:NN}
-% \begin{function}[EXP,pTF]
+% \begin{function}[EXP, pTF]
 %   {
+%     \str_if_eq:NN,
 %     \str_if_eq:nn, \str_if_eq:Vn, \str_if_eq:on, \str_if_eq:no,
 %     \str_if_eq:nV, \str_if_eq:VV, \str_if_eq:xx
 %   }
@@ -300,10 +336,9 @@
 %   expandable (including those involving an \texttt{x}-type
 %   expansion).
 % \end{function}
-% \end{function}
 %
-% \begin{function}[EXP,pTF]{\str_if_contains_char:NN}
-% \begin{function}[EXP,pTF]{\str_if_contains_char:nN}
+% \begin{function}[EXP, pTF]
+%   {\str_if_contains_char:NN, \str_if_contains_char:nN}
 %   \begin{syntax}
 %     \cs{str_if_contains_char:nN} \Arg{token list} \meta{char}
 %   \end{syntax}
@@ -312,43 +347,43 @@
 %   The \meta{char} can be given either directly, or as a one
 %   letter control sequence.
 % \end{function}
-% \end{function}
 %
-% \subsection{Bytes and encoding}
+% \subsection{Byte conditionals}
 %
-% \subsubsection{Conditionals}
-%
-% \begin{function}[EXP,pTF]{\str_if_bytes:N}
+% \begin{function}[EXP, pTF]{\str_if_bytes:N}
 %   \begin{syntax}
 %     \cs{str_if_bytes:NTF} \meta{str var} \Arg{true code} \Arg{false code}
 %   \end{syntax}
 %   Tests whether the \meta{str var} only contains characters
-%   in the range $0$--$255$.
-% \end{function}
-%
-% \begin{function}[EXP,pTF]{\str_if_UTF_viii:N}
-%   \begin{syntax}
-%     \cs{str_if_UTF_viii:N} \meta{str var} \Arg{true code} \Arg{false code}
-%   \end{syntax}
-%   Tests whether the \meta{str var} only contains characters
-%   in the range $0$--$255$, and forms a valid \texttt{UTF8} string.
-%   \textbf{Missing!} ^^A Missing.
+%   in the range $0$ to $255$.
 % \end{function}
 %
-% \subsubsection{Conversion}
+% ^^A\begin{function}[EXP, pTF]{\str_if_UTF_viii:N}
+% ^^A  \begin{syntax}
+% ^^A    \cs{str_if_UTF_viii:N} \meta{str var} \Arg{true code} \Arg{false code}
+% ^^A  \end{syntax}
+% ^^A  Tests whether the \meta{str var} only contains characters
+% ^^A  in the range $0$--$255$, and forms a valid \texttt{UTF8} string.
+% ^^A  \textbf{Missing!} ^^A Missing.
+% ^^A\end{function}
+%
+% \subsection{Byte conversion}
+% 
+% Byte conversions are necessary where strings are to be used in PDF
+% string objects or within URLs. In both cases, only a restricted subset
+% of characters are permitted.
 %
 % \begin{function}{\str_native_from_UTF_viii:NN}
 %   \begin{syntax}
 %     \cs{str_native_from_UTF_viii:NN} \meta{str~var1} \meta{str~var2}
 %   \end{syntax}
-%   Reads the contents of the \meta{str~var2} as an \texttt{UTF8}-encoded
+%   Reads the contents of the \meta{str~var2} as an \textsc{utf8}-encoded
 %   sequence of bytes, and stores the resulting characters (which can
 %   now have any character code) into \meta{str~var1}.
 %   This function raises an error if the \meta{str~var2} is not
-%   a valid sequence of bytes in the \texttt{UTF8} encoding.
+%   a valid sequence of bytes in the \textsc{utf8} encoding.
 %   In the \pdfTeX{} engine, this function raises an error if any of the
-%   resulting characters is outside the range $0$--$255$ (in other words,
-%   don't use this function with \pdfTeX{}).
+%   resulting characters is outside the range $0$ to $255$.
 % \end{function}
 %
 % \begin{function}{\str_UTF_viii_from_native:NN}
@@ -356,58 +391,123 @@
 %     \cs{str_UTF_viii_from_native:NN} \meta{str~var1} \meta{str~var2}
 %   \end{syntax}
 %   Converts each character of the \meta{str~var2} into
-%   a sequence of bytes, as defined by the \texttt{UTF8}
+%   a sequence of bytes, as defined by the \textsc{utf8}
 %   encoding, and stores the result in \meta{str~var1}.
 %   In the \pdfTeX{} engine, this function is of course
 %   of very little use, but can be used without harm:
-%   characters in the range $0$--$127$ are left unchanged,
-%   and characters in the range $128$--$255$ become two-byte
+%   characters in the range $0$ to $127$ are left unchanged,
+%   and characters in the range $128$ to $255$ become two-byte
 %   sequences, as per the definition of \texttt{UTF8}.
 % \end{function}
 %
-% \begin{function}{\str_bytes_escape_hexadecimal:NN}
-% \begin{function}{\str_bytes_unescape_hexadecimal:NN}
+% \begin{function}
+%   {\str_bytes_escape_hexadecimal:NN, \str_bytes_unescape_hexadecimal:NN}
 %   \begin{syntax}
 %     \cs{str_bytes_escape_hexadecimal:NN} \meta{str var1} \meta{str var2}
 %     \cs{str_bytes_unescape_hexadecimal:NN} \meta{str var1} \meta{str var2}
 %   \end{syntax}
-%   See \tn{pdfescapehex}. ^^A missing doc
-% \end{function}
+%   The \texttt{escape} variant takes each character in \meta{str var1}
+%   and converts it into the hexadecimal representation. The resulting
+%   string is stored in \meta{str var2} within the current \TeX{} group
+%   level. The \texttt{unescape} variant reverses this process.
+%   Thus for example
+%   \begin{verbatim}
+%     \str_set:Nn \l_mya_str { Hello ( ) }
+%     \str_bytes_escape_hexadecimal:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |48656C6C6F2829|,
+%   while
+%   \begin{verbatim}
+%     \str_set:Nn \l_mya_str { 48656C6C6F2829 }
+%     \str_bytes_unescape_hexadecimal:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello()|.
+%   See also \tn{pdfescapehex}.
 % \end{function}
 %
-% \begin{function}{\str_bytes_escape_name:NN}
-% \begin{function}{\str_bytes_unescape_name:NN}
+% \begin{function}
+%   {\str_bytes_escape_name:NN, \str_bytes_unescape_name:NN}
 %   \begin{syntax}
 %     \cs{str_bytes_escape_name:NN} \meta{str var1} \meta{str var2}
 %     \cs{str_bytes_unescape_name:NN} \meta{str var1} \meta{str var2}
 %   \end{syntax}
-%   See \tn{pdfescapename}. ^^A missing doc
-% \end{function}
+%   The \texttt{escape} variant takes each character in \meta{str var1}
+%   and replaces any which cannot be used directly in a PDF string object
+%   with the appropriate hexadecimal representation preceded by the |#|
+%   character. The resulting
+%   string is stored in \meta{str var2} within the current \TeX{} group
+%   level. The \texttt{unescape} variant reverses this process. Thus for
+%   example
+%   \begin{verbatim}
+%     \str_set:Nn \l_mya_str { Hello ( ) }
+%     \str_bytes_escape_name:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello#28#29|,
+%   while
+%   \begin{verbatim}
+%     \char_set_catcode_other:N \#
+%     \str_set:Nn \l_mya_str { Hello#28#29  }
+%     \str_bytes_unescape_name:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello()|.
+%   See also \tn{pdfescapename}.
 % \end{function}
 %
-% \begin{function}{\str_bytes_escape_string:NN}
-% \begin{function}{\str_bytes_unescape_string:NN}
+% \begin{function}{\str_bytes_escape_string:NN, \str_bytes_unescape_string:NN}
 %   \begin{syntax}
 %     \cs{str_bytes_escape_string:NN} \meta{str var1} \meta{str var2}
 %     \cs{str_bytes_unescape_string:NN} \meta{str var1} \meta{str var2}
 %   \end{syntax}
-%   See \tn{pdfescapestring}. ^^A missing doc
-% \end{function}
+%   The \texttt{escape} variant takes each character in \meta{str var1}
+%   and prepends a |\| to any which cannot be used directly in a PDF string
+%   object. The resulting string is stored in \meta{str var2} within the
+%   current \TeX{} group level. The \texttt{unescape} variant reverses this
+%   process. Thus for example
+%   \begin{verbatim}
+%     \str_set:Nn \l_mya_str { Hello [ ] }
+%     \str_bytes_escape_string:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello\(\)|,
+%   while
+%   \begin{verbatim}
+%     \str_set:Nn \l_mya_str { Hello\(\) }
+%     \str_bytes_unescape_string:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello()|.
+%   Some characters (for example a space) are converted to a three-digit
+%   octal representation, so for example a space gives |\040|.
+%   See also \tn{pdfescapename}.
 % \end{function}
 %
-% \begin{function}{\str_bytes_percent_encode:NN}
-% \begin{function}{\str_bytes_percent_decode:NN}
+% \begin{function}{\str_bytes_percent_encode:NN, \str_bytes_percent_decode:NN}
 %   \begin{syntax}
 %     \cs{str_bytes_percent_encode:NN} meta{str var1} \meta{str var2}
 %     \cs{str_bytes_percent_decode:NN} meta{str var1} \meta{str var2}
 %   \end{syntax}
-%   Used for urls. ^^A missing doc
-% \end{function}
+%   The \texttt{escape} variant takes each character in \meta{str var1}
+%   and replaces any which cannot be used directly in a URL
+%   with the appropriate hexadecimal representation preceded by the |%|
+%   character. The resulting
+%   string is stored in \meta{str var2} within the current \TeX{} group
+%   level. The \texttt{unescape} variant reverses this process. Thus for
+%   example
+%   \begin{verbatim}
+%     \str_set:Nn \l_mya_str { Hello ( ) }
+%     \str_bytes_precent_encode:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello%28%29|,
+%   while
+%   \begin{verbatim}
+%     \char_set_catcode_other:N \%
+%     \str_set:Nn \l_mya_str { Hello%28%29  }
+%     \str_bytes_unescape_name:NN \l_mya_str \l_myb_str
+%   \end{verbatim}
+%   will result in \cs{l_myb_str} containing the string |Hello()|.
 % \end{function}
 %
 % \subsection{Internal string functions}
 %
-% \begin{function}[EXP]{\tl_to_other_str:N,\tl_to_other_str:n}
+% \begin{function}[EXP]{\tl_to_other_str:N, \tl_to_other_str:n}
 %   \begin{syntax}
 %     \cs{tl_to_other_str:n} \Arg{token list}
 %   \end{syntax}
@@ -421,7 +521,7 @@
 %   \end{texnote}
 % \end{function}
 %
-% \begin{function}[EXP]{\str_sanitize_args:Nn,\str_sanitize_args:Nnn}
+% \begin{function}[EXP]{\str_sanitize_args:Nn, \str_sanitize_args:Nnn}
 %   \begin{syntax}
 %     \cs{str_sanitize_args:Nnn} \meta{function}
 %     ~~\Arg{token list1} \Arg{token list2}
@@ -473,7 +573,6 @@
 % Some functionalities of \pkg{stringstrings} and \pkg{xstring} as well.
 %
 %^^A Should "str_item" be "str_char"?
-%^^A Should "str_from_to" be "str_substr"?
 %
 % \end{documentation}
 %
@@ -482,7 +581,7 @@
 % \section{\pkg{l3str} implementation}
 %
 %    \begin{macrocode}
-%<*package>
+%<*initex|package>
 %    \end{macrocode}
 %
 %    \begin{macrocode}
@@ -492,31 +591,18 @@
 %
 % Those string-related functions are defined in \pkg{l3kernel}.
 % \begin{itemize}
-% \item \cs{str_if_eq:nn}[pTF] and variants,
-% \item \cs{str_if_eq_return:on},
-% \item \cs{tl_to_str:n}, \cs{tl_to_str:N}, \cs{tl_to_str:c},
-% \item \cs{token_to_str:N}, \cs{cs_to_str:N}
-% \item \cs{str_head:n}, \cs{str_head_aux:w}, (changed behaviour slightly)
-% \item \cs{str_tail:n}, \cs{str_tail_aux:w}, (changed behaviour slightly)
-% \item \cs{str_length_skip_spaces} (deprecated)
-% \item \cs{str_length_loop:NNNNNNNNN} (unchanged)
+%   \item \cs{str_if_eq:nn}[pTF] and variants,
+%   \item \cs{str_if_eq_return:on},
+%   \item \cs{tl_to_str:n}, \cs{tl_to_str:N}, \cs{tl_to_str:c},
+%   \item \cs{token_to_str:N}, \cs{cs_to_str:N}
+%   \item \cs{str_head:n}, \cs{str_head_aux:w}, (copied here)
+%   \item \cs{str_tail:n}, \cs{str_tail_aux:w}, (copied here)
+%   \item \cs{str_length_skip_spaces} (deprecated)
+%   \item \cs{str_length_loop:NNNNNNNNN} (unchanged)
 % \end{itemize}
 %
 % \subsection{General functions}
 %
-% \begin{macro}[EXP,aux]{\cs_if_exist_use:cF}
-%   This function could be moved to a different module in \pkg{l3kernel}.
-%   If the control sequence exists, use it,
-%   otherwise fall back to a default behaviour.
-%    \begin{macrocode}
-\cs_if_exist:NF \cs_if_exist_use:cF
-  {
-    \cs_new:Npn \cs_if_exist_use:cF #1
-      { \cs_if_exist:cTF {#1} { \use:c {#1} } }
-  }
-%    \end{macrocode}
-% \end{macro}
-%
 % \begin{macro}[EXP,aux]{\use_i:nnnnnnnn}
 %   A function which may already be defined elsewhere.
 %    \begin{macrocode}
@@ -542,18 +628,20 @@
 %   }
 %   Simply convert the token list inputs to \meta{strings}.
 %    \begin{macrocode}
-\cs_set:Npn \str_tmp:w #1
-  {
-    \cs_new_protected:cpx { str_#1:Nn } ##1##2
-      { \exp_not:c { tl_#1:Nx } ##1 { \exp_not:N \tl_to_str:n {##2} } }
-    \exp_args:Nc \cs_generate_variant:Nn { str_#1:Nn } { Nx , cn , cx }
-  }
-\str_tmp:w {set}
-\str_tmp:w {gset}
-\str_tmp:w {put_left}
-\str_tmp:w {gput_left}
-\str_tmp:w {put_right}
-\str_tmp:w {gput_right}
+\group_begin:
+  \cs_set_protected_nopar:Npn \str_tmp:w #1
+    {
+      \cs_new_protected:cpx { str_ #1 :Nn } ##1##2
+        { \exp_not:c { tl_ #1 :Nx } ##1 { \exp_not:N \tl_to_str:n {##2} } }
+      \exp_args:Nc \cs_generate_variant:Nn { str_ #1 :Nn } { Nx , cn , cx }
+    }
+  \str_tmp:w { set }
+  \str_tmp:w { gset }
+  \str_tmp:w { put_left }
+  \str_tmp:w { gput_left }
+  \str_tmp:w { put_right }
+  \str_tmp:w { gput_right }
+\group_end:
 %    \end{macrocode}
 % \end{macro}
 %
@@ -563,7 +651,7 @@
 % \begin{variable}{\g_str_tmpa_tl}
 %   Internal scratch space for some functions.
 %    \begin{macrocode}
-\cs_set_protected_nopar:Npn \str_tmp:w { }
+\cs_new_protected_nopar:Npn \str_tmp:w { }
 \tl_new:N \g_str_tmpa_tl
 %    \end{macrocode}
 % \end{variable}
@@ -579,11 +667,11 @@
 %    \end{macrocode}
 % \end{variable}
 %
-% \begin{variable}{\l_str_char_int,\l_str_bytes_int}
+% \begin{variable}{\l_str_char_int, \l_str_bytes_int}
 %   When converting from various escaped forms to raw characters,
 %   we often need to read several digits (hexadecimal or octal depending
 %   on the case) and keep track of the corresponding character code
-%   in \cs{l_str_char_int}. For UTF-8 support, the number of bytes
+%   in \cs{l_str_char_int}. For \textsc{utf8} support, the number of bytes
 %   of for the current character is stored in \cs{l_str_bytes_int}.
 %    \begin{macrocode}
 \int_new:N \l_str_char_int
@@ -591,8 +679,14 @@
 %    \end{macrocode}
 % \end{variable}
 %
-% \begin{variable}{\c_backslash_str,
-%     \c_lbrace_str,\c_rbrace_str,\c_hash_str,\c_percent_str}
+% \begin{variable}
+%   {
+%     \c_backslash_str,
+%     \c_lbrace_str,
+%     \c_rbrace_str,
+%     \c_hash_str,
+%     \c_percent_str
+%   }
 %   For all of those strings, \cs{cs_to_str:N} produce characters
 %   with the correct category code.
 %    \begin{macrocode}
@@ -606,48 +700,45 @@
 %
 % \subsection{Escaping spaces}
 %
-% \begin{macro}[EXP]{\tl_to_other_str:N,\tl_to_other_str:n}
-% \begin{macro}[EXP,aux]{\tl_to_other_str_loop:w,\tl_to_other_str_end:w}
+% \begin{macro}[EXP]{\tl_to_other_str:N, \tl_to_other_str:n}
+% \begin{macro}[EXP,aux]{\tl_to_other_str_loop:w, \tl_to_other_str_end:w}
 %   Replaces all spaces by \enquote{other} spaces, after converting
 %   the token list to a string via \cs{tl_to_str:n}.
 %    \begin{macrocode}
 \group_begin:
-\char_set_lccode:nn {`\*}{`\ }
-\char_set_lccode:nn {`\A}{`\A}
-\tl_to_lowercase:n {
-  \group_end:
-  \cs_new:Npn \tl_to_other_str:n #1
-    {
-      \exp_after:wN \tl_to_other_str_loop:w \tl_to_str:n {#1} ~ %
-      A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ \q_mark \q_stop
-    }
-  \cs_new_nopar:Npn \tl_to_other_str_loop:w
+\char_set_lccode:nn { `\* } { `\  }
+\char_set_lccode:nn { `\A } { `\A }
+\tl_to_lowercase:n
+  {
+    \group_end:
+    \cs_new:Npn \tl_to_other_str:n #1
+      {
+        \exp_after:wN \tl_to_other_str_loop:w \tl_to_str:n {#1} ~ %
+        A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ \q_mark \q_stop
+      }
+    \cs_new_nopar:Npn \tl_to_other_str_loop:w
       #1 ~ #2 ~ #3 ~ #4 ~ #5 ~ #6 ~ #7 ~ #8 ~ #9 \q_stop
-    {
-      \if_meaning:w A #8
-        \tl_to_other_str_end:w
-      \fi:
-      \tl_to_other_str_loop:w
-      #9 #1 * #2 * #3 * #4 * #5 * #6 * #7 * #8 * \q_stop
-    }
-  \cs_new_nopar:Npn \tl_to_other_str_end:w \fi: #1 \q_mark #2 * A #3 \q_stop
-    { \fi: #2 }
-}
-\cs_new_nopar:Npn \tl_to_other_str:N
-  { \exp_args:No \tl_to_other_str:n }
+      {
+        \if_meaning:w A #8
+          \tl_to_other_str_end:w
+        \fi:
+        \tl_to_other_str_loop:w
+        #9 #1 * #2 * #3 * #4 * #5 * #6 * #7 * #8 * \q_stop
+      }
+    \cs_new_nopar:Npn \tl_to_other_str_end:w \fi: #1 \q_mark #2 * A #3 \q_stop
+      { \fi: #2 }
+  }
+\cs_new_nopar:Npn \tl_to_other_str:N { \exp_args:No \tl_to_other_str:n }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 %
-% \begin{macro}[EXP]{\str_sanitize_args:Nn,\str_sanitize_args:Nnn}
+% \begin{macro}[EXP]{\str_sanitize_args:Nn, \str_sanitize_args:Nnn}
 %   Here, \texttt{f}-expansion does not lose leading spaces,
 %   since they have catcode \enquote{other} after \cs{str_sanitize:n}.
 %    \begin{macrocode}
-\cs_new:Npn \str_sanitize_args:Nn #1 #2
-  {
-    \exp_args:Nf #1
-      { \tl_to_other_str:n {#2} }
-  }
+\cs_new:Npn \str_sanitize_args:Nn #1#2
+  { \exp_args:Nf #1 { \tl_to_other_str:n {#2} } }
 \cs_new:Npn \str_sanitize_args:Nnn #1#2#3
   {
     \exp_args:Nff #1
@@ -726,15 +817,15 @@
 %   gives an empty result after passing through
 %   \cs{use_i_delimit_by_q_stop:nw}.
 %    \begin{macrocode}
-\cs_set_nopar:Npn \str_head:N { \exp_args:No \str_head:n }
+\cs_new_nopar:Npn \str_head:N { \exp_args:No \str_head:n }
 \cs_set:Npn \str_head:n #1
   {
     \exp_after:wN \str_head_aux:w
     \tl_to_str:n {#1}
     { { } } ~ \q_stop
   }
-\cs_set_nopar:Npx \str_head_aux:w #1 ~ %
-  { \exp_not:N \use_i_delimit_by_q_stop:nw #1 { ~ } }
+\cs_set_nopar:Npn \str_head_aux:w #1 ~ %
+  { \use_i_delimit_by_q_stop:nw #1 { ~ } }
 \cs_new:Npn \str_head_ignore_spaces:n #1
   { \exp_after:wN \use_i_delimit_by_q_stop:nw \tl_to_str:n {#1} { } \q_stop }
 \cs_new_nopar:Npn \str_head_unsafe:n #1
@@ -779,7 +870,7 @@
   }
 \cs_new_nopar:Npn \str_tail_unsafe:n #1
   { \str_tail_aux_ii:w #1 X { } X \q_stop }
-\cs_set_nopar:Npn \str_tail_aux_ii:w #1 #2 X #3 \q_stop { #2 }
+\cs_new_nopar:Npn \str_tail_aux_ii:w #1 #2 X #3 \q_stop { #2 }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
@@ -800,12 +891,14 @@
 %    \begin{macrocode}
 \cs_new:Npn \str_skip_do:nn #1
   {
-    \int_compare:nNnTF {#1} > \c_seven
-      { \str_skip_aux:nnnnnnnnn }
-      { \str_skip_end:n }
+    \if_num:w \int_eval:w #1 > \c_seven
+      \exp_after:wN \str_skip_aux:nnnnnnnnn
+    \else:
+      \exp_after:wN \str_skip_end:n
+    \fi:
       {#1}
   }
-\cs_new:Npn \str_skip_aux:nnnnnnnnn #1#2 #3#4#5#6#7#8#9
+\cs_new:Npn \str_skip_aux:nnnnnnnnn #1#2#3#4#5#6#7#8#9
   { \exp_args:Nf \str_skip_do:nn { \int_eval:n { #1 - \c_seven } } {#2} }
 \cs_new:Npn \str_skip_end:n #1
   {
@@ -821,7 +914,7 @@
     \else: \str_skip_end_ii:nwn { XXXXXXX }
     \fi:
   }
-\cs_new:Npn \str_skip_end_ii:nwn #1 #2 \fi: #3
+\cs_new:Npn \str_skip_end_ii:nwn #1#2 \fi: #3
   { \fi: \use_i:nnnnnnnn {#3} #1 }
 %    \end{macrocode}
 % \end{macro}
@@ -861,18 +954,18 @@
 \cs_new:Npn \str_collect_end:n #1
   {
     \if_case:w \int_eval:w #1 \int_eval_end:
-         \str_collect_end_ii:nwn { {}{}{}{}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{} }
-    \or: \str_collect_end_ii:nwn { {} }
+         \str_collect_end_ii:nwn { { } { } { } { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } }
+    \or: \str_collect_end_ii:nwn { { } }
     \or: \str_collect_end_ii:nwn {  }
-    \else: \str_collect_end_ii:nwn { {}{}{}{}{}{}{} }
+    \else: \str_collect_end_ii:nwn { { } { } { } { } { } { } { } }
     \fi:
   }
-\cs_new:Npn \str_collect_end_ii:nwn #1 #2 \fi: #3
+\cs_new:Npn \str_collect_end_ii:nwn #1#2 \fi: #3
   { \fi: #3 \q_stop #1 }
 \cs_new:Npn \str_collect_end_iii:nwNNNNNNN #1 #2 \q_stop #3#4#5#6#7#8#9
   { #1 {#2#3#4#5#6#7#8#9} }
@@ -938,12 +1031,12 @@
 % \end{macro}
 % \end{macro}
 %
-% \begin{macro}[EXP]{\str_from_to:Nnn}
-% \begin{macro}[EXP]{\str_from_to:nnn}
-% \begin{macro}[EXP]{\str_from_to_ignore_spaces:nnn}
-% \begin{macro}[EXP]{\str_from_to_unsafe:nnn}
-% \begin{macro}[EXP,aux]{\str_from_to_aux:nnnw}
-% \begin{macro}[EXP,aux]{\str_from_to_aux_ii:nnw}
+% \begin{macro}[EXP]{\str_substr:Nnn}
+% \begin{macro}[EXP]{\str_substr:nnn}
+% \begin{macro}[EXP]{\str_substr_ignore_spaces:nnn}
+% \begin{macro}[EXP]{\str_substr_unsafe:nnn}
+% \begin{macro}[EXP,aux]{\str_substr_aux:nnnw}
+% \begin{macro}[EXP,aux]{\str_substr_aux_ii:nnw}
 % \begin{macro}[EXP,aux]{\str_aux_eval_args:Nnnn}
 % \begin{macro}[EXP,aux]{\str_aux_normalize_range:nn}
 %   Sanitize the string, then limit the second and third arguments
@@ -952,30 +1045,30 @@
 %   Afterwards, skip characters, then keep some more, and finally
 %   drop the end of the string.
 %    \begin{macrocode}
-\cs_new_nopar:Npn \str_from_to:Nnn { \exp_args:No \str_from_to:nnn }
-\cs_new:Npn \str_from_to:nnn #1#2#3
+\cs_new_nopar:Npn \str_substr:Nnn { \exp_args:No \str_substr:nnn }
+\cs_new:Npn \str_substr:nnn #1#2#3
   {
     \exp_args:Nf \tl_to_str:n
-      { \str_sanitize_args:Nn \str_from_to_unsafe:nnn {#1}{#2}{#3} }
+      { \str_sanitize_args:Nn \str_substr_unsafe:nnn {#1} {#2} {#3} }
   }
-\cs_new:Npn \str_from_to_ignore_spaces:nnn #1
-  { \exp_args:No \str_from_to_unsafe:nnn { \tl_to_str:n {#1} } }
-\cs_new:Npn \str_from_to_unsafe:nnn #1#2#3 % <string> <from> <to>
+\cs_new:Npn \str_substr_ignore_spaces:nnn #1
+  { \exp_args:No \str_substr_unsafe:nnn { \tl_to_str:n {#1} } }
+\cs_new:Npn \str_substr_unsafe:nnn #1#2#3
   {
-    \str_aux_eval_args:Nnnn \str_from_to_aux:nnnw
+    \str_aux_eval_args:Nnnn \str_substr_aux:nnnw
       { \str_length_unsafe:n {#1} }
       {#2}
       {#3}
       #1
     \q_stop
   }
-\cs_new:Npn \str_from_to_aux:nnnw #1#2#3 % <len> <from> <to>
+\cs_new:Npn \str_substr_aux:nnnw #1#2#3
   {
-    \exp_args:Nf \str_from_to_aux_ii:nnw
+    \exp_args:Nf \str_substr_aux_ii:nnw
       { \str_aux_normalize_range:nn {#2} {#1} }
       { \str_aux_normalize_range:nn {#3} {#1} }
   }
-\cs_new:Npn \str_from_to_aux_ii:nnw #1#2
+\cs_new:Npn \str_substr_aux_ii:nnw #1#2
   {
     \str_skip_do:nn {#1}
       {
@@ -1127,7 +1220,7 @@
 %
 % \subsection{Internal conditionals}
 %
-% \begin{macro}[aux]{\str_aux_hexadecimal_test:N}
+% \begin{macro}[aux]{\str_aux_hexadecimal_test:NTF}
 %   This test is used when reading hexadecimal digits, for the |\x| escape
 %   sequence, and some conversion functions. It returns \meta{true} if the
 %   token is a hexadecimal digit, and \meta{false} otherwise. It has the
@@ -1137,7 +1230,7 @@
 %    \begin{macrocode}
 \prg_new_protected_conditional:Npnn \str_aux_hexadecimal_test:N #1 { TF }
   {
-    \tl_if_in:onTF { \tl_to_str:n {abcdef} } {#1}
+    \tl_if_in:onTF { \tl_to_str:n { abcdef } } {#1}
       {
         \int_set:Nn \l_str_char_int
           { \c_sixteen * \l_str_char_int + `#1 - 87 }
@@ -1156,7 +1249,7 @@
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}[aux]{\str_aux_octal_test:N}
+% \begin{macro}[aux]{\str_aux_octal_test:NTF}
 %   This test is used when reading octal digits, for
 %   some conversion functions. It returns \meta{true} if the
 %   token is an octal digit, and \meta{false} otherwise.
@@ -1193,7 +1286,8 @@
 % and in the regular expression module to go through the regular expression
 % once before actually parsing it. The goal in that case is to turn any
 % character with a meaning in regular expressions (\texttt{*}, \texttt{?},
-% \texttt{\{}, etc.) into a marker indicating that this was a special character,
+% \texttt{\{}, etc.) into a marker indicating that this was a special
+% character,
 % and replace any escaped character by the corresponding unescaped character,
 % so that the \pkg{l3regex} code can avoid caring about escaping issues
 % (those can become quite complex to handle in combination with ranges
@@ -1201,7 +1295,7 @@
 %
 % The idea is to feed unescaped characters to one function,
 % escaped characters to another, and feed |\a|, |\e|, |\f|,
-% |\n|, |\r|, |\t| and |\x| converted to the approriate
+% |\n|, |\r|, |\t| and |\x| converted to the appropriate
 % character to a third function. Spaces are ignored unless
 % escaped.
