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+% \iffalse meta-comment
+%
+% Copyright (C) 2023-2024
+% The LaTeX Project and any individual authors listed elsewhere
+% in this file.
+%
+% This file is part of the LaTeX base system.
+% -------------------------------------------
+%
+% It may be distributed and/or modified under the
+% conditions of the LaTeX Project Public License, either version 1.3c
+% of this license or (at your option) any later version.
+% The latest version of this license is in
+% https://www.latex-project.org/lppl.txt
+% and version 1.3c or later is part of all distributions of LaTeX
+% version 2008 or later.
+%
+% This file has the LPPL maintenance status "maintained".
+%
+% The list of all files belonging to the LaTeX base distribution is
+% given in the file `manifest.txt'. See also `legal.txt' for additional
+% information.
+%
+% The list of derived (unpacked) files belonging to the distribution
+% and covered by LPPL is defined by the unpacking scripts (with
+% extension .ins) which are part of the distribution.
+%
+% \fi
+%
+% \iffalse
+%%% From File: lttagging.dtx
+%
+%<*driver>
+% \fi
+\ProvidesFile{lttagging.dtx}
+ [2023/12/19 v1.0a LaTeX Kernel (tagging support)]
+% \iffalse
+\documentclass{l3doc}
+\GetFileInfo{lttagging.dtx}
+\title{\filename}
+\date{\filedate}
+\author{\LaTeX{} project}
+
+\begin{document}
+% \MaintainedByLaTeXTeam{latex} % should be added again the moment
+ % it is supported by l3doc
+ \maketitle
+ \DocInput{\filename}
+\end{document}
+%</driver>
+% \fi
+%
+% \providecommand\env[1]{\texttt{#1}}
+%
+% \providecommand\hook[1]{\texttt{#1\DescribeHook[noprint]{#1}}}
+% \providecommand\socket[1]{\texttt{#1\DescribeSocket[noprint]{#1}}}
+% \providecommand\plug[1]{\texttt{#1\DescribePlug[noprint]{#1}}}
+%
+% \let\ProvideDocElement\NewDocElement
+%
+% \ProvideDocElement[printtype=\textit{socket},idxtype=socket,idxgroup=Sockets]{Socket}{socketdecl}
+% \ProvideDocElement[printtype=\textit{hook},idxtype=hook,idxgroup=Hooks]{Hook}{hookdecl}
+% \ProvideDocElement[printtype=\textit{plug},idxtype=plug,idxgroup=Plugs]{Plug}{plugdecl}
+%
+%
+% \section{}
+%
+%
+%
+% \MaybeStop{}
+%
+% \begin{macrocode}
+%<*2ekernel|latexrelease>
+% \end{macrocode}
+%
+% \begin{macrocode}
+\ExplSyntaxOn
+% \end{macrocode}
+%
+%
+% \section{General support for tagged output}
+%
+% \DescribeMacro\SuspendTagging
+% \DescribeMacro\ResumeTagging
+%
+% The are places in code where it is import top stop any tagging
+% activities, e.g., when we are doing trial typesetting that it is
+% done several times. In such a case one must tag only the final
+% version that is actually used, otherwise tagging structures are
+% allowed which then do not end up in the PDF and confuse the
+% mechanism. For this we have two commands that can be used in
+% packages: \cs{SuspendTagging} and \cs{ResumeTagging}. They are
+% available as part of the \LaTeX{} kernel, so that they can be
+% safely used in packages whether or not tagging is requested .They
+% both take string argument that is used for debugging to easily
+% identify why tagging was suspended or restarted, for example, in
+% \pkg{tabularx} you find \verb=\SuspendTagging{tabularx}=. By default
+% they two commands do nothing.
+%
+% TODO: the corresponding L3 layer commands should also have a dummy
+% definition in the kernel!
+%
+% \DescribeMacro\UseTaggingSocket
+% \DescribeMacro\tag_socket_use:n
+% \DescribeMacro\tag_socket_use:nn
+% To support tagging in packages we use sockets with names starting
+% with \texttt{tagsupport/}. Usually, these sockets have exactly two
+% plugs defined:
+% \plug{noop} (when no tagging is requested or tagging is not wanted
+% for some reason) and a second plug that enables the tagging. There
+% may be more, e.g., tagging with special debugging, etc., but right
+% now it is usually just on or off.
