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+% \iffalse meta-comment
+%
+%% File: l3str.dtx
+%
+% Copyright (C) 2011-2024 The LaTeX Project
+%
+% It may be distributed and/or modified under the conditions of the
+% LaTeX Project Public License (LPPL), either version 1.3c of this
+% license or (at your option) any later version. The latest version
+% of this license is in the file
+%
+% https://www.latex-project.org/lppl.txt
+%
+% This file is part of the "l3kernel bundle" (The Work in LPPL)
+% and all files in that bundle must be distributed together.
+%
+% -----------------------------------------------------------------------
+%
+% The development version of the bundle can be found at
+%
+% https://github.com/latex3/latex3
+%
+% for those people who are interested.
+%
+%<*driver>
+\documentclass[full,kernel]{l3doc}
+\begin{document}
+ \DocInput{\jobname.dtx}
+\end{document}
+%</driver>
+% \fi
+%
+% \title{^^A
+% The \pkg{l3str} module\\ Strings^^A
+% }
+%
+% \author{^^A
+% The \LaTeX{} Project\thanks
+% {^^A
+% E-mail:
+% \href{mailto:latex-team@latex-project.org}
+% {latex-team@latex-project.org}^^A
+% }^^A
+% }
+%
+% \date{Released 2024-04-11}
+%
+% \maketitle
+%
+% \begin{documentation}
+%
+% \TeX{} associates each character with a category code: as such, there is no
+% concept of a \enquote{string} as commonly understood in many other
+% programming languages. However, there are places where we wish to manipulate
+% token lists while in some sense \enquote{ignoring} category codes: this is
+% done by treating token lists as strings in a \TeX{} sense.
+%
+% A \TeX{} string (and thus an \pkg{expl3} string) is a series of characters
+% which have category code $12$ (\enquote{other}) with the exception of
+% space characters which have category code $10$ (\enquote{space}). Thus
+% at a technical level, a \TeX{} string is a token list with the appropriate
+% category codes. In this documentation, these are simply referred to as
+% strings.
+%
+% 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
+% functions in this module which accept a token list argument first
+% convert it to a string using \cs{tl_to_str:n} for internal processing,
+% and do not treat a token list or the corresponding string
+% representation differently.
+%
+% As a string is a subset of the more general token list, it is sometimes unclear
+% when one should be used over the other.
+% Use a string variable for data that isn't primarily intended for typesetting
+% and for which a level of protection from unwanted expansion is suitable.
+% This data type simplifies comparison of variables since there are no concerns
+% about expansion of their contents.
+%
+% The functions \cs{cs_to_str:N}, \cs{tl_to_str:n}, \cs{tl_to_str:N} and
+% \cs{token_to_str:N} (and variants) generate strings from the appropriate
+% input: these are documented in \pkg{l3basics}, \pkg{l3tl} and \pkg{l3token},
+% respectively.
+%
+% Most expandable functions in this module come in three flavours:
+% \begin{itemize}
+% \item \cs[no-index]{str_\ldots{}:N}, which expect a token list or string
+% variable as their argument;
+% \item \cs[no-index]{str_\ldots{}:n}, taking any token list (or string) as an
+% argument;
+% \item \cs[no-index]{str_\ldots{}_ignore_spaces:n}, which ignores any space
+% encountered during the operation: these functions are typically
+% faster than those which take care of escaping spaces
+% appropriately.
+% \end{itemize}
+%
+% \section{Creating and initialising string variables}
+%
+% \begin{function}[added = 2015-09-18]{\str_new:N, \str_new:c}
+% \begin{syntax}
+% \cs{str_new:N} \meta{str~var}
+% \end{syntax}
+% Creates a new \meta{str~var} or raises an error if the name is
+% already taken. The declaration is global. The \meta{str~var} is
+% initially empty.
+% \end{function}
+%
+% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
+% {
+% \str_const:Nn, \str_const:NV, \str_const:Ne,
+% \str_const:cn, \str_const:cV, \str_const:ce
+% }
+% \begin{syntax}
+% \cs{str_const:Nn} \meta{str~var} \Arg{token list}
+% \end{syntax}
+% Creates a new constant \meta{str~var} or raises an error if the name
+% is already taken. The value of the \meta{str~var} is set
+% globally to the \meta{token list}, converted to a string.
+% \end{function}
+%
+% \begin{function}[added = 2015-09-18]
+% {\str_clear:N, \str_clear:c, \str_gclear:N, \str_gclear:c}
+% \begin{syntax}
+% \cs{str_clear:N} \meta{str~var}
+% \end{syntax}
+% Clears the content of the \meta{str~var}.
+% \end{function}
+%
+% \begin{function}[added = 2015-09-18]
+% {
+% \str_clear_new:N, \str_clear_new:c,
+% \str_gclear_new:N, \str_gclear_new:c
+% }
+% \begin{syntax}
+% \cs{str_clear_new:N} \meta{str~var}
+% \end{syntax}
+% Ensures that the \meta{str~var} exists globally by applying
+% \cs{str_new:N} if necessary, then applies
+% \cs[index=str_clear:N]{str_(g)clear:N} to leave
+% the \meta{str~var} empty.
+% \end{function}
+%
+% \begin{function}[added = 2015-09-18]
+% {
+% \str_set_eq:NN, \str_set_eq:cN, \str_set_eq:Nc, \str_set_eq:cc,
+% \str_gset_eq:NN, \str_gset_eq:cN, \str_gset_eq:Nc, \str_gset_eq:cc
+% }
+% \begin{syntax}
+% \cs{str_set_eq:NN} \meta{str~var_1} \meta{str~var_2}
+% \end{syntax}
+% Sets the content of \meta{str~var_1} equal to that of
+% \meta{str~var_2}.
+% \end{function}
+%
+% \begin{function}[added = 2017-10-08]
+% {
+% \str_concat:NNN, \str_concat:ccc,
+% \str_gconcat:NNN, \str_gconcat:ccc
+% }
+% \begin{syntax}
+% \cs{str_concat:NNN} \meta{str~var_1} \meta{str~var_2} \meta{str~var_3}
+% \end{syntax}
+% Concatenates the content of \meta{str~var_2} and \meta{str~var_3}
+% together and saves the result in \meta{str~var_1}. The \meta{str~var_2}
+% is placed at the left side of the new string variable.
+% The \meta{str~var_2} and \meta{str~var_3} must indeed be strings, as
+% this function does not convert their contents to a string.
+% \end{function}
+%
+% \begin{function}[EXP, pTF, added = 2015-09-18]
+% {\str_if_exist:N, \str_if_exist:c}
+% \begin{syntax}
+% \cs{str_if_exist_p:N} \meta{str~var}
+% \cs{str_if_exist:NTF} \meta{str~var} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Tests whether the \meta{str~var} is currently defined. This does not
+% check that the \meta{str~var} really is a string.
+% \end{function}
+%
+% \section{Adding data to string variables}
+%
+% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
+% {
+% \str_set:Nn, \str_set:NV, \str_set:Ne,
+% \str_set:cn, \str_set:cV, \str_set:ce,
+% \str_gset:Nn, \str_gset:NV, \str_gset:Ne,
+% \str_gset:cn, \str_gset:cV, \str_gset:ce
+% }
+% \begin{syntax}
+% \cs{str_set:Nn} \meta{str var} \Arg{token list}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string}, and stores the
+% result in \meta{str var}.
+% \end{function}
+%
+% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
+% {
+% \str_put_left:Nn, \str_put_left:NV, \str_put_left:Ne,
+% \str_put_left:cn, \str_put_left:cV, \str_put_left:ce,
+% \str_gput_left:Nn, \str_gput_left:NV, \str_gput_left:Ne,
+% \str_gput_left:cn, \str_gput_left:cV, \str_gput_left:ce
+% }
+% \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}[added = 2015-09-18, updated = 2018-07-28]
+% {
+% \str_put_right:Nn, \str_put_right:NV, \str_put_right:Ne,
+% \str_put_right:cn, \str_put_right:cV, \str_put_right:Ne,
+% \str_gput_right:Nn, \str_gput_right:NV, \str_gput_right:Ne,
+% \str_gput_right:cn, \str_gput_right:cV, \str_gput_right:ce
+% }
+% \begin{syntax}
+% \cs{str_put_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}. The current contents of the \meta{str
+% var} are not automatically converted to a string.
+% \end{function}
+%
+% \section{String conditionals}
+%
+% \begin{function}[EXP,pTF, added = 2015-09-18, updated = 2022-03-21]
+% {\str_if_empty:N, \str_if_empty:c, \str_if_empty:n}
+% \begin{syntax}
+% \cs{str_if_empty_p:N} \meta{str~var}
+% \cs{str_if_empty:NTF} \meta{str~var} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Tests if the \meta{string variable} is entirely empty
+% (\emph{i.e.}~contains no characters at all).
+% \end{function}
+%
+% \begin{function}[EXP,pTF, added = 2015-09-18]
+% {\str_if_eq:NN, \str_if_eq:Nc, \str_if_eq:cN, \str_if_eq:cc}
+% \begin{syntax}
+% \cs{str_if_eq_p:NN} \meta{str~var_1} \meta{str~var_2}
+% \cs{str_if_eq:NNTF} \meta{str~var_1} \meta{str~var_2} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Compares the content of two \meta{str variables} and
+% is logically \texttt{true} if the two contain the same characters
+% in the same order. See \cs{tl_if_eq:NNTF} to compare tokens
+% (including their category codes) rather than characters.
+% \end{function}
+%
+% \begin{function}[EXP,pTF, updated = 2018-06-18]
+% {
+% \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:vn, \str_if_eq:nv,
+% \str_if_eq:ee
+% }
+% \begin{syntax}
+% \cs{str_if_eq_p:nn} \Arg{tl_1} \Arg{tl_2}
+% \cs{str_if_eq:nnTF} \Arg{tl_1} \Arg{tl_2} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Compares the two \meta{token lists} on a character by character
+% basis (namely after converting them to strings),
+% and is \texttt{true} if the two \meta{strings} contain the same
+% characters in the same order. Thus for example
+% \begin{verbatim}
+% \str_if_eq_p:no { abc } { \tl_to_str:n { abc } }
+% \end{verbatim}
+% is logically \texttt{true}. See \cs{tl_if_eq:nnTF} to compare
+% tokens (including their category codes) rather than characters.
+% \end{function}
+%
+% \begin{function}[TF, added = 2017-10-08]{\str_if_in:Nn, \str_if_in:cn}
+% \begin{syntax}
+% \cs{str_if_in:NnTF} \meta{str~var} \Arg{token list} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} and
+% tests if that \meta{string} is found in the content of the
+% \meta{str~var}.
+% \end{function}
+%
+% \begin{function}[TF, added = 2017-10-08]{\str_if_in:nn}
+% \begin{syntax}
+% \cs{str_if_in:nnTF} \Arg{tl_1} \Arg{tl_2} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Converts both \meta{token lists} to \meta{strings} and
+% tests whether \meta{string_2} is found inside \meta{string_1}.
+% \end{function}
+%
+% \begin{function}[added = 2013-07-24, updated = 2022-03-21, EXP, noTF]
+% {
+% \str_case:nn, \str_case:Vn, \str_case:Nn, \str_case:on, \str_case:en,
+% \str_case:nV, \str_case:nv
+% }
+% \begin{syntax}
+% \cs{str_case:nnTF} \Arg{test string} \\
+% ~~|{| \\
+% ~~~~\Arg{string case_1} \Arg{code case_1} \\
+% ~~~~\Arg{string case_2} \Arg{code case_2} \\
+% ~~~~\ldots \\
+% ~~~~\Arg{string case_n} \Arg{code case_n} \\
+% ~~|}| \\
+% ~~\Arg{true code}
+% ~~\Arg{false code}
+% \end{syntax}
+% Compares the \meta{test string} in turn with each
+% of the \meta{string case}s (all token lists are converted to strings).
+% If the two are equal (as described for
+% \cs{str_if_eq:nnTF}) then the associated \meta{code} is left in the
+% input stream and other cases are discarded. If any of the
+% cases are matched, the \meta{true code} is also inserted into the
+% input stream (after the code for the appropriate case), while if none
+% match then the \meta{false code} is inserted. The function
+% \cs{str_case:nn}, which does nothing if there is no match, is also
+% available.