 % For the \cs{str_(g)input:Nn} application, all the functions are simply
@@ -1245,7 +1339,7 @@
       \cs_set_nopar:Npn \str_aux_escape_unescaped:N { #1 }
       \cs_set_nopar:Npn \str_aux_escape_escaped:N { #2 }
       \cs_set_nopar:Npn \str_aux_escape_raw:N { #3 }
-      \int_set:Nn \tex_escapechar:D {92}
+      \int_set:Nn \tex_escapechar:D { 92 }
       \tl_gset:Nx \g_str_result_tl { \tl_to_other_str:n {#4} }
       \tl_gset:Nx \g_str_result_tl
         {
@@ -1278,9 +1372,11 @@
 % \begin{macro}[aux]+\str_aux_escape_\q_recursion_tail:w+
 % \begin{macro}[aux]+\str_aux_escape_/\q_recursion_tail:w+
 % \begin{macro}[aux]+\str_aux_escape_ :w+
-% \begin{macro}[aux]{
+% \begin{macro}[aux]
+%   {
 %     \str_aux_escape_/a:w, \str_aux_escape_/e:w, \str_aux_escape_/f:w,
-%     \str_aux_escape_/n:w, \str_aux_escape_/r:w, \str_aux_escape_/t:w}
+%     \str_aux_escape_/n:w, \str_aux_escape_/r:w, \str_aux_escape_/t:w
+%   }
 %   The loop is ended upon seeing \cs{q_recursion_tail}.
 %   Spaces are ignored, and |\a|, |\e|, |\f|, |\n|, |\r|, |\t| take
 %   their meaning here.
@@ -1396,12 +1492,6 @@
         }
     }
 \group_end:
-\msg_new:nnn { str } { x-missing-brace }
-  {
-    You~wrote~something~like~
-    `\iow_char:N\\x\{ \int_to_hexadecimal:n { \l_str_char_int }'.~
-    The~closing~brace~is~missing.
-  }
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
@@ -1411,21 +1501,21 @@
 % \end{macro}
 % \end{macro}
 %
-% \subsubsection{Escape and unescape strings for pdf use}
+% \subsubsection{Escape and unescape strings for PDF use}
 %
 % \begin{macro}{\str_aux_convert_store:}
 % \begin{macro}{\str_aux_convert_store:NNn}
 %    \begin{macrocode}
 \group_begin:
-  \char_set_catcode_other:n {`\^^@}
+  \char_set_catcode_other:n { `\^^@ }
   \cs_new_protected_nopar:Npn \str_aux_convert_store:
     {
-      \char_set_lccode:nn {\c_zero} {\l_str_char_int}
+      \char_set_lccode:nn { \c_zero } { \l_str_char_int }
       \tl_to_lowercase:n { \tl_gput_right:Nx \g_str_result_tl {^^@} }
     }
   \cs_new_protected_nopar:Npn \str_aux_convert_store:NNn #1#2#3
     {
-      \char_set_lccode:nn {\c_zero} {#3}
+      \char_set_lccode:nn { \c_zero } {#3}
       \tl_to_lowercase:n { #1 #2 {^^@} }
     }
 \group_end:
@@ -1438,7 +1528,7 @@
 %    \begin{macrocode}
 \cs_new_nopar:Npn \str_aux_byte_to_hexadecimal:N #1
   {
-    \int_compare:nNnTF {`#1} < {256}
+    \int_compare:nNnTF {`#1} < { 256 }
       {
         \int_to_letter:n { \int_div_truncate:nn {`#1} \c_sixteen }
         \int_to_letter:n { \int_mod:nn {`#1} \c_sixteen }
@@ -1447,14 +1537,14 @@
   }
 \cs_new_nopar:Npn \str_aux_byte_to_octal:N #1
   {
-    \int_compare:nNnTF {`#1} < {64}
+    \int_compare:nNnTF {`#1} < { 64 }
       {
         0
         \int_to_letter:n { \int_div_truncate:nn {`#1} \c_eight }
         \int_to_letter:n { \int_mod:nn {`#1} \c_eight }
       }
       {
-        \int_compare:nNnTF {`#1} < {256}
+        \int_compare:nNnTF {`#1} < { 256 }
           { \int_to_octal:n {`#1} }
           { \msg_expandable_error:n { Invalid~byte~`#1'. } }
       }
@@ -1476,7 +1566,7 @@
 % \begin{macro}{\str_bytes_escape_name:NN}
 %    \begin{macrocode}
 \tl_const:Nx \c_str_bytes_escape_name_str
-  { \c_hash_str \c_percent_str \c_lbrace_str \c_rbrace_str () /<>[] }
+  { \c_hash_str \c_percent_str \c_lbrace_str \c_rbrace_str ()/<>[] }
 \cs_new_protected_nopar:Npn \str_bytes_escape_name:NN #1#2
   {
     \str_set:Nx #1
@@ -1484,10 +1574,10 @@
   }
 \cs_new_nopar:Npn \str_bytes_escape_name_aux:N #1
   {
-    \int_compare:nNnTF {`#1} < {"21}
+    \int_compare:nNnTF {`#1} < { "21 }
       { \c_hash_str \str_aux_byte_to_hexadecimal:N #1 }
       {
-        \int_compare:nNnTF {`#1} > {"7E}
+        \int_compare:nNnTF {`#1} > { "7E }
           { \c_hash_str \str_aux_byte_to_hexadecimal:N #1 }
           {
             \str_if_contains_char:NNTF \c_str_bytes_escape_name_str #1
@@ -1501,7 +1591,7 @@
 %
 % \begin{macro}{\str_bytes_escape_string:NN}
 %   Any character below (and including) space, and any character
-%   above (anc including) \texttt{del}, are converted to octal.
+%   above (and including) \texttt{del}, are converted to octal.
 %   One backslash is added before each parenthesis and backslash.
 %    \begin{macrocode}
 \tl_const:Nx \c_str_bytes_escape_string_str { \c_backslash_str ( ) }
@@ -1512,10 +1602,10 @@
   }
 \cs_new_nopar:Npn \str_bytes_escape_string_aux:N #1
   {
-    \int_compare:nNnTF {`#1} < {"21}
+    \int_compare:nNnTF {`#1} < { "21 }
       { \c_backslash_str \str_aux_byte_to_octal:N #1 }
       {
-        \int_compare:nNnTF {`#1} > {"7E}
+        \int_compare:nNnTF {`#1} > { "7E }
           { \c_backslash_str \str_aux_byte_to_octal:N #1 }
           {
             \str_if_contains_char:NNT \c_str_bytes_escape_string_str #1
@@ -1639,7 +1729,7 @@
 %   If followed by an end-of-line character, the backslash and
 %   the end-of-line are ignored. If followed by anything else,
 %   the backslash is ignored.
-%   The pdf specification indicates that LF, CR, and CRLF should be
+%   The PDF specification indicates that LF, CR, and CRLF should be
 %   converted to LF: \emph{this is not implemented here}.
 %    \begin{macrocode}
 \group_begin:
@@ -1671,16 +1761,16 @@
                 {
                   \prg_case_str:xxn {#2}
                     {
-                      {n} {10}
-                      {r} {13}
-                      {t} {9}
-                      {b} {8}
-                      {f} {12}
-                      {(} {40}
-                      {)} {41}
-                      {\c_backslash_str} {92}
-                      {^^J} {-1}
-                      {^^M} {-1}
+                      { n } { 10 }
+                      { r } { 13 }
+                      { t } { 9 }
+                      { b } { 8 }
+                      { f } { 12 }
+                      { ( } { 40 }
+                      { ) } { 41 }
+                      { \c_backslash_str } { 92 }
+                      { ^^J } { -1 }
+                      { ^^M } { -1 }
                     }
                     {`#2}
                 }
@@ -1727,14 +1817,14 @@
   }
 \cs_new_nopar:Npn \str_bytes_percent_encode_aux:N #1
   {
-    \int_compare:nNnTF {`#1} < {"41}
+    \int_compare:nNnTF {`#1} < { "41 }
       {
         \str_if_contains_char:NNTF \c_str_bytes_percent_encode_not_str #1
           { #1 }
           { \c_percent_str \str_aux_byte_to_hexadecimal:N #1 }
       }
       {
-        \int_compare:nNnTF {`#1} > {"7E}
+        \int_compare:nNnTF {`#1} > { "7E }
           { \c_percent_str \str_aux_byte_to_hexadecimal:N #1 }
           {
             \str_if_contains_char:NNTF \c_str_bytes_percent_encode_str #1
@@ -1798,6 +1888,14 @@
 % \subsubsection{UTF-8 support}
 %
 % \begin{macro}{\str_native_from_UTF_viii:NN}
+% \begin{macro}[aux]
+%   {
+%     \str_native_from_UTF_viii_aux_i:N,
+%     \str_native_from_UTF_viii_aux_ii:nN,
+%     \str_native_from_UTF_viii_aux_iii:N,
+%     \str_native_from_UTF_viii_aux_iv:,
+%     \str_native_from_UTF_viii_aux_v:
+%   }
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \str_native_from_UTF_viii:NN #1#2
   {
@@ -1812,19 +1910,18 @@
 \cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_i:N #1
   {
     \quark_if_recursion_tail_stop:N #1
-    \int_set:Nn \l_str_char_int { `#1 }
-    \str_native_from_UTF_viii_aux_ii:nN {128} \c_one
-    \str_native_from_UTF_viii_aux_ii:nN {64}  \c_zero
-    \str_native_from_UTF_viii_aux_ii:nN {32}  \c_two
-    \str_native_from_UTF_viii_aux_ii:nN {16}  \c_three
-    \str_native_from_UTF_viii_aux_ii:nN {8}   \c_four
+    \int_set:Nn \l_str_char_int {`#1}
+    \str_native_from_UTF_viii_aux_ii:nN { 128 } \c_one
+    \str_native_from_UTF_viii_aux_ii:nN { 64 }  \c_zero
+    \str_native_from_UTF_viii_aux_ii:nN { 32 }  \c_two
+    \str_native_from_UTF_viii_aux_ii:nN { 16 }  \c_three
+    \str_native_from_UTF_viii_aux_ii:nN { 8 }   \c_four
     \msg_error:nnx { str } { utf8-invalid-byte } {#1}
     \use_i:nnn \str_native_from_UTF_viii_aux_i:N
     \q_stop
     \str_native_from_UTF_viii_aux_iii:N
   }
-\cs_new_protected_nopar:Npn
-  \str_native_from_UTF_viii_aux_ii:nN #1#2
+\cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_ii:nN #1#2
   {
     \int_compare:nNnTF \l_str_char_int < {#1}
       {
@@ -1833,8 +1930,7 @@
       }
       { \int_sub:Nn \l_str_char_int {#1} }
   }
-\cs_new_protected_nopar:Npn
-  \str_native_from_UTF_viii_aux_iii:N #1
+\cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_iii:N #1
   {
     \int_compare:nNnTF \l_str_bytes_int < \c_two
       { \str_native_from_UTF_viii_aux_iv: #1 }
@@ -1844,11 +1940,11 @@
           \exp_after:wN \use_none_delimit_by_q_recursion_stop:w
         \fi:
         \quark_if_recursion_tail_stop:N #1
-        \tex_multiply:D \l_str_char_int by 64 \scan_stop: % no interface??
+        \tex_multiply:D \l_str_char_int by 64 \scan_stop:
         \int_decr:N \l_str_bytes_int
-        \int_compare:nNnTF {`#1} < {128}
+        \int_compare:nNnTF {`#1} < { 128 }
           { \use_ii:nn }
-          { \int_compare:nNnTF {`#1} < {192} }
+          { \int_compare:nNnTF {`#1} < { 192 } }
           {
             \int_add:Nn \l_str_char_int { `#1 - 128 }
             \str_native_from_UTF_viii_aux_iii:N
@@ -1859,49 +1955,35 @@
           }
       }
   }
-\cs_new_protected_nopar:Npn
-  \str_native_from_UTF_viii_aux_iv:
+\cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_iv:
   {
     \int_compare:nNnTF \l_str_bytes_int = \c_zero
       {
         \msg_error:nnx { str } { utf8-extra-byte }
           { \int_eval:n { \l_str_char_int + 128 } }
       }
+      { \str_native_from_UTF_viii_aux_v: }
+    \str_native_from_UTF_viii_aux_i:N
+  }
+\pdftex_if_engine:TF
+  {
+    \cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_v:
       {
-        \pdftex_if_engine:TF
+        \int_compare:nNnTF { \l_str_char_int } < { 256 }
+          { \str_aux_convert_store: }
           {
-            \int_compare:nNnTF { \l_str_char_int } < { 256 }
-              { \str_aux_convert_store: }
-              {
-                \msg_error:nnx { str } { utf8-pdftex-overflow }
-                  { \int_use:N \l_str_char_int }
-              }
+            \msg_error:nnx { str } { utf8-pdftex-overflow }
+              { \int_use:N \l_str_char_int }
           }
-          { \str_aux_convert_store: }
       }
-    \str_native_from_UTF_viii_aux_i:N
-  }
-\msg_new:nnn { str } { utf8-invalid-byte }
-  {
-    \int_compare:nNnTF {`#1} < {256}
-      { Byte~number~\int_eval:n {`#1}~invalid~in~utf-8~encoding. }
-      { The~character~number~\int_eval:n {`#1}~is~not~a~byte. }
   }
-\msg_new:nnn { str } { utf8-missing-byte }
-  { The~byte~number~\int_eval:n {`#1}~is~not~a~valid~continuation~byte. }
-\msg_new:nnn { str } { utf8-extra-byte }
-  { The~byte~number~\int_eval:n {`#1}~is~only~valid~as~a~continuation~byte. }
-\msg_new:nnnn { str } { utf8-premature-end }
-  { Incomplete~last~utf8~character. }
   {
-    The~sequence~of~byte~that~I~need~to~convert~to~utf8 \
-    ended~before~the~last~character~was~complete.~Perhaps \
-    it~was~mistakenly~truncated?
+    \cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_v:
+      { \str_aux_convert_store: }
   }
-\msg_new:nnn { str } { utf8-pdftex-overflow }
-  { The~character~number~#1~is~too~big~for~pdfTeX. }
 %    \end{macrocode}
 % \end{macro}
+% \end{macro}
 %
 % \begin{macro}{\str_UTF_viii_from_native:NN}
 %    \begin{macrocode}
@@ -1916,14 +1998,14 @@
 \cs_new_protected_nopar:Npn \str_UTF_viii_from_native_aux_i:N #1
   {
     \int_set:Nn \l_str_char_int {`#1}
-    \int_compare:nNnTF \l_str_char_int < {128}
+    \int_compare:nNnTF \l_str_char_int < { 128 }
       { \tl_gput_right:Nx \g_str_result_tl {#1} }
       {
         \tl_gclear:N \g_str_tmpa_tl
         \int_set:Nn \l_str_bytes_int { 64 }
-        \str_UTF_viii_from_native_aux_ii:n {32}
-        \str_UTF_viii_from_native_aux_ii:n {16}
-        \str_UTF_viii_from_native_aux_ii:n {8}
+        \str_UTF_viii_from_native_aux_ii:n { 32 }
+        \str_UTF_viii_from_native_aux_ii:n { 16 }
+        \str_UTF_viii_from_native_aux_ii:n { 8 }
         \ERROR % somehow the unicode char was > "1FFFFF > "10FFFF
         \tl_gclear:N \g_str_tmpa_tl
         \use_none:n \q_stop
@@ -1936,29 +2018,60 @@
   {
     \str_aux_convert_store:NNn
       \tl_gput_left:Nx \g_str_tmpa_tl
-      { 128 + \int_mod:nn { \l_str_char_int } {64} }
-    \tex_divide:D \l_str_char_int by 64 \scan_stop: % no interface??
+      { 128 + \int_mod:nn { \l_str_char_int } { 64 } }
+    \tex_divide:D \l_str_char_int by 64 \scan_stop:
     \int_add:Nn \l_str_bytes_int {#1}
     \int_compare:nNnT \l_str_char_int < {#1}
       { \use_none_delimit_by_q_stop:w }
   }
 %    \end{macrocode}
 % \end{macro}
+% 
+% \subsection{Messages}
+% 
+%    \begin{macrocode}
+\msg_new:nnnn { str } { x-missing-brace }
+  { Missing~closing~brace~in~ \token_to_str:N \x ~byte~sequence. }
+  {
+    You~wrote~something~like~
+    `\iow_char:N\\x\{ \int_to_hexadecimal:n { \l_str_char_int }'.~
+    The~closing~brace~is~missing.
+  }
+\msg_new:nnn { str } { utf8-invalid-byte }
+  {
+    \int_compare:nNnTF {`#1} < { 256 }
+      { Byte~number~ \int_eval:n {`#1} ~invalid~in~utf-8~encoding. }
+      { The~character~number~ \int_eval:n {`#1} ~is~not~a~byte. }
+  }
+\msg_new:nnn { str } { utf8-missing-byte }
+  { The~byte~number~ \int_eval:n {`#1} ~is~not~a~valid~continuation~byte. }
+\msg_new:nnn { str } { utf8-extra-byte }
+  { The~byte~number~ \int_eval:n {`#1} ~is~only~valid~as~a~continuation~byte. }
+\msg_new:nnnn { str } { utf8-premature-end }
+  { Incomplete~last~UTF8~character. }
+  {
+    The~sequence~of~byte~that~to~be~converted~to~UTF8~
+    ended~before~the~last~character~was~complete.~Perhaps~
+    it~was~mistakenly~truncated?
+  }
+\msg_new:nnn { str } { utf8-pdftex-overflow }
+  { The~character~number~#1~is~too~big~for~pdfTeX. }
+%    \end{macrocode}
 %
 % \subsection{Deprecated string functions}
 %
-% \begin{macro}{\str_length_skip_spaces:N,\str_length_skip_spaces:n}
+% \begin{macro}{\str_length_skip_spaces:N, \str_length_skip_spaces:n}
 %   The naming scheme is a little bit more consistent
 %   with \enquote{ignore_spaces} instead of \enquote{skip_spaces}.
 %    \begin{macrocode}
-\cs_gset:Npn \str_length_skip_spaces:N
+\cs_set:Npn \str_length_skip_spaces:N
   { \exp_args:No \str_length_skip_spaces:n }
-\cs_gset_eq:NN \str_length_skip_spaces:n \str_length_ignore_spaces:n
+\cs_set_eq:NN \str_length_skip_spaces:n \str_length_ignore_spaces:n
 %    \end{macrocode}
 % \end{macro}
 %
 %    \begin{macrocode}
-%</package>
+%</initex|package>
 %    \end{macrocode}
 %
 % \end{implementation}
diff --git a/Master/texmf-dist/source/latex/l3experimental/xcoffins/xcoffins.dtx b/Master/texmf-dist/source/latex/l3experimental/xcoffins/xcoffins.dtx
index 103934d5fe8..30a58c18817 100644
--- a/Master/texmf-dist/source/latex/l3experimental/xcoffins/xcoffins.dtx
+++ b/Master/texmf-dist/source/latex/l3experimental/xcoffins/xcoffins.dtx
@@ -36,7 +36,7 @@
 %
 %<*driver|package>
 \RequirePackage{xparse}
-\GetIdInfo$Id: xcoffins.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: xcoffins.dtx 2963 2011-11-15 22:06:41Z joseph $
   {L3 Experimental design-level coffins}
 %</driver|package>
 %<*driver>
@@ -583,6 +583,47 @@
 %   coffin is therefore analogous to carrying out an alignment where the
 %   \enquote{parent} coffin is the current insertion point.
 % \end{function}
+% 
+% \section{Measuring coffins}
+%
+% There are places in the design process where it is useful to be able to
+% measure coffins outside of pole-setting procedures.
+% 
+% \begin{function}{\CoffinDepth}
+%   \begin{syntax}
+%     \cs{CoffinDepth} \meta{coffin}
+%   \end{syntax}
+%   Calculates the depth (below the baseline) of the \meta{coffin}
+%   in a form suitable for use in a \meta{dimension expression}, for example
+%   |\setlength{\mylength}{\CoffinDepth\ExampleCoffin}|.
+% \end{function}
+%
+% \begin{function}{\CoffinHeight}
+%   \begin{syntax}
+%     \cs{CoffinHeight} \meta{coffin}
+%   \end{syntax}
+%   Calculates the height (above the baseline) of the \meta{coffin}
+%   in a form suitable for use in a \meta{dimension expression}, for example
+%   |\setlength{\mylength}{\CoffinHeight\ExampleCoffin}|.
+% \end{function}
+% 
+% \begin{function}{\CoffinTotalHeight}
+%   \begin{syntax}
+%     \cs{CoffinTotalHeight} \meta{coffin}
+%   \end{syntax}
+%   Calculates the total height of the \meta{coffin}
+%   in a form suitable for use in a \meta{dimension expression}, for example
+%   |\setlength{\mylength}{\CoffinTotalHeight\ExampleCoffin}|.
+% \end{function}
+%
+% \begin{function}{\CoffinWidth}
+%   \begin{syntax}
+%     \cs{CoffinHeight} \meta{coffin}
+%   \end{syntax}
+%   Calculates the width of the \meta{coffin} in a form
+%   suitable for use in a \meta{dimension expression}, for example
+%   |\setlength{\mylength}{\CoffinWidth\ExampleCoffin}|.
+% \end{function}
 %
 % \section{Diagnostic functions}
 %
@@ -839,6 +880,22 @@
 % \end{macro}
 % \end{macro}
 % \end{macro}
+% 
+% \begin{macro}{\CoffinDepth, \CoffinHeight, \CoffinTotalHeigth, \CoffinWidth}
+%   Nothing too complex, except that the total height is set up as an
+%   expression so that it will act correctly if prefixed with a negative
+%   sign, \emph{etc.}
+%    \begin{macrocode}
+\NewDocumentCommand \CoffinDepth { m }
+  { \coffin_dp:N #1 }
+\NewDocumentCommand \CoffinHeight { m }
+  { \coffin_ht:N #1 }
+\NewDocumentCommand \CoffinTotalHeight { m }
+  { \dim_eval:w \coffin_ht:N #1 + \coffin_dp:N #1 \dim_eval_end: }
+\NewDocumentCommand \CoffinWidth { m }
+  { \coffin_wd:N #1 }
+%    \end{macrocode}
+% \end{macro}
 %
 % \begin{macro}{\DisplayCoffinHandles}
 %   Displaying all of the handles is a bit easier, as there is no need
diff --git a/Master/texmf-dist/source/latex/l3experimental/xgalley/l3galley.dtx b/Master/texmf-dist/source/latex/l3experimental/xgalley/l3galley.dtx
index fa54ac37e59..57fbb9ecca4 100644
--- a/Master/texmf-dist/source/latex/l3experimental/xgalley/l3galley.dtx
+++ b/Master/texmf-dist/source/latex/l3experimental/xgalley/l3galley.dtx
@@ -37,7 +37,7 @@
 %
 %<*driver|package>
 \RequirePackage{l3names}
-\GetIdInfo$Id: l3galley.dtx 2899 2011-10-09 21:22:06Z joseph $
+\GetIdInfo$Id: l3galley.dtx 2938 2011-10-25 18:41:20Z joseph $
   {L3 Experimental galley code}
 %</driver|package>
 %<*driver>
@@ -535,10 +535,22 @@
 %   paragraph started.
 % \end{variable}
 %
-% \begin{variable}{\g_galley_whatsit_previous_hook_tl}
+% \begin{variable}{\g_galley_whatsit_previous_tl}
 %   Token list for whatsits to be inserted at the very end of the last
 %   paragraph started.
 % \end{variable}
+% 
+% \section{Additional effects}
+%
+% \begin{function}{\galley_end_par:n}
+%   \begin{syntax}
+%     \cs{galley_end_par:n} \Arg{tokens}
+%   \end{syntax}
+%   Adds the \meta{tokens} to the material collected for the last paragraph
+%   before finalising the last paragraph in the usual way. This function should
+%   therefore be the \emph{first} non-expandable entry used when a function
+%   needs to add tokens to the preceding paragraph.
+% \end{function}
 %
 % \section{Internal variables}
 %
@@ -641,6 +653,17 @@
 \package_check_loaded_expl:
 %</package>
 %    \end{macrocode}
+%    
+% \subsection{TO BE MOVED}
+%
+% \begin{macro}{\scan_marker_new:N, \scan_marker_new:c}
+% Temporary: needs to go somewhere else if this concept is retained.
+%    \begin{macrocode}
+\cs_new_protected:Npn \scan_marker_new:N #1
+  { \cs_new_eq:NN #1 \scan_stop: }
+\cs_generate_variant:Nn \scan_marker_new:N { c }
+%    \end{macrocode}
+% \end{macro}
 %
 % \subsection{Support items}
 %
@@ -755,11 +778,11 @@
 %    \begin{macrocode}
 \bool_new:N \g_galley_begin_level_bool
 \bool_new:N \l_galley_begin_level_bool
-\bool_gset_true:N \g_galley_begin_level_bool
 %    \end{macrocode}
 % \end{variable}
 %
-% \begin{variable}{\g_galley_omit_next_indent_bool, \l_galley_omit_next_indent_bool}
+% \begin{variable}
+%   {\g_galley_omit_next_indent_bool, \l_galley_omit_next_indent_bool}
 %   A global flag is needed for suppressing indentation of the next
 %   paragraph. This does not need a \enquote{running} version since that
 %   should be handled using the \texttt{justification} object: the two
@@ -907,9 +930,10 @@
     \bool_gset_false:N \g_galley_parshape_set_bool
     \int_gzero:N \g_galley_previous_par_lines_int
     \tl_gclear:N \g_galley_restore_running_tl
-    \tl_gclear:N \g_galley_whatsits_previous_tl
-    \tl_gclear:N \g_galley_whatsits_next_tl
+    \tl_gclear:N \g_galley_whatsit_previous_tl
+    \tl_gclear:N \g_galley_whatsit_next_tl
   }
+\galley_initialise_variables:
 %    \end{macrocode}
 % \end{macro}
 %
@@ -955,10 +979,10 @@
       \g_galley_previous_par_lines_int
     \tl_set_eq:NN \l_galley_restore_running_tl
       \g_galley_restore_running_tl
-    \tl_set_eq:NN \l_galley_whatsits_previous_tl
-      \g_galley_whatsits_previous_tl
-    \tl_set_eq:NN \l_galley_whatsits_next_tl
-      \g_galley_whatsits_next_tl
+    \tl_set_eq:NN \l_galley_whatsit_previous_tl
+      \g_galley_whatsit_previous_tl
+    \tl_set_eq:NN \l_galley_whatsit_next_tl
+      \g_galley_whatsit_next_tl
   }
 \cs_new_protected_nopar:Npn \galley_restore_parameters:
   {
@@ -984,10 +1008,10 @@
       \l_galley_previous_par_lines_int
     \tl_gset_eq:NN \g_galley_restore_running_tl
       \l_galley_restore_running_tl
-    \tl_gset_eq:NN \g_galley_whatsits_previous_tl
-      \l_galley_whatsits_previous_tl
-    \tl_gset_eq:NN \g_galley_whatsits_next_tl
-      \l_galley_whatsits_next_tl
+    \tl_gset_eq:NN \g_galley_whatsit_previous_tl
+      \l_galley_whatsit_previous_tl
+    \tl_gset_eq:NN \g_galley_whatsit_next_tl
+      \l_galley_whatsit_next_tl
   }
 %    \end{macrocode}
 % \end{macro}
@@ -1025,13 +1049,46 @@
 % \end{macro}
 %
 % \subsection{The \cs{par} token}
+% 
+% \begin{variable}{\s_par_omit}
+%   Used to indicate that a paragraph should be omitted.
+%    \begin{macrocode}
+\scan_marker_new:N \s_par_omit
+%    \end{macrocode}
+% \end{variable}
 %
 % \begin{macro}{\galley_std_par:}
-%   In vertical mode, the standard paragraph insert is just the primitive
-%   \cs{tex_par:D}.
+% \begin{macro}[aux]{\galley_std_par_aux_i:, \galley_std_par_aux_ii:}
+% \begin{macro}[aux]{\galley_std_par_aux:N}
+%   The idea here is to expand the next token in exactly the same way as \TeX{}
+%   would do anyway. The \texttt{f}-type expansion will ignore any protection,
+%   but will stop at a scan marker. Thus the code can test for an
+%   \enquote{omit paragraph} marker.
 %    \begin{macrocode}
 \cs_new_protected_nopar:Npn \galley_std_par:
   {
+    \s_par_omit
+    \exp_after:wN \galley_std_par_aux_i: \tex_romannumeral:D - `0
+  }
+\cs_new_protected:Npn \galley_std_par_aux_i:
+  {
+    \peek_meaning:NTF \s_par_omit
+      { \galley_std_par_aux:N }
+      { \galley_std_par_aux_ii: }
+  }
+\cs_new_protected:Npn \galley_std_par_aux:N #1
+  {
+    \str_if_eq:xxF {#1} { \s_par_omit }
+      {
+        \galley_std_par_aux_ii:
+        #1
+      }
+  }
+%    \end{macrocode}
+%   No marker, so really insert a paragraph. In vertical mode, 
+%    \begin{macrocode}
+\cs_new_protected_nopar:Npn \galley_std_par_aux_ii:
+  {
     \mode_if_vertical:TF
       { \tex_par:D }
 %    \end{macrocode}
@@ -1064,6 +1121,24 @@
   }
 %    \end{macrocode}
 % \end{macro}
+% \end{macro}
+% \end{macro}
+% 
+% \begin{macro}{\galley_end_par:n}
+%   Inserts tokens such that they are appended to the end of the last
+%   paragraph, using the paragraph-omitting system.