+%
+% Given that we sometimes have to suspend tagging, it would be fairly
+% inefficient to put different plugs into these sockets whenever that
+% happens. We therefore offer \cs{UseTaggingSocket} which is like
+% \cs{UseSocket} except that the socket name is specified without
+% \texttt{tagsupport/}, i.e.,
+% \begin{quote}
+% \verb=\UseTaggingSocket{foo}= $\to$
+% \verb=\UseSocket{tagsupport/foo}=
+% \end{quote}
+% Beside being slightly shorter, the big advantage is that this way
+% we can change \cs{UseTaggingSocket} to do nothing when tagging is
+% suspended with \cs{SuspendTagging} instead of changing the plugs of
+% the tagging support sockets back and forth.
+%
+% It is possible to use the tagging support sockets with
+% \cs{UseSocket} directly, but in this case the socket remains active
+% if \cs{SuspendTagging} is in force. There my be reasons for doing
+% that but in general we expect to always use \cs{UseTaggingSocket}.
+%
+% The L3 programming layer versions \cs{tag_socket_use:n} and
+% \cs{tag_socket_use:nn} are slightly more efficient than
+% \cs{UseTaggingSocket} because they do not have to determine how
+% many arguments the socket takes when disabling it, so in code that
+% is using the L3 programming layer we recommend to use them instead
+% of the CamelCase command.
+%
+%
+%
+% \begin{macro}{\SuspendTagging,\ResumeTagging}
+%
+% In the kernel, these two commands get dummy definitions so that
+% they can be used without harm in packages. The real definition is
+% used when tagging gets enabled.
+% \begin{macrocode}
+\cs_new_eq:NN \SuspendTagging \use_none:n
+\cs_new_eq:NN \ResumeTagging \use_none:n
+% \end{macrocode}
+%
+% A simplified version of this defnition should move to
+% \pkg{tagpdf} and dropped here, eventually.
+% \begin{macrocode}
+\AddToHook{begindocument/before}{
+ \cs_if_exist:NT \tag_stop:n
+ {
+ \cs_set:Npn \SuspendTagging #1 {
+% \end{macrocode}%
+% This stops tagging and also disables all tagging sockets so we are done.
+% \begin{macrocode}
+ \tag_stop:n {#1}
+ }
+% \end{macrocode}
+%
+% \begin{macrocode}
+ \cs_set:Npn \ResumeTagging #1 { \tag_start:n {#1} }
+ }
+}
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\tag_socket_use:n,
+% \tag_socket_use:nn,
+% \UseTaggingSocket,
+% }
+% Again this is not the final definition for the kernel; it is just
+% a version to get going while some parts of the kernel support are
+% still missing.
+% \begin{macrocode}
+\AddToHook{begindocument}[kernel]{
+ \cs_if_exist:NF \tag_if_active:T
+ {
+ \prg_new_conditional:Npnn \tag_if_active: { p , T , TF, F }
+ { \prg_return_false: }
+ }
+}
+% \end{macrocode}
+%
+% Dummy definitions in the kernel.
+% These definitions will get updated in \pkg{tagpdf}.
+% \begin{macrocode}
+\cs_new_protected:Npn \tag_socket_use:n #1 { }
+\cs_new_protected:Npn \tag_socket_use:nn #1#2 { }
+% \end{macrocode}
+% The default in the kernel is just to get rid of the argument:
+% \begin{macrocode}
+\cs_new_protected:Npn \UseTaggingSocket #1 {
+ \int_case:nnF
+ { \int_use:c { c__socket_tagsupport/#1_args_int } }
+ {
+ 0 \prg_do_nothing:
+ 1 \use_none:n
+ 2 \use_none:nn
+% \end{macrocode}
+% We do not expect tagging sockets with more than one or two
+% arguments, so for now we only provide those.
+% \begin{macrocode}
+ }
+ \ERRORusetaggingsocket % that should get a proper error message
+}
+\ExplSyntaxOff
+% \end{macrocode}
+%
+% \end{macro}
+%
+%
+%
+%
+%
+%
+% \subsection{Tagging support for table/tabular packages}
+%
+% The code uses a number of sockets to inject the tagging
+% commands. These can be easily set to a noop-plug in case the
+% automated tagging is not wanted.
+%
+% \begin{socketdecl}{tagsupport/tbl/cell/begin,
+% tagsupport/tbl/cell/end,
+% tagsupport/tbl/pcell/end,
+% tagsupport/tbl/pcell/end,
+% tagsupport/tbl/row/begin,
+% tagsupport/tbl/row/end,
+% }
+% At first sockets for the begin and end of cells and table rows:
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/cell/begin}{0}
+\NewSocket{tagsupport/tbl/cell/end}{0}
+% \end{macrocode}
+%
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/row/begin}{0}
+\NewSocket{tagsupport/tbl/row/end}{0}
+% \end{macrocode}
+% Multi-line cells have their own sockets (as they start out in
+% vertical mode and need different treatment).