+%
+% This set of functions performs no expansion on each
+% \meta{string~case} argument, so any variable in there will be
+% compared as a string. If expansion is needed in the
+% \meta{string~case}s, then \cs[no-index]{str_case_e:nn(TF)} should
+% be used instead.
+% \end{function}
+%
+% \begin{function}[added = 2018-06-19, EXP, noTF]
+% {\str_case_e:nn, \str_case_e:en}
+% \begin{syntax}
+% \cs{str_case_e:nnTF} \Arg{test string} \\
+% ~~|{| \\
+% ~~~~\Arg{string case_1} \Arg{code case_1} \\
+% ~~~~\Arg{string case_2} \Arg{code case_2} \\
+% ~~~~\ldots \\
+% ~~~~\Arg{string case_n} \Arg{code case_n} \\
+% ~~|}| \\
+% ~~\Arg{true code}
+% ~~\Arg{false code}
+% \end{syntax}
+% Compares the full expansion of the \meta{test string}
+% in turn with the full expansion of the \meta{string case}s
+% (all token lists are converted to strings). If the two
+% full expansions are equal (as described for \cs{str_if_eq:eeTF}) then the
+% associated \meta{code} is left in the input stream
+% and other cases are discarded. If any of the
+% cases are matched, the \meta{true code} is also inserted into the
+% input stream (after the code for the appropriate case), while if none
+% match then the \meta{false code} is inserted. The function
+% \cs{str_case_e:nn}, which does nothing if there is no match, is also
+% available.
+% In \cs[index=str_case_e:nnTF]{str_case_e:nn(TF)}, the \meta{test string}
+% is expanded in each comparison, and must always yield the same result:
+% for example, random numbers must not be used within this string.
+% \end{function}
+%
+% \begin{function}[EXP, pTF, added = 2021-05-17]{\str_compare:nNn, \str_compare:eNe}
+% \begin{syntax}
+% \cs{str_compare_p:nNn} \Arg{tl_1} \meta{relation} \Arg{tl_2}
+% \cs{str_compare:nNnTF} \Arg{tl_1} \meta{relation} \Arg{tl_2} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Compares the two \meta{token lists} on a character by character
+% basis (namely after converting them to strings) in a lexicographic
+% order according to the character codes of the characters. The
+% \meta{relation} can be |<|, |=|, or~|>| and the test is
+% \texttt{true} under the following conditions:
+% \begin{itemize}
+% \item for |<|, if the first string is earlier than the second in lexicographic order;
+% \item for |=|, if the two strings have exactly the same characters;
+% \item for |>|, if the first string is later than the second in lexicographic order.
+% \end{itemize}
+% Thus for example the following is logically \texttt{true}:
+% \begin{verbatim}
+% \str_compare_p:nNn { ab } < { abc }
+% \end{verbatim}
+% \begin{texnote}
+% This is a wrapper around the \TeX{} primitive
+% \cs[index=pdfstrcmp]{(pdf)strcmp}. It is meant for programming
+% and not for sorting textual contents, as it simply considers
+% character codes and not more elaborate considerations of grapheme
+% clusters, locale, etc.
+% \end{texnote}
+% \end{function}
+%
+% \section{Mapping over strings}
+%
+% All mappings are done at the current group level, \emph{i.e.}~any
+% local assignments made by the \meta{function} or \meta{code} discussed
+% below remain in effect after the loop.
+%
+% \begin{function}[added = 2017-11-14, rEXP]
+% {\str_map_function:nN, \str_map_function:NN, \str_map_function:cN}
+% \begin{syntax}
+% \cs{str_map_function:nN} \Arg{token list} \meta{function}
+% \cs{str_map_function:NN} \meta{str~var} \meta{function}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} then
+% applies \meta{function} to every \meta{character} in the
+% \meta{string} including spaces.
+% \end{function}
+%
+% \begin{function}[added = 2017-11-14]
+% {\str_map_inline:nn, \str_map_inline:Nn, \str_map_inline:cn}
+% \begin{syntax}
+% \cs{str_map_inline:nn} \Arg{token list} \Arg{inline function}
+% \cs{str_map_inline:Nn} \meta{str~var} \Arg{inline function}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} then
+% applies the \meta{inline function} to every \meta{character} in the
+% \meta{str~var} including spaces.
+% The \meta{inline function} should consist of code which
+% receives the \meta{character} as |#1|.
+% \end{function}
+%
+% \begin{function}[rEXP, added = 2021-05-05]
+% {\str_map_tokens:nn, \str_map_tokens:Nn, \str_map_tokens:cn}
+% \begin{syntax}
+% \cs{str_map_tokens:nn} \Arg{token list} \Arg{code}
+% \cs{str_map_tokens:Nn} \meta{str~var} \Arg{code}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} then applies
+% \meta{code} to every \meta{character} in the \meta{string} including
+% spaces. The \meta{code} receives each character as a trailing brace
+% group. This is equivalent to \cs{str_map_function:nN} if the
+% \meta{code} consists of a single function.
+% \end{function}
+%
+% \begin{function}[added = 2017-11-14]
+% {\str_map_variable:nNn, \str_map_variable:NNn, \str_map_variable:cNn}
+% \begin{syntax}
+% \cs{str_map_variable:nNn} \Arg{token list} \meta{variable} \Arg{code}
+% \cs{str_map_variable:NNn} \meta{str~var} \meta{variable} \Arg{code}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} then stores each
+% \meta{character} in the \meta{string} (including spaces) in turn in
+% the (string or token list) \meta{variable} and applies the
+% \meta{code}. The \meta{code} will usually make use of the
+% \meta{variable}, but this is not enforced. The assignments to the
+% \meta{variable} are local. Its value after the loop is the last
+% \meta{character} in the \meta{string}, or its original value if the
+% \meta{string} is empty. See also \cs{str_map_inline:Nn}.
+% \end{function}
+%
+% \begin{function}[added = 2017-10-08, rEXP]{\str_map_break:}
+% \begin{syntax}
+% \cs{str_map_break:}
+% \end{syntax}
+% Used to terminate a \cs[no-index]{str_map_\ldots} function before all
+% characters in the \meta{string} have been processed. This
+% normally takes place within a conditional statement, for example
+% \begin{verbatim}
+% \str_map_inline:Nn \l_my_str
+% {
+% \str_if_eq:nnT { #1 } { bingo } { \str_map_break: }
+% % Do something useful
+% }
+% \end{verbatim}
+% See also \cs{str_map_break:n}.
+% Use outside of a \cs[no-index]{str_map_\ldots} scenario leads to low
+% level \TeX{} errors.
+% \begin{texnote}
+% When the mapping is broken, additional tokens may be inserted
+% before continuing with the
+% code that follows the loop.
+% This depends on the design of the mapping function.
+% \end{texnote}
+% \end{function}
+%
+% \begin{function}[added = 2017-10-08, rEXP]{\str_map_break:n}
+% \begin{syntax}
+% \cs{str_map_break:n} \Arg{code}
+% \end{syntax}
+% Used to terminate a \cs[no-index]{str_map_\ldots} function before all
+% characters in the \meta{string} have been processed, inserting
+% the \meta{code} after the mapping has ended. This
+% normally takes place within a conditional statement, for example
+% \begin{verbatim}
+% \str_map_inline:Nn \l_my_str
+% {
+% \str_if_eq:nnT { #1 } { bingo }
+% { \str_map_break:n { <code> } }
+% % Do something useful
+% }
+% \end{verbatim}
+% Use outside of a \cs[no-index]{str_map_\ldots} scenario leads to low
+% level \TeX{} errors.
+% \begin{texnote}
+% When the mapping is broken, additional tokens may be inserted
+% before the \meta{code} is
+% inserted into the input stream.
+% This depends on the design of the mapping function.
+% \end{texnote}
+% \end{function}
+%
+% \section{Working with the content of strings}
+%
+% \begin{function}[EXP, added = 2015-09-18]{\str_use:N, \str_use:c}
+% \begin{syntax}
+% \cs{str_use:N} \meta{str~var}
+% \end{syntax}
+% Recovers the content of a \meta{str~var} and places it
+% directly in the input stream. An error is raised if the variable
+% does not exist or if it is invalid. Note that it is possible to use
+% a \meta{str} directly without an accessor function.
+% \end{function}
+%
+% \begin{function}[EXP, added = 2015-09-18]
+% {\str_count:N, \str_count:c, \str_count:n, \str_count_ignore_spaces:n}
+% \begin{syntax}
+% \cs{str_count:n} \Arg{token list}
+% \end{syntax}
+% Leaves in the input stream the number of characters in the string
+% representation of \meta{token list}, as an integer denotation. The
+% functions differ in their treatment of spaces. In the case of
+% \cs{str_count:N} and \cs{str_count:n}, all characters including
+% spaces are counted. The \cs{str_count_ignore_spaces:n} function
+% leaves the number of non-space characters in the input stream.
+% \end{function}
+%
+% \begin{function}[EXP, added = 2015-09-18]
+% {\str_count_spaces:N, \str_count_spaces:c, \str_count_spaces:n}
+% \begin{syntax}
+% \cs{str_count_spaces:n} \Arg{token list}
+% \end{syntax}
+% Leaves in the input stream the number of space characters in the
+% string representation of \meta{token list}, as an integer
+% denotation. Of course, this function has no \texttt{_ignore_spaces}
+% variant.
+% \end{function}
+%
+% \begin{function}[EXP, added = 2015-09-18]
+% {\str_head:N, \str_head:c, \str_head:n, \str_head_ignore_spaces:n}
+% \begin{syntax}
+% \cs{str_head:n} \Arg{token list}
+% \end{syntax}
+% Converts the \meta{token list} into a \meta{string}. The first
+% character in the \meta{string} is then left in the input stream,
+% with category code \enquote{other}. The functions differ if the
+% first character is a space: \cs{str_head:N} and \cs{str_head:n}
+% return a space token with category code~$10$ (blank space), while
+% the \cs{str_head_ignore_spaces:n} function ignores this space
+% character and leaves the first non-space character in the input
+% stream. If the \meta{string} is empty (or only contains spaces in
+% the case of the \texttt{_ignore_spaces} function), then nothing is
+% left on the input stream.
+% \end{function}
+%
+% \begin{function}[EXP, added = 2015-09-18]
+% {\str_tail:N, \str_tail:c, \str_tail:n, \str_tail_ignore_spaces:n}
+% \begin{syntax}
+% \cs{str_tail:n} \Arg{token list}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string}, removes the first
+% character, and leaves the remaining characters (if any) in the input
+% stream, with category codes $12$ and $10$ (for spaces). The
+% functions differ in the case where the first character is a space:
+% \cs{str_tail:N} and \cs{str_tail:n} only trim that space, while
+% \cs{str_tail_ignore_spaces:n} removes the first non-space character
+% and any space before it. 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}
+%
+% \begin{function}[EXP, added = 2015-09-18]
+% {\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}
+% Converts the \meta{token list} to a \meta{string}, and leaves in the
+% input stream the character in position \meta{integer expression} of
+% the \meta{string}, starting at $1$ for the first (left-most)
+% character. In the case of \cs{str_item:Nn} and \cs{str_item:nn},
+% all characters including spaces are taken into account. The
+% \cs{str_item_ignore_spaces:nn} function skips spaces when counting
+% characters. If the \meta{integer expression} is negative,
+% characters are counted from the end of the \meta{string}. Hence,
+% $-1$ is the right-most character, \emph{etc.}
+% \end{function}
+%
+% \begin{function}[EXP, added = 2015-09-18]
+% {
+% \str_range:Nnn, \str_range:cnn, \str_range:nnn,
+% \str_range_ignore_spaces:nnn
+% }
+% \begin{syntax}
+% \cs{str_range: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 from the \meta{start index} to the
+% \meta{end index} inclusive. Spaces are preserved and counted as items
+% (contrast this with \cs{tl_range:nnn} where spaces are not counted as
+% items and are possibly discarded from the output).
+%
+% Here \meta{start index} and \meta{end index} should be integer denotations.
+% For describing in detail the functions' behavior, let $m$ and $n$ be the start
+% and end index respectively. If either is $0$, the result is empty. A positive
+% index means `start counting from the left end', a negative index means
+% `start counting from the right end'. Let $l$ be the count of the token list.
