bug#62892: proposal to extend mark-sexp to go forward and backward on command

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: Zachary Kanfer <zkanfer@gmail.com>,  mardani29@yahoo.es,
>   ruijie@netyu.xyz,  monnier@iro.umontreal.ca,  62892@debbugs.gnu.org
> Date: Thu, 27 Apr 2023 21:12:55 +0300
> 
> > I tried to describe the behavior in the doc string as follows:
> >
> >   (defun mark-sexp (&optional arg allow-extend)
> >     "Set mark ARG sexps from point or move mark one sexp.
> >   When called from Lisp with ALLOW-EXTEND ommitted or nil, mark is
> >   set ARG sexps from point; ARG defaults to 1.
> >   With ALLOW-EXTEND non-nil (interactively, with prefix argument),
> >   the place mark goes is the same place \\[forward-sexp] would move
> >   with the same value of ARG; if the mark is active, it moves ARG
> >   sexps from its current position, otherwise it is set ARG sexps
> >   from point; ARG defaults to 1.
> >   When invoked interactively without a prefix argument and no active
> >   region, mark moves one sexp forward.
> >   When invoked interactively without a prefix argument, and region
> >   is active, mark moves one sexp away of point (i.e., forward
> >   if mark is at or after point, back if mark is before point), thus
> >   extending the region by one sexp.  Since the direction of region
> >   extension depends on the relative position of mark and point, you
> >   can change the direction by \\[exchange-point-and-mark].
> >   This command assumes point is not in a string or comment."
> >
> > It is still somewhat complicated and confusing, but at least it's
> > accurate, I think.
> 
> mark-sexp has a counterpart mark-word that has almost the same
> implementation and docstring.  So this could be fixed in both places.

Done on the emacs-29 branch.