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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 to another keymap or to a command. When an event type is bound to a keymap, that keymap is used to look up the next input event; 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 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 events 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 one key sequence. In other words, removing one or more events from the end of any valid key sequence must always yield a prefix key. For example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key sequence.

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.

Several kinds of elements may appear in a keymap, after the symbol keymap that begins it:

(type . binding)
This specifies one binding, for 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.
(t . binding)
This specifies 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, codes 0 through 127; vector element n is the binding for the character with code n. This is a 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 each ASCII character, even if the vector contains nil for that character. Such a binding of nil overrides any default key binding in the keymap, for ASCII characters. However, default bindings are still meaningful for events other than 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. 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 (see section Prefix Keys).

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. More precisely, 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 containing 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 that 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, 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)

Prefix Keys

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:

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. See 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

Function: define-prefix-command symbol
This function prepares symbol for use as a prefix key's binding: it creates a full 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.

This function also sets symbol as a variable, with the keymap as its value. It returns symbol.

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. The current buffer's local keymap is always active except when overriding-local-map overrides it. Text properties can specify an alternative local map for certain parts of the buffer; see section Properties with Special Meanings.

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

The variable overriding-local-map, if non-nil, specifies another local keymap that overrides the buffer's local map and all the minor mode keymaps.

All the active keymaps are used together to determine what command to execute when a key is entered. Emacs searches these maps one by one, in order of decreasing precedence, until it finds a binding in one of the maps. The procedure for searching a single keymap is called key lookup; see section Key Lookup.

Normally, Emacs first searches for the key in the minor mode maps, in the order specified by minor-mode-map-alist; 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. However, if overriding-local-map is non-nil, Emacs searches that map first, before the global map.

Since every buffer that uses the same major mode normally uses the same local keymap, you can think of the keymap as local to the mode. A change to the local keymap of a buffer (using local-set-key, for example) is seen also in the other buffers that share that keymap.

The local keymaps that are used for Lisp mode and some other major modes exist even if they have not yet been used. These local maps are the values of variables such as lisp-mode-map. For most major 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 Introduction to Minibuffers.

Emacs has other keymaps that are used in a different way--translating events within read-key-sequence. See section Translating Input Events.

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. The global keymap is normally this keymap. The default global keymap is a full keymap that binds self-insert-command to all of the printing characters.

It is normal practice to change the bindings in the global map, but you should not assign this variable any value other than the keymap it starts out with.

Function: current-global-map
This function returns the current global keymap. This is 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 local keymap of the current buffer. If keymap is nil, then the buffer has no local keymap. use-local-map returns nil. Most major mode commands 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 that enables or disables a minor mode. See section Keymaps and Minor Modes.

Note that elements of minor-mode-map-alist do not have the same structure as elements of minor-mode-alist. The map must be the CDR of the element; a list with the map as the CADR will not do. The CADR can be either a keymap (a list) or a symbol whose function definition is a keymap.

When more than one minor mode keymap is active, their order of priority is the order of minor-mode-map-alist. But you should design minor modes so that they don't interfere with each other. If you do this properly, the order will not matter.

See section Keymaps and Minor Modes, for more information about minor modes. See also minor-mode-key-binding (see section Functions for Key Lookup).

Variable: minor-mode-overriding-map-alist
This variable allows major modes to override the key bindings for particular minor modes. The elements of this alist look like the elements of minor-mode-map-alist: (variable . keymap).

If a variable appears as an element of minor-mode-overriding-map-alist, the map specified by that element totally replaces any map specified for the same variable in minor-mode-map-alist.

minor-mode-overriding-map-alist is automatically buffer-local in all buffers.

Variable: overriding-local-map
If non-nil, this variable holds a keymap to use instead of the buffer's local keymap and instead of all the minor mode keymaps. This keymap, if any, overrides all other maps that would have been active, except for the current global map.

Variable: overriding-terminal-local-map
If non-nil, this variable holds a keymap to use instead of overriding-local-map, the buffer's local keymap and all the minor mode keymaps.

This variable is always local to the current terminal and cannot be buffer-local. See section Multiple Displays. It is used to implement incremental search mode.

Variable: overriding-local-map-menu-flag
If this variable is non-nil, the value of overriding-local-map or overriding-terminal-local-map can affect the display of the menu bar. The default value is nil, so those map variables have no effect on the menu bar.

Note that these two map variables do affect the execution of key sequences entered using the menu bar, even if they do not affect the menu bar display. So if a menu bar key sequence comes in, you should clear the variables before looking up and executing that key sequence. Modes that use the variables would typically do this anyway; normally they respond to events that they do not handle by "unreading" them and exiting.

