Fix buffer overflow in make-docfile

[emacs.git] / doc / lispref / keymaps.texi

@c -*- mode: texinfo; coding: utf-8 -*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990-1994, 1998-2017 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Keymaps
@chapter Keymaps
@cindex keymap

  The command bindings of input events are recorded in data structures
called @dfn{keymaps}.  Each entry in a keymap associates (or
@dfn{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 @dfn{key lookup}.

@menu
* Key Sequences::               Key sequences as Lisp objects.
* Keymap Basics::               Basic concepts of keymaps.
* Format of Keymaps::           What a keymap looks like as a Lisp object.
* Creating Keymaps::            Functions to create and copy keymaps.
* Inheritance and Keymaps::     How one keymap can inherit the bindings
                                   of another keymap.
* Prefix Keys::                 Defining a key with a keymap as its definition.
* Active Keymaps::              How Emacs searches the active keymaps
                                   for a key binding.
* Searching Keymaps::           A pseudo-Lisp summary of searching active maps.
* Controlling Active Maps::     Each buffer has a local keymap
                                   to override the standard (global) bindings.
                                   A minor mode can also override them.
* Key Lookup::                  Finding a key's binding in one keymap.
* Functions for Key Lookup::    How to request key lookup.
* Changing Key Bindings::       Redefining a key in a keymap.
* Remapping Commands::          A keymap can translate one command to another.
* Translation Keymaps::         Keymaps for translating sequences of events.
* Key Binding Commands::        Interactive interfaces for redefining keys.
* Scanning Keymaps::            Looking through all keymaps, for printing help.
* Menu Keymaps::                Defining a menu as a keymap.
@end menu

@node Key Sequences
@section Key Sequences
@cindex key
@cindex keystroke
@cindex key sequence

  A @dfn{key sequence}, or @dfn{key} for short, is a sequence of one
or more input events that form a unit.  Input events include
characters, function keys, mouse actions, or system events external to
Emacs, such as @code{iconify-frame} (@pxref{Input Events}).
The Emacs Lisp representation for a key sequence is a string or
vector.  Unless otherwise stated, any Emacs Lisp function that accepts
a key sequence as an argument can handle both representations.

  In the string representation, alphanumeric characters ordinarily
stand for themselves; for example, @code{"a"} represents @kbd{a}
and @code{"2"} represents @kbd{2}.  Control character events are
prefixed by the substring @code{"\C-"}, and meta characters by
@code{"\M-"}; for example, @code{"\C-x"} represents the key @kbd{C-x}.
In addition, the @key{TAB}, @key{RET}, @key{ESC}, and @key{DEL} events
are represented by @code{"\t"}, @code{"\r"}, @code{"\e"}, and
@code{"\d"} respectively.  The string representation of a complete key
sequence is the concatenation of the string representations of the
constituent events; thus, @code{"\C-xl"} represents the key sequence
@kbd{C-x l}.

  Key sequences containing function keys, mouse button events, system
events, or non-@acronym{ASCII} characters such as @kbd{C-=} or
@kbd{H-a} cannot be represented as strings; they have to be
represented as vectors.

  In the vector representation, each element of the vector represents
an input event, in its Lisp form.  @xref{Input Events}.  For example,
the vector @code{[?\C-x ?l]} represents the key sequence @kbd{C-x l}.

  For examples of key sequences written in string and vector
representations, @ref{Init Rebinding,,, emacs, The GNU Emacs Manual}.

@defun kbd keyseq-text
This function converts the text @var{keyseq-text} (a string constant)
into a key sequence (a string or vector constant).  The contents of
@var{keyseq-text} should use the same syntax as in the buffer invoked
by the @kbd{C-x C-k @key{RET}} (@code{kmacro-edit-macro}) command; in
particular, you must surround function key names with
@samp{<@dots{}>}.  @xref{Edit Keyboard Macro,,, emacs, The GNU Emacs
Manual}.

@example
(kbd "C-x") @result{} "\C-x"
(kbd "C-x C-f") @result{} "\C-x\C-f"
(kbd "C-x 4 C-f") @result{} "\C-x4\C-f"
(kbd "X") @result{} "X"
(kbd "RET") @result{} "\^M"
(kbd "C-c SPC") @result{} "\C-c@ "
(kbd "<f1> SPC") @result{} [f1 32]
(kbd "C-M-<down>") @result{} [C-M-down]
@end example
@end defun

@node Keymap Basics
@section Keymap Basics
@cindex key binding
@cindex binding of a key
@cindex complete key
@cindex undefined key

  A keymap is a Lisp data structure that specifies @dfn{key bindings}
for various key sequences.

  A single keymap directly specifies definitions for individual
events.  When a key sequence consists of a single event, its binding
in a keymap is the keymap's definition for that event.  The binding of
a longer key sequence is found by an iterative process: first find the
definition of the first event (which must itself be a keymap); then
find the second event's definition in that keymap, and so on until all
the events in the key sequence have been processed.

  If the binding of a key sequence is a keymap, we call the key sequence
a @dfn{prefix key}.  Otherwise, we call it a @dfn{complete key} (because
no more events can be added to it).  If the binding is @code{nil},
we call the key @dfn{undefined}.  Examples of prefix keys are @kbd{C-c},
@kbd{C-x}, and @kbd{C-x 4}.  Examples of defined complete keys are
@kbd{X}, @key{RET}, and @kbd{C-x 4 C-f}.  Examples of undefined complete
keys are @kbd{C-x C-g}, and @kbd{C-c 3}.  @xref{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, @kbd{C-f C-n} is not a key sequence;
@kbd{C-f} is not a prefix key, so a longer sequence starting with
@kbd{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 @dfn{active}---that is, in
use for finding key bindings.  These are the @dfn{global map}, which is
shared by all buffers; the @dfn{local keymap}, which is usually
associated with a specific major mode; and zero or more @dfn{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.  @xref{Active Keymaps},
for details.

@node Format of Keymaps
@section Format of Keymaps
@cindex format of keymaps
@cindex keymap format
@cindex full keymap
@cindex sparse keymap

  Each keymap is a list whose @sc{car} is the symbol @code{keymap}.  The
remaining elements of the list define the key bindings of the keymap.
A symbol whose function definition is a keymap is also a keymap.  Use
the function @code{keymapp} (see below) to test whether an object is a
keymap.

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

@table @code
@item (@var{type} .@: @var{binding})
This specifies one binding, for events of type @var{type}.  Each
ordinary binding applies to events of a particular @dfn{event type},
which is always a character or a symbol.  @xref{Classifying Events}.
In this kind of binding, @var{binding} is a command.

@item (@var{type} @var{item-name} .@: @var{binding})
This specifies a binding which is also a simple menu item that
displays as @var{item-name} in the menu.  @xref{Simple Menu Items}.

@item (@var{type} @var{item-name} @var{help-string} .@: @var{binding})
This is a simple menu item with help string @var{help-string}.

@item (@var{type} menu-item .@: @var{details})
This specifies a binding which is also an extended menu item.  This
allows use of other features.  @xref{Extended Menu Items}.

@item (t .@: @var{binding})
@cindex default key binding
This specifies a @dfn{default key binding}; any event not bound by other
elements of the keymap is given @var{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, except for events
explicitly bound to @code{nil} (see below).

@item @var{char-table}
If an element of a keymap is a char-table, it counts as holding
bindings for all character events with no modifier bits
(@pxref{modifier bits}): the element whose index is @var{c} is the
binding for the character @var{c}.  This is a compact way to record
lots of bindings.  A keymap with such a char-table is called a
@dfn{full keymap}.  Other keymaps are called @dfn{sparse keymaps}.

@item @var{vector}
This kind of element is similar to a char-table: the element whose
index is @var{c} is the binding for the character @var{c}.  Since the
range of characters that can be bound this way is limited by the
vector size, and vector creation allocates space for all character
codes from 0 up, this format should not be used except for creating
menu keymaps (@pxref{Menu Keymaps}), where the bindings themselves
don't matter.

@item @var{string}
@cindex keymap prompt string
@cindex overall prompt string
@cindex prompt string of keymap
Aside from elements that specify bindings for keys, a keymap can also
have a string as an element.  This is called the @dfn{overall prompt
string} and makes it possible to use the keymap as a menu.
@xref{Defining Menus}.

@item (keymap @dots{})
If an element of a keymap is itself a keymap, it counts as if this inner keymap
were inlined in the outer keymap.  This is used for multiple-inheritance, such
as in @code{make-composed-keymap}.
@end table

When the binding is @code{nil}, it doesn't constitute a definition
but it does take precedence over a default binding or a binding in the
parent keymap.  On the other hand, a binding of @code{nil} does
@emph{not} override lower-precedence keymaps; thus, if the local map
gives a binding of @code{nil}, Emacs uses the binding from the
global map.

@cindex meta characters lookup
  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 @key{ESC} (or
whatever is currently the value of @code{meta-prefix-char}).  Thus, the
key @kbd{M-a} is internally represented as @kbd{@key{ESC} a}, and its
global binding is found at the slot for @kbd{a} in @code{esc-map}
(@pxref{Prefix Keys}).

  This conversion applies only to characters, not to function keys or
other input events; thus, @kbd{M-@key{end}} has nothing to do with
@kbd{@key{ESC} @key{end}}.

  Here as an example is the local keymap for Lisp mode, a sparse
keymap.  It defines bindings for @key{DEL}, @kbd{C-c C-z},
@kbd{C-M-q}, and @kbd{C-M-x} (the actual value also contains a menu
binding, which is omitted here for the sake of brevity).

@example
@group
lisp-mode-map
@result{}
@end group
@group
(keymap
 (3 keymap
    ;; @kbd{C-c C-z}
    (26 . run-lisp))
@end group
@group
 (27 keymap
     ;; @r{@kbd{C-M-x}, treated as @kbd{@key{ESC} C-x}}
     (24 . lisp-send-defun))
@end group
@group
 ;; @r{This part is inherited from @code{lisp-mode-shared-map}.}
 keymap
 ;; @key{DEL}
 (127 . backward-delete-char-untabify)
@end group
@group
 (27 keymap
     ;; @r{@kbd{C-M-q}, treated as @kbd{@key{ESC} C-q}}
     (17 . indent-sexp)))
@end group
@end example

@defun keymapp object
This function returns @code{t} if @var{object} is a keymap, @code{nil}
otherwise.  More precisely, this function tests for a list whose
@sc{car} is @code{keymap}, or for a symbol whose function definition
satisfies @code{keymapp}.

@example
@group
(keymapp '(keymap))
    @result{} t
@end group
@group
(fset 'foo '(keymap))
(keymapp 'foo)
    @result{} t
@end group
@group
(keymapp (current-global-map))
    @result{} t
@end group
@end example
@end defun

@node Creating Keymaps
@section Creating Keymaps
@cindex creating keymaps

  Here we describe the functions for creating keymaps.

@defun make-sparse-keymap &optional prompt
This function creates and returns a new sparse keymap with no entries.
(A sparse keymap is the kind of keymap you usually want.)  The new
keymap does not contain a char-table, unlike @code{make-keymap}, and
does not bind any events.

