Tagging support for array, tabularx, and longtable (#1209)

* take latex-lab-table.dtx from uf-review-05

* latex-lab-table: move   \@@_show_curr_cell_data: into socket ;
array: put sockets into array ;
array: updated \insert@column to use sockets

* first stab at tabularx (WIP)

* getting there (tabularx)

* fix docu

* fix so that the code runs when tagging is not used

* leftover \end{macrocode}

* add verst version of lttag.dtx

* simplify tabularx

* provide \ProvideDocElement

* change lttag -> lttagging;
us separate \insert@pcolumn with its own sockets

* WIP (broken)

* WIP

* WIP (working again)

* WIP

* medium rewrite/restructure (WIP)

* would have been too easy

* and a doc issue

* and one more

* move multicolumn changed into array;
change begindocument hook chunk to "kernel"

* better also add the socket declaration in the right file

* starting with L3 layer in array (WIP)

* added missing \MaintainedBy defs

* l3doc needs amsmath :-(

* updated \@array in array

* move \ar@ialign into array

* tracing/debugging now optional

* move \@addamp

* move \@Arraycr

* move \endarry ; add \ar@crcr

* move cell data handling to lttaging;
start with longtable (WIP)

* stray macrocode

* use   \tbl_update_multicolumn_cell_data:n

* more work on longtable (WIP)

* update \endlongtable and \LT@t@bularcr (WIP)

* hopefully fixed logic for \endhead and friends;
also fixed \hline issue (guess \cline needs also attention but not tonight)

* trying to get around l3bitset issue

* using newer kernel with l3bitset included

* l3bibset vanished

* sigh

* and a docu fix

* cleanup docu (WIP)

* docu changes (fail table-14-pbox)

* doc updates for "array"

* renamed a couple of sockets; but more docu

* more updates and documentation

* getting ready for first draft

* implemented most of Ulrike's suggestions

* more suggestions

* cleanup after merge

* drop definitions now in tagpdf

* ltnews entry

* fix tests

* updated with David's comments

base/changes.txt

@@ -6,8 +6,6 @@ to completeness or accuracy and it contains some references to files that are
 not part of the distribution.
 ================================================================================
 
-
-
 2024-01-30  David Carlisle  <David.Carlisle@latex-project.org>
 	* ltclass.dtx: check that \RequirePackage, \documentclass, \usepackage
 	  and related commands are at top level (gh/1185)
@@ -54,6 +52,10 @@ not part of the distribution.
 	* ltfilehook.dtx
 	Change flag markup in macro env
 
+2023-12-16  Frank Mittelbach  <Frank.Mittelbach@latex-project.org>
+	* lttagging.dtx:
+	First version of lttagging module added
+
 2023-12-07 Ulrike Fischer <Ulrike.Fischer@latex-project.org>
 	* ltproperties.dtx: use \protected@write, (gh1200)
 

base/doc/ltnews39.tex

@@ -147,6 +147,33 @@ \section{Introduction}
 \emph{to write}
 
 
+\section{News from the \enquote{\LaTeX{} Tagged PDF} project}
+
+In the previous \LaTeX{} News~\cite{39:ltnews38} we announced a first prototype
+support for tagged tabulars. Some of the necessary support code has
+now been moved from \texttt{latex-lab} to the corresponding packages
+(using sockets and plugs) and to the \LaTeX{} kernel (for those parts
+that are also necessary for other aspects of tagging).
+
+The kernel code specific to tagging is implemented in the file
+\texttt{lttagging.dtx}.  For now it contains \cs{UseTaggingSocket}, a
+special invocation command for sockets that are specific to
+tagging. This enables us to also provide \cs{SuspendTagging} and
+\cs{ResumeTagging}, i.e., a very efficient way to temporarily disable
+the whole tagging process. This is, for example, necessary, if some
+code is doing trial typesetting. In that case the trials should not
+generate tagging structures\Dash only the finally chosen version
+should. Thus, \pkg{tabularx}, for example, stops the tagging while
+doing its trials to figure out the correct column widths to use, and
+then renables tagging when the table is finally typeset.
+
+Over time, \texttt{lttagging.dtx} will hold more general tagging code
+as appropriate. For now it is only documented as part of
+\texttt{source2e.pdf} but long term we will provide a separate guide
+for tagging, which will then also include the information currently
+found in various other places, e.g., \texttt{tagpdf.pdf}.
+
+
 \section{Enhancements to the new mark mechanism}
 
 In June 2022 we introduced a new mark mechanism in
@@ -423,6 +450,20 @@ \subsection{Declaring appropriate sub-encodings for \texttt{TS1} symbol fonts}
 
 \section{Changes to packages in the \pkg{tools} category}
 
+
+\subsection{\pkg{array}, \pkg{longtable}, \pkg{tabularx}: support tagging}
+
+The three packages are now extended to enable producing tagged tabulars upon
+request. This is done by adding a number of sockets (see
+\cite{39:ltnews38}) that, by default, do nothing, but are equipped
+with appropriate plugs if tagged PDF is requested.
+
+In the previous \LaTeX{} release this was handled in
+\texttt{latex-lab} patching the packages when tagging was requested.
+
+
+
+
 \subsection{\pkg{verbatim}: \cs{verb} showed visible spaces}
 
 A recent change in the kernel was not reflected in the \pkg{verbatim}
@@ -465,6 +506,7 @@ \subsection{\pkg{showkeys}: Allow \cs{newline} in \pkg{amsthm} to work}
 \githubissue{1123}
 
 
+
 \section{Changes to files in the \pkg{cyrillic} category}
 
 \subsection{Correct definition of \cs{k}}
@@ -510,6 +552,10 @@ \subsection{Correct definition of \cs{k}}
   \emph{\LaTeXe{} news 37}. June 2023.\\
   \url{https://latex-project.org/news/latex2e-news/ltnews37.pdf}
 
+\bibitem{39:ltnews38} \LaTeX{} Project Team.
+  \emph{\LaTeXe{} news 38}. November 2023.\\
+  \url{https://latex-project.org/news/latex2e-news/ltnews38.pdf}
+
 %\bibitem{39:blueprint} Frank Mittelbach and Chris Rowley.
 %  \emph{\LaTeX{} Tagged PDF \Dash A blueprint for a large project}.\\
 %  \url{https://latex-project.org/publications/indexbyyear/2020/}

base/doc/source2e.tex

@@ -342,6 +342,8 @@
 
  \DocInclude{ltoutput} % Output routine
 
+ \DocInclude{lttagging}% Tagging support
+
  \DocInclude{lthyphen} % Hyphenation (hyphen.ltx).
 
  \DocInclude{ltfinal}  % Last minute initialisations and dump

base/format.ins

@@ -206,11 +206,12 @@ the system are in the document `cfgguide.tex'.
           \from{ltbibl.dtx}{2ekernel}
           \from{ltmarks.dtx}{trace,2ekernel}    % L3 layer module
           \from{ltpage.dtx}{2ekernel}
-         \from{ltclass.dtx}{2ekernel,tracerollback}
+          \from{ltclass.dtx}{2ekernel,tracerollback}
           \from{ltkeys.dtx}{2ekernel}           % L3 layer module
           \from{ltfilehook.dtx}{2ekernel}       % L3 layer module
           \from{ltshipout.dtx}{2ekernel}        % L3 layer module
           \from{ltoutput.dtx}{2ekernel}
+          \from{lttagging.dtx}{2ekernel}
           \from{ltfinal.dtx}{2ekernel}}
    \file{tracefnt.sty}{%
           \from{ltfsstrc.dtx}{package,trace}}