Variable: special-event-map
This variable holds a keymap for special events. If an event type has a binding in this keymap, then it is special, and the binding for the event is run directly by read-event. See section Special Events.

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 type 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 "key-sequence" is insufficient for command-execute to run, 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 found by looking up an event type in a keymap. (This doesn't include the item string and other extra elements in menu key bindings, because lookup-key and other key lookup functions don't include them in the returned value.) While any Lisp object may be stored in a keymap as a keymap entry, not all make sense for key lookup. Here is a table 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, and has no default binding, that is equivalent to a binding of nil for that event type.
The events used so far in the lookup form a complete key, and command is its binding. See section What Is a Function?.
The array (either a string or a vector) is a keyboard macro. The events used so far in the lookup form a complete key, and the array is its binding. See section Keyboard Macros, for more information.
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 meaning of a list depends on the types of the elements of the list.
  • If the CAR of list is the symbol keymap, then the list is a keymap, and is treated as a keymap (see above).
  • If the CAR of list is lambda, then the list is a lambda expression. This is presumed to be a command, and is treated as such (see above).
  • If the CAR of list is a keymap and the CDR is an event type, then this is an indirect entry:
    (othermap . othertype)
    When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that. This feature permits you to define one key as an alias for another key. For example, an entry whose CAR is the keymap called esc-map and whose CDR is 32 (the code for SPC) means, "Use the global binding of Meta-SPC, whatever that may be."
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 that 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 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 that 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. All the other functions described in this chapter that look up keys use lookup-key. Here are examples:

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

If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap, it must be "too long" and have extra events at the end that do not fit into a single key sequence. 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 you explicitly ask about them. (To do this, supply t as an element of key; see section Format of Keymaps.)

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

Unlike read-key-sequence, this function does not modify the specified events in ways that discard information (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 (above).

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 variable that 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 found is not a prefix definition (a keymap or a symbol defined as a keymap), 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. Here is an illustration:

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. If you change a binding in the global keymap, the change is effective in all buffers (though it has no direct effect in buffers that shadow the global binding with a local one). If you change the current buffer's local map, that usually affects all buffers using the same major mode. The global-set-key and local-set-key functions are convenient interfaces for these operations (see section Commands for Binding Keys). You can also use define-key, a more general function; then you must specify explicitly the map to change.

In writing the key sequence to rebind, it is good 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. You can also use this escape syntax in vectors, as well as others that aren't allowed in strings; one example is `[?\C-\H-x home]'. See section Character Type.

The key definition and lookup functions accept an alternate syntax for event types in a key sequence that is a vector: you can use a list containing modifier names plus one base event (a character or function key name). For example, (control ?a) is equivalent to ?\C-a and (hyper control left) is equivalent to C-H-left. One advantage of such lists is that the precise numeric codes for the modifier bits don't appear in compiled files.

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. 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 can be defined as specified.

If there was previously no binding for key in keymap, the new binding is added at the beginning of keymap. The order of bindings in a keymap makes no difference in most cases, but it does matter for menu keymaps (see section Menu Keymaps).

Here is an example that creates a sparse keymap and makes a number of bindings in it:

(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 keymap, 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 making all the printing characters undefined. More precisely, it binds them to the command undefined. This makes ordinary insertion of text impossible. suppress-keymap returns nil.

If nodigits is nil, then suppress-keymap defines digits to run digit-argument, and - to run negative-argument. Otherwise it makes them undefined like the rest of the printing characters.

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.

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)


(global-set-key [(control ?x) (control ?\\)] '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.

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 that uses key 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 reached (via zero or more 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 is also the value of the variable 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 actuality.

Function: where-is-internal command &optional keymap firstonly noindirect
This function is a subroutine used by the where-is command (see section `Help' in The GNU Emacs Manual). It returns a list of key sequences (of any length) that are bound to command in a set of keymaps.

The argument command can be any object; it is compared with all keymap entries using eq.

If keymap is nil, then the maps used are the current active keymaps, disregarding overriding-local-map (that is, pretending its value is nil). If keymap is non-nil, then the maps searched are keymap and the global keymap.

Usually it's best to use overriding-local-map as the expression for keymap. Then where-is-internal searches precisely the keymaps that are active. To search only the global map, pass (keymap) (an empty keymap) as keymap.

If firstonly is non-ascii, then the value is a single string representing the first key sequence found, rather than a list of all possible key sequences. If firstonly is t, then the value is the first key sequence, except that key sequences consisting entirely of ASCII characters (or meta variants of ASCII characters) are preferred to all other key sequences.

