bug#69709: `sort` interface improvement and universal ordering predicate

[Eli Zaretskii]

> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Fri, 29 Mar 2024 11:59:39 +0100
> Cc: Dmitry Gutov <dmitry@gutov.dev>,
>  Eli Zaretskii <eliz@gnu.org>,
>  69709@debbugs.gnu.org,
>  Gerd Möllmann <gerd.moellmann@gmail.com>
> 
> 25 mars 2024 kl. 12.11 skrev Mattias Engdegård <mattias.engdegard@gmail.com>:
> 
> > The plan is to add scratch/sort-key to master in a few days if no serious 
> > issues turn up.
> 
> Plan executed.

Thanks.

I have a few comments/questions about value<:

 . The description of value< says "lexicographic order" about some
   types, but I think that is not clear enough, and we should tell
   explicitly how the comparison works in those cases.  AFAIU, the
   corresponding elements are compared by recursively calling value<
   for them? And what happens if one has more elements than the other?
   These are all questions that popped up when I read the new text,
   and I think they should be answered in the text.
 . AFAICT, no ordering is defined for overlays, and I wonder why.  I
   think this could be very useful; we certainly sort overlays in C in
   several places.
 . Various fine details about value< are never mentioned: the fact
   that there's a limit to recursion, the special treatment of nil in
   some cases, etc.  I think we should document them, at least in the
   doc string if not in the manual as well.