@example
@group
(make-sparse-keymap)
    @result{} (keymap)
@end group
@end example

If you specify @var{prompt}, that becomes the overall prompt string
for the keymap.  You should specify this only for menu keymaps
(@pxref{Defining Menus}).  A keymap with an overall prompt string will
always present a mouse menu or a keyboard menu if it is active for
looking up the next input event.  Don't specify an overall prompt string
for the main map of a major or minor mode, because that would cause
the command loop to present a keyboard menu every time.
@end defun

@defun make-keymap &optional prompt
This function creates and returns a new full keymap.  That keymap
contains a char-table (@pxref{Char-Tables}) with slots for all
characters without modifiers.  The new keymap initially binds all
these characters to @code{nil}, and does not bind any other kind of
event.  The argument @var{prompt} specifies a
prompt string, as in @code{make-sparse-keymap}.

@c This example seems kind of pointless, but I guess it serves
@c to contrast the result with make-sparse-keymap above.
@example
@group
(make-keymap)
    @result{} (keymap #^[nil nil keymap nil nil nil @dots{}])
@end group
@end example

A full keymap is more efficient than a sparse keymap when it holds
lots of bindings; for just a few, the sparse keymap is better.
@end defun

@defun copy-keymap keymap
This function returns a copy of @var{keymap}.  This is almost never
needed.  If you want a keymap that's like another yet with a few
changes, you should use map inheritance rather than copying.
I.e., something like:

@example
@group
(let ((map (make-sparse-keymap)))
  (set-keymap-parent map <theirmap>)
  (define-key map ...)
  ...)
@end group
@end example

When performing @code{copy-keymap}, any keymaps that
appear directly as bindings in @var{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.
@c Emacs 19 feature

@example
@group
(setq map (copy-keymap (current-local-map)))
@result{} (keymap
@end group
@group
     ;; @r{(This implements meta characters.)}
     (27 keymap
         (83 . center-paragraph)
         (115 . center-line))
     (9 . tab-to-tab-stop))
@end group

@group
(eq map (current-local-map))
    @result{} nil
@end group
@group
(equal map (current-local-map))
    @result{} t
@end group
@end example
@end defun

@node Inheritance and Keymaps
@section Inheritance and Keymaps
@cindex keymap inheritance
@cindex inheritance, keymap

  A keymap can inherit the bindings of another keymap, which we call the
@dfn{parent keymap}.  Such a keymap looks like this:

@example
(keymap @var{elements}@dots{} . @var{parent-keymap})
@end example

@noindent
The effect is that this keymap inherits all the bindings of
@var{parent-keymap}, whatever they may be at the time a key is looked up,
but can add to them or override them with @var{elements}.

If you change the bindings in @var{parent-keymap} using
@code{define-key} or other key-binding functions, these changed
bindings are visible in the inheriting keymap, unless shadowed by the
bindings made by @var{elements}.  The converse is not true: if you use
@code{define-key} to change bindings in the inheriting keymap, these
changes are recorded in @var{elements}, but have no effect on
@var{parent-keymap}.

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

@defun keymap-parent keymap
This returns the parent keymap of @var{keymap}.  If @var{keymap}
has no parent, @code{keymap-parent} returns @code{nil}.
@end defun

@defun set-keymap-parent keymap parent
This sets the parent keymap of @var{keymap} to @var{parent}, and returns
@var{parent}.  If @var{parent} is @code{nil}, this function gives
@var{keymap} no parent at all.

If @var{keymap} has submaps (bindings for prefix keys), they too receive
new parent keymaps that reflect what @var{parent} specifies for those
prefix keys.
@end defun

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

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

  A non-sparse keymap can have a parent too, but this is not very
useful.  A non-sparse keymap always specifies something as the binding
for every numeric character code without modifier bits, even if it is
@code{nil}, so these character's bindings are never inherited from
the parent keymap.

@cindex keymap inheritance from multiple maps
  Sometimes you want to make a keymap that inherits from more than one
map.  You can use the function @code{make-composed-keymap} for this.

@defun make-composed-keymap maps &optional parent
This function returns a new keymap composed of the existing keymap(s)
@var{maps}, and optionally inheriting from a parent keymap
@var{parent}.  @var{maps} can be a single keymap or a list of more
than one.  When looking up a key in the resulting new map, Emacs
searches in each of the @var{maps} in turn, and then in @var{parent},
stopping at the first match.  A @code{nil} binding in any one of
@var{maps} overrides any binding in @var{parent}, but it does not
override any non-@code{nil} binding in any other of the @var{maps}.
@end defun

@noindent For example, here is how Emacs sets the parent of
@code{help-mode-map}, such that it inherits from both
@code{button-buffer-map} and @code{special-mode-map}:

@example
(defvar help-mode-map
  (let ((map (make-sparse-keymap)))
    (set-keymap-parent map
      (make-composed-keymap button-buffer-map special-mode-map))
    ... map) ... )
@end example


@node Prefix Keys
@section Prefix Keys
@cindex prefix key

  A @dfn{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, @kbd{C-x} is a prefix key, and it uses a keymap that is
also stored in the variable @code{ctl-x-map}.  This keymap defines
bindings for key sequences starting with @kbd{C-x}.

  Some of the standard Emacs prefix keys use keymaps that are
also found in Lisp variables:

@itemize @bullet
@item
@vindex esc-map
@findex ESC-prefix
@code{esc-map} is the global keymap for the @key{ESC} prefix key.  Thus,
the global definitions of all meta characters are actually found here.
This map is also the function definition of @code{ESC-prefix}.

@item
@cindex @kbd{C-h}
@code{help-map} is the global keymap for the @kbd{C-h} prefix key.

@item
@cindex @kbd{C-c}
@vindex mode-specific-map
@code{mode-specific-map} is the global keymap for the prefix key
@kbd{C-c}.  This map is actually global, not mode-specific, but its name
provides useful information about @kbd{C-c} in the output of @kbd{C-h b}
(@code{display-bindings}), since the main use of this prefix key is for
mode-specific bindings.

@item
@cindex @kbd{C-x}
@vindex ctl-x-map
@findex Control-X-prefix
@code{ctl-x-map} is the global keymap used for the @kbd{C-x} prefix key.
This map is found via the function cell of the symbol
@code{Control-X-prefix}.

@item
@cindex @kbd{C-x @key{RET}}
@vindex mule-keymap
@code{mule-keymap} is the global keymap used for the @kbd{C-x @key{RET}}
prefix key.

@item
@cindex @kbd{C-x 4}
@vindex ctl-x-4-map
@code{ctl-x-4-map} is the global keymap used for the @kbd{C-x 4} prefix
key.

@item
@cindex @kbd{C-x 5}
@vindex ctl-x-5-map
@code{ctl-x-5-map} is the global keymap used for the @kbd{C-x 5} prefix
key.

@item
@cindex @kbd{C-x 6}
@vindex 2C-mode-map
@code{2C-mode-map} is the global keymap used for the @kbd{C-x 6} prefix
key.

@item
@cindex @kbd{C-x v}
@vindex vc-prefix-map
@code{vc-prefix-map} is the global keymap used for the @kbd{C-x v} prefix
key.

@item
@cindex @kbd{M-g}
@vindex goto-map
@code{goto-map} is the global keymap used for the @kbd{M-g} prefix
key.

@item
@cindex @kbd{M-s}
@vindex search-map
@code{search-map} is the global keymap used for the @kbd{M-s} prefix
key.

@item
@cindex @kbd{M-o}
@vindex facemenu-keymap
@code{facemenu-keymap} is the global keymap used for the @kbd{M-o}
prefix key.

@item
The other Emacs prefix keys are @kbd{C-x @@}, @kbd{C-x a i}, @kbd{C-x
@key{ESC}} and @kbd{@key{ESC} @key{ESC}}.  They use keymaps that have
no special names.
@end itemize

  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 @kbd{C-x} is the
symbol @code{Control-X-prefix}, whose function cell holds the keymap
for @kbd{C-x} commands.  (The same keymap is also the value of
@code{ctl-x-map}.)

  Prefix key definitions can appear in any active keymap.  The
definitions of @kbd{C-c}, @kbd{C-x}, @kbd{C-h} and @key{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.  @xref{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 @kbd{C-p} a prefix key in the local
keymap, in such a way that @kbd{C-p} is identical to @kbd{C-x}.  Then
the binding for @kbd{C-p C-f} is the function @code{find-file}, just
like @kbd{C-x C-f}.  The key sequence @kbd{C-p 6} is not found in any
active keymap.

@example
@group
(use-local-map (make-sparse-keymap))
    @result{} nil
@end group
@group
(local-set-key "\C-p" ctl-x-map)
    @result{} nil
@end group
@group
(key-binding "\C-p\C-f")
    @result{} find-file
@end group

@group
(key-binding "\C-p6")
    @result{} nil
@end group
@end example

@defun define-prefix-command symbol &optional mapvar prompt
@cindex prefix command
@anchor{Definition of define-prefix-command}
This function prepares @var{symbol} for use as a prefix key's binding:
it creates a sparse keymap and stores it as @var{symbol}'s function
definition.  Subsequently binding a key sequence to @var{symbol} will
make that key sequence into a prefix key.  The return value is @code{symbol}.

This function also sets @var{symbol} as a variable, with the keymap as
its value.  But if @var{mapvar} is non-@code{nil}, it sets @var{mapvar}
as a variable instead.

If @var{prompt} is non-@code{nil}, that becomes the overall prompt
string for the keymap.  The prompt string should be given for menu keymaps
(@pxref{Defining Menus}).
@end defun

@node Active Keymaps
@section Active Keymaps
@cindex active keymap

  Emacs contains many keymaps, but at any time only a few keymaps are
@dfn{active}.  When Emacs receives user input, it translates the input
event (@pxref{Translation Keymaps}), and looks for a key binding in
the active keymaps.

  Usually, the active keymaps are: (i) the keymap specified by the
@code{keymap} property, (ii) the keymaps of enabled minor modes, (iii)
the current buffer's local keymap, and (iv) the global keymap, in that
order.  Emacs searches for each input key sequence in all these
keymaps.

  Of these usual keymaps, the highest-precedence one is specified
by the @code{keymap} text or overlay property at point, if any.  (For
a mouse input event, Emacs uses the event position instead of point;
@iftex
see the next section for details.)
@end iftex
@ifnottex
@pxref{Searching Keymaps}.)
@end ifnottex

  Next in precedence are keymaps specified by enabled minor modes.
These keymaps, if any, are specified by the variables
@code{emulation-mode-map-alists},
@code{minor-mode-overriding-map-alist}, and
@code{minor-mode-map-alist}.  @xref{Controlling Active Maps}.

@cindex local keymap
  Next in precedence is the buffer's @dfn{local keymap}, containing
key bindings specific to the buffer.  The minibuffer also has a local
keymap (@pxref{Intro to Minibuffers}).  If there is a @code{local-map}
text or overlay property at point, that specifies the local keymap to
use, in place of the buffer's default local keymap.

