@DonHosek -- It's well after midnight so I'm not going to try to check. However, there may be examples in the testmath document that's part of the amsmath package. If so, they were definitely drawn from material that was published.
@FaheemMitha you could use \pdfsavepos at each end of the cell, but nothing set up. If the inserted text is a heading usually you want to linebreak by hand in which case you can use a nested tabular and don't need to specify a width, so this doesn't come up often.
While one could certainly use LuaTeX for this, I wonder how robust it would be at things like parsing, as opposed to an apparently pure TeX solution like spreadtab. And it would presumably be entirely DIY, since it seems nothing like this currently exists in TeX Live.
@FaheemMitha well it's called \savepos there but yes
@FaheemMitha almost always do that for headings (some packages give you a \thead command for that: \multicolumn{1}{c}{\begin{tabular}{@{}c@{}} this\\heading\end{tabular}}
@DavidCarlisle Yes, I see. So a standard technique, then.
If I just use \multicolumn, I don't understand the breaking behavior. I have an example where it is breaking for some columns, and not for one. I was planning to post it. I suppose here, because it's probably not worth asking as a question.
@FaheemMitha multicolumn does nothing at all about line breaking, it's just the same as tabular, if you use a c column it won't break unless you nest a something that does, and if you use a p column then it's a parbox and will (try to) break to that width
@samcarter -- Thanks. I've flagged the ad, asking for moderator to delete it, Sad, very sad. The usefulness of the ads is becoming marginal for anything that isn't "permanent".
Microsoft Office is a word processor and LaTeX is a typesetting system. But, what can they be commonly called? Documentation systems? Or any specific name is used?
@raf -- I'd go with "document processing systems". "Documentation" has a more limiting meaning. (I once had the title "Documentalist" on my business card, and it was meant to mean that I wrote documentation for both systems and end users.) LaTeX can be used to prepare letters, novels, journal articles, any kind of printed material. (So can LibreOffice,of course.)
@DavidCarlisle no it isn't that. It is the checkinit_hook function, if I remove it it works again. And this is new, in texlive 2020 it worked. I'm just opening an issue for l3build.