latex-dev (22oct21)

git-svn-id: svn://tug.org/texlive/trunk@60842 c570f23f-e606-0410-a88d-b1316a301751

22 files changed, 950 insertions, 268 deletions

diff --git a/Master/texmf-dist/source/latex-dev/amsmath/amsmath.dtx b/Master/texmf-dist/source/latex-dev/amsmath/amsmath.dtx
index eec51f50cbe..a5cf333e797 100644
--- a/Master/texmf-dist/source/latex-dev/amsmath/amsmath.dtx
+++ b/Master/texmf-dist/source/latex-dev/amsmath/amsmath.dtx
@@ -86,7 +86,7 @@ Bug reports can be opened (category \texttt{#1}) at\\%
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\ProvidesPackage{amsmath}[2021/08/28 v2.17k AMS math features]
+\ProvidesPackage{amsmath}[2021/10/15 v2.17l AMS math features]
 %    \end{macrocode}
 %
 % \section{Catcode defenses}
@@ -3012,7 +3012,13 @@ ill-advised in LaTeX.%
 %    the \cs{maketag@@} macro above.
 %    \begin{macrocode}
 \let\df@tag\@empty
-\def\make@df@tag{\@ifstar\make@df@tag@@\make@df@tag@@@}
+\def\make@df@tag{%
+%    \end{macrocode}
+%    We set \cs{@currentcounter} here so that it applies to both branches.
+%\changes{v2.17l}{2021/10/15}{Explicitly set \cs{@currentcounter} (gh/687)}
+%    \begin{macrocode}
+  \def\@currentcounter{equation}%
+  \@ifstar\make@df@tag@@\make@df@tag@@@}
 %    \end{macrocode}
 %    \cs{make@df@tag} sets \cs{@currentlabel} and defines
 %    \cs{df@tag} appropriately.
diff --git a/Master/texmf-dist/source/latex-dev/base/classes.dtx b/Master/texmf-dist/source/latex-dev/base/classes.dtx
index fdf0ef3a5b0..a13053b871a 100644
--- a/Master/texmf-dist/source/latex-dev/base/classes.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/classes.dtx
@@ -53,7 +53,7 @@
 %<*driver>
 \ProvidesFile{classes.drv}
 %</driver>
-              [2021/09/11 v1.4n
+              [2021/10/04 v1.4n
 %<article|report|book> Standard LaTeX document class]
 %<10pt|11pt|12pt>      Standard LaTeX file (size option)]
 %    \end{macrocode}
@@ -1622,7 +1622,7 @@
 % \label{sec:classes:pagestyle}
 %
 %    The pagestyles \pstyle{empty} and \pstyle{plain} are defined in
-%    \file{latex.dtx}.
+%    the \LaTeX{} format.
 %
 % \begin{macro}{\ps@headings}
 %    The definition of the page style \pstyle{headings} has to be
@@ -1771,7 +1771,7 @@
 % \begin{macro}{\title}
 % \begin{macro}{\author}
 % \begin{macro}{\date}
-%    These three macros are provided by \file{latex.dtx} to provide
+%    These three macros are provided by the \LaTeX{} format to provide
 %    information about the title, author(s) and date of the document.
 %    The information is stored away in internal control sequences.
 %    It is the task of the |\maketitle| command to use the
@@ -2056,7 +2056,7 @@
 %    Default initializations of |\...mark| commands.  These commands
 %    are used in the definition of the page styles (see
 %    section~\ref{sec:classes:pagestyle}) Most of them are already defined by
-%    \file{latex.dtx}, so they are only shown here.
+%    the \LaTeX{} format, so they are only shown here.
 %
 %    \begin{macrocode}
 %<!article>\newcommand*\chaptermark[1]{}
@@ -2891,7 +2891,7 @@
 % \begin{macro}{\theenumii}
 % \begin{macro}{\theenumiii}
 % \begin{macro}{\theenumiv}
-%    The counters are already defined in \file{latex.dtx}, but their
+%    The counters are already defined in the \LaTeX{} format, but their
 %    representation is changed here.
 %
 %    \begin{macrocode}
@@ -2990,7 +2990,7 @@
 %
 % \begin{environment}{description}
 %    The description environment is defined here -- while the itemize
-%    and enumerate environments are defined in \file{latex.dtx}.
+%    and enumerate environments are defined in the \LaTeX{} format.
 %
 %    \begin{macrocode}
 \newenvironment{description}
@@ -3123,7 +3123,7 @@
 % \subsubsection{Theorem}
 %
 %    This document class does not define it's own theorem environments,
-%    the defaults, supplied by \file{latex.dtx} are available.
+%    the defaults, supplied by the \LaTeX{} format are available.
 %
 % \subsubsection{Titlepage}
 %
@@ -3365,7 +3365,7 @@
 %
 % \subsection{Floating objects}
 %
-%    The file \file{latex.dtx} only defines a number of tools with
+%    The \LaTeX{} format only defines a number of tools with
 %    which floating objects can be defined. This is done in the
 %    document class. It needs to define the following macros for each
 %    floating object of type \texttt{TYPE} (e.g., \texttt{TYPE} =
@@ -3402,7 +3402,7 @@
 %
 %    The actual environment that implements a floating object such as
 %    a figure is defined using the macros |\@float| and |\end@float|,
-%    which are defined in \file{latex.dtx}.
+%    which are defined in the \LaTeX{} format.
 %
 %    An environment that implements a single-column floating object is
 %    started with |\@float{|\texttt{TYPE}|}[|\meta{placement}|]| of type
@@ -4194,7 +4194,7 @@
 %
 % \begin{macro}{\@biblabel}
 %    The label for a |\bibitem[...]| command is produced by this
-%    macro. The default from \file{latex.dtx} is used.
+%    macro. The default from the \LaTeX{} format is used.
 %    \begin{macrocode}
 % \renewcommand*{\@biblabel}[1]{[#1]\hfill}
 %    \end{macrocode}
@@ -4202,7 +4202,7 @@
 %
 % \begin{macro}{\@cite}
 %    The output of the |\cite| command is produced by this macro. The
-%    default from \file{latex.dtx} is used.
+%    default from the \LaTeX{} format is used.
 %    \begin{macrocode}
 % \renewcommand*{\@cite}[1]{[#1]}
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/doc.dtx b/Master/texmf-dist/source/latex-dev/base/doc.dtx
index fb3412f21f4..41bc0733155 100644
--- a/Master/texmf-dist/source/latex-dev/base/doc.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/doc.dtx
@@ -35,7 +35,7 @@
 %<+package|shortvrb>\NeedsTeXFormat{LaTeX2e}[1994/12/01]
 %<+package> \ProvidesPackage{doc}
 %<+shortvrb>\ProvidesPackage{shortvrb}
-%<+package|shortvrb>  [2021/05/28 v2.1n
+%<+package|shortvrb>  [2021/10/04 v2.1n
 %<+package|shortvrb>   Standard LaTeX documentation package (FMi)]
 %\catcode`\<=12
 %
@@ -885,7 +885,7 @@
 % We provide macros for logos such as \Web, \AmSTeX, \BibTeX,
 % \SliTeX{} and \PlainTeX. Just type |\Web|, |\AmSTeX|,
 % |\BibTeX|, |\SliTeX| or |\PlainTeX|, respectively.
-% \LaTeX{} and \TeX{} are already defined in \texttt{latex.tex}.
+% \LaTeX{} and \TeX{} are already defined in the \LaTeX{} format.
 %
 % \DescribeMacro\meta
 % Another useful macro is |\meta| which has one argument and
@@ -938,7 +938,8 @@
 % argument and produces a verbatim listing of the file, indexing every
 % command as it goes along.  This might be handy, if you want to learn
 % something about macros without enough documentation.  I used this
-% feature to cross-reference \texttt{latex.tex} getting a verbatim
+% feature to cross-reference \texttt{latex.tex} (these days
+% called \texttt{latex.ltx}) getting a verbatim
 % copy with about 15 pages index.\footnote{It took quite a long time
 % and the resulting \texttt{.idx} file was longer than the
 % \texttt{.dvi} file.  Actually too long to be handled by the
@@ -2031,7 +2032,7 @@
 % \begin{macro}{\@verbatim}
 %    Additionally we redefine the |\@verbatim| macro so that it
 %    suppresses |%| characters at the beginning of the line.  The
-%    first lines are copied literally from \texttt{latex.tex}.
+%    first lines are copied literally from the \LaTeX{} format.
 % \changes{v1.7i}{1992/07/12}{Added \cs{@@par} to clear possible
 %                             \cs{parshape}.}
 %    \begin{macrocode}
@@ -2055,7 +2056,7 @@
 %    \begin{macrocode}
    \check@percent}%
 %    \end{macrocode}
-%    The rest is again copied literally from \texttt{latex.tex} (less
+%    The rest is again copied literally from the \LaTeX{} format (less
 %    "\tt").
 % \changes{v1.7a}{1992/02/26}{Removed redundant \cs{tt}.}
 % \changes{v1.8b}{1993/09/21}{Changed to conform to new LaTeX verbatim,
diff --git a/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx b/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx
index 8499d3ab8b9..92d9228a8af 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx
@@ -33,7 +33,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltboxes.dtx}
-             [2021/02/10 v1.4b LaTeX Kernel (Box Commands)]
+             [2021/10/14 v1.4c LaTeX Kernel (Box Commands)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltboxes.dtx}
@@ -1137,10 +1137,12 @@
 %     {Color groups restored here.}
 % \changes{v1.4b}{2021/02/10}
 %         {Explicitly run \cs{par} in support for paragraph tagging}
+% \changes{v1.4c}{2021/10/14}
+%         {Explicitly set \cs{@currentcounter} (gh/687)}
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>\IncludeInRelease{2021/11/15}%
 %<latexrelease>                 {\@mpfootnotetext}{footnotetext tagging}%
 \long\def\@mpfootnotetext#1{%
   \global\setbox\@mpfootins\vbox{%
@@ -1148,6 +1150,7 @@
     \reset@font\footnotesize
     \hsize\columnwidth
     \@parboxrestore
+    \def\@currentcounter{mpfootnote}%
     \protected@edef\@currentlabel
          {\csname p@mpfootnote\endcsname\@thefnmark}%
     \color@begingroup
@@ -1158,6 +1161,24 @@
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>                 {\@mpfootnotetext}{footnotetext tagging}%
+%<latexrelease>\long\def\@mpfootnotetext#1{%
+%<latexrelease>  \global\setbox\@mpfootins\vbox{%
+%<latexrelease>    \unvbox\@mpfootins
+%<latexrelease>    \reset@font\footnotesize
+%<latexrelease>    \hsize\columnwidth
+%<latexrelease>    \@parboxrestore
+%<latexrelease>    \protected@edef\@currentlabel
+%<latexrelease>         {\csname p@mpfootnote\endcsname\@thefnmark}%
+%<latexrelease>    \color@begingroup
+%<latexrelease>      \@makefntext{%
+%<latexrelease>        \rule\z@\footnotesep\ignorespaces#1\@finalstrut\strutbox}%
+%<latexrelease>    \par
+%<latexrelease>    \color@endgroup}}
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
 %
 %    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}%
diff --git a/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx b/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx
index b6c57a41acc..208f7c3d22c 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx
@@ -13,21 +13,14 @@
 %
 %%% From File: ltcmdhooks.dtx
 %
-\def\ltcmdhooksversion{v1.0d}
-\def\ltcmdhooksdate{2021/08/25}
+\def\ltcmdhooksversion{v1.0f}
+\def\ltcmdhooksdate{2021/10/20}
 %
 %
 %
 %<*driver>
 \documentclass{l3doc}
 %\usepackage{ltcmdhooks}
-\makeatletter
-\providecommand\footref[1]{%
-  \begingroup
-    \unrestored@protected@xdef\@thefnmark{\ref{#1}}%
-  \endgroup
-  \@footnotemark}
-\makeatother
 \EnableCrossrefs
 \CodelineIndex
 \begin{document}
@@ -360,19 +353,46 @@
 % \end{macro}
 %
 % \begin{macro}{\l_@@_patch_prefixes_tl}
-% \begin{macro}{\l_@@_patch_param_text_tl}
-% \begin{macro}{\l_@@_patch_replacement_tl}
+% \begin{macro}{\l_@@_param_text_tl}
+% \begin{macro}{\l_@@_replace_text_tl}
 %   The prefixes and parameters of the definition for the macro being
 %   patched.
 %    \begin{macrocode}
 \tl_new:N \l_@@_patch_prefixes_tl
-\tl_new:N \l_@@_patch_param_text_tl
-\tl_new:N \l_@@_patch_replacement_tl
+\tl_new:N \l_@@_param_text_tl
+\tl_new:N \l_@@_replace_text_tl
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}{\c_@@_hash_tl}
+%   A constant token list that contains two parameter tokens.
+%    \begin{macrocode}
+\tl_const:Nn \c_@@_hash_tl { # # }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_exp_not:NN}
+% \begin{macro}{\@@_def_cmd:w}
+%   Two temporary macros that change depending on the macro being
+%   patched.
