Prefix Keymaps
A prefix key such as C-x or <ESC> has its own keymap, which holds the definition for the event that immediately follows that prefix.
The definition of a prefix key is usually the keymap to use for looking up the following event. The definition can also be a Lisp symbol whose function definition is the following keymap; the effect is the same, but it provides a command name for the prefix key that can be used as a description of what the prefix key is for. Thus, the binding of C-x is the symbol Ctl-X-Prefix, whose function definition is the keymap for C-x commands. 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.
Aside from ordinary prefix keys, there is a fictitious "prefix key" which represents the menu bar; see Menu Bar, for special information about menu bar key bindings. Mouse button events that invoke pop-up menus are also prefix keys; see Menu Keymaps, for more details.
Some prefix keymaps are stored in variables with names:
- ctl-x-map is the variable name for the map used for characters that follow C-x.
- help-map is for characters that follow C-h.
- esc-map is for characters that follow <ESC>. Thus, all Meta characters are actually defined by this map.
- ctl-x-4-map is for characters that follow C-x 4.
- mode-specific-map is for characters that follow C-c.
