doc: /* Return a copy of the keymap KEYMAP.
Note that this is almost never needed. If you want a keymap that's like
-another yet with a few changes, you should use map inheritance rather
-than copying. I.e. something like:
+another yet with a few changes, you should use keymap inheritance rather
+than copying. That is, something like:
+
+ (defvar-keymap foo-map
+ :parent <theirmap>
+ ...)
+
+Or, if you need to support Emacs versions older than 29:
(let ((map (make-sparse-keymap)))
(set-keymap-parent map <theirmap>)