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The bindings between input events and commands are recorded in data structures called keymaps. Each binding in a keymap associates (or binds) an individual event type either with another keymap or with a command. When an event is bound to a keymap, that keymap is used to look up the next character typed; this continues until a command is found. The whole process is called key lookup.

Keymap Terminology

A keymap is a table mapping event types to definitions (which can be any Lisp objects, though only certain types are meaningful for execution by the command loop). Given an event (or an event type) and a keymap, Emacs can get the event's definition. Events include ordinary ASCII characters, function keys, and mouse actions (see section Input Events).

A sequence of input events that form a unit is called a key sequence, or key for short. A sequence of one event is always a key sequence, and so are some multi-event sequences.

A keymap determines a binding or definition for any key sequence. If the key sequence is a single event, its binding is the definition of the event in the keymap. The binding of a key sequence of more than one event is found by an iterative process: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up.

If the binding of a key sequence is a keymap, we call the key sequence a prefix key. Otherwise, we call it a complete key (because no more characters can be added to it). If the binding is nil, we call the key undefined. Examples of prefix keys are C-c, C-x, and C-x 4. Examples of defined complete keys are X, RET, and C-x 4 C-f. Examples of undefined complete keys are C-x C-g, and C-c 3. See section Prefix Keys, for more details.

The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit--it is not really a key sequence. In other words, removing one or more events from the end of any valid key must always yield a prefix key. For example, C-f C-f is not a key; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key.

Note that the set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.

At any time, several primary keymaps are active---that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See section Active Keymaps, for details.

Format of Keymaps

A keymap is a list whose CAR is the symbol keymap. The remaining elements of the list define the key bindings of the keymap. Use the function keymapp (see below) to test whether an object is a keymap.

An ordinary element is a cons cell of the form (type . binding). This specifies one binding which applies to events of type type. Each ordinary binding applies to events of a particular event type, which is always a character or a symbol. See section Classifying Events.

A cons cell whose CAR is t is a default key binding; any event not bound by other elements of the keymap is given binding as its binding. Default bindings allow a keymap to bind all possible event types without having to enumerate all of them. A keymap that has a default binding completely masks any lower-precedence keymap.

If an element of a keymap is a vector, the vector counts as bindings for all the ASCII characters; vector element n is the binding for the character with code n. This is a more compact way to record lots of bindings. A keymap with such a vector is called a full keymap. Other keymaps are called sparse keymaps.

When a keymap contains a vector, it always defines a binding for every ASCII character even if the vector element is nil. Such a binding of nil overrides any default binding in the keymap. However, default bindings are still meaningful for events that are not ASCII characters. A binding of nil does not override lower-precedence keymaps; thus, if the local map gives a binding of nil, Emacs uses the binding from the global map.

Aside from bindings, a keymap can also have a string as an element. This is called the overall prompt string and makes it possible to use the keymap as a menu. See section Menu Keymaps.

Keymaps do not directly record bindings for the meta characters, whose codes are from 128 to 255. Instead, meta characters are regarded for purposes of key lookup as sequences of two characters, the first of which is ESC (or whatever is currently the value of meta-prefix-char). Thus, the key M-a is really represented as ESC a, and its global binding is found at the slot for a in esc-map.

Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for DEL and TAB, plus C-c C-l, M-C-q, and M-C-x.

 ;; TAB
 (9 . lisp-indent-line)                 
 ;; DEL
 (127 . backward-delete-char-untabify)  
 (3 keymap 
    ;; C-c C-l
    (12 . run-lisp))                    
 (27 keymap 
     ;; M-C-q, treated as ESC C-q
     (17 . indent-sexp)                 
     ;; M-C-x, treated as ESC C-x
     (24 . lisp-send-defun)))           

Function: keymapp object

This function returns t if object is a keymap, nil otherwise. Practically speaking, this function tests for a list whose CAR is keymap.

(keymapp '(keymap))
    => t
(keymapp (current-global-map))
    => t

Creating Keymaps

Here we describe the functions for creating keymaps.