+%    \begin{macrocode}
+\cs_new_eq:NN \@@_exp_not:NN ?
+\cs_new_eq:NN \@@_def_cmd:w ?
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\q_@@_recursion_tail,\q_@@_recursion_stop}
+%   Internal quarks for recursion:  they can't appear in any macro being
+%   patched.
+%    \begin{macrocode}
+\quark_new:N \q_@@_recursion_tail
+\quark_new:N \q_@@_recursion_stop
+%    \end{macrocode}
+% \end{macro}
+%
 % \begin{macro}{\g_@@_delayed_patches_prop}
 %   A list containing the patches delayed to |\begin{document}|, so that
 %   patching is not attempted twice.
@@ -670,13 +690,71 @@
 %
 %
 %
+%
 % \begin{macro}{\@@_patch_expand_redefine:NNnn}
+% \begin{macro}{\@@_redefine_with_hooks:Nnnn}
 % \begin{macro}[EXP]{\@@_make_prefixes:w}
 %   Now the real action begins.  Here we have in |#1| a boolean
-%   indicating if the command has a |[|\ldots|]|-delimited argument, in
-%   |#2| the command control sequence, in |#3| the name of the command
-%   (note that |#1|${}\ne{}$|\csname#2\endcsname| at this point!), and
-%   in |#4| the hook position, either |before| or |after|.
+%   indicating if the command has a leading |[|\ldots|]|-delimited
+%   argument, in |#2| the command control sequence, in |#3| the name of
+%   the command (note that |#1|${}\ne{}$|\csname#2\endcsname| at this
+%   point!), and in |#4| the hook position, either |before| or |after|.
+%
+% \changes{v1.0f}{2021/10/20}
+%         {Correct patching by expansion+redefinition when the macro
+%          contains a parameter tokens (gh/697).}
+%   Patching with expansion+redefinition is trickier than it looks like
+%   at first glance.  Suppose the simple definition:
+% \begin{verbatim}
+%   \def\foo#1{#1##2}
+% \end{verbatim}
+%   When defined, its \meta{replacement text} will be a token list
+%   containing:
+%   \begin{quote}
+%     \itshape
+%     out\_param |1|, mac\_param |#|, character |2|
+%   \end{quote}
+%
+%   Then, after expanding \cs{foo}|{##1}| (here |##| denotes a single
+%   |#|$_6$) we end up with a token list with \textit{out\_param}~|1|
+%   replaced:
+%   \begin{quote}
+%     \itshape
+%     mac\_param |#|, character |1|, mac\_param |#|, character |2|
+%   \end{quote}
+%   that is, the definition would be:
+% \begin{verbatim}
+%   \def\foo#1{#1#2}
+% \end{verbatim}
+%   which obviously fails, because the original input in the definition
+%   was |##| but \TeX{} reduced that to a single parameter token |#|$_6$
+%   when carrying out the definition.  That leaves no room for a clever
+%   solution with (say) \cs{unexpanded}, because anything that would
+%   double the second |#|$_6$, would also (incorrectly) double the
+%   first, so there's not much to do other than a manual solution.
+%
+%   There are three cases we can distinguish to make things hopefully
+%   faster on simpler cases:
+%   \begin{enumerate}
+%     \item a macro with no parameters;
+%     \item a macro with no parameter tokens in its definition;
+%     \item a macro with parameters \emph{and} parameter tokens.
+%   \end{enumerate}
+%
+%   The first case is trivial:  if the macro has no parameters, we can
+%   just use \cs{unexpanded} around it, and if there is a parameter
+%   token in it, it is handled correctly (the macro can be treated as a
+%   |tl| variable).
+%
+%   The second case requires looking at the \meta{replacement text} of
+%   the macro to see if it has a parameter token in there.  If it does
+%   not, then there is no worry, and the macro can be redefined normally
+%   (without \cs{unexpanded}).
+%
+%   The third case, as usual, is the devious one.  Here we'll have to
+%   loop through the definition token by token, and double every
+%   parameter token, so that this case can be handled like the previous
+%   one.
 %    \begin{macrocode}
 \cs_new_protected:Npn \@@_patch_expand_redefine:NNnn #1 #2 #3 #4
   {
@@ -696,36 +774,93 @@
 %    \end{macrocode}
 %   Now build two token lists:
 %   \begin{description}
-%     \item[\cs{l_@@_patch_param_text_tl}] will contain the
+%     \item[\cs{l_@@_param_text_tl}] will contain the
 %       \meta{parameter text} to be used when redefining the macro.  It
 %       should be identical to the \meta{parameter text} used when
 %       originally defining that macro.
-%     \item[\cs{l_@@_patch_replacement_tl}] will contain braced pairs of
-%       |#|$_{12}$\meta{num} to feed to the macro when expanded.  This
-%       token list as well as the previous will have the first item
+%     \item[\cs{l_@@_replace_text_tl}] will contain braced pairs of
+%       \cs{c_@@_hash_tl}\meta{num} to feed to the macro when expanded.
+%       This token list as well as the previous will have the first item
 %       surrounded by |[|\ldots|]| in the case of an optional argument.
 %   \end{description}
+%
+%   The use of \cs{c_@@_hash_tl} here is to differentiate actual
+%   parameters in the macro from parameter tokens in the original
+%   definition of the macro.  Later on, \cs{c_@@_hash_tl} is either
+%   replaced by actual parameter tokens, or expanded into them.
 %    \begin{macrocode}
     \int_compare:nNnTF { \l_@@_patch_num_args_int } > { \c_zero_int }
       {
-        \tl_set:Nx \l_@@_patch_param_text_tl
-          { \bool_if:NTF #1 { [####1] } {  ####1  } }
-        \tl_set:Nx \l_@@_patch_replacement_tl
-          { \bool_if:NTF #1 { [####1] } { {####1} } }
+%    \end{macrocode}
+%   We'll first check if the command has any parameter token in its
+%   definition (feeding it empty arguments), and set \cs{@@_exp_not:n}
+%   accordingly.  \cs{@@_exp_not:n} will be used later to either leave
+%   \cs{c_@@_hash_tl} or expand it, and also to remember the result of
+%   \cs{@@_if_has_hash:nTF} to avoid testing twice (the test can be
+%   rather slow).
+%    \begin{macrocode}
+        \tl_set:Nx \l_@@_tmpa_tl { \bool_if:NTF #1 { [ ] } { { } } }
+        \int_step_inline:nnn { 2 } { \l_@@_patch_num_args_int }
+          { \tl_put_right:Nn \l_@@_tmpa_tl { { } } }
+        \exp_args:NNo \exp_args:No \@@_if_has_hash:nTF
+            { \exp_after:wN #2 \l_@@_tmpa_tl }
+          { \cs_set_eq:NN \@@_exp_not:n \exp_not:n }
+          { \cs_set_eq:NN \@@_exp_not:n \use:n }
+        \cs_set_protected:Npn \@@_tmp:w ##1 ##2
+          {
+            ##1 \l_@@_param_text_tl   { \use:n ##2 }
+            ##1 \l_@@_replace_text_tl { \@@_exp_not:n {##2} }
+          }
+%    \end{macrocode}
+%   Here we'll conditionally add |[|\ldots|]| around the first
+%   parameter:
+%    \begin{macrocode}
+        \bool_if:NTF #1
+          { \@@_tmp:w \tl_set:Nx { [ \c_@@_hash_tl 1 ] } }
+          { \@@_tmp:w \tl_set:Nx { { \c_@@_hash_tl 1 } } }
+%    \end{macrocode}
+%   Then, for every parameter from the second, just add it normally:
+%    \begin{macrocode}
         \int_step_inline:nnn { 2 } { \l_@@_patch_num_args_int }
+          { \@@_tmp:w \tl_put_right:Nx { { \c_@@_hash_tl ##1 } } }
+%    \end{macrocode}
+%   Now, if the command has any parameter token in its definition
+%   (then \cs{@@_exp_not:n} is \cs{exp_not:n}), call
+%   \cs{@@_double_hashes:n} to double them, and replace every
+%   \cs{c_@@_hash_tl} by |#|:
+%    \begin{macrocode}
+        \tl_set:Nx \l_@@_replace_text_tl
+          { \exp_not:N #2 \exp_not:V \l_@@_replace_text_tl }
+        \tl_set:Nx \l_@@_replace_text_tl
           {
-            \tl_put_right:Nn \l_@@_patch_param_text_tl    { ## ####1 }
-            \tl_put_right:Nn \l_@@_patch_replacement_tl { { ## ####1 } }
+            \token_if_eq_meaning:NNTF \@@_exp_not:n \exp_not:n
+              { \exp_args:NNV \exp_args:No \@@_double_hashes:n }
+              { \exp_args:NV \exp_not:o }
+                  \l_@@_replace_text_tl
           }
+%    \end{macrocode}
+%   And now, set a few auxiliaries for the case that the macro has
+%   parameters, so it won't be passed through \cs{unexpanded} (twice):
+%    \begin{macrocode}
+        \cs_set_eq:NN \@@_def_cmd:w \tex_gdef:D
+        \cs_set_eq:NN \@@_exp_not:NN \prg_do_nothing:
       }
       {
-        \tl_clear:N \l_@@_patch_param_text_tl
-        \tl_clear:N \l_@@_patch_replacement_tl
+%    \end{macrocode}
+%   In the case the macro has no parameters, we'll treat it as a token
+%   list and things are much simpler (expansion control looks a bit
+%   complicated, but it's just a pair of \cs{exp_not:N} preventing
+%   another \cs{exp_not:n} from expanding):
+%    \begin{macrocode}
+        \tl_clear:N \l_@@_param_text_tl
+        \tl_set_eq:NN \l_@@_replace_text_tl #2
+        \cs_set_eq:NN \@@_def_cmd:w \tex_xdef:D
+        \cs_set:Npn \@@_exp_not:NN ##1 { \exp_not:N ##1 \exp_not:N }
       }
 %    \end{macrocode}
-%   Finally, before redefining, we need to also get the prefixes used
-%   when defining the command.  Here we ensure that the \tn{escapechar}
-%   is printable, otherwise a macro defined with prefixes
+%   Before redefining, we need to also get the prefixes used when
+%   defining the command.  Here we ensure that the \tn{escapechar} is
+%   printable, otherwise a macro defined with prefixes
 %   |\protected \long| will have it \tn{meaning} printed as
 %   |protectedlong|, making life unnecessarily complicated.  Here the
 %   \tn{escapechar} is changed to |/|, then we loop between pairs of
@@ -740,34 +875,47 @@
       { \exp_not:N \@@_make_prefixes:w \cs_prefix_spec:N #2 / / }
         }
 %    \end{macrocode}
-%   Now that all the needed tools are ready, without further ado we'll
-%   redefine the command |#2|.  The definition uses the prefixes
-%   gathered in \cs{l_@@_patch_prefixes_tl}, a primitive \cs{tex_def:D}
-%   to avoid adding extra prefixes, and the \meta{parameter text} from
-%   \cs{l_@@_patch_param_text_tl}.
-%
-%   Then finally, in the body of the definition, we insert
-%   \hook{cmd/\#3/before} if |#4| is |before|, the code of the
-%   command expanded once grabbing the parameters in
-%   \cs{l_@@_patch_replacement_tl}, and \hook{cmd/\#3/after} if |#4| is
-%   |after|.
+%   Finally, call \cs{@@_redefine_with_hooks:Nnnn} with the macro being
+%   redefined in |#1|, then \cs{UseHook}|{cmd/<name>/before}| in |#2| or
+%   \cs{UseHook}|{cmd/<name>/after}| in |#3| (one is always empty), and
+%   in |#4| the \meta{replacement text} of the macro.
 %    \begin{macrocode}
     \use:x
       {
-        \l_@@_patch_prefixes_tl \tex_def:D
-            \exp_not:N #2 \exp_not:V \l_@@_patch_param_text_tl
-          {
-            \str_if_eq:nnT {#4} { before }
-              { \exp_not:N \UseHook { cmd / #3 / #4 } }
-            \exp_args:No \exp_not:o
-              { \exp_after:wN #2 \l_@@_patch_replacement_tl }
-            \str_if_eq:nnT {#4} { after }
-              { \exp_not:N \UseHook { cmd / #3 / #4 } }
-          }
+        \@@_redefine_with_hooks:Nnnn \exp_not:N #2
+        \str_if_eq:nnTF {#4} { after }
+          { \use_ii_i:nn }
+          { \use:nn }
+            { { \@@_exp_not:NN \exp_not:N \UseHook { cmd / #3 / #4 } } }
+            { { } }
+            { \@@_exp_not:NN \exp_not:V \l_@@_replace_text_tl }
       }
   }
 %    \end{macrocode}
 %
+%   Now that all the needed tools are ready, without further ado we'll
+%   redefine the command.  The definition uses the prefixes gathered in
+%   \cs{l_@@_patch_prefixes_tl}, a primitive \cs{@@_def_cmd:w} (which is
+%   \cs{tex_gdef:D} or \cs{tex_xdef:D}) to avoid adding extra prefixes,
+%   and the \meta{parameter text} from \cs{l_@@_param_text_tl}.
