Sometimes it is useful to make menu items that use the same
command but with different enable conditions. The best way to do this
in Emacs now is with extended menu items; before that feature existed,
it could be done by defining alias commands and using them in menu
items. Here’s an example that makes two aliases for
read-only-mode and gives them different enable conditions:
(defalias 'make-read-only 'read-only-mode) (put 'make-read-only 'menu-enable '(not buffer-read-only)) (defalias 'make-writable 'read-only-mode) (put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the
equivalent key bindings for the real command name, not the aliases
(which typically don’t have any key bindings except for the menu
itself). To request this, give the alias symbol a non-nil
menu-alias property. Thus,
(put 'make-read-only 'menu-alias t) (put 'make-writable 'menu-alias t)
causes menu items for make-read-only and make-writable to
show the keyboard bindings for read-only-mode.