Function: make-keymap &optional prompt

This function creates and returns a new full keymap (i.e., one which contains a vector of length 128 for defining all the ASCII characters). The new keymap initially binds all ASCII characters to nil, and does not bind any other kind of event.

    => (keymap [nil nil nil ... nil nil])

If you specify prompt, that becomes the overall prompt string for the keymap. The prompt string is useful for menu keymaps (see section Menu Keymaps).

Function: make-sparse-keymap &optional prompt

This function creates and returns a new sparse keymap with no entries. The new keymap does not bind any events. The argument prompt specifies a prompt string, as in make-keymap.

    => (keymap)

Function: copy-keymap keymap

This function returns a copy of keymap. Any keymaps which appear directly as bindings in keymap are also copied recursively, and so on to any number of levels. However, recursive copying does not take place when the definition of a character is a symbol whose function definition is a keymap; the same symbol appears in the new copy.

(setq map (copy-keymap (current-local-map)))
=> (keymap
     ;; (This implements meta characters.)
     (27 keymap         
         (83 . center-paragraph)
         (115 . center-line))
     (9 . tab-to-tab-stop))

(eq map (current-local-map))
    => nil
(equal map (current-local-map))
    => t

Inheritance and Keymaps

A keymap can inherit the bindings of another keymap. Do do this, make a keymap whose "tail" is another existing keymap to inherit from. Such a keymap looks like this:

(keymap bindings... . other-keymap)

The effect is that this keymap inherits all the bindings of other-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 other-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 other-keymap.

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

(setq my-mode-map (cons 'keymap text-mode-map))

Prefix Keys

A prefix key has an associated keymap which defines what to do with key sequences that start with the prefix key. For example, C-x is a prefix key, and it uses a keymap which is also stored in the variable ctl-x-map. Here is a list of the standard prefix keys of Emacs and their keymaps:

The binding of a prefix key is the keymap to use for looking up the events that follow 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 definition is the keymap for C-x commands. (The same keymap is also the value of ctl-x-map.)

Prefix key definitions of this sort 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. See section Active Keymaps.

If a key is defined as a prefix in more than one active map, then the 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

Function: define-prefix-command symbol

This function defines symbol as a prefix command: it creates a full keymap and stores it as symbol's function definition. Storing the symbol as the binding of a key makes the key a prefix key which has a name. It also sets symbol as a variable, to have the keymap as its value. The function returns symbol.

In Emacs version 18, only the function definition of symbol was set, not the value as a variable.

Menu Keymaps

A keymap can define a menu as well as ordinary keys and mouse button meanings. Menus are normally actuated with the mouse, but they can work with the keyboard also.

Defining Menus

A keymap is suitable for menu use if it has an overall prompt string, which is a string that appears as an element of the keymap. (See section Format of Keymaps.) The string should describe the purpose of the menu. The easiest way to construct a keymap with a prompt string is to specify the string as an argument when you call make-keymap or make-sparse-keymap (see section Creating Keymaps).

The individual bindings in the menu keymap should also have prompt strings; these strings become the items displayed in the menu. A binding with a prompt string looks like this:

(string . real-binding)

As far as define-key and lookup-key are concerned, the string is part of the event's binding. However, only real-binding is used for executing the key.

You can also supply a second string, called the help string, as follows:

(string help-string . real-binding)

Currently Emacs does not actually use help-string; it knows only how to ignore help-string in order to extract real-binding. In the future we hope to make help-string serve as extended documentation for the menu item, available on request.

The prompt string for a binding should be short--one or two words. It should describe the action of the command it corresponds to.

If real-binding is nil, then string appears in the menu but cannot be selected.

If real-binding is a symbol, and has a non-nil menu-enable property, that property is an expression which controls whether the menu item is enabled. Every time the keymap is used to display a menu, Emacs evaluates the expression, and it enables the menu item only if the expression's value is non-nil. When a menu item is disabled, it is displayed in a "fuzzy" fashion, and cannot be selected with the mouse.

