Eli Zaretskii <eliz@gnu.org> writes:

>> From: Ikumi Keita <ikumi@ikumi.que.jp>
>> 
>> >   . what is the rationale for not using align-tex-modes here, only
>> >     latex-mode?
>> 
>> Because the current `tex-tabbing-separator' entry in `align-rules-list'
>> excludes other modes by `run-if' form.

Which is correct, in general.  The tabbing environment looks like this
and is only available in LaTeX and not in other formats (AFAICT):

\begin{tabbing}
  Zero \=One \=Two \=Three\\
  \>First tab stop\\
  \>A\>\>B\\
  \>\>Second tab stop
\end{tabbing}

And the rule is designed to match these separators.

> Then I'm okay with installing the proposed change.

Thanks, the change is attached; I can push it myself, or you can do it
in case you want to change the commit message etc.  I will close the
report once the change is installed.

@Keita: Thanks for the report and answering Eli's questions.

Best, Arash