+%
+% The \emph{actual start point} is determined as $M=m$ if~$m>0$ and as $M=l+m+1$
+% if~$m<0$. Similarly the \emph{actual end point} is $N=n$ if~$n>0$ and $N=l+n+1$
+% if~$n<0$. If $M>N$, the result is empty. Otherwise it consists of all items from
+% position $M$ to position $N$ inclusive; for the purpose of this rule, we can
+% imagine that the token list extends at infinity on either side, with void items
+% at positions $s$ for $s\le0$ or $s>l$.
+% For instance,
+% \begin{verbatim}
+% \iow_term:e { \str_range:nnn { abcdef } { 2 } { 5 } }
+% \iow_term:e { \str_range:nnn { abcdef } { -4 } { -1 } }
+% \iow_term:e { \str_range:nnn { abcdef } { -2 } { -1 } }
+% \iow_term:e { \str_range:nnn { abcdef } { 0 } { -1 } }
+% \end{verbatim}
+% prints \texttt{bcde}, \texttt{cdef}, \texttt{ef}, and an empty
+% line to the terminal. The \meta{start index} must always be smaller than
+% or equal to the \meta{end index}: if this is not the case then no output
+% is generated. Thus
+% \begin{verbatim}
+% \iow_term:e { \str_range:nnn { abcdef } { 5 } { 2 } }
+% \iow_term:e { \str_range:nnn { abcdef } { -1 } { -4 } }
+% \end{verbatim}
+% both yield empty strings.
+% \end{function}
+%
+% ^^A If this stays in the same {function} environment, we get a really
+% ^^A awful page break. Perhaps we should add a way to allow a page break
+% ^^A in a function environment...
+% The behavior of \cs{str_range_ignore_spaces:nnn} is similar, but spaces
+% are removed before starting the job. The input
+% \begin{verbatim}
+% \iow_term:e { \str_range:nnn { abcdefg } { 2 } { 5 } }
+% \iow_term:e { \str_range:nnn { abcdefg } { 2 } { -3 } }
+% \iow_term:e { \str_range:nnn { abcdefg } { -6 } { 5 } }
+% \iow_term:e { \str_range:nnn { abcdefg } { -6 } { -3 } }
+%
+% \iow_term:e { \str_range:nnn { abc~efg } { 2 } { 5 } }
+% \iow_term:e { \str_range:nnn { abc~efg } { 2 } { -3 } }
+% \iow_term:e { \str_range:nnn { abc~efg } { -6 } { 5 } }
+% \iow_term:e { \str_range:nnn { abc~efg } { -6 } { -3 } }
+%
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcdefg } { 2 } { 5 } }
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcdefg } { 2 } { -3 } }
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcdefg } { -6 } { 5 } }
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcdefg } { -6 } { -3 } }
+%
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcd~efg } { 2 } { 5 } }
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcd~efg } { 2 } { -3 } }
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcd~efg } { -6 } { 5 } }
+% \iow_term:e { \str_range_ignore_spaces:nnn { abcd~efg } { -6 } { -3 } }
+% \end{verbatim}
+% will print four instances of |bcde|, four instances of |bc e| and eight
+% instances of |bcde|.
+% ^^A\end{function}
+%
+% \section{Modifying string variables}
+%
+% \begin{function}[added = 2017-10-08]
+% {
+% \str_replace_once:Nnn, \str_replace_once:cnn,
+% \str_greplace_once:Nnn, \str_greplace_once:cnn
+% }
+% \begin{syntax}
+% \cs{str_replace_once:Nnn} \meta{str~var} \Arg{old} \Arg{new}
+% \end{syntax}
+% Converts the \meta{old} and \meta{new} token lists to strings, then
+% replaces the first (leftmost) occurrence of \meta{old string} in the
+% \meta{str~var} with \meta{new string}.
+% \end{function}
+%
+% \begin{function}[added = 2017-10-08]
+% {
+% \str_replace_all:Nnn, \str_replace_all:cnn,
+% \str_greplace_all:Nnn, \str_greplace_all:cnn
+% }
+% \begin{syntax}
+% \cs{str_replace_all:Nnn} \meta{str~var} \Arg{old} \Arg{new}
+% \end{syntax}
+% Converts the \meta{old} and \meta{new} token lists to strings, then
+% replaces all occurrences of \meta{old string} in the
+% \meta{str~var} with \meta{new string}.
+% As this function
+% operates from left to right, the pattern \meta{old string}
+% may remain after the replacement (see \cs{str_remove_all:Nn}
+% for an example).
+% \end{function}
+%
+% \begin{function}[added = 2017-10-08]
+% {
+% \str_remove_once:Nn, \str_remove_once:cn,
+% \str_gremove_once:Nn, \str_gremove_once:cn
+% }
+% \begin{syntax}
+% \cs{str_remove_once:Nn} \meta{str~var} \Arg{token list}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} then
+% removes the first (leftmost) occurrence of \meta{string} from the
+% \meta{str~var}.
+% \end{function}
+%
+% \begin{function}[added = 2017-10-08]
+% {
+% \str_remove_all:Nn, \str_remove_all:cn,
+% \str_gremove_all:Nn, \str_gremove_all:cn
+% }
+% \begin{syntax}
+% \cs{str_remove_all:Nn} \meta{str~var} \Arg{token list}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{string} then
+% removes all occurrences of \meta{string} from the
+% \meta{str~var}.
+% As this function
+% operates from left to right, the pattern \meta{string}
+% may remain after the removal, for instance,
+% \begin{quote}
+% \cs{str_set:Nn} \cs{l_tmpa_str} |{abbccd}|
+% \cs{str_remove_all:Nn} \cs{l_tmpa_str} |{bc}|
+% \end{quote}
+% results in \cs{l_tmpa_str} containing \texttt{abcd}.
+% \end{function}
+%
+% \section{String manipulation}
+%
+% \begin{function}[EXP, added = 2019-11-26]
+% {
+% \str_lowercase:n, \str_lowercase:f,
+% \str_uppercase:n, \str_uppercase:f
+% }
+% \begin{syntax}
+% \cs{str_lowercase:n} \Arg{tokens}
+% \cs{str_uppercase:n} \Arg{tokens}
+% \end{syntax}
+% Converts the input \meta{tokens} to their string representation, as
+% described for \cs{tl_to_str:n}, and then to the lower or upper
+% case representation using a one-to-one mapping as described by the
+% Unicode Consortium file |UnicodeData.txt|.
+%
+% These functions are intended for case changing programmatic data in
+% places where upper/lower case distinctions are meaningful. One example
+% would be automatically generating a function name from user input where
+% some case changing is needed. In this situation the input is programmatic,
+% not textual, case does have meaning and a language-independent one-to-one
+% mapping is appropriate. For example
+% \begin{verbatim}
+% \cs_new_protected:Npn \myfunc:nn #1#2
+% {
+% \cs_set_protected:cpn
+% {
+% user
+% \str_uppercase:f { \tl_head:n {#1} }
+% \str_lowercase:f { \tl_tail:n {#1} }
+% }
+% { #2 }
+% }
+% \end{verbatim}
+% would be used to generate a function with an auto-generated name consisting
+% of the upper case equivalent of the supplied name followed by the lower
+% case equivalent of the rest of the input.
+%
+% These functions should \emph{not} be used for
+% \begin{itemize}
+% \item Caseless comparisons: use \cs{str_casefold:n} for this
+% situation (case folding is distinct from lower casing).
+% \item Case changing text for typesetting: see the
+% \cs[index=text_lowercase:n]{text_lowercase:n(n)},
+% \cs[index=text_uppercase:n]{text_uppercase:n(n)} and
+% \cs[index=text_titlecase_all:n]{text_titlecase_(all|once):n(n)} functions which
+% correctly deal with context-dependence and other factors appropriate
+% to text case changing.
+% \end{itemize}
+% \end{function}
+%
+% \begin{function}[EXP, added = 2022-10-16]
+% {\str_casefold:n, \str_casefold:V}
+% \begin{syntax}
+% \cs{str_casefold:n} \Arg{tokens}
+% \end{syntax}
+% Converts the input \meta{tokens} to their string representation, as
+% described for \cs{tl_to_str:n}, and then folds the case of the resulting
+% \meta{string} to remove case information. The result of this process is
+% left in the input stream.
+%
+% String folding is a process used for material such as identifiers rather
+% than for \enquote{text}. The folding provided by \cs{str_casefold:n}
+% follows the mappings provided by the \href{http://www.unicode.org}^^A
+% {Unicode Consortium}, who
+% \href{http://www.unicode.org/faq/casemap_charprop.html#2}{state}:
+% \begin{quote}
+% Case folding is primarily used for caseless comparison of text, such
+% as identifiers in a computer program, rather than actual text
+% transformation. Case folding in Unicode is based on the lowercase
+% mapping, but includes additional changes to the source text to help make
+% it language-insensitive and consistent. As a result, case-folded text
+% should be used solely for internal processing and generally should not be
+% stored or displayed to the end user.
+% \end{quote}
+% The folding approach implemented by \cs{str_casefold:n} follows the
+% \enquote{full} scheme defined by the Unicode Consortium
+% (\emph{e.g.}~\SS folds to \texttt{SS}). As case-folding is
+% a language-insensitive process, there is no special treatment of
+% Turkic input (\emph{i.e.}~\texttt{I} always folds to \texttt{i} and
+% not to \texttt{\i}).
+% \end{function}
+%
+% \begin{function}[added = 2023-05-19, EXP]{\str_mdfive_hash:n, \str_mdfive_hash:e}
+% \begin{syntax}
+% \cs{str_mdfive_hash:n} \Arg{tl}
+% \end{syntax}
+% Expands to the MD5 sum generated from the \meta{tl}, which is converted
+% to a \meta{string} as described for \cs{tl_to_str:n}.
+% \end{function}
+%
+% \section{Viewing strings}
+%
+% \begin{function}[added = 2015-09-18, updated = 2021-04-29]
+% {\str_show:N, \str_show:c, \str_show:n}
+% \begin{syntax}
+% \cs{str_show:N} \meta{str~var}
+% \end{syntax}
+% Displays the content of the \meta{str~var} on the terminal.
+% \end{function}
+%
+% \begin{function}[added = 2019-02-15, updated = 2021-04-29]
+% {\str_log:N, \str_log:c, \str_log:n}
+% \begin{syntax}
+% \cs{str_log:N} \meta{str~var}
+% \end{syntax}
+% Writes the content of the \meta{str~var} in the log file.
+% \end{function}
+%
+% \section{Constant strings}
+%
+% \begin{variable}[added = 2015-09-19, updated = 2020-12-22, module = str]
+% {
+% \c_ampersand_str,
+% \c_atsign_str,
+% \c_backslash_str,
+% \c_left_brace_str,
+% \c_right_brace_str,
+% \c_circumflex_str,
+% \c_colon_str,
+% \c_dollar_str,
+% \c_hash_str,
+% \c_percent_str,
+% \c_tilde_str,
+% \c_underscore_str,
+% \c_zero_str
+% }
+% Constant strings, containing a single character token, with category
+% code $12$.
+% \end{variable}
+%
+% \begin{variable}[added = 2023-12-07]{\c_empty_str}
+% Constant that is always empty.
+% \end{variable}
+%
+% \section{Scratch strings}
+%
+% \begin{variable}{\l_tmpa_str, \l_tmpb_str}
+% Scratch strings for local assignment. These are never used by
+% the kernel code, and so are safe for use with any \LaTeX3-defined
+% function. However, they may be overwritten by other non-kernel
+% code and so should only be used for short-term storage.
+% \end{variable}
+%
+% \begin{variable}{\g_tmpa_str, \g_tmpb_str}
+% Scratch strings for global assignment. These are never used by
+% the kernel code, and so are safe for use with any \LaTeX3-defined
+% function. However, they may be overwritten by other non-kernel
+% code and so should only be used for short-term storage.
+% \end{variable}
+%
+% \end{documentation}
+%
+% \begin{implementation}
+%
+% \section{\pkg{l3str} implementation}
+%
+% \begin{macrocode}
+%<*package>
+% \end{macrocode}
+%
+% \begin{macrocode}
+%<@@=str>
+% \end{macrocode}
+%
+% \subsection{Internal auxiliaries}
+%
+% \begin{variable}{\s_@@_mark,\s_@@_stop}
+% Internal scan marks.
