With beamer, "Missing { inserted." (regression)

[Zdenek Wagner]

Sorry, I meant subscript, not underscore.

Zdeněk Wagner
http://ttsm.icpf.cas.cz/team/wagner.shtml

čt 17. 2. 2022 v 17:42 odesílatel Zdenek Wagner
<zdenek.wagner at gmail.com> napsal:
>
> You have to use $e_{\textnormal{m}}$ because the _ character expect a
> token and wothiut braces it is \textnormal. When it is expanded, it
> finds that an argument is missing, it does not see {m}. That's why you
> have to use the outer braces because _ then takse a balanced text,
> i.e. \textnormal{m} will be used as the underscore.
>
> Zdeněk Wagner
> http://ttsm.icpf.cas.cz/team/wagner.shtml
>
> čt 17. 2. 2022 v 17:37 odesílatel Vincent Lefevre <vincent at vinc17.net> napsal:
> >
> > Under Debian/unstable with the TeX Live 2021 Debian packages
> > and with the old TeX Live 2020 Debian packages, pdflatex on
> >
> > \documentclass{beamer}
> > \begin{document}
> > \begin{frame}
> > $e_\textnormal{m}$
> > \end{frame}
> > \end{document}
> >
> > gives the following error:
> >
> > ! Missing { inserted.
> > <to be read again>
> >                    \def
> > l.5 \end{frame}
> >
> > There are no issues with TeX Live 2018 under Debian 10 buster.
> > The author of the full .tex file uses a macOS machine, so I assume
> > that there are no issues there either (but I don't know which
> > TeX distribution it is).
> >
> > --
> > Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
> > 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
> > Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)