@cindex major mode keymap
  The local keymap is normally set by the buffer's major mode, and
every buffer with the same major mode shares the same local keymap.
Hence, if you call @code{local-set-key} (@pxref{Key Binding Commands})
to change the local keymap in one buffer, that also affects the local
keymaps in other buffers with the same major mode.

@cindex global keymap
  Finally, the @dfn{global keymap} contains key bindings that are
defined regardless of the current buffer, such as @kbd{C-f}.  It is
always active, and is bound to the variable @code{global-map}.

  Apart from the above usual keymaps, Emacs provides special ways
for programs to make other keymaps active.  Firstly, the variable
@code{overriding-local-map} specifies a keymap that replaces the usual
active keymaps, except for the global keymap.  Secondly, the
terminal-local variable @code{overriding-terminal-local-map} specifies
a keymap that takes precedence over @emph{all} other keymaps
(including @code{overriding-local-map}); this is normally used for
modal/transient keybindings (the function @code{set-transient-map}
provides a convenient interface for this).  @xref{Controlling Active
Maps}, for details.

  Making keymaps active is not the only way to use them.  Keymaps are
also used in other ways, such as for translating events within
@code{read-key-sequence}.  @xref{Translation Keymaps}.

  @xref{Standard Keymaps}, for a list of some standard keymaps.

@defun current-active-maps &optional olp position
This returns the list of active keymaps that would be used by the
command loop in the current circumstances to look up a key sequence.
Normally it ignores @code{overriding-local-map} and
@code{overriding-terminal-local-map}, but if @var{olp} is non-@code{nil}
then it pays attention to them.  @var{position} can optionally be either
an event position as returned by @code{event-start} or a buffer
position, and may change the keymaps as described for
@code{key-binding}.
@end defun

@defun key-binding key &optional accept-defaults no-remap position
This function returns the binding for @var{key} according to the
current active keymaps.  The result is @code{nil} if @var{key} is
undefined in the keymaps.

The argument @var{accept-defaults} controls checking for default
bindings, as in @code{lookup-key} (@pxref{Functions for Key Lookup}).

When commands are remapped (@pxref{Remapping Commands}),
@code{key-binding} normally processes command remappings so as to
return the remapped command that will actually be executed.  However,
if @var{no-remap} is non-@code{nil}, @code{key-binding} ignores
remappings and returns the binding directly specified for @var{key}.

If @var{key} starts with a mouse event (perhaps following a prefix
event), the maps to be consulted are determined based on the event's
position.  Otherwise, they are determined based on the value of point.
However, you can override either of them by specifying @var{position}.
If @var{position} is non-@code{nil}, it should be either a buffer
position or an event position like the value of @code{event-start}.
Then the maps consulted are determined based on @var{position}.

Emacs signals an error if @var{key} is not a string or a vector.

@example
@group
(key-binding "\C-x\C-f")
    @result{} find-file
@end group
@end example
@end defun

@node Searching Keymaps
@section Searching the Active Keymaps
@cindex searching active keymaps for keys

Here is a pseudo-Lisp summary of how Emacs searches the active
keymaps:

@lisp
(or (if overriding-terminal-local-map
        (@var{find-in} overriding-terminal-local-map))
    (if overriding-local-map
        (@var{find-in} overriding-local-map)
      (or (@var{find-in} (get-char-property (point) 'keymap))
          (@var{find-in-any} emulation-mode-map-alists)
          (@var{find-in-any} minor-mode-overriding-map-alist)
          (@var{find-in-any} minor-mode-map-alist)
          (if (get-text-property (point) 'local-map)
              (@var{find-in} (get-char-property (point) 'local-map))
            (@var{find-in} (current-local-map)))))
    (@var{find-in} (current-global-map)))
@end lisp

@noindent
Here, @var{find-in} and @var{find-in-any} are pseudo functions that
search in one keymap and in an alist of keymaps, respectively.  Note
that the @code{set-transient-map} function works by setting
@code{overriding-terminal-local-map} (@pxref{Controlling Active
Maps}).

  In the above pseudo-code, if a key sequence starts with a mouse
event (@pxref{Mouse Events}), that event's position is used instead of
point, and the event's buffer is used instead of the current buffer.
In particular, this affects how the @code{keymap} and @code{local-map}
properties are looked up.  If a mouse event occurs on a string
embedded with a @code{display}, @code{before-string}, or
@code{after-string} property (@pxref{Special Properties}), and the
string has a non-@code{nil} @code{keymap} or @code{local-map}
property, that overrides the corresponding property in the underlying
buffer text (i.e., the property specified by the underlying text is
ignored).

  When a key binding is found in one of the active keymaps, and that
binding is a command, the search is over---the command is executed.
However, if the binding is a symbol with a value or a string, Emacs
replaces the input key sequences with the variable's value or the
string, and restarts the search of the active keymaps.  @xref{Key
Lookup}.

  The command which is finally found might also be remapped.
@xref{Remapping Commands}.

@node Controlling Active Maps
@section Controlling the Active Keymaps
@cindex active keymap, controlling

@defvar 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
@code{self-insert-command} to all of the printing characters.

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

@defun current-global-map
This function returns the current global keymap.  This is the same as
the value of @code{global-map} unless you change one or the other.
The return value is a reference, not a copy; if you use
@code{define-key} or other functions on it you will alter global
bindings.

@example
@group
(current-global-map)
@result{} (keymap [set-mark-command beginning-of-line @dots{}
            delete-backward-char])
@end group
@end example
@end defun

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

@example
@group
(current-local-map)
@result{} (keymap
    (10 . eval-print-last-sexp)
    (9 . lisp-indent-line)
    (127 . backward-delete-char-untabify)
@end group
@group
    (27 keymap
        (24 . eval-defun)
        (17 . indent-sexp)))
@end group
@end example
@end defun

@code{current-local-map} returns a reference to the local keymap, not
a copy of it; if you use @code{define-key} or other functions on it
you will alter local bindings.

@defun current-minor-mode-maps
This function returns a list of the keymaps of currently enabled minor modes.
@end defun

@defun use-global-map keymap
This function makes @var{keymap} the new current global keymap.  It
returns @code{nil}.

It is very unusual to change the global keymap.
@end defun

@defun use-local-map keymap
This function makes @var{keymap} the new local keymap of the current
buffer.  If @var{keymap} is @code{nil}, then the buffer has no local
keymap.  @code{use-local-map} returns @code{nil}.  Most major mode
commands use this function.
@end defun

@defvar minor-mode-map-alist
@anchor{Definition of 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:

@example
(@var{variable} . @var{keymap})
@end example

The keymap @var{keymap} is active whenever @var{variable} has a
non-@code{nil} value.  Typically @var{variable} is the variable that
enables or disables a minor mode.  @xref{Keymaps and Minor Modes}.

Note that elements of @code{minor-mode-map-alist} do not have the same
structure as elements of @code{minor-mode-alist}.  The map must be the
@sc{cdr} of the element; a list with the map as the second element will
not do.  The @sc{cdr} 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, the earlier one in
@code{minor-mode-map-alist} takes priority.  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 @ref{Keymaps and Minor Modes}, for more information about minor
modes.  See also @code{minor-mode-key-binding} (@pxref{Functions for Key
Lookup}).
@end defvar

@defvar 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 @code{minor-mode-map-alist}: @code{(@var{variable}
. @var{keymap})}.

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

@code{minor-mode-overriding-map-alist} is automatically buffer-local in
all buffers.
@end defvar

@defvar overriding-local-map
If non-@code{nil}, this variable holds a keymap to use instead of the
buffer's local keymap, any text property or overlay keymaps, and any
minor mode keymaps.  This keymap, if specified, overrides all other
maps that would have been active, except for the current global map.
@end defvar

@defvar overriding-terminal-local-map
If non-@code{nil}, this variable holds a keymap to use instead of
@code{overriding-local-map}, the buffer's local keymap, text property
or overlay keymaps, and all the minor mode keymaps.

This variable is always local to the current terminal and cannot be
buffer-local.  @xref{Multiple Terminals}.  It is used to implement
incremental search mode.
@end defvar

@defvar overriding-local-map-menu-flag
If this variable is non-@code{nil}, the value of
@code{overriding-local-map} or @code{overriding-terminal-local-map} can
affect the display of the menu bar.  The default value is @code{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.
@end defvar

@defvar 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 @code{read-event}.  @xref{Special Events}.
@end defvar

@defvar emulation-mode-map-alists
This variable holds a list of keymap alists to use for emulation
modes.  It is intended for modes or packages using multiple minor-mode
keymaps.  Each element is a keymap alist which has the same format and
meaning as @code{minor-mode-map-alist}, or a symbol with a variable
binding which is such an alist.  The active keymaps in each alist
are used before @code{minor-mode-map-alist} and
@code{minor-mode-overriding-map-alist}.
@end defvar

@cindex transient keymap
@defun set-transient-map keymap &optional keep-pred on-exit
This function adds @var{keymap} as a @dfn{transient} keymap, which
takes precedence over other keymaps for one (or more) subsequent keys.

Normally, @var{keymap} is used just once, to look up the very next key.
If the optional argument @var{keep-pred} is @code{t}, the map stays
active as long as the user types keys defined in @var{keymap}; when the
user types a key that is not in @var{keymap}, the transient keymap is
deactivated and normal key lookup continues for that key.

The @var{keep-pred} argument can also be a function.  In that case, the
function is called with no arguments, prior to running each command,
while @var{keymap} is active; it should return non-@code{nil} if
@var{keymap} should stay active.

The optional argument @var{on-exit}, if non-nil, specifies a function
that is called, with no arguments, after @var{keymap} is deactivated.

This function works by adding and removing @var{keymap} from the
variable @code{overriding-terminal-local-map}, which takes precedence
over all other active keymaps (@pxref{Searching Keymaps}).
@end defun

@node Key Lookup
@section Key Lookup
@cindex key lookup
@cindex keymap entry

  @dfn{Key lookup} is the process of finding the binding of a key
sequence from a given keymap.  The execution or use 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 a mouse event with just its types (a symbol)
instead of the entire event (a list).  @xref{Input Events}.  Such
a key sequence is insufficient for @code{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 @dfn{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 a keymap element for a menu item, because
@code{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 types of keymap entries:

@table @asis
@item @code{nil}
@cindex @code{nil} in keymap
@code{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 @code{nil}
for that event type.

@item @var{command}
@cindex command in keymap
The events used so far in the lookup form a complete key,
and @var{command} is its binding.  @xref{What Is a Function}.

@item @var{array}
@cindex string in keymap
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 @ref{Keyboard Macros}, for more information.

@item @var{keymap}
@cindex keymap in keymap
The events used so far in the lookup form a prefix key.  The next
event of the key sequence is looked up in @var{keymap}.

@item @var{list}
@cindex list in keymap
The meaning of a list depends on what it contains:

@itemize @bullet
@item
If the @sc{car} of @var{list} is the symbol @code{keymap}, then the list
is a keymap, and is treated as a keymap (see above).