The order of items in the menu is the same as the order of bindings in the keymap. Since define-key puts new bindings at the front, you should define the menu items starting at the bottom of the menu and moving to the top, if you care about the order.

Menus and the Mouse

The way to make a menu keymap produce a menu is to make it the definition of a prefix key.

When the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding which brought about that menu item.

It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.

A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings a prompt string that starts with `@'. The rest of the prompt string becomes the name of the pane. See the file `lisp/mouse.el' for an example of this. Any ordinary bindings with `@'-less prompt strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.

You can also get multiple panes from separate keymaps. The full definition of a prefix key always comes from merging the definitions supplied by the various active keymaps (minor mode, local, and global). When more than one of these keymaps is a menu, each of them makes a separate pane or panes. See section Active Keymaps.

A Lisp program can explicitly pop up a menu and receive the user's choice. You can use keymaps for this also. See section Pop-Up Menus.

Menus and the Keyboard

When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the user can use the keyboard to choose a menu item.

Emacs displays the menu alternatives (the prompt strings of the bindings) in the echo area. If they don't all fit at once, the user can type SPC to see the next line of alternatives. Successive uses of SPC eventually get to the end of the menu and then cycle around to the beginning.

When the user has found the desired alternative from the menu, he or she should type the corresponding character--the one whose binding is that alternative.

In a menu intended for keyboard use, each menu item must clearly indicate what character to type. The best convention to use is to make the character the first letter of the menu item prompt string. That is something users will understand without being told.

This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.

Variable: menu-prompt-more-char

This variable specifies the character to use to ask to see the next line of a menu. Its initial value is 32, the code for SPC.

Menu Example

Here is a simple example of how to set up a menu for mouse use.

(defvar my-menu-map
  (make-sparse-keymap "Key Commands <==> Functions"))
(fset 'help-for-keys my-menu-map)

(define-key my-menu-map [bindings]
  '("List all keystroke commands" . describe-bindings))
(define-key my-menu-map [key]
  '("Describe key briefly" . describe-key-briefly))
(define-key my-menu-map [key-verbose]
  '("Describe key verbose" . describe-key))
(define-key my-menu-map [function]
  '("Describe Lisp function" . describe-function))
(define-key my-menu-map [where-is]
  '("Where is this command" . where-is))

(define-key global-map [C-S-down-mouse-1] 'help-for-keys)

The symbols used in the key sequences bound in the menu are fictitious "function keys"; they don't appear on the keyboard, but that doesn't stop you from using them in the menu. Their names were chosen to be mnemonic, because they show up in the output of where-is and apropos to identify the corresponding menu items.

However, if you want the menu to be usable from the keyboard as well, you must use real ASCII characters instead of fictitious function keys.

The Menu Bar

Under X Windows, each frame can have a menu bar---a permanently displayed menu stretching horizontally across the top of the frame. The items of the menu bar are the subcommands of the fake "function key" menu-bar, as defined by all the active keymaps.

To add an item to the menu bar, invent a fake "function key" of your own (let's call it key), and make a binding for the key sequence [menu-bar key]. Most often, the binding is a menu keymap, so that pressing a button on the menu bar item leads to another menu.

When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined submenu containing all the subcommands of that item--the global subcommands, the local subcommands, and the minor mode subcommands, all together.

In order for a frame to display a menu bar, its menu-bar-lines property must be greater than zero. Emacs uses just one line for the menu bar itself; if you specify more than one line, the other lines serve to separate the menu bar from the windows in the frame. We recommend you try one or two as the value of menu-bar-lines. See section X Window Frame Parameters.

Here's an example of setting up a menu bar item:

(modify-frame-parameters (selected-frame) '((menu-bar-lines . 2)))

;; Make a menu keymap (with a prompt string)
;; to be the menu bar item's definition.
(define-key global-map [menu-bar words]
  (cons "Words" (make-sparse-keymap "Words")))

;; Make specific subcommands in the item's submenu.
(define-key global-map
  [menu-bar words forward]
  '("Forward word" . forward-word))
(define-key global-map
  [menu-bar words backward]
  '("Backward word" . backward-word))

A local keymap can cancel a menu bar item made by the global keymap by rebinding the same fake function key with undefined as the binding. For example, this is how Dired suppresses the `Edit' menu bar item:

(define-key dired-mode-map [menu-bar edit] 'undefined)

edit is the fake function key used by the global map for the `Edit' menu bar item. The main reason to suppress a global menu bar item is to regain space for mode-specific items.