+% \begin{macrocode}
+\scan_new:N \s_@@_mark
+\scan_new:N \s_@@_stop
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{macro}[EXP]{
+% \@@_use_none_delimit_by_s_stop:w,
+% \@@_use_i_delimit_by_s_stop:nw
+% }
+% Functions to gobble up to a scan mark.
+% \begin{macrocode}
+\cs_new:Npn \@@_use_none_delimit_by_s_stop:w #1 \s_@@_stop { }
+\cs_new:Npn \@@_use_i_delimit_by_s_stop:nw #1 #2 \s_@@_stop {#1}
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{variable}{\q_@@_recursion_tail,\q_@@_recursion_stop}
+% Internal recursion quarks.
+% \begin{macrocode}
+\quark_new:N \q_@@_recursion_tail
+\quark_new:N \q_@@_recursion_stop
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{macro}[EXP]{
+% \@@_if_recursion_tail_break:NN,
+% \@@_if_recursion_tail_stop_do:Nn
+% }
+% Functions to query recursion quarks.
+% \begin{macrocode}
+\__kernel_quark_new_test:N \@@_if_recursion_tail_break:NN
+\__kernel_quark_new_test:N \@@_if_recursion_tail_stop_do:Nn
+% \end{macrocode}
+% \end{macro}
+%
+% \subsection{Creating and setting string variables}
+%
+% \begin{macro}
+% {
+% \str_new:N, \str_new:c,
+% \str_use:N, \str_use:c,
+% \str_clear:N, \str_clear:c,
+% \str_gclear:N,\str_gclear:c,
+% \str_clear_new:N, \str_clear_new:c,
+% \str_gclear_new:N, \str_gclear_new:c
+% }
+% \begin{macro}
+% {
+% \str_set_eq:NN, \str_set_eq:cN, \str_set_eq:Nc, \str_set_eq:cc,
+% \str_gset_eq:NN, \str_gset_eq:cN, \str_gset_eq:Nc, \str_gset_eq:cc
+% }
+% \begin{macro}
+% {\str_concat:NNN, \str_concat:ccc, \str_gconcat:NNN, \str_gconcat:ccc}
+% A string is simply a token list. The full mapping system isn't set up
+% yet so do things by hand.
+% \begin{macrocode}
+\group_begin:
+ \cs_set_protected:Npn \@@_tmp:n #1
+ {
+ \tl_if_blank:nF {#1}
+ {
+ \cs_new_eq:cc { str_ #1 :N } { tl_ #1 :N }
+ \exp_args:Nc \cs_generate_variant:Nn { str_ #1 :N } { c }
+ \@@_tmp:n
+ }
+ }
+ \@@_tmp:n
+ { new }
+ { use }
+ { clear }
+ { gclear }
+ { clear_new }
+ { gclear_new }
+ { }
+\group_end:
+\cs_new_eq:NN \str_set_eq:NN \tl_set_eq:NN
+\cs_new_eq:NN \str_gset_eq:NN \tl_gset_eq:NN
+\cs_generate_variant:Nn \str_set_eq:NN { c , Nc , cc }
+\cs_generate_variant:Nn \str_gset_eq:NN { c , Nc , cc }
+\cs_new_eq:NN \str_concat:NNN \tl_concat:NNN
+\cs_new_eq:NN \str_gconcat:NNN \tl_gconcat:NNN
+\cs_generate_variant:Nn \str_concat:NNN { ccc }
+\cs_generate_variant:Nn \str_gconcat:NNN { ccc }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}
+% {
+% \str_set:Nn, \str_set:NV, \str_set:Ne, \str_set:Nx,
+% \str_set:cn, \str_set:cV, \str_set:ce, \str_set:cx,
+% \str_gset:Nn, \str_gset:NV, \str_gset:Ne, \str_gset:Nx,
+% \str_gset:cn, \str_gset:cV, \str_gset:ce, \str_gset:cx,
+% \str_const:Nn, \str_const:NV, \str_const:Ne, \str_const:Nx,
+% \str_const:cn, \str_const:cV, \str_const:ce, \str_const:cx,
+% \str_put_left:Nn, \str_put_left:NV, \str_put_left:Ne, \str_put_left:Nx,
+% \str_put_left:cn, \str_put_left:cV, \str_put_left:ce, \str_put_left:cx,
+% \str_gput_left:Nn, \str_gput_left:NV, \str_gput_left:Ne, \str_gput_left:Nx,
+% \str_gput_left:cn, \str_gput_left:cV, \str_gput_left:ce, \str_gput_left:cx,
+% \str_put_right:Nn, \str_put_right:NV, \str_put_right:Ne, \str_put_right:Nx,
+% \str_put_right:cn, \str_put_right:cV, \str_put_right:ce, \str_put_right:cx,
+% \str_gput_right:Nn, \str_gput_right:NV, \str_gput_right:Ne, \str_gput_right:Nx,
+% \str_gput_right:cn, \str_gput_right:cV, \str_gput_right:ce, \str_gput_right:cx
+% }
+% Similar to corresponding \pkg{l3tl} base functions, except that
+% \cs{__kernel_exp_not:w} is replaced with \cs{__kernel_tl_to_str:w}.
+% Just like token list, string constants use \cs{cs_gset_nopar:Npe}
+% instead of \cs{__kernel_tl_gset:Nx} so that the scope checking for
+% |c| is applied when \pkg{l3debug} is used.
+% To maintain backward compatibility, in
+% \cs[index=str_put_left:Nn]{str_(g)put_left:Nn} and
+% \cs[index=str_put_right:Nn]{str_(g)put_right:Nn},
+% contents of string variables are wrapped in \cs{__kernel_exp_not:w}
+% to prevent further expansion.
+% \begin{macrocode}
+\cs_new_protected:Npn \str_set:Nn #1#2
+ { \__kernel_tl_set:Nx #1 { \__kernel_tl_to_str:w {#2} } }
+\cs_gset_protected:Npn \str_gset:Nn #1#2
+ { \__kernel_tl_gset:Nx #1 { \__kernel_tl_to_str:w {#2} } }
+\cs_new_protected:Npn \str_const:Nn #1#2
+ {
+ \__kernel_chk_if_free_cs:N #1
+ \cs_gset_nopar:Npe #1 { \__kernel_tl_to_str:w {#2} }
+ }
+\cs_new_protected:Npn \str_put_left:Nn #1#2
+ {
+ \__kernel_tl_set:Nx #1
+ { \__kernel_tl_to_str:w {#2} \__kernel_exp_not:w \exp_after:wN {#1} }
+ }
+\cs_new_protected:Npn \str_gput_left:Nn #1#2
+ {
+ \__kernel_tl_gset:Nx #1
+ { \__kernel_tl_to_str:w {#2} \__kernel_exp_not:w \exp_after:wN {#1} }
+ }
+\cs_new_protected:Npn \str_put_right:Nn #1#2
+ {
+ \__kernel_tl_set:Nx #1
+ { \__kernel_exp_not:w \exp_after:wN {#1} \__kernel_tl_to_str:w {#2} }
+ }
+\cs_new_protected:Npn \str_gput_right:Nn #1#2
+ {
+ \__kernel_tl_gset:Nx #1
+ { \__kernel_exp_not:w \exp_after:wN {#1} \__kernel_tl_to_str:w {#2} }
+ }
+\cs_generate_variant:Nn \str_set:Nn { NV , Ne , Nx , c , cV , ce , cx }
+\cs_generate_variant:Nn \str_gset:Nn { NV , Ne , Nx , c , cV , ce , cx }
+\cs_generate_variant:Nn \str_const:Nn { NV , Ne , Nx , c , cV , ce , cx }
+\cs_generate_variant:Nn \str_put_left:Nn { NV , Ne , Nx , c , cV , ce , cx }
+\cs_generate_variant:Nn \str_gput_left:Nn { NV , Ne , Nx , c , cV , ce , cx }
+\cs_generate_variant:Nn \str_put_right:Nn { NV , Ne , Nx , c , cV , ce , cx }
+\cs_generate_variant:Nn \str_gput_right:Nn { NV , Ne , Nx , c , cV , ce , cx }
+% \end{macrocode}
+% \end{macro}
+%
+% \subsection{Modifying string variables}
+%
+% \begin{macro}
+% {
+% \str_replace_all:Nnn, \str_replace_all:cnn,
+% \str_greplace_all:Nnn, \str_greplace_all:cnn,
+% \str_replace_once:Nnn, \str_replace_once:cnn,
+% \str_greplace_once:Nnn, \str_greplace_once:cnn
+% }
+% \begin{macro}{\@@_replace:NNNnn}
+% \begin{macro}{\@@_replace_aux:NNNnnn}
+% \begin{macro}{\@@_replace_next:w}
+% Start by applying \cs{tl_to_str:n} to convert the old and new token
+% lists to strings, and also apply \cs{tl_to_str:N} to avoid any
+% issues if we are fed a token list variable. Then the code is a much
+% simplified version of the token list code because neither the
+% delimiter nor the replacement can contain macro parameters or
+% braces. The delimiter \cs{s_@@_mark} cannot appear in the string to
+% edit so it is used in all cases. Some |e|-expansion is unnecessary.
+% There is no need to avoid losing braces nor to protect against
+% expansion. The ending code is much simplified and does not need to
+% hide in braces.
+% \begin{macrocode}
+\cs_new_protected:Npn \str_replace_once:Nnn
+ { \@@_replace:NNNnn \prg_do_nothing: \__kernel_tl_set:Nx }
+\cs_new_protected:Npn \str_greplace_once:Nnn
+ { \@@_replace:NNNnn \prg_do_nothing: \__kernel_tl_gset:Nx }
+\cs_new_protected:Npn \str_replace_all:Nnn
+ { \@@_replace:NNNnn \@@_replace_next:w \__kernel_tl_set:Nx }
+\cs_new_protected:Npn \str_greplace_all:Nnn
+ { \@@_replace:NNNnn \@@_replace_next:w \__kernel_tl_gset:Nx }
+\cs_generate_variant:Nn \str_replace_once:Nnn { c }
+\cs_generate_variant:Nn \str_greplace_once:Nnn { c }
+\cs_generate_variant:Nn \str_replace_all:Nnn { c }
+\cs_generate_variant:Nn \str_greplace_all:Nnn { c }
+\cs_new_protected:Npn \@@_replace:NNNnn #1#2#3#4#5
+ {
+ \tl_if_empty:nTF {#4}
+ {
+ \msg_error:nne { kernel } { empty-search-pattern } {#5}
+ }
+ {
+ \use:e
+ {
+ \exp_not:n { \@@_replace_aux:NNNnnn #1 #2 #3 }
+ { \tl_to_str:N #3 }
+ { \tl_to_str:n {#4} } { \tl_to_str:n {#5} }
+ }
+ }
+ }
+\cs_new_protected:Npn \@@_replace_aux:NNNnnn #1#2#3#4#5#6
+ {
+ \cs_set:Npn \@@_replace_next:w ##1 #5 { ##1 #6 #1 }
+ #2 #3
+ {
+ \@@_replace_next:w
+ #4
+ \@@_use_none_delimit_by_s_stop:w
+ #5
+ \s_@@_stop
+ }
+ }
+\cs_new_eq:NN \@@_replace_next:w ?
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\str_remove_once:Nn, \str_remove_once:cn}
+% \begin{macro}{\str_gremove_once:Nn, \str_gremove_once:cn}
+% Removal is just a special case of replacement.
+% \begin{macrocode}
+\cs_new_protected:Npn \str_remove_once:Nn #1#2
+ { \str_replace_once:Nnn #1 {#2} { } }
+\cs_new_protected:Npn \str_gremove_once:Nn #1#2
+ { \str_greplace_once:Nnn #1 {#2} { } }
+\cs_generate_variant:Nn \str_remove_once:Nn { c }
+\cs_generate_variant:Nn \str_gremove_once:Nn { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\str_remove_all:Nn, \str_remove_all:cn}
+% \begin{macro}{\str_gremove_all:Nn, \str_gremove_all:cn}
+% Removal is just a special case of replacement.