@item
@cindex @code{lambda} in keymap
If the @sc{car} of @var{list} is @code{lambda}, then the list is a
lambda expression.  This is presumed to be a function, and is treated
as such (see above).  In order to execute properly as a key binding,
this function must be a command---it must have an @code{interactive}
specification.  @xref{Defining Commands}.
@end itemize

@item @var{symbol}
@cindex symbol in keymap
The function definition of @var{symbol} is used in place of
@var{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.

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 @code{command-execute}
(@pxref{Interactive Call}).

@cindex @code{undefined} in keymap
The symbol @code{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 @code{undefined}; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling @code{ding}) but does not signal an error.

@cindex preventing prefix key
@code{undefined} is used in local keymaps to override a global key
binding and make the key undefined locally.  A local binding of
@code{nil} would fail to do this because it would not override the
global binding.

@item @var{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.
@end table

  In short, a keymap entry may be a keymap, a command, a keyboard
macro, a symbol that leads to one of them, or @code{nil}.

@node Functions for Key Lookup
@section Functions for Key Lookup

  Here are the functions and variables pertaining to key lookup.

@defun lookup-key keymap key &optional accept-defaults
This function returns the definition of @var{key} in @var{keymap}.  All
the other functions described in this chapter that look up keys use
@code{lookup-key}.  Here are examples:

@example
@group
(lookup-key (current-global-map) "\C-x\C-f")
    @result{} find-file
@end group
@group
(lookup-key (current-global-map) (kbd "C-x C-f"))
    @result{} find-file
@end group
@group
(lookup-key (current-global-map) "\C-x\C-f12345")
    @result{} 2
@end group
@end example

If the string or vector @var{key} is not a valid key sequence according
to the prefix keys specified in @var{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 @var{key} that compose a complete key.

@c Emacs 19 feature
If @var{accept-defaults} is non-@code{nil}, then @code{lookup-key}
considers default bindings as well as bindings for the specific events
in @var{key}.  Otherwise, @code{lookup-key} reports only bindings for
the specific sequence @var{key}, ignoring default bindings except when
you explicitly ask about them.  (To do this, supply @code{t} as an
element of @var{key}; see @ref{Format of Keymaps}.)

If @var{key} contains a meta character (not a function key), that
character is implicitly replaced by a two-character sequence: the value
of @code{meta-prefix-char}, followed by the corresponding non-meta
character.  Thus, the first example below is handled by conversion into
the second example.

@example
@group
(lookup-key (current-global-map) "\M-f")
    @result{} forward-word
@end group
@group
(lookup-key (current-global-map) "\ef")
    @result{} forward-word
@end group
@end example

Unlike @code{read-key-sequence}, this function does not modify the
specified events in ways that discard information (@pxref{Key Sequence
Input}).  In particular, it does not convert letters to lower case and
it does not change drag events to clicks.
@end defun

@deffn Command undefined
Used in keymaps to undefine keys.  It calls @code{ding}, but does
not cause an error.
@end deffn

@defun local-key-binding key &optional accept-defaults
This function returns the binding for @var{key} in the current
local keymap, or @code{nil} if it is undefined there.

@c Emacs 19 feature
The argument @var{accept-defaults} controls checking for default bindings,
as in @code{lookup-key} (above).
@end defun

@defun global-key-binding key &optional accept-defaults
This function returns the binding for command @var{key} in the
current global keymap, or @code{nil} if it is undefined there.

@c Emacs 19 feature
The argument @var{accept-defaults} controls checking for default bindings,
as in @code{lookup-key} (above).
@end defun

@c Emacs 19 feature
@defun minor-mode-key-binding key &optional accept-defaults
This function returns a list of all the active minor mode bindings of
@var{key}.  More precisely, it returns an alist of pairs
@code{(@var{modename} . @var{binding})}, where @var{modename} is the
variable that enables the minor mode, and @var{binding} is @var{key}'s
binding in that mode.  If @var{key} has no minor-mode bindings, the
value is @code{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 @var{accept-defaults} controls checking for default
bindings, as in @code{lookup-key} (above).
@end defun

@defopt meta-prefix-char
@cindex @key{ESC}
This variable is the meta-prefix character code.  It is used for
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 (@pxref{Prefix Keys}).  The default value is 27, which is
the @acronym{ASCII} code for @key{ESC}.

As long as the value of @code{meta-prefix-char} remains 27, key lookup
translates @kbd{M-b} into @kbd{@key{ESC} b}, which is normally defined
as the @code{backward-word} command.  However, if you were to set
@code{meta-prefix-char} to 24, the code for @kbd{C-x}, then Emacs will
translate @kbd{M-b} into @kbd{C-x b}, whose standard binding is the
@code{switch-to-buffer} command.  (Don't actually do this!)  Here is an
illustration of what would happen:

@smallexample
@group
meta-prefix-char                    ; @r{The default value.}
     @result{} 27
@end group
@group
(key-binding "\M-b")
     @result{} backward-word
@end group
@group
?\C-x                               ; @r{The print representation}
     @result{} 24                          ;   @r{of a character.}
@end group
@group
(setq meta-prefix-char 24)
     @result{} 24
@end group
@group
(key-binding "\M-b")
     @result{} switch-to-buffer            ; @r{Now, typing @kbd{M-b} is}
                                    ;   @r{like typing @kbd{C-x b}.}

(setq meta-prefix-char 27)          ; @r{Avoid confusion!}
     @result{} 27                          ; @r{Restore the default value!}
@end group
@end smallexample

This translation of one event into two happens only for characters, not
for other kinds of input events.  Thus, @kbd{M-@key{F1}}, a function
key, is not converted into @kbd{@key{ESC} @key{F1}}.
@end defopt

@node Changing Key Bindings
@section Changing Key Bindings
@cindex changing key bindings
@cindex rebinding

  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 @code{global-set-key} and @code{local-set-key} functions are
convenient interfaces for these operations (@pxref{Key Binding
Commands}).  You can also use @code{define-key}, a more general
function; then you must explicitly specify the map to change.

  When choosing the key sequences for Lisp programs to rebind, please
follow the Emacs conventions for use of various keys (@pxref{Key
Binding Conventions}).

@cindex meta character key constants
@cindex control character key constants
  In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (@pxref{String Type}).
The syntax @samp{\C-} means that the following character is a control
character and @samp{\M-} means that the following character is a meta
character.  Thus, the string @code{"\M-x"} is read as containing a
single @kbd{M-x}, @code{"\C-f"} is read as containing a single
@kbd{C-f}, and @code{"\M-\C-x"} and @code{"\C-\M-x"} are both read as
containing a single @kbd{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 @samp{[?\C-\H-x home]}.  @xref{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, @code{(control ?a)} is equivalent to
@code{?\C-a} and @code{(hyper control left)} is equivalent to
@code{C-H-left}.  One advantage of such lists is that the precise
numeric codes for the modifier bits don't appear in compiled files.

  The functions below signal an error if @var{keymap} is not a keymap,
or if @var{key} is not a string or vector representing a key sequence.
You can use event types (symbols) as shorthand for events that are
lists.  The @code{kbd} function (@pxref{Key Sequences}) is a
convenient way to specify the key sequence.

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

If @var{key} is @code{[t]}, this sets the default binding in
@var{keymap}.  When an event has no binding of its own, the Emacs
command loop uses the keymap's default binding, if there is one.

@cindex invalid prefix key error
@cindex key sequence error
Every prefix of @var{key} must be a prefix key (i.e., bound to a keymap)
or undefined; otherwise an error is signaled.  If some prefix of
@var{key} is undefined, then @code{define-key} defines it as a prefix
key so that the rest of @var{key} can be defined as specified.

If there was previously no binding for @var{key} in @var{keymap}, the
new binding is added at the beginning of @var{keymap}.  The order of
bindings in a keymap makes no difference for keyboard input, but it
does matter for menu keymaps (@pxref{Menu Keymaps}).
@end defun

  This example creates a sparse keymap and makes a number of
bindings in it:

@smallexample
@group
(setq map (make-sparse-keymap))
    @result{} (keymap)
@end group
@group
(define-key map "\C-f" 'forward-char)
    @result{} forward-char
@end group
@group
map
    @result{} (keymap (6 . forward-char))
@end group

@group
;; @r{Build sparse submap for @kbd{C-x} and bind @kbd{f} in that.}
(define-key map (kbd "C-x f") 'forward-word)
    @result{} forward-word
@end group
@group
map
@result{} (keymap
    (24 keymap                ; @kbd{C-x}
        (102 . forward-word)) ;      @kbd{f}
    (6 . forward-char))       ; @kbd{C-f}
@end group

@group
;; @r{Bind @kbd{C-p} to the @code{ctl-x-map}.}
(define-key map (kbd "C-p") ctl-x-map)
;; @code{ctl-x-map}
@result{} [nil @dots{} find-file @dots{} backward-kill-sentence]
@end group

@group
;; @r{Bind @kbd{C-f} to @code{foo} in the @code{ctl-x-map}.}
(define-key map (kbd "C-p C-f") 'foo)
@result{} 'foo
@end group
@group
map
@result{} (keymap     ; @r{Note @code{foo} in @code{ctl-x-map}.}
    (16 keymap [nil @dots{} foo @dots{} backward-kill-sentence])
    (24 keymap
        (102 . forward-word))
    (6 . forward-char))
@end group
@end smallexample

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

  The function @code{substitute-key-definition} scans a keymap for
keys that have a certain binding and rebinds them with a different
binding.  Another feature which is cleaner and can often produce the
same results is to remap one command into another (@pxref{Remapping
Commands}).

@defun substitute-key-definition olddef newdef keymap &optional oldmap
@cindex replace bindings
This function replaces @var{olddef} with @var{newdef} for any keys in
@var{keymap} that were bound to @var{olddef}.  In other words,
@var{olddef} is replaced with @var{newdef} wherever it appears.  The
function returns @code{nil}.

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

@smallexample
@group
(substitute-key-definition
 'find-file 'find-file-read-only (current-global-map))
@end group
@end smallexample

@c Emacs 19 feature
If @var{oldmap} is non-@code{nil}, that changes the behavior of
@code{substitute-key-definition}: the bindings in @var{oldmap} determine
which keys to rebind.  The rebindings still happen in @var{keymap}, not
in @var{oldmap}.  Thus, you can change one map under the control of the
bindings in another.  For example,

@smallexample
(substitute-key-definition
  'delete-backward-char 'my-funny-delete
  my-map global-map)
@end smallexample

@noindent
puts the special deletion command in @code{my-map} for whichever keys
are globally bound to the standard deletion command.

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

@smallexample
@group
(setq map '(keymap
            (?1 . olddef-1)
            (?2 . olddef-2)
            (?3 . olddef-1)))
@result{} (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))
@end group

@group
(substitute-key-definition 'olddef-1 'newdef map)
@result{} nil
@end group
@group
map
@result{} (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
@end group
@end smallexample
@end defun

@defun suppress-keymap keymap &optional nodigits
@cindex @code{self-insert-command} override
This function changes the contents of the full keymap @var{keymap} by
remapping @code{self-insert-command} to the command @code{undefined}
(@pxref{Remapping Commands}).  This has the effect of undefining all
printing characters, thus making ordinary insertion of text impossible.
@code{suppress-keymap} returns @code{nil}.