Variable: menu-bar-final-items

Normally the menu bar shows global items followed by items defined by the local maps.

This variable holds a list of fake function keys for items to display at the end of the menu bar rather than in normal sequence. The default value is (help); thus, the `Help' menu item normally appears at the end of the menu bar, following local menu items.

Modifying Menus

When you insert a new item in an existing menu, you probably want to put it in a particular place among the menu's existing items. If you use define-key to add the item, it normally goes at the front of the menu. To put it elsewhere, use define-key-after:

Function: define-key-after map key binding after

Define a binding in map for key, with value binding, just like define-key, but position the binding in map after the binding for the key after. For example,

(define-key my-menu [drink]
            '("Drink" . drink-command) [eat])

makes a binding for the fake function key drink and puts it right after the binding for eat.

Active Keymaps

Emacs normally contains many keymaps; at any given time, just a few of them are active in that they participate in the interpretation of user input. These are the global keymap, the current buffer's local keymap, and the keymaps of any enabled minor modes.

The global keymap holds the bindings of keys that are defined regardless of the current buffer, such as C-f. The variable global-map holds this keymap, which is always active.

Each buffer may have another keymap, its local keymap, which may contain new or overriding definitions for keys. At all times, the current buffer's local keymap is active. Text properties can specify an alternative local map for certain parts of the buffer; see section Special Properties.

Each minor mode may have a keymap; if it does, the keymap is active whenever the minor mode is enabled.

All the active keymaps are used together to determine what command to execute when a key is entered. The key lookup proceeds as described earlier (see section Key Lookup), but Emacs first searches for the key in the minor mode maps (one map at a time); if they do not supply a binding for the key, Emacs searches the local map; if that too has no binding, Emacs then searches the global map.

Since every buffer that uses the same major mode normally uses the very same local keymap, it may appear as if the keymap is local to the mode. A change to the local keymap of a buffer (using local-set-key, for example) will be seen also in the other buffers that share that keymap.

The local keymaps that are used for Lisp mode, C mode, and several other major modes exist even if they have not yet been used. These local maps are the values of the variables lisp-mode-map, c-mode-map, and so on. For most other modes, which are less frequently used, the local keymap is constructed only when the mode is used for the first time in a session.

The minibuffer has local keymaps, too; they contain various completion and exit commands. See section Minibuffers.

See section Standard Keymaps, for a list of standard keymaps.

Variable: global-map

This variable contains the default global keymap that maps Emacs keyboard input to commands. Normally this keymap is the global keymap. The default global keymap is a full keymap that binds self-insert-command to all of the printing characters.

Function: current-global-map

This function returns the current global keymap. This is always the same as the value of global-map unless you change one or the other.

=> (keymap [set-mark-command beginning-of-line ... 

Function: current-local-map

This function returns the current buffer's local keymap, or nil if it has none. In the following example, the keymap for the `*scratch*' buffer (using Lisp Interaction mode) is a sparse keymap in which the entry for ESC, ASCII code 27, is another sparse keymap.

=> (keymap 
    (10 . eval-print-last-sexp) 
    (9 . lisp-indent-line) 
    (127 . backward-delete-char-untabify) 
    (27 keymap 
        (24 . eval-defun) 
        (17 . indent-sexp)))

Function: current-minor-mode-maps

This function returns a list of the keymaps of currently enabled minor modes.

Function: use-global-map keymap

This function makes keymap the new current global keymap. It returns nil.

It is very unusual to change the global keymap.

Function: use-local-map keymap

This function makes keymap the new current local keymap of the current buffer. If keymap is nil, then there will be no local keymap. It returns nil. Most major modes use this function.

