Fix doc strings of 'mark-sexp' and 'mark-word'

* lisp/emacs-lisp/lisp.el (mark-sexp):
* lisp/simple.el (mark-word): Clarify the doc strings in various
usage cases.  (Bug#62892)

1 files changed, 16 insertions, 6 deletions

diff --git a/lisp/emacs-lisp/lisp.el b/lisp/emacs-lisp/lisp.el
index e3ed28f097a..b91d56cfb4f 100644
--- a/lisp/emacs-lisp/lisp.el
+++ b/lisp/emacs-lisp/lisp.el
@@ -92,12 +92,22 @@ report errors as appropriate for this kind of usage."
   (forward-sexp (- arg) interactive))
 
 (defun mark-sexp (&optional arg allow-extend)
-  "Set mark ARG sexps from point.
-The place mark goes is the same place \\[forward-sexp] would
-move to with the same argument.
-Interactively, if this command is repeated
-or (in Transient Mark mode) if the mark is active,
-it marks the next ARG sexps after the ones already marked.
+  "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.
+With ARG and ALLOW-EXTEND both non-nil (interactively, with prefix
+argument), the place to which mark goes is the same place \\[forward-sexp]
+would move to with the same argument; if the mark is active, it moves
+ARG sexps from its current position, otherwise it is set ARG sexps
+from point.
+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."
   (interactive "P\np")
   (cond ((and allow-extend