+%    \begin{macrocode}
+\cs_new_protected:Npn \galley_end_par:n #1
+  {
+    \s_par_omit
+    \bool_if:nF \g_galley_begin_level_bool
+      {
+        #1
+        \galley_std_par:
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
 %
 % \begin{macro}{\par}
 %   The meaning of the token \cs{par} itself starts off as a standard
@@ -1375,14 +1450,14 @@
   {
     \g_galley_whatsit_next_tl
     \tl_gclear:N \g_galley_whatsit_next_tl
-    \bool_if:NT \g_galley_omit_next_indent_bool
+    \bool_if:NF \g_galley_omit_next_indent_bool
       {
-       \box_if_empty:NF \g_galley_last_box
+        \box_if_empty:NF \g_galley_last_box
           { \hbox_to_wd:nn \l_galley_par_indent_dim { } }
       }
     \skip_horizontal:N \l_galley_par_begin_skip
     \g_galley_par_begin_hook_tl
-    \bool_gset_true:N \g_galley_omit_next_indent_bool
+    \bool_gset_false:N \g_galley_omit_next_indent_bool
   }
 %    \end{macrocode}
 % \end{macro}
@@ -2066,16 +2141,57 @@
 % \end{macro}
 % \end{macro}
 % \end{macro}
+% 
 %
-% \subsection{\LaTeXe{} fixes}
-%
+% \subsection{\LaTeXe{} functions}
+% 
 %    \begin{macrocode}
 %<*package>
 %    \end{macrocode}
 %
+% \begin{macro}{\nobreak}
+% \begin{macro}{\noindent}
+% \begin{macro}{\vspace}
+% In package mode, some of \LaTeXe{}'s functions are re-implemented using
+% the galley system. Not all of the optional arguments currently work!
+%    \begin{macrocode}
+\cs_set_protected_nopar:Npn \nobreak
+  { \bool_gset_true:N \g_galley_no_break_next_bool }
+%    \end{macrocode}
+%  The \tn{noindent} primitive will causes problems, as it is used by
+%  \LaTeXe{} documents to implicitly leave vertical mode as well as to
+%  prevent indentation. Rather than patch \emph{every} place where we
+%  need leave vertical mode, at the moment we stick with the primitive as
+%  well as setting the galley flag.
+%    \begin{macrocode}
+\cs_set_protected_nopar:Npn \noindent
+  {
+    \tex_noindent:D
+    \bool_gset_false:N \g_galley_omit_next_indent_bool
+  }
+\cs_set_protected_nopar:Npn \vspace #1
+  {
+    \@ifstar
+      { \galley_set_user_vspace:n {#1} }
+      { \galley_set_user_vspace:n {#1} }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{\LaTeXe{} fixes}
+%
 % Purely for testing, some internal \LaTeXe{} functions are altered to work
 % with the mechanism here. This material is not comprehensive: additions are
 % made as-needed for test purposes.
+% 
+% \begin{macro}{\@@par}
+%   The primitive is moved as otherwise the clever skipping code will fail.
+%    \begin{macrocode}
+\cs_set_eq:NN \@@par \galley_std_par:
+%    \end{macrocode}
+% \end{macro}
 %
 % \begin{macro}{\@afterheading}
 %   Set some flags and hope for the best!
@@ -2098,6 +2214,8 @@
 %    \begin{macrocode}
 \cs_set_protected:Npn \@hangfrom #1
   {
+    \bool_gset_true:N \g_galley_omit_next_indent_bool
+    \leavevmode
     \setbox \@tempboxa = \hbox { {#1} }
     \galley_parshape_single_par:nnnN
       \c_one
@@ -2105,28 +2223,12 @@
       \c_zero_dim
       \c_false_bool
     \bool_gset_true:N \g_galley_no_break_next_bool
-    \bool_gset_true:N \galley_omit_next_indent_bool
+    \bool_gset_true:N \g_galley_omit_next_indent_bool
     \box \@tempboxa
   }
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}{\@makefntext}
-%   Here, the paragraph indent is set up using the template system, and
-%   as in other places the code ensures that the label is set in horizontal
-%   mode. The flag used for omitting the indent is once again the galley
-%   one.
-%    \begin{macrocode}
-\cs_set_protected:Npn \@makefntext #1
-  {
-    \UseTemplate { justification } { std } { indent-width = 1 em }
-    \bool_gset_true:N \galley_omit_next_indent_bool
-    \galley_leave_vmode:
-    \hb@xt@ 1.8em { \hss \@makefnmark } #1
-  }
-%    \end{macrocode}
-% \end{macro}
-%
 %    \begin{macrocode}
 %</package>
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex/l3experimental/xgalley/xgalley.dtx b/Master/texmf-dist/source/latex/l3experimental/xgalley/xgalley.dtx
index 0dc1c85b610..f573668fde8 100644
--- a/Master/texmf-dist/source/latex/l3experimental/xgalley/xgalley.dtx
+++ b/Master/texmf-dist/source/latex/l3experimental/xgalley/xgalley.dtx
@@ -37,7 +37,7 @@
 %
 %<*driver|package>
 \RequirePackage{l3names}
-\GetIdInfo$Id: xgalley.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: xgalley.dtx 2922 2011-10-17 19:01:04Z joseph $
   {L3 Experimental galley}
 %</driver|package>
 %<*driver>
@@ -1575,24 +1575,6 @@
   }
 %    \end{macrocode}
 %
-% \subsection{\LaTeXe{} functions}
-%
-% \begin{macro}{\nobreak}
-% \begin{macro}{\noindent}
-% \begin{macro}{\vspace}
-% In package mode, some of \LaTeXe{}'s functions are re-implemented using
-% the galley system. Not all of the optional arguments currently work!
-%    \begin{macrocode}
-\RenewDocumentCommand \nobreak { }
-  { \bool_gset_true:N \g_galley_no_break_next_bool }
-\RenewDocumentCommand \noindent { }
-  { \bool_gset_false:N \g_galley_omit_next_indent_bool }
-\RenewDocumentCommand \vspace { s m } { \galley_set_vspace_user:n {#2} }
-%    \end{macrocode}
-% \end{macro}
-% \end{macro}
-% \end{macro}
-%
 %    \begin{macrocode}
 %</package>
 %    \end{macrocode}
diff --git a/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex-trace.sty b/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex-trace.sty
index 29045fcdea9..07d568d94e9 100644
--- a/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex-trace.sty
+++ b/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex-trace.sty
@@ -46,113 +46,121 @@
 %%
 %% -----------------------------------------------------------------------
 \RequirePackage{expl3}
-\GetIdInfo$Id: l3regex.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: l3regex.dtx 2943 2011-10-30 15:59:43Z bruno $
   {L3 Experimental Regular Expressions}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
 \RequirePackage{l3str}
+\int_const:Nn \c_forty_eight  { 48 }
+\int_const:Nn \c_fifty_eight  { 58 }
+\int_const:Nn \c_sixty_five   { 65 }
+\int_const:Nn \c_ninety_one   { 91 }
+\int_const:Nn \c_ninety_seven { 97 }
+\int_const:Nn \c_one_hundred_twenty_three { 123 }
+\int_const:Nn \c_one_hundred_twenty_seven { 127 }
 \cs_new:Npn \regex_tmp:w { }
 \tl_new:N   \g_regex_tmpa_tl
 \tl_new:N   \l_regex_tmpa_tl
 \tl_new:N   \l_regex_tmpb_tl
 \int_new:N  \l_regex_tmpa_int
-\tl_new:N  \l_regex_pattern_str
+\int_new:N  \l_regex_tmpb_int
 \int_new:N  \l_regex_max_state_int
 \int_new:N  \l_regex_left_state_int
 \int_new:N  \l_regex_right_state_int
-\seq_new:N  \l_regex_left_state_seq
-\seq_new:N  \l_regex_right_state_seq
+\seq_new:N  \l_regex_group_begin_seq
+\seq_new:N  \l_regex_group_end_seq
 \int_new:N  \l_regex_capturing_group_int
 \seq_new:N  \l_regex_capturing_group_seq
 \tl_new:N   \l_regex_one_or_group_tl
-\int_new:N  \l_regex_repetition_int
-\bool_new:N \l_regex_look_behind_bool
-\tl_new:N \l_regex_look_behind_str
 \cs_new_eq:NN \regex_build_tmp_class:n \use_none:n
 \bool_new:N \l_regex_class_bool
 \tl_new:N   \l_regex_class_tl
 \tl_const:Nn \c_regex_d_tl
   {
-    \regex_item_range:nn {48} {57} % 0--9
+    \regex_item_range:nn { \c_forty_eight } { 57 } % 0--9
   }
 \tl_const:Nn \c_regex_D_tl
   {
-    \regex_item_more:n {57} % 9
-    \regex_item_range:nn {0} {47} % 0
+    \regex_item_geq:n { \c_fifty_eight } % > `9
+    \regex_item_range:nn { \c_zero } { 47 } % 0
   }
 \tl_const:Nn \c_regex_h_tl
   {
-    \regex_item_equal:n {32} % space
-    \regex_item_equal:n {9}  % tab
+    \regex_item_equal:n { \c_thirty_two } % space
+    \regex_item_equal:n { \c_nine } % tab
   }
 \tl_const:Nn \c_regex_H_tl
   {
-    \regex_item_neq:n {32} % space
-    \regex_item_neq:n {9}  % tab
-    \regex_break_true:w
+    \regex_item_geq:n { 33 } % > space
+    \regex_item_range:nn { \c_ten } { 31 } % tab < ... < space
+    \regex_item_range:nn { \c_zero } { \c_eight } % < tab
   }
 \tl_const:Nn \c_regex_s_tl
   {
-    \regex_item_equal:n  {32}     % space
-    \regex_item_neq:n    {11}     % vtab
-    \regex_item_range:nn {9} {13} % tab, lf, vtab, ff, cr
+    \regex_item_equal:n  { \c_thirty_two } % space
+    \regex_item_range:nn { \c_nine } { \c_ten } % tab, lf
+    \regex_item_range:nn { \c_twelve } { \c_thirteen } % ff, cr
   }
 \tl_const:Nn \c_regex_S_tl
   {
-    \regex_item_more:n   {32}      % > space
-    \regex_item_range:nn {14} {31} % tab < ... < space
-    \regex_item_range:nn {0}  {8}  % < tab
-    \regex_item_equal:n  {11}      % vtab
+    \regex_item_geq:n    { 33 } % > space
+    \regex_item_range:nn { \c_fourteen } { 31 } % tab < ... < space
+    \regex_item_range:nn { \c_zero } { \c_eight } % < tab
+    \regex_item_equal:n  { \c_eleven } % vtab
   }
 \tl_const:Nn \c_regex_v_tl
   {
-    \regex_item_range:nn {10} {13} % lf, vtab, ff, cr
+    \regex_item_range:nn { \c_ten } { \c_thirteen } % lf, vtab, ff, cr
   }
 \tl_const:Nn \c_regex_V_tl
   {
-    \regex_item_more:n   {13}    % cr
-    \regex_item_range:nn {0} {9} % < lf
+    \regex_item_geq:n    { \c_fourteen } % >cr
+    \regex_item_range:nn { \c_zero } { \c_nine } % < lf
   }
 \tl_const:Nn \c_regex_w_tl
   {
-    \regex_item_range:nn {97} {122} % a--z
-    \regex_item_range:nn {65}  {90} % A--Z
-    \regex_item_range:nn {48}  {57} % 0--9
-    \regex_item_equal:n  {95}       % _
+    \regex_item_range:nn { \c_ninety_seven } { 122 } % a--z
+    \regex_item_range:nn { \c_sixty_five } { 90 } % A--Z
+    \regex_item_range:nn { \c_forty_eight } { 57 } % 0--9
+    \regex_item_equal:n  { 95 } % _
   }
 \tl_const:Nn \c_regex_W_tl
   {
-    \regex_item_range:nn  {0} {47} % <`0
-    \regex_item_range:nn {58} {64} % (`9+1)--(`A-1)
-    \regex_item_range:nn {91} {94} % (`Z+1)--(`_-1)
-    \regex_item_equal:n  {96}      % `
-    \regex_item_more:n  {122}      % z
+    \regex_item_range:nn { \c_zero } { 47 } % <`0
+    \regex_item_range:nn { \c_fifty_eight } { 64 } % (`9+1)--(`A-1)
+    \regex_item_range:nn { \c_ninety_one } { 94 } % (`Z+1)--(`_-1)
+    \regex_item_equal:n  { 96 } % `
+    \regex_item_geq:n    { \c_one_hundred_twenty_three } % z
   }
 \tl_const:Nn \c_regex_N_tl
   {
-    \regex_item_neq:n {10} % lf
-    \regex_break_true:w
+    \regex_item_geq:n { \c_eleven } % > lf
+    \regex_item_range:nn { \c_zero } { \c_nine } % < lf
   }
-\tl_new:N \l_regex_query_str
-\int_new:N \l_regex_start_step_int
-\int_new:N \l_regex_current_char_int
+\tl_new:N \l_regex_query_other_str
 \int_new:N \l_regex_current_step_int
+\int_new:N \l_regex_start_step_int
+\int_new:N \l_regex_success_step_int
 \int_new:N \l_regex_unique_step_int
+\int_new:N \l_regex_current_char_int
+\int_new:N \l_regex_last_char_int
+\int_new:N \l_regex_case_changed_char_int
+\bool_new:N \l_regex_caseless_bool
 \int_new:N \l_regex_current_state_int
 \prop_new:N \l_regex_current_submatches_prop
+\prop_new:N \l_regex_success_submatches_prop
 \int_new:N \l_regex_max_index_int
 \tl_new:N \l_regex_every_match_tl
+\bool_new:N \l_regex_success_bool
 \cs_new_protected:Npn \regex_last_match_empty_no:F #1 {#1}
 \cs_new_protected:Npn \regex_last_match_empty_yes:F
   { \int_compare:nNnF \l_regex_start_step_int = \l_regex_current_step_int }
 \cs_new_eq:NN \regex_last_match_empty:F \regex_last_match_empty_no:F
-\bool_new:N \l_regex_success_bool
 \bool_new:N \l_regex_success_empty_bool
-\int_new:N  \l_regex_success_step_int
-\prop_new:N \l_regex_success_submatches_prop
 \bool_new:N \l_regex_fresh_thread_bool
 \seq_new:N  \g_regex_submatches_seq
 \int_new:N \g_regex_match_count_int
+\seq_new:N \g_regex_extract_all_seq
 \seq_new:N \g_regex_split_seq
 \tl_new:N \l_regex_replacement_tl
 \tl_new:N \g_regex_replaced_str
@@ -169,40 +177,43 @@
     \tex_toks:D #1 \exp_after:wN
       { \tex_the:D \tex_toks:D \exp_after:wN #1 \regex_tmp:w }
   }
-\cs_new_eq:NN \regex_if_tail_stop:N \quark_if_recursion_tail_stop:N
-\cs_new_protected_nopar:Npn \regex_if_tail_error:Nn #1#2
-  { \quark_if_recursion_tail_stop_do:Nn #1 { \regex_build_error:n {#2} } }
-\cs_new_protected_nopar:Npn \regex_build_error:n #1
+\cs_new_nopar:Npn \regex_query_substr:NN #1#2
   {
-    \msg_error:nnxx { regex } { build-error } {\int_eval:n{#1}}
-      {
-        \prg_case_int:nnn {#1}
-          {
-            {-999} {File~not~found}
-            {-998} {Unsupported~construct}
-            {-997} {The~regular~expression~is~too~large~(32768~states).}
-            {1}  {\iow_char:N\\~at~end~of~pattern }
-            {4}  {Numbers~out~of~order~in~\iow_char:N\{\iow_char\}~quantifier.}
-            {6}  {Missing~terminating~\iow_char:N\]~for~character~class }
-            {7}  {Invalid~escape~sequence~in~character~class}
-            {8}  {Range~out~of~order~in~character~class}
-            {22} {Mismatched~parentheses}
-            {34} {Character~value~in~\iow_char:N\\x{...}~sequence~is~too~large}
-          }
-          { Internal~bug. }
-      }
+    \exp_after:wN \regex_query_substr_aux:NN
+    \exp_after:wN #1
+    \exp_after:wN #2
+    \l_regex_query_other_str
+    \q_stop
+  }
+\cs_new:Npn \regex_query_substr_aux:NN #1#2
+  {
+    \str_skip_do:nn {#1}
+      { \str_collect_do:nn { #2 - #1 } { \use_i_delimit_by_q_stop:nw } }
+  }
+\cs_new_protected_nopar:Npn \regex_seq_pop:N #1
+  {
+    \seq_pop:NN #1 \l_regex_tmpa_tl
+    \l_regex_tmpa_tl
+  }
+\cs_new_protected_nopar:Npn \regex_seq_get:N #1
+  {
+    \seq_get:NN #1 \l_regex_tmpa_tl
+    \l_regex_tmpa_tl
   }
-\msg_new:nnn { regex } { build-error } { (error~#1): ~ #2 }
-\cs_new_nopar:Npn \regex_break_true:w #1 \regex_break_point:TF #2 #3 {#2}
-\cs_new_nopar:Npn \regex_break_false:w #1 \regex_break_point:TF #2 #3 {#3}
-\cs_new_eq:NN \regex_break_point:TF \use_ii:nn
-\cs_new_nopar:Npn \regex_item_equal:n #1
+\cs_new_protected_nopar:Npn \regex_item_dot:T
+  { \int_compare:nNnF \l_regex_current_char_int = \c_minus_one }
+\cs_new_protected_nopar:Npn \regex_break_true:w
+   #1 \regex_break_point:TF #2 #3 {#2}
+\cs_new_protected_nopar:Npn \regex_break_false:w
+   #1 \regex_break_point:TF #2 #3 {#3}
+\cs_new_protected_nopar:Npn \regex_break_point:TF #1 #2 { #2 }
+\cs_new_protected_nopar:Npn \regex_item_caseful_equal:n #1
   {
     \if_num:w #1 = \l_regex_current_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_range:nn #1 #2
+\cs_new_protected_nopar:Npn \regex_item_caseful_range:nn #1 #2
   {
     \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
       \reverse_if:N \if_num:w #2 < \l_regex_current_char_int
@@ -210,24 +221,60 @@
       \fi:
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_less:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseful_geq:n #1
   {
-    \if_num:w #1 > \l_regex_current_char_int
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_more:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseless_equal:n #1
   {
-    \if_num:w #1 < \l_regex_current_char_int
+    \if_num:w #1 = \l_regex_current_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+    \if_num:w #1 = \l_regex_case_changed_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_neq:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseless_range:nn #1 #2
   {
-    \if_num:w #1 = \l_regex_current_char_int
-      \exp_after:wN \regex_break_false:w
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
+      \reverse_if:N \if_num:w #2 < \l_regex_current_char_int
+        \exp_after:wN \exp_after:wN \exp_after:wN \regex_break_true:w
+      \fi:
+    \fi:
+    \reverse_if:N \if_num:w #1 > \l_regex_case_changed_char_int
+      \reverse_if:N \if_num:w #2 < \l_regex_case_changed_char_int
+        \exp_after:wN \exp_after:wN \exp_after:wN \regex_break_true:w
+      \fi:
     \fi:
   }
+\cs_new_protected_nopar:Npn \regex_item_caseless_geq:n #1
+  {
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+    \reverse_if:N \if_num:w #1 > \l_regex_case_changed_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+  }
+\cs_new:Npn \regex_item_equal:n  { \regex_item_caseful_equal:n }
+\cs_new:Npn \regex_item_range:nn { \regex_item_caseful_range:nn }
+\cs_new:Npn \regex_item_geq:n    { \regex_item_caseful_geq:n }
+\cs_new_protected_nopar:Npn \regex_build_caseless:
+  {
+    \bool_set_true:N \l_regex_caseless_bool
+    \cs_set:Npn \regex_item_equal:n  { \regex_item_caseless_equal:n }
+    \cs_set:Npn \regex_item_range:nn { \regex_item_caseless_range:nn }
+    \cs_set:Npn \regex_item_geq:n    { \regex_item_caseless_geq:n }
+  }
+\cs_new_protected_nopar:Npn \regex_build_caseful:
+  {
+    \bool_set_false:N \l_regex_caseless_bool
+    \cs_set:Npn \regex_item_equal:n  { \regex_item_caseful_equal:n }
+    \cs_set:Npn \regex_item_range:nn { \regex_item_caseful_range:nn }
+    \cs_set:Npn \regex_item_geq:n    { \regex_item_caseful_geq:n }
+  }
 \cs_new_protected:Npn \regex_get_digits:nw #1
   {
     \tex_afterassignment:D \regex_tmp:w
@@ -235,65 +282,71 @@
       {
         \exp_not:n {#1}
         { \if_false: } } \fi:
-        \regex_get_digits_aux:N
+        \regex_get_digits_aux:NN
   }
-\cs_new_nopar:Npn \regex_get_digits_aux:N #1
+\cs_new_nopar:Npn \regex_get_digits_aux:NN #1#2
   {
-    \if_num:w 9 < 1 \exp_not:N #1 \exp_stop_f:
-    \else:
-      \if_charcode:w \c_space_token \exp_not:N #1
+    \if_meaning:w \regex_build_raw:N #1
+      \if_charcode:w \c_space_token \exp_not:N #2
       \else:
-        \regex_get_digits_end:w
+        \if_num:w 9 < 1 \exp_not:N #2 \exp_stop_f:
+          #2
+        \else:
+          \regex_get_digits_end:w #1 #2
+        \fi:
       \fi:
+    \else:
+      \regex_get_digits_end:w #1 #2
     \fi:
-    #1 \regex_get_digits_aux:N
+    \regex_get_digits_aux:NN
   }
-\cs_new_nopar:Npn \regex_get_digits_end:w
-    \fi: \fi: #1 \regex_get_digits_aux:N
+\cs_new_nopar:Npn \regex_get_digits_end:w #1 \fi: #2 \regex_get_digits_aux:NN
   {
-    \fi: \fi:
+    \fi: #2
     \if_false: { { \fi: } }
     #1
   }
+\prg_new_conditional:Npnn \regex_token_if_other_digit:N #1 { TF }
+  {
+    \if_num:w \c_nine < 1 \exp_not:N #1 \exp_stop_f:
+      \prg_return_true: \else: \prg_return_false: \fi:
+  }
 \prg_new_conditional:Npnn \regex_aux_char_if_special:N #1 { TF }
   {
-    \if_num:w `#1 < 97 \exp_stop_f:
-      \if_num:w `#1 < 58 \exp_stop_f:
-        \if_num:w \int_eval:w (`#1 - \c_eight)/\c_sixteen = \c_two
-          \prg_return_true:
-        \else:
-          \prg_return_false:
-        \fi:
+    \if_num:w `#1 < \c_ninety_one
+      \if_num:w `#1 < \c_fifty_eight
+        \if_num:w `#1 < \c_forty_eight
+          \if_num:w `#1 < \c_thirty_two
+            \prg_return_false: \else: \prg_return_true: \fi:
+        \else: \prg_return_false: \fi:
       \else:
-        \if_num:w \int_eval:w `#1 / 26 = \c_three
-          \prg_return_false:
-        \else:
-          \prg_return_true:
-        \fi:
+        \if_num:w `#1 < \c_sixty_five
+          \prg_return_true: \else: \prg_return_false: \fi:
       \fi:
     \else:
-      \if_num:w \int_eval:w `#1 / \c_five = 25 \exp_stop_f:
-        \prg_return_true:
+      \if_num:w `#1 < \c_one_hundred_twenty_three
+        \if_num:w `#1 < \c_ninety_seven
+          \prg_return_true: \else: \prg_return_false: \fi:
       \else:
-        \prg_return_false:
+        \if_num:w `#1 < \c_one_hundred_twenty_seven
+          \prg_return_true: \else: \prg_return_false: \fi:
       \fi:
     \fi:
   }
 \prg_new_conditional:Npnn \regex_aux_char_if_alphanumeric:N #1 { TF }
   {
-    \if_num:w `#1 < 91 \exp_stop_f:
-      \if_num:w `#1 < 65 \exp_stop_f:
-        \if_num:w \c_nine < 1 #1 \exp_stop_f:
-          \prg_return_true:
-        \else:
-          \prg_return_false:
-        \fi:
+    \if_num:w `#1 < \c_ninety_one
+      \if_num:w `#1 < \c_fifty_eight
+        \if_num:w `#1 < \c_forty_eight
+          \prg_return_false: \else: \prg_return_true: \fi:
       \else:
-        \prg_return_true:
+        \if_num:w `#1 < \c_sixty_five
+          \prg_return_false: \else: \prg_return_true: \fi:
       \fi:
     \else:
-      \if_num:w \int_eval:w (`#1-\c_six)/26 = \c_four
-        \prg_return_true:
+      \if_num:w `#1 < \c_one_hundred_twenty_three
+        \if_num:w `#1 < \c_ninety_seven
+          \prg_return_false: \else: \prg_return_true: \fi:
       \else:
         \prg_return_false:
       \fi:
@@ -301,8 +354,8 @@
   }
 \cs_new_protected_nopar:Npn \regex_build_new_state:
   {
-    \int_compare:nNnTF \l_regex_max_state_int > {32766}
-      { \regex_build_error:n {-997} }
+    \int_compare:nNnTF \l_regex_max_state_int > { 32766 }
+      { \msg_error:nn { regex } { -997 } }
       {
         \int_incr:N \l_regex_max_state_int
         \tex_toks:D \l_regex_max_state_int { \s_regex_toks }
@@ -314,15 +367,15 @@
   {
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      { #1 { \int_use:N #2 } }
+      { #1 { \int_eval:n { #2 - \l_regex_left_state_int } } }
   }
 \cs_new_protected_nopar:Npn \regex_build_transitions_aux:NNNN #1#2#3#4
   {
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
-        #1 { \int_use:N #2 }
-        #3 { \int_use:N #4 }
+        #1 { \int_eval:n { #2 - \l_regex_left_state_int } }
+        #3 { \int_eval:n { #4 - \l_regex_left_state_int } }
       }
   }
 \cs_new_protected:Npn \regex_build:n #1
@@ -363,25 +416,19 @@
     \cs_set_eq:NN \regex_build_control:N \regex_build_default_control:N
     \cs_set_eq:NN \regex_build_raw:N \regex_build_default_raw:N
     \int_set_eq:NN \l_regex_capturing_group_int \c_zero
-    \int_zero:N \l_regex_left_state_int
-    \int_zero:N \l_regex_right_state_int
     \int_zero:N \l_regex_max_state_int
     \regex_build_new_state:
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_action_start_wildcard:nn
-          { \int_use:N \l_regex_left_state_int }
-          { \int_use:N \l_regex_right_state_int }
-      }
+      { \regex_action_start_wildcard:nn {0} {1} }
   }
 \cs_new_protected_nopar:Npn \regex_build_end:
   {
     \seq_if_empty:NF \l_regex_capturing_group_seq
       {
-        \regex_build_error:n {22}
+        \msg_error:nn { regex } {22}
         \prg_replicate:nn
-          { \seq_length:N \l_regex_capturing_group_seq } % (
+          { \seq_length:N \l_regex_capturing_group_seq }
           { \regex_build_close_aux: \regex_build_group_: }
       }
     \regex_toks_put_right:Nx \l_regex_right_state_int
@@ -399,7 +446,13 @@
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \int_compare:nNnT {#1} = \l_regex_current_step_int
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_protected_nopar:cpn { regex_build_$: } % $
@@ -409,71 +462,72 @@
       {
         \exp_not:N \int_compare:nNnT
           \c_minus_one = \l_regex_current_char_int
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_eq:Nc \regex_build_Z: { regex_build_$: } %$
 \cs_new_eq:Nc \regex_build_z: { regex_build_$: } %$
 \cs_new_protected_nopar:Npn \regex_build_b:
   {
-    \bool_set_true:N \l_regex_look_behind_bool
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \regex_if_word_boundary:TF
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
           { }
       }
   }
 \cs_new_protected_nopar:Npn \regex_build_B:
   {
-    \bool_set_true:N \l_regex_look_behind_bool
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \regex_if_word_boundary:TF
           { }
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_protected_nopar:Npn \regex_if_word_boundary:TF
   {
-    \tl_if_empty:NTF \l_regex_look_behind_str
-      { \c_regex_w_tl }
-      {
-        \group_begin:
-          \cs_set_nopar:Npx \regex_tmp:w
-            {
-              \int_set:Nn \l_regex_current_char_int
-                { ` \str_head:N \l_regex_look_behind_str }
-            }
-          \regex_tmp:w
-          \c_regex_w_tl
-          \regex_break_point:TF
-            { \group_end: \c_regex_W_tl }
-            { \group_end: \c_regex_w_tl }
-      }
+    \group_begin:
+      \int_set_eq:NN \l_regex_current_char_int \l_regex_last_char_int
+      \c_regex_w_tl
+      \regex_break_point:TF
+        { \group_end: \c_regex_W_tl \regex_item_equal:n { -1 } }
+        { \group_end: \c_regex_w_tl }
     \regex_break_point:TF
   }
 \cs_new_protected_nopar:Npn \regex_build_default_raw:N #1
   {
     \cs_set:Npx \regex_build_tmp_class:n ##1
       {
-        \exp_not:n { \exp_not:N \if_num:w }
-            \int_value:w `#1 = \l_regex_current_char_int
-          \regex_action_cost:n { ##1 }
-        \exp_not:n { \exp_not:N \fi: }
+        \regex_item_equal:n { \int_value:w `#1 }
+        \regex_break_point:TF { \regex_action_cost:n { ##1 } } { }
       }
     \regex_build_one_quantifier:
   }
 \cs_new_protected_nopar:cpn { regex_build_.: }
   {
     \cs_set:Npn \regex_build_tmp_class:n ##1
-      {
-        \exp_not:N \if_num:w \c_minus_one < \l_regex_current_char_int
-          \regex_action_cost:n {##1}
-        \exp_not:N \fi:
-      }
+      { \regex_item_dot:T { \regex_action_cost:n {##1} } }
     \regex_build_one_quantifier:
   }
 \cs_new_protected_nopar:Npn \regex_build_char_type:N #1
@@ -481,9 +535,7 @@
     \cs_set:Npn \regex_build_tmp_class:n ##1
       {
         \exp_not:N #1
-        \exp_not:N \regex_break_point:TF
-          { \regex_action_cost:n {##1} }
-          { }
+        \regex_break_point:TF { \regex_action_cost:n {##1} } { }
       }
     \regex_build_one_quantifier:
   }
@@ -518,16 +570,8 @@
           {
             \exp_not:o \l_regex_class_tl
             \bool_if:NTF \l_regex_class_bool
-              {
-                \exp_not:N \regex_break_point:TF
-                  { \regex_action_cost:n {##1} }
-                  { }
-              }
-              {
-                \exp_not:N \regex_break_point:TF
-                  { }
-                  { \regex_action_cost:n {##1} }
-              }
+              { \regex_break_point:TF { \regex_action_cost:n {##1} } { } }
+              { \regex_break_point:TF { } { \regex_action_cost:n {##1} } }
           }
         \regex_build_one_quantifier:
       }
@@ -553,7 +597,7 @@
 \cs_new_protected_nopar:Npn \regex_class_single:N #1
   {
     \tl_put_right:Nx \l_regex_class_tl
-      { \exp_not:N \regex_item_equal:n { \int_value:w `#1 } }
+      { \regex_item_equal:n { \int_value:w `#1 } }
   }
 \cs_new_protected_nopar:Npn \regex_class_range:Nw #1#2#3
   {
@@ -572,14 +616,14 @@
 \cs_new_protected_nopar:Npn \regex_class_range_put:NN #1#2
   {
     \if_num:w `#1 > `#2 \exp_stop_f:
-      \regex_build_error:n {8}
+      \msg_error:nn { regex } {8}
     \else:
       \tl_put_right:Nx \l_regex_class_tl
         {
           \if_num:w `#1 = `#2 \exp_stop_f:
-            \exp_not:N \regex_item_equal:n
+            \regex_item_equal:n
           \else:
-            \exp_not:N \regex_item_range:nn { \int_value:w `#1 }
+            \regex_item_range:nn { \int_value:w `#1 }
           \fi:
           { \int_value:w `#2 }
         }
@@ -651,26 +695,29 @@
         \exp_not:N \regex_build_raw:N \c_lbrace_str #1#2
       }
   }
-\cs_new_protected_nopar:Npn \regex_build_quantifier_lbrace:nnw #1#2#3
+\cs_new_protected_nopar:Npn \regex_build_quantifier_lbrace:nnw #1#2#3#4
   {
-    \str_if_eq:xxTF { \exp_not:N #3 } { \c_rbrace_str }
+    \str_if_eq:xxTF
+      { \exp_not:n {#3#4} }
+      { \exp_not:N \regex_build_control:N \c_rbrace_str }
       {
         \tl_if_empty:nTF {#2}
-          { \regex_build_quantifier_aux:nnN { {#1} {\c_max_int} } {nn} }
+          { \regex_build_quantifier_aux:nnNN { {#1} } { n* } }
           {
             \int_compare:nNnT {#1} > {#2}
-              { \regex_build_error:n {4} }
-            \regex_build_quantifier_aux:nnN { {#1} {#2} } {nn}
+              { \msg_error:nn { regex } {4} }
+            \regex_build_quantifier_aux:nnNN { {#1} {#2} } { nn }
           }
       }
       {
         \regex_build_quantifier_end:n { }
         \use:x
           {
-            \exp_not:n { \exp_args:No \tl_map_function:nN }
-              { \c_lbrace_str #1 #2 , }
-            \regex_build_raw:N
+            \exp_args:No \tl_map_function:nN
+              { \c_lbrace_str #1 , #2 }
+              \regex_build_raw:N
           }
+        #3 #4
       }
   }
 \cs_new_protected_nopar:Npn \regex_build_quantifier_end:n #1
@@ -726,71 +773,27 @@
       \regex_action_free:n \l_regex_tmpa_int
   }
 \cs_new_protected_nopar:Npn \regex_build_one_n: #1
-  {
-    \int_set_eq:NN \l_regex_tmpa_int \l_regex_right_state_int
-    \regex_build_new_state:
-    \regex_build_new_state:
-    \regex_toks_put_right:Nx \l_regex_tmpa_int
-      { %^^A safe \if nesting?