Variable: minor-mode-map-alist

This variable is an alist describing keymaps that may or may not be active according to the values of certain variables. Its elements look like this:

(variable . keymap)

The keymap keymap is active whenever variable has a non-nil value. Typically variable is the variable which enables or disables a minor mode. See section Keymaps and Minor Modes.

When more than one minor mode keymap is active, their order of priority is the order of minor-mode-map-alist.

See also minor-mode-key-binding in section Functions for Key Lookup.

Key Lookup

Key lookup is the process of finding the binding of a key sequence from a given keymap. Actual execution of the binding is not part of key lookup.

Key lookup uses just the event types of each event in the key sequence; the rest of the event is ignored. In fact, a key sequence used for key lookup may designate mouse events with just their types (symbols) instead of with entire mouse events (lists). See section Input Events. Such a pseudo-key-sequence is insufficient for command-execute, but it is sufficient for looking up or rebinding a key.

When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.

Let's use the term keymap entry to describe the value directly associated with an event type in a keymap. While any Lisp object may be stored as a keymap entry, not all make sense for key lookup. Here is a list of the meaningful kinds of keymap entries:

nil means that the events used so far in the lookup form an undefined key. When a keymap fails to mention an event type at all, that is equivalent to an entry of nil for that type.

The events used so far in the lookup form a prefix key. The next event of the key sequence is looked up in keymap.

The events used so far in the lookup form a complete key, and command is its binding.

The events used so far in the lookup form a complete key, whose binding is a keyboard macro. See section Keyboard Macros, for more information.

The meaning of a list depends on the types of the elements of the list.

The function definition of symbol is used in place of symbol. If that too is a symbol, then this process is repeated, any number of times. Ultimately this should lead to an object which is a keymap, a command or a keyboard macro. A list is allowed if it is a keymap or a command, but indirect entries are not understood when found via symbols.

Note that keymaps and keyboard macros (strings and vectors) are not valid functions, so a symbol with a keymap, string or vector as its function definition is also invalid as a function. It is, however, valid as a key binding. If the definition is a keyboard macro, then the symbol is also valid as an argument to command-execute (see section Interactive Call).

The symbol undefined is worth special mention: it means to treat the key as undefined. Strictly speaking, the key is defined, and its binding is the command undefined; but that command does the same thing that is done automatically for an undefined key: it rings the bell (by calling ding) but does not signal an error.

undefined is used in local keymaps to override a global key binding and make the key "undefined" locally. A local binding of nil would fail to do this because it would not override the global binding.

anything else
If any other type of object is found, the events used so far in the lookup form a complete key, and the object is its binding, but the binding is not executable as a command.

In short, a keymap entry may be a keymap, a command, a keyboard macro, a symbol which leads to one of them, or an indirection or nil. Here is an example of a sparse keymap with two characters bound to commands and one bound to another keymap. This map is the normal value of emacs-lisp-mode-map. Note that 9 is the code for TAB, 127 for DEL, 27 for ESC, 17 for C-q and 24 for C-x.

(keymap (9 . lisp-indent-line)
        (127 . backward-delete-char-untabify)
        (27 keymap (17 . indent-sexp) (24 . eval-defun)))

Functions for Key Lookup

Here are the functions and variables pertaining to key lookup.

Function: lookup-key keymap key &optional accept-defaults

This function returns the definition of key in keymap. If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap (which means it is "too long" and has extra events at the end), then the value is a number, the number of events at the front of key that compose a complete key.

If accept-defaults is non-nil, then lookup-key considers default bindings as well as bindings for the specific events in key. Otherwise, lookup-key reports only bindings for the specific sequence key, ignoring default bindings except when an element of key is t.

All the other functions described in this chapter that look up keys use lookup-key.

(lookup-key (current-global-map) "\C-x\C-f")
    => find-file
(lookup-key (current-global-map) "\C-x\C-f12345")
    => 2

If key contains a meta character, that character is implicitly replaced by a two-character sequence: the value of meta-prefix-char, followed by the corresponding non-meta character. Thus, the first example below is handled by conversion into the second example.