+%
+%   Then finally, in the body of the definition, we insert |#2|, which
+%   is \hook{cmd/\#1/before} or empty, |#4| which is the
+%   \meta{replacement text}, and |#3| which is \hook{cmd/\#1/after} or
+%   empty.
+%
+% \changes{v1.0e}{2021/09/28}
+%                {Make patching of commands a global operation (gh/674)}
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_redefine_with_hooks:Nnnn #1 #2 #3 #4
+  {
+    \l_@@_patch_prefixes_tl
+      \exp_after:wN \@@_def_cmd:w
+        \exp_after:wN #1 \l_@@_param_text_tl
+      { #2  #4  #3 }
+  }
+%    \end{macrocode}
+%
 %   Here's the auxiliary that makes the prefix control sequences for the
 %   redefinition.  Each item has to be \cs{tl_trim_spaces:n}'d because
 %   the last item (and not any other) has a trailing space.
@@ -783,11 +931,125 @@
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
+% \end{macro}
 %
 %
+% Here are some auxiliaries for the contraption above.
 %
+% \begin{macro}[pTF]{\@@_if_has_hash:n}
+% \begin{macro}{\@@_if_has_hash:w,\@@_if_has_hash_check:w}
+%   \cs{@@_if_has_hash:nTF} searches the token list |#1| for a catcode~6
+%   token, and if any is found, it returns |true|, and |false|
+%   otherwise.  The searching doesn't care about preserving groups or
+%   spaces:  we can ignore those safely (braces are removed) so that
+%   searching is as fast as possible.
+%    \begin{macrocode}
+\prg_new_conditional:Npnn \@@_if_has_hash:n #1 { TF }
+  { \@@_if_has_hash:w #1 ## \s_@@_mark }
+\cs_new:Npn \@@_if_has_hash:w #1
+  {
+    \tl_if_single_token:nTF {#1}
+      {
+        \token_if_eq_catcode:NNTF ## #1
+          { \@@_if_has_hash_check:w }
+          { \@@_if_has_hash:w }
+      }
+      { \@@_if_has_hash:w #1 }
+  }
+\cs_new:Npn \@@_if_has_hash_check:w #1 \s_@@_mark
+  { \tl_if_empty:nTF {#1} { \prg_return_false: } { \prg_return_true: } }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
 %
 %
+% \begin{macro}[rEXP]{\@@_double_hashes:n}
+% \begin{macro}[rEXP]{
+%     \@@_double_hashes:w,
+%     \@@_double_hashes_output:N,
+%     \@@_double_hashes_stop:w,
+%     \@@_double_hashes_group:n,
+%     \@@_double_hashes_space:w,
+%   }
+%   \cs{@@_double_hashes:n} loops through the token list |#1| and
+%   duplicates any catcode~6 token, and expands tokens \cs{ifx}-equal to
+%   \cs{c_@@_hash_tl}, and leaves all other tokens \cs{notexpanded} with
+%   \cs{exp_not:N}.  Unfortunately pairs of explicit catcode~1 and
+%   catcode~2 character tokens are normalised to |{|$_1$ and |}|$_1$
+%   because it's not feasible to expandably detect the character code
+%   (\emph{maybe} it could be done using something along the lines of
+%   \url{https://tex.stackexchange.com/a/527538}, but it's far too much
+%   work for close to zero benefit).
+%
+%   \cs{@@_double_hashes:w} is the tail-recursive loop macro, that tests
+%   which of the three types of item is in the head of the token list.
+%    \begin{macrocode}
+\cs_new:Npn \@@_double_hashes:n #1
+  { \@@_double_hashes:w #1 \q_@@_recursion_tail \q_@@_recursion_stop }
+\cs_new:Npn \@@_double_hashes:w #1 \q_@@_recursion_stop
+  {
+    \tl_if_head_is_N_type:nTF {#1}
+      { \@@_double_hashes_output:N }
+      {
+        \tl_if_head_is_group:nTF {#1}
+          { \@@_double_hashes_group:n }
+          { \@@_double_hashes_space:w }
+      }
+    #1 \q_@@_recursion_stop
+  }
+%    \end{macrocode}
+%
+%   \cs{@@_double_hashes_output:N} checks for the end of the token list,
+%   then checks if the token is \cs{c_@@_hash_tl}, and if so just leaves
+%   it.
+%    \begin{macrocode}
+\cs_new:Npn \@@_double_hashes_output:N #1
+  {
+    \if_meaning:w \q_@@_recursion_tail #1
+      \@@_double_hashes_stop:w
+    \fi:
+    \if_meaning:w \c_@@_hash_tl #1
+%    \end{macrocode}
+%   (this \cs{use_i:nnnn} uses \cs{fi:} and consumes \cs{use:n}, the
+%   whole \cs{if_catcode:w} block, and the \cs{exp_not:N}, leaving just
+%   |#1| which is \cs{c_@@_hash_tl}.)
+%    \begin{macrocode}
+      \use_i:nnnn
+    \fi:
+    \use:n
+      {
+%    \end{macrocode}
+%   If |#1| is not \cs{c_@@_hash_tl}, then check if its catcode is~6,
+%   and if so, leave it doubled in \cs{exp_not:n} and consume the
+%   following |\exp_not:N #1|.
+%    \begin{macrocode}
+        \if_catcode:w ## \exp_not:N #1
+          \exp_after:wN \use_ii:nnnn
+        \fi:
+        \use_none:n
+          { \exp_not:n { #1 #1 } }
+      }
+%    \end{macrocode}
+%   If both previous tests returned |false|, then leave the token
+%   unexpanded and resume the loop.
+%    \begin{macrocode}
+    \exp_not:N #1
+    \@@_double_hashes:w
+  }
+\cs_new:Npn \@@_double_hashes_stop:w #1 \q_@@_recursion_stop { \fi: }
+%    \end{macrocode}
+%
+%   Dealing with spaces and grouped tokens is trivial:
+%    \begin{macrocode}
+\cs_new:Npn \@@_double_hashes_group:n #1
+  { { \@@_double_hashes:n {#1} } \@@_double_hashes:w }
+\exp_last_unbraced:NNo
+\cs_new:Npn \@@_double_hashes_space:w \c_space_tl
+  { ~ \@@_double_hashes:w }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
 %
 % \subsubsection{Patching by retokenization}
 %
@@ -1061,8 +1323,11 @@
 %    \end{macrocode}
 %   And to close, copy the newly-defined command into the old name and
 %   the patching is finally completed:
+%
+% \changes{v1.0e}{2021/09/28}
+%                {Make patching of commands a global operation (gh/674)}
 %    \begin{macrocode}
-    \cs_set_eq:NN #1 \kerneltmpDoNotUse
+    \cs_gset_eq:NN #1 \kerneltmpDoNotUse
   }
 %    \end{macrocode}
 % \end{macro}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx b/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx
index 4dee83c4d6e..4c24716df65 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx
@@ -32,7 +32,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltfiles.dtx}
-             [2021/08/25 v1.2o LaTeX Kernel (File Handling)]
+             [2021/10/14 v1.2p LaTeX Kernel (File Handling)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltfiles.dtx}
@@ -823,8 +823,16 @@
 %    
 % \changes{v1.2j}{2020/10/04}{Quotes around the aux file name removed,
 %                       they are not needed and upset BibTeX (gh/400)}
+% \changes{v1.2p}{2021/10/14}{Warn about use in preamble}
 %    \begin{macrocode}
 \def\@include#1 {%
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\ifx\@nodocument\relax
+%    \end{macrocode}
+%
+%    \begin{macrocode}
   \clearpage
   \if@filesw
     \immediate\write\@mainaux{\string\@input{#1.aux}}%
@@ -892,7 +900,15 @@
     \deadcycles\z@
     \@nameuse{cp@#1}%
   \fi
-  \let\@auxout\@mainaux}
+  \let\@auxout\@mainaux
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\else
+\@latex@warning{%
+  \noexpand\include should only be used after \string\begin{document}}%
+\@input@{#1}%
+\fi}
 %    \end{macrocode}
 %
 % \changes{v1.2o}{2021/08/25}{Declare non-generic include hooks}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx b/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx
index 5d77fb2e834..40017a205a4 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx
@@ -1246,32 +1246,33 @@
 % \end{macro}
 % \end{macro}
 %
-%  \subsection{Prepare for supporting PDF management in backends}
+%  \subsection{Preparation for supporting PDF in backends}
 %
-%    At the current point in time support for PDF management in
-%    backends is not part of \LaTeX{} core but provided by external
+%    At the current point in time, basic support for PDF in
+%    backends is not part of \LaTeX{} core; it is provided by external
 %    packages. At some time in the future that work will be placed
 %    into the kernel but for now it is separate and has to be
 %    explicitly loaded in the document.
 %
-%    There is a command \cs{IfPDFManagementActiveTF} in that code
-%    which checks if the PDF management code is activated, which can
-%    be used by packages to execute different code branches depending
-%    on the state.
+%    In that code there is a command \cs{IfPDFManagementActiveTF} 
+%    which can be used by packages in order to execute different 
+%    code depending on the whether this basic backend support is loaded.
 %
-%    To make this also work properly if the external package is not
-%    loaded at all this command is already made available in the
-%    kernel (with a trivial definition) so that other packages can
-%    query the state in all circumstances.  Once the PDF management
-%    support moves to the kernel this definition here will vanish
-%    again or rather will be replaced by a real test.
+%    To make this also work properly when this external package is not
+%    loaded at all, we here add this command already in the
+%    kernel (with a trivial definition); thus any package can
+%    query this loading state in all circumstances.  
+%    Once this basic PDF backend
+%    support gets moved to the kernel, this definition will vanish
+%    again from here or, rather, it will be replaced by a real test.
 %
-% 
 %  \begin{macro}{\IfPDFManagementActiveTF}
-%    While the PDF management code is not loaded, the test will
-%    always return the false branch. Once this code is loaded, it
-%    is replaced by a real test (as then it is possible that the
-%    management code is activate or not activated).
+%    So long as the code for the basic backend support for PDF is not 
+%    loaded, the test that is implicit here will
+%    always return the false branch. 
+%    Once this code is loaded, this definition will get
+%    replaced by a real test (as it is then possible that the
+%    management code is either activated or not activated).
 % \changes{v2.2p}{2021/08/08}{Default definition added (gh/640)}
 %    \begin{macrocode}
 \let \IfPDFManagementActiveTF \@secondoftwo
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx b/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx
index ed25db3ed10..ac3b6418171 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx
@@ -31,7 +31,7 @@
 %
 %<*driver>
 % \fi
-\ProvidesFile{ltfloat.dtx}[2021/03/03 v1.2f LaTeX Kernel (Floats)]
+\ProvidesFile{ltfloat.dtx}[2021/10/14 v1.2g LaTeX Kernel (Floats)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltfloat.dtx}
@@ -1510,10 +1510,12 @@
 %         {Missing percent, again}
 % \changes{v1.2e}{2021/02/10}{Explicitly run \cs{par} at the end of footnote text
 %      in preparation for paragraph hooks}
+% \changes{v1.2g}{2021/10/14}
+%         {Explicitly set \cs{@currentcounter} (gh/687)}
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>\IncludeInRelease{2021/11/15}%
 %<latexrelease>                 {\@footnotetext}{footnotetext tagging}%
 \long\def\@footnotetext#1{\insert\footins{%
     \reset@font\footnotesize
@@ -1521,6 +1523,7 @@
     \splittopskip\footnotesep
     \splitmaxdepth \dp\strutbox \floatingpenalty \@MM
     \hsize\columnwidth \@parboxrestore
+    \def\@currentcounter{footnote}%
     \protected@edef\@currentlabel{%
        \csname p@footnote\endcsname\@thefnmark
     }%
@@ -1534,6 +1537,26 @@
 %    \end{macrocode}
 %
 %    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>                 {\@footnotetext}{footnotetext tagging}%
+%<latexrelease>\long\def\@footnotetext#1{\insert\footins{%
+%<latexrelease>    \reset@font\footnotesize
+%<latexrelease>    \interlinepenalty\interfootnotelinepenalty
+%<latexrelease>    \splittopskip\footnotesep
+%<latexrelease>    \splitmaxdepth \dp\strutbox \floatingpenalty \@MM
+%<latexrelease>    \hsize\columnwidth \@parboxrestore
+%<latexrelease>    \protected@edef\@currentlabel{%
+%<latexrelease>       \csname p@footnote\endcsname\@thefnmark
+%<latexrelease>    }%
+%<latexrelease>    \color@begingroup
+%<latexrelease>      \@makefntext{%
+%<latexrelease>        \rule\z@\footnotesep\ignorespaces#1\@finalstrut\strutbox}%
+%<latexrelease>    \par
+%<latexrelease>    \color@endgroup}}%
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}%
 %<latexrelease>                 {\@footnotetext}{footnotetext tagging}%
 %<latexrelease>
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfssdcl.dtx b/Master/texmf-dist/source/latex-dev/base/ltfssdcl.dtx
index 9710d543829..4f2cabd613b 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfssdcl.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfssdcl.dtx
@@ -36,7 +36,7 @@
 %
 %
 \ProvidesFile{ltfssdcl.dtx}
-            [2021/02/15 v3.0w LaTeX Kernel (NFSS Declarative Interface)]
+            [2021/10/15 v3.0y LaTeX Kernel (NFSS Declarative Interface)]
 % \iffalse
 \documentclass{ltxdoc}
 \begin{document}
@@ -454,25 +454,88 @@
 %    \end{macrocode}
 % \end{macro}
 %
+%
+%
+%
+%  \begin{macro}{\c@localalphabets}
+% \changes{v3.0x}{2021/09/26}{Counter added for (gh/676)}
+%    To avoid hitting the ``no more math fams available'' limit of 16, we
+%    keep a defined number of math alphabets flexible/local. If we have to
+%    allocate any of those we roll back the allocation after the
+%    formula has ended, so the next formula can use other alphabets in
+%    the slot(s). This makes the processing a bit slower if you are
+%    working at the limit, but that is better than dying with ``out of memory''.