+% \begin{macrocode}
+\cs_new_protected:Npn \str_remove_all:Nn #1#2
+ { \str_replace_all:Nnn #1 {#2} { } }
+\cs_new_protected:Npn \str_gremove_all:Nn #1#2
+ { \str_greplace_all:Nnn #1 {#2} { } }
+\cs_generate_variant:Nn \str_remove_all:Nn { c }
+\cs_generate_variant:Nn \str_gremove_all:Nn { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{String comparisons}
+%
+% \begin{macro}[pTF, EXP]
+% {
+% \str_if_empty:N, \str_if_empty:c, \str_if_empty:n,
+% \str_if_exist:N, \str_if_exist:c
+% }
+% More copy-paste!
+% \begin{macrocode}
+\prg_new_eq_conditional:NNn \str_if_exist:N \tl_if_exist:N
+ { p , T , F , TF }
+\prg_new_eq_conditional:NNn \str_if_exist:c \tl_if_exist:c
+ { p , T , F , TF }
+\prg_new_eq_conditional:NNn \str_if_empty:N \tl_if_empty:N
+ { p , T , F , TF }
+\prg_new_eq_conditional:NNn \str_if_empty:c \tl_if_empty:c
+ { p , T , F , TF }
+\prg_new_eq_conditional:NNn \str_if_empty:n \tl_if_empty:n
+ { p , T , F , TF }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[EXP]{\@@_if_eq:nn}
+% String comparisons rely on the primitive \tn[index=pdfstrcmp]{(pdf)strcmp},
+% so we define a new name for it.
+% \begin{macrocode}
+\cs_new_eq:NN \@@_if_eq:nn \tex_strcmp:D
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[pTF, EXP]{\str_compare:nNn, \str_compare:eNe}
+% Simply rely on \cs{@@_if_eq:nn}, which expands to |-1|, |0|
+% or~|1|. The |ee| version is created directly because it is more efficient.
+% \begin{macrocode}
+\prg_new_conditional:Npnn \str_compare:nNn #1#2#3 { p , T , F , TF }
+ {
+ \if_int_compare:w
+ \@@_if_eq:nn { \exp_not:n {#1} } { \exp_not:n {#3} }
+ #2 \c_zero_int
+ \prg_return_true: \else: \prg_return_false: \fi:
+ }
+\prg_new_conditional:Npnn \str_compare:eNe #1#2#3 { p , T , F , TF }
+ {
+ \if_int_compare:w \@@_if_eq:nn {#1} {#3} #2 \c_zero_int
+ \prg_return_true: \else: \prg_return_false: \fi:
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[pTF, EXP]
+% {
+% \str_if_eq:nn, \str_if_eq:Vn, \str_if_eq:on, \str_if_eq:nV,
+% \str_if_eq:no, \str_if_eq:VV,
+% \str_if_eq:ee
+% }
+% Modern engines provide a direct way of comparing two token lists,
+% but returning a number. This set of conditionals therefore makes life
+% a bit clearer. The \texttt{nn} and \texttt{ee} versions are created
+% directly as this is most efficient. Since \cs{@@_if_eq:nn} will expand to
+% |0| as an explicit character with category 12 if the two lists match (and
+% either |-1| or |1| if they don't) we can use \cs{if:w} here which is faster
+% than using \cs{if_int_compare:w}.
+% \begin{macrocode}
+\prg_new_conditional:Npnn \str_if_eq:nn #1#2 { p , T , F , TF }
+ {
+ \if:w 0 \@@_if_eq:nn { \exp_not:n {#1} } { \exp_not:n {#2} }
+ \prg_return_true: \else: \prg_return_false: \fi:
+ }
+\prg_generate_conditional_variant:Nnn \str_if_eq:nn
+ { V , v , o , nV , no , VV , nv } { p , T , F , TF }
+\prg_new_conditional:Npnn \str_if_eq:ee #1#2 { p , T , F , TF }
+ {
+ \if:w 0 \@@_if_eq:nn {#1} {#2}
+ \prg_return_true: \else: \prg_return_false: \fi:
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[EXP, pTF]
+% {\str_if_eq:NN, \str_if_eq:Nc, \str_if_eq:cN, \str_if_eq:cc}
+% Note that \cs{str_if_eq:NNTF} is different from
+% \cs{tl_if_eq:NNTF} because it needs to ignore category codes.
+% \begin{macrocode}
+\prg_new_conditional:Npnn \str_if_eq:NN #1#2 { p , TF , T , F }
+ {
+ \if:w 0 \@@_if_eq:nn { \tl_to_str:N #1 } { \tl_to_str:N #2 }
+ \prg_return_true: \else: \prg_return_false: \fi:
+ }
+\prg_generate_conditional_variant:Nnn \str_if_eq:NN
+ { c , Nc , cc } { T , F , TF , p }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[TF]{\str_if_in:Nn, \str_if_in:cn, \str_if_in:nn}
+% Everything here needs to be detokenized but beyond that it is a
+% simple token list test. It would be faster to fine-tune the |T|,
+% |F|, |TF| variants by calling the appropriate variant of
+% \cs{tl_if_in:nnTF} directly but that takes more code.
+% \begin{macrocode}
+\prg_new_protected_conditional:Npnn \str_if_in:Nn #1#2 { T , F , TF }
+ {
+ \use:e
+ { \tl_if_in:nnTF { \tl_to_str:N #1 } { \tl_to_str:n {#2} } }
+ { \prg_return_true: } { \prg_return_false: }
+ }
+\prg_generate_conditional_variant:Nnn \str_if_in:Nn
+ { c } { T , F , TF }
+\prg_new_protected_conditional:Npnn \str_if_in:nn #1#2 { T , F , TF }
+ {
+ \use:e
+ { \tl_if_in:nnTF { \tl_to_str:n {#1} } { \tl_to_str:n {#2} } }
+ { \prg_return_true: } { \prg_return_false: }
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[EXP, noTF]
+% {
+% \str_case:nn, \str_case:Vn, \str_case:Nn, \str_case:on, \str_case:en, \str_case:nV, \str_case:nv,
+% \str_case_e:nn, \str_case_e:en
+% }
+% \begin{macro}[EXP]{\@@_case:nnTF, \@@_case_e:nnTF}
+% \begin{macro}[EXP]
+% {\@@_case:nw, \@@_case_e:nw, \@@_case_end:nw}
+% The aim here is to allow the case statement to be evaluated
+% using a known number of expansion steps (two), and without
+% needing to use an explicit \enquote{end of recursion} marker.
+% That is achieved by using the test input as the final case,
+% as this is always true. The trick is then to tidy up
+% the output such that the appropriate case code plus either
+% the \texttt{true} or \texttt{false} branch code is inserted.
+% \begin{macrocode}
+\cs_new:Npn \str_case:nn #1#2
+ {
+ \exp:w
+ \@@_case:nnTF {#1} {#2} { } { }
+ }
+\cs_new:Npn \str_case:nnT #1#2#3
+ {
+ \exp:w
+ \@@_case:nnTF {#1} {#2} {#3} { }
+ }
+\cs_new:Npn \str_case:nnF #1#2
+ {
+ \exp:w
+ \@@_case:nnTF {#1} {#2} { }
+ }
+\cs_new:Npn \str_case:nnTF #1#2
+ {
+ \exp:w
+ \@@_case:nnTF {#1} {#2}
+ }
+\cs_new:Npn \@@_case:nnTF #1#2#3#4
+ { \@@_case:nw {#1} #2 {#1} { } \s_@@_mark {#3} \s_@@_mark {#4} \s_@@_stop }
+\cs_generate_variant:Nn \str_case:nn { V , o , e , nV , nv }
+\prg_generate_conditional_variant:Nnn \str_case:nn
+ { V , o , e , nV , nv } { T , F , TF }
+\cs_new_eq:NN \str_case:Nn \str_case:Vn
+\cs_new_eq:NN \str_case:NnT \str_case:VnT
+\cs_new_eq:NN \str_case:NnF \str_case:VnF
+\cs_new_eq:NN \str_case:NnTF \str_case:VnTF
+\cs_new:Npn \@@_case:nw #1#2#3
+ {
+ \str_if_eq:nnTF {#1} {#2}
+ { \@@_case_end:nw {#3} }
+ { \@@_case:nw {#1} }
+ }
+\cs_new:Npn \str_case_e:nn #1#2
+ {
+ \exp:w
+ \@@_case_e:nnTF {#1} {#2} { } { }
+ }
+\cs_new:Npn \str_case_e:nnT #1#2#3
+ {
+ \exp:w
+ \@@_case_e:nnTF {#1} {#2} {#3} { }
+ }
+\cs_new:Npn \str_case_e:nnF #1#2
+ {
+ \exp:w
+ \@@_case_e:nnTF {#1} {#2} { }
+ }
+\cs_new:Npn \str_case_e:nnTF #1#2
+ {
+ \exp:w
+ \@@_case_e:nnTF {#1} {#2}
+ }
+\cs_new:Npn \@@_case_e:nnTF #1#2#3#4
+ { \@@_case_e:nw {#1} #2 {#1} { } \s_@@_mark {#3} \s_@@_mark {#4} \s_@@_stop }
+\cs_generate_variant:Nn \str_case_e:nn { e }
+\prg_generate_conditional_variant:Nnn \str_case_e:nn { e } { T , F , TF }
+\cs_new:Npn \@@_case_e:nw #1#2#3
+ {
+ \str_if_eq:eeTF {#1} {#2}
+ { \@@_case_end:nw {#3} }
+ { \@@_case_e:nw {#1} }
+ }
+% \end{macrocode}
+% To tidy up the recursion, there are two outcomes. If there was a hit to
+% one of the cases searched for, then |#1| is the code to insert,
+% |#2| is the \emph{next} case to check on and |#3| is all of
+% the rest of the cases code. That means that |#4| is the \texttt{true}
+% branch code, and |#5| tidies up the spare \cs{s_@@_mark} and the
+% \texttt{false} branch. On the other hand, if none of the cases matched
+% then we arrive here using the \enquote{termination} case of comparing
+% the search with itself. That means that |#1| is empty, |#2| is
+% the first \cs{s_@@_mark} and so |#4| is the \texttt{false} code (the
+% \texttt{true} code is mopped up by |#3|).
+% \begin{macrocode}
+\cs_new:Npn \@@_case_end:nw #1#2#3 \s_@@_mark #4#5 \s_@@_stop
+ { \exp_end: #1 #4 }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Mapping over strings}
+%
+% \begin{macro}[rEXP]{\str_map_function:NN, \str_map_function:cN}
+% \begin{macro}[rEXP]{\str_map_function:nN}
+% \begin{macro}{\str_map_inline:Nn, \str_map_inline:cn}
+% \begin{macro}{\str_map_inline:nn}
+% \begin{macro}{\str_map_variable:NNn, \str_map_variable:cNn}
+% \begin{macro}{\str_map_variable:nNn}
+% \begin{macro}{\str_map_break:}
+% \begin{macro}{\str_map_break:n}
+% \begin{macro}[rEXP]{\@@_map_function:w, \@@_map_function:nn}
+% \begin{macro}{\@@_map_inline:NN, \@@_map_variable:NnN}
+% The inline and variable mappings are similar to the usual token list
+% mappings but start out by turning the argument to an ``other
+% string''. Doing the same for the expandable function mapping would
+% require \cs{__kernel_str_to_other:n}, quadratic in the string length. To deal
+% with spaces in that case, \cs{@@_map_function:w} replaces the
+% following space by a braced space and a further call to itself.
+% These are received by \cs{@@_map_function:nn}, which passes
+% the space to |#1| and calls \cs{@@_map_function:w} to deal with the
+% next space. The space before the braced space allows to optimize
+% the \cs{q_@@_recursion_tail} test. Of course we need to include a
+% trailing space (the question mark is needed to avoid losing the
+% space when \TeX{} tokenizes the line).
+% At the cost of about three more auxiliaries this code could get a $9$
+% times speed up by testing only every $9$-th character for whether it
+% is \cs{q_@@_recursion_tail} (also by converting $9$ spaces at a time in
+% the \cs{str_map_function:nN} case).
+%
+% For the \texttt{map_variable} functions we use a string assignment
+% to store each character because spaces are made catcode~$12$ before
+% the loop.
