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(elisp)Inheritance and Keymaps

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Inheritance and Keymaps
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   A keymap can inherit the bindings of another keymap, which we call
the "parent keymap".  Such a keymap looks like this:

     (keymap BINDINGS... . PARENT-KEYMAP)

The effect is that this keymap inherits all the bindings of
PARENT-KEYMAP, whatever they may be at the time a key is looked up, but
can add to them or override them with BINDINGS.

   If you change the bindings in PARENT-KEYMAP using `define-key' or
other key-binding functions, these changes are visible in the
inheriting keymap unless shadowed by BINDINGS.  The converse is not
true: if you use `define-key' to change the inheriting keymap, that
affects BINDINGS, but has no effect on PARENT-KEYMAP.

   The proper way to construct a keymap with a parent is to use
`set-keymap-parent'; if you have code that directly constructs a keymap
with a parent, please convert the program to use `set-keymap-parent'
instead.

 - Function: keymap-parent keymap
     This returns the parent keymap of KEYMAP.  If KEYMAP has no
     parent, `keymap-parent' returns `nil'.

 - Function: set-keymap-parent keymap parent
     This sets the parent keymap of KEYMAP to PARENT, and returns
     PARENT.  If PARENT is `nil', this function gives KEYMAP no parent
     at all.

     If KEYMAP has submaps (bindings for prefix keys), they too receive
     new parent keymaps that reflect what PARENT specifies for those
     prefix keys.

   Here is an example showing how to make a keymap that inherits from
`text-mode-map':

     (let ((map (make-sparse-keymap)))
       (set-keymap-parent map text-mode-map)
       map)