(lookup-key (current-global-map) "\M-f")
    => forward-word
(lookup-key (current-global-map) "\ef")
    => forward-word

This function does not modify the specified events in ways that discard information as read-key-sequence does (see section Key Sequence Input). In particular, it does not convert letters to lower case and it does not change drag events to clicks.

Command: undefined

Used in keymaps to undefine keys. It calls ding, but does not cause an error.

Function: key-binding key &optional accept-defaults

This function returns the binding for key in the current keymaps, trying all the active keymaps. The result is nil if key is undefined in the keymaps.

The argument accept-defaults controls checking for default bindings, as in lookup-key.

An error is signaled if key is not a string or a vector.

(key-binding "\C-x\C-f")
    => find-file

Function: local-key-binding key &optional accept-defaults

This function returns the binding for key in the current local keymap, or nil if it is undefined there.

The argument accept-defaults controls checking for default bindings, as in lookup-key (above).

Function: global-key-binding key &optional accept-defaults

This function returns the binding for command key in the current global keymap, or nil if it is undefined there.

The argument accept-defaults controls checking for default bindings, as in lookup-key (above).

Function: minor-mode-key-binding key &optional accept-defaults

This function returns a list of all the active minor mode bindings of key. More precisely, it returns an alist of pairs (modename . binding), where modename is the the variable which enables the minor mode, and binding is key's binding in that mode. If key has no minor-mode bindings, the value is nil.

If the first binding is a non-prefix, all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.

The argument accept-defaults controls checking for default bindings, as in lookup-key (above).

Variable: meta-prefix-char

This variable is the meta-prefix character code. It is used when translating a meta character to a two-character sequence so it can be looked up in a keymap. For useful results, the value should be a prefix event (see section Prefix Keys). The default value is 27, which is the ASCII code for ESC.

As long as the value of meta-prefix-char remains 27, key lookup translates M-b into ESC b, which is normally defined as the backward-word command. However, if you set meta-prefix-char to 24, the code for C-x, then Emacs will translate M-b into C-x b, whose standard binding is the switch-to-buffer command.

meta-prefix-char                    ; The default value.
     => 27
(key-binding "\M-b")
     => backward-word
?\C-x                               ; The print representation
     => 24                          ;   of a character.
(setq meta-prefix-char 24)
     => 24      
(key-binding "\M-b")
     => switch-to-buffer            ; Now, typing M-b is
                                    ;   like typing C-x b.

(setq meta-prefix-char 27)          ; Avoid confusion!
     => 27                          ; Restore the default value!

Changing Key Bindings

The way to rebind a key is to change its entry in a keymap. You can change the global keymap, so that the change is effective in all buffers (except those that override the global binding with a local one). Or you can change the current buffer's local map, which usually affects all buffers using the same major mode. The global-set-key and local-set-key functions are convenient interfaces for these operations. Or you can use define-key and specify explicitly which map to change.

People often use global-set-key in their `.emacs' file for simple customization. For example,

(global-set-key "\C-x\C-\\" 'next-line)


(global-set-key [?\C-x ?\C-\\] 'next-line)

redefines C-x C-\ to move down a line.

(global-set-key [M-mouse-1] 'mouse-set-point)

redefines the first (leftmost) mouse button, typed with the Meta key, to set point where you click.

In writing the key sequence to rebind, it is useful to use the special escape sequences for control and meta characters (see section String Type). The syntax `\C-' means that the following character is a control character and `\M-' means that the following character is a meta character. Thus, the string "\M-x" is read as containing a single M-x, "\C-f" is read as containing a single C-f, and "\M-\C-x" and "\C-\M-x" are both read as containing a single C-M-x.

For the functions below, an error is signaled if keymap is not a keymap or if key is not a string or vector representing a key sequence. However, you can use event types (symbols) as shorthand for events that are lists.