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

@cindex yank suppression
@cindex @code{quoted-insert} suppression
The @code{suppress-keymap} function does not make it impossible to
modify a buffer, as it does not suppress commands such as @code{yank}
and @code{quoted-insert}.  To prevent any modification of a buffer, make
it read-only (@pxref{Read Only Buffers}).

Since this function modifies @var{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 @code{global-map} would make it impossible to use
most of Emacs.

This function can be used to initialize the local keymap of a major
mode for which insertion of text is not desirable.  But usually such a
mode should be derived from @code{special-mode} (@pxref{Basic Major
Modes}); then its keymap will automatically inherit from
@code{special-mode-map}, which is already suppressed.  Here is how
@code{special-mode-map} is defined:

@smallexample
@group
(defvar special-mode-map
  (let ((map (make-sparse-keymap)))
    (suppress-keymap map)
    (define-key map "q" 'quit-window)
    @dots{}
    map))
@end group
@end smallexample
@end defun

@node Remapping Commands
@section Remapping Commands
@cindex remapping commands

  A special kind of key binding can be used to @dfn{remap} one command
to another, without having to refer to the key sequence(s) bound to
the original command.  To use this feature, make a key binding for a
key sequence that starts with the dummy event @code{remap}, followed
by the command name you want to remap; for the binding, specify the
new definition (usually a command name, but possibly any other valid
definition for a key binding).

  For example, suppose My mode provides a special command
@code{my-kill-line}, which should be invoked instead of
@code{kill-line}.  To establish this, its mode keymap should contain
the following remapping:

@smallexample
(define-key my-mode-map [remap kill-line] 'my-kill-line)
@end smallexample

@noindent
Then, whenever @code{my-mode-map} is active, if the user types
@kbd{C-k} (the default global key sequence for @code{kill-line}) Emacs
will instead run @code{my-kill-line}.

  Note that remapping only takes place through active keymaps; for
example, putting a remapping in a prefix keymap like @code{ctl-x-map}
typically has no effect, as such keymaps are not themselves active.
In addition, remapping only works through a single level; in the
following example,

@smallexample
(define-key my-mode-map [remap kill-line] 'my-kill-line)
(define-key my-mode-map [remap my-kill-line] 'my-other-kill-line)
@end smallexample

@noindent
@code{kill-line} is @emph{not} remapped to @code{my-other-kill-line}.
Instead, if an ordinary key binding specifies @code{kill-line}, it is
remapped to @code{my-kill-line}; if an ordinary binding specifies
@code{my-kill-line}, it is remapped to @code{my-other-kill-line}.

To undo the remapping of a command, remap it to @code{nil}; e.g.,

@smallexample
(define-key my-mode-map [remap kill-line] nil)
@end smallexample

@defun command-remapping command &optional position keymaps
This function returns the remapping for @var{command} (a symbol),
given the current active keymaps.  If @var{command} is not remapped
(which is the usual situation), or not a symbol, the function returns
@code{nil}.  @code{position} can optionally specify a buffer position
or an event position to determine the keymaps to use, as in
@code{key-binding}.

If the optional argument @code{keymaps} is non-@code{nil}, it
specifies a list of keymaps to search in.  This argument is ignored if
@code{position} is non-@code{nil}.
@end defun

@node Translation Keymaps
@section Keymaps for Translating Sequences of Events
@cindex translation keymap
@cindex keymaps for translating events

  When the @code{read-key-sequence} function reads a key sequence
(@pxref{Key Sequence Input}), it uses @dfn{translation keymaps} to
translate certain event sequences into others.  The translation
keymaps are @code{input-decode-map}, @code{local-function-key-map},
and @code{key-translation-map} (in order of priority).

  Translation keymaps have the same structure as other keymaps, but
are used differently: they specify translations to make while reading
key sequences, rather than bindings for complete key sequences.  As
each key sequence is read, it is checked against each translation
keymap.  If one of the translation keymaps binds @var{k} to a
vector @var{v}, then whenever @var{k} appears as a sub-sequence
@emph{anywhere} in a key sequence, that sub-sequence is replaced with
the events in @var{v}.

  For example, VT100 terminals send @kbd{@key{ESC} O P} when the
keypad key @key{PF1} is pressed.  On such terminals, Emacs must
translate that sequence of events into a single event @code{pf1}.
This is done by binding @kbd{@key{ESC} O P} to @code{[pf1]} in
@code{input-decode-map}.  Thus, when you type @kbd{C-c @key{PF1}} on
the terminal, the terminal emits the character sequence @kbd{C-c
@key{ESC} O P}, and @code{read-key-sequence} translates this back into
@kbd{C-c @key{PF1}} and returns it as the vector @code{[?\C-c pf1]}.

  Translation keymaps take effect only after Emacs has decoded the
keyboard input (via the input coding system specified by
@code{keyboard-coding-system}).  @xref{Terminal I/O Encoding}.

@defvar input-decode-map
This variable holds a keymap that describes the character sequences sent
by function keys on an ordinary character terminal.

The value of @code{input-decode-map} is usually set up automatically
according to the terminal's Terminfo or Termcap entry, but sometimes
those need help from terminal-specific Lisp files.  Emacs comes with
terminal-specific files for many common terminals; their main purpose is
to make entries in @code{input-decode-map} beyond those that can be
deduced from Termcap and Terminfo.  @xref{Terminal-Specific}.
@end defvar

@defvar local-function-key-map
This variable holds a keymap similar to @code{input-decode-map} except
that it describes key sequences which should be translated to
alternative interpretations that are usually preferred.  It applies
after @code{input-decode-map} and before @code{key-translation-map}.

Entries in @code{local-function-key-map} are ignored if they conflict
with bindings made in the minor mode, local, or global keymaps.  I.e.,
the remapping only applies if the original key sequence would
otherwise not have any binding.

@code{local-function-key-map} inherits from @code{function-key-map},
but the latter should not be used directly.
@end defvar

@defvar key-translation-map
This variable is another keymap used just like @code{input-decode-map}
to translate input events into other events.  It differs from
@code{input-decode-map} in that it goes to work after
@code{local-function-key-map} is finished rather than before; it
receives the results of translation by @code{local-function-key-map}.

Just like @code{input-decode-map}, but unlike
@code{local-function-key-map}, this keymap is applied regardless of
whether the input key-sequence has a normal binding.  Note however
that actual key bindings can have an effect on
@code{key-translation-map}, even though they are overridden by it.
Indeed, actual key bindings override @code{local-function-key-map} and
thus may alter the key sequence that @code{key-translation-map}
receives.  Clearly, it is better to avoid this type of situation.

The intent of @code{key-translation-map} is for users to map one
character set to another, including ordinary characters normally bound
to @code{self-insert-command}.
@end defvar

@cindex key translation function
You can use @code{input-decode-map}, @code{local-function-key-map},
and @code{key-translation-map} for more than simple aliases, by using
a function, instead of a key sequence, as the translation of a
key.  Then this function is called to compute the translation of that
key.

The key translation function receives one argument, which is the prompt
that was specified in @code{read-key-sequence}---or @code{nil} if the
key sequence is being read by the editor command loop.  In most cases
you can ignore the prompt value.

If the function reads input itself, it can have the effect of altering
the event that follows.  For example, here's how to define @kbd{C-c h}
to turn the character that follows into a Hyper character:

@example
@group
(defun hyperify (prompt)
  (let ((e (read-event)))
    (vector (if (numberp e)
                (logior (lsh 1 24) e)
              (if (memq 'hyper (event-modifiers e))
                  e
                (add-event-modifier "H-" e))))))

(defun add-event-modifier (string e)
  (let ((symbol (if (symbolp e) e (car e))))
    (setq symbol (intern (concat string
                                 (symbol-name symbol))))
    (if (symbolp e)
        symbol
      (cons symbol (cdr e)))))

(define-key local-function-key-map "\C-ch" 'hyperify)
@end group
@end example

@subsection Interaction with normal keymaps

The end of a key sequence is detected when that key sequence either is bound
to a command, or when Emacs determines that no additional event can lead
to a sequence that is bound to a command.

This means that, while @code{input-decode-map} and @code{key-translation-map}
apply regardless of whether the original key sequence would have a binding, the
presence of such a binding can still prevent translation from taking place.
For example, let us return to our VT100 example above and add a binding for
@kbd{C-c @key{ESC}} to the global map; now when the user hits @kbd{C-c
@key{PF1}} Emacs will fail to decode @kbd{C-c @key{ESC} O P} into @kbd{C-c
@key{PF1}} because it will stop reading keys right after @kbd{C-x @key{ESC}},
leaving @kbd{O P} for later.  This is in case the user really hit @kbd{C-c
@key{ESC}}, in which case Emacs should not sit there waiting for the next key
to decide whether the user really pressed @kbd{@key{ESC}} or @kbd{@key{PF1}}.

For that reason, it is better to avoid binding commands to key sequences where
the end of the key sequence is a prefix of a key translation.  The main such
problematic suffixes/prefixes are @kbd{@key{ESC}}, @kbd{M-O} (which is really
@kbd{@key{ESC} O}) and @kbd{M-[} (which is really @kbd{@key{ESC} [}).

@node Key Binding Commands
@section Commands for Binding Keys

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

  People often use @code{global-set-key} in their init files
(@pxref{Init File}) for simple customization.  For example,

@smallexample
(global-set-key (kbd "C-x C-\\") 'next-line)
@end smallexample

@noindent
or

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

@noindent
or

@smallexample
(global-set-key [(control ?x) (control ?\\)] 'next-line)
@end smallexample

@noindent
redefines @kbd{C-x C-\} to move down a line.

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

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

@cindex non-@acronym{ASCII} text in keybindings
  Be careful when using non-@acronym{ASCII} text characters in Lisp
specifications of keys to bind.  If these are read as multibyte text, as
they usually will be in a Lisp file (@pxref{Loading Non-ASCII}), you
must type the keys as multibyte too.  For instance, if you use this:

@smallexample
(global-set-key "ö" 'my-function) ; bind o-umlaut
@end smallexample

@noindent
or

@smallexample
(global-set-key ?ö 'my-function) ; bind o-umlaut
@end smallexample

@noindent
and your language environment is multibyte Latin-1, these commands
actually bind the multibyte character with code 246, not the byte
code 246 (@kbd{M-v}) sent by a Latin-1 terminal.  In order to use this
binding, you need to teach Emacs how to decode the keyboard by using an
appropriate input method (@pxref{Input Methods, , Input Methods, emacs, The GNU
Emacs Manual}).

@deffn Command global-set-key key binding
This function sets the binding of @var{key} in the current global map
to @var{binding}.

@smallexample
@group
(global-set-key @var{key} @var{binding})
@equiv{}
(define-key (current-global-map) @var{key} @var{binding})
@end group
@end smallexample
@end deffn

@deffn Command global-unset-key key
@cindex unbinding keys
This function removes the binding of @var{key} from the current
global map.

