\newtheorem does not use trivlist settings

[mbertucci47]

I know there is some discrepancy expected in output between the tagging code \newtheorem and the usual one. However, I think with minimal effort they could look much closer than they currently do. Right now \@begintheorem calls \UseInstance{block}{theorem}{} but this could be changed to \UseInstance{blockenv}{theorem}{par-skip=\parskip,parindent=\parindent}. This makes the heading indented but adding \noindent before \mode_leave_vertical: seems to fix this without affecting tagging (I don't claim this is the correct fix).

\documentclass{article}
\usepackage{kantlipsum}

\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
\kant[1][1-2]

\kant[2][1-2]
\begin{enumerate}
\item abc
\item \kant[3][1-2]

\kant[4][1-2]
\end{enumerate}
\end{theorem}

\end{document}

Here's the output without tagging.

Now adding

\DocumentMetadata
  {
    lang=en-US,
    pdfversion=2.0,
    pdfstandard=ua-2,
    testphase={phase-III,math,title,table,firstaid}
  }

to the example above gives

With the proposed fix:

% !TeX TXS-program:compile = txs:///lualatex
\DocumentMetadata
  {
    lang=en-US,
    pdfversion=2.0,
    pdfstandard=ua-2,
    testphase={phase-III,math,title,table,firstaid}
  }
\documentclass{article}

\usepackage{kantlipsum}

\makeatletter
\ExplSyntaxOn
\def\@begintheorem#1#2{
  \UseInstance{blockenv}{theorem}{par-skip=\parskip,parindent=\parindent} % Changed
  \tagpdfparaOff
  \noindent % Added
  \mode_leave_vertical:
  \MakeLinkTarget{\l__block_thm_current_counter_tl}
  \tag_struct_begin:n{tag=Caption}
   \group_begin:
   \bfseries
   \tag_mc_begin:n {}
     #1\
   \tag_mc_end:
    \tag_struct_begin:n{tag=Lbl}
      \tag_mc_begin:n {}
          #2
      \tag_mc_end:
    \tag_struct_end:
    \group_end:
  \tag_struct_end:
  \tagpdfparaOn
  \__block_start_para_structure_unconditionally:n { \PARALABEL }
  \itshape
  \hskip\labelsep
  \ignorespaces
}
\ExplSyntaxOff
\makeatother

\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
\kant[1][1-2]

\kant[2][1-2]
\begin{enumerate}
\item abc
\item \kant[3][1-2]

\kant[4][1-2]
\end{enumerate}
\end{theorem}

\end{document}

Similar changes would need to be made for the amsthm firstaid.

Edit

Hmm I see the proposed fix also affects the indent in enumerate. Not sure about that at the moment.

[FrankMittelbach]

Your examples, seem to be a white lie @mbertucci47 :-). You say Now adding ... which fooled me at first. In reality, I think your first display was typeset with pdftex and the second with tagging was typeset with luatex. It is a bit surprising that we see so much change in the paragraphs, but I guess that is CM to LM.

Anyhow, your proposed solution goes in the wrong direction in my opinion. You do not want to hardwire such settings somewhere in the middle of the code (this is worse than allowing \@listi to mess things up, I would say). What you want to do instead is to make use of the template/instance machinery.

So a better solution, in my opinion, might be this:

\DeclareInstance{blockenv}{theorem}{display}
{
  env-name       = theorem-like,
  tag-name       = theorem-like,
  tag-class      = ,
  tagging-recipe = standalone,
  inner-level-counter  = ,
  level-increase = false,
  setup-code     = ,
  block-instance = theoremblock ,   % <--- do not reuse the displayblock, use your own
}

\DeclareInstance{block}{theoremblock-0}{display}
  {
    parindent      = \parindent ,
    par-skip        = \parskip ,
  } 

That doesn't solve this, unfortunately:

Hmm I see the proposed fix also affects the indent in enumerate. Not sure about that at the moment.

That is a bug in the code; I guess I confused myself trying to support the various legacy setting possibilities. For the moment that could be (partly) repaired with

\DeclareInstance{block}{list-1}{display}{  parindent  = 0pt } 

but this way you can't alter the \listparindent globally any longer. The correct fix has to happen in the code.

[mbertucci47]

In reality, I think your first display was typeset with pdftex and the second with tagging was typeset with luatex.

@FrankMittelbach Wow I did not even notice that, yes you are right. Sorry about that!

What you want to do instead is to make use of the template/instance machinery.

Yes that's definitely better. When I naively add your proposed code to my example it seems to indent the entire block, but I suspect some other changes being made in latex3/latex2e#1561 might fix this.

[FrankMittelbach]

but I suspect some other changes being made in latex3/latex2e#1561 might fix this.

It needed more than my handwaving reply (due to one or two bugs discovered this way. I think it is now correct and will show up in the next dev release in a couple of days.