Function: define-key keymap key binding

This function sets the binding for key in keymap. (If key is more than one event long, the change is actually made in another keymap reached from keymap.) The argument binding can be any Lisp object, but only certain types are meaningful. (For a list of meaningful types, see section Key Lookup.) The value returned by define-key is binding.

Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled.

If some prefix of key is undefined, then define-key defines it as a prefix key so that the rest of key may be defined as specified.

The following example creates a sparse keymap and makes a number of bindings:

(setq map (make-sparse-keymap))
    => (keymap)
(define-key map "\C-f" 'forward-char)
    => forward-char
    => (keymap (6 . forward-char))

;; Build sparse submap for C-x and bind f in that.
(define-key map "\C-xf" 'forward-word)
    => forward-word
=> (keymap 
    (24 keymap                ; C-x
        (102 . forward-word)) ;      f
    (6 . forward-char))       ; C-f

;; Bind C-p to the ctl-x-map.
(define-key map "\C-p" ctl-x-map)
;; ctl-x-map
=> [nil ... find-file ... backward-kill-sentence] 

;; Bind C-f to foo in the ctl-x-map.
(define-key map "\C-p\C-f" 'foo)
=> 'foo
=> (keymap     ; Note foo in ctl-x-map.
    (16 keymap [nil ... foo ... backward-kill-sentence])
    (24 keymap 
        (102 . forward-word))
    (6 . forward-char))

Note that storing a new binding for C-p C-f actually works by changing an entry in ctl-x-map, and this has the effect of changing the bindings of both C-p C-f and C-x C-f in the default global map.

Function: substitute-key-definition olddef newdef keymap &optional oldmap

This function replaces olddef with newdef for any keys in keymap that were bound to olddef. In other words, olddef is replaced with newdef wherever it appears. The function returns nil.

For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:

 'find-file 'find-file-read-only (current-global-map))

If oldmap is non-nil, then its bindings determine which keys to rebind. The rebindings still happen in newmap, not in oldmap. Thus, you can change one map under the control of the bindings in another. For example,

  'delete-backward-char 'my-funny-delete
  my-map global-map)

puts the special deletion command in my-map for whichever keys are globally bound to the standard deletion command.

Here is an example showing a keymap before and after substitution:

(setq map '(keymap 
            (?1 . olddef-1) 
            (?2 . olddef-2) 
            (?3 . olddef-1)))
=> (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))

(substitute-key-definition 'olddef-1 'newdef map)
=> nil
=> (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))

Function: suppress-keymap keymap &optional nodigits

This function changes the contents of the full keymap keymap by replacing the self-insertion commands for numbers with the digit-argument function, unless nodigits is non-nil, and by replacing the functions for the rest of the printing characters with undefined. This means that ordinary insertion of text is impossible in a buffer with a local keymap on which suppress-keymap has been called.

suppress-keymap returns nil.

The suppress-keymap function does not make it impossible to modify a buffer, as it does not suppress commands such as yank and quoted-insert. To prevent any modification of a buffer, make it read-only (see section Read-Only Buffers).

Since this function modifies keymap, you would normally use it on a newly created keymap. Operating on an existing keymap that is used for some other purpose is likely to cause trouble; for example, suppressing global-map would make it impossible to use most of Emacs.

Most often, suppress-keymap is used to initialize local keymaps of modes such as Rmail and Dired where insertion of text is not desirable and the buffer is read-only. Here is an example taken from the file `emacs/lisp/dired.el', showing how the local keymap for Dired mode is set up:

  (setq dired-mode-map (make-keymap))
  (suppress-keymap dired-mode-map)
  (define-key dired-mode-map "r" 'dired-rename-file)
  (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted)
  (define-key dired-mode-map "d" 'dired-flag-file-deleted)
  (define-key dired-mode-map "v" 'dired-view-file)
  (define-key dired-mode-map "e" 'dired-find-file)
  (define-key dired-mode-map "f" 'dired-find-file)

Commands for Binding Keys

This section describes some convenient interactive interfaces for changing key bindings. They work by calling define-key.

Command: global-set-key key definition

This function sets the binding of key in the current global map to definition.