+% \begin{macrocode}
+\cs_new:Npn \str_map_function:nN #1#2
+ {
+ \exp_after:wN \@@_map_function:w
+ \exp_after:wN \@@_map_function:nn \exp_after:wN #2
+ \__kernel_tl_to_str:w {#1}
+ \q_@@_recursion_tail ? ~
+ \prg_break_point:Nn \str_map_break: { }
+ }
+\cs_new:Npn \str_map_function:NN
+ { \exp_args:No \str_map_function:nN }
+\cs_new:Npn \@@_map_function:w #1 ~
+ { #1 { ~ { ~ } \@@_map_function:w } }
+\cs_new:Npn \@@_map_function:nn #1#2
+ {
+ \if_meaning:w \q_@@_recursion_tail #2
+ \exp_after:wN \str_map_break:
+ \fi:
+ #1 #2 \@@_map_function:nn {#1}
+ }
+\cs_generate_variant:Nn \str_map_function:NN { c }
+\cs_new_protected:Npn \str_map_inline:nn #1#2
+ {
+ \int_gincr:N \g__kernel_prg_map_int
+ \cs_gset_protected:cpn
+ { @@_map_ \int_use:N \g__kernel_prg_map_int :w } ##1 {#2}
+ \use:e
+ {
+ \exp_not:N \@@_map_inline:NN
+ \exp_not:c { @@_map_ \int_use:N \g__kernel_prg_map_int :w }
+ \__kernel_str_to_other_fast:n {#1}
+ }
+ \q_@@_recursion_tail
+ \prg_break_point:Nn \str_map_break:
+ { \int_gdecr:N \g__kernel_prg_map_int }
+ }
+\cs_new_protected:Npn \str_map_inline:Nn
+ { \exp_args:No \str_map_inline:nn }
+\cs_generate_variant:Nn \str_map_inline:Nn { c }
+\cs_new:Npn \@@_map_inline:NN #1#2
+ {
+ \@@_if_recursion_tail_break:NN #2 \str_map_break:
+ \exp_args:No #1 { \token_to_str:N #2 }
+ \@@_map_inline:NN #1
+ }
+\cs_new_protected:Npn \str_map_variable:nNn #1#2#3
+ {
+ \use:e
+ {
+ \exp_not:n { \@@_map_variable:NnN #2 {#3} }
+ \__kernel_str_to_other_fast:n {#1}
+ }
+ \q_@@_recursion_tail
+ \prg_break_point:Nn \str_map_break: { }
+ }
+\cs_new_protected:Npn \str_map_variable:NNn
+ { \exp_args:No \str_map_variable:nNn }
+\cs_new_protected:Npn \@@_map_variable:NnN #1#2#3
+ {
+ \@@_if_recursion_tail_break:NN #3 \str_map_break:
+ \str_set:Nn #1 {#3}
+ \use:n {#2}
+ \@@_map_variable:NnN #1 {#2}
+ }
+\cs_generate_variant:Nn \str_map_variable:NNn { c }
+\cs_new:Npn \str_map_break:
+ { \prg_map_break:Nn \str_map_break: { } }
+\cs_new:Npn \str_map_break:n
+ { \prg_map_break:Nn \str_map_break: }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[rEXP]{\str_map_tokens:Nn, \str_map_tokens:cn}
+% \begin{macro}[rEXP]{\str_map_tokens:nn}
+% Uses an auxiliary of \cs{str_map_function:NN}.
+% \begin{macrocode}
+\cs_new:Npn \str_map_tokens:nn #1#2
+ {
+ \exp_args:Nno \use:nn
+ { \@@_map_function:w \@@_map_function:nn {#2} }
+ { \__kernel_tl_to_str:w {#1} }
+ \q_@@_recursion_tail ? ~
+ \prg_break_point:Nn \str_map_break: { }
+ }
+\cs_new:Npn \str_map_tokens:Nn { \exp_args:No \str_map_tokens:nn }
+\cs_generate_variant:Nn \str_map_tokens:Nn { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Accessing specific characters in a string}
+%
+% \begin{macro}[EXP]{\__kernel_str_to_other:n}
+% \begin{macro}[EXP]{\@@_to_other_loop:w, \@@_to_other_end:w}
+% First apply \cs{tl_to_str:n}, then replace all spaces by
+% \enquote{other} spaces, $8$ at a time, storing the converted part of
+% the string between the \cs{s_@@_mark} and \cs{s_@@_stop} markers. The end
+% is detected when \cs{@@_to_other_loop:w} finds one of the trailing
+% |A|, distinguished from any contents of the initial token list by
+% their category. Then \cs{@@_to_other_end:w} is called, and finds
+% the result between \cs{s_@@_mark} and the first |A| (well, there is
+% also the need to remove a space).
+% \begin{macrocode}
+\cs_new:Npn \__kernel_str_to_other:n #1
+ {
+ \exp_after:wN \@@_to_other_loop:w
+ \tl_to_str:n {#1} ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ \s_@@_mark \s_@@_stop
+ }
+\group_begin:
+\tex_lccode:D `\* = `\ %
+\tex_lccode:D `\A = `\A %
+\tex_lowercase:D
+ {
+ \group_end:
+ \cs_new:Npn \@@_to_other_loop:w
+ #1 ~ #2 ~ #3 ~ #4 ~ #5 ~ #6 ~ #7 ~ #8 ~ #9 \s_@@_stop
+ {
+ \if_meaning:w A #8
+ \@@_to_other_end:w
+ \fi:
+ \@@_to_other_loop:w
+ #9 #1 * #2 * #3 * #4 * #5 * #6 * #7 * #8 * \s_@@_stop
+ }
+ \cs_new:Npn \@@_to_other_end:w \fi: #1 \s_@@_mark #2 * A #3 \s_@@_stop
+ { \fi: #2 }
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[rEXP]{\__kernel_str_to_other_fast:n}
+% \begin{macro}[rEXP]{\__kernel_str_to_other_fast_loop:w, \@@_to_other_fast_end:w}
+% The difference with \cs{__kernel_str_to_other:n} is that the converted part is
+% left in the input stream, making these commands only
+% restricted-expandable.
+% \begin{macrocode}
+\cs_new:Npn \__kernel_str_to_other_fast:n #1
+ {
+ \exp_after:wN \@@_to_other_fast_loop:w \tl_to_str:n {#1} ~
+ A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ A ~ \s_@@_stop
+ }
+\group_begin:
+\tex_lccode:D `\* = `\ %
+\tex_lccode:D `\A = `\A %
+\tex_lowercase:D
+ {
+ \group_end:
+ \cs_new:Npn \@@_to_other_fast_loop:w
+ #1 ~ #2 ~ #3 ~ #4 ~ #5 ~ #6 ~ #7 ~ #8 ~ #9 ~
+ {
+ \if_meaning:w A #9
+ \@@_to_other_fast_end:w
+ \fi:
+ #1 * #2 * #3 * #4 * #5 * #6 * #7 * #8 * #9
+ \@@_to_other_fast_loop:w *
+ }
+ \cs_new:Npn \@@_to_other_fast_end:w #1 * A #2 \s_@@_stop {#1}
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]
+% {\str_item:Nn, \str_item:cn, \str_item:nn, \str_item_ignore_spaces:nn}
+% \begin{macro}[EXP]{\@@_item:nn, \@@_item:w}
+% The \cs{str_item:nn} hands its argument with spaces escaped to
+% \cs{@@_item:nn}, and makes sure to turn the result back into
+% a proper string (with category code~$10$ spaces) eventually. The
+% \cs{str_item_ignore_spaces:nn} function does not escape spaces,
+% which are thus ignored by \cs{@@_item:nn} since
+% everything else is done with undelimited arguments.
+% Evaluate the \meta{index} argument~|#2| and count characters in
+% the string, passing those two numbers to \cs{@@_item:w} for
+% further analysis. If the \meta{index} is negative, shift it by
+% the \meta{count} to know the how many character to discard, and if
+% that is still negative give an empty result. If the \meta{index}
+% is larger than the \meta{count}, give an empty result, and
+% otherwise discard $\meta{index}-1$ characters before returning the
+% following one. The shift by $-1$ is obtained by inserting an empty
+% brace group before the string in that case: that brace group also
+% covers the case where the \meta{index} is zero.
+% \begin{macrocode}
+\cs_new:Npn \str_item:Nn { \exp_args:No \str_item:nn }
+\cs_generate_variant:Nn \str_item:Nn { c }
+\cs_new:Npn \str_item:nn #1#2
+ {
+ \exp_args:Nf \tl_to_str:n
+ {
+ \exp_args:Nf \@@_item:nn
+ { \__kernel_str_to_other:n {#1} } {#2}
+ }
+ }
+\cs_new:Npn \str_item_ignore_spaces:nn #1
+ { \exp_args:No \@@_item:nn { \tl_to_str:n {#1} } }
+\cs_new:Npn \@@_item:nn #1#2
+ {
+ \exp_after:wN \@@_item:w
+ \int_value:w \int_eval:n {#2} \exp_after:wN ;
+ \int_value:w \@@_count:n {#1} ;
+ #1 \s_@@_stop
+ }
+\cs_new:Npn \@@_item:w #1; #2;
+ {
+ \int_compare:nNnTF {#1} < 0
+ {
+ \int_compare:nNnTF {#1} < {-#2}
+ { \@@_use_none_delimit_by_s_stop:w }
+ {
+ \exp_after:wN \@@_use_i_delimit_by_s_stop:nw
+ \exp:w \exp_after:wN \@@_skip_exp_end:w
+ \int_value:w \int_eval:n { #1 + #2 } ;
+ }
+ }
+ {
+ \int_compare:nNnTF {#1} > {#2}
+ { \@@_use_none_delimit_by_s_stop:w }
+ {
+ \exp_after:wN \@@_use_i_delimit_by_s_stop:nw
+ \exp:w \@@_skip_exp_end:w #1 ; { }
+ }
+ }
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]{\@@_skip_exp_end:w}
+% \begin{macro}[EXP]
+% {\@@_skip_loop:wNNNNNNNN, \@@_skip_end:w, \@@_skip_end:NNNNNNNN}
+% Removes |max(#1,0)| characters from the input stream, and then
+% leaves \cs{exp_end:}. This should be expanded using
+% \cs{exp:w}. We remove characters $8$ at a time until
+% there are at most $8$ to remove. Then we do a dirty trick: the
+% \cs{if_case:w} construction leaves between $0$ and $8$ times the
+% \cs{or:} control sequence, and those \cs{or:} become arguments of
+% \cs{@@_skip_end:NNNNNNNN}. If the number of characters to remove
+% is $6$, say, then there are two \cs{or:} left, and the $8$ arguments
+% of \cs{@@_skip_end:NNNNNNNN} are the two \cs{or:}, and $6$
+% characters from the input stream, exactly what we wanted to
+% remove. Then close the \cs{if_case:w} conditional with \cs{fi:}, and
+% stop the initial expansion with \cs{exp_end:} (see places where
+% \cs{@@_skip_exp_end:w} is called).
+% \begin{macrocode}
+\cs_new:Npn \@@_skip_exp_end:w #1;
+ {
+ \if_int_compare:w #1 > 8 \exp_stop_f:
+ \exp_after:wN \@@_skip_loop:wNNNNNNNN
+ \else:
+ \exp_after:wN \@@_skip_end:w
+ \int_value:w \int_eval:w
+ \fi:
+ #1 ;
+ }
+\cs_new:Npn \@@_skip_loop:wNNNNNNNN #1; #2#3#4#5#6#7#8#9
+ {
+ \exp_after:wN \@@_skip_exp_end:w
+ \int_value:w \int_eval:n { #1 - 8 } ;
+ }
+\cs_new:Npn \@@_skip_end:w #1 ;
+ {
+ \exp_after:wN \@@_skip_end:NNNNNNNN
+ \if_case:w #1 \exp_stop_f: \or: \or: \or: \or: \or: \or: \or: \or:
+ }
+\cs_new:Npn \@@_skip_end:NNNNNNNN #1#2#3#4#5#6#7#8 { \fi: \exp_end: }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]
+% {\str_range:Nnn, \str_range:nnn, \str_range_ignore_spaces:nnn}
+% \begin{macro}[EXP]{\@@_range:nnn}
+% \begin{macro}[EXP]{\@@_range:w, \@@_range:nnw}
+% Sanitize the string. Then evaluate the arguments. At this stage we
+% also decrement the \meta{start index}, since our goal is to know how
+% many characters should be removed. Then limit the range to be
+% non-negative and at most the length of the string (this avoids
+% needing to check for the end of the string when grabbing
+% characters), shifting negative numbers by the appropriate amount.