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

@smallexample
@group
(global-unset-key "\C-l")
    @result{} nil
@end group
@group
(global-set-key "\C-l\C-l" 'redraw-display)
    @result{} nil
@end group
@end smallexample

This function is equivalent to using @code{define-key} as follows:

@smallexample
@group
(global-unset-key @var{key})
@equiv{}
(define-key (current-global-map) @var{key} nil)
@end group
@end smallexample
@end deffn

@deffn Command local-set-key key binding
This function sets the binding of @var{key} in the current local
keymap to @var{binding}.

@smallexample
@group
(local-set-key @var{key} @var{binding})
@equiv{}
(define-key (current-local-map) @var{key} @var{binding})
@end group
@end smallexample
@end deffn

@deffn Command local-unset-key key
This function removes the binding of @var{key} from the current
local map.

@smallexample
@group
(local-unset-key @var{key})
@equiv{}
(define-key (current-local-map) @var{key} nil)
@end group
@end smallexample
@end deffn

@node Scanning Keymaps
@section Scanning Keymaps
@cindex scanning keymaps
@cindex keymaps, scanning

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

@defun 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 @var{keymap}.  The value is an
association list with elements of the form @code{(@var{key} .@:
@var{map})}, where @var{key} is a prefix key whose definition in
@var{keymap} is @var{map}.

The elements of the alist are ordered so that the @var{key} increases
in length.  The first element is always @code{([] .@: @var{keymap})},
because the specified keymap is accessible from itself with a prefix of
no events.

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

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

@smallexample
@group
(accessible-keymaps (current-local-map))
@result{}(([] keymap
      (27 keymap   ; @r{Note this keymap for @key{ESC} is repeated below.}
          (83 . center-paragraph)
          (115 . center-line))
      (9 . tab-to-tab-stop))
@end group

@group
   ("^[" keymap
    (83 . center-paragraph)
    (115 . foo)))
@end group
@end smallexample

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

@smallexample
@group
(accessible-keymaps (current-global-map))
@result{} (([] keymap [set-mark-command beginning-of-line @dots{}
                   delete-backward-char])
@end group
@group
    ("^H" keymap (118 . describe-variable) @dots{}
     (8 . help-for-help))
@end group
@group
    ("^X" keymap [x-flush-mouse-queue @dots{}
     backward-kill-sentence])
@end group
@group
    ("^[" keymap [mark-sexp backward-sexp @dots{}
     backward-kill-word])
@end group
    ("^X4" keymap (15 . display-buffer) @dots{})
@group
    ([mode-line] keymap
     (S-mouse-2 . mouse-split-window-horizontally) @dots{}))
@end group
@end smallexample

@noindent
These are not all the keymaps you would see in actuality.
@end defun

@defun map-keymap function keymap
The function @code{map-keymap} calls @var{function} once
for each binding in @var{keymap}.  It passes two arguments,
the event type and the value of the binding.  If @var{keymap}
has a parent, the parent's bindings are included as well.
This works recursively: if the parent has itself a parent, then the
grandparent's bindings are also included and so on.

This function is the cleanest way to examine all the bindings
in a keymap.
@end defun

@defun where-is-internal command &optional keymap firstonly noindirect no-remap
This function is a subroutine used by the @code{where-is} command
(@pxref{Help, , Help, emacs,The GNU Emacs Manual}).  It returns a list
of all key sequences (of any length) that are bound to @var{command} in a
set of keymaps.

The argument @var{command} can be any object; it is compared with all
keymap entries using @code{eq}.

If @var{keymap} is @code{nil}, then the maps used are the current active
keymaps, disregarding @code{overriding-local-map} (that is, pretending
its value is @code{nil}).  If @var{keymap} is a keymap, then the
maps searched are @var{keymap} and the global keymap.  If @var{keymap}
is a list of keymaps, only those keymaps are searched.

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

If @var{firstonly} is @code{non-ascii}, then the value is a single
vector representing the first key sequence found, rather than a list of
all possible key sequences.  If @var{firstonly} is @code{t}, then the
value is the first key sequence, except that key sequences consisting
entirely of @acronym{ASCII} characters (or meta variants of @acronym{ASCII}
characters) are preferred to all other key sequences and that the
return value can never be a menu binding.

If @var{noindirect} is non-@code{nil}, @code{where-is-internal} doesn't look
inside menu-items to find their commands.  This makes it possible to search for
a menu-item itself.

The fifth argument, @var{no-remap}, determines how this function
treats command remappings (@pxref{Remapping Commands}).  There are two
cases of interest:

@table @asis
@item If a command @var{other-command} is remapped to @var{command}:
If @var{no-remap} is @code{nil}, find the bindings for
@var{other-command} and treat them as though they are also bindings
for @var{command}.  If @var{no-remap} is non-@code{nil}, include the
vector @code{[remap @var{other-command}]} in the list of possible key
sequences, instead of finding those bindings.

@item If @var{command} is remapped to @var{other-command}:
If @var{no-remap} is @code{nil}, return the bindings for
@var{other-command} rather than @var{command}.  If @var{no-remap} is
non-@code{nil}, return the bindings for @var{command}, ignoring the
fact that it is remapped.
@end table
@end defun

@deffn Command describe-bindings &optional prefix buffer-or-name
This function creates a listing of all current key bindings, and
displays it in a buffer named @file{*Help*}.  The text is grouped by
modes---minor modes first, then the major mode, then global bindings.

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

When several characters with consecutive @acronym{ASCII} codes have the
same definition, they are shown together, as
@samp{@var{firstchar}..@var{lastchar}}.  In this instance, you need to
know the @acronym{ASCII} codes to understand which characters this means.
For example, in the default global map, the characters @samp{@key{SPC}
..@: ~} are described by a single line.  @key{SPC} is @acronym{ASCII} 32,
@kbd{~} is @acronym{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 @code{self-insert-command}.

If @var{buffer-or-name} is non-@code{nil}, it should be a buffer or a
buffer name.  Then @code{describe-bindings} lists that buffer's bindings,
instead of the current buffer's.
@end deffn

@node Menu Keymaps
@section Menu Keymaps
@cindex menu keymaps

A keymap can operate as a menu as well as defining bindings for
keyboard keys and mouse buttons.  Menus are usually actuated with the
mouse, but they can function with the keyboard also.  If a menu keymap
is active for the next input event, that activates the keyboard menu
feature.

@menu
* Defining Menus::     How to make a keymap that defines a menu.
* Mouse Menus::        How users actuate the menu with the mouse.
* Keyboard Menus::     How users actuate the menu with the keyboard.
* Menu Example::       Making a simple menu.
* Menu Bar::           How to customize the menu bar.
* Tool Bar::           A tool bar is a row of images.
* Modifying Menus::    How to add new items to a menu.
* Easy Menu::      A convenience macro for making menus.
@end menu

@node Defining Menus
@subsection Defining Menus
@cindex defining menus
@cindex menu prompt string
@cindex prompt string (of menu)
@cindex menu item

A keymap acts as a menu if it has an @dfn{overall prompt string},
which is a string that appears as an element of the keymap.
(@xref{Format of Keymaps}.)  The string should describe the purpose of
the menu's commands.  Emacs displays the overall prompt string as the
menu title in some cases, depending on the toolkit (if any) used for
displaying menus.@footnote{It is required for menus which do not use a
toolkit, e.g., on a text terminal.}  Keyboard menus also display the
overall prompt string.

The easiest way to construct a keymap with a prompt string is to
specify the string as an argument when you call @code{make-keymap},
@code{make-sparse-keymap} (@pxref{Creating Keymaps}), or
@code{define-prefix-command} (@pxref{Definition of
define-prefix-command}).  If you do not want the keymap to operate as
a menu, don't specify a prompt string for it.

@defun keymap-prompt keymap
This function returns the overall prompt string of @var{keymap},
or @code{nil} if it has none.
@end defun

The menu's items are the bindings in the keymap.  Each binding
associates an event type to a definition, but the event types have no
significance for the menu appearance.  (Usually we use pseudo-events,
symbols that the keyboard cannot generate, as the event types for menu
item bindings.)  The menu is generated entirely from the bindings that
correspond in the keymap to these events.

The order of items in the menu is the same as the order of bindings in
the keymap.  Since @code{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
@code{define-key-after} (@pxref{Modifying Menus}).

@menu
* Simple Menu Items::       A simple kind of menu key binding.
* Extended Menu Items::     More complex menu item definitions.
* Menu Separators::         Drawing a horizontal line through a menu.
* Alias Menu Items::        Using command aliases in menu items.
@end menu

@node Simple Menu Items
@subsubsection Simple Menu Items

  The simpler (and original) way to define a menu item is to bind some
event type (it doesn't matter what event type) to a binding like this:

@example
(@var{item-string} . @var{real-binding})
@end example

@noindent
The @sc{car}, @var{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.  Note that not
all graphical toolkits can display non-@acronym{ASCII} text in menus
(it will work for keyboard menus and will work to a large extent with
the GTK+ toolkit).

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

@example
(@var{item-string} @var{help} . @var{real-binding})
@end example

@noindent
@var{help} specifies a help-echo string to display while the mouse
is on that item in the same way as @code{help-echo} text properties
(@pxref{Help display}).

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

  If @var{real-binding} is @code{nil}, then @var{item-string} appears in
the menu but cannot be selected.

  If @var{real-binding} is a symbol and has a non-@code{nil}
@code{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-@code{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
@code{force-mode-line-update} (@pxref{Mode Line Format}).

@node Extended Menu Items
@subsubsection Extended Menu Items
@kindex menu-item
@cindex extended menu item

  An extended-format menu item is a more flexible and also cleaner
alternative to the simple format.  You define an event type with a
binding that's a list starting with the symbol @code{menu-item}.
For a non-selectable string, the binding looks like this:

@example
(menu-item @var{item-name})
@end example

@noindent
A string starting with two or more dashes specifies a separator line;
see @ref{Menu Separators}.

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

@example
(menu-item @var{item-name} @var{real-binding}
    . @var{item-property-list})
@end example

@noindent
Here, @var{item-name} is an expression which evaluates to the menu item
string.  Thus, the string need not be a constant.  The third element,
@var{real-binding}, is the command to execute.  The tail of the list,
@var{item-property-list}, has the form of a property list which contains
other information.

  Here is a table of the properties that are supported:

@table @code
@item :enable @var{form}
The result of evaluating @var{form} determines whether the item is
enabled (non-@code{nil} means yes).  If the item is not enabled,
you can't really click on it.

@item :visible @var{form}
The result of evaluating @var{form} determines whether the item should
actually appear in the menu (non-@code{nil} means yes).  If the item
does not appear, then the menu is displayed as if this item were
not defined at all.

@item :help @var{help}
The value of this property, @var{help}, specifies a help-echo string
to display while the mouse is on that item.  This is displayed in the
same way as @code{help-echo} text properties (@pxref{Help display}).
Note that this must be a constant string, unlike the @code{help-echo}
property for text and overlays.

