bug#73709: 29.4; Doc of `file-newer-than-file-p'

[Michael Albinus via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

Hi,

>> Apart from that: if it is hard or not practical to describe what the
>> function returns in every case, we can instead try to describe major use
>> cases.
>
> That'd mean a lot of text to write to describe what should be clear
> enough, at least as far as Emacs is concerned.  I don't think it's our
> job to describe how the various filesystems work.

In the Tramp case, we couldn'tz even be sure that the remote file is
treated there as "file". See for example the Tramp gdrive method, or
think about AWS S3 buckets.

Tramp asks the remote system about whether a file is newer than the
other, and it returns this answer in its file-newer-than-file-p
implementations. On classical filesystems, it is the last modification
time, yes. But we cannot guarantee, because we simply don't know the
details of the remote filesystem.

Best regards, Michael.