+%    \begin{macrocode}
+%</2ekernel>
+%<latexrelease>\IncludeInRelease{2021/11/15}
+%<latexrelease>  {\document@select@group}{\document@select@group}%
+%<*2ekernel|latexrelease>
+%    \end{macrocode}
+%    We don't really undo the declaration on rollback (as that would
+%    be hard to maintain), so rolling
+%    forward needs to check if the declaration was already made.
+%    \begin{macrocode}
+\ifx\c@localmathalphabets\@undefined
+%    \end{macrocode}
+%    There is no need to have this counter as part of the include
+%    checkpoints, given that it makes little sense to alter its
+%    settings mid document. All we want is the ability to change it
+%    using the \cs{setcounter} interface.
+%
+%    By default we keep two math fams flexible.
+%    \begin{macrocode}
+  \newcount\c@localmathalphabets
+  \setcounter{localmathalphabets}{2}
+\fi
+%    \end{macrocode}
+%  \end{macro}
+%
+%
+%
+%
+%
 % \begin{macro}{\document@select@group}
-%    We surround |\select@group| with braces so that functions using it
-%    can be used directly after |_| or |^|.
-% \changes{v2.1p}{1994/12/10}{Surround with braces (add fourth arg)}
-% \changes{v2.1q}{1995/04/02}{fix problem for pr/1275}
+%    The \cs{document@select@group} command is the version of
+%    \cs{select@group} (inside math versions) that is used in the
+%    document body to set up math alphabets (if used).
+%
 % \changes{v3.0g}{1997/11/20}
 %      {(DPC) inline use of \cs{stepcounter} (faster, and saves a csname
 %       per math version as no reset list)}
 % \changes{v3.0q}{2015/03/18}{Introduce \cs{e@mathgroup@top}}
 %    \begin{macrocode}
-%</2ekernel>
-%<latexrelease>\IncludeInRelease{2020/10/01}
-%<latexrelease>  {\document@select@group}{\document@select@group}%
-%<*2ekernel|latexrelease>
 \def\document@select@group#1#2#3#4{%
  \ifx\math@bgroup\bgroup\else\relax\expandafter\@firstofone\fi
  {%
  \ifmmode
+%    \end{macrocode}
+%    We first check if there is still room for allocating another
+%    mathgroup. If there is, we check if it can be globally allocated
+%    or if we have reached the limit which is given by
+%    \cs{e@mathgroup@top} with \cs{c@localmathalphabets} subtracted.
+% 
+% \changes{v3.0x}{2021/09/26}{Test if we should freeze the version (gh/676)}
+%    \begin{macrocode}
    \ifnum\csname c@mv@\math@version\endcsname<\e@mathgroup@top
+     \ifnum \numexpr\e@mathgroup@top-\c@localmathalphabets
+              >\csname c@mv@\math@version\endcsname
+     \else
+%    \end{macrocode}
+%    If we are past this point we freeze the current state of the math
+%    version so that we can return to it after the formula has
+%    ended. Of course, that should be done only once, so we check if
+%    \cs{mv@\meta{version}@frozen} already exists.
+%    \begin{macrocode}
+       \ifcsname mv@\math@version @frozen\endcsname \else
+%    \end{macrocode}
+%    We have to pass the current value of \cs{math@version} not the
+%    macro itself, because some of the processing is delayed to a
+%    point where the value may have changed again---not doing this
+%    caused a puzzling error in one setup.
+%    \begin{macrocode}
+         \expandafter\freeze@math@version\expandafter{\math@version}%
+       \fi
+     \fi
      \begingroup
        \escapechar\m@ne
        \getanddefine@fonts{\csname c@mv@\math@version\endcsname}#3%
@@ -486,16 +549,21 @@
      \global\advance\csname c@mv@\math@version\endcsname\@ne
    \else
      \let#1\relax
-     \@latex@error{Too many math alphabets used
-                   in version \math@version}%
+     \@latex@error{Too many math alphabets used in
+                   version \math@version}%
         \@eha
   \fi
 %    \end{macrocode}
-% extra \cs{expandafter} to remove the \cs{expandafter} added below
-% \changes{v3.0w}{2021/02/115}{fix for (gh/501)}
+%    Extra \cs{expandafter} to remove the \cs{expandafter} added below
+% \changes{v3.0w}{2021/02/15}{fix for (gh/501)}
 %    \begin{macrocode}
  \else \expandafter\expandafter\expandafter\non@alpherr\fi
 %    \end{macrocode}
+%    We surround |\select@group| with braces so that functions using it
+%    can be used directly after |_| or |^|.
+% \changes{v2.1p}{1994/12/10}{Surround with braces (add fourth arg)}
+% \changes{v2.1q}{1995/04/02}{fix problem for pr/1275}
+%
 %    If the legacy interface is used, e.g., \verb=$\sf -1$= the math
 %    alphabet \verb=#1= does not take an argument so we better do not
 %    surround \verb=#4= with braces, because then we get
@@ -507,8 +575,142 @@
  \expandafter#1\ifx\math@bgroup\bgroup{#4}\else#4\fi
  }%
 }
+%    \end{macrocode}
+%
+%
+%
+%  \begin{macro}{\freeze@math@version}
+% \changes{v3.0x}{2021/09/26}{Macro added for (gh/676)}
+%    This command stores the current state of the math version and sets
+%    things up to return to it after each formula from now on. We use
+%    L3 programming layer code to set it up.
+%    \begin{macrocode}
+\ExplSyntaxOn
+\cs_new_protected:Npn\freeze@math@version #1 {
+%    \end{macrocode}
+%    Save the current \cs{mv@\meta{version}} code and the number of
+%    allocated mathgroups inside.
+%    \begin{macrocode}
+  \@font@info{Freeze~ math~ alphabet~ allocation~ in~ version~
+              #1.\MessageBreak
+              Allocated~math~groups:~\int_use:c{ c@mv@ #1 }~ 
+              (local:~  \int_use:N\c@localmathalphabets)      }
+  \cs_gset_eq:cc { mv@#1@frozen }{ mv@#1 }
+  \tl_gset:cx { g__nfss_frozen_mv_ #1 _tl }{ \int_use:c { c@mv@#1 } }
+%    \end{macrocode}
+%    Doing the reset the first time, we wait until we are out of
+%    math mode, so we use some recursive \cs{group_insert_after:N} for this
+%    before we execute \cs{mv@\meta{version}@reset}.
+%    \begin{macrocode}
+  \group_insert_after:N \__nfss_init_mv_freeze:N \exp_after:wN
+    \group_insert_after:N \cs:w mv@#1@reset \cs_end:
+%    \end{macrocode}
+%    The \cs{check@mathfonts} is called at the very beginning of each
+%    math formula, so it is a good way to hook in the resetting.
+%    Again that has to happen after the formula has ended, but we know
+%    because of the place where \cs{check@mathfonts} is used
+%    that a single \cs{aftergoup} is sufficient.
+%    \begin{macrocode}
+  \tl_gput_right:No \check@mathfonts 
+       {
+         \exp_after:wN \group_insert_after:N \cs:w mv@#1@reset \cs_end:
+       }
+%    \end{macrocode}
+%    Here is the definition of \cs{mv@\meta{version}@reset}. If there
+%    has been no new math alphabet allocation, doing a reset would
+%    just cause a lot of unnecessary processing, so we do a quick
+%    check upfront for this.
+%    \begin{macrocode}
+  \cs_gset:cpn{mv@#1@reset}
+     {
+         \int_compare:nNnTF { \int_use:c{c@mv@#1} } > 
+                            { \tl_use:c{g__nfss_frozen_mv_ #1 _tl} }
+             {
+               \@font@info{Undo~ math~ alphabet~ allocation~ in~ version~ #1}
+%    \end{macrocode}
+%    If the undo is necessary, we restore the \cs{mv@\meta{version}} code.
+%    \begin{macrocode}
+               \cs_gset_eq:cc { mv@#1 }{ mv@#1@frozen }
+               \int_gset:cn { c@mv@#1 }{ \tl_use:c {g__nfss_frozen_mv_ #1 _tl} }
+%    \end{macrocode}
+%    But we also should undo changes to the math alphabet
+%    definitions. We therefore run this code with a modified
+%    definition for \cs{getanddefine@fonts} because there is no need
+%    to do anything to the symbol fonts that are permanently allocated.
+%    \begin{macrocode}
+               \group_begin:
+                 \cs_set_eq:NN \getanddefine@fonts \use_none:nn
+                 \use:c {mv@#1}
+               \group_end:
+             }
+             {
+%    \end{macrocode}
+%    If there was no change, we report that in the log (but this
+%    branch could go completely).
+%    \begin{macrocode}
+               \@font@info{No~ math~ alphabet~ change~ to~ frozen~ version~ #1}
+             }
+    }
+}
+%    \end{macrocode}
+%  \end{macro}
+%
+%
+%  \begin{macro}{\__nfss_init_mv_freeze:N}
+% \changes{v3.0x}{2021/09/26}{Macro added for (gh/676)}
+%    To do the initial freeze in a safe place, we check if we are in
+%    math mode and if so try again after the group has ended by pushing
+%    the command and its  single token argument with two
+%    \cs{group_insert_after:N}s after the current group. If we are no longer in
+%    math mode we bypass the
+%    conditional and so the next token is our argument
+%    which is then finally executed.
+%    \begin{macrocode}
+\cs_new_protected:Npn \__nfss_init_mv_freeze:N #1 {%
+  \mode_if_math:T { \group_insert_after:N \__nfss_init_mv_freeze:N
+                    \group_insert_after:N } #1
+}
+%    \end{macrocode}
+%  \end{macro}
+%
+%
+%    \begin{macrocode}
+\ExplSyntaxOff 
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{2020/10/01}
+%<latexrelease>  {\document@select@group}{\document@select@group}%
+%<latexrelease>
+%<latexrelease>\def\document@select@group#1#2#3#4{%
+%<latexrelease> \ifx\math@bgroup\bgroup\else\relax\expandafter\@firstofone\fi
+%<latexrelease> {%
+%<latexrelease> \ifmmode
+%<latexrelease>   \ifnum\csname c@mv@\math@version\endcsname<\e@mathgroup@top
+%<latexrelease>     \begingroup
+%<latexrelease>       \escapechar\m@ne
+%<latexrelease>       \getanddefine@fonts{\csname c@mv@\math@version\endcsname}#3%
+%<latexrelease>       \globaldefs\@ne  \math@fonts
+%<latexrelease>     \endgroup
+%<latexrelease>     \expandafter\extract@alph@from@version
+%<latexrelease>         \csname mv@\math@version\expandafter\endcsname
+%<latexrelease>         \expandafter{\number\csname
+%<latexrelease>                       c@mv@\math@version\endcsname}%
+%<latexrelease>          #1%
+%<latexrelease>     \global\advance\csname c@mv@\math@version\endcsname\@ne
+%<latexrelease>   \else
+%<latexrelease>     \let#1\relax
+%<latexrelease>     \@latex@error{Too many math alphabets used
+%<latexrelease>                   in version \math@version}%
+%<latexrelease>        \@eha
+%<latexrelease>  \fi
+%<latexrelease> \else \expandafter\expandafter\expandafter\non@alpherr\fi
+%<latexrelease> \expandafter#1\ifx\math@bgroup\bgroup{#4}\else#4\fi
+%<latexrelease> }%
+%<latexrelease>}
+%<latexrelease>\EndIncludeInRelease
 %<latexrelease>\IncludeInRelease{2015/01/01}
 %<latexrelease>  {\document@select@group}{\document@select@group}%
 %<latexrelease>
@@ -653,9 +855,36 @@
 %
 % \begin{macro}{\DeclareMathVersion}
 %    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2021/11/15}%
+%<latexrelease>                 {\DeclareMathVersion}{local alphabets}%
 \def\DeclareMathVersion#1{%
+%    \end{macrocode}
+%    When declaring a new math version we need to instantiate an L3
+%    variable that is used when we freeze the version, because too many
+%    alphabets got allocated. If we don't do this, L3 programming layer
+%    complains if it is run in checking mode.