-        \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \else:
-          \regex_action_no_repeat_move:n
-            { \int_use:N \l_regex_right_state_int }
-        \exp_not:N \fi:
-      }
-    \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_build_tmp_class:n
-          { \int_use:N \l_regex_tmpa_int }
-      }
-  }
+  { \prg_replicate:nn {#1} { \regex_build_one_: } }
 \cs_new_eq:cN { regex_build_one_n?: } \regex_build_one_n:
-\cs_new_protected_nopar:Npn \regex_build_one_nn: #1#2
+\cs_new_protected_nopar:cpx { regex_build_one_n*: } #1
   {
-    \regex_build_one_nn_aux:nn {#1}
-      {
-        \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-          \regex_action_repeat_copy:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \fi:
-        \regex_action_no_repeat_move:n
-          { \int_use:N \l_regex_right_state_int }
-      }
+    \exp_not:N \prg_replicate:nn {#1} { \exp_not:N \regex_build_one_: }
+    \exp_not:c { regex_build_one_*: }
   }
-\cs_new_protected_nopar:cpn { regex_build_one_nn?: } #1#2
+\cs_new_protected_nopar:cpx { regex_build_one_n*?: } #1
   {
-    \regex_build_one_nn_aux:nn {#1}
-      {
-        \regex_action_no_repeat_copy:n
-          { \int_use:N \l_regex_right_state_int }
-        \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \fi:
-      }
+    \exp_not:N \prg_replicate:nn {#1} { \exp_not:N \regex_build_one_: }
+    \exp_not:c { regex_build_one_*?: }
   }
-\cs_new_protected_nopar:Npn \regex_build_one_nn_aux:nn #1#2
+\cs_new_protected_nopar:Npn \regex_build_one_nn_aux:Nnn #1#2#3
   {
-    \int_set_eq:NN \l_regex_tmpa_int \l_regex_right_state_int
-    \regex_build_new_state:
-    \regex_build_new_state:
-    \regex_toks_put_right:Nx \l_regex_tmpa_int
-      {
-        \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \else:
-          #2
-        \exp_not:N \fi:
-      }
-    \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_build_tmp_class:n
-          { \int_use:N \l_regex_tmpa_int }
-      }
+    \prg_replicate:nn {#2} { \regex_build_one_: }
+    \prg_replicate:nn {#3-#2} {#1}
   }
+\cs_new_protected_nopar:Npx \regex_build_one_nn:
+  { \regex_build_one_nn_aux:Nnn \exp_not:c { regex_build_one_?: } }
+\cs_new_protected_nopar:cpx { regex_build_one_nn?: }
+  { \regex_build_one_nn_aux:Nnn \exp_not:c { regex_build_one_??: } }
 \cs_new_protected_nopar:cpn { regex_build_(: } #1#2
   {
     \str_if_eq:nnTF { #1 #2 } { \regex_build_control:N ? }
@@ -806,10 +809,19 @@
 \cs_new_protected_nopar:Npn \regex_build_open_aux:
   {
     \regex_build_new_state:
-    \seq_push:Nx \l_regex_left_state_seq
-      { \int_use:N \l_regex_left_state_int }
-    \seq_push:Nx \l_regex_right_state_seq
-      { \int_use:N \l_regex_right_state_int }
+    \seq_push:Nx \l_regex_group_begin_seq
+      {
+        \int_set:Nn \l_regex_left_state_int
+          { \int_use:N \l_regex_left_state_int }
+      }
+    \bool_if:NTF \l_regex_caseless_bool
+      { \seq_push:Nn \l_regex_group_end_seq { \regex_build_caseless: } }
+      { \seq_push:Nn \l_regex_group_end_seq { \regex_build_caseful: } }
+    \seq_push:Nx \l_regex_group_end_seq
+      {
+        \int_set:Nn \l_regex_right_state_int
+          { \int_use:N \l_regex_right_state_int }
+      }
     \regex_build_begin_alternation:
   }
 \cs_new_protected_nopar:cpn { regex_build_|: }
@@ -820,7 +832,7 @@
 \cs_new_protected_nopar:cpn { regex_build_): }
   {
     \seq_if_empty:NTF \l_regex_capturing_group_seq
-      { \regex_build_error:n {22} }
+      { \msg_error:nn { regex } { 22 } }
       {
         \regex_build_close_aux:
         \regex_build_group_quantifier:
@@ -829,30 +841,41 @@
 \cs_new_protected_nopar:Npn \regex_build_close_aux:
   {
     \regex_build_end_alternation:
-    \seq_pop:NN \l_regex_left_state_seq  \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_left_state_int  \l_regex_tmpa_tl
-    \seq_pop:NN \l_regex_right_state_seq \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_right_state_int \l_regex_tmpa_tl
+    \regex_seq_pop:N \l_regex_group_begin_seq
+    \regex_seq_pop:N \l_regex_group_end_seq
+    \regex_seq_pop:N \l_regex_group_end_seq
   }
 \cs_new_protected_nopar:Npn \regex_build_begin_alternation:
   {
     \regex_build_new_state:
-    \seq_get:NN \l_regex_left_state_seq \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_left_state_int \l_regex_tmpa_tl
+    \regex_seq_get:N \l_regex_group_begin_seq
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+      {
+        \regex_action_free:n
+          {
+            \int_eval:n
+              { \l_regex_right_state_int - \l_regex_left_state_int }
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_build_end_alternation:
   {
-    \seq_get:NN \l_regex_right_state_seq \l_regex_tmpa_tl
-    \regex_toks_put_right:Nx \l_regex_right_state_int
-      { \regex_action_free:n { \l_regex_tmpa_tl } }
+    \int_set_eq:NN \l_regex_left_state_int \l_regex_right_state_int
+    \regex_seq_get:N \l_regex_group_end_seq
+    \regex_toks_put_right:Nx \l_regex_left_state_int
+      {
+        \regex_action_free:n
+          {
+            \int_eval:n
+              { \l_regex_right_state_int - \l_regex_left_state_int }
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_build_special_group:NN #1#2
   {
     \cs_if_exist_use:cF { regex_build_special_group_\token_to_str:N #2 : }
       {
-        \regex_build_error:n { -998 }
+        \msg_error:nn { regex } { -998 }
         \regex_build_control:N ( % )
         \regex_build_raw:N ?
         #1 #2
@@ -863,6 +886,40 @@
     \seq_push:Nx \l_regex_capturing_group_seq { * }
     \regex_build_open_aux:
   }
+\cs_new_protected_nopar:Npn \regex_build_special_group_i:
+  {
+    \regex_build_options:NNN +
+    \regex_build_raw:N i
+  }
+\cs_new_protected_nopar:cpn { regex_build_special_group_-: }
+  {
+    \regex_build_options:NNN -
+  }
+\cs_new_protected_nopar:Npn \regex_build_options:NNN #1#2#3
+  {
+    \token_if_eq_meaning:NNTF \regex_build_raw:N #2
+      {
+        \cs_if_exist_use:cF { regex_build_option_#1#3: }
+          { \msg_error:nnx { regex } { unknown-option } { #3 } }
+        \regex_build_options:NNN #1
+      }
+      {
+        \prg_case_str:nnn { #3 }
+          { % (
+            { ) } { }
+            { - } { \regex_build_options:NNN - }
+          }
+          { \msg_error:nnx { regex } { invalid-in-option } { #3 } }
+      }
+  }
+\cs_new_protected_nopar:cpn { regex_build_option_+i: }
+  {
+    \regex_build_caseless:
+    \cs_set_eq:NN \regex_match_loop_case_hook:
+      \regex_match_loop_caseless_hook:
+  }
+\cs_new_protected_nopar:cpn { regex_build_option_-i: }
+  { \regex_build_caseful: }
 \cs_new_protected_nopar:Npn \regex_build_group_quantifier:
   {
     \tl_set:Nn \l_regex_one_or_group_tl { group }
@@ -891,21 +948,33 @@
     \int_set_eq:NN \l_regex_tmpa_int \l_regex_left_state_int
     \regex_build_new_state:
     \tex_toks:D \l_regex_right_state_int = \tex_toks:D \l_regex_tmpa_int
-    \use:x
+    \regex_toks_put_left:Nx \l_regex_right_state_int
+      {
+        \int_set:Nn \l_regex_current_state_int
+          { \int_use:N \l_regex_tmpa_int } % ^^A here we lie!
+      }
+    \cs_set:Npx \regex_tmp:w
       {
         \tex_toks:D \l_regex_tmpa_int
-          { \s_regex_toks #1 { \int_use:N \l_regex_right_state_int } }
+          {
+            \s_regex_toks
+            #1 { \int_eval:n { \l_regex_right_state_int - \l_regex_tmpa_int } }
+          }
       }
+    \regex_tmp:w
     \regex_build_group_submatches:NN
       \l_regex_right_state_int \l_regex_left_state_int
-    \int_set_eq:NN \l_regex_right_state_int \l_regex_left_state_int
   }
 \cs_new_protected_nopar:Npn \regex_build_group_qs_aux:NN #1#2
   {
     \regex_build_group_shift:N \regex_action_free:n
+    \int_set_eq:NN \l_regex_right_state_int \l_regex_left_state_int
     \regex_build_transition_aux:NN \regex_action_free:n #1
     #2 \l_regex_tmpa_int
-      { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+      {
+        \regex_action_free:n
+          { \int_eval:n { \l_regex_right_state_int - \l_regex_tmpa_int } }
+      }
   }
 \cs_new_protected_nopar:cpn { regex_build_group_?: }
   {
@@ -945,77 +1014,63 @@
       \regex_action_free:n \l_regex_right_state_int
       \regex_action_free:n \l_regex_tmpa_int
   }
-\cs_new_protected_nopar:Npn \regex_build_group_n: #1
+\cs_new_protected_nopar:Npn \regex_build_group_n_aux:n #1
   {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
-    \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
+    \regex_toks_put_right:Nx \l_regex_right_state_int
       {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \regex_action_no_repeat_move:n
-                { \int_use:N \l_regex_right_state_int }
-            \exp_not:N \fi:
-          }
+        \regex_action_free:n
+          { \int_eval:n { \l_regex_max_state_int - \l_regex_left_state_int } }
       }
-  }
-\cs_new_eq:cN { regex_build_group_n?: } \regex_build_group_n:
-\cs_new_protected_nopar:Npn \regex_build_group_nn: #1#2
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
-    \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
+    \int_set_eq:NN \l_regex_tmpa_int \l_regex_left_state_int
+    \int_set:Nn \l_regex_tmpb_int { \l_regex_max_state_int + \c_one }
+    \int_set:Nn \l_regex_max_state_int
       {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-                \tex_the:D \tex_toks:D \l_regex_tmpa_int
-              \exp_not:N \fi:
-              \regex_action_no_repeat_copy:n
-                { \int_use:N \l_regex_right_state_int }
-            \exp_not:N \fi:
-          }
+        \l_regex_left_state_int - \c_one
+        + #1 * ( \l_regex_max_state_int - \l_regex_left_state_int + \c_one )
+      }
+    \int_until_do:nNnn \l_regex_tmpb_int > \l_regex_max_state_int
+      {
+        \tex_toks:D \l_regex_tmpb_int = \tex_toks:D \l_regex_tmpa_int
+        \int_incr:N \l_regex_tmpa_int
+        \int_incr:N \l_regex_tmpb_int
       }
   }
-\cs_new_protected_nopar:cpn { regex_build_group_nn?: } #1#2
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
+\cs_new_protected_nopar:Npn \regex_build_group_n: #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
     \regex_build_transition_aux:NN
+      \regex_action_free:n \l_regex_right_state_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
+  }
+\cs_new_eq:cN { regex_build_group_n?: } \regex_build_group_n:
+\cs_new_protected_nopar:cpn { regex_build_group_n*: } #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
+    \regex_build_transitions_aux:NNNN
       \regex_action_free:n \l_regex_tmpa_int
-    \use:x
-      {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \regex_action_no_repeat_copy:n
-                { \int_use:N \l_regex_right_state_int }
-              \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-                \tex_the:D \tex_toks:D \l_regex_tmpa_int
-              \exp_not:N \fi:
-            \exp_not:N \fi:
-          }
-      }
+      \regex_action_free:n \l_regex_right_state_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
   }
-\cs_new_protected:Npn \regex_if_state_free:nT #1
-  {
-    \if_num:w \tex_dimen:D #1 = \l_regex_unique_step_int
-      \exp_after:wN \use_none:n
-    \else:
-      \exp_after:wN \use:n
-    \fi:
+\cs_new_protected_nopar:cpn { regex_build_group_n*?: } #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
+    \regex_build_transitions_aux:NNNN
+      \regex_action_free:n \l_regex_right_state_int
+      \regex_action_free:n \l_regex_tmpa_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
+  }
+\cs_new_protected_nopar:Npn \regex_build_group_nn: #1#2
+  { % ^^A Not Implemented Yet!
+    \msg_expandable_error:n { Quantifier~{m,n}~not~implemented~yet }
+    \use:c { regex_build_group_n*: } {#1}
+  }
+\cs_new_protected_nopar:cpn { regex_build_group_nn?: } #1#2
+  { % ^^A Not Implemented Yet!
+    \msg_expandable_error:n { Quantifier~{m,n}~not~implemented~yet }
+    \use:c { regex_build_group_n*?: } {#1}
   }
 \cs_new_protected:Npn \regex_store_state:n #1
   {
@@ -1023,23 +1078,24 @@
     \tex_skip:D \l_regex_max_index_int #1 sp \scan_stop:
     \regex_store_submatches:n {#1}
   }
-\cs_new_protected_nopar:Npn \regex_state_use_submatches:
+\cs_new_protected_nopar:Npn \regex_state_use_with_submatches:
   { \regex_state_use_aux:n { } }
 \cs_new_protected_nopar:Npn \regex_state_use:
   { \regex_state_use_aux:n { \exp_after:wN \regex_state_use_aux_ii:w } }
-\cs_new:Npn \regex_state_use_aux_ii:w #1 \s_regex_toks { }
-\cs_new_protected:Npn \regex_state_use_aux:n #1
-  {
-    \regex_if_state_free:nT {  \l_regex_current_state_int }
-      {
-        \tex_dimen:D \l_regex_current_state_int
-          = \l_regex_unique_step_int sp \scan_stop:
-        #1 \tex_the:D \tex_toks:D \l_regex_current_state_int \scan_stop:
-      }
+\cs_new_nopar:Npn \regex_state_use_aux_ii:w #1 \s_regex_toks { }
+\cs_new_protected_nopar:Npn \regex_state_use_aux:n #1
+  {
+    \if_num:w \tex_dimen:D \l_regex_current_state_int
+        < \l_regex_unique_step_int
+      \tex_dimen:D \l_regex_current_state_int
+        = \l_regex_unique_step_int sp \scan_stop:
+      #1 \tex_the:D \tex_toks:D \exp_after:wN \l_regex_current_state_int
+    \fi:
+    \scan_stop:
   }
 \cs_new_protected_nopar:Npn \regex_disable_submatches:
   {
-    \cs_set_eq:NN \regex_state_use_submatches: \regex_state_use:
+    \cs_set_eq:NN \regex_state_use_with_submatches: \regex_state_use:
     \cs_set_eq:NN \regex_store_submatches:n
       \regex_protected_use_none:n
     \cs_set_eq:NN \regex_action_submatches:n
@@ -1048,55 +1104,73 @@
 \cs_new_protected:Npn \regex_protected_use_none:n #1 { }
 \cs_new_protected:Npn \regex_store_submatches:n #1
   {
-    \exp_after:wN \regex_store_submatches_aux:Nw
-    \exp_after:wN \l_regex_current_submatches_prop
-    \tex_the:D \tex_toks:D #1 \scan_stop: \q_stop
-    { #1 }
+    \tex_toks:D #1 \exp_after:wN
+      {
+        \tex_romannumeral:D
+        \exp_after:wN \regex_store_submatches_aux:w
+        \tex_the:D \tex_toks:D #1
+      }
   }
-\cs_new_protected:Npn \regex_store_submatches_aux:Nw #1 #2 \s_regex_toks
+\cs_new_protected:Npn \regex_store_submatches_aux:w #1 \s_regex_toks
   {
-    \exp_args:No \regex_store_submatches_aux_ii:wnnwwn { #1 }
-      #2
-      \regex_state_submatches:nn { \c_minus_one } { \q_prop }
+    \regex_store_submatches_aux_ii:Nnnw
+      #1
+      \regex_state_submatches:nn \c_minus_one \q_prop
     \s_regex_toks
   }
-\cs_new_protected:Npn \regex_store_submatches_aux_ii:wnnwwn
-    #1 \regex_state_submatches:nn #2#3 #4 \s_regex_toks #5 \q_stop #6
+\cs_new_protected:Npn \regex_store_submatches_aux_ii:Nnnw
+    \regex_state_submatches:nn #1 #2 #3 \s_regex_toks
   {
-    \tex_toks:D #6 \exp_after:wN
+    \exp_after:wN \c_zero
+    \exp_after:wN \regex_state_submatches:nn \exp_after:wN
       {
-        \exp_after:wN \regex_state_submatches:nn \exp_after:wN
-          { \int_value:w \int_eval:w \l_regex_unique_step_int + \c_one }
-          { #1 }
-        \regex_state_submatches:nn {#2} {#3}
-        \s_regex_toks
-        #5
+        \int_value:w \int_eval:w
+          \l_regex_unique_step_int + \c_one
+        \exp_after:wN
       }
+      \exp_after:wN { \l_regex_current_submatches_prop }
+    \regex_state_submatches:nn {#1} {#2}
+    \s_regex_toks
   }
 \cs_new_protected:Npn \regex_state_submatches:nn #1#2
   {
     \if_num:w #1 = \l_regex_unique_step_int
-      \tl_set:Nn \l_regex_current_submatches_prop {#2}
+      \tl_set:Nn \l_regex_current_submatches_prop { #2 }
     \fi:
   }
 \cs_new_protected:Npn \regex_match:n #1
   {
-    \tl_set:Nx \l_regex_query_str { \tl_to_other_str:n {#1} }
+    \tl_set:Nx \l_regex_query_other_str { \tl_to_other_str:n {#1} }
     \regex_match_initial_setup:
     \regex_match_once:
   }
 \cs_new_protected_nopar:Npn \regex_match_once:
   {
     \regex_match_setup:
-    \exp_after:wN \regex_match_once_aux: \l_regex_query_str
+    \exp_after:wN \regex_match_once_aux: \l_regex_query_other_str
       \q_recursion_tail \q_recursion_stop
     \bool_if:NT \l_regex_success_bool { \l_regex_every_match_tl }
   }
 \cs_new_protected_nopar:Npn \regex_match_once_aux:
-  { \str_skip_do:nn { \l_regex_start_step_int } { \regex_match_loop:N } }
+  {
+    \int_compare:nNnTF \l_regex_start_step_int = \c_zero
+      {
+        \int_set_eq:NN \l_regex_current_char_int \c_minus_one
+        \regex_match_loop:N
+      }
+      {
+        \str_skip_do:nn
+          { \l_regex_start_step_int - \c_one }
+          { \regex_match_once_aux_ii:N }
+      }
+  }
+\cs_new_protected_nopar:Npn \regex_match_once_aux_ii:N #1
+  {
+    \int_set:Nn \l_regex_current_char_int { `#1 }
+    \regex_match_loop:N
+  }
 \cs_new_protected_nopar:Npn \regex_match_initial_setup:
   {
-    \tl_clear:N \l_regex_look_behind_str
     \prg_stepwise_inline:nnnn {1} {1} { \l_regex_max_state_int }
       { \tex_dimen:D ##1 \c_minus_one sp \scan_stop: }
     \int_set_eq:NN \l_regex_unique_step_int  \c_minus_one
@@ -1118,20 +1192,11 @@
     \int_zero:N \l_regex_max_index_int
     \regex_store_state:n {1}
   }
-\cs_new_protected_nopar:Npn \regex_match_loop_setup:
-  {
-    \int_incr:N \l_regex_current_step_int
-    \int_incr:N \l_regex_unique_step_int
-    \bool_set_false:N \l_regex_fresh_thread_bool
-  }
 \cs_new_eq:NN \s_regex_step \scan_stop:
 \cs_new:Npn \regex_break_step:w #1 \s_regex_step { }
 \cs_new_protected_nopar:Npn \regex_match_loop:N #1
   {
-    \regex_match_loop_setup:
-    \token_if_eq_meaning:NNTF #1 \q_recursion_tail
-      { \int_set_eq:NN \l_regex_current_char_int \c_minus_one }
-      { \int_set:Nn \l_regex_current_char_int {`#1} }
+    \regex_match_loop_setup:N #1
     \cs_set_nopar:Npx \regex_tmp:w
       {
         \int_zero:N \l_regex_max_index_int
@@ -1145,19 +1210,49 @@
       \exp_after:wN \use_none_delimit_by_q_recursion_stop:w
     \fi:
     \quark_if_recursion_tail_stop:N #1
-    \bool_if:NT \l_regex_look_behind_bool
-      { \tl_put_left:Nx \l_regex_look_behind_str {#1} }
     \regex_match_loop:N
   }
 \cs_new_nopar:Npn \regex_match_one_index:n #1
   {
-    \regex_match_one_index_aux:n { \int_value:w \tex_skip:D #1 }
+    \regex_match_one_index_aux:n
+      { \int_value:w \tex_skip:D #1 }
   }
 \cs_new_protected_nopar:Npn \regex_match_one_index_aux:n #1
   {
     \int_set:Nn \l_regex_current_state_int {#1}
     \prop_clear:N \l_regex_current_submatches_prop
-    \regex_state_use_submatches:
+    \regex_state_use_with_submatches:
+  }
+\cs_new_protected_nopar:Npn \regex_match_loop_setup:N #1
+  {
+    \int_incr:N \l_regex_current_step_int
+    \int_incr:N \l_regex_unique_step_int
+    \bool_set_false:N \l_regex_fresh_thread_bool
+    \int_set_eq:NN \l_regex_last_char_int \l_regex_current_char_int
+    \if_meaning:w #1 \q_recursion_tail
+      \int_set_eq:NN \l_regex_current_char_int \c_minus_one
+    \else:
+      \int_set:Nn \l_regex_current_char_int {`#1}
+    \fi:
+    \regex_match_loop_case_hook:
+  }
+\cs_new_protected_nopar:Npn \regex_match_loop_case_hook: { }
+\cs_new_protected_nopar:Npn \regex_match_loop_caseless_hook:
+  {
+    \int_set_eq:NN \l_regex_case_changed_char_int \l_regex_current_char_int
+    \if_num:w \l_regex_current_char_int < \c_ninety_one
+      \if_num:w \l_regex_current_char_int < \c_sixty_five
+      \else:
+        \int_add:Nn \l_regex_case_changed_char_int { \c_thirty_two }
+      \fi:
+    \else:
+      \if_num:w \l_regex_current_char_int < \c_one_hundred_twenty_three
+        \if_num:w \l_regex_current_char_int < \c_ninety_seven
+        \else:
+          \int_sub:Nn \l_regex_case_changed_char_int { \c_thirty_two }
+        \fi:
+      \fi:
+    \fi:
   }
 \cs_new_protected_nopar:Npn \regex_action_start_wildcard:nn #1#2
   {
@@ -1167,7 +1262,10 @@
     \regex_action_cost:n {#1}
   }
 \cs_new_protected_nopar:Npn \regex_action_cost:n #1
-  { \regex_store_state:n {#1} }
+  {
+    \exp_args:Nf \regex_store_state:n %^^A optimize!
+      { \int_eval:n { \l_regex_current_state_int + #1 } }
+  }
 \cs_new_protected_nopar:Npn \regex_action_success:
   {
     \regex_last_match_empty:F
@@ -1184,30 +1282,22 @@
   }
 \cs_new_protected_nopar:Npn \regex_action_free:n #1
   {
-    \regex_if_state_free:nT {#1}
+    \cs_set_nopar:Npx \regex_tmp:w
       {
-        \use:x
-          {
-            \int_set:Nn \l_regex_current_state_int {#1}
-            \regex_store_submatches:n { \l_regex_current_state_int }
-            \regex_state_use:
-            \int_set:Nn \l_regex_current_state_int
-              { \int_use:N \l_regex_current_state_int }
-            \tl_set:Nn \exp_not:N \l_regex_current_submatches_prop
-              { \exp_not:o \l_regex_current_submatches_prop }
-          }
+        \int_add:Nn \l_regex_current_state_int {#1}
+        \regex_state_use:
+        \int_set:Nn \l_regex_current_state_int
+          { \int_use:N \l_regex_current_state_int }
+        \tl_set:Nn \exp_not:N \l_regex_current_submatches_prop
+          { \exp_not:o \l_regex_current_submatches_prop }
       }
+    \regex_tmp:w
   }
 \cs_new_protected_nopar:Npn \regex_action_submatch:n #1
   {
     \prop_put:Nno \l_regex_current_submatches_prop {#1}
       { \int_use:N \l_regex_current_step_int }
-    \regex_store_submatches:n { \l_regex_current_state_int }
   }
-\cs_new_protected_nopar:Npn \regex_action_repeat_copy:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_repeat_move:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_no_repeat_copy:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_no_repeat_move:n { \ERROR }
 \cs_new_protected_nopar:Npn \regex_extract:
   {
     \seq_gclear:N \g_regex_submatches_seq
@@ -1217,11 +1307,7 @@
         \regex_extract_aux:nTF { ##1 }
           {
             \seq_gput_right:Nx \g_regex_submatches_seq
-              {
-                \str_from_to:Nnn \l_regex_query_str
-                  { \l_regex_tmpa_tl }
-                  { \l_regex_tmpb_tl }
-              }
+              { \regex_query_substr:NN \l_regex_tmpa_tl \l_regex_tmpb_tl }
           }
           { \seq_gput_right:Nn \g_regex_submatches_seq { } }
       }
@@ -1253,9 +1339,13 @@
             = \int_use:N \l_regex_max_state_int
           \l_regex_capturing_group_int
             = \int_use:N \l_regex_capturing_group_int
-          \bool_if:NTF \l_regex_look_behind_bool
-            { \bool_set_true:N \l_regex_look_behind_bool }
-            { \bool_set_false:N \l_regex_look_behind_bool }
+          \token_if_eq_meaning:NNT
+            \regex_match_loop_case_hook:
+            \regex_match_loop_caseless_hook:
+            {
+              \cs_set_eq:NN \regex_match_loop_case_hook:
+                \regex_match_loop_caseless_hook:
+            }
           \prg_stepwise_function:nnnN
             {1} {1} {\l_regex_max_state_int}
             \regex_set_aux:n
@@ -1269,7 +1359,7 @@
 \cs_new:Npn \regex_nfa:Nw #1 #2 \regex_nfa_end:
   { \msg_expandable_error:n { Automaton~#1 used~incorrectly. } }
 \cs_new_eq:NN \regex_nfa_end: \scan_stop:
-\prg_new_protected_conditional:Npnn \regex_check_nfa:N #1 { TF }
+\prg_new_protected_conditional:Npnn \regex_check_nfa:N #1 { T , TF }
   { \exp_after:wN \regex_check_nfa_aux:Nw #1 \q_stop }
 \cs_new:Npn \regex_check_nfa_aux:Nw #1 #2 \q_stop
   {
@@ -1280,11 +1370,6 @@
       \prg_return_false:
     \fi:
   }
-\msg_new:nnn { regex } { not-nfa }
-  {
-    I~was~expecting~a~regular~expression~variable.\\
-    Instead,~I~got~#1.