If noindirect is non-nil, where-is-internal doesn't follow indirect keymap bindings. This makes it possible to search for an indirect definition itself.

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

Command: describe-bindings &optional prefix
This function creates a listing of all current key bindings, and displays it in a buffer named `*Help*'. The text is grouped by modes--minor modes first, then the major mode, then global bindings.

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

The listing describes meta characters as ESC followed by the corresponding non-meta character.

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.

Menu Keymaps

A keymap can define a menu as well as bindings for keyboard keys and mouse button. Menus are usually 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 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. When you add an item to an existing menu, you can specify its position in the menu using define-key-after (see section Modifying Menus).

Simple Menu Items

The simpler and older way to define a menu keymap binding looks like this:

(item-string . real-binding)

The CAR, item-string, is the string to be displayed in the menu. It should be short--preferably one to three words. It should describe the action of the command it corresponds to.

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

(item-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 may use help-string as extended documentation for the menu item, available on request.

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

If real-binding is nil, then item-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 that 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.

The menu bar does not recalculate which items are enabled every time you look at a menu. This is because the X toolkit requires the whole tree of menus in advance. To force recalculation of the menu bar, call force-mode-line-update (see section Mode Line Format).

You've probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this:

(item-string [help-string] (key-binding-data) . real-binding)

Don't put these sublists in the menu item yourself; menu display calculates them automatically. Don't mention keyboard equivalents in the item strings themselves, since that is redundant.

Extended Menu Items

An extended-format menu item is a more flexible and also cleaner alternative to the simple format. It consists of a list that starts with the symbol menu-item. To define a non-selectable string, the item looks like this:

(menu-item item-name)

where a string consisting of two or more dashes specifies a separator line.

To define a real menu item which can be selected, the extended format item looks like this:

(menu-item item-name real-binding
    . item-property-list)

Here, item-name is an expression which evaluates to the menu item string. Thus, the string need not be a constant. The third element, real-binding, is the command to execute. The tail of the list, item-property-list, has the form of a property list which contains other information. Here is a table of the properties that are supported:

:enable FORM
The result of evaluating form determines whether the item is enabled (non-nil means yes).
:visible FORM
The result of evaluating form determines whether the item should actually appear in the menu (non-nil means yes). If the item does not appear, then the menu is displayed as if this item were not defined at all.
:help help
The value of this property, help, is the extra help string (not currently used by Emacs).
:button (type . selected)
This property provides a way to define radio buttons and toggle buttons. The CAR, type, says which: is should be :toggle or :radio. The CDR, selected, should be a form; the result of evaluating it says whether this button is currently selected. A toggle is a menu item which is labeled as either "on" or "off" according to the value of selected. The command itself should toggle selected, setting it to t if it is nil, and to nil if it is t. Here is how the menu item to toggle the debug-on-error flag is defined:
(menu-item "Debug on Error" toggle-debug-on-error
           :button (:toggle
                    . (and (boundp 'debug-on-error)
This works because toggle-debug-on-error is defined as a command which toggles the variable debug-on-error. Radio buttons are a group of menu items, in which at any time one and only one is "selected." There should be a variable whose value says which one is selected at any time. The selected form for each radio button in the group should check whether the variable has the right value for selecting that button. Clicking on the button should set the variable so that the button you clicked on becomes selected.
:key-sequence key-sequence
This property specifies which key sequence is likely to be bound to the same command invoked by this menu item. If you specify the right key sequence, that makes preparing the menu for display run much faster. If you specify the wrong key sequence, it has no effect; before Emacs displays key-sequence in the menu, it verifies that key-sequence is really equivalent to this menu item.
:key-sequence nil
This property indicates that there is normally no key binding which is equivalent to this menu item. Using this property saves time in preparing the menu for display, because Emacs does not need to search the keymaps for a keyboard equivalent for this menu item. However, if the user has rebound this item's definition to a key sequence, Emacs ignores the :keys property and finds the keyboard equivalent anyway.
:keys string
This property specifies that string is the string to display as the keyboard equivalent for this menu item. You can use the `\\[...]' documentation construct in string.
:filter filter-fn
This property provides a way to compute the menu item dynamically. The property value filter-fn should be a function of one argument; when it is called, its argument will be real-binding. The function should return the binding to use instead.

Alias Menu Items

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 toggle-read-only and gives them different enable conditions:

(defalias 'make-read-only 'toggle-read-only)
(put 'make-read-only 'menu-enable '(not buffer-read-only))
(defalias 'make-writable 'toggle-read-only)
(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 toggle-read-only.

Menus and the Mouse

The usual way to make a menu keymap produce a menu is to make it the definition of a prefix key. (A Lisp program can explicitly pop up a menu and receive the user's choice--see section Pop-Up Menus.)