+% \changes{v3.0y}{2021/10/15}{Initialize variable for freezing
+%       math version (gh/676)}
+%    \begin{macrocode}
+  \@namedef{g__nfss_frozen_mv_#1_tl}{}%
+%    \end{macrocode}
+%
+%    \begin{macrocode}
   \expandafter\new@mathversion\csname mv@#1\endcsname}
 \@onlypreamble\DeclareMathVersion
+%</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {\DeclareMathVersion}{local alphabets}%
+%<latexrelease>\def\DeclareMathVersion#1{%
+%<latexrelease>  \expandafter\new@mathversion\csname mv@#1\endcsname}
+%<latexrelease>\EndIncludeInRelease
+%<*2ekernel>
 %    \end{macrocode}
 % \end{macro}
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/lthooks.dtx b/Master/texmf-dist/source/latex-dev/base/lthooks.dtx
index 3969a2be567..5b3d80e9844 100644
--- a/Master/texmf-dist/source/latex-dev/base/lthooks.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/lthooks.dtx
@@ -31,8 +31,8 @@
 %%% From File: lthooks.dtx
 %
 %    \begin{macrocode}
-\def\lthooksversion{v1.0r}
-\def\lthooksdate{2021/09/06}
+\def\lthooksversion{v1.0s}
+\def\lthooksdate{2021/09/28}
 %    \end{macrocode}
 %
 %<*driver>
@@ -959,13 +959,14 @@
 %   \begin{syntax}
 %     \cs{hook_activate_generic:n} \Arg{hook}
 %   \end{syntax}
-%    Like \cs{hook_new:n} but does nothing if the hook was previously
-%    declared with \cs{hook_new:n}.  This declaration should only be used
-%    in special situations, e.g., when a command of another package
-%    needs to be altered and it is not clear if for that command a
-%    generic \hook{cmd} hook was already explicitly declared before.
-%
-%    Normally \cs{hook_new:n} should be used instead.
+%    This is like \cs{hook_new:n} but it does nothing if the hook was previously
+%    declared with \cs{hook_new:n}.  This declaration should be used
+%    only in special situations, e.g., when a command from another package
+%    needs to be altered and it is not clear whether a
+%    generic \hook{cmd} hook (for that command) has been previously 
+%    explicitly declared.
+%
+%    Normally \cs{hook_new:n} should be used instead of this.
 % \end{function}
 %
 %
@@ -3138,10 +3139,13 @@
 %   component to see if we have to make a reversed hook.  In either case
 %   the function returns \meta{true} for a generic hook and \meta{false}
 %   in other cases.
+%
+% \changes{v1.0s}{2021/09/28}
+%                {Correct usage of older \cs{@@_if_file_hook:wTF} (gh/675)}
 %    \begin{macrocode}
 %<latexrelease>\cs_new_protected:Npn \@@_try_declaring_generic_hook:nNNnn #1
 %<latexrelease>  {
-%<latexrelease>    \@@_if_file_hook:wTF #1 / \s_@@_mark {#1}
+%<latexrelease>    \@@_if_file_hook:wTF #1 / \s_@@_mark
 %<latexrelease>      {
 %<latexrelease>        \exp_args:Ne \@@_try_declaring_generic_hook_split:nNNnn
 %<latexrelease>          { \exp_args:Ne \@@_file_hook_normalize:n {#1} }
@@ -4777,10 +4781,12 @@
 %<latexrelease>  }
 %    \end{macrocode}
 %
+% \changes{v1.0s}{2021/09/28}
+%                {Correct usage of older \cs{@@_if_file_hook:wTF} (gh/675)}
 %    \begin{macrocode}
 %<latexrelease>\cs_new_protected:Npn \@@_try_file_hook:n #1
 %<latexrelease>  {
-%<latexrelease>    \@@_if_file_hook:wTF #1 / \s_@@_mark {#1}
+%<latexrelease>    \@@_if_file_hook:wTF #1 / \s_@@_mark
 %<latexrelease>      {
 %<latexrelease>        \exp_args:Ne \@@_if_usable_use:n
 %<latexrelease>          { \exp_args:Ne \@@_file_hook_normalize:n {#1} }
diff --git a/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx b/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx
index 2508f5a7cc2..258ac482977 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx
@@ -28,7 +28,7 @@
 \ProvidesFile{ltluatex.dtx}
 %</driver>
 %<*tex>
-[2021/08/11 v1.1u
+[2021/10/15 v1.1v
 %</tex>
 %<plain>  LuaTeX support for plain TeX (core)
 %<*tex>
@@ -1415,6 +1415,7 @@ local callbacktypes = callbacktypes or {
 % \changes{v1.1j}{2019/06/18}{font\_descriptor\_objnum\_provider added}
 % \changes{v1.1l}{2020/02/02}{glyph\_info added}
 % \changes{v1.1t}{2021/04/18}{input\_level\_string added}
+% \changes{v1.1v}{2021/10/15}{provide\_charproc\_data added}
 %    \begin{macrocode}
   define_font                     = exclusive,
   glyph_info                      = exclusive,
@@ -1423,6 +1424,7 @@ local callbacktypes = callbacktypes or {
   make_extensible                 = exclusive,
   font_descriptor_objnum_provider = exclusive,
   input_level_string              = exclusive,
+  provide_charproc_data           = exclusive,
 %    \end{macrocode}
 % \changes{v1.0m}{2016/02/11}{pdf\_stream\_filter\_callback removed}
 %    \begin{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltmath.dtx b/Master/texmf-dist/source/latex-dev/base/ltmath.dtx
index aadb96fb023..59e0d89a106 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltmath.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltmath.dtx
@@ -38,7 +38,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltmath.dtx}
-              [2021/04/20 v1.2i LaTeX Kernel (Math Setup)]
+              [2021/10/14 v1.2j LaTeX Kernel (Math Setup)]
 % \iffalse
 %</driver>
 %
@@ -915,10 +915,13 @@
 %    whole display. Note that we can't use \cs{refstepcounter} as this
 %    results in |\@currentlabel| getting restored at the wrong and
 %    thus always writing the first label to the \texttt{.aux} file.
+% \changes{v1.2j}{2021/10/14}
+%         {Explicitly set \cs{@currentcounter} (gh/687)}
 %    \begin{macrocode}
 \def\eqnarray{%
    \stepcounter{equation}%
    \def\@currentlabel{\p@equation\theequation}%
+   \def\@currentcounter{equation}%
    \global\@eqnswtrue
    \m@th
    \global\@eqcnt\z@
@@ -1231,10 +1234,13 @@
 %
 % \begin{environment}{eqnarray}
 %    The \textsf{eqnarray} environment
+% \changes{v1.2j}{2021/10/14}
+%         {Explicitly set \cs{@currentcounter} (gh/687)}
 %    \begin{macrocode}
 \renewenvironment{eqnarray}{%
     \stepcounter{equation}%
     \def\@currentlabel{\p@equation\theequation}%
+    \def\@currentcounter{equation}%
     \global\@eqnswtrue\m@th
     \global\@eqcnt\z@
     \tabskip\mathindent
diff --git a/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx b/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx
index 14518d2fb24..61ea381823c 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx
@@ -44,7 +44,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltoutenc.dtx}
-             [2021/09/12 v2.0w LaTeX Kernel (font encodings)]
+             [2021/10/16 v2.0x LaTeX Kernel (font encodings)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltoutenc.dtx}
@@ -199,7 +199,7 @@
 %    commands, such as accents.  It also contains the code for some of
 %    the encoding files, including |omlenc.def|,
 %    |omsenc.def|, |t1enc.def| and |ot1enc.def| files, which define
-%    the |OLM|,
+%    the |OML|,
 %    |OMS|, |T1| and |OT1| encodings, and the |fontenc| package
 %    for selecting encodings.
 %
@@ -845,10 +845,11 @@
 %    We also ignore \cs{ignorespaces} which has the same issue and may
 %    show up as part of \cs{normalfont} if that is used.
 % \changes{v2.0m}{2019/12/18}{Avoid code that breaks \cs{accent}}
+% \changes{v2.0x}{2021/10/16}{Dont set \cs{spacefactor in math mode gh/643}}
 %    \begin{macrocode}
    \let\maybe@load@fontshape\relax
    \let\ignorespaces\relax
-   \accent#1 #2\egroup\spacefactor\accent@spacefactor}
+   \accent#1 #2\egroup\ifmmode\else\spacefactor\accent@spacefactor\fi}
 %    \end{macrocode}
 %
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/ltpara.dtx b/Master/texmf-dist/source/latex-dev/base/ltpara.dtx
index bc51e4688ff..9802bfd63a2 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltpara.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltpara.dtx
@@ -14,8 +14,8 @@
 %%% From File: ltpara.dtx
 %
 %    \begin{macrocode}
-\def\ltparaversion{v1.0j}
-\def\ltparadate{2021/09/18}
+\def\ltparaversion{v1.0k}
+\def\ltparadate{2021/10/19}
 %    \end{macrocode}
 %<*driver>
 \documentclass{l3doc}
@@ -122,8 +122,8 @@
 %    \verb=\hbox{a\par b}= is ignored, but \verb=$a\par b$= would complain.
 %
 %    If this primitive ends the paragraph it does some special
-%    \enquote{end of horizontal list} processing, then calls \TeX{} paragraph
-%    builder that breaks the horizontal list into lines then these
+%    \enquote{end of horizontal list} processing, then calls \TeX{}’s paragraph
+%    builder; this breaks the horizontal list into lines and then these
 %    lines are added as boxes to the enclosing vertical list and
 %    \TeX{} returns to vertical mode.
 %
@@ -133,13 +133,14 @@
 %    automatically changed to a \cs{par} command which is then
 %    executed. The other possibility is that \TeX{} encounters a
 %    command which is incompatible with horizontal processing, e.g.,
-%    \cs{vskip} (a request for adding vertical space). In such case it
+%    \cs{vskip} (a request for adding vertical space). In such cases it
 %    silently backs up, and inserts a \cs{par} in the hope that this
-%    gets it out of horizontal mode and makes the offending command
+%    gets it out of horizontal mode and makes the vertical command
 %    acceptable.
 
 %    The important point to note here is that \TeX{} really inserts
-%    the command \cs{par} which can be redefined. Thus, it may not have
+%    the command with the name \cs{par}, which can be redefined. 
+%    Thus, it may not have
 %    its original \enquote{primitive} meaning and therefore may not end the
 %    horizontal list and call the paragraph builder. This approach
 %    offers some flexibility but also allows you  to easily produce a
@@ -151,31 +152,30 @@
 %    then sees \cs{vskip} and inserts \cs{par} to end the
 %    paragraph. But this now only runs \cs{relax} so nothing changes
 %    and \cs{vskip} is read again, issues a \cs{par} which \ldots. In
-%    short, it takes a plain \TeX{} document with five tokens to run
-%    forever (as not even memory is consumed and therefore eventually
+%    short, it only takes a plain \TeX{} document with five tokens to run
+%    forever (since no memory is consumed and therefore eventually
 %    exhausted).
 %
-%    There are no other ways than changing \cs{par} to gain control at
+%    There is no way other than changing \cs{par} to gain control at
 %    the end of a paragraph, i.e., there is no token list like
-%    \cs{everypar} that is inserted, i.e., the only way to change the
-%    default behavior is to modify the action that \cs{par} executes
+%    \cs{everypar} that is inserted.  Hence the only way to change the
+%    default behavior is to modify the action that \cs{par} executes,
 %    with similar issues as outlined before: different processes need
 %    to ensure that they do not overwrite their modifications or
 %    worse, think that the \cs{par} in front of them is the engine
 %    primitive while in fact it has already been changed by other
 %    code.
 %
-%
 %    To make matters slightly worse there are a few places where
 %    \TeX{} handles the situation differently (most likely for speed
 %    reasons back when computers were much slower). If \TeX{} finds
 %    itself in unrestricted horizontal mode at the end of building a
-%    vertical box (or an \cs{insert}, \cs{vadjust} or at the end of
+%    vertical box (for an \cs{insert}, \cs{vadjust} or 
 %    executing the output routine code), it will finish the horizontal
 %    list not by issuing a \cs{par} command (which would be consistent
-%    with all other places, but by simply executing the primitive version
-%    of \cs{par} regardless of the definition that \cs{par} has at the
-%    time.
+%    with all other places) but by simply executing the primitive meaning
+%    of \cs{par}, regardless of the actual definition that \cs{par} 
+%    has at the time.