-  }
 \cs_new_protected_nopar:Npn \regex_use:N #1
   { \exp_after:wN \use_none:nn #1 }
 \cs_new_protected:Npn \regex_user_aux:n #1
@@ -1296,7 +1381,7 @@
   }
 \cs_new_protected_nopar:Npn \regex_return_after_group:
   {
-    \if_bool:N \l_regex_success_bool
+    \if_meaning:w \c_true_bool \l_regex_success_bool
       \group_insert_after:N \prg_return_true:
     \else:
       \group_insert_after:N \prg_return_false:
@@ -1304,7 +1389,7 @@
   }
 \cs_new_protected_nopar:Npn \regex_extract_after_group:N #1
   {
-    \if_bool:N \l_regex_success_bool
+    \if_meaning:w \c_true_bool \l_regex_success_bool
       \regex_extract:
       \group_insert_after:N \seq_set_eq:NN
       \group_insert_after:N #1
@@ -1359,7 +1444,7 @@
   }
 \cs_new_protected:Npn \regex_count:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -1375,9 +1460,8 @@
             \regex_count_after_group:N #3
           }
       }
-      { }
   }
-\cs_new_protected:Npn \regex_extract:nnN #1#2#3
+\cs_new_protected:Npn \regex_extract_once:nnN #1#2#3
   {
     \regex_user_aux:n
       {
@@ -1386,7 +1470,8 @@
         \regex_extract_after_group:N #3
       }
   }
-\prg_new_protected_conditional:Npnn \regex_extract:nnN #1#2#3 { T , F , TF }
+\prg_new_protected_conditional:Npnn \regex_extract_once:nnN #1#2#3
+  { T , F , TF }
   {
     \regex_user_aux:n
       {
@@ -1396,9 +1481,9 @@
         \regex_return_after_group:
       }
   }
-\cs_new_protected:Npn \regex_extract:NnN #1#2#3
+\cs_new_protected:Npn \regex_extract_once:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -1407,9 +1492,9 @@
             \regex_extract_after_group:N #3
           }
       }
-      { }
   }
-\prg_new_protected_conditional:Npnn \regex_extract:NnN #1#2#3 { T , F , TF }
+\prg_new_protected_conditional:Npnn \regex_extract_once:NnN #1#2#3
+  { T , F , TF }
   {
     \regex_check_nfa:NTF #1
       {
@@ -1423,6 +1508,48 @@
       }
       { \prg_return_false: }
   }
+\cs_new_protected:Npn \regex_extract_all:nnN #1#2#3
+  {
+    \regex_user_aux:n
+      {
+        \seq_gclear:N \g_regex_extract_all_seq
+        \tl_set:Nn \l_regex_every_match_tl { \regex_extract_all_aux: }
+        \regex_build:n {#1}
+        \regex_match:n {#2}
+        \regex_extract_all_after_group:N #3
+      }
+  }
+\cs_new_protected:Npn \regex_extract_all:NnN #1#2#3
+  {
+    \regex_check_nfa:NT #1
+      {
+        \regex_user_aux:n
+          {
+            \seq_gclear:N \g_regex_extract_all_seq
+            \tl_set:Nn \l_regex_every_match_tl { \regex_extract_all_aux: }
+            \regex_use:N #1
+            \regex_match:n {#2}
+            \regex_extract_all_after_group:N #3
+          }
+      }
+  }
+\cs_new_protected_nopar:Npn \regex_extract_all_aux:
+  {
+    \regex_extract:
+    \seq_gconcat:NNN \g_regex_extract_all_seq
+      \g_regex_extract_all_seq \g_regex_submatches_seq
+    \regex_match_once:
+  }
+\cs_new_protected_nopar:Npn \regex_extract_all_after_group:N #1
+  {
+    \seq_if_empty:NF \g_regex_extract_all_seq
+      {
+        \regex_extract:
+        \group_insert_after:N \seq_set_eq:NN
+        \group_insert_after:N #1
+        \group_insert_after:N \g_regex_extract_all_seq
+      }
+  }
 \cs_new_protected:Npn \regex_split:nnN #1#2#3
   {
     \regex_user_aux:n
@@ -1436,7 +1563,7 @@
   }
 \cs_new_protected:Npn \regex_split:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -1447,7 +1574,6 @@
             \regex_split_after_group:N #3
           }
       }
-      { }
   }
 \cs_new_protected_nopar:Npn \regex_split_aux:
   {
@@ -1459,9 +1585,8 @@
           {
             \seq_gput_left:Nx \g_regex_submatches_seq
               {
-                \str_from_to:Nnn \l_regex_query_str
-                  { \int_use:N \l_regex_start_step_int }
-                  { \l_regex_tmpa_tl }
+                \regex_query_substr:NN
+                  \l_regex_start_step_int \l_regex_tmpa_tl
               }
           }
           { \msg_error:nn { regex } { internal } }
@@ -1480,9 +1605,8 @@
       {
         \seq_gput_right:Nx \g_regex_split_seq
           {
-            \str_from_to:Nnn \l_regex_query_str
-              { \int_use:N \l_regex_start_step_int }
-              { \int_use:N \l_regex_current_step_int }
+            \regex_query_substr:NN
+              \l_regex_start_step_int \l_regex_current_step_int
           }
       }
     \group_insert_after:N \seq_set_eq:NN
@@ -1494,40 +1618,57 @@
     \str_aux_escape:NNNn
       \prg_do_nothing:
       \regex_replacement_escaped:N
-      \regex_replacement_raw:N
+      \prg_do_nothing:
       {#1}
     \tl_set_eq:NN \l_regex_replacement_tl \g_str_result_tl
     \tl_set:Nx \l_regex_replacement_tl
       { \l_regex_replacement_tl \prg_do_nothing: }
   }
-\cs_new_nopar:Npn \regex_replacement_raw:N { \exp_not:N \prg_do_nothing: }
 \cs_new_nopar:Npn \regex_replacement_escaped:N #1
   {
-    \if_num:w 9 < 1 #1 \exp_stop_f:
-      \exp_not:N \regex_replacement_escaped_ii:nN {#1}
-    \else:
-      #1
-    \fi:
+    \regex_token_if_other_digit:NTF #1
+      {
+        \exp_not:n
+          { \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } } {#1}
+      }
+      {
+        \token_if_eq_charcode:NNTF g #1
+          { \exp_not:N \regex_replacement_submatch:w }
+          { #1 }
+      }
   }
-\cs_new_nopar:Npn \regex_replacement_escaped_ii:nN #1#2
+\cs_new_nopar:Npn \regex_replacement_submatch:w #1
   {
-    \regex_token_if_other_digit:NTF #2
-      { \regex_replacement_escaped_ii:nN {#1#2} }
-      { \exp_not:N \seq_item:Nn \exp_not:N \g_regex_submatches_seq {#1} #2 }
+    \exp_after:wN \token_if_eq_meaning:NNTF \c_lbrace_str #1
+      { \regex_replacement_submatch_aux:nN { } }
+      {
+        \regex_token_if_other_digit:NTF #1
+          { \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } }
+          { \msg_expandable_error:n { \g misused~in~replacement~text. } }
+        #1
+      }
   }
-\prg_new_conditional:Npnn \regex_token_if_other_digit:N #1 { TF }
+\cs_new_nopar:Npn \regex_replacement_submatch_aux:nN #1 #2
   {
-    \if_num:w 9 < 1 \exp_not:N #1 \exp_stop_f:
-      \prg_return_true:
-    \else:
-      \prg_return_false:
-    \fi:
+    \regex_token_if_other_digit:NTF #2
+      { \regex_replacement_submatch_aux:nN {#1#2} }
+      {
+        \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } {#1}
+        \exp_after:wN \token_if_eq_meaning:NNF \c_rbrace_str #2
+          {
+            \msg_expandable_error:n { \g misused~in~replacement~text. }
+            #2
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_replace_after_group:N #1
   {
-    \group_insert_after:N \tl_set_eq:NN
+    \group_insert_after:N \tl_set:Nx
     \group_insert_after:N #1
-    \group_insert_after:N \g_regex_replaced_str
+    \group_insert_after:N {
+      \group_insert_after:N \tl_to_str:N
+      \group_insert_after:N \g_regex_replaced_str
+    \group_insert_after:N }
   }
 \cs_new_protected:Npn \regex_replace_once_aux:Nn #1#2
   {
@@ -1539,15 +1680,16 @@
       \regex_extract:
       \regex_extract_aux:nTF {0}
         {
+          \cs_set_nopar:Npn \regex_tmp:w
+            { \str_skip_do:nn { \l_regex_tmpb_tl } { } }
           \tl_gset:Nx \g_regex_replaced_str
             {
-              \str_from_to:Nnn \l_regex_query_str {0} { \l_regex_tmpa_tl }
+              \regex_query_substr:NN \c_zero \l_regex_tmpa_tl
               \l_regex_replacement_tl
-              \str_from_to:Nnn \l_regex_query_str
-                { \l_regex_tmpb_tl } { \c_max_int }
+              \exp_after:wN \regex_tmp:w \l_regex_query_other_str
             }
         }
-        { \tl_gset_eq:NN \g_regex_replaced_str \l_regex_query_str }
+        { \tl_gset_eq:NN \g_regex_replaced_str \l_regex_query_other_str }
     \group_end:
   }
 \cs_new_protected:Npn \regex_replace_once:nnN #1#2#3
@@ -1592,12 +1734,10 @@
       \tl_gclear:N \g_regex_replaced_str
       #2
       \exp_args:No \regex_match:n {#1}
+      \cs_set_nopar:Npn \regex_tmp:w
+        { \str_skip_do:nn { \l_regex_start_step_int } { } }
       \tl_gput_right:Nx \g_regex_replaced_str
-        {
-          \str_from_to:Nnn \l_regex_query_str
-            { \int_use:N \l_regex_start_step_int }
-            { \c_max_int }
-        }
+        { \exp_after:wN \regex_tmp:w \l_regex_query_other_str }
     \group_end:
   }
 \cs_new_protected_nopar:Npn \regex_replace_all_aux:
@@ -1607,9 +1747,8 @@
       {
         \tl_gput_right:Nx \g_regex_replaced_str
           {
-            \str_from_to:Nnn \l_regex_query_str
-              { \int_use:N \l_regex_start_step_int }
-              { \l_regex_tmpa_tl }
+            \regex_query_substr:NN
+              \l_regex_start_step_int \l_regex_tmpa_tl
             \l_regex_replacement_tl
           }
       }
@@ -1632,6 +1771,26 @@
         \regex_replacement:n {#2}
       }
   }
+\msg_new:nnn { regex } { -998 } { Unsupported~construct }
+\msg_new:nnn { regex } { -997 }
+  { The~regular~expression~is~too~large~(32768~states). }
+\msg_new:nnn { regex } { 1 } { \iow_char:N\\~at~end~of~pattern }
+\msg_new:nnn { regex } { 4 }
+  { Numbers~out~of~order~in~\iow_char:N\{\iow_char\}~quantifier. }
+\msg_new:nnn { regex } { 6 }
+  { Missing~terminating~\iow_char:N\]~for~character~class }
+\msg_new:nnn { regex } { 7 }
+  { Invalid~escape~sequence~in~character~class }
+\msg_new:nnn { regex } { 8 }
+  { Range~out~of~order~in~character~class }
+\msg_new:nnn { regex } { 22 } { Mismatched~parentheses }
+\msg_new:nnn { regex } { 34 }
+  { Character~value~in~\iow_char:N\\x{...}~sequence~is~too~large }
+\msg_new:nnn { regex } { not-nfa }
+  {
+    LaTeX~was~expecting~a~regular~expression~variable.\\
+    Instead,~LaTeX~found~'#1'.
+  }
 %% 
 %%
 %% End of file `l3regex-trace.sty'.
diff --git a/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex.sty b/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex.sty
index 5da00fdd3d0..c57f415bc47 100644
--- a/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex.sty
+++ b/Master/texmf-dist/tex/latex/l3experimental/l3str/l3regex.sty
@@ -46,113 +46,121 @@
 %%
 %% -----------------------------------------------------------------------
 \RequirePackage{expl3}
-\GetIdInfo$Id: l3regex.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: l3regex.dtx 2943 2011-10-30 15:59:43Z bruno $
   {L3 Experimental Regular Expressions}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
 \RequirePackage{l3str}
+\int_const:Nn \c_forty_eight  { 48 }
+\int_const:Nn \c_fifty_eight  { 58 }
+\int_const:Nn \c_sixty_five   { 65 }
+\int_const:Nn \c_ninety_one   { 91 }
+\int_const:Nn \c_ninety_seven { 97 }
+\int_const:Nn \c_one_hundred_twenty_three { 123 }
+\int_const:Nn \c_one_hundred_twenty_seven { 127 }
 \cs_new:Npn \regex_tmp:w { }
 \tl_new:N   \g_regex_tmpa_tl
 \tl_new:N   \l_regex_tmpa_tl
 \tl_new:N   \l_regex_tmpb_tl
 \int_new:N  \l_regex_tmpa_int
-\tl_new:N  \l_regex_pattern_str
+\int_new:N  \l_regex_tmpb_int
 \int_new:N  \l_regex_max_state_int
 \int_new:N  \l_regex_left_state_int
 \int_new:N  \l_regex_right_state_int
-\seq_new:N  \l_regex_left_state_seq
-\seq_new:N  \l_regex_right_state_seq
+\seq_new:N  \l_regex_group_begin_seq
+\seq_new:N  \l_regex_group_end_seq
 \int_new:N  \l_regex_capturing_group_int
 \seq_new:N  \l_regex_capturing_group_seq
 \tl_new:N   \l_regex_one_or_group_tl
-\int_new:N  \l_regex_repetition_int
-\bool_new:N \l_regex_look_behind_bool
-\tl_new:N \l_regex_look_behind_str
 \cs_new_eq:NN \regex_build_tmp_class:n \use_none:n
 \bool_new:N \l_regex_class_bool
 \tl_new:N   \l_regex_class_tl
 \tl_const:Nn \c_regex_d_tl
   {
-    \regex_item_range:nn {48} {57} % 0--9
+    \regex_item_range:nn { \c_forty_eight } { 57 } % 0--9
   }
 \tl_const:Nn \c_regex_D_tl
   {
-    \regex_item_more:n {57} % 9
-    \regex_item_range:nn {0} {47} % 0
+    \regex_item_geq:n { \c_fifty_eight } % > `9
+    \regex_item_range:nn { \c_zero } { 47 } % 0
   }
 \tl_const:Nn \c_regex_h_tl
   {
-    \regex_item_equal:n {32} % space
-    \regex_item_equal:n {9}  % tab
+    \regex_item_equal:n { \c_thirty_two } % space
+    \regex_item_equal:n { \c_nine } % tab
   }
 \tl_const:Nn \c_regex_H_tl
   {
-    \regex_item_neq:n {32} % space
-    \regex_item_neq:n {9}  % tab
-    \regex_break_true:w
+    \regex_item_geq:n { 33 } % > space
+    \regex_item_range:nn { \c_ten } { 31 } % tab < ... < space
+    \regex_item_range:nn { \c_zero } { \c_eight } % < tab
   }
 \tl_const:Nn \c_regex_s_tl
   {
-    \regex_item_equal:n  {32}     % space
-    \regex_item_neq:n    {11}     % vtab
-    \regex_item_range:nn {9} {13} % tab, lf, vtab, ff, cr
+    \regex_item_equal:n  { \c_thirty_two } % space
+    \regex_item_range:nn { \c_nine } { \c_ten } % tab, lf
+    \regex_item_range:nn { \c_twelve } { \c_thirteen } % ff, cr
   }
 \tl_const:Nn \c_regex_S_tl
   {
-    \regex_item_more:n   {32}      % > space
-    \regex_item_range:nn {14} {31} % tab < ... < space
-    \regex_item_range:nn {0}  {8}  % < tab
-    \regex_item_equal:n  {11}      % vtab
+    \regex_item_geq:n    { 33 } % > space
+    \regex_item_range:nn { \c_fourteen } { 31 } % tab < ... < space
+    \regex_item_range:nn { \c_zero } { \c_eight } % < tab
+    \regex_item_equal:n  { \c_eleven } % vtab
   }
 \tl_const:Nn \c_regex_v_tl
   {
-    \regex_item_range:nn {10} {13} % lf, vtab, ff, cr
+    \regex_item_range:nn { \c_ten } { \c_thirteen } % lf, vtab, ff, cr
   }
 \tl_const:Nn \c_regex_V_tl
   {
-    \regex_item_more:n   {13}    % cr
-    \regex_item_range:nn {0} {9} % < lf
+    \regex_item_geq:n    { \c_fourteen } % >cr
+    \regex_item_range:nn { \c_zero } { \c_nine } % < lf
   }
 \tl_const:Nn \c_regex_w_tl
   {
-    \regex_item_range:nn {97} {122} % a--z
-    \regex_item_range:nn {65}  {90} % A--Z
-    \regex_item_range:nn {48}  {57} % 0--9
-    \regex_item_equal:n  {95}       % _
+    \regex_item_range:nn { \c_ninety_seven } { 122 } % a--z
+    \regex_item_range:nn { \c_sixty_five } { 90 } % A--Z
+    \regex_item_range:nn { \c_forty_eight } { 57 } % 0--9
+    \regex_item_equal:n  { 95 } % _
   }
 \tl_const:Nn \c_regex_W_tl
   {
-    \regex_item_range:nn  {0} {47} % <`0
-    \regex_item_range:nn {58} {64} % (`9+1)--(`A-1)
-    \regex_item_range:nn {91} {94} % (`Z+1)--(`_-1)
-    \regex_item_equal:n  {96}      % `
-    \regex_item_more:n  {122}      % z
+    \regex_item_range:nn { \c_zero } { 47 } % <`0
+    \regex_item_range:nn { \c_fifty_eight } { 64 } % (`9+1)--(`A-1)
+    \regex_item_range:nn { \c_ninety_one } { 94 } % (`Z+1)--(`_-1)
+    \regex_item_equal:n  { 96 } % `
+    \regex_item_geq:n    { \c_one_hundred_twenty_three } % z
   }
 \tl_const:Nn \c_regex_N_tl
   {
-    \regex_item_neq:n {10} % lf
-    \regex_break_true:w
+    \regex_item_geq:n { \c_eleven } % > lf
+    \regex_item_range:nn { \c_zero } { \c_nine } % < lf
   }
-\tl_new:N \l_regex_query_str
-\int_new:N \l_regex_start_step_int
-\int_new:N \l_regex_current_char_int
+\tl_new:N \l_regex_query_other_str
 \int_new:N \l_regex_current_step_int
+\int_new:N \l_regex_start_step_int
+\int_new:N \l_regex_success_step_int
 \int_new:N \l_regex_unique_step_int
+\int_new:N \l_regex_current_char_int
+\int_new:N \l_regex_last_char_int
+\int_new:N \l_regex_case_changed_char_int
+\bool_new:N \l_regex_caseless_bool
 \int_new:N \l_regex_current_state_int
 \prop_new:N \l_regex_current_submatches_prop
+\prop_new:N \l_regex_success_submatches_prop
 \int_new:N \l_regex_max_index_int
 \tl_new:N \l_regex_every_match_tl
+\bool_new:N \l_regex_success_bool
 \cs_new_protected:Npn \regex_last_match_empty_no:F #1 {#1}
 \cs_new_protected:Npn \regex_last_match_empty_yes:F
   { \int_compare:nNnF \l_regex_start_step_int = \l_regex_current_step_int }
 \cs_new_eq:NN \regex_last_match_empty:F \regex_last_match_empty_no:F
-\bool_new:N \l_regex_success_bool
 \bool_new:N \l_regex_success_empty_bool
-\int_new:N  \l_regex_success_step_int
-\prop_new:N \l_regex_success_submatches_prop
 \bool_new:N \l_regex_fresh_thread_bool
 \seq_new:N  \g_regex_submatches_seq
 \int_new:N \g_regex_match_count_int
+\seq_new:N \g_regex_extract_all_seq
 \seq_new:N \g_regex_split_seq
 \tl_new:N \l_regex_replacement_tl
 \tl_new:N \g_regex_replaced_str
@@ -169,40 +177,43 @@
     \tex_toks:D #1 \exp_after:wN
       { \tex_the:D \tex_toks:D \exp_after:wN #1 \regex_tmp:w }
   }
-\cs_new_eq:NN \regex_if_tail_stop:N \quark_if_recursion_tail_stop:N
-\cs_new_protected_nopar:Npn \regex_if_tail_error:Nn #1#2
-  { \quark_if_recursion_tail_stop_do:Nn #1 { \regex_build_error:n {#2} } }
-\cs_new_protected_nopar:Npn \regex_build_error:n #1
+\cs_new_nopar:Npn \regex_query_substr:NN #1#2
   {
-    \msg_error:nnxx { regex } { build-error } {\int_eval:n{#1}}
-      {
-        \prg_case_int:nnn {#1}
-          {
-            {-999} {File~not~found}
-            {-998} {Unsupported~construct}
-            {-997} {The~regular~expression~is~too~large~(32768~states).}
-            {1}  {\iow_char:N\\~at~end~of~pattern }
-            {4}  {Numbers~out~of~order~in~\iow_char:N\{\iow_char\}~quantifier.}
-            {6}  {Missing~terminating~\iow_char:N\]~for~character~class }
-            {7}  {Invalid~escape~sequence~in~character~class}
-            {8}  {Range~out~of~order~in~character~class}
-            {22} {Mismatched~parentheses}
-            {34} {Character~value~in~\iow_char:N\\x{...}~sequence~is~too~large}
-          }
-          { Internal~bug. }
-      }
+    \exp_after:wN \regex_query_substr_aux:NN
+    \exp_after:wN #1
+    \exp_after:wN #2
+    \l_regex_query_other_str
+    \q_stop
+  }
+\cs_new:Npn \regex_query_substr_aux:NN #1#2
+  {
+    \str_skip_do:nn {#1}
+      { \str_collect_do:nn { #2 - #1 } { \use_i_delimit_by_q_stop:nw } }
+  }
+\cs_new_protected_nopar:Npn \regex_seq_pop:N #1
+  {
+    \seq_pop:NN #1 \l_regex_tmpa_tl
+    \l_regex_tmpa_tl
+  }
+\cs_new_protected_nopar:Npn \regex_seq_get:N #1
+  {
+    \seq_get:NN #1 \l_regex_tmpa_tl
+    \l_regex_tmpa_tl
   }
-\msg_new:nnn { regex } { build-error } { (error~#1): ~ #2 }
-\cs_new_nopar:Npn \regex_break_true:w #1 \regex_break_point:TF #2 #3 {#2}
-\cs_new_nopar:Npn \regex_break_false:w #1 \regex_break_point:TF #2 #3 {#3}
-\cs_new_eq:NN \regex_break_point:TF \use_ii:nn
-\cs_new_nopar:Npn \regex_item_equal:n #1
+\cs_new_protected_nopar:Npn \regex_item_dot:T
+  { \int_compare:nNnF \l_regex_current_char_int = \c_minus_one }
+\cs_new_protected_nopar:Npn \regex_break_true:w
+   #1 \regex_break_point:TF #2 #3 {#2}
+\cs_new_protected_nopar:Npn \regex_break_false:w
+   #1 \regex_break_point:TF #2 #3 {#3}
+\cs_new_protected_nopar:Npn \regex_break_point:TF #1 #2 { #2 }
+\cs_new_protected_nopar:Npn \regex_item_caseful_equal:n #1
   {
     \if_num:w #1 = \l_regex_current_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_range:nn #1 #2
+\cs_new_protected_nopar:Npn \regex_item_caseful_range:nn #1 #2
   {
     \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
       \reverse_if:N \if_num:w #2 < \l_regex_current_char_int
@@ -210,24 +221,60 @@
       \fi:
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_less:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseful_geq:n #1
   {
-    \if_num:w #1 > \l_regex_current_char_int
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_more:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseless_equal:n #1
   {
-    \if_num:w #1 < \l_regex_current_char_int
+    \if_num:w #1 = \l_regex_current_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+    \if_num:w #1 = \l_regex_case_changed_char_int
       \exp_after:wN \regex_break_true:w
     \fi:
   }
-\cs_new_nopar:Npn \regex_item_neq:n #1
+\cs_new_protected_nopar:Npn \regex_item_caseless_range:nn #1 #2
   {
-    \if_num:w #1 = \l_regex_current_char_int
-      \exp_after:wN \regex_break_false:w
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
+      \reverse_if:N \if_num:w #2 < \l_regex_current_char_int
+        \exp_after:wN \exp_after:wN \exp_after:wN \regex_break_true:w
+      \fi:
+    \fi:
+    \reverse_if:N \if_num:w #1 > \l_regex_case_changed_char_int
+      \reverse_if:N \if_num:w #2 < \l_regex_case_changed_char_int
+        \exp_after:wN \exp_after:wN \exp_after:wN \regex_break_true:w
+      \fi:
     \fi:
   }
+\cs_new_protected_nopar:Npn \regex_item_caseless_geq:n #1
+  {
+    \reverse_if:N \if_num:w #1 > \l_regex_current_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+    \reverse_if:N \if_num:w #1 > \l_regex_case_changed_char_int
+      \exp_after:wN \regex_break_true:w
+    \fi:
+  }
+\cs_new:Npn \regex_item_equal:n  { \regex_item_caseful_equal:n }
+\cs_new:Npn \regex_item_range:nn { \regex_item_caseful_range:nn }
+\cs_new:Npn \regex_item_geq:n    { \regex_item_caseful_geq:n }
+\cs_new_protected_nopar:Npn \regex_build_caseless:
+  {
+    \bool_set_true:N \l_regex_caseless_bool
+    \cs_set:Npn \regex_item_equal:n  { \regex_item_caseless_equal:n }
+    \cs_set:Npn \regex_item_range:nn { \regex_item_caseless_range:nn }
+    \cs_set:Npn \regex_item_geq:n    { \regex_item_caseless_geq:n }
+  }
+\cs_new_protected_nopar:Npn \regex_build_caseful:
+  {
+    \bool_set_false:N \l_regex_caseless_bool
+    \cs_set:Npn \regex_item_equal:n  { \regex_item_caseful_equal:n }
+    \cs_set:Npn \regex_item_range:nn { \regex_item_caseful_range:nn }
+    \cs_set:Npn \regex_item_geq:n    { \regex_item_caseful_geq:n }
+  }
 \cs_new_protected:Npn \regex_get_digits:nw #1
   {
     \tex_afterassignment:D \regex_tmp:w
@@ -235,65 +282,71 @@
       {
         \exp_not:n {#1}
         { \if_false: } } \fi:
-        \regex_get_digits_aux:N
+        \regex_get_digits_aux:NN
   }
-\cs_new_nopar:Npn \regex_get_digits_aux:N #1
+\cs_new_nopar:Npn \regex_get_digits_aux:NN #1#2
   {
-    \if_num:w 9 < 1 \exp_not:N #1 \exp_stop_f:
-    \else:
-      \if_charcode:w \c_space_token \exp_not:N #1
+    \if_meaning:w \regex_build_raw:N #1
+      \if_charcode:w \c_space_token \exp_not:N #2
       \else:
-        \regex_get_digits_end:w
+        \if_num:w 9 < 1 \exp_not:N #2 \exp_stop_f:
+          #2
+        \else:
+          \regex_get_digits_end:w #1 #2
+        \fi:
       \fi:
+    \else:
+      \regex_get_digits_end:w #1 #2
     \fi:
-    #1 \regex_get_digits_aux:N
+    \regex_get_digits_aux:NN
   }
-\cs_new_nopar:Npn \regex_get_digits_end:w
-    \fi: \fi: #1 \regex_get_digits_aux:N
+\cs_new_nopar:Npn \regex_get_digits_end:w #1 \fi: #2 \regex_get_digits_aux:NN
   {
-    \fi: \fi:
+    \fi: #2
     \if_false: { { \fi: } }
     #1
   }
+\prg_new_conditional:Npnn \regex_token_if_other_digit:N #1 { TF }
+  {
+    \if_num:w \c_nine < 1 \exp_not:N #1 \exp_stop_f:
+      \prg_return_true: \else: \prg_return_false: \fi:
+  }
 \prg_new_conditional:Npnn \regex_aux_char_if_special:N #1 { TF }
   {
-    \if_num:w `#1 < 97 \exp_stop_f:
-      \if_num:w `#1 < 58 \exp_stop_f:
-        \if_num:w \int_eval:w (`#1 - \c_eight)/\c_sixteen = \c_two
-          \prg_return_true:
-        \else:
-          \prg_return_false:
-        \fi:
+    \if_num:w `#1 < \c_ninety_one
+      \if_num:w `#1 < \c_fifty_eight
+        \if_num:w `#1 < \c_forty_eight
+          \if_num:w `#1 < \c_thirty_two
+            \prg_return_false: \else: \prg_return_true: \fi:
+        \else: \prg_return_false: \fi:
       \else:
-        \if_num:w \int_eval:w `#1 / 26 = \c_three
-          \prg_return_false:
-        \else:
-          \prg_return_true:
-        \fi:
+        \if_num:w `#1 < \c_sixty_five
+          \prg_return_true: \else: \prg_return_false: \fi:
       \fi:
     \else:
-      \if_num:w \int_eval:w `#1 / \c_five = 25 \exp_stop_f:
-        \prg_return_true:
+      \if_num:w `#1 < \c_one_hundred_twenty_three
+        \if_num:w `#1 < \c_ninety_seven
+          \prg_return_true: \else: \prg_return_false: \fi:
       \else:
-        \prg_return_false:
+        \if_num:w `#1 < \c_one_hundred_twenty_seven
+          \prg_return_true: \else: \prg_return_false: \fi:
       \fi:
     \fi:
   }
 \prg_new_conditional:Npnn \regex_aux_char_if_alphanumeric:N #1 { TF }
   {
-    \if_num:w `#1 < 91 \exp_stop_f:
-      \if_num:w `#1 < 65 \exp_stop_f:
-        \if_num:w \c_nine < 1 #1 \exp_stop_f:
-          \prg_return_true:
-        \else:
-          \prg_return_false:
-        \fi:
+    \if_num:w `#1 < \c_ninety_one
+      \if_num:w `#1 < \c_fifty_eight
+        \if_num:w `#1 < \c_forty_eight
+          \prg_return_false: \else: \prg_return_true: \fi:
       \else:
-        \prg_return_true:
+        \if_num:w `#1 < \c_sixty_five
+          \prg_return_false: \else: \prg_return_true: \fi:
       \fi:
     \else:
-      \if_num:w \int_eval:w (`#1-\c_six)/26 = \c_four
-        \prg_return_true:
+      \if_num:w `#1 < \c_one_hundred_twenty_three
+        \if_num:w `#1 < \c_ninety_seven
+          \prg_return_false: \else: \prg_return_true: \fi:
       \else:
         \prg_return_false:
       \fi:
@@ -301,8 +354,8 @@
   }
 \cs_new_protected_nopar:Npn \regex_build_new_state:
   {
-    \int_compare:nNnTF \l_regex_max_state_int > {32766}
-      { \regex_build_error:n {-997} }
+    \int_compare:nNnTF \l_regex_max_state_int > { 32766 }
+      { \msg_error:nn { regex } { -997 } }
       {
         \int_incr:N \l_regex_max_state_int
         \tex_toks:D \l_regex_max_state_int { \s_regex_toks }
@@ -314,15 +367,15 @@
   {
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      { #1 { \int_use:N #2 } }
+      { #1 { \int_eval:n { #2 - \l_regex_left_state_int } } }
   }
 \cs_new_protected_nopar:Npn \regex_build_transitions_aux:NNNN #1#2#3#4
   {
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
-        #1 { \int_use:N #2 }
-        #3 { \int_use:N #4 }
+        #1 { \int_eval:n { #2 - \l_regex_left_state_int } }
+        #3 { \int_eval:n { #4 - \l_regex_left_state_int } }
       }
   }
 \cs_new_protected:Npn \regex_build:n #1
@@ -363,25 +416,19 @@
     \cs_set_eq:NN \regex_build_control:N \regex_build_default_control:N
     \cs_set_eq:NN \regex_build_raw:N \regex_build_default_raw:N
     \int_set_eq:NN \l_regex_capturing_group_int \c_zero
-    \int_zero:N \l_regex_left_state_int
-    \int_zero:N \l_regex_right_state_int
     \int_zero:N \l_regex_max_state_int
     \regex_build_new_state:
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_action_start_wildcard:nn
-          { \int_use:N \l_regex_left_state_int }
-          { \int_use:N \l_regex_right_state_int }
-      }
+      { \regex_action_start_wildcard:nn {0} {1} }
   }
 \cs_new_protected_nopar:Npn \regex_build_end:
   {
     \seq_if_empty:NF \l_regex_capturing_group_seq
       {
-        \regex_build_error:n {22}
+        \msg_error:nn { regex } {22}
         \prg_replicate:nn
-          { \seq_length:N \l_regex_capturing_group_seq } % (
+          { \seq_length:N \l_regex_capturing_group_seq }
           { \regex_build_close_aux: \regex_build_group_: }
       }
     \regex_toks_put_right:Nx \l_regex_right_state_int
@@ -399,7 +446,13 @@
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \int_compare:nNnT {#1} = \l_regex_current_step_int
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_protected_nopar:cpn { regex_build_$: } % $
@@ -409,71 +462,72 @@
       {
         \exp_not:N \int_compare:nNnT
           \c_minus_one = \l_regex_current_char_int
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_eq:Nc \regex_build_Z: { regex_build_$: } %$
 \cs_new_eq:Nc \regex_build_z: { regex_build_$: } %$
 \cs_new_protected_nopar:Npn \regex_build_b:
   {
-    \bool_set_true:N \l_regex_look_behind_bool
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \regex_if_word_boundary:TF
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
           { }
       }
   }
 \cs_new_protected_nopar:Npn \regex_build_B:
   {
-    \bool_set_true:N \l_regex_look_behind_bool
     \regex_build_new_state:
     \regex_toks_put_right:Nx \l_regex_left_state_int
       {
         \exp_not:N \regex_if_word_boundary:TF
           { }
-          { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+          {
+            \regex_action_free:n
+              {
+                \int_eval:n
+                  { \l_regex_right_state_int - \l_regex_left_state_int }
+              }
+          }
       }
   }
 \cs_new_protected_nopar:Npn \regex_if_word_boundary:TF
   {
-    \tl_if_empty:NTF \l_regex_look_behind_str
-      { \c_regex_w_tl }
-      {
-        \group_begin:
-          \cs_set_nopar:Npx \regex_tmp:w
-            {
-              \int_set:Nn \l_regex_current_char_int
-                { ` \str_head:N \l_regex_look_behind_str }
-            }
-          \regex_tmp:w
-          \c_regex_w_tl
-          \regex_break_point:TF
-            { \group_end: \c_regex_W_tl }
-            { \group_end: \c_regex_w_tl }
-      }
+    \group_begin:
+      \int_set_eq:NN \l_regex_current_char_int \l_regex_last_char_int
+      \c_regex_w_tl
+      \regex_break_point:TF
+        { \group_end: \c_regex_W_tl \regex_item_equal:n { -1 } }
+        { \group_end: \c_regex_w_tl }
     \regex_break_point:TF
   }
 \cs_new_protected_nopar:Npn \regex_build_default_raw:N #1
   {
     \cs_set:Npx \regex_build_tmp_class:n ##1
       {
-        \exp_not:n { \exp_not:N \if_num:w }
-            \int_value:w `#1 = \l_regex_current_char_int
-          \regex_action_cost:n { ##1 }
-        \exp_not:n { \exp_not:N \fi: }
+        \regex_item_equal:n { \int_value:w `#1 }
+        \regex_break_point:TF { \regex_action_cost:n { ##1 } } { }
       }
     \regex_build_one_quantifier:
   }
 \cs_new_protected_nopar:cpn { regex_build_.: }
   {
     \cs_set:Npn \regex_build_tmp_class:n ##1
-      {
-        \exp_not:N \if_num:w \c_minus_one < \l_regex_current_char_int
-          \regex_action_cost:n {##1}
-        \exp_not:N \fi:
-      }
+      { \regex_item_dot:T { \regex_action_cost:n {##1} } }
     \regex_build_one_quantifier:
   }
 \cs_new_protected_nopar:Npn \regex_build_char_type:N #1
@@ -481,9 +535,7 @@
     \cs_set:Npn \regex_build_tmp_class:n ##1
       {
         \exp_not:N #1
-        \exp_not:N \regex_break_point:TF
-          { \regex_action_cost:n {##1} }
-          { }
+        \regex_break_point:TF { \regex_action_cost:n {##1} } { }
       }
     \regex_build_one_quantifier:
   }
@@ -518,16 +570,8 @@
           {
             \exp_not:o \l_regex_class_tl
             \bool_if:NTF \l_regex_class_bool
-              {
-                \exp_not:N \regex_break_point:TF
-                  { \regex_action_cost:n {##1} }
-                  { }
-              }
-              {
-                \exp_not:N \regex_break_point:TF
-                  { }
-                  { \regex_action_cost:n {##1} }
-              }
+              { \regex_break_point:TF { \regex_action_cost:n {##1} } { } }
+              { \regex_break_point:TF { } { \regex_action_cost:n {##1} } }
           }
         \regex_build_one_quantifier:
       }
@@ -553,7 +597,7 @@
 \cs_new_protected_nopar:Npn \regex_class_single:N #1
   {
     \tl_put_right:Nx \l_regex_class_tl
-      { \exp_not:N \regex_item_equal:n { \int_value:w `#1 } }
+      { \regex_item_equal:n { \int_value:w `#1 } }
   }
 \cs_new_protected_nopar:Npn \regex_class_range:Nw #1#2#3
   {
@@ -572,14 +616,14 @@
 \cs_new_protected_nopar:Npn \regex_class_range_put:NN #1#2
   {
     \if_num:w `#1 > `#2 \exp_stop_f:
-      \regex_build_error:n {8}
+      \msg_error:nn { regex } {8}
     \else:
       \tl_put_right:Nx \l_regex_class_tl
         {
           \if_num:w `#1 = `#2 \exp_stop_f:
-            \exp_not:N \regex_item_equal:n
+            \regex_item_equal:n
           \else:
-            \exp_not:N \regex_item_range:nn { \int_value:w `#1 }
+            \regex_item_range:nn { \int_value:w `#1 }
           \fi:
           { \int_value:w `#2 }
         }
@@ -651,26 +695,29 @@
         \exp_not:N \regex_build_raw:N \c_lbrace_str #1#2
       }
   }
-\cs_new_protected_nopar:Npn \regex_build_quantifier_lbrace:nnw #1#2#3
+\cs_new_protected_nopar:Npn \regex_build_quantifier_lbrace:nnw #1#2#3#4
   {
-    \str_if_eq:xxTF { \exp_not:N #3 } { \c_rbrace_str }
+    \str_if_eq:xxTF
+      { \exp_not:n {#3#4} }
+      { \exp_not:N \regex_build_control:N \c_rbrace_str }
       {
         \tl_if_empty:nTF {#2}
-          { \regex_build_quantifier_aux:nnN { {#1} {\c_max_int} } {nn} }
+          { \regex_build_quantifier_aux:nnNN { {#1} } { n* } }
           {
             \int_compare:nNnT {#1} > {#2}
-              { \regex_build_error:n {4} }
-            \regex_build_quantifier_aux:nnN { {#1} {#2} } {nn}
+              { \msg_error:nn { regex } {4} }
+            \regex_build_quantifier_aux:nnNN { {#1} {#2} } { nn }
           }
       }
       {
         \regex_build_quantifier_end:n { }
         \use:x
           {
-            \exp_not:n { \exp_args:No \tl_map_function:nN }
-              { \c_lbrace_str #1 #2 , }
-            \regex_build_raw:N
+            \exp_args:No \tl_map_function:nN
+              { \c_lbrace_str #1 , #2 }
+              \regex_build_raw:N
           }
+        #3 #4
       }
   }
 \cs_new_protected_nopar:Npn \regex_build_quantifier_end:n #1
@@ -726,71 +773,27 @@
       \regex_action_free:n \l_regex_tmpa_int
   }
 \cs_new_protected_nopar:Npn \regex_build_one_n: #1
-  {
-    \int_set_eq:NN \l_regex_tmpa_int \l_regex_right_state_int
-    \regex_build_new_state:
-    \regex_build_new_state:
-    \regex_toks_put_right:Nx \l_regex_tmpa_int
-      { %^^A safe \if nesting?
-        \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \else:
-          \regex_action_no_repeat_move:n
-            { \int_use:N \l_regex_right_state_int }
-        \exp_not:N \fi:
-      }
-    \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_build_tmp_class:n
-          { \int_use:N \l_regex_tmpa_int }
-      }
-  }
+  { \prg_replicate:nn {#1} { \regex_build_one_: } }
 \cs_new_eq:cN { regex_build_one_n?: } \regex_build_one_n:
-\cs_new_protected_nopar:Npn \regex_build_one_nn: #1#2
+\cs_new_protected_nopar:cpx { regex_build_one_n*: } #1
   {
-    \regex_build_one_nn_aux:nn {#1}
-      {
-        \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-          \regex_action_repeat_copy:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \fi:
-        \regex_action_no_repeat_move:n
-          { \int_use:N \l_regex_right_state_int }
-      }
+    \exp_not:N \prg_replicate:nn {#1} { \exp_not:N \regex_build_one_: }
+    \exp_not:c { regex_build_one_*: }
   }
-\cs_new_protected_nopar:cpn { regex_build_one_nn?: } #1#2
+\cs_new_protected_nopar:cpx { regex_build_one_n*?: } #1
   {
-    \regex_build_one_nn_aux:nn {#1}
-      {
-        \regex_action_no_repeat_copy:n
-          { \int_use:N \l_regex_right_state_int }
-        \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \fi:
-      }
+    \exp_not:N \prg_replicate:nn {#1} { \exp_not:N \regex_build_one_: }
+    \exp_not:c { regex_build_one_*?: }
   }
-\cs_new_protected_nopar:Npn \regex_build_one_nn_aux:nn #1#2
+\cs_new_protected_nopar:Npn \regex_build_one_nn_aux:Nnn #1#2#3
   {
-    \int_set_eq:NN \l_regex_tmpa_int \l_regex_right_state_int
-    \regex_build_new_state:
-    \regex_build_new_state:
-    \regex_toks_put_right:Nx \l_regex_tmpa_int
-      {
-        \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-          \regex_action_repeat_move:n
-            { \int_use:N \l_regex_left_state_int }
-        \exp_not:N \else:
-          #2
-        \exp_not:N \fi:
-      }
-    \regex_toks_put_right:Nx \l_regex_left_state_int
-      {
-        \regex_build_tmp_class:n
-          { \int_use:N \l_regex_tmpa_int }
-      }
+    \prg_replicate:nn {#2} { \regex_build_one_: }
+    \prg_replicate:nn {#3-#2} {#1}
   }
+\cs_new_protected_nopar:Npx \regex_build_one_nn:
+  { \regex_build_one_nn_aux:Nnn \exp_not:c { regex_build_one_?: } }
+\cs_new_protected_nopar:cpx { regex_build_one_nn?: }
+  { \regex_build_one_nn_aux:Nnn \exp_not:c { regex_build_one_??: } }
 \cs_new_protected_nopar:cpn { regex_build_(: } #1#2
   {
     \str_if_eq:nnTF { #1 #2 } { \regex_build_control:N ? }
@@ -806,10 +809,19 @@
 \cs_new_protected_nopar:Npn \regex_build_open_aux:
   {
     \regex_build_new_state:
-    \seq_push:Nx \l_regex_left_state_seq
-      { \int_use:N \l_regex_left_state_int }
-    \seq_push:Nx \l_regex_right_state_seq
-      { \int_use:N \l_regex_right_state_int }
+    \seq_push:Nx \l_regex_group_begin_seq
+      {
+        \int_set:Nn \l_regex_left_state_int
+          { \int_use:N \l_regex_left_state_int }
+      }
+    \bool_if:NTF \l_regex_caseless_bool
+      { \seq_push:Nn \l_regex_group_end_seq { \regex_build_caseless: } }
+      { \seq_push:Nn \l_regex_group_end_seq { \regex_build_caseful: } }
+    \seq_push:Nx \l_regex_group_end_seq
+      {
+        \int_set:Nn \l_regex_right_state_int
+          { \int_use:N \l_regex_right_state_int }
+      }
     \regex_build_begin_alternation:
   }
 \cs_new_protected_nopar:cpn { regex_build_|: }
@@ -820,7 +832,7 @@
 \cs_new_protected_nopar:cpn { regex_build_): }
   {
     \seq_if_empty:NTF \l_regex_capturing_group_seq
-      { \regex_build_error:n {22} }
+      { \msg_error:nn { regex } { 22 } }
       {
         \regex_build_close_aux:
         \regex_build_group_quantifier:
@@ -829,30 +841,41 @@
 \cs_new_protected_nopar:Npn \regex_build_close_aux:
   {
     \regex_build_end_alternation:
-    \seq_pop:NN \l_regex_left_state_seq  \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_left_state_int  \l_regex_tmpa_tl
-    \seq_pop:NN \l_regex_right_state_seq \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_right_state_int \l_regex_tmpa_tl
+    \regex_seq_pop:N \l_regex_group_begin_seq
+    \regex_seq_pop:N \l_regex_group_end_seq
+    \regex_seq_pop:N \l_regex_group_end_seq
   }
 \cs_new_protected_nopar:Npn \regex_build_begin_alternation:
   {
     \regex_build_new_state:
-    \seq_get:NN \l_regex_left_state_seq \l_regex_tmpa_tl
-    \int_set:Nn \l_regex_left_state_int \l_regex_tmpa_tl
+    \regex_seq_get:N \l_regex_group_begin_seq
     \regex_toks_put_right:Nx \l_regex_left_state_int
-      { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+      {
+        \regex_action_free:n
+          {
+            \int_eval:n
+              { \l_regex_right_state_int - \l_regex_left_state_int }
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_build_end_alternation:
   {
-    \seq_get:NN \l_regex_right_state_seq \l_regex_tmpa_tl
-    \regex_toks_put_right:Nx \l_regex_right_state_int
-      { \regex_action_free:n { \l_regex_tmpa_tl } }
+    \int_set_eq:NN \l_regex_left_state_int \l_regex_right_state_int
+    \regex_seq_get:N \l_regex_group_end_seq
+    \regex_toks_put_right:Nx \l_regex_left_state_int
+      {
+        \regex_action_free:n
+          {
+            \int_eval:n
+              { \l_regex_right_state_int - \l_regex_left_state_int }
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_build_special_group:NN #1#2
   {
     \cs_if_exist_use:cF { regex_build_special_group_\token_to_str:N #2 : }
       {
-        \regex_build_error:n { -998 }
+        \msg_error:nn { regex } { -998 }
         \regex_build_control:N ( % )
         \regex_build_raw:N ?
         #1 #2
@@ -863,6 +886,40 @@
     \seq_push:Nx \l_regex_capturing_group_seq { * }
     \regex_build_open_aux:
   }
+\cs_new_protected_nopar:Npn \regex_build_special_group_i:
+  {
+    \regex_build_options:NNN +
+    \regex_build_raw:N i
+  }
+\cs_new_protected_nopar:cpn { regex_build_special_group_-: }
+  {
+    \regex_build_options:NNN -
+  }
+\cs_new_protected_nopar:Npn \regex_build_options:NNN #1#2#3
+  {
+    \token_if_eq_meaning:NNTF \regex_build_raw:N #2
+      {
+        \cs_if_exist_use:cF { regex_build_option_#1#3: }
+          { \msg_error:nnx { regex } { unknown-option } { #3 } }
+        \regex_build_options:NNN #1
+      }
+      {
+        \prg_case_str:nnn { #3 }
+          { % (
+            { ) } { }
+            { - } { \regex_build_options:NNN - }
+          }
+          { \msg_error:nnx { regex } { invalid-in-option } { #3 } }
+      }
+  }
+\cs_new_protected_nopar:cpn { regex_build_option_+i: }
+  {
+    \regex_build_caseless:
+    \cs_set_eq:NN \regex_match_loop_case_hook:
+      \regex_match_loop_caseless_hook:
+  }
+\cs_new_protected_nopar:cpn { regex_build_option_-i: }
+  { \regex_build_caseful: }
 \cs_new_protected_nopar:Npn \regex_build_group_quantifier:
   {
     \tl_set:Nn \l_regex_one_or_group_tl { group }
@@ -891,21 +948,33 @@
     \int_set_eq:NN \l_regex_tmpa_int \l_regex_left_state_int
     \regex_build_new_state:
     \tex_toks:D \l_regex_right_state_int = \tex_toks:D \l_regex_tmpa_int
-    \use:x
+    \regex_toks_put_left:Nx \l_regex_right_state_int
+      {
+        \int_set:Nn \l_regex_current_state_int
+          { \int_use:N \l_regex_tmpa_int } % ^^A here we lie!
+      }
+    \cs_set:Npx \regex_tmp:w
       {
         \tex_toks:D \l_regex_tmpa_int
-          { \s_regex_toks #1 { \int_use:N \l_regex_right_state_int } }
+          {
+            \s_regex_toks
+            #1 { \int_eval:n { \l_regex_right_state_int - \l_regex_tmpa_int } }
+          }
       }
+    \regex_tmp:w
     \regex_build_group_submatches:NN
       \l_regex_right_state_int \l_regex_left_state_int
-    \int_set_eq:NN \l_regex_right_state_int \l_regex_left_state_int
   }
 \cs_new_protected_nopar:Npn \regex_build_group_qs_aux:NN #1#2
   {
     \regex_build_group_shift:N \regex_action_free:n
+    \int_set_eq:NN \l_regex_right_state_int \l_regex_left_state_int
     \regex_build_transition_aux:NN \regex_action_free:n #1
     #2 \l_regex_tmpa_int
-      { \regex_action_free:n { \int_use:N \l_regex_right_state_int } }
+      {
+        \regex_action_free:n
+          { \int_eval:n { \l_regex_right_state_int - \l_regex_tmpa_int } }
+      }
   }
 \cs_new_protected_nopar:cpn { regex_build_group_?: }
   {
@@ -945,77 +1014,63 @@
       \regex_action_free:n \l_regex_right_state_int
       \regex_action_free:n \l_regex_tmpa_int
   }
-\cs_new_protected_nopar:Npn \regex_build_group_n: #1
+\cs_new_protected_nopar:Npn \regex_build_group_n_aux:n #1
   {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
-    \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
+    \regex_toks_put_right:Nx \l_regex_right_state_int
       {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \regex_action_no_repeat_move:n
-                { \int_use:N \l_regex_right_state_int }
-            \exp_not:N \fi:
-          }
+        \regex_action_free:n
+          { \int_eval:n { \l_regex_max_state_int - \l_regex_left_state_int } }
       }
-  }
-\cs_new_eq:cN { regex_build_group_n?: } \regex_build_group_n:
-\cs_new_protected_nopar:Npn \regex_build_group_nn: #1#2
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
-    \regex_build_transition_aux:NN
-      \regex_action_free:n \l_regex_tmpa_int
-    \use:x
+    \int_set_eq:NN \l_regex_tmpa_int \l_regex_left_state_int
+    \int_set:Nn \l_regex_tmpb_int { \l_regex_max_state_int + \c_one }
+    \int_set:Nn \l_regex_max_state_int
       {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-                \tex_the:D \tex_toks:D \l_regex_tmpa_int
-              \exp_not:N \fi:
-              \regex_action_no_repeat_copy:n
-                { \int_use:N \l_regex_right_state_int }
-            \exp_not:N \fi:
-          }
+        \l_regex_left_state_int - \c_one
+        + #1 * ( \l_regex_max_state_int - \l_regex_left_state_int + \c_one )
+      }
+    \int_until_do:nNnn \l_regex_tmpb_int > \l_regex_max_state_int
+      {
+        \tex_toks:D \l_regex_tmpb_int = \tex_toks:D \l_regex_tmpa_int
+        \int_incr:N \l_regex_tmpa_int
+        \int_incr:N \l_regex_tmpb_int
       }
   }
-\cs_new_protected_nopar:cpn { regex_build_group_nn?: } #1#2
-  {
-    \regex_build_group_shift:N \regex_action_repeat_move:n
+\cs_new_protected_nopar:Npn \regex_build_group_n: #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
     \regex_build_transition_aux:NN
+      \regex_action_free:n \l_regex_right_state_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
+  }
+\cs_new_eq:cN { regex_build_group_n?: } \regex_build_group_n:
+\cs_new_protected_nopar:cpn { regex_build_group_n*: } #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
+    \regex_build_transitions_aux:NNNN
       \regex_action_free:n \l_regex_tmpa_int
-    \use:x
-      {
-        \tex_toks:D \l_regex_tmpa_int
-          {
-            \s_regex_toks
-            \exp_not:N \if_num:w #1 > \l_regex_repetition_int
-              \tex_the:D \tex_toks:D \l_regex_tmpa_int
-            \exp_not:N \else:
-              \regex_action_no_repeat_copy:n
-                { \int_use:N \l_regex_right_state_int }
-              \exp_not:N \if_num:w #2 > \l_regex_repetition_int
-                \tex_the:D \tex_toks:D \l_regex_tmpa_int
-              \exp_not:N \fi:
-            \exp_not:N \fi:
-          }
-      }
+      \regex_action_free:n \l_regex_right_state_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
   }
-\cs_new_protected:Npn \regex_if_state_free:nT #1
-  {
-    \if_num:w \tex_dimen:D #1 = \l_regex_unique_step_int
-      \exp_after:wN \use_none:n
-    \else:
-      \exp_after:wN \use:n
-    \fi:
+\cs_new_protected_nopar:cpn { regex_build_group_n*?: } #1
+  { % ^^A todo: catch case #1 <= 0.
+    \regex_build_group_n_aux:n {#1}
+    \regex_build_transitions_aux:NNNN
+      \regex_action_free:n \l_regex_right_state_int
+      \regex_action_free:n \l_regex_tmpa_int
+    \regex_build_group_submatches:NN
+      \l_regex_tmpa_int \l_regex_left_state_int
+  }
+\cs_new_protected_nopar:Npn \regex_build_group_nn: #1#2
+  { % ^^A Not Implemented Yet!
+    \msg_expandable_error:n { Quantifier~{m,n}~not~implemented~yet }
+    \use:c { regex_build_group_n*: } {#1}
+  }
+\cs_new_protected_nopar:cpn { regex_build_group_nn?: } #1#2
+  { % ^^A Not Implemented Yet!
