bug#52934: format-time-string year error

[david]

Now I have read about ISO 8601 in Wikipedia and, of course, your replies
are correct; now I know that we are in week 52 of 2021.

However, someone writing Emacs code to produce a timestamp for, e.g.,
.html code, does not see the need to study an ISO specification to avoid a
tripwire that is not even obvious - the problem only occurs, if it occurs,
in a few days of the year.  Otherwise there is no reason to suspect that
personal code is faulty: it will perform correctly, including under test,
for about 360 days of the year.

I should like to suggest a note in the Emacs Info documentation that warns
the reader that ISO weeks do not map nicely into the calendar that the
reader lives by.  That would be helpful.  I am not suggesting that the
Emacs documentation should describe ISO 8601, only that it warns of the
potential problems, and, ideally, gives a reference to a description of the
standard.

dajo