 %
 %    Thus, if you have carefully crafted a redefined \cs{par} to execute
 %    some special actions at the end of a paragraph and you write
@@ -183,27 +183,28 @@
 %\begin{verbatim}
 %   \vbox{Some paragraph ... text.}
 %\end{verbatim}
-%    you will find that your code has never run for the last paragraph
+%    you will find that your code does not get run for the last paragraph
 %    in that box. \LaTeX{} avoids this problem, by making sure that
-%    all its boxes (such as \cs{parbox} or the \env{minipage}
+%    its boxes (such as \cs{parbox} or the \env{minipage}
 %    environment, etc.) all internally add an explicit \cs{par} at the
 %    end so that such code is run and \TeX{} finds itself in vertical
 %    mode already without the need to start up the paragraph builder
 %    internally. But, of course, this only works for boxes under direct
-%    control of the \LaTeX{} kernel, if some package uses low-level
+%    control of the \LaTeX{} kernel; if some package uses low-level
 %    \cs{vbox}es without adding this precaution the \TeX{}
 %    optimization kicks in and no special \cs{par} code is executed.
 %
 %    And there is another optimization that is painful: if a paragraph
 %    is interrupted by a mathematical display, e.g., \verb=\[...\]= in
 %    \LaTeX{} or \verb=$$...$$= in plain \TeX{}, then \TeX{} will
-%    resume horizontal mode afterward, i.e., build a new horizontal
-%    list (without inserting an indentation box or \cs{everypar} at
-%    that point). However, if that list immediately ends with an
+%    resume horizontal mode afterward, i.e., it will start to build 
+%    a new horizontal
+%    list without inserting an indentation box or \cs{everypar} at
+%    that point.  However, if that list immediately ends with an
 %    explicit or implicit \cs{par} then \TeX{} will simply throw away
 %    this \enquote{null} paragraph and not do its usual \enquote{end
-%    of horizontal list} processing, so this special case need to be
-%    accounted for when introducing some extended processing.
+%    of horizontal list} processing, so this special case also needs to be
+%    accounted for when introducing any extended processing.
 %
 %
 %
@@ -214,8 +215,8 @@
 %    the start and end of the paragraph processing. The public hooks
 %    can be used by packages (or by the user in the preamble or
 %    within the document) and using the hook mechanisms it is possible
-%    to reorder or arrange code from different packages in a way that
-%    it can safely coexist.
+%    to reorder or arrange code from different packages in such a way that
+%    these can safely coexist.
 %
 %    To make that happen we have to make use of the basic
 %    functionality that is offered by \TeX{}, e.g., we install
@@ -248,7 +249,7 @@
 %    Fortunately, \LaTeX{} has already redefined \cs{par} for its own
 %    purposes. As a result there aren't many packages that attempt to
 %    change \cs{par}, because without a lot of extra care that would
-%    fail miserably. But bottom line, if you load a package that
+%    fail miserably. But the bottom line is that, if you load a package that
 %    alters \cs{par} then the end of paragraph hooks are most likely
 %    not executing while that redefinition is
 %    active.\footnote{Similarly to the \cs{everypar} situation, the
@@ -326,7 +327,7 @@
 %
 %      This hook is executed at the end of a paragraph when \TeX{} is
 %      ready to return to vertical mode and after it has removed the
-%      last horizontal glue (but not kern) placed on the horizontal
+%      last horizontal glue (but not any kerns) placed on the horizontal
 %      list. The code is still executed in horizontal mode so it is
 %      possible to add further horizontal material at this point, but
 %      it should not alter the mode (even a temporary exit from
@@ -415,20 +416,30 @@
 % \subsection{Altered and newly provided commands}
 %
 % \begin{function}{\par,\endgraf,\para_end:}
-%    An explicit request for ending a paragraph is known in plain
-%    \TeX{} under the name \cs{endgraf} where it simply calls the
-%    paragraph primitive (regardless of what \cs{par} may have as its
-%    current definition). In \LaTeX{} \cs{endgraf} with that behavior
-%    was also made available.
+%    An explicit request for ending a paragraph is provided in plain
+%    \TeX{} under the name \cs{endgraf}, which simply uses the
+%    primitive meaning (regardless of what \cs{par} may have as its
+%    current definition). In \LaTeX{} \cs{endgraf} (with that behavior)
+%    was originally also available.
 %
 %    With the new paragraph handling in \LaTeX{}, ending a paragraph
 %    means a bit more than just calling the engine's paragraph
 %    builder: the process also has to add any hook code for the end of
 %    a paragraph. Thus
 %    \cs{endgraf} was changed to provide this additional functionality
-%    (and so by extension \cs{par} subject to its current meaning).
-%
-%    The \pkg{expl3} name for the functionality is \cs{para_end:}.
+%    (along with \cs{par} remaining subject to its current meaning).
+%
+%    TEMP NOTE: Maybe endgraf should not be changed by LaTeX as it is 
+%    essentially not at all a part of LaTeX.  
+%    If it is too dangerous to leave it as 
+%    a synonym for the primitive, then we could just disable it.
+%    [FMi:]
+%     not in my opinion. It is used in many places and the redefinition is safe and does the right thing.
+%     disabling it just means it breaks a lot of stuff for no reason.
+%    [FMi:]
+%    Note that the 2e kernel has been completely purged of endgrafs.
+%
+%    The \pkg{expl3} name for this functionality is \cs{para_end:}.
 % \end{function}
 %
 % \begin{quote}
@@ -538,7 +549,7 @@
 %    sequence numbers. This is most easily done using \pkg{expl3}
 %    functions, so we switch over. This is not a very general
 %    implementation, just enough for what we need and a bit of
-%    \LaTeXe{} thrown in as well. When popping the result gets stored
+%    \LaTeXe{} thrown in as well. When popping, the result gets stored
 %    in \cs{paracntvalue} and the \cs{ERROR}  should never happen
 %    because it means we have tried to pop from an empty stack.
 %\begin{verbatim}
@@ -629,7 +640,7 @@
 % \subsubsection{Glue items between paragraphs (found with \pkg{fancypar})}
 %
 %    In the past \LaTeX{} placed two glue items between two
-%    consecutive paragraph, e.g.,
+%    consecutive paragraphs, e.g.,
 %\begin{verbatim}
 %   text1 \par text2 \par
 %\end{verbatim}
@@ -644,12 +655,12 @@
 % \glue(\parskip) 0.0
 % \glue(\baselineskip) 5.16669
 %\end{verbatim}
-%    The reason is that we generate a \enquote{fake}'' paragraph to
+%    The reason is that we generate a \enquote{fake} paragraph to
 %    gain control and safely add the early hooks, but this generates
 %    an additional glue item. That item doesn't contribute anything
-%    vertically but ifsomebody writes code the unravels a constructed
+%    vertically but if somebody writes code that unravels a constructed
 %    list using \cs{lastbox}, \cs{unskip} and \cs{unpenalty} then the
-%    code has to remove one additional glue item  or else will fail.
+%    code has to remove one additional glue item  or else it will fail.
 
 %
 % ^^A \subsubsection{}
@@ -828,8 +839,8 @@
 %
 %    But if we have already replaced it by a token register then all
 %    they do is to give that token register a new name. Thus our code
-%    in \cs{tex_everypar:D} would call \cs{everypar} (which is their
-%    now token register) and the code that they added ends up in our
+%    in \cs{tex_everypar:D} would call \cs{everypar} (which is now their
+%    token register) and the code that they added ends up in our
 %    token register which is then never used at all. A bit mind
 %    boggling I guess.
 %
@@ -927,7 +938,7 @@
 %    \end{itemize}
 %
 %    Unfortunately, \TeX{} has some (these days) unnecessary
-%    optimization: if a \cs{vbox} ends and \TeX{} is still in
+%    optimizations: if a \cs{vbox} ends and \TeX{} is still in
 %    horizontal mode it simply exercises the paragraph builder instead
 %    of issuing a \cs{par}. It is therefore necessary for \LaTeX{} to
 %    ensure that this case doesn't happen and all boxes internally
@@ -940,11 +951,12 @@
 %    \texttt{latex.ltx}.  For this \LaTeXe{} code has the following
 %    conventions: \cs{@@@@par} and \cs{endgraf} both refer to the
 %    default meaning (in the past this was the initex primitive) while
-%    \cs{par} is the current meaning which may does something else.
+%    \cs{par} is the current meaning which maybe does something else.
 %
+%    TEMP NOTE: See earlier note re endgraf.
 %
-%    We are now going to change this default meaning to run
-%    \cs{para_end:} instead, which ultimately executes the initex
+%    We are now going to change this default meaning to instead run
+%    \cs{para_end:}, which ultimately executes the initex
 %    primitive but additionally adds our hooks when appropriate.
 %    This way the change is again transparent to the legacy \LaTeXe{}
 %    code.
@@ -953,22 +965,24 @@
 %    primitive and we achieve this by simply expanding it to the
 %    primitive which is available to us as \cs{tex_par:D}. This way we
 %    don't have to care about whether \TeX{} just does nothing (e.g.,
-%    if in vertical mode already) or generate an error, etc.
+%    if in vertical mode already) or generates an error, etc.
 %    \begin{macrocode}
 \cs_new_protected:Npn \para_end: {
 %    \end{macrocode}
 %
+%    TEMP NOTE: What should happen if in outer hmode with an empty hlist? 
+%
 %    The only case we care about is when we are in horizontal mode
 %    (i.e., doing typesetting) and not also in inner mode (i.e.,
 %    making paragraphs and not building an \cs{hbox}.
-%    \begin{macrocode}
+%\begin{verbatim}
 %  \bool_lazy_and:nnT
 %       { \mode_if_horizontal_p: }
 %       { \bool_not_p:n { \mode_if_inner_p: } }
 %       { ...
-%    \end{macrocode}
+%\end{verbatim}
 %    Since this is executed for each and every paragraph in a document
-%    we try to stay a fast as possible, So we are aren't using the
+%    we try to stay as fast as possible, so we do not use the
 %    above construct but two conditionals instead. Using low-level
 %    \cs{if_mode...} conditions would be even faster but has the
 %    danger to conflict with conditionals in the user hooks.
@@ -981,17 +995,18 @@
 %   \afterassignment\lst@vskip\@tempskipa \z@ \par
 %\end{verbatim}
 %    If \TeX{} is in hmode while that assignment happens then the
-%    \cs{par} is seen in hmode (because in the above case the
-%    assignment isn't finished (one should have used \cs{z@skip} and
+%    \cs{par} is seen in hmode because in the above case the
+%    assignment may not be finished (one should have used \cs{z@skip}) and
 %    the \cs{lst@vskip} will get inserted into the middle of the
 %    conditional. The \cs{lst@vskip} then changes to vmode and you get
 %    a surprising error about the \texttt{para/end} hook having
-%    changed modes even if you don't have any hook code because it is
-%    the instered \cs{lst@vskip} that is causing it. That happened
+%    changed modes even if you don't have any hook code(!): it is
+%    the inserted \cs{lst@vskip} that is actually causing the change of 
+%    mode.This is what happened
 %    when the output routines got started while a \texttt{lstlisting}
 %    environment (that redefines \cs{vskip} in this way) was
 %    active. This is really faulty coding, but we try to be proactive
-%    and guard the conditional so thatany scanning is stopped before it:
+%    and guard the conditional so that any scanning is first stopped, thus:
 %    \begin{macrocode}
   \scan_stop:
 %    \end{macrocode}
@@ -1001,17 +1016,26 @@
     \mode_if_inner:F {
 %    \end{macrocode}
 %    In that case the action of the primitive would be to remove the
-%    last glue (not kern) from the horizontal list constructed to form
-%    a paragraph then append the a penalty of 10000 and the
-%    \cs{parfillskip} at the end and pass the whole list to the
-%    paragraph builder which breaks it into lines and \TeX{} then
+%    last glue (but no kerns) from the horizontal list (constructed to form
+%    a paragraph) and then to append a penalty of 10000 and the
+%    \cs{parfillskip}; it then passes the whole list to the
+%    paragraph builder, which breaks it into lines and \TeX{} then
 %    returns to vertical mode.
 %
-%    What we want to do instead is to add our hook code at the end of
-%    the horizontal list before that happens and the code is passed to
-%    the paragraph builder. If there was a glue item at the end then
+%    What we want to do is to add this hook code at the end of
+%    the horizontal list before any of the above happens. 
+%    If there was a glue item at the end of the list then
 %    it should get removed before the hook code gets added so we have
-%    to arrange for its removal ourselves.
+%    to arrange for this removal.  
+%
+%    TEMP NOTE: maybe a ‘nobreak’ should also be added?
+%
+%    [FMi:]
+%      sounds wrong to me, why?  
+%      [CCC:] See email: because the hook may add some material,
+%                such as glue that might produce an unintended linebreak. 
+%    [FMi:]
+%
 %
 %    There is not much point in checking if there was really a glue
 %    item at the end of the horizontal list, instead we simply try to
@@ -1020,38 +1044,44 @@
 %    \begin{macrocode}
          \tex_unskip:D
 %    \end{macrocode}
-%    The we execute the public hook (which may add final typesetting
-%    material) followed by the kernel hook we need for adding tagging
+%    We then execute the public hook (which may add some final typeset
+%    material) followed by the kernel hook that we need for adding tagging
 %    support. None of this is supposed to change the mode---at the
 %    moment we make only a very simple test for this, more devious
-%      changes go unnoticed, but too bad, that will then probably
-%      badly backfire.