+% Afterwards, skip characters, then keep some more, and finally drop
+% the end of the string.
+% \begin{macrocode}
+\cs_new:Npn \str_range:Nnn { \exp_args:No \str_range:nnn }
+\cs_generate_variant:Nn \str_range:Nnn { c }
+\cs_new:Npn \str_range:nnn #1#2#3
+ {
+ \exp_args:Nf \tl_to_str:n
+ {
+ \exp_args:Nf \@@_range:nnn
+ { \__kernel_str_to_other:n {#1} } {#2} {#3}
+ }
+ }
+\cs_new:Npn \str_range_ignore_spaces:nnn #1
+ { \exp_args:No \@@_range:nnn { \tl_to_str:n {#1} } }
+\cs_new:Npn \@@_range:nnn #1#2#3
+ {
+ \exp_after:wN \@@_range:w
+ \int_value:w \@@_count:n {#1} \exp_after:wN ;
+ \int_value:w \int_eval:n { (#2) - 1 } \exp_after:wN ;
+ \int_value:w \int_eval:n {#3} ;
+ #1 \s_@@_stop
+ }
+\cs_new:Npn \@@_range:w #1; #2; #3;
+ {
+ \exp_args:Nf \@@_range:nnw
+ { \@@_range_normalize:nn {#2} {#1} }
+ { \@@_range_normalize:nn {#3} {#1} }
+ }
+\cs_new:Npn \@@_range:nnw #1#2
+ {
+ \exp_after:wN \@@_collect_delimit_by_q_stop:w
+ \int_value:w \int_eval:n { #2 - #1 } \exp_after:wN ;
+ \exp:w \@@_skip_exp_end:w #1 ;
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \begin{macro}[EXP]{\@@_range_normalize:nn}
+% This function converts an \meta{index} argument into an explicit
+% position in the string (a result of $0$ denoting \enquote{out of
+% bounds}). Expects two explicit integer arguments: the
+% \meta{index} |#1| and the string count~|#2|. If |#1| is negative,
+% replace it by $|#1| + |#2| + 1$, then limit to the range $[0,
+% |#2|]$.
+% \begin{macrocode}
+\cs_new:Npn \@@_range_normalize:nn #1#2
+ {
+ \int_eval:n
+ {
+ \if_int_compare:w #1 < \c_zero_int
+ \if_int_compare:w #1 < -#2 \exp_stop_f:
+ 0
+ \else:
+ #1 + #2 + 1
+ \fi:
+ \else:
+ \if_int_compare:w #1 < #2 \exp_stop_f:
+ #1
+ \else:
+ #2
+ \fi:
+ \fi:
+ }
+ }
+% \end{macrocode}
+% \end{macro}
+% \begin{macro}[EXP]{\@@_collect_delimit_by_q_stop:w}
+% \begin{macro}[EXP]
+% {
+% \@@_collect_loop:wn, \@@_collect_loop:wnNNNNNNN,
+% \@@_collect_end:wn, \@@_collect_end:nnnnnnnnw
+% }
+% Collects |max(#1,0)| characters, and removes everything else until
+% \cs{s_@@_stop}. This is somewhat similar to \cs{@@_skip_exp_end:w}, but
+% accepts integer expression arguments. This time we can only grab
+% $7$ characters at a time. At the end, we use an \cs{if_case:w}
+% trick again, so that the $8$ first arguments of
+% \cs{@@_collect_end:nnnnnnnnw} are some \cs{or:}, followed by an
+% \cs{fi:}, followed by |#1| characters from the input stream. Simply
+% leaving this in the input stream closes the conditional properly
+% and the \cs{or:} disappear.
+% \begin{macrocode}
+\cs_new:Npn \@@_collect_delimit_by_q_stop:w #1;
+ { \@@_collect_loop:wn #1 ; { } }
+\cs_new:Npn \@@_collect_loop:wn #1 ;
+ {
+ \if_int_compare:w #1 > 7 \exp_stop_f:
+ \exp_after:wN \@@_collect_loop:wnNNNNNNN
+ \else:
+ \exp_after:wN \@@_collect_end:wn
+ \fi:
+ #1 ;
+ }
+\cs_new:Npn \@@_collect_loop:wnNNNNNNN #1; #2 #3#4#5#6#7#8#9
+ {
+ \exp_after:wN \@@_collect_loop:wn
+ \int_value:w \int_eval:n { #1 - 7 } ;
+ { #2 #3#4#5#6#7#8#9 }
+ }
+\cs_new:Npn \@@_collect_end:wn #1 ;
+ {
+ \exp_after:wN \@@_collect_end:nnnnnnnnw
+ \if_case:w \if_int_compare:w #1 > \c_zero_int
+ #1 \else: 0 \fi: \exp_stop_f:
+ \or: \or: \or: \or: \or: \or: \fi:
+ }
+\cs_new:Npn \@@_collect_end:nnnnnnnnw #1#2#3#4#5#6#7#8 #9 \s_@@_stop
+ { #1#2#3#4#5#6#7#8 }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Counting characters}
+%
+% \begin{macro}[EXP]
+% {\str_count_spaces:N, \str_count_spaces:c, \str_count_spaces:n}
+% \begin{macro}[EXP]{\@@_count_spaces_loop:w}
+% To speed up this function, we grab and discard $9$ space-delimited
+% arguments in each iteration of the loop. The loop stops when the
+% last argument is one of the trailing |X|\meta{number}, and that
+% \meta{number} is added to the sum of $9$ that precedes, to adjust
+% the result.
+% \begin{macrocode}
+\cs_new:Npn \str_count_spaces:N
+ { \exp_args:No \str_count_spaces:n }
+\cs_generate_variant:Nn \str_count_spaces:N { c }
+\cs_new:Npn \str_count_spaces:n #1
+ {
+ \int_eval:n
+ {
+ \exp_after:wN \@@_count_spaces_loop:w
+ \tl_to_str:n {#1} ~
+ X 7 ~ X 6 ~ X 5 ~ X 4 ~ X 3 ~ X 2 ~ X 1 ~ X 0 ~ X -1 ~
+ \s_@@_stop
+ }
+ }
+\cs_new:Npn \@@_count_spaces_loop:w #1~#2~#3~#4~#5~#6~#7~#8~#9~
+ {
+ \if_meaning:w X #9
+ \@@_use_i_delimit_by_s_stop:nw
+ \fi:
+ 9 + \@@_count_spaces_loop:w
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]
+% {\str_count:N, \str_count:c, \str_count:n, \str_count_ignore_spaces:n}
+% \begin{macro}[EXP]{\@@_count:n}
+% \begin{macro}[EXP]{\@@_count_aux:n, \@@_count_loop:NNNNNNNNN}
+% To count characters in a string we could first escape all spaces
+% using \cs{__kernel_str_to_other:n}, then pass the result to \cs{tl_count:n}.
+% However, the escaping step would be quadratic in the number of
+% characters in the string, and we can do better. Namely, sum the
+% number of spaces (\cs{str_count_spaces:n}) and the result of
+% \cs{tl_count:n}, which ignores spaces. Since strings tend to be
+% longer than token lists, we use specialized functions to count
+% characters ignoring spaces. Namely, loop, grabbing $9$ non-space
+% characters at each step, and end as soon as we reach one of the $9$
+% trailing items. The internal function \cs{@@_count:n}, used in
+% \cs{str_item:nn} and \cs{str_range:nnn}, is similar to
+% \cs{str_count_ignore_spaces:n} but expects its argument to already
+% be a string or a string with spaces escaped.
+% \begin{macrocode}
+\cs_new:Npn \str_count:N { \exp_args:No \str_count:n }
+\cs_generate_variant:Nn \str_count:N { c }
+\cs_new:Npn \str_count:n #1
+ {
+ \@@_count_aux:n
+ {
+ \str_count_spaces:n {#1}
+ + \exp_after:wN \@@_count_loop:NNNNNNNNN \tl_to_str:n {#1}
+ }
+ }
+\cs_new:Npn \@@_count:n #1
+ {
+ \@@_count_aux:n
+ { \@@_count_loop:NNNNNNNNN #1 }
+ }
+\cs_new:Npn \str_count_ignore_spaces:n #1
+ {
+ \@@_count_aux:n
+ { \exp_after:wN \@@_count_loop:NNNNNNNNN \tl_to_str:n {#1} }
+ }
+\cs_new:Npn \@@_count_aux:n #1
+ {
+ \int_eval:n
+ {
+ #1
+ { X 8 } { X 7 } { X 6 }
+ { X 5 } { X 4 } { X 3 }
+ { X 2 } { X 1 } { X 0 }
+ \s_@@_stop
+ }
+ }
+\cs_new:Npn \@@_count_loop:NNNNNNNNN #1#2#3#4#5#6#7#8#9
+ {
+ \if_meaning:w X #9
+ \exp_after:wN \@@_use_none_delimit_by_s_stop:w
+ \fi:
+ 9 + \@@_count_loop:NNNNNNNNN
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{The first character in a string}
+%
+% \begin{macro}[EXP]
+% {\str_head:N, \str_head:c, \str_head:n, \str_head_ignore_spaces:n}
+% \begin{macro}[EXP]{\@@_head:w}
+% The \texttt{_ignore_spaces} variant applies \cs{tl_to_str:n} then
+% grabs the first item, thus skipping spaces.
+% As usual, \cs{str_head:N} expands its argument and
+% hands it to \cs{str_head:n}. To circumvent the fact that \TeX{}
+% skips spaces when grabbing undelimited macro parameters,
+% \cs{@@_head:w} takes an argument delimited by a space. If |#1|
+% starts with a non-space character, \cs{@@_use_i_delimit_by_s_stop:nw}
+% leaves that in the input stream. On the other hand, if |#1| starts
+% with a space, the \cs{@@_head:w} takes an empty argument, and the
+% single (initially braced) space in the definition of \cs{@@_head:w}
+% makes its way to the output. Finally, for an empty argument, the
+% (braced) empty brace group in the definition of \cs{str_head:n}
+% gives an empty result after passing through
+% \cs{@@_use_i_delimit_by_s_stop:nw}.
+% \begin{macrocode}
+\cs_new:Npn \str_head:N { \exp_args:No \str_head:n }
+\cs_generate_variant:Nn \str_head:N { c }
+\cs_new:Npn \str_head:n #1
+ {
+ \exp_after:wN \@@_head:w
+ \tl_to_str:n {#1}
+ { { } } ~ \s_@@_stop
+ }
+\cs_new:Npn \@@_head:w #1 ~ %
+ { \@@_use_i_delimit_by_s_stop:nw #1 { ~ } }
+\cs_new:Npn \str_head_ignore_spaces:n #1
+ {
+ \exp_after:wN \@@_use_i_delimit_by_s_stop:nw
+ \tl_to_str:n {#1} { } \s_@@_stop
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]
+% {\str_tail:N, \str_tail:c, \str_tail:n, \str_tail_ignore_spaces:n}
+% \begin{macro}[EXP]{\@@_tail_auxi:w, \@@_tail_auxii:w}
+% Getting the tail is a little bit more convoluted than the head of a
+% string. We hit the front of the string with \cs{reverse_if:N}
+% \cs{if_charcode:w} \cs{scan_stop:}. This removes the first
+% character, and necessarily makes the test true, since the character
+% cannot match \cs{scan_stop:}. The auxiliary function then inserts
+% the required \cs{fi:} to close the conditional, and leaves the tail
+% of the string in the input stream. The details are such that an
+% empty string has an empty tail (this requires in particular that the
+% end-marker |X| be unexpandable and not a control sequence). The
+% \texttt{_ignore_spaces} is rather simpler: after converting the
+% input to a string, \cs{@@_tail_auxii:w} removes one undelimited
+% argument and leaves everything else until an end-marker \cs{s_@@_mark}.