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/pcell/begin}{0}
+\NewSocket{tagsupport/tbl/pcell/end}{0}
+% \end{macrocode}
+% \end{socketdecl}
+%
+% \begin{socketdecl}{tagsupport/tbl/init}
+% This socket should be at the begin of the table, inside a group.
+% It is used for settings such as disabling para-tagging inside the
+% table. This socket
+% can perhaps be merged later into the begin-sockets.
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/init}{0}
+% \end{macrocode}
+% \end{socketdecl}
+%
+%
+% \begin{socketdecl}{tagsupport/tbl/finalize}
+% To fine tune the structure (change cells to header cells, remove
+% unwanted structures, move a foot to the end, etc.). We also need a
+% socket that is executed at the end of the table but \emph{before}
+% all the variables are restored to the outer or default values.
+% The code in the socket can make assignments, but probably
+% shouldn't do typesetting and not write whatsits.
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/finalize}{0}
+% \end{macrocode}
+% \end{socketdecl}
+%
+
+
+% \begin{socketdecl}{tagsupport/tbl/colspan}
+% This socket is used to manage spanning cells, e.g., a
+% \cs{multicolumn}. It expects one argument (the number of cells
+% spanned) and if tagging is enabled set appropriate tag attributes
+% in the background. We probably need a similar socket for row
+% spans eventually.
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/colspan}{1}
+% \end{macrocode}
+% \end{socketdecl}
+%
+
+
+% \begin{socketdecl}{tagsupport/tbl/hmode/begin,
+% tagsupport/tbl/hmode/end,
+% tagsupport/tbl/vmode/begin,
+% tagsupport/tbl/vmode/end
+% }
+%
+% These sockets are used in the begin and end code of environments,
+% to allow a fast enabling and disabling of the tagging. We
+% distinguish between tables that can be used inside paragraphs and
+% standalone tables such as \env{longtable} that are always in
+% vertical mode.
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/hmode/begin}{0}
+\NewSocket{tagsupport/tbl/hmode/end}{0}
+\NewSocket{tagsupport/tbl/vmode/begin}{0}
+\NewSocket{tagsupport/tbl/vmode/end}{0}
+% \end{macrocode}
+% \end{socketdecl}
+%
+%
+%
+% \begin{socketdecl}{tagsupport/tbl/longtable/init,
+% tagsupport/tbl/longtable/finalize}
+% \env{longtable} needs its own sockets to fine tune the structure.
+% Simply switching the plug in the previous socket interferes with
+% enabling/disabling the tagging.
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/longtable/init}{0}
+\NewSocket{tagsupport/tbl/longtable/finalize}{0}
+% \end{macrocode}
+% \end{socketdecl}
+%
+% \begin{socketdecl}{tagsupport/tbl/longtable/head,
+% tagsupport/tbl/longtable/foot}
+% Header and footer boxes need special handling because they are repeatedly
+% used.
+% \begin{macrocode}
+\NewSocket{tagsupport/tbl/longtable/head}{0}
+\NewSocket{tagsupport/tbl/longtable/foot}{0}
+% \end{macrocode}
+% \end{socketdecl}
+%
+%
+%
+%
+%
+% \section{For lttab.dtx parked here for now}
+%
+%
+% \begin{macrocode}
+%<@@=tbl>
+\ExplSyntaxOn
+% \end{macrocode}
+%
+%
+% \subsection{Variables for row, column and span counting}
+%
+% This part needs a decision on names for various integer registers
+% as well as a decision if those should be also made available for
+% \LaTeXe{}-style packages in form of 2e names and or as
+% non-internals for the L3 programming layer.
+%
+% At the moment they are all internal but this probably has to change.
+%
+% \begin{macro}{
+% \g_@@_col_int,
+% \g_@@_row_int,
+% \g_@@_span_tl,
+% \g_@@_table_cols_tl}
+%
+% \cs{g_@@_row_int} holds the current row number in the table. The
+% value \texttt{0} means we haven't yet processed the table
+% preamble (or in case of longtable are just in front of the next
+% chunk to be processed). It is incremented by every \cs{cr}
+% including the one ending the table preamble.