+%      changes go unnoticed, but too bad as they will then probably
+%      backfire badly.
 %    \begin{macrocode}
          \hook_use:n{para/end}
          \@kernel@after@para@end
          \mode_if_horizontal:TF {
 %    \end{macrocode}
 %    The final action (before getting to the point where
-%    \cs{tex_par:D} is called) is to add a glue item so that the
-%    primitive is prevented from removing glue (if there was some). If
-%      we don't do this and the
-%    horizontal list ended in several glue items we would end up  with
-%    removing two instead of just the last one, which would be wrong.
-%    We use glue (rather than a kern) as that will be removed by the primitive
-%    par.
+%    \cs{tex_par:D} is called) is to add an extra glue item so that the
+%    primitive is prevented from removing intended glue
+%    (if there was some). If we don't do this and the
+%    horizontal list ends in several glue items we would end up removing 
+%    two glue items instead of just the last one, which would be wrong.  
+%    We use glue (rather than a kern) as that will be removed by the 
+%    primitive.
 %
 %    There is however one other \TeX{} optimization that hurts: in a
 %    sequence like this \verb=$$ ... $$ \par=  \TeX{} will be in
 %    horizontal mode after the display, ready to receive further
 %    paragraph text, but since the \cs{par} follows immediately there
 %    is a ``null'' paragraph at the end and \TeX{} simply throws that
-%    away. The space between \verb=$$= and \cs{par} got already
+%    away. 
+%    The space between \verb=$$= and \cs{par} got already
 %    dropped during the display processing so the \cs{par} is not
 %    removing any space and appending \cs{parfillskip}, instead it
-%    simply goes silently to vmode. Now if we would have added something (to
+%    simply goes silently to vmode. 
+%
+%    TEMP NOTE: Is this actually how it works? 
+%       For any current definition of par?
+%
+%    Now if we would have added something (to
 %    prevent glue removal) that would look to \TeX{} like material
 %    after the display and so we would end up with an empty paragraph
-%    just containing \cs{parfillskip}.
+%    just containing a penalty and \cs{parfillskip}.
 %
 %    We therefore check if the current hlist does end in glue
 %    (\cs{tex_lastnodetype:D} has the value \texttt{11}) and
@@ -1066,15 +1096,16 @@
 %    To run the \hook{para/after} hook we first end the
 %    paragraph. This means that the \cs{tex_par:D} at the very end is
 %    unnecessary but executing it there unnecessarily is better than
-%    having code that test for all the different mode possibilities.
+%    having code that tests for all the different mode possibilities.
 %    \begin{macrocode}
            \tex_par:D
            \hook_use:n{para/after}
            \@kernel@after@para@after
          }
 %    \end{macrocode}
-%    If we haven't been in horizontal mode then the earlier hook
-%    \hook{para/end} is at fault and we report that.
+%    If we were not horizontal mode (the F case from above) 
+%    then the earlier hook
+%    \hook{para/end} must have been at fault, so we report that.
 %    \begin{macrocode}
          { \msg_error:nnnn { hooks }{ para-mode }{end}{horizontal} }
 %    \end{macrocode}
@@ -1083,7 +1114,7 @@
     }
   }
 %    \end{macrocode}
-%
+%     And then we can use the primitive to truly end the paragraph.
 %    \begin{macrocode}
   \tex_par:D
 }
@@ -1160,10 +1191,13 @@
 %  \begin{macro}[int]{\@@par}
 %
 %    Having the new default definition for \cs{par} we also have to
-%    set it up so that it gets used. This is needed in three places
+%    set it up so that it gets used. This involves three commands:
 %    \cs{par}, \cs{@@par} (to which \LaTeX{} resets \cs{par}
-%    occasionally) and \cs{endgraf} which is another name for the
+%    occasionally) and \cs{endgraf}, which is another name for the
 %    ``default'' action of \cs{par}.
+%
+%    TEMP NOTE: re endgraf again.
+%
 %    \begin{macrocode}
 \cs_set_eq:NN \par     \para_end:
 \cs_set_eq:NN \@@par   \para_end:
@@ -1235,6 +1269,16 @@
 %<latexrelease>\cs_set_eq:NN \@@par   \tex_par:D
 %<latexrelease>\cs_set_eq:NN \endgraf \tex_par:D
 %<latexrelease>
+%    \end{macrocode}
+%    We also need to clean up the primitive ``everypar'' as that
+%    should no longer execute any code by default. And, of course,
+%    make \cs{everypar} become the primitive again.
+% \changes{v1.0k}{2021/10/19}{Remove content from \cs{tex_everypar:D}
+%    on rollback}
+%    \begin{macrocode}
+%<latexrelease>\tex_everypar:D {}
+%<latexrelease>\cs_set_eq:NN \everypar \tex_everypar:D
+%<latexrelease>
 %<latexrelease>\EndModuleRelease
 \ExplSyntaxOff
 %</2ekernel|latexrelease>
diff --git a/Master/texmf-dist/source/latex-dev/base/ltvers.dtx b/Master/texmf-dist/source/latex-dev/base/ltvers.dtx
index 3f2f119cb1b..7c17069aea0 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltvers.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltvers.dtx
@@ -115,7 +115,7 @@
    {2021-11-15}
 %</2ekernel|latexrelease>
 %<*2ekernel>
-\def\patch@level{-2}
+\def\patch@level{-3}
 %    \end{macrocode}
 %
 % \begin{macro}{\development@branch@name}
diff --git a/Master/texmf-dist/source/latex-dev/base/makeindx.dtx b/Master/texmf-dist/source/latex-dev/base/makeindx.dtx
index e8e48e60b06..9dc03a8431e 100644
--- a/Master/texmf-dist/source/latex-dev/base/makeindx.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/makeindx.dtx
@@ -121,7 +121,7 @@
 %    \begin{macrocode}
 %<makeidx>\ProvidesPackage{makeidx}
 %<showidx>\ProvidesPackage{showidx}
-                [2014/09/29 v1.0m Standard LaTeX package]
+                [2021/10/04 v1.0m Standard LaTeX package]
 %    \end{macrocode}
 %
 % \subsection{Makeidx}
@@ -261,7 +261,7 @@
 %
 % \begin{macro}{\raggedbottom}
 % \begin{macro}{\flushbottom}
-%    The definition of these macros from \texttt{latex.dtx} is changed
+%    The definitions of these macros from the \LaTeX{} format are changed
 %    here to add the execution of |\@mkidx| to |\@texttop|, which is
 %    executed at the top of each page.
 %    \begin{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/preload.dtx b/Master/texmf-dist/source/latex-dev/base/preload.dtx
index b2ca24bce5b..bf2bfebbfa9 100644
--- a/Master/texmf-dist/source/latex-dev/base/preload.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/preload.dtx
@@ -45,7 +45,7 @@
 %<+tex> \ProvidesFile{preload.ltx}
 % \fi
 %       \ProvidesFile{preload.dtx}
-         [2014/09/29 v2.1g LaTeX Kernel (Font Preloading)]
+         [2021/10/04 v2.1g LaTeX Kernel (Font Preloading)]
 %
 %
 %
@@ -179,7 +179,7 @@
 %    We begin by loading the math extension font (cmex10)
 %    and the \LaTeX{} line and circle fonts.
 %    It is necessary to do this explicitly since these are
-%    used by \texttt{lplain.tex} and \texttt{latex.tex}.
+%    used by the \LaTeX{} format.
 %    Since the internal font name contains |/| characters
 %    and digits we construct the name via |\csname|.
 %    These are the only fonts (!) that must be loaded in this file.
diff --git a/Master/texmf-dist/source/latex-dev/base/slides.dtx b/Master/texmf-dist/source/latex-dev/base/slides.dtx
index 883e7d34f04..e63c1901d6d 100644
--- a/Master/texmf-dist/source/latex-dev/base/slides.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/slides.dtx
@@ -53,7 +53,7 @@
 %<*driver>
        \ProvidesFile{slides.drv}
 %</driver>
-              [2020/11/23 v2.4b
+              [2021/10/04 v2.4b
 %<+class>               Standard LaTeX document class]
 %<+cmd>               SLiTeX definitions]
 %    \end{macrocode}
@@ -1342,7 +1342,7 @@
 %
 % \begin{environment}{description}
 %    The description environment is defined here -- while the itemize
-%    and enumerate environments are defined in \file{latex.dtx}.
+%    and enumerate environments are defined in the \LaTeX{} format.
 %
 %    \begin{macrocode}
 \newenvironment{description}{\list{}{\labelwidth\z@
@@ -1373,7 +1373,7 @@
 % \begin{macro}{\theenumii}
 % \begin{macro}{\theenumiii}
 % \begin{macro}{\theenumiv}
-%    The counters are already defined in \file{latex.dtx}, but their
+%    The counters are already defined in the \LaTeX{} format, but their
 %    representation is changed here.
 %
 %    \begin{macrocode}
@@ -2349,7 +2349,7 @@ COLOR LAYER\\[.75in]%
 %
 % \changes{v2.2j}{1994/03/11}{Corrected \cs{@oval}, like previous
 % \changes{v2.4a}{2016/03/29}{Initialize in \cs{@oval}tests added for
-%    latex/4452} change to \file{latex.dtx}.}
+%    latex/4452} change to the \LaTeX{} format.}
 %    \begin{macrocode}
 \def\line(#1,#2)#3{\if@visible\@xarg #1\relax \@yarg #2\relax
 \@linelen #3\unitlength
diff --git a/Master/texmf-dist/source/latex-dev/graphics/color.dtx b/Master/texmf-dist/source/latex-dev/graphics/color.dtx
index 2dfbb238daa..9418a124773 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/color.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/color.dtx
@@ -21,7 +21,7 @@
 %<driver> \ProvidesFile{color.drv}
 % \fi
 %         \ProvidesFile{color.dtx}
-          [2020/02/24 v1.2b Standard LaTeX Color (DPC)]
+          [2021/10/11 v1.3b Standard LaTeX Color (DPC)]
 %
 % \iffalse
 %<*driver>
@@ -78,6 +78,9 @@
 % fixed values whilst this file is being read.
 % \changes{v0.3b}{1994/09/14}
 %     {Save and restore catcodes}
+% \changes{v1.3a}{2021/09/27}
+%     {Use \cs{@backslashchar} in preference to \cs{string} gh/659}
+%
 %    \begin{macrocode}
 \edef\Gin@codes{%
  \catcode`\noexpand\^^A\the\catcode`\^^A\relax
@@ -185,9 +188,11 @@
 % \begin{option}{dvipdfm}
 % \changes{v1.0h}{1999/01/13}
 %     {dvipdfm added}
-% Mark Wick's dvipdfm driver.
+% \changes{v1.3b}{2021/10/11}
+%     {make dvipdfm an alias for dvipdfmx}
+% Mark Wick's dvipdfm driver (now merged with xdvipdfmx).
 %    \begin{macrocode}
-\DeclareOption{dvipdfm}{\def\Gin@driver{dvipdfm.def}}
+\DeclareOption{dvipdfm}{\def\Gin@driver{dvipdfmx.def}}
 %    \end{macrocode}
 % \end{option}
 %
@@ -375,7 +380,7 @@
 %    \begin{macrocode}
 \DeclareOption{usenames}{%
   \def\c@lor@usename#1{%
-    \expandafter\color@named\csname\string\color @#1\endcsname{#1}}}
+    \expandafter\color@named\csname\@backslashchar color @#1\endcsname{#1}}}
 %    \end{macrocode}
 % \end{option}
 %
@@ -432,10 +437,10 @@
 % Finally call |\set@color| to effect the colour change.
 %    \begin{macrocode}
 \def\@declaredcolor#1{%
-  \@ifundefined{\string\color @#1}%
+  \@ifundefined{\@backslashchar color @#1}%
     {\c@lor@error{`#1'}}%
     {\expandafter\let\expandafter\current@color
-     \csname\string\color @#1\endcsname
+     \csname\@backslashchar color @#1\endcsname
      \set@color}%
   \ignorespaces}
 %    \end{macrocode}
@@ -506,7 +511,7 @@
 %    \begin{macrocode}
 \protected\def\nopagecolor{%
   \@ifundefined{no@page@color}{%
-    \PackageInfo{color}{\string\nopagecolor\space is not supported}%
+    \PackageInfo{color}{\@backslashchar nopagecolor\space is not supported}%
   }{%
     \no@page@color
   }%
@@ -545,10 +550,10 @@
 \protected\def\definecolor#1#2#3{%
   \@ifundefined{color@#2}%
     {\c@lor@error{model `#2'}}%
-    {\@ifundefined{\string\color @#1}{}%
+    {\@ifundefined{\@backslashchar color @#1}{}%
       {\PackageInfo{color}{Redefining color #1}}%
      \csname color@#2\expandafter\endcsname
-         \csname\string\color @#1\endcsname{#3}}}
+         \csname\@backslashchar color @#1\endcsname{#3}}}
 %    \end{macrocode}
 %  \end{macro}
 %
diff --git a/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx b/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx
index 0c5c9e88eca..cec35559ef8 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx
@@ -616,7 +616,7 @@
 %    \end{macrocode}
 % \end{option}
 %
-% \begin{option}{luatex}
+% \begin{option}{dvisvgm}
 % \changes{v1.0r}{2016/05/09}
 %     {dvisvgm added}
 %  dvisvgm driver.
diff --git a/Master/texmf-dist/source/latex-dev/tools/array.dtx b/Master/texmf-dist/source/latex-dev/tools/array.dtx
index eab451fccd0..ba88aba7c26 100644
--- a/Master/texmf-dist/source/latex-dev/tools/array.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/array.dtx
@@ -33,7 +33,7 @@
 %<+package>\DeclareCurrentRelease{}{2020-10-01}
 %<+package>
 %<+package>\ProvidesPackage{array}
-%<+package>         [2021/07/12 v2.5f Tabular extension package (FMi)]
+%<+package>         [2021/10/04 v2.5f Tabular extension package (FMi)]
 %
 % \fi
 %
@@ -927,12 +927,12 @@
 %    \textsf{token} is stored in the
 %    \textsf{count} register =\@lastchclass=.
