suggestion: individual cell alignment in luamml/mtable

[nbeisert]

The alignment in the multline environment is adjusted using \UseTaggingSocket{math/luamml/mtable/aligncol}{...}. This ends up calling set_row_attribute to set the columnalign attribute for the present mtable mtr row. I wonder if the behaviour could be changed or extended to set the columnalign attribute for individual mtable mtd cells? This should not make a difference for the single-column environment multline, but it can come to use in, e.g., extended multi-column environments, where individual cells might want to get shoved around. At the level of the html / mathml representation, shifting the attribute from mtr to mtd tags worked fine in a manual test.

A related issue is that align cells are out of sync with the preset columnalign="right left" due to the presence of tags at the beginning of each row (and because "right left" apparently does not repeat as a pattern). With the above extension, one might explicitly feed in the desired alignment for each cell to resolve the issue (or change the mtable attribute columnalign="right right left right left right ..."). In all this, I assume that the html / mathml representation of an mtable matters not only in terms of content but also with regard to layout...?

\DocumentMetadata{testphase=latest}
\documentclass{article}
\tagpdfsetup{math/setup={mathml-SE}}

\begin{document}

\begin{align}
x&=\sin y
\\
\sin y&=x
\end{align}

\begin{multline}
\text{first}\\
\text{middle}\\
\text{last}
\end{multline}

\end{document}

[u-fischer]

I wonder if the behaviour could be changed or extended to set the columnalign attribute for individual mtable mtd cells?

A lots of things can be done, and luamml will be extended, but one need real examples to test.

A related issue is that align cells are out of sync with the preset columnalign="right left" due

That will be handled with the next luamml update.

[nbeisert]

Thanks for the information. My package eqnlines provides a version of the gathered environment which allows several columns (essentially add a & to the preamble of \halign in gathered), and it allows to realign individual cells as left, center, right. Whether the combination of these features serves a purpose or whether someone will actually use it, can be debated with good reason. Not that likely. Nevertheless, that's what it currently offers and as the best approximation I can come up with at the moment, I shall use \UseTaggingSocket{math/luamml/mtable/aligncol} to indicate the alignment of an individual cell rather than the complete containing row. A release of the package with tagging support will enable concrete tests.