+% One can check that an empty (or blank) string yields an empty
+% tail.
+% \begin{macrocode}
+\cs_new:Npn \str_tail:N { \exp_args:No \str_tail:n }
+\cs_generate_variant:Nn \str_tail:N { c }
+\cs_new:Npn \str_tail:n #1
+ {
+ \exp_after:wN \@@_tail_auxi:w
+ \reverse_if:N \if_charcode:w
+ \scan_stop: \tl_to_str:n {#1} X X \s_@@_stop
+ }
+\cs_new:Npn \@@_tail_auxi:w #1 X #2 \s_@@_stop { \fi: #1 }
+\cs_new:Npn \str_tail_ignore_spaces:n #1
+ {
+ \exp_after:wN \@@_tail_auxii:w
+ \tl_to_str:n {#1} \s_@@_mark \s_@@_mark \s_@@_stop
+ }
+\cs_new:Npn \@@_tail_auxii:w #1 #2 \s_@@_mark #3 \s_@@_stop { #2 }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{String manipulation}
+%
+% \begin{macro}[EXP]
+% {
+% \str_casefold:n, \str_casefold:V,
+% \str_lowercase:n, \str_lowercase:f,
+% \str_uppercase:n, \str_uppercase:f
+% }
+% \begin{macro}[EXP]{\@@_change_case:nn}
+% \begin{macro}[EXP]{\@@_change_case_aux:nn}
+% \begin{macro}[EXP]{\@@_change_case_result:n}
+% \begin{macro}[EXP]{\@@_change_case_output:nw, \@@_change_case_output:fw}
+% \begin{macro}[EXP]{\@@_change_case_end:nw}
+% \begin{macro}[EXP]{\@@_change_case_loop:nw}
+% \begin{macro}[EXP]{\@@_change_case_space:n}
+% \begin{macro}[EXP]
+% {\@@_change_case_char:nN, \@@_change_case_char_auxi:nN, \@@_change_case_char_auxii:nN}
+% \begin{macro}[EXP]{\@@_change_case_codepoint:nN}
+% \begin{macro}[EXP]{\@@_change_case_codepoint:nNN}
+% \begin{macro}[EXP]{\@@_change_case_codepoint:nNNN}
+% \begin{macro}[EXP]{\@@_change_case_codepoint:nNNNN}
+% \begin{macro}[EXP]{\@@_change_case_char:nnn, \@@_change_case_char_aux:nnn}
+% \begin{macro}[EXP]{\@@_change_case_char:nnnnn}
+% Case changing for programmatic reasons is done by first detokenizing
+% input then doing a simple loop that only has to worry about spaces
+% and everything else. The output is detokenized to allow data sharing
+% with text-based case changing. Similarly, for $8$-bit engines the
+% multi-byte information is shared.
+% \begin{macrocode}
+\cs_new:Npn \str_casefold:n #1 { \@@_change_case:nn {#1} { casefold } }
+\cs_new:Npn \str_lowercase:n #1 { \@@_change_case:nn {#1} { lowercase } }
+\cs_new:Npn \str_uppercase:n #1 { \@@_change_case:nn {#1} { uppercase } }
+\cs_generate_variant:Nn \str_casefold:n { V }
+\cs_generate_variant:Nn \str_lowercase:n { f }
+\cs_generate_variant:Nn \str_uppercase:n { f }
+\cs_new:Npn \@@_change_case:nn #1
+ {
+ \exp_after:wN \@@_change_case_aux:nn \exp_after:wN
+ { \tl_to_str:n {#1} }
+ }
+\cs_new:Npn \@@_change_case_aux:nn #1#2
+ {
+ \@@_change_case_loop:nw {#2} #1 \q_@@_recursion_tail \q_@@_recursion_stop
+ \@@_change_case_result:n { }
+ }
+\cs_new:Npn \@@_change_case_output:nw #1#2 \@@_change_case_result:n #3
+ { #2 \@@_change_case_result:n { #3 #1 } }
+\cs_generate_variant:Nn \@@_change_case_output:nw { f }
+\cs_new:Npn \@@_change_case_end:wn #1 \@@_change_case_result:n #2
+ { \tl_to_str:n {#2} }
+\cs_new:Npn \@@_change_case_loop:nw #1#2 \q_@@_recursion_stop
+ {
+ \tl_if_head_is_space:nTF {#2}
+ { \@@_change_case_space:n }
+ { \@@_change_case_char:nN }
+ {#1} #2 \q_@@_recursion_stop
+ }
+\exp_last_unbraced:NNNNo
+ \cs_new:Npn \@@_change_case_space:n #1 \c_space_tl
+ {
+ \@@_change_case_output:nw { ~ }
+ \@@_change_case_loop:nw {#1}
+ }
+\cs_new:Npn \@@_change_case_char:nN #1#2
+ {
+ \@@_if_recursion_tail_stop_do:Nn #2
+ { \@@_change_case_end:wn }
+ \@@_change_case_codepoint:nN {#1} #2
+ }
+\if_int_compare:w 0
+ \cs_if_exist:NT \tex_XeTeXversion:D { 1 }
+ \cs_if_exist:NT \tex_luatexversion:D { 1 }
+ > 0 \exp_stop_f:
+ \cs_new:Npn \@@_change_case_codepoint:nN #1#2
+ { \@@_change_case_char:fnn { \int_eval:n {`#2} } {#1} {#2} }
+\else:
+ \cs_new:Npe \@@_change_case_codepoint:nN #1#2
+ {
+ \exp_not:N \int_compare:nNnTF {`#2} > { "80 }
+ {
+ \cs_if_exist:NTF \tex_pdftexversion:D
+ { \exp_not:N \@@_change_case_char_auxi:nN }
+ {
+ \exp_not:N \int_compare:nNnTF {`#2} > { "FF }
+ { \exp_not:N \@@_change_case_char_auxii:nN }
+ { \exp_not:N \@@_change_case_char_auxi:nN }
+ }
+ }
+ { \exp_not:N \@@_change_case_char_auxii:nN }
+ {#1} #2
+ }
+ \cs_new:Npn \@@_change_case_char_auxi:nN #1#2
+ {
+ \int_compare:nNnTF {`#2} < { "E0 }
+ { \@@_change_case_codepoint:nNN }
+ {
+ \int_compare:nNnTF {`#2} < { "F0 }
+ { \@@_change_case_codepoint:nNNN }
+ { \@@_change_case_codepoint:nNNNNN }
+ }
+ {#1} #2
+ }
+ \cs_new:Npn \@@_change_case_char_auxii:nN #1#2
+ { \@@_change_case_char:fnn { \int_eval:n {`#2} } {#1} {#2} }
+ \cs_new:Npn \@@_change_case_codepoint:nNN #1#2#3
+ {
+ \@@_change_case_char:fnn
+ { \int_eval:n { (`#2 - "C0) * "40 + `#3 - "80 } }
+ {#1} {#2#3}
+ }
+ \cs_new:Npn \@@_change_case_codepoint:nNNN #1#2#3#4
+ {
+ \@@_change_case_char:fnn
+ {
+ \int_eval:n
+ { (`#2 - "E0) * "1000 + (`#3 - "80) * "40 + `#4 - "80 }
+ }
+ {#1} {#2#3#4}
+ }
+ \cs_new:Npn \@@_change_case_codepoint:nNNNN #1#2#3#4#5
+ {
+ \@@_change_case_char:fnn
+ {
+ \int_eval:n
+ {
+ (`#2 - "F0) * "40000
+ + (`#3 - "80) * "1000
+ + (`#4 - "80) * "40
+ + `#5 - "80
+ }
+ }
+ {#1} {#2#3#4#5}
+ }
+\fi:
+\cs_new:Npn \@@_change_case_char:nnn #1#2#3
+ {
+ \@@_change_case_output:fw
+ {
+ \exp_args:Ne \@@_change_case_char_aux:nnn
+ { \__kernel_codepoint_case:nn {#2} {#1} } {#1} {#3}
+ }
+ \@@_change_case_loop:nw {#2}
+ }
+\cs_generate_variant:Nn \@@_change_case_char:nnn { f }
+\cs_new:Npn \@@_change_case_char_aux:nnn #1#2#3
+ {
+ \use:e { \@@_change_case_char:nnnnn #1 {#2} {#3} }
+ }
+\cs_new:Npn \@@_change_case_char:nnnnn #1#2#3#4#5
+ {
+ \int_compare:nNnTF {#1} = {#4}
+ { \tl_to_str:n {#5} }
+ {
+ \codepoint_str_generate:n {#1}
+ \tl_if_blank:nF {#2}
+ {
+ \codepoint_str_generate:n {#2}
+ \tl_if_blank:nF {#3}
+ { \codepoint_str_generate:n {#3} }
+ }
+ }
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]{\str_mdfive_hash:n, \str_mdfive_hash:e}
+% \begin{macrocode}
+\cs_new:Npn \str_mdfive_hash:n #1 { \tex_mdfivesum:D { \tl_to_str:n {#1} } }
+\cs_new:Npn \str_mdfive_hash:e #1 { \tex_mdfivesum:D {#1} }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{variable}
+% {
+% \c_ampersand_str,
+% \c_atsign_str,
+% \c_backslash_str,
+% \c_left_brace_str,
+% \c_right_brace_str,
+% \c_circumflex_str,
+% \c_colon_str,
+% \c_dollar_str,
+% \c_hash_str,
+% \c_percent_str,
+% \c_tilde_str,
+% \c_underscore_str,
+% \c_zero_str
+% }
+% For all of those strings, use \cs{cs_to_str:N} to get characters with
+% the correct category code without worries
+% \begin{macrocode}
+\str_const:Ne \c_ampersand_str { \cs_to_str:N \& }
+\str_const:Ne \c_atsign_str { \cs_to_str:N \@ }
+\str_const:Ne \c_backslash_str { \cs_to_str:N \\ }
+\str_const:Ne \c_left_brace_str { \cs_to_str:N \{ }
+\str_const:Ne \c_right_brace_str { \cs_to_str:N \} }
+\str_const:Ne \c_circumflex_str { \cs_to_str:N \^ }
+\str_const:Ne \c_colon_str { \cs_to_str:N \: }
+\str_const:Ne \c_dollar_str { \cs_to_str:N \$ }
+\str_const:Ne \c_hash_str { \cs_to_str:N \# }
+\str_const:Ne \c_percent_str { \cs_to_str:N \% }
+\str_const:Ne \c_tilde_str { \cs_to_str:N \~ }
+\str_const:Ne \c_underscore_str { \cs_to_str:N \_ }
+\str_const:Ne \c_zero_str { 0 }
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{variable}{\c_empty_str}
+% An empty string is simply an empty token list.
+% \begin{macrocode}
+\cs_new_eq:NN \c_empty_str \c_empty_tl
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{variable}{\l_tmpa_str, \l_tmpb_str, \g_tmpa_str, \g_tmpb_str}
+% Scratch strings.
+% \begin{macrocode}
+\str_new:N \l_tmpa_str
+\str_new:N \l_tmpb_str
+\str_new:N \g_tmpa_str
+\str_new:N \g_tmpb_str
+% \end{macrocode}
+% \end{variable}
+%
+% \subsection{Viewing strings}
+%
+% \begin{macro}{\str_show:n, \str_show:N, \str_show:c}
+% \begin{macro}{\str_log:n, \str_log:N, \str_log:c}
+% Displays a string on the terminal.
+% \begin{macrocode}
+\cs_new_eq:NN \str_show:n \tl_show:n
+\cs_new_protected:Npn \str_show:N #1
+ {
+ \__kernel_chk_tl_type:NnnT #1 { str } { \tl_to_str:N #1 }
+ { \tl_show:N #1 }
+ }
+\cs_generate_variant:Nn \str_show:N { c }
+\cs_new_eq:NN \str_log:n \tl_log:n
+\cs_new_protected:Npn \str_log:N #1
+ {
+ \__kernel_chk_tl_type:NnnT #1 { str } { \tl_to_str:N #1 }
+ { \tl_log:N #1 }
+ }
+\cs_generate_variant:Nn \str_log:N { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macrocode}
+%</package>
+% \end{macrocode}
+%
+% \end{implementation}
+%
+% \PrintIndex