bug#60930: 30.0.50; 24.3 Choosing File Modes section of Emacs manual does not explain dealing with backup files

[Eli Zaretskii <eliz@gnu.org>]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: 60930-done@debbugs.gnu.org
> Date: Thu, 19 Jan 2023 11:36:09 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > The feature of "recursive extension stripping" was already documented
> > there.  I added a few words about two examples of its usage (backup
> > files aren't the only one, and I see no reason to treat them specially
> > in this regard, let alone have the actual regexp in the manual).
> > However, I sincerely doubt that having this described in that place
> > will be discoverable enough.  I also am not sure why you thought it
> > was so important to mention: it's an obscure implementation detail
> > intended to make Emacs DTRT, and as long it does TRT, why should users
> > worry?
> 
> I thought that it is important to mention because we got a bug report
> claiming that opening backups of Org files in org-mode is not expected:
> https://list.orgmode.org/25543.50706.554658.6937@gargle.gargle.HOWL/

It isn't clear from that complaint what mistakes could happen.

Anyway, all that was requested there was to mention this in the
manual, so that others won't be surprised (if they read the manual).

> As for discoverability, an index entry might do.

Please suggest a useful index entry.