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A prefix key is a key sequence whose binding is a keymap. The keymap
defines what to do with key sequences that extend the prefix key. For
example, C-x is a prefix key, and it uses a keymap that is also stored
in the variable ctl-x-map. This keymap defines bindings for key
sequences starting with C-x.
Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables:
esc-map is the global keymap for the <ESC> prefix key. Thus, the
global definitions of all meta characters are actually found here. This map
is also the function definition of ESC-prefix.
help-map is the global keymap for the C-h prefix key.
mode-specific-map is the global keymap for the prefix key C-c.
This map is actually global, not mode-specific, but its name provides useful
information about C-c in the output of C-h b
(display-bindings), since the main use of this prefix key is for
mode-specific bindings.
ctl-x-map is the global keymap used for the C-x prefix key.
This map is found via the function cell of the symbol
Control-X-prefix.
mule-keymap is the global keymap used for the C-x <RET>
prefix key.
ctl-x-4-map is the global keymap used for the C-x 4 prefix key.
ctl-x-5-map is the global keymap used for the C-x 5 prefix key.
2C-mode-map is the global keymap used for the C-x 6 prefix key.
vc-prefix-map is the global keymap used for the C-x v prefix
key.
facemenu-keymap is the global keymap used for the M-o prefix
key.
The keymap binding of a prefix key is used for looking up the event that
follows the prefix key. (It may instead be a symbol whose function
definition is a keymap. The effect is the same, but the symbol serves as a
name for the prefix key.) Thus, the binding of C-x is the symbol
Control-X-prefix, whose function cell holds the keymap for C-x
commands. (The same keymap is also the value of ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and <ESC> as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. Voir la section Active Keymaps.
If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then the
binding for C-p C-f is the function find-file, just like
C-x C-f. The key sequence C-p 6 is not found in any active
keymap.
(use-local-map (make-sparse-keymap))
⇒ nil
(local-set-key "\C-p" ctl-x-map)
⇒ nil
(key-binding "\C-p\C-f")
⇒ find-file
(key-binding "\C-p6")
⇒ nil
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This function prepares symbol for use as a prefix key's binding: it
creates a sparse keymap and stores it as symbol's function
definition. Subsequently binding a key sequence to symbol will make
that key sequence into a prefix key. The return value is symbol.
This function also sets symbol as a variable, with the keymap as its
value. But if mapvar is non-nil, it sets mapvar as a
variable instead.
If prompt is non-nil, that becomes the overall prompt string
for the keymap. The prompt string should be given for menu keymaps
(voir la section Defining Menus).
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Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.