 %    All of the mentioned registers are already allocated in
-%    \texttt{latex.tex},
+%    the \LaTeX{} format,
 %    which is the reason why the following three lines of code are
 %    commented out.
 %    Later throughout the text I will not mention it again explicitly
 %    whenever I use a =%= sign. These parts are already defined in
-%    \texttt{latex.tex}.
+%    the \LaTeX{} format.
 %    \begin{macrocode}
 % \newcount \@chclass
 % \newcount \@chnum
diff --git a/Master/texmf-dist/source/latex-dev/tools/multicol.dtx b/Master/texmf-dist/source/latex-dev/tools/multicol.dtx
index 25d4bc68db1..2b74d85af92 100644
--- a/Master/texmf-dist/source/latex-dev/tools/multicol.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/multicol.dtx
@@ -98,7 +98,7 @@
 %<driver> \ProvidesFile{multicol.drv}
 % \fi
 %         \ProvidesFile{multicol.dtx}
-          [2021/07/06 v1.8z  multicolumn formatting (FMi)]
+          [2021/10/08 v1.9a  multicolumn formatting (FMi)]
 %
 %
 %%
@@ -564,6 +564,13 @@
 % forced into the second column  (resulting in some white
 % space between paragraphs in the first column).
 %
+% From version 1.9 onwards \cs{columnbreak} accepts an optional
+% argument (just like \cs{pagebreak}) in which you can specify the
+% desirability to break the column at that point: supported values are
+% \texttt{1} to \texttt{4}. This version also adds \cs{newcolumn}
+% which forces a column break but runs the column short (comparible to
+% \cs{newpage}). 
+%
 % \subsection{Floats inside a \mc{} environment}
 %
 % Within the \mc{} environment the usual star float commands are
@@ -981,7 +988,8 @@
 % \changes{v1.8x}{2019/10/15}{Use \cs{@maxdepth} not \cs{maxdepth} (gh/190)}
 %    \begin{macrocode}
 \let\mc@gridwarn\maxdimen
-\DeclareOption{grid}{\def\mc@gridwarn{\@maxdepth}}
+\DeclareOption{grid}
+    {\def\mc@gridwarn{\@maxdepth}}
 %    \end{macrocode}
 %
 % \changes{v1.8e}{2014/04/23}{Support \cs{docolaction}}
@@ -1071,7 +1079,8 @@
 % \changes{v1.6e}{2004/02/14}{Avoid self-referencing definition of
 %    \cs{@footnotetext} (pr/3618)}.
 %    \begin{macrocode}
-     \ifx\@footnotetext\mult@footnotetext\else
+     \ifx\@footnotetext\mult@footnotetext
+     \else
        \let\orig@footnotetext\@footnotetext
        \let\@footnotetext\mult@footnotetext
      \fi
@@ -1512,10 +1521,13 @@
    \def\clearpage{%
      \ifx\@deferlist\@empty\else
        \PackageError{multicol}%
-          {Deferred floats not cleared}%
-          {A \string\clearpage\space inside multicols acts like
-           \string\newpage\space and doesn't clear floats.\MessageBreak
-           Move it before the multicols environment if you need it.}%
+        {Deferred floats not cleared}%
+        {A \string\clearpage\space inside
+         multicols acts like
+         \string\newpage\space and doesn't
+         clear floats.\MessageBreak
+         Move it before the multicols
+         environment if you need it.}%
      \fi
     \newpage}%
 %    \end{macrocode}
@@ -1701,7 +1713,8 @@
 %   for later.
 % \changes{v1.8r}{2018/01/28}{Macro added}
 %    \begin{macrocode}
-\mathchardef\@Mvi=10006  % 10005 is \columnbreak
+\mathchardef\@Mvi=10006  % 10005 is
+                         % \columnbreak
 %    \end{macrocode}
 %  \end{macro}
 %
@@ -1724,7 +1737,8 @@
 % \changes{v1.8c}{2013/11/03}{Add \cs{color@endgroup} to prevent color leak}
 % \changes{v1.8f}{2014/06/19}{Discard spaces before adding \cs{color@endgroup}}
 %    \begin{macrocode}
-    \remove@discardable@items\color@endgroup\egroup
+    \remove@discardable@items
+    \color@endgroup\egroup
 %    \end{macrocode}
 %    Now we call |\balance@columns| the routine that balances material
 %    stored in the box |\mult@box|.
@@ -1754,7 +1768,7 @@
       {Restore kept marks to\MessageBreak
        first: \meaning\kept@firstmark
        \MessageBreak bot\space\space:
-                     \meaning\kept@botmark }%
+              \meaning\kept@botmark }%
 %</marktrace>
 %    \end{macrocode}
 %    This finishes the code for the ``boxed'' case.
@@ -2203,7 +2217,7 @@
 % \changes{v1.8x}{2019/10/15}{Use \cs{@maxdepth} not \cs{maxdepth} (gh/190)}
 %    \begin{macrocode}
 \def\vfilmaxdepth{\vskip \z@ \@plus .0001fil
-                           \@minus \@maxdepth}
+                         \@minus \@maxdepth}
 %    \end{macrocode}
 % \end{macro}
 %
@@ -2335,7 +2349,8 @@
             \setbox\count@
                  \vbox to\dimen@
                   {\unvbox\count@
-                   \ifshr@nking\vfilmaxdepth\fi}%
+                   \ifshr@nking
+                    \vfilmaxdepth\fi}%
            }%
 %    \end{macrocode}
 %    Then the last column follows.
@@ -2615,7 +2630,8 @@
 % \changes{v1.8r}{2018/01/28}{Handling end of env through special penalty}
 %    \begin{macrocode}
        \ifnum\outputpenalty = -\@Mvi
-         \mult@info\@ne{End penalty of multicols seen}%
+         \mult@info\@ne{End penalty of
+                        multicols seen}%
 %    \end{macrocode}
 %    If we are at this point then we have to run the balancing code
 %    (which was previously its own output routine). First we pretend
@@ -2626,7 +2642,9 @@
 %    in a better way; basically it is like this, because of the older
 %    code was using different ORs and I simply reused most of it.
 %    \begin{macrocode}
-         \outputpenalty\@M   % pretend we had a natural forced break
+         \outputpenalty\@M % pretend we had
+                           % a natural
+                           % forced break
          \balance@columns@out
        \else
 %    \end{macrocode}
@@ -2647,7 +2665,8 @@
 %    this is possible with |\xdef|.)
 % \changes{v1.2a}{1990/02/05}{Float boxes freed.}
 %    \begin{macrocode}
-        \xdef\@freelist{\@freelist\@currlist}%
+        \xdef\@freelist{\@freelist
+                        \@currlist}%
         \gdef\@currlist{}%
       \fi
     \fi
@@ -2822,8 +2841,9 @@
 %    |\enlargethispage| command.
 % \changes{v1.8a}{2011/12/20}{Support for \cs{enlargethispage}}
 %    \begin{macrocode}
-     \ifvbox\@kludgeins\insert\@kludgeins
-                        {\unvbox\@kludgeins}\fi
+     \ifvbox\@kludgeins
+        \insert\@kludgeins
+               {\unvbox\@kludgeins}\fi
 %    \end{macrocode}
 %    Then we |\unvbox| the |\partial@page| (which may be void if we
 %    are not processing the first page of this \mc{} environment.
@@ -2833,7 +2853,8 @@
 %    Then we return the first and bottom mark and the gathered
 %    material to the main vertical list.
 %    \begin{macrocode}
-     \return@nonemptymark{first}\kept@firstmark
+     \return@nonemptymark{first}%
+                         \kept@firstmark
      \return@nonemptymark{bot}\kept@botmark
      \page@sofar
 %    \end{macrocode}
@@ -2960,12 +2981,14 @@
 % \changes{v1.8w}{2019/03/01}{Provide minrows counter for balancing}
 %    \begin{macrocode}
    \@tempdima\dimexpr
-       \topskip +\c@minrows\baselineskip-\baselineskip\relax
+      \topskip +\c@minrows\baselineskip
+               -\baselineskip\relax
    \ifnum\dimen@<\@tempdima
      \mult@info\@ne
        {Start value
           \the\dimen@  \space ->
-          \the\@tempdima \space (corrected for minrows)}%
+          \the\@tempdima \space
+          (corrected for minrows)}%
      \dimen@\@tempdima
    \fi
 %    \end{macrocode}
@@ -3466,7 +3489,9 @@
 %    directly at the values of the allocation counters.
 % \changes{v1.8y}{2019/12/09}{Allow for 20 columns (gh/237)}
 %    \begin{macrocode}
-\ifnum\numexpr \count20-\count14-1<41   % = 2 * 20 + 1
+\ifnum\numexpr
+        \count20-\count14-1<41
+        % this is = 2 * 20 + 1
   \count14=\@cclv
 \fi
 %    \end{macrocode}
@@ -4071,34 +4096,65 @@
 %
 %  \begin{macro}{\columnbreak}
 % \changes{v1.5u}{1999/05/25}{Macro added}
+% \changes{v1.9a}{2021/10/08}{Added optional argument for conditional break}
 %    |\columnbreak| is modeled after |\pagebreak| except that we
 %    generate a penalty -10005.
 %    \begin{macrocode}
 \mathchardef\@Mv=10005
-\def\columnbreak{%
+\newcommand\columnbreak[1][4]{%
 %    \end{macrocode}
 %    We have to ensure that it is only used within a \mc{}
 %    environment since if that penalty would be seen by the unmodified
 %    \LaTeX{} output routine strange things would happen.
 %    \begin{macrocode}
- \ifnum\col@number<\tw@
-  \PackageError{multicol}%
-   {\noexpand\columnbreak outside multicols}%
-   {This command can only be used within
-    a multicols or multicols* environment.}%
- \else
-  \ifvmode
-    \penalty -\@Mv\relax
-  \else
-    \@bsphack
-    \vadjust{\penalty -\@Mv\relax}%
-    \@esphack
-  \fi
- \fi}
+   \ifnum\col@number<\tw@
+   \PackageError{multicol}%
+    {\noexpand\newcolumn outside multicols}%
+    {This command can only be used within
+     a multicols or multicols* environment.}%
+    \else
+%    \end{macrocode}
+%    Increasingly lower penalty based on argument value. This is like
+%    \cs{pagebreak} but we use other penalty values are the \LaTeX{}
+%    defaults aree rather pointless for pagination.
+%    \begin{macrocode}
+    \edef\mc@break@pen
+	{-\ifcase#1\@m\or 3333\or 6666\or 9999\else\@Mv\fi\relax}%
+    \ifvmode
+     \penalty \mc@break@pen
+   \else
+     \@bsphack
+     \vadjust{\penalty \mc@break@pen}%
+     \@esphack
+   \fi
+  \fi}
 %    \end{macrocode}
 %  \end{macro}
 %
 %
+%
+%  \begin{macro}{\newcolumn}
+% \changes{v1.9a}{2021/10/08}{Macro added}
+%    This is modeled after \cs{newpage} but for column breaks.
+%    \begin{macrocode}
+\newcommand\newcolumn{%
+   \ifnum\col@number<\tw@
+   \PackageError{multicol}%
+    {\noexpand\newcolumn outside multicols}%
+    {This command can only be used within
+     a multicols or multicols* environment.}%
+  \else
+    \ifvmode
+     \nobreak\vfill\penalty -\@Mv\relax
+   \else
+     \@bsphack
+     \vadjust{\nobreak\vfill\kern\z@\penalty -\@Mv\relax}%
+     \@esphack
+   \fi
+  \fi}
+%    \end{macrocode}
+%  \end{macro}
+%
 %  \begin{macro}{\colbreak@box}
 % \changes{v1.5u}{1999/05/25}{Macro added}
 %    Need a box to collect the galley up to the column break.