+    \msg_expandable_error:n { Quantifier~{m,n}~not~implemented~yet }
+    \use:c { regex_build_group_n*?: } {#1}
   }
 \cs_new_protected:Npn \regex_store_state:n #1
   {
@@ -1023,23 +1078,24 @@
     \tex_skip:D \l_regex_max_index_int #1 sp \scan_stop:
     \regex_store_submatches:n {#1}
   }
-\cs_new_protected_nopar:Npn \regex_state_use_submatches:
+\cs_new_protected_nopar:Npn \regex_state_use_with_submatches:
   { \regex_state_use_aux:n { } }
 \cs_new_protected_nopar:Npn \regex_state_use:
   { \regex_state_use_aux:n { \exp_after:wN \regex_state_use_aux_ii:w } }
-\cs_new:Npn \regex_state_use_aux_ii:w #1 \s_regex_toks { }
-\cs_new_protected:Npn \regex_state_use_aux:n #1
-  {
-    \regex_if_state_free:nT {  \l_regex_current_state_int }
-      {
-        \tex_dimen:D \l_regex_current_state_int
-          = \l_regex_unique_step_int sp \scan_stop:
-        #1 \tex_the:D \tex_toks:D \l_regex_current_state_int \scan_stop:
-      }
+\cs_new_nopar:Npn \regex_state_use_aux_ii:w #1 \s_regex_toks { }
+\cs_new_protected_nopar:Npn \regex_state_use_aux:n #1
+  {
+    \if_num:w \tex_dimen:D \l_regex_current_state_int
+        < \l_regex_unique_step_int
+      \tex_dimen:D \l_regex_current_state_int
+        = \l_regex_unique_step_int sp \scan_stop:
+      #1 \tex_the:D \tex_toks:D \exp_after:wN \l_regex_current_state_int
+    \fi:
+    \scan_stop:
   }
 \cs_new_protected_nopar:Npn \regex_disable_submatches:
   {
-    \cs_set_eq:NN \regex_state_use_submatches: \regex_state_use:
+    \cs_set_eq:NN \regex_state_use_with_submatches: \regex_state_use:
     \cs_set_eq:NN \regex_store_submatches:n
       \regex_protected_use_none:n
     \cs_set_eq:NN \regex_action_submatches:n
@@ -1048,55 +1104,73 @@
 \cs_new_protected:Npn \regex_protected_use_none:n #1 { }
 \cs_new_protected:Npn \regex_store_submatches:n #1
   {
-    \exp_after:wN \regex_store_submatches_aux:Nw
-    \exp_after:wN \l_regex_current_submatches_prop
-    \tex_the:D \tex_toks:D #1 \scan_stop: \q_stop
-    { #1 }
+    \tex_toks:D #1 \exp_after:wN
+      {
+        \tex_romannumeral:D
+        \exp_after:wN \regex_store_submatches_aux:w
+        \tex_the:D \tex_toks:D #1
+      }
   }
-\cs_new_protected:Npn \regex_store_submatches_aux:Nw #1 #2 \s_regex_toks
+\cs_new_protected:Npn \regex_store_submatches_aux:w #1 \s_regex_toks
   {
-    \exp_args:No \regex_store_submatches_aux_ii:wnnwwn { #1 }
-      #2
-      \regex_state_submatches:nn { \c_minus_one } { \q_prop }
+    \regex_store_submatches_aux_ii:Nnnw
+      #1
+      \regex_state_submatches:nn \c_minus_one \q_prop
     \s_regex_toks
   }
-\cs_new_protected:Npn \regex_store_submatches_aux_ii:wnnwwn
-    #1 \regex_state_submatches:nn #2#3 #4 \s_regex_toks #5 \q_stop #6
+\cs_new_protected:Npn \regex_store_submatches_aux_ii:Nnnw
+    \regex_state_submatches:nn #1 #2 #3 \s_regex_toks
   {
-    \tex_toks:D #6 \exp_after:wN
+    \exp_after:wN \c_zero
+    \exp_after:wN \regex_state_submatches:nn \exp_after:wN
       {
-        \exp_after:wN \regex_state_submatches:nn \exp_after:wN
-          { \int_value:w \int_eval:w \l_regex_unique_step_int + \c_one }
-          { #1 }
-        \regex_state_submatches:nn {#2} {#3}
-        \s_regex_toks
-        #5
+        \int_value:w \int_eval:w
+          \l_regex_unique_step_int + \c_one
+        \exp_after:wN
       }
+      \exp_after:wN { \l_regex_current_submatches_prop }
+    \regex_state_submatches:nn {#1} {#2}
+    \s_regex_toks
   }
 \cs_new_protected:Npn \regex_state_submatches:nn #1#2
   {
     \if_num:w #1 = \l_regex_unique_step_int
-      \tl_set:Nn \l_regex_current_submatches_prop {#2}
+      \tl_set:Nn \l_regex_current_submatches_prop { #2 }
     \fi:
   }
 \cs_new_protected:Npn \regex_match:n #1
   {
-    \tl_set:Nx \l_regex_query_str { \tl_to_other_str:n {#1} }
+    \tl_set:Nx \l_regex_query_other_str { \tl_to_other_str:n {#1} }
     \regex_match_initial_setup:
     \regex_match_once:
   }
 \cs_new_protected_nopar:Npn \regex_match_once:
   {
     \regex_match_setup:
-    \exp_after:wN \regex_match_once_aux: \l_regex_query_str
+    \exp_after:wN \regex_match_once_aux: \l_regex_query_other_str
       \q_recursion_tail \q_recursion_stop
     \bool_if:NT \l_regex_success_bool { \l_regex_every_match_tl }
   }
 \cs_new_protected_nopar:Npn \regex_match_once_aux:
-  { \str_skip_do:nn { \l_regex_start_step_int } { \regex_match_loop:N } }
+  {
+    \int_compare:nNnTF \l_regex_start_step_int = \c_zero
+      {
+        \int_set_eq:NN \l_regex_current_char_int \c_minus_one
+        \regex_match_loop:N
+      }
+      {
+        \str_skip_do:nn
+          { \l_regex_start_step_int - \c_one }
+          { \regex_match_once_aux_ii:N }
+      }
+  }
+\cs_new_protected_nopar:Npn \regex_match_once_aux_ii:N #1
+  {
+    \int_set:Nn \l_regex_current_char_int { `#1 }
+    \regex_match_loop:N
+  }
 \cs_new_protected_nopar:Npn \regex_match_initial_setup:
   {
-    \tl_clear:N \l_regex_look_behind_str
     \prg_stepwise_inline:nnnn {1} {1} { \l_regex_max_state_int }
       { \tex_dimen:D ##1 \c_minus_one sp \scan_stop: }
     \int_set_eq:NN \l_regex_unique_step_int  \c_minus_one
@@ -1118,20 +1192,11 @@
     \int_zero:N \l_regex_max_index_int
     \regex_store_state:n {1}
   }
-\cs_new_protected_nopar:Npn \regex_match_loop_setup:
-  {
-    \int_incr:N \l_regex_current_step_int
-    \int_incr:N \l_regex_unique_step_int
-    \bool_set_false:N \l_regex_fresh_thread_bool
-  }
 \cs_new_eq:NN \s_regex_step \scan_stop:
 \cs_new:Npn \regex_break_step:w #1 \s_regex_step { }
 \cs_new_protected_nopar:Npn \regex_match_loop:N #1
   {
-    \regex_match_loop_setup:
-    \token_if_eq_meaning:NNTF #1 \q_recursion_tail
-      { \int_set_eq:NN \l_regex_current_char_int \c_minus_one }
-      { \int_set:Nn \l_regex_current_char_int {`#1} }
+    \regex_match_loop_setup:N #1
     \cs_set_nopar:Npx \regex_tmp:w
       {
         \int_zero:N \l_regex_max_index_int
@@ -1145,19 +1210,49 @@
       \exp_after:wN \use_none_delimit_by_q_recursion_stop:w
     \fi:
     \quark_if_recursion_tail_stop:N #1
-    \bool_if:NT \l_regex_look_behind_bool
-      { \tl_put_left:Nx \l_regex_look_behind_str {#1} }
     \regex_match_loop:N
   }
 \cs_new_nopar:Npn \regex_match_one_index:n #1
   {
-    \regex_match_one_index_aux:n { \int_value:w \tex_skip:D #1 }
+    \regex_match_one_index_aux:n
+      { \int_value:w \tex_skip:D #1 }
   }
 \cs_new_protected_nopar:Npn \regex_match_one_index_aux:n #1
   {
     \int_set:Nn \l_regex_current_state_int {#1}
     \prop_clear:N \l_regex_current_submatches_prop
-    \regex_state_use_submatches:
+    \regex_state_use_with_submatches:
+  }
+\cs_new_protected_nopar:Npn \regex_match_loop_setup:N #1
+  {
+    \int_incr:N \l_regex_current_step_int
+    \int_incr:N \l_regex_unique_step_int
+    \bool_set_false:N \l_regex_fresh_thread_bool
+    \int_set_eq:NN \l_regex_last_char_int \l_regex_current_char_int
+    \if_meaning:w #1 \q_recursion_tail
+      \int_set_eq:NN \l_regex_current_char_int \c_minus_one
+    \else:
+      \int_set:Nn \l_regex_current_char_int {`#1}
+    \fi:
+    \regex_match_loop_case_hook:
+  }
+\cs_new_protected_nopar:Npn \regex_match_loop_case_hook: { }
+\cs_new_protected_nopar:Npn \regex_match_loop_caseless_hook:
+  {
+    \int_set_eq:NN \l_regex_case_changed_char_int \l_regex_current_char_int
+    \if_num:w \l_regex_current_char_int < \c_ninety_one
+      \if_num:w \l_regex_current_char_int < \c_sixty_five
+      \else:
+        \int_add:Nn \l_regex_case_changed_char_int { \c_thirty_two }
+      \fi:
+    \else:
+      \if_num:w \l_regex_current_char_int < \c_one_hundred_twenty_three
+        \if_num:w \l_regex_current_char_int < \c_ninety_seven
+        \else:
+          \int_sub:Nn \l_regex_case_changed_char_int { \c_thirty_two }
+        \fi:
+      \fi:
+    \fi:
   }
 \cs_new_protected_nopar:Npn \regex_action_start_wildcard:nn #1#2
   {
@@ -1167,7 +1262,10 @@
     \regex_action_cost:n {#1}
   }
 \cs_new_protected_nopar:Npn \regex_action_cost:n #1
-  { \regex_store_state:n {#1} }
+  {
+    \exp_args:Nf \regex_store_state:n %^^A optimize!
+      { \int_eval:n { \l_regex_current_state_int + #1 } }
+  }
 \cs_new_protected_nopar:Npn \regex_action_success:
   {
     \regex_last_match_empty:F
@@ -1184,30 +1282,22 @@
   }
 \cs_new_protected_nopar:Npn \regex_action_free:n #1
   {
-    \regex_if_state_free:nT {#1}
+    \cs_set_nopar:Npx \regex_tmp:w
       {
-        \use:x
-          {
-            \int_set:Nn \l_regex_current_state_int {#1}
-            \regex_store_submatches:n { \l_regex_current_state_int }
-            \regex_state_use:
-            \int_set:Nn \l_regex_current_state_int
-              { \int_use:N \l_regex_current_state_int }
-            \tl_set:Nn \exp_not:N \l_regex_current_submatches_prop
-              { \exp_not:o \l_regex_current_submatches_prop }
-          }
+        \int_add:Nn \l_regex_current_state_int {#1}
+        \regex_state_use:
+        \int_set:Nn \l_regex_current_state_int
+          { \int_use:N \l_regex_current_state_int }
+        \tl_set:Nn \exp_not:N \l_regex_current_submatches_prop
+          { \exp_not:o \l_regex_current_submatches_prop }
       }
+    \regex_tmp:w
   }
 \cs_new_protected_nopar:Npn \regex_action_submatch:n #1
   {
     \prop_put:Nno \l_regex_current_submatches_prop {#1}
       { \int_use:N \l_regex_current_step_int }
-    \regex_store_submatches:n { \l_regex_current_state_int }
   }
-\cs_new_protected_nopar:Npn \regex_action_repeat_copy:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_repeat_move:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_no_repeat_copy:n { \ERROR }
-\cs_new_protected_nopar:Npn \regex_action_no_repeat_move:n { \ERROR }
 \cs_new_protected_nopar:Npn \regex_extract:
   {
     \seq_gclear:N \g_regex_submatches_seq
@@ -1217,11 +1307,7 @@
         \regex_extract_aux:nTF { ##1 }
           {
             \seq_gput_right:Nx \g_regex_submatches_seq
-              {
-                \str_from_to:Nnn \l_regex_query_str
-                  { \l_regex_tmpa_tl }
-                  { \l_regex_tmpb_tl }
-              }
+              { \regex_query_substr:NN \l_regex_tmpa_tl \l_regex_tmpb_tl }
           }
           { \seq_gput_right:Nn \g_regex_submatches_seq { } }
       }
@@ -1253,9 +1339,13 @@
             = \int_use:N \l_regex_max_state_int
           \l_regex_capturing_group_int
             = \int_use:N \l_regex_capturing_group_int
-          \bool_if:NTF \l_regex_look_behind_bool
-            { \bool_set_true:N \l_regex_look_behind_bool }
-            { \bool_set_false:N \l_regex_look_behind_bool }
+          \token_if_eq_meaning:NNT
+            \regex_match_loop_case_hook:
+            \regex_match_loop_caseless_hook:
+            {
+              \cs_set_eq:NN \regex_match_loop_case_hook:
+                \regex_match_loop_caseless_hook:
+            }
           \prg_stepwise_function:nnnN
             {1} {1} {\l_regex_max_state_int}
             \regex_set_aux:n
@@ -1269,7 +1359,7 @@
 \cs_new:Npn \regex_nfa:Nw #1 #2 \regex_nfa_end:
   { \msg_expandable_error:n { Automaton~#1 used~incorrectly. } }
 \cs_new_eq:NN \regex_nfa_end: \scan_stop:
-\prg_new_protected_conditional:Npnn \regex_check_nfa:N #1 { TF }
+\prg_new_protected_conditional:Npnn \regex_check_nfa:N #1 { T , TF }
   { \exp_after:wN \regex_check_nfa_aux:Nw #1 \q_stop }
 \cs_new:Npn \regex_check_nfa_aux:Nw #1 #2 \q_stop
   {
@@ -1280,11 +1370,6 @@
       \prg_return_false:
     \fi:
   }
-\msg_new:nnn { regex } { not-nfa }
-  {
-    I~was~expecting~a~regular~expression~variable.\\
-    Instead,~I~got~#1.
-  }
 \cs_new_protected_nopar:Npn \regex_use:N #1
   { \exp_after:wN \use_none:nn #1 }
 \cs_new_protected:Npn \regex_user_aux:n #1
@@ -1296,7 +1381,7 @@
   }
 \cs_new_protected_nopar:Npn \regex_return_after_group:
   {
-    \if_bool:N \l_regex_success_bool
+    \if_meaning:w \c_true_bool \l_regex_success_bool
       \group_insert_after:N \prg_return_true:
     \else:
       \group_insert_after:N \prg_return_false:
@@ -1304,7 +1389,7 @@
   }
 \cs_new_protected_nopar:Npn \regex_extract_after_group:N #1
   {
-    \if_bool:N \l_regex_success_bool
+    \if_meaning:w \c_true_bool \l_regex_success_bool
       \regex_extract:
       \group_insert_after:N \seq_set_eq:NN
       \group_insert_after:N #1
@@ -1359,7 +1444,7 @@
   }
 \cs_new_protected:Npn \regex_count:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -1375,9 +1460,8 @@
             \regex_count_after_group:N #3
           }
       }
-      { }
   }
-\cs_new_protected:Npn \regex_extract:nnN #1#2#3
+\cs_new_protected:Npn \regex_extract_once:nnN #1#2#3
   {
     \regex_user_aux:n
       {
@@ -1386,7 +1470,8 @@
         \regex_extract_after_group:N #3
       }
   }
-\prg_new_protected_conditional:Npnn \regex_extract:nnN #1#2#3 { T , F , TF }
+\prg_new_protected_conditional:Npnn \regex_extract_once:nnN #1#2#3
+  { T , F , TF }
   {
     \regex_user_aux:n
       {
@@ -1396,9 +1481,9 @@
         \regex_return_after_group:
       }
   }
-\cs_new_protected:Npn \regex_extract:NnN #1#2#3
+\cs_new_protected:Npn \regex_extract_once:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -1407,9 +1492,9 @@
             \regex_extract_after_group:N #3
           }
       }
-      { }
   }
-\prg_new_protected_conditional:Npnn \regex_extract:NnN #1#2#3 { T , F , TF }
+\prg_new_protected_conditional:Npnn \regex_extract_once:NnN #1#2#3
+  { T , F , TF }
   {
     \regex_check_nfa:NTF #1
       {
@@ -1423,6 +1508,48 @@
       }
       { \prg_return_false: }
   }
+\cs_new_protected:Npn \regex_extract_all:nnN #1#2#3
+  {
+    \regex_user_aux:n
+      {
+        \seq_gclear:N \g_regex_extract_all_seq
+        \tl_set:Nn \l_regex_every_match_tl { \regex_extract_all_aux: }
+        \regex_build:n {#1}
+        \regex_match:n {#2}
+        \regex_extract_all_after_group:N #3
+      }
+  }
+\cs_new_protected:Npn \regex_extract_all:NnN #1#2#3
+  {
+    \regex_check_nfa:NT #1
+      {
+        \regex_user_aux:n
+          {
+            \seq_gclear:N \g_regex_extract_all_seq
+            \tl_set:Nn \l_regex_every_match_tl { \regex_extract_all_aux: }
+            \regex_use:N #1
+            \regex_match:n {#2}
+            \regex_extract_all_after_group:N #3
+          }
+      }
+  }
+\cs_new_protected_nopar:Npn \regex_extract_all_aux:
+  {
+    \regex_extract:
+    \seq_gconcat:NNN \g_regex_extract_all_seq
+      \g_regex_extract_all_seq \g_regex_submatches_seq
+    \regex_match_once:
+  }
+\cs_new_protected_nopar:Npn \regex_extract_all_after_group:N #1
+  {
+    \seq_if_empty:NF \g_regex_extract_all_seq
+      {
+        \regex_extract:
+        \group_insert_after:N \seq_set_eq:NN
+        \group_insert_after:N #1
+        \group_insert_after:N \g_regex_extract_all_seq
+      }
+  }
 \cs_new_protected:Npn \regex_split:nnN #1#2#3
   {
     \regex_user_aux:n
@@ -1436,7 +1563,7 @@
   }
 \cs_new_protected:Npn \regex_split:NnN #1#2#3
   {
-    \regex_check_nfa:NTF #1
+    \regex_check_nfa:NT #1
       {
         \regex_user_aux:n
           {
@@ -1447,7 +1574,6 @@
             \regex_split_after_group:N #3
           }
       }
-      { }
   }
 \cs_new_protected_nopar:Npn \regex_split_aux:
   {
@@ -1459,9 +1585,8 @@
           {
             \seq_gput_left:Nx \g_regex_submatches_seq
               {
-                \str_from_to:Nnn \l_regex_query_str
-                  { \int_use:N \l_regex_start_step_int }
-                  { \l_regex_tmpa_tl }
+                \regex_query_substr:NN
+                  \l_regex_start_step_int \l_regex_tmpa_tl
               }
           }
           { \msg_error:nn { regex } { internal } }
@@ -1480,9 +1605,8 @@
       {
         \seq_gput_right:Nx \g_regex_split_seq
           {
-            \str_from_to:Nnn \l_regex_query_str
-              { \int_use:N \l_regex_start_step_int }
-              { \int_use:N \l_regex_current_step_int }
+            \regex_query_substr:NN
+              \l_regex_start_step_int \l_regex_current_step_int
           }
       }
     \group_insert_after:N \seq_set_eq:NN
@@ -1494,40 +1618,57 @@
     \str_aux_escape:NNNn
       \prg_do_nothing:
       \regex_replacement_escaped:N
-      \regex_replacement_raw:N
+      \prg_do_nothing:
       {#1}
     \tl_set_eq:NN \l_regex_replacement_tl \g_str_result_tl
     \tl_set:Nx \l_regex_replacement_tl
       { \l_regex_replacement_tl \prg_do_nothing: }
   }
-\cs_new_nopar:Npn \regex_replacement_raw:N { \exp_not:N \prg_do_nothing: }
 \cs_new_nopar:Npn \regex_replacement_escaped:N #1
   {
-    \if_num:w 9 < 1 #1 \exp_stop_f:
-      \exp_not:N \regex_replacement_escaped_ii:nN {#1}
-    \else:
-      #1
-    \fi:
+    \regex_token_if_other_digit:NTF #1
+      {
+        \exp_not:n
+          { \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } } {#1}
+      }
+      {
+        \token_if_eq_charcode:NNTF g #1
+          { \exp_not:N \regex_replacement_submatch:w }
+          { #1 }
+      }
   }
-\cs_new_nopar:Npn \regex_replacement_escaped_ii:nN #1#2
+\cs_new_nopar:Npn \regex_replacement_submatch:w #1
   {
-    \regex_token_if_other_digit:NTF #2
-      { \regex_replacement_escaped_ii:nN {#1#2} }
-      { \exp_not:N \seq_item:Nn \exp_not:N \g_regex_submatches_seq {#1} #2 }
+    \exp_after:wN \token_if_eq_meaning:NNTF \c_lbrace_str #1
+      { \regex_replacement_submatch_aux:nN { } }
+      {
+        \regex_token_if_other_digit:NTF #1
+          { \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } }
+          { \msg_expandable_error:n { \g misused~in~replacement~text. } }
+        #1
+      }
   }
-\prg_new_conditional:Npnn \regex_token_if_other_digit:N #1 { TF }
+\cs_new_nopar:Npn \regex_replacement_submatch_aux:nN #1 #2
   {
-    \if_num:w 9 < 1 \exp_not:N #1 \exp_stop_f:
-      \prg_return_true:
-    \else:
-      \prg_return_false:
-    \fi:
+    \regex_token_if_other_digit:NTF #2
+      { \regex_replacement_submatch_aux:nN {#1#2} }
+      {
+        \exp_not:n { \seq_item:Nn \g_regex_submatches_seq } {#1}
+        \exp_after:wN \token_if_eq_meaning:NNF \c_rbrace_str #2
+          {
+            \msg_expandable_error:n { \g misused~in~replacement~text. }
+            #2
+          }
+      }
   }
 \cs_new_protected_nopar:Npn \regex_replace_after_group:N #1
   {
-    \group_insert_after:N \tl_set_eq:NN
+    \group_insert_after:N \tl_set:Nx
     \group_insert_after:N #1
-    \group_insert_after:N \g_regex_replaced_str
+    \group_insert_after:N {
+      \group_insert_after:N \tl_to_str:N
+      \group_insert_after:N \g_regex_replaced_str
+    \group_insert_after:N }
   }
 \cs_new_protected:Npn \regex_replace_once_aux:Nn #1#2
   {
@@ -1539,15 +1680,16 @@
       \regex_extract:
       \regex_extract_aux:nTF {0}
         {
+          \cs_set_nopar:Npn \regex_tmp:w
+            { \str_skip_do:nn { \l_regex_tmpb_tl } { } }
           \tl_gset:Nx \g_regex_replaced_str
             {
-              \str_from_to:Nnn \l_regex_query_str {0} { \l_regex_tmpa_tl }
+              \regex_query_substr:NN \c_zero \l_regex_tmpa_tl
               \l_regex_replacement_tl
-              \str_from_to:Nnn \l_regex_query_str
-                { \l_regex_tmpb_tl } { \c_max_int }
+              \exp_after:wN \regex_tmp:w \l_regex_query_other_str
             }
         }
-        { \tl_gset_eq:NN \g_regex_replaced_str \l_regex_query_str }
+        { \tl_gset_eq:NN \g_regex_replaced_str \l_regex_query_other_str }
     \group_end:
   }
 \cs_new_protected:Npn \regex_replace_once:nnN #1#2#3
@@ -1592,12 +1734,10 @@
       \tl_gclear:N \g_regex_replaced_str
       #2
       \exp_args:No \regex_match:n {#1}
+      \cs_set_nopar:Npn \regex_tmp:w
+        { \str_skip_do:nn { \l_regex_start_step_int } { } }
       \tl_gput_right:Nx \g_regex_replaced_str
-        {
-          \str_from_to:Nnn \l_regex_query_str
-            { \int_use:N \l_regex_start_step_int }
-            { \c_max_int }
-        }
+        { \exp_after:wN \regex_tmp:w \l_regex_query_other_str }
     \group_end:
   }
 \cs_new_protected_nopar:Npn \regex_replace_all_aux:
@@ -1607,9 +1747,8 @@
       {
         \tl_gput_right:Nx \g_regex_replaced_str
           {
-            \str_from_to:Nnn \l_regex_query_str
-              { \int_use:N \l_regex_start_step_int }
-              { \l_regex_tmpa_tl }
+            \regex_query_substr:NN
+              \l_regex_start_step_int \l_regex_tmpa_tl
             \l_regex_replacement_tl
           }
       }
@@ -1632,6 +1771,26 @@
         \regex_replacement:n {#2}
       }
   }
+\msg_new:nnn { regex } { -998 } { Unsupported~construct }
+\msg_new:nnn { regex } { -997 }
+  { The~regular~expression~is~too~large~(32768~states). }
+\msg_new:nnn { regex } { 1 } { \iow_char:N\\~at~end~of~pattern }
+\msg_new:nnn { regex } { 4 }
+  { Numbers~out~of~order~in~\iow_char:N\{\iow_char\}~quantifier. }
+\msg_new:nnn { regex } { 6 }
+  { Missing~terminating~\iow_char:N\]~for~character~class }
+\msg_new:nnn { regex } { 7 }
+  { Invalid~escape~sequence~in~character~class }
+\msg_new:nnn { regex } { 8 }
+  { Range~out~of~order~in~character~class }
+\msg_new:nnn { regex } { 22 } { Mismatched~parentheses }
+\msg_new:nnn { regex } { 34 }
+  { Character~value~in~\iow_char:N\\x{...}~sequence~is~too~large }
+\msg_new:nnn { regex } { not-nfa }
+  {
+    LaTeX~was~expecting~a~regular~expression~variable.\\
+    Instead,~LaTeX~found~'#1'.
+  }
 %% 
 %%
 %% End of file `l3regex.sty'.
diff --git a/Master/texmf-dist/tex/latex/l3experimental/l3str/l3str.sty b/Master/texmf-dist/tex/latex/l3experimental/l3str/l3str.sty
index 9a69d0da0a6..c705f6366b3 100644
--- a/Master/texmf-dist/tex/latex/l3experimental/l3str/l3str.sty
+++ b/Master/texmf-dist/tex/latex/l3experimental/l3str/l3str.sty
@@ -46,30 +46,27 @@
 %%
 %% -----------------------------------------------------------------------
 \RequirePackage{expl3}
-\GetIdInfo$Id: l3str.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: l3str.dtx 2921 2011-10-17 13:23:36Z bruno $
   {L3 Experimental Strings}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
-\cs_if_exist:NF \cs_if_exist_use:cF
-  {
-    \cs_new:Npn \cs_if_exist_use:cF #1
-      { \cs_if_exist:cTF {#1} { \use:c {#1} } }
-  }
 \cs_if_exist:NF \use_i:nnnnnnnn
   { \cs_new:Npn \use_i:nnnnnnnn #1#2#3#4#5#6#7#8 {#1} }
-\cs_set:Npn \str_tmp:w #1
-  {
-    \cs_new_protected:cpx { str_#1:Nn } ##1##2
-      { \exp_not:c { tl_#1:Nx } ##1 { \exp_not:N \tl_to_str:n {##2} } }
-    \exp_args:Nc \cs_generate_variant:Nn { str_#1:Nn } { Nx , cn , cx }
-  }
-\str_tmp:w {set}
-\str_tmp:w {gset}
-\str_tmp:w {put_left}
-\str_tmp:w {gput_left}
-\str_tmp:w {put_right}
-\str_tmp:w {gput_right}
-\cs_set_protected_nopar:Npn \str_tmp:w { }
+\group_begin:
+  \cs_set_protected_nopar:Npn \str_tmp:w #1
+    {
+      \cs_new_protected:cpx { str_ #1 :Nn } ##1##2
+        { \exp_not:c { tl_ #1 :Nx } ##1 { \exp_not:N \tl_to_str:n {##2} } }
+      \exp_args:Nc \cs_generate_variant:Nn { str_ #1 :Nn } { Nx , cn , cx }
+    }
+  \str_tmp:w { set }
+  \str_tmp:w { gset }
+  \str_tmp:w { put_left }
+  \str_tmp:w { gput_left }
+  \str_tmp:w { put_right }
+  \str_tmp:w { gput_right }
+\group_end:
+\cs_new_protected_nopar:Npn \str_tmp:w { }
 \tl_new:N \g_str_tmpa_tl
 \tl_new:N \g_str_result_tl
 \int_new:N \l_str_char_int
@@ -80,34 +77,31 @@
 \tl_const:Nx \c_hash_str      { \cs_to_str:N \# }
 \tl_const:Nx \c_percent_str   { \cs_to_str:N \% }
 \group_begin:
-\char_set_lccode:nn {`\*}{`\ }
-\char_set_lccode:nn {`\A}{`\A}
-\tl_to_lowercase:n {
-  \group_end:
-  \cs_new:Npn \tl_to_other_str:n #1
-    {
-      \exp_after:wN \tl_to_other_str_loop:w \tl_to_str:n {#1} ~ %
-      A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ \q_mark \q_stop
-    }
-  \cs_new_nopar:Npn \tl_to_other_str_loop:w
+\char_set_lccode:nn { `\* } { `\  }
+\char_set_lccode:nn { `\A } { `\A }
+\tl_to_lowercase:n
+  {
+    \group_end:
+    \cs_new:Npn \tl_to_other_str:n #1
+      {
+        \exp_after:wN \tl_to_other_str_loop:w \tl_to_str:n {#1} ~ %
+        A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ \q_mark \q_stop
+      }
+    \cs_new_nopar:Npn \tl_to_other_str_loop:w
       #1 ~ #2 ~ #3 ~ #4 ~ #5 ~ #6 ~ #7 ~ #8 ~ #9 \q_stop
-    {
-      \if_meaning:w A #8
-        \tl_to_other_str_end:w
-      \fi:
-      \tl_to_other_str_loop:w
-      #9 #1 * #2 * #3 * #4 * #5 * #6 * #7 * #8 * \q_stop
-    }
-  \cs_new_nopar:Npn \tl_to_other_str_end:w \fi: #1 \q_mark #2 * A #3 \q_stop
-    { \fi: #2 }
-}
-\cs_new_nopar:Npn \tl_to_other_str:N
-  { \exp_args:No \tl_to_other_str:n }
-\cs_new:Npn \str_sanitize_args:Nn #1 #2
-  {
-    \exp_args:Nf #1
-      { \tl_to_other_str:n {#2} }
+      {
+        \if_meaning:w A #8
+          \tl_to_other_str_end:w
+        \fi:
+        \tl_to_other_str_loop:w
+        #9 #1 * #2 * #3 * #4 * #5 * #6 * #7 * #8 * \q_stop
+      }
+    \cs_new_nopar:Npn \tl_to_other_str_end:w \fi: #1 \q_mark #2 * A #3 \q_stop
+      { \fi: #2 }
   }
+\cs_new_nopar:Npn \tl_to_other_str:N { \exp_args:No \tl_to_other_str:n }
+\cs_new:Npn \str_sanitize_args:Nn #1#2
+  { \exp_args:Nf #1 { \tl_to_other_str:n {#2} } }
 \cs_new:Npn \str_sanitize_args:Nnn #1#2#3
   {
     \exp_args:Nff #1
@@ -141,15 +135,15 @@
     \fi:
     \c_nine + \str_length_loop:NNNNNNNNN
   }
-\cs_set_nopar:Npn \str_head:N { \exp_args:No \str_head:n }
+\cs_new_nopar:Npn \str_head:N { \exp_args:No \str_head:n }
 \cs_set:Npn \str_head:n #1
   {
     \exp_after:wN \str_head_aux:w
     \tl_to_str:n {#1}
     { { } } ~ \q_stop
   }
-\cs_set_nopar:Npx \str_head_aux:w #1 ~ %
-  { \exp_not:N \use_i_delimit_by_q_stop:nw #1 { ~ } }
+\cs_set_nopar:Npn \str_head_aux:w #1 ~ %
+  { \use_i_delimit_by_q_stop:nw #1 { ~ } }
 \cs_new:Npn \str_head_ignore_spaces:n #1
   { \exp_after:wN \use_i_delimit_by_q_stop:nw \tl_to_str:n {#1} { } \q_stop }
 \cs_new_nopar:Npn \str_head_unsafe:n #1
@@ -169,15 +163,17 @@
   }
 \cs_new_nopar:Npn \str_tail_unsafe:n #1
   { \str_tail_aux_ii:w #1 X { } X \q_stop }
-\cs_set_nopar:Npn \str_tail_aux_ii:w #1 #2 X #3 \q_stop { #2 }
+\cs_new_nopar:Npn \str_tail_aux_ii:w #1 #2 X #3 \q_stop { #2 }
 \cs_new:Npn \str_skip_do:nn #1
   {
-    \int_compare:nNnTF {#1} > \c_seven
-      { \str_skip_aux:nnnnnnnnn }
-      { \str_skip_end:n }
+    \if_num:w \int_eval:w #1 > \c_seven
+      \exp_after:wN \str_skip_aux:nnnnnnnnn
+    \else:
+      \exp_after:wN \str_skip_end:n
+    \fi:
       {#1}
   }
-\cs_new:Npn \str_skip_aux:nnnnnnnnn #1#2 #3#4#5#6#7#8#9
+\cs_new:Npn \str_skip_aux:nnnnnnnnn #1#2#3#4#5#6#7#8#9
   { \exp_args:Nf \str_skip_do:nn { \int_eval:n { #1 - \c_seven } } {#2} }
 \cs_new:Npn \str_skip_end:n #1
   {
@@ -193,7 +189,7 @@
     \else: \str_skip_end_ii:nwn { XXXXXXX }
     \fi:
   }
-\cs_new:Npn \str_skip_end_ii:nwn #1 #2 \fi: #3
+\cs_new:Npn \str_skip_end_ii:nwn #1#2 \fi: #3
   { \fi: \use_i:nnnnnnnn {#3} #1 }
 \cs_new:Npn \str_collect_do:nn #1#2
   { \str_collect_aux:n {#1} { \str_collect_end_iii:nwNNNNNNN {#2} } }
@@ -213,18 +209,18 @@
 \cs_new:Npn \str_collect_end:n #1
   {
     \if_case:w \int_eval:w #1 \int_eval_end:
-         \str_collect_end_ii:nwn { {}{}{}{}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{}{} }
-    \or: \str_collect_end_ii:nwn { {}{} }
-    \or: \str_collect_end_ii:nwn { {} }
+         \str_collect_end_ii:nwn { { } { } { } { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } { } }
+    \or: \str_collect_end_ii:nwn { { } { } }
+    \or: \str_collect_end_ii:nwn { { } }
     \or: \str_collect_end_ii:nwn {  }
-    \else: \str_collect_end_ii:nwn { {}{}{}{}{}{}{} }
+    \else: \str_collect_end_ii:nwn { { } { } { } { } { } { } { } }
     \fi:
   }
-\cs_new:Npn \str_collect_end_ii:nwn #1 #2 \fi: #3
+\cs_new:Npn \str_collect_end_ii:nwn #1#2 \fi: #3
   { \fi: #3 \q_stop #1 }
 \cs_new:Npn \str_collect_end_iii:nwNNNNNNN #1 #2 \q_stop #3#4#5#6#7#8#9
   { #1 {#2#3#4#5#6#7#8#9} }
@@ -264,30 +260,30 @@
           { \use_none_delimit_by_q_stop:w }
       }
   }
-\cs_new_nopar:Npn \str_from_to:Nnn { \exp_args:No \str_from_to:nnn }
-\cs_new:Npn \str_from_to:nnn #1#2#3
+\cs_new_nopar:Npn \str_substr:Nnn { \exp_args:No \str_substr:nnn }
+\cs_new:Npn \str_substr:nnn #1#2#3
   {
     \exp_args:Nf \tl_to_str:n
-      { \str_sanitize_args:Nn \str_from_to_unsafe:nnn {#1}{#2}{#3} }
+      { \str_sanitize_args:Nn \str_substr_unsafe:nnn {#1} {#2} {#3} }
   }
-\cs_new:Npn \str_from_to_ignore_spaces:nnn #1
-  { \exp_args:No \str_from_to_unsafe:nnn { \tl_to_str:n {#1} } }
-\cs_new:Npn \str_from_to_unsafe:nnn #1#2#3 % <string> <from> <to>
+\cs_new:Npn \str_substr_ignore_spaces:nnn #1
+  { \exp_args:No \str_substr_unsafe:nnn { \tl_to_str:n {#1} } }
+\cs_new:Npn \str_substr_unsafe:nnn #1#2#3
   {
-    \str_aux_eval_args:Nnnn \str_from_to_aux:nnnw
+    \str_aux_eval_args:Nnnn \str_substr_aux:nnnw
       { \str_length_unsafe:n {#1} }
       {#2}
       {#3}
       #1
     \q_stop
   }
-\cs_new:Npn \str_from_to_aux:nnnw #1#2#3 % <len> <from> <to>
+\cs_new:Npn \str_substr_aux:nnnw #1#2#3
   {
-    \exp_args:Nf \str_from_to_aux_ii:nnw
+    \exp_args:Nf \str_substr_aux_ii:nnw
       { \str_aux_normalize_range:nn {#2} {#1} }
       { \str_aux_normalize_range:nn {#3} {#1} }
   }
-\cs_new:Npn \str_from_to_aux_ii:nnw #1#2
+\cs_new:Npn \str_substr_aux_ii:nnw #1#2
   {
     \str_skip_do:nn {#1}
       {
@@ -376,7 +372,7 @@
   }
 \prg_new_protected_conditional:Npnn \str_aux_hexadecimal_test:N #1 { TF }
   {
-    \tl_if_in:onTF { \tl_to_str:n {abcdef} } {#1}
+    \tl_if_in:onTF { \tl_to_str:n { abcdef } } {#1}
       {
         \int_set:Nn \l_str_char_int
           { \c_sixteen * \l_str_char_int + `#1 - 87 }
@@ -423,7 +419,7 @@
       \cs_set_nopar:Npn \str_aux_escape_unescaped:N { #1 }
       \cs_set_nopar:Npn \str_aux_escape_escaped:N { #2 }
       \cs_set_nopar:Npn \str_aux_escape_raw:N { #3 }
-      \int_set:Nn \tex_escapechar:D {92}
+      \int_set:Nn \tex_escapechar:D { 92 }
       \tl_gset:Nx \g_str_result_tl { \tl_to_other_str:n {#4} }
       \tl_gset:Nx \g_str_result_tl
         {
@@ -531,28 +527,22 @@
         }
     }
 \group_end:
-\msg_new:nnn { str } { x-missing-brace }
-  {
-    You~wrote~something~like~
-    `\iow_char:N\\x\{ \int_to_hexadecimal:n { \l_str_char_int }'.~
-    The~closing~brace~is~missing.