+%
+% TODO: due to the gymnastics needed inside the longtable code the
+% row counter is directly exposed there rather than hidden by
+% interfaces. This needs changing when it is decided how to manage
+% these counters.
+%
+% \cs{g_@@_col_int} holds the current column number. The value
+% \texttt{0} means we have not yet started the table or just finished a table row
+% (with \verb=\\= typically); any other positive value means we
+% are currently typesetting a cell in that column in some row
+% (denoted by the \cs{g_@@_row_int}).
+%
+% In a \cs{multicolumn} it holds the column number of the first
+% spanned column and \cs{g_@@_span_tl} the info how many cells are
+% spanned.
+%
+% \cs{g_@@_span_tl} is normally \texttt{1} except in a
+% \cs{multicolumn} cell.
+% \begin{macrocode}
+\int_new:N \g_@@_col_int
+\int_new:N \g_@@_row_int
+\tl_new:N \g_@@_span_tl
+\tl_new:N \g_@@_table_cols_tl
+
+\tl_gset:Nn \g_@@_span_tl {1}
+\tl_gset:Nn \g_@@_table_cols_tl {0} % indicates outer level
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\l_@@_saved_col_tl,\l_@@_saved_row_tl,
+% \l_@@_saved_span_tl,\l_@@_saved_table_cols_tl}
+%
+% Saving the outer values if we are nesting tables is necessary (as
+% the above variables are globally altered). For this we always use
+% token lists because they don't change and we do not need to blow
+% additional integer registers.
+% \begin{macrocode}
+\tl_new:N \l_@@_saved_col_tl
+\tl_new:N \l_@@_saved_row_tl
+\tl_new:N \l_@@_saved_span_tl
+\tl_new:N \l_@@_saved_table_cols_tl
+
+\tl_set:Nn \l_@@_saved_col_tl{0}
+\tl_set:Nn \l_@@_saved_row_tl{0}
+\tl_set:Nn \l_@@_saved_span_tl{1}
+\tl_set:Nn \l_@@_saved_table_cols_tl{0} % indicates outer level
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\g_@@_missingcells_int}
+% This will contain the number of missing cells in a row:
+% \begin{macrocode}
+\int_new:N \g_@@_missing_cells_int
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+%
+% \subsection{Tracing/debugging}
+%
+% \begin{macro}{\DebugTablesOn,\DebugTablesOff}
+%
+% \begin{macrocode}
+\def\DebugTablesOn{
+ \cs_set_eq:NN \@@_trace:n \typeout
+}
+\def\DebugTablesOff{
+ \cs_set_eq:NN \@@_trace:n \use_none:n
+}
+% \end{macrocode}
+%
+% \begin{macrocode}
+\cs_new_eq:NN \@@_trace:n \use_none:n
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \subsection{Interface commands}
+%
+% All interface commands for the cell number determination have to be
+% public on some level because they are needed in other packages as
+% well, e.g., longtable. We may or may not also want to provide 2e
+% style names for them.
+%
+% \begin{macro}{\tbl_update_cell_data:}
+% Updating cell data in columns after the first means we have to
+% increment the \cs{g_@@_col_int} by the span count of the previous
+% cell (in case it was a \cs{multicolumn}) and then reset the
+% \cs{g_@@_span_tl} to one (as the default).
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_update_cell_data: {
+ \int_gadd:Nn \g_@@_col_int { \g_@@_span_tl }
+ \tl_gset:Nn \g_@@_span_tl {1}
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\tbl_count_table_cols:}
+% Current implementation of \cs{@mkpream} uses the scratch counter
+% \cs{count@} to keep track of the number of toks registers it needs
+% (2 per column), but this can't be used as it counts also
+% insertions made with \verb+!{}+ and \verb+@{}+.
+% So similar as does longtable for \cs{LT@cols} we count the
+% numbers of ampersands instead.
+% \begin{macrocode}
+\cs_new:Npn \tbl_count_table_cols: {
+ \seq_set_split:NnV\l_@@_tmpa_seq {&}\@preamble
+ \tl_gset:Ne \g_@@_table_cols_tl { \seq_count:N \l_@@_tmpa_seq }
+ \@@_trace:n { ==>~ Table~ has~ \g_@@_table_cols_tl \space columns }
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\l_@@_tmpa_seq}
+%
+% \begin{macrocode}
+\seq_new:N \l_@@_tmpa_seq
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\tbl_count_missing_cells:n}
+%
+% We might have the situation that some table package has not
+% implemented the \cs{tbl_count_table_cols:} in which case
+% \cs{g_@@_table_cols_tl} would always be zero and we would get an
+% error below when we try to determine the missing cells, so bypass
+% that calculation if we aren't doing tagging (there the packages
+% should have the proper code added). Recall that this is code,
+% that is called by \verb=\\= and an old table packagee might rely
+% on whatever the \LaTeX{} kernel offers here.