If 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 that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)

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 an item string that starts with `@'. The rest of the item string becomes the name of the pane. See the file `lisp/mouse.el' for an example of this. Any ordinary bindings with `@'-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.

X toolkit menus don't have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with `@' or not. In a toolkit version of Emacs, the only thing special about `@' at the beginning of an item string is that the `@' doesn't appear in the menu item.

You can also produce multiple panes or submenus 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 (when Emacs does not use an X-toolkit) or a separate submenu (when using an X-toolkit). See section Active Keymaps.

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 item 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. (The variable menu-prompt-more-char specifies which character is used for this; SPC is the default.)

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.

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 complete example of defining a menu keymap. It is the definition of the `Print' submenu in the `Tools' menu in the menu bar, and it uses the simple menu item format (see section Simple Menu Items). First we create the keymap, and give it a name:

(defvar menu-bar-print-menu (make-sparse-keymap "Print"))

Next we define the menu items:

(define-key menu-bar-print-menu [ps-print-region]
  '("Postscript Print Region" . ps-print-region-with-faces))
(define-key menu-bar-print-menu [ps-print-buffer]
  '("Postscript Print Buffer" . ps-print-buffer-with-faces))
(define-key menu-bar-print-menu [separator-ps-print]
(define-key menu-bar-print-menu [print-region]
  '("Print Region" . print-region))
(define-key menu-bar-print-menu [print-buffer]
  '("Print Buffer" . print-buffer))

Note the symbols which the bindings are "made for"; these appear inside square brackets, in the key sequence being defined. In some cases, this symbol is the same as the command name; sometimes it is different. These symbols are treated as "function keys", but they are not real function keys on the keyboard. They do not affect the functioning of the menu itself, but they are "echoed" in the echo area when the user selects from the menu, and they appear in the output of where-is and apropos.

The binding whose definition is ("--") is a separator line. Like a real menu item, the separator has a key symbol, in this case separator-ps-print. If one menu has two separators, they must have two different key symbols.

Here is code to define enable conditions for two of the commands in the menu:

(put 'print-region 'menu-enable 'mark-active)
(put 'ps-print-region-with-faces 'menu-enable 'mark-active)

Here is how we make this menu appear as an item in the parent menu:

(define-key menu-bar-tools-menu [print]
  (cons "Print" menu-bar-print-menu))

Note that this incorporates the submenu keymap, which is the value of the variable menu-bar-print-menu, rather than the symbol menu-bar-print-menu itself. Using that symbol in the parent menu item would be meaningless because menu-bar-print-menu is not a command.

If you wanted to attach the same print menu to a mouse click, you can do it this way:

(define-key global-map [C-S-down-mouse-1]

We could equally well use an extended menu item (see section Extended Menu Items) for print-region, like this:

(define-key menu-bar-print-menu [print-region]
  '(menu-item "Print Region" print-region
              :enable (mark-active)))

With the extended menu item, the enable condition is specified inside the menu item itself. If we wanted to make this item disappear from the menu entirely when the mark is inactive, we could do it this way:

(define-key menu-bar-print-menu [print-region]
  '(menu-item "Print Region" print-region
              :visible (mark-active)))

The Menu Bar

Most window systems allow each frame to 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 menu containing all the subcommands of that item--the global subcommands, the local subcommands, and the minor mode subcommands.

The variable overriding-local-map is normally ignored when determining the menu bar contents. That is, the menu bar is computed from the keymaps that would be active if overriding-local-map were nil. See section Active Keymaps.

In order for a frame to display a menu bar, its menu-bar-lines parameter 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 1 or 2 as the value of menu-bar-lines. See section 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)
;; and make it the menu bar item's definition.
(define-key global-map [menu-bar words]
  (cons "Words" (make-sparse-keymap "Words")))

;; Define specific subcommands in this menu.
(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-menu); thus, the `Help' menu item normally appears at the end of the menu bar, following local menu items.

Variable: menu-bar-update-hook
This normal hook is run whenever the user clicks on the menu bar, before displaying a submenu. You can use it to update submenus whose contents should vary.

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 in the menu, 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 event after. The argument key should be of length one--a vector or string with just one element. But after should be a single event type--a symbol or a character, not a sequence. The new binding goes after the binding for after. If after is t, then the new binding goes last, at the end of the keymap.

Here is an example:

(define-key-after 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.

Here is how to insert an item called `Work' in the `Signals' menu of Shell mode, after the item break:

  (lookup-key shell-mode-map [menu-bar signals])
  [work] '("Work" . work-command) 'break)

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