@item :button (@var{type} . @var{selected})
This property provides a way to define radio buttons and toggle buttons.
The @sc{car}, @var{type}, says which: it should be @code{:toggle} or
@code{:radio}.  The @sc{cdr}, @var{selected}, should be a form; the
result of evaluating it says whether this button is currently selected.

A @dfn{toggle} is a menu item which is labeled as either on or off
according to the value of @var{selected}.  The command itself should
toggle @var{selected}, setting it to @code{t} if it is @code{nil},
and to @code{nil} if it is @code{t}.  Here is how the menu item
to toggle the @code{debug-on-error} flag is defined:

@example
(menu-item "Debug on Error" toggle-debug-on-error
           :button (:toggle
                    . (and (boundp 'debug-on-error)
                           debug-on-error)))
@end example

@noindent
This works because @code{toggle-debug-on-error} is defined as a command
which toggles the variable @code{debug-on-error}.

@dfn{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 @var{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.

@item :key-sequence @var{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 @var{key-sequence} in the menu, it verifies that
@var{key-sequence} is really equivalent to this menu item.

@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 @code{:keys} property and finds the keyboard
equivalent anyway.

@item :keys @var{string}
This property specifies that @var{string} is the string to display
as the keyboard equivalent for this menu item.  You can use
the @samp{\\[...]} documentation construct in @var{string}.

@item :filter @var{filter-fn}
This property provides a way to compute the menu item dynamically.
The property value @var{filter-fn} should be a function of one argument;
when it is called, its argument will be @var{real-binding}.  The
function should return the binding to use instead.

Emacs can call this function at any time that it does redisplay or
operates on menu data structures, so you should write it so it can
safely be called at any time.
@end table

@node Menu Separators
@subsubsection Menu Separators
@cindex menu separators

  A menu separator is a kind of menu item that doesn't display any
text---instead, it divides the menu into subparts with a horizontal line.
A separator looks like this in the menu keymap:

@example
(menu-item @var{separator-type})
@end example

@noindent
where @var{separator-type} is a string starting with two or more dashes.

  In the simplest case, @var{separator-type} consists of only dashes.
That specifies the default kind of separator.  (For compatibility,
@code{""} and @code{-} also count as separators.)

  Certain other values of @var{separator-type} specify a different
style of separator.  Here is a table of them:

@table @code
@item "--no-line"
@itemx "--space"
An extra vertical space, with no actual line.

@item "--single-line"
A single line in the menu's foreground color.

@item "--double-line"
A double line in the menu's foreground color.

@item "--single-dashed-line"
A single dashed line in the menu's foreground color.

@item "--double-dashed-line"
A double dashed line in the menu's foreground color.

@item "--shadow-etched-in"
A single line with a 3D sunken appearance.  This is the default,
used separators consisting of dashes only.

@item "--shadow-etched-out"
A single line with a 3D raised appearance.

@item "--shadow-etched-in-dash"
A single dashed line with a 3D sunken appearance.

@item "--shadow-etched-out-dash"
A single dashed line with a 3D raised appearance.

@item "--shadow-double-etched-in"
Two lines with a 3D sunken appearance.

@item "--shadow-double-etched-out"
Two lines with a 3D raised appearance.

@item "--shadow-double-etched-in-dash"
Two dashed lines with a 3D sunken appearance.

@item "--shadow-double-etched-out-dash"
Two dashed lines with a 3D raised appearance.
@end table

  You can also give these names in another style, adding a colon after
the double-dash and replacing each single dash with capitalization of
the following word.  Thus, @code{"--:singleLine"}, is equivalent to
@code{"--single-line"}.

  You can use a longer form to specify keywords such as @code{:enable}
and @code{:visible} for a menu separator:

@code{(menu-item @var{separator-type} nil . @var{item-property-list})}

For example:

@example
(menu-item "--" nil :visible (boundp 'foo))
@end example

  Some systems and display toolkits don't really handle all of these
separator types.  If you use a type that isn't supported, the menu
displays a similar kind of separator that is supported.

@node Alias Menu Items
@subsubsection 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
@code{read-only-mode} and gives them different enable conditions:

@example
(defalias 'make-read-only 'read-only-mode)
(put 'make-read-only 'menu-enable '(not buffer-read-only))
(defalias 'make-writable 'read-only-mode)
(put 'make-writable 'menu-enable 'buffer-read-only)
@end example

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-@code{nil}
@code{menu-alias} property.  Thus,

@example
(put 'make-read-only 'menu-alias t)
(put 'make-writable 'menu-alias t)
@end example

@noindent
causes menu items for @code{make-read-only} and @code{make-writable} to
show the keyboard bindings for @code{read-only-mode}.

@node Mouse Menus
@subsection 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 @ref{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.

@cindex submenu
  If the menu keymap contains a binding to a nested keymap, the nested
keymap specifies a @dfn{submenu}.  There will be a menu item, labeled
by the nested keymap's item string, and clicking on this item
automatically pops up the specified submenu.  As a special exception,
if the menu keymap contains a single nested keymap and no other menu
items, the menu shows the contents of the nested keymap directly, not
as a submenu.

  However, if Emacs is compiled without X toolkit support, or on text
terminals, submenus are not supported.  Each nested keymap is shown as
a menu item, but clicking on it does not automatically pop up the
submenu.  If you wish to imitate the effect of submenus, you can do
that by giving a nested keymap an item string which starts with
@samp{@@}.  This causes Emacs to display the nested keymap using a
separate @dfn{menu pane}; the rest of the item string after the
@samp{@@} is the pane label.  If Emacs is compiled without X toolkit
support, or if a menu is displayed on a text terminal, menu panes are
not used; in that case, a @samp{@@} at the beginning of an item string
is omitted when the menu label is displayed, and has no other effect.

@node Keyboard Menus
@subsection 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 keymap
operates as a keyboard menu; the user specifies the next event by
choosing a menu item with the keyboard.

  Emacs displays the keyboard menu with the map's overall prompt
string, followed by the alternatives (the item strings of the map's
bindings), in the echo area.  If the bindings don't all fit at once,
the user can type @key{SPC} to see the next line of alternatives.
Successive uses of @key{SPC} eventually get to the end of the menu and
then cycle around to the beginning.  (The variable
@code{menu-prompt-more-char} specifies which character is used for
this; @key{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.

@defvar 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 @key{SPC}.
@end defvar

@node Menu Example
@subsection Menu Example
@cindex menu definition example

  Here is a complete example of defining a menu keymap.  It is the
definition of the @samp{Replace} submenu in the @samp{Edit} menu in
the menu bar, and it uses the extended menu item format
(@pxref{Extended Menu Items}).  First we create the keymap, and give
it a name:

@smallexample
(defvar menu-bar-replace-menu (make-sparse-keymap "Replace"))
@end smallexample

@noindent
Next we define the menu items:

@smallexample
(define-key menu-bar-replace-menu [tags-repl-continue]
  '(menu-item "Continue Replace" tags-loop-continue
              :help "Continue last tags replace operation"))
(define-key menu-bar-replace-menu [tags-repl]
  '(menu-item "Replace in tagged files" tags-query-replace
              :help "Interactively replace a regexp in all tagged files"))
(define-key menu-bar-replace-menu [separator-replace-tags]
  '(menu-item "--"))
;; @r{@dots{}}
@end smallexample

@noindent
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
@code{where-is} and @code{apropos}.

  The menu in this example is intended for use with the mouse.  If a
menu is intended for use with the keyboard, that is, if it is bound to
a key sequence ending with a keyboard event, then the menu items
should be bound to characters or real function keys, that can be
typed with the keyboard.

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

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

@example
(define-key menu-bar-edit-menu [replace]
  (list 'menu-item "Replace" menu-bar-replace-menu))
@end example

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

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

@example
(define-key global-map [C-S-down-mouse-1]
   menu-bar-replace-menu)
@end example

@node Menu Bar
@subsection The Menu Bar
@cindex menu bar

  Emacs usually shows a @dfn{menu bar} at the top of each frame.
@xref{Menu Bars,,,emacs, The GNU Emacs Manual}.  Menu bar items are
subcommands of the fake function key @code{menu-bar}, as defined
in the active keymaps.

  To add an item to the menu bar, invent a fake function key of your
own (let's call it @var{key}), and make a binding for the key sequence
@code{[menu-bar @var{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 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 @code{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 @code{overriding-local-map}
were @code{nil}.  @xref{Active Keymaps}.

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

@example
@group
;; @r{Make a menu keymap (with a prompt string)}
;; @r{and make it the menu bar item's definition.}
(define-key global-map [menu-bar words]
  (cons "Words" (make-sparse-keymap "Words")))
@end group

@group
;; @r{Define specific subcommands in this menu.}
(define-key global-map
  [menu-bar words forward]
  '("Forward word" . forward-word))
@end group
@group
(define-key global-map
  [menu-bar words backward]
  '("Backward word" . backward-word))
@end group
@end example

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

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

@noindent
Here, @code{edit} is the fake function key used by the global map for
the @samp{Edit} menu bar item.  The main reason to suppress a global
menu bar item is to regain space for mode-specific items.

@defvar 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 @code{(help-menu)}; thus, the @samp{Help} menu item normally appears
at the end of the menu bar, following local menu items.
@end defvar

@defvar menu-bar-update-hook
This normal hook is run by redisplay to update the menu bar contents,
before redisplaying the menu bar.  You can use it to update menus
whose contents should vary.  Since this hook is run frequently, we
advise you to ensure that the functions it calls do not take much time
in the usual case.
@end defvar

Next to every menu bar item, Emacs displays a key binding that runs
the same command (if such a key binding exists).  This serves as a
convenient hint for users who do not know the key binding.  If a
command has multiple bindings, Emacs normally displays the first one
it finds.  You can specify one particular key binding by assigning an
@code{:advertised-binding} symbol property to the command.  @xref{Keys
in Documentation}.

@node Tool Bar
@subsection Tool bars
@cindex tool bar

  A @dfn{tool bar} is a row of clickable icons at the top of a frame,
just below the menu bar.  @xref{Tool Bars,,,emacs, The GNU Emacs
Manual}.  Emacs normally shows a tool bar on graphical displays.

  On each frame, the frame parameter @code{tool-bar-lines} controls
how many lines' worth of height to reserve for the tool bar.  A zero
value suppresses the tool bar.  If the value is nonzero, and
@code{auto-resize-tool-bars} is non-@code{nil}, the tool bar expands
and contracts automatically as needed to hold the specified contents.
If the value is @code{grow-only}, the tool bar expands automatically,
but does not contract automatically.

  The tool bar contents are controlled by a menu keymap attached to a
fake function key called @code{tool-bar} (much like the way the menu
bar is controlled).  So you define a tool bar item using
@code{define-key}, like this:

@example
(define-key global-map [tool-bar @var{key}] @var{item})
@end example

@noindent
where @var{key} is a fake function key to distinguish this item from
other items, and @var{item} is a menu item key binding (@pxref{Extended
Menu Items}), which says how to display this item and how it behaves.