+% \begin{macrocode}
+\cs_new:Npn \tbl_count_missing_cells:n #1 {
+ \tag_if_active:T {
+ \int_compare:nNnT \g_@@_col_int > 0
+ {
+ \int_gset:Nn \g_@@_missing_cells_int
+ {
+ \g_@@_table_cols_tl
+ - \g_@@_col_int
+ - \g_@@_span_tl
+ + 1
+ }
+ \int_compare:nNnT \g_@@_missing_cells_int < 0 \ERRORmissingcells % should not happen
+ \@@_trace:n{==>~
+ (#1)~
+ This~ row~ needs~
+ \int_use:N \g_@@_missing_cells_int \space
+ additional~ cell(s)
+ }
+ }
+ }
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\tbl_save_outer_table_cols:}
+%
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_save_outer_table_cols: {
+ \tl_set_eq:NN \l_@@_saved_table_cols_tl \g_@@_table_cols_tl
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\tbl_init_cell_data_for_table:}
+%
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_init_cell_data_for_table: {
+ \tl_set:No \l_@@_saved_col_tl {\int_use:N \g_@@_col_int }
+ \tl_set:No \l_@@_saved_row_tl {\int_use:N \g_@@_row_int }
+ \tl_set_eq:NN \l_@@_saved_span_tl \g_@@_span_tl
+%
+ \@@_trace:n { ==>~ saved~cell~data:~
+ \l_@@_saved_row_tl,
+ \l_@@_saved_col_tl,
+ \l_@@_saved_span_tl \space
+ (
+ \int_compare:nNnTF \l_@@_saved_table_cols_tl = 0
+ { outer~ level }
+ { max:~ \l_@@_saved_table_cols_tl }
+ )
+ }
+% \end{macrocode}
+% These are the initial values when starting a table:
+% \begin{macrocode}
+ \int_gzero:N \g_@@_row_int
+ \int_gzero:N \g_@@_col_int
+ \tl_gset:Nn \g_@@_span_tl {1}
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+% \begin{macro}{\tbl_update_cell_data_for_next_row:}
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_update_cell_data_for_next_row: {
+ \int_gincr:N \g_@@_row_int % this row about to start
+ \int_gzero:N \g_@@_col_int % we are before first col
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\tbl_init_cell_data_for_row:}
+% If we start processing a cell in the first column we set
+% \cs{g_@@_col_int} to \texttt{1} as we are no longer "at" but "in"
+% the first column. We also set \cs{g_@@_span_tl} to its default
+% value (not spanning cells).
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_init_cell_data_for_row: {
+ \int_gset:Nn \g_@@_col_int {1}
+ \tl_gset:Nn \g_@@_span_tl {1}
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\tbl_if_row_was_started:T,
+% \tbl_if_row_was_started:TF}
+% We use \cs{g_@@_col_int} equal zero to indicate that we are just
+% after a TR (i.e.n between rows or at the very beginning of the
+% table). Using the row
+% count is not so good as longtable may split the table in chunks.
+%
+% These conditionals have to be expandable (i.e., unprotected) as
+% they are sometimes executed when \TeX{} is scanning inside a table.
+% \begin{macrocode}
+\cs_new:Npn \tbl_if_row_was_started:T {
+ \int_compare:nNnT \g_@@_col_int > 0
+}
+\cs_new:Npn \tbl_if_row_was_started:TF {
+ \int_compare:nNnTF \g_@@_col_int > 0
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\tbl_gzero_row_count:,\tbl_gincr_row_count:,\tbl_gdecr_row_count:}
+% This here is basically a temporary interface. What it will be in
+% the end depends on what we decide concerning exposing row and
+% column counters, if they stay internal we need something like
+% this here (perhaps using \texttt{gincr} etc, or perhaps some
+% other names in the first place).
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_gzero_row_count: {
+ \int_gzero:N \g_@@_row_int
+}
+\cs_new_protected:Npn \tbl_gincr_row_count: {
+ \int_gincr:N \g_@@_row_int
+}
+\cs_new_protected:Npn \tbl_gdecr_row_count: {
+ \int_gdecr:N \g_@@_row_int
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}{\tbl_inbetween_rows:}
+% Again name is not really brilliant so far.