(global-set-key key definition)
(define-key (current-global-map) key definition)

Command: global-unset-key key

This function removes the binding of key from the current global map.

One use of this function is in preparation for defining a longer key which uses it implicitly as a prefix--which would not be allowed if key has a non-prefix binding. For example:

(global-unset-key "\C-l")
    => nil
(global-set-key "\C-l\C-l" 'redraw-display)
    => nil

This function is implemented simply using define-key:

(global-unset-key key)
(define-key (current-global-map) key nil)

Command: local-set-key key definition

This function sets the binding of key in the current local keymap to definition.

(local-set-key key definition)
(define-key (current-local-map) key definition)

Command: local-unset-key key

This function removes the binding of key from the current local map.

(local-unset-key key)
(define-key (current-local-map) key nil)

Scanning Keymaps

This section describes functions used to scan all the current keymaps for the sake of printing help information.

Function: accessible-keymaps keymap &optional prefix

This function returns a list of all the keymaps that can be accessed (via prefix keys) from keymap. The value is an association list with elements of the form (key . map), where key is a prefix key whose definition in keymap is map.

The elements of the alist are ordered so that the key increases in length. The first element is always ("" . keymap), because the specified keymap is accessible from itself with a prefix of no events.

If prefix is given, it should be a prefix key sequence; then accessible-keymaps includes only the submaps whose prefixes start with prefix. These elements look just as they do in the value of (accessible-keymaps); the only difference is that some elements are omitted.

In the example below, the returned alist indicates that the key ESC, which is displayed as `^[', is a prefix key whose definition is the sparse keymap (keymap (83 . center-paragraph) (115 . foo)).

(accessible-keymaps (current-local-map))
=>(("" keymap 
      (27 keymap   ; Note this keymap for ESC is repeated below.
          (83 . center-paragraph)
          (115 . center-line))
      (9 . tab-to-tab-stop))

   ("^[" keymap 
    (83 . center-paragraph) 
    (115 . foo)))

In the following example, C-h is a prefix key that uses a sparse keymap starting with (keymap (118 . describe-variable)...). Another prefix, C-x 4, uses a keymap which happens to be ctl-x-4-map. The event mode-line is one of several dummy events used as prefixes for mouse actions in special parts of a window.

(accessible-keymaps (current-global-map))
=> (("" keymap [set-mark-command beginning-of-line ... 
    ("^H" keymap (118 . describe-variable) ...
     (8 . help-for-help))
    ("^X" keymap [x-flush-mouse-queue ...
    ("^[" keymap [mark-sexp backward-sexp ...
    ("^X4" keymap (15 . display-buffer) ...)
    ([mode-line] keymap
     (S-mouse-2 . mouse-split-window-horizontally) ...))

These are not all the keymaps you would see in an actual case.

Function: where-is-internal command &optional keymap firstonly

This function returns a list of key sequences (of any length) that are bound to command in keymap and the global keymap. The argument command can be any object; it is compared with all keymap entries using eq. If keymap is not supplied, then the global map alone is used.

If firstonly is non-nil, then the value is a single string representing the first key sequence found, rather than a list of all possible key sequences.

This function is used by where-is (see section `Help' in The GNU Emacs Manual).

(where-is-internal 'describe-function)
    => ("\^hf" "\^hd")

Command: describe-bindings prefix

This function creates a listing of all defined keys, and their definitions. The listing is put in a buffer named `*Help*', which is then displayed in a window.

A meta character is shown as ESC followed by the corresponding non-meta character. Control characters are indicated with C-.

When several characters with consecutive ASCII codes have the same definition, they are shown together, as `firstchar..lastchar'. In this instance, you need to know the ASCII codes to understand which characters this means. For example, in the default global map, the characters `SPC .. ~' are described by a single line. SPC is ASCII 32, ~ is ASCII 126, and the characters between them include all the normal printing characters, (e.g., letters, digits, punctuation, etc.); all these characters are bound to self-insert-command.

If prefix is non-nil, it should be a prefix key; then only keys that start with prefix are described.

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