Advertize set-keymap-parent as replacement for copy-keymap

* doc/lispref/keymaps.texi (Creating Keymaps):
* src/keymap.c (Fcopy_keymap): Advertize set-keymap-parent as replacement.

1 files changed, 12 insertions, 2 deletions

diff --git a/src/keymap.c b/src/keymap.c
index 44335aded87..b27df1d0452 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -971,8 +971,18 @@ copy_keymap_1 (Lisp_Object chartable, Lisp_Object idx, Lisp_Object elt)
 
 DEFUN ("copy-keymap", Fcopy_keymap, Scopy_keymap, 1, 1, 0,
        doc: /* Return a copy of the keymap KEYMAP.
-The copy starts out with the same definitions of KEYMAP,
-but changing either the copy or KEYMAP does not affect the other.
+
+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:
+
+    (let ((map (make-sparse-keymap)))
+      (set-keymap-parent map <theirmap>)
+      (define-key map ...)
+      ...)
+
+After performing `copy-keymap', the copy starts out with the same definitions
+of KEYMAP, but changing either the copy or KEYMAP does not affect the other.
 Any key definitions that are subkeymaps are recursively copied.
 However, a key definition which is a symbol whose definition is a keymap
 is not copied.  */)