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_inbetween_rows: {
+ \int_gzero:N \g_@@_col_int
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+%
+%
+% \begin{macro}{\tbl_restore_outer_cell_data:}
+%
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_restore_outer_cell_data: {
+ \int_gset:Nn \g_@@_col_int { \l_@@_saved_col_tl }
+ \int_gset:Nn \g_@@_row_int { \l_@@_saved_row_tl }
+ \tl_gset_eq:NN \g_@@_span_tl \l_@@_saved_span_tl
+ \tl_gset_eq:NN \g_@@_table_cols_tl \l_@@_saved_table_cols_tl
+ \@@_trace:n { ==>~ restored~cell~data:~
+ \int_use:N \g_@@_row_int,
+ \int_use:N \g_@@_col_int,
+ \l_@@_saved_span_tl \space
+ (
+ \int_compare:nNnTF \g_@@_table_cols_tl = 0
+ { outer~ level }
+ { max:~ \g_@@_table_cols_tl }
+ )
+ }
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\tbl_update_multicolumn_cell_data:n}
+% This macro updates \cs{g_@@_col_int} and \cs{g_@@_span_tl} inside
+% a \cs{multicolumn} and possibly calls the tagging socket
+% \texttt{tbl/row/begin}.
+% \begin{macrocode}
+\cs_new_protected:Npn \tbl_update_multicolumn_cell_data:n #1 {
+% \end{macrocode}
+% We execute socket for tagging only if this \cs{multicolumn}
+% replaces the preamble of the first column. In that case we also have
+% to set \cs{g_@@_col_int} to 1 because this is no longer done in the
+% preamble for the cell either.
+% \begin{macrocode}
+ \int_compare:nNnTF \g_@@_col_int = 0
+ {
+ \UseTaggingSocket{tbl/row/begin}
+ \int_gset:Nn \g_@@_col_int {1}
+ }
+% \end{macrocode}
+% If we are in a later column we use \cs{g_@@_span_tl} from the
+% previous column to update.
+% \begin{macrocode}
+ {
+ \int_gadd:Nn \g_@@_col_int { \g_@@_span_tl }
+ }
+% \end{macrocode}
+% Then we set the span value so that it can be use in the next column.
+% \begin{macrocode}
+ \tl_gset:Nn \g_@@_span_tl {#1}
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\tbl_crcr:n}
+% This macro is used instead of the usual \cs{crcr} at the end of a
+% table. It is deliberately defined without protection because it
+% may get expanded by the scanning mechanism of low-level \TeX{}
+% after a final \cs{cr} (aka \verb=\\=) in the table. In that case
+% it shouldn't stop the expansion and the conditional inside will
+% be false, thus it just vanishes without doing anything. If there
+% are missing cells (in which case we also haven't see \cs{cr} yet)
+% the macro \cs{tbl_count_missing_cells:n} is executed and
+% then the row is finished with a final \cs{cr}.
+% \begin{macrocode}
+\cs_new:Npn \tbl_crcr:n #1 {
+ \int_compare:nNnT \g_@@_col_int > 0
+ {
+ \tbl_count_missing_cells:n {#1}
+ \cr
+ }
+}
+% \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macrocode}
+\ExplSyntaxOff
+%<@@=>
+% \end{macrocode}
+%
+% This is needed for \pkg{longtable} because \cs{refstepcounter} is
+% setting up a target when \pkg{hyperref} is loaded and we don't
+% want that in \pkg{longtable}.
+%
+% TODO: move to right .dtx file
+% \begin{macrocode}
+\let\@kernel@refstepcounter\refstepcounter
+% \end{macrocode}
+% Prevent longtable patching by hyperref until hyperref does so automatically:
+% \begin{macrocode}
+\def\hyper@nopatch@longtable{}
+% \end{macrocode}
+%
+%
+% Should there be a module?
+%
+% \begin{macrocode}
+%<latexrelease>\NewModuleRelease{2024/06/01}{lttagging}
+%<latexrelease> {Tagging support}
+% \end{macrocode}
+%
+%
+%
+%
+% \begin{macrocode}
+%<latexrelease>\IncludeInRelease{0000/00/00}{lttagging}%
+%<latexrelease> {Undo tagging support}
+%<latexrelease>
+%<latexrelease>
+%<latexrelease>
+%<latexrelease>\EndModuleRelease
+% \end{macrocode}
+%
+% \begin{macrocode}
+%</2ekernel|latexrelease>
+% \end{macrocode}
+%
+% \Finale
+%