item patches clash with paragraph tagging

[u-fischer]

Description

As has been reported in the tagpdf issue tracker latex3/tagpdf#49 the patches microtype adds to \item clash with the automatic paragraph tagging of tagpdf.

The problem is that the paragraph hooks are executed twice at the item as microtype stores something in a box and issues a \noindent in the box which triggers the hooks. Imho the right fix is to use \RawNoindent instead. The difference can be shown also without tagpdf:

\documentclass{article}
\usepackage{microtype}
\makeatletter
%\patchcmd{\MT@get@prot}{\noindent}{\RawNoindent}{}{\fail}
\AddToHook{para/begin}{\show\blub}
\makeatletter
\begin{document}
\begin{quotation}
Hello world
\end{quotation}

\end{document}

Without the patch \show\blub is shown twice, with the patch only once.

[schlcht]

Thanks, I can change that.

However, it seems to me that the problem is a bit more general with tagpdf (or the new hook management?), because it will fail in the same way with other packages that do some "test typesetting". Just off the top of my head, think of tabularx and csquotes's \blockquote.

[u-fischer]

Yes test typesetting is also a problem and I'm already pondering about it too. One probably will have to unify the amsmath if@measuring and other "trial" booleans. Then tagging could simply pause in such contexts.