-  }
 \group_begin:
-  \char_set_catcode_other:n {`\^^@}
+  \char_set_catcode_other:n { `\^^@ }
   \cs_new_protected_nopar:Npn \str_aux_convert_store:
     {
-      \char_set_lccode:nn {\c_zero} {\l_str_char_int}
+      \char_set_lccode:nn { \c_zero } { \l_str_char_int }
       \tl_to_lowercase:n { \tl_gput_right:Nx \g_str_result_tl {^^@} }
     }
   \cs_new_protected_nopar:Npn \str_aux_convert_store:NNn #1#2#3
     {
-      \char_set_lccode:nn {\c_zero} {#3}
+      \char_set_lccode:nn { \c_zero } {#3}
       \tl_to_lowercase:n { #1 #2 {^^@} }
     }
 \group_end:
 \cs_new_nopar:Npn \str_aux_byte_to_hexadecimal:N #1
   {
-    \int_compare:nNnTF {`#1} < {256}
+    \int_compare:nNnTF {`#1} < { 256 }
       {
         \int_to_letter:n { \int_div_truncate:nn {`#1} \c_sixteen }
         \int_to_letter:n { \int_mod:nn {`#1} \c_sixteen }
@@ -561,14 +551,14 @@
   }
 \cs_new_nopar:Npn \str_aux_byte_to_octal:N #1
   {
-    \int_compare:nNnTF {`#1} < {64}
+    \int_compare:nNnTF {`#1} < { 64 }
       {
         0
         \int_to_letter:n { \int_div_truncate:nn {`#1} \c_eight }
         \int_to_letter:n { \int_mod:nn {`#1} \c_eight }
       }
       {
-        \int_compare:nNnTF {`#1} < {256}
+        \int_compare:nNnTF {`#1} < { 256 }
           { \int_to_octal:n {`#1} }
           { \msg_expandable_error:n { Invalid~byte~`#1'. } }
       }
@@ -579,7 +569,7 @@
       { \str_map_tokens:Nn #2 \str_aux_byte_to_hexadecimal:N }
   }
 \tl_const:Nx \c_str_bytes_escape_name_str
-  { \c_hash_str \c_percent_str \c_lbrace_str \c_rbrace_str () /<>[] }
+  { \c_hash_str \c_percent_str \c_lbrace_str \c_rbrace_str ()/<>[] }
 \cs_new_protected_nopar:Npn \str_bytes_escape_name:NN #1#2
   {
     \str_set:Nx #1
@@ -587,10 +577,10 @@
   }
 \cs_new_nopar:Npn \str_bytes_escape_name_aux:N #1
   {
-    \int_compare:nNnTF {`#1} < {"21}
+    \int_compare:nNnTF {`#1} < { "21 }
       { \c_hash_str \str_aux_byte_to_hexadecimal:N #1 }
       {
-        \int_compare:nNnTF {`#1} > {"7E}
+        \int_compare:nNnTF {`#1} > { "7E }
           { \c_hash_str \str_aux_byte_to_hexadecimal:N #1 }
           {
             \str_if_contains_char:NNTF \c_str_bytes_escape_name_str #1
@@ -607,10 +597,10 @@
   }
 \cs_new_nopar:Npn \str_bytes_escape_string_aux:N #1
   {
-    \int_compare:nNnTF {`#1} < {"21}
+    \int_compare:nNnTF {`#1} < { "21 }
       { \c_backslash_str \str_aux_byte_to_octal:N #1 }
       {
-        \int_compare:nNnTF {`#1} > {"7E}
+        \int_compare:nNnTF {`#1} > { "7E }
           { \c_backslash_str \str_aux_byte_to_octal:N #1 }
           {
             \str_if_contains_char:NNT \c_str_bytes_escape_string_str #1
@@ -719,16 +709,16 @@
                 {
                   \prg_case_str:xxn {#2}
                     {
-                      {n} {10}
-                      {r} {13}
-                      {t} {9}
-                      {b} {8}
-                      {f} {12}
-                      {(} {40}
-                      {)} {41}
-                      {\c_backslash_str} {92}
-                      {^^J} {-1}
-                      {^^M} {-1}
+                      { n } { 10 }
+                      { r } { 13 }
+                      { t } { 9 }
+                      { b } { 8 }
+                      { f } { 12 }
+                      { ( } { 40 }
+                      { ) } { 41 }
+                      { \c_backslash_str } { 92 }
+                      { ^^J } { -1 }
+                      { ^^M } { -1 }
                     }
                     {`#2}
                 }
@@ -768,14 +758,14 @@
   }
 \cs_new_nopar:Npn \str_bytes_percent_encode_aux:N #1
   {
-    \int_compare:nNnTF {`#1} < {"41}
+    \int_compare:nNnTF {`#1} < { "41 }
       {
         \str_if_contains_char:NNTF \c_str_bytes_percent_encode_not_str #1
           { #1 }
           { \c_percent_str \str_aux_byte_to_hexadecimal:N #1 }
       }
       {
-        \int_compare:nNnTF {`#1} > {"7E}
+        \int_compare:nNnTF {`#1} > { "7E }
           { \c_percent_str \str_aux_byte_to_hexadecimal:N #1 }
           {
             \str_if_contains_char:NNTF \c_str_bytes_percent_encode_str #1
@@ -837,19 +827,18 @@
 \cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_i:N #1
   {
     \quark_if_recursion_tail_stop:N #1
-    \int_set:Nn \l_str_char_int { `#1 }
-    \str_native_from_UTF_viii_aux_ii:nN {128} \c_one
-    \str_native_from_UTF_viii_aux_ii:nN {64}  \c_zero
-    \str_native_from_UTF_viii_aux_ii:nN {32}  \c_two
-    \str_native_from_UTF_viii_aux_ii:nN {16}  \c_three
-    \str_native_from_UTF_viii_aux_ii:nN {8}   \c_four
+    \int_set:Nn \l_str_char_int {`#1}
+    \str_native_from_UTF_viii_aux_ii:nN { 128 } \c_one
+    \str_native_from_UTF_viii_aux_ii:nN { 64 }  \c_zero
+    \str_native_from_UTF_viii_aux_ii:nN { 32 }  \c_two
+    \str_native_from_UTF_viii_aux_ii:nN { 16 }  \c_three
+    \str_native_from_UTF_viii_aux_ii:nN { 8 }   \c_four
     \msg_error:nnx { str } { utf8-invalid-byte } {#1}
     \use_i:nnn \str_native_from_UTF_viii_aux_i:N
     \q_stop
     \str_native_from_UTF_viii_aux_iii:N
   }
-\cs_new_protected_nopar:Npn
-  \str_native_from_UTF_viii_aux_ii:nN #1#2
+\cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_ii:nN #1#2
   {
     \int_compare:nNnTF \l_str_char_int < {#1}
       {
@@ -858,8 +847,7 @@
       }
       { \int_sub:Nn \l_str_char_int {#1} }
   }
-\cs_new_protected_nopar:Npn
-  \str_native_from_UTF_viii_aux_iii:N #1
+\cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_iii:N #1
   {
     \int_compare:nNnTF \l_str_bytes_int < \c_two
       { \str_native_from_UTF_viii_aux_iv: #1 }
@@ -869,11 +857,11 @@
           \exp_after:wN \use_none_delimit_by_q_recursion_stop:w
         \fi:
         \quark_if_recursion_tail_stop:N #1
-        \tex_multiply:D \l_str_char_int by 64 \scan_stop: % no interface??
+        \tex_multiply:D \l_str_char_int by 64 \scan_stop:
         \int_decr:N \l_str_bytes_int
-        \int_compare:nNnTF {`#1} < {128}
+        \int_compare:nNnTF {`#1} < { 128 }
           { \use_ii:nn }
-          { \int_compare:nNnTF {`#1} < {192} }
+          { \int_compare:nNnTF {`#1} < { 192 } }
           {
             \int_add:Nn \l_str_char_int { `#1 - 128 }
             \str_native_from_UTF_viii_aux_iii:N
@@ -884,47 +872,32 @@
           }
       }
   }
-\cs_new_protected_nopar:Npn
-  \str_native_from_UTF_viii_aux_iv:
+\cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_iv:
   {
     \int_compare:nNnTF \l_str_bytes_int = \c_zero
       {
         \msg_error:nnx { str } { utf8-extra-byte }
           { \int_eval:n { \l_str_char_int + 128 } }
       }
+      { \str_native_from_UTF_viii_aux_v: }
+    \str_native_from_UTF_viii_aux_i:N
+  }
+\pdftex_if_engine:TF
+  {
+    \cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_v:
       {
-        \pdftex_if_engine:TF
+        \int_compare:nNnTF { \l_str_char_int } < { 256 }
+          { \str_aux_convert_store: }
           {
-            \int_compare:nNnTF { \l_str_char_int } < { 256 }
-              { \str_aux_convert_store: }
-              {
-                \msg_error:nnx { str } { utf8-pdftex-overflow }
-                  { \int_use:N \l_str_char_int }
-              }
+            \msg_error:nnx { str } { utf8-pdftex-overflow }
+              { \int_use:N \l_str_char_int }
           }
-          { \str_aux_convert_store: }
       }
-    \str_native_from_UTF_viii_aux_i:N
   }
-\msg_new:nnn { str } { utf8-invalid-byte }
   {
-    \int_compare:nNnTF {`#1} < {256}
-      { Byte~number~\int_eval:n {`#1}~invalid~in~utf-8~encoding. }
-      { The~character~number~\int_eval:n {`#1}~is~not~a~byte. }
+    \cs_new_protected_nopar:Npn \str_native_from_UTF_viii_aux_v:
+      { \str_aux_convert_store: }
   }
-\msg_new:nnn { str } { utf8-missing-byte }
-  { The~byte~number~\int_eval:n {`#1}~is~not~a~valid~continuation~byte. }
-\msg_new:nnn { str } { utf8-extra-byte }
-  { The~byte~number~\int_eval:n {`#1}~is~only~valid~as~a~continuation~byte. }
-\msg_new:nnnn { str } { utf8-premature-end }
-  { Incomplete~last~utf8~character. }
-  {
-    The~sequence~of~byte~that~I~need~to~convert~to~utf8 \
-    ended~before~the~last~character~was~complete.~Perhaps \
-    it~was~mistakenly~truncated?
-  }
-\msg_new:nnn { str } { utf8-pdftex-overflow }
-  { The~character~number~#1~is~too~big~for~pdfTeX. }
 \cs_new_protected_nopar:Npn \str_UTF_viii_from_native:NN #1#2
   {
     \group_begin:
@@ -936,14 +909,14 @@
 \cs_new_protected_nopar:Npn \str_UTF_viii_from_native_aux_i:N #1
   {
     \int_set:Nn \l_str_char_int {`#1}
-    \int_compare:nNnTF \l_str_char_int < {128}
+    \int_compare:nNnTF \l_str_char_int < { 128 }
       { \tl_gput_right:Nx \g_str_result_tl {#1} }
       {
         \tl_gclear:N \g_str_tmpa_tl
         \int_set:Nn \l_str_bytes_int { 64 }
-        \str_UTF_viii_from_native_aux_ii:n {32}
-        \str_UTF_viii_from_native_aux_ii:n {16}
-        \str_UTF_viii_from_native_aux_ii:n {8}
+        \str_UTF_viii_from_native_aux_ii:n { 32 }
+        \str_UTF_viii_from_native_aux_ii:n { 16 }
+        \str_UTF_viii_from_native_aux_ii:n { 8 }
         \ERROR % somehow the unicode char was > "1FFFFF > "10FFFF
         \tl_gclear:N \g_str_tmpa_tl
         \use_none:n \q_stop
@@ -956,15 +929,41 @@
   {
     \str_aux_convert_store:NNn
       \tl_gput_left:Nx \g_str_tmpa_tl
-      { 128 + \int_mod:nn { \l_str_char_int } {64} }
-    \tex_divide:D \l_str_char_int by 64 \scan_stop: % no interface??
+      { 128 + \int_mod:nn { \l_str_char_int } { 64 } }
+    \tex_divide:D \l_str_char_int by 64 \scan_stop:
     \int_add:Nn \l_str_bytes_int {#1}
     \int_compare:nNnT \l_str_char_int < {#1}
       { \use_none_delimit_by_q_stop:w }
   }
-\cs_gset:Npn \str_length_skip_spaces:N
+\msg_new:nnnn { str } { x-missing-brace }
+  { Missing~closing~brace~in~ \token_to_str:N \x ~byte~sequence. }
+  {
+    You~wrote~something~like~
+    `\iow_char:N\\x\{ \int_to_hexadecimal:n { \l_str_char_int }'.~
+    The~closing~brace~is~missing.
+  }
+\msg_new:nnn { str } { utf8-invalid-byte }
+  {
+    \int_compare:nNnTF {`#1} < { 256 }
+      { Byte~number~ \int_eval:n {`#1} ~invalid~in~utf-8~encoding. }
+      { The~character~number~ \int_eval:n {`#1} ~is~not~a~byte. }
+  }
+\msg_new:nnn { str } { utf8-missing-byte }
+  { The~byte~number~ \int_eval:n {`#1} ~is~not~a~valid~continuation~byte. }
+\msg_new:nnn { str } { utf8-extra-byte }
+  { The~byte~number~ \int_eval:n {`#1} ~is~only~valid~as~a~continuation~byte. }
+\msg_new:nnnn { str } { utf8-premature-end }
+  { Incomplete~last~UTF8~character. }
+  {
+    The~sequence~of~byte~that~to~be~converted~to~UTF8~
+    ended~before~the~last~character~was~complete.~Perhaps~
+    it~was~mistakenly~truncated?
+  }
+\msg_new:nnn { str } { utf8-pdftex-overflow }
+  { The~character~number~#1~is~too~big~for~pdfTeX. }
+\cs_set:Npn \str_length_skip_spaces:N
   { \exp_args:No \str_length_skip_spaces:n }
-\cs_gset_eq:NN \str_length_skip_spaces:n \str_length_ignore_spaces:n
+\cs_set_eq:NN \str_length_skip_spaces:n \str_length_ignore_spaces:n
 %% 
 %%
 %% End of file `l3str.sty'.
diff --git a/Master/texmf-dist/tex/latex/l3experimental/xcoffins/xcoffins.sty b/Master/texmf-dist/tex/latex/l3experimental/xcoffins/xcoffins.sty
index 79490432742..9d4a42407e3 100644
--- a/Master/texmf-dist/tex/latex/l3experimental/xcoffins/xcoffins.sty
+++ b/Master/texmf-dist/tex/latex/l3experimental/xcoffins/xcoffins.sty
@@ -47,7 +47,7 @@
 %% -----------------------------------------------------------------------
 %%
 \RequirePackage{xparse}
-\GetIdInfo$Id: xcoffins.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: xcoffins.dtx 2963 2011-11-15 22:06:41Z joseph $
   {L3 Experimental design-level coffins}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
@@ -146,6 +146,14 @@
   { \coffin_resize:Nnn #1 {#2} {#3} }
 \NewDocumentCommand \ScaleCoffin  { m m m }
   { \coffin_scale:Nnn #1 {#2} {#3} }
+\NewDocumentCommand \CoffinDepth { m }
+  { \coffin_dp:N #1 }
+\NewDocumentCommand \CoffinHeight { m }
+  { \coffin_ht:N #1 }
+\NewDocumentCommand \CoffinTotalHeight { m }
+  { \dim_eval:w \coffin_ht:N #1 + \coffin_dp:N #1 \dim_eval_end: }
+\NewDocumentCommand \CoffinWidth { m }
+  { \coffin_wd:N #1 }
 \NewDocumentCommand \DisplayCoffinHandles { m m }
   {
     \cs_if_exist:cTF { l_coffin_poles_ \int_value:w #1 _prop }
diff --git a/Master/texmf-dist/tex/latex/l3experimental/xgalley/l3galley.sty b/Master/texmf-dist/tex/latex/l3experimental/xgalley/l3galley.sty
index b626f072d30..e8a3345204f 100644
--- a/Master/texmf-dist/tex/latex/l3experimental/xgalley/l3galley.sty
+++ b/Master/texmf-dist/tex/latex/l3experimental/xgalley/l3galley.sty
@@ -48,11 +48,14 @@
 %% -----------------------------------------------------------------------
 %%
 \RequirePackage{l3names}
-\GetIdInfo$Id: l3galley.dtx 2899 2011-10-09 21:22:06Z joseph $
+\GetIdInfo$Id: l3galley.dtx 2938 2011-10-25 18:41:20Z joseph $
   {L3 Experimental galley code}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
 \package_check_loaded_expl:
+\cs_new_protected:Npn \scan_marker_new:N #1
+  { \cs_new_eq:NN #1 \scan_stop: }
+\cs_generate_variant:Nn \scan_marker_new:N { c }
 \cs_new_protected_nopar:Npn \galley_leave_vmode:
   { \tex_unhbox:D \c_empty_box }
 \clist_new:N \l_galley_parshape_left_indent_clist
@@ -69,7 +72,6 @@
 \cs_new_eq:NN \l_galley_width_dim \tex_hsize:D
 \bool_new:N \g_galley_begin_level_bool
 \bool_new:N \l_galley_begin_level_bool
-\bool_gset_true:N \g_galley_begin_level_bool
 \bool_new:N \g_galley_omit_next_indent_bool
 \bool_new:N \l_galley_omit_next_indent_bool
 \bool_new:N \g_galley_parshape_set_bool
@@ -107,9 +109,10 @@
     \bool_gset_false:N \g_galley_parshape_set_bool
     \int_gzero:N \g_galley_previous_par_lines_int
     \tl_gclear:N \g_galley_restore_running_tl
-    \tl_gclear:N \g_galley_whatsits_previous_tl
-    \tl_gclear:N \g_galley_whatsits_next_tl
+    \tl_gclear:N \g_galley_whatsit_previous_tl
+    \tl_gclear:N \g_galley_whatsit_next_tl
   }
+\galley_initialise_variables:
 \cs_new_protected_nopar:Npn \galley_initialise_settings:
   {
     \dim_set_eq:NN \l_galley_text_width_dim \l_galley_width_dim
@@ -142,10 +145,10 @@
       \g_galley_previous_par_lines_int
     \tl_set_eq:NN \l_galley_restore_running_tl
       \g_galley_restore_running_tl
-    \tl_set_eq:NN \l_galley_whatsits_previous_tl
-      \g_galley_whatsits_previous_tl
-    \tl_set_eq:NN \l_galley_whatsits_next_tl
-      \g_galley_whatsits_next_tl
+    \tl_set_eq:NN \l_galley_whatsit_previous_tl
+      \g_galley_whatsit_previous_tl
+    \tl_set_eq:NN \l_galley_whatsit_next_tl
+      \g_galley_whatsit_next_tl
   }
 \cs_new_protected_nopar:Npn \galley_restore_parameters:
   {
@@ -171,10 +174,10 @@
       \l_galley_previous_par_lines_int
     \tl_gset_eq:NN \g_galley_restore_running_tl
       \l_galley_restore_running_tl
-    \tl_gset_eq:NN \g_galley_whatsits_previous_tl
-      \l_galley_whatsits_previous_tl
-    \tl_gset_eq:NN \g_galley_whatsits_next_tl
-      \l_galley_whatsits_next_tl
+    \tl_gset_eq:NN \g_galley_whatsit_previous_tl
+      \l_galley_whatsit_previous_tl
+    \tl_gset_eq:NN \g_galley_whatsit_next_tl
+      \l_galley_whatsit_next_tl
   }
 \cs_new_protected_nopar:Npn \galley_level:
   {
@@ -190,8 +193,28 @@
       \galley_restore_parameters:
     \group_end:
   }
+\scan_marker_new:N \s_par_omit
 \cs_new_protected_nopar:Npn \galley_std_par:
   {
+    \s_par_omit
+    \exp_after:wN \galley_std_par_aux_i: \tex_romannumeral:D - `0
+  }
+\cs_new_protected:Npn \galley_std_par_aux_i:
+  {
+    \peek_meaning:NTF \s_par_omit
+      { \galley_std_par_aux:N }
+      { \galley_std_par_aux_ii: }
+  }
+\cs_new_protected:Npn \galley_std_par_aux:N #1
+  {
+    \str_if_eq:xxF {#1} { \s_par_omit }
+      {
+        \galley_std_par_aux_ii:
+        #1
+      }
+  }
+\cs_new_protected_nopar:Npn \galley_std_par_aux_ii:
+  {
     \mode_if_vertical:TF
       { \tex_par:D }
       {
@@ -206,6 +229,15 @@
     \tl_gclear:N \g_galley_par_after_hook_tl
     \tex_penalty:D \c_ten_thousand
   }
+\cs_new_protected:Npn \galley_end_par:n #1
+  {
+    \s_par_omit
+    \bool_if:nF \g_galley_begin_level_bool
+      {
+        #1
+        \galley_std_par:
+      }
+  }
 \cs_set_protected_nopar:Npn \par { \galley_std_par: }
 \tl_set:Nn \@par { \galley_std_par: }
 \cs_new_protected_nopar:Npn \galley_display_begin:
@@ -354,14 +386,14 @@
   {
     \g_galley_whatsit_next_tl
     \tl_gclear:N \g_galley_whatsit_next_tl
-    \bool_if:NT \g_galley_omit_next_indent_bool
+    \bool_if:NF \g_galley_omit_next_indent_bool
       {
-       \box_if_empty:NF \g_galley_last_box
+        \box_if_empty:NF \g_galley_last_box
           { \hbox_to_wd:nn \l_galley_par_indent_dim { } }
       }
     \skip_horizontal:N \l_galley_par_begin_skip
     \g_galley_par_begin_hook_tl
-    \bool_gset_true:N \g_galley_omit_next_indent_bool
+    \bool_gset_false:N \g_galley_omit_next_indent_bool
   }
 \cs_new_protected_nopar:Npn \galley_restore_running_parameters:
   {
@@ -732,6 +764,20 @@
   { \int_use:N \etex_widowpenalties:D \int_eval:w #1 \int_eval_end: , }
 \cs_new_protected_nopar:Npn \galley_interline_penalty:
   { \int_use:N \etex_interlinepenalties:D \etex_interlinepenalties:D \c_zero }
+\cs_set_protected_nopar:Npn \nobreak
+  { \bool_gset_true:N \g_galley_no_break_next_bool }
+\cs_set_protected_nopar:Npn \noindent
+  {
+    \tex_noindent:D
+    \bool_gset_false:N \g_galley_omit_next_indent_bool
+  }
+\cs_set_protected_nopar:Npn \vspace #1
+  {
+    \@ifstar
+      { \galley_set_user_vspace:n {#1} }
+      { \galley_set_user_vspace:n {#1} }
+  }
+\cs_set_eq:NN \@@par \galley_std_par:
 \cs_set_protected_nopar:Npn \@afterheading
   {
     \bool_gset_true:N \g_galley_no_break_next_bool
@@ -742,6 +788,8 @@
   }
 \cs_set_protected:Npn \@hangfrom #1
   {
+    \bool_gset_true:N \g_galley_omit_next_indent_bool
+    \leavevmode
     \setbox \@tempboxa = \hbox { {#1} }
     \galley_parshape_single_par:nnnN
       \c_one
@@ -749,16 +797,9 @@
       \c_zero_dim
       \c_false_bool
     \bool_gset_true:N \g_galley_no_break_next_bool
-    \bool_gset_true:N \galley_omit_next_indent_bool
+    \bool_gset_true:N \g_galley_omit_next_indent_bool
     \box \@tempboxa
   }
-\cs_set_protected:Npn \@makefntext #1
-  {
-    \UseTemplate { justification } { std } { indent-width = 1 em }
-    \bool_gset_true:N \galley_omit_next_indent_bool
-    \galley_leave_vmode:
-    \hb@xt@ 1.8em { \hss \@makefnmark } #1
-  }
 %% 
 %%
 %% End of file `l3galley.sty'.
diff --git a/Master/texmf-dist/tex/latex/l3experimental/xgalley/xgalley.sty b/Master/texmf-dist/tex/latex/l3experimental/xgalley/xgalley.sty
index 160fca57631..5ebe766a12b 100644
--- a/Master/texmf-dist/tex/latex/l3experimental/xgalley/xgalley.sty
+++ b/Master/texmf-dist/tex/latex/l3experimental/xgalley/xgalley.sty
@@ -48,7 +48,7 @@
 %% -----------------------------------------------------------------------
 %%
 \RequirePackage{l3names}
-\GetIdInfo$Id: xgalley.dtx 2895 2011-10-09 15:58:19Z joseph $
+\GetIdInfo$Id: xgalley.dtx 2922 2011-10-17 19:01:04Z joseph $
   {L3 Experimental galley}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
@@ -606,11 +606,6 @@
           { \skip_eval:n { \l_galley_display_end_vspace_tl } }
       }
   }
-\RenewDocumentCommand \nobreak { }
-  { \bool_gset_true:N \g_galley_no_break_next_bool }
-\RenewDocumentCommand \noindent { }
-  { \bool_gset_false:N \g_galley_omit_next_indent_bool }
-\RenewDocumentCommand \vspace { s m } { \galley_set_vspace_user:n {#2} }
 %% 
 %%
 %% End of file `xgalley.sty'.