  The usual menu keymap item properties, @code{:visible},
@code{:enable}, @code{:button}, and @code{:filter}, are useful in
tool bar bindings and have their normal meanings.  The @var{real-binding}
in the item must be a command, not a keymap; in other words, it does not
work to define a tool bar icon as a prefix key.

  The @code{:help} property specifies a help-echo string to display
while the mouse is on that item.  This is displayed in the same way as
@code{help-echo} text properties (@pxref{Help display}).

  In addition, you should use the @code{:image} property;
this is how you specify the image to display in the tool bar:

@table @code
@item :image @var{image}
@var{image} is either a single image specification (@pxref{Images}) or
a vector of four image specifications.  If you use a vector of four,
one of them is used, depending on circumstances:

@table @asis
@item item 0
Used when the item is enabled and selected.
@item item 1
Used when the item is enabled and deselected.
@item item 2
Used when the item is disabled and selected.
@item item 3
Used when the item is disabled and deselected.
@end table
@end table

The GTK+ and NS versions of Emacs ignores items 1 to 3, because disabled and/or
deselected images are autocomputed from item 0.

If @var{image} is a single image specification, Emacs draws the tool bar
button in disabled state by applying an edge-detection algorithm to the
image.

The @code{:rtl} property specifies an alternative image to use for
right-to-left languages.  Only the GTK+ version of Emacs supports this
at present.

Like the menu bar, the tool bar can display separators (@pxref{Menu
Separators}).  Tool bar separators are vertical rather than
horizontal, though, and only a single style is supported.  They are
represented in the tool bar keymap by @code{(menu-item "--")} entries;
properties like @code{:visible} are not supported for tool bar
separators.  Separators are rendered natively in GTK+ and Nextstep
tool bars; in the other cases, they are rendered using an image of a
vertical line.

The default tool bar is defined so that items specific to editing do not
appear for major modes whose command symbol has a @code{mode-class}
property of @code{special} (@pxref{Major Mode Conventions}).  Major
modes may add items to the global bar by binding @code{[tool-bar
@var{foo}]} in their local map.  It makes sense for some major modes to
replace the default tool bar items completely, since not many can be
accommodated conveniently, and the default bindings make this easy by
using an indirection through @code{tool-bar-map}.

@defvar tool-bar-map
By default, the global map binds @code{[tool-bar]} as follows:

@example
(global-set-key [tool-bar]
                `(menu-item ,(purecopy "tool bar") ignore
                            :filter tool-bar-make-keymap))
@end example

@noindent
The function @code{tool-bar-make-keymap}, in turn, derives the actual
tool bar map dynamically from the value of the variable
@code{tool-bar-map}.  Hence, you should normally adjust the default
(global) tool bar by changing that map.  Some major modes, such as
Info mode, completely replace the global tool bar by making
@code{tool-bar-map} buffer-local and setting it to a different keymap.
@end defvar

There are two convenience functions for defining tool bar items, as
follows.

@defun tool-bar-add-item icon def key &rest props
This function adds an item to the tool bar by modifying
@code{tool-bar-map}.  The image to use is defined by @var{icon}, which
is the base name of an XPM, XBM or PBM image file to be located by
@code{find-image}.  Given a value @samp{"exit"}, say, @file{exit.xpm},
@file{exit.pbm} and @file{exit.xbm} would be searched for in that order
on a color display.  On a monochrome display, the search order is
@samp{.pbm}, @samp{.xbm} and @samp{.xpm}.  The binding to use is the
command @var{def}, and @var{key} is the fake function key symbol in the
prefix keymap.  The remaining arguments @var{props} are additional
property list elements to add to the menu item specification.

To define items in some local map, bind @code{tool-bar-map} with
@code{let} around calls of this function:
@example
(defvar foo-tool-bar-map
  (let ((tool-bar-map (make-sparse-keymap)))
    (tool-bar-add-item @dots{})
    @dots{}
    tool-bar-map))
@end example
@end defun

@defun tool-bar-add-item-from-menu command icon &optional map &rest props
This function is a convenience for defining tool bar items which are
consistent with existing menu bar bindings.  The binding of
@var{command} is looked up in the menu bar in @var{map} (default
@code{global-map}) and modified to add an image specification for
@var{icon}, which is found in the same way as by
@code{tool-bar-add-item}.  The resulting binding is then placed in
@code{tool-bar-map}, so use this function only for global tool bar
items.

@var{map} must contain an appropriate keymap bound to
@code{[menu-bar]}.  The remaining arguments @var{props} are additional
property list elements to add to the menu item specification.
@end defun

@defun tool-bar-local-item-from-menu command icon in-map &optional from-map &rest props
This function is used for making non-global tool bar items.  Use it
like @code{tool-bar-add-item-from-menu} except that @var{in-map}
specifies the local map to make the definition in.  The argument
@var{from-map} is like the @var{map} argument of
@code{tool-bar-add-item-from-menu}.
@end defun

@defvar auto-resize-tool-bars
If this variable is non-@code{nil}, the tool bar automatically resizes to
show all defined tool bar items---but not larger than a quarter of the
frame's height.

If the value is @code{grow-only}, the tool bar expands automatically,
but does not contract automatically.  To contract the tool bar, the
user has to redraw the frame by entering @kbd{C-l}.

If Emacs is built with GTK or Nextstep, the tool bar can only show one
line, so this variable has no effect.
@end defvar

@defvar auto-raise-tool-bar-buttons
If this variable is non-@code{nil}, tool bar items display
in raised form when the mouse moves over them.
@end defvar

@defvar tool-bar-button-margin
This variable specifies an extra margin to add around tool bar items.
The value is an integer, a number of pixels.  The default is 4.
@end defvar

@defvar tool-bar-button-relief
This variable specifies the shadow width for tool bar items.
The value is an integer, a number of pixels.  The default is 1.
@end defvar

@defvar tool-bar-border
This variable specifies the height of the border drawn below the tool
bar area.  An integer specifies height as a number of pixels.
If the value is one of @code{internal-border-width} (the default) or
@code{border-width}, the tool bar border height corresponds to the
corresponding frame parameter.
@end defvar

  You can define a special meaning for clicking on a tool bar item with
the shift, control, meta, etc., modifiers.  You do this by setting up
additional items that relate to the original item through the fake
function keys.  Specifically, the additional items should use the
modified versions of the same fake function key used to name the
original item.

  Thus, if the original item was defined this way,

@example
(define-key global-map [tool-bar shell]
  '(menu-item "Shell" shell
              :image (image :type xpm :file "shell.xpm")))
@end example

@noindent
then here is how you can define clicking on the same tool bar image with
the shift modifier:

@example
(define-key global-map [tool-bar S-shell] 'some-command)
@end example

@xref{Function Keys}, for more information about how to add modifiers to
function keys.

@node Modifying Menus
@subsection Modifying Menus
@cindex menu modification

  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 @code{define-key} to add the item, it normally goes at the front of
the menu.  To put it elsewhere in the menu, use @code{define-key-after}:

@defun define-key-after map key binding &optional after
Define a binding in @var{map} for @var{key}, with value @var{binding},
just like @code{define-key}, but position the binding in @var{map} after
the binding for the event @var{after}.  The argument @var{key} should be
of length one---a vector or string with just one element.  But
@var{after} should be a single event type---a symbol or a character, not
a sequence.  The new binding goes after the binding for @var{after}.  If
@var{after} is @code{t} or is omitted, then the new binding goes last, at
the end of the keymap.  However, new bindings are added before any
inherited keymap.

Here is an example:

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

@noindent
makes a binding for the fake function key @key{DRINK} and puts it
right after the binding for @key{EAT}.

Here is how to insert an item called @samp{Work} in the @samp{Signals}
menu of Shell mode, after the item @code{break}:

@example
(define-key-after
  (lookup-key shell-mode-map [menu-bar signals])
  [work] '("Work" . work-command) 'break)
@end example
@end defun

@node Easy Menu
@subsection Easy Menu

  The following macro provides a convenient way to define pop-up menus
and/or menu bar menus.

@defmac easy-menu-define symbol maps doc menu
This macro defines a pop-up menu and/or menu bar submenu, whose
contents are given by @var{menu}.

If @var{symbol} is non-@code{nil}, it should be a symbol; then this
macro defines @var{symbol} as a function for popping up the menu
(@pxref{Pop-Up Menus}), with @var{doc} as its documentation string.
@var{symbol} should not be quoted.

Regardless of the value of @var{symbol}, if @var{maps} is a keymap,
the menu is added to that keymap, as a top-level menu for the menu bar
(@pxref{Menu Bar}).  It can also be a list of keymaps, in which case
the menu is added separately to each of those keymaps.

The first element of @var{menu} must be a string, which serves as the
menu label.  It may be followed by any number of the following
keyword-argument pairs:

@table @code
@item :filter @var{function}
@var{function} must be a function which, if called with one
argument---the list of the other menu items---returns the actual items
to be displayed in the menu.

@item :visible @var{include}
@var{include} is an expression; if it evaluates to @code{nil}, the
menu is made invisible.  @code{:included} is an alias for
@code{:visible}.

@item :active @var{enable}
@var{enable} is an expression; if it evaluates to @code{nil}, the menu
is not selectable.  @code{:enable} is an alias for @code{:active}.
@end table

The remaining elements in @var{menu} are menu items.

A menu item can be a vector of three elements, @code{[@var{name}
@var{callback} @var{enable}]}.  @var{name} is the menu item name (a
string).  @var{callback} is a command to run, or an expression to
evaluate, when the item is chosen.  @var{enable} is an expression; if
it evaluates to @code{nil}, the item is disabled for selection.

Alternatively, a menu item may have the form:

@smallexample
   [ @var{name} @var{callback} [ @var{keyword} @var{arg} ]... ]
@end smallexample

@noindent
where @var{name} and @var{callback} have the same meanings as above,
and each optional @var{keyword} and @var{arg} pair should be one of
the following:

@table @code
@item :keys @var{keys}
@var{keys} is a keyboard equivalent to the menu item (a string).  This
is normally not needed, as keyboard equivalents are computed
automatically.  @var{keys} is expanded with
@code{substitute-command-keys} before it is displayed (@pxref{Keys in
Documentation}).

@item :key-sequence @var{keys}
@var{keys} is a hint for speeding up Emacs's first display of the
menu.  It should be @code{nil} if you know that the menu item has no keyboard
equivalent; otherwise it should be a string or vector specifying a
keyboard equivalent for the menu item.

@item :active @var{enable}
@var{enable} is an expression; if it evaluates to @code{nil}, the item
is make unselectable..  @code{:enable} is an alias for @code{:active}.

@item :visible @var{include}
@var{include} is an expression; if it evaluates to @code{nil}, the
item is made invisible.  @code{:included} is an alias for
@code{:visible}.

@item :label @var{form}
@var{form} is an expression that is evaluated to obtain a value which
serves as the menu item's label (the default is @var{name}).

@item :suffix @var{form}
@var{form} is an expression that is dynamically evaluated and whose
value is concatenated with the menu entry's label.

@item :style @var{style}
@var{style} is a symbol describing the type of menu item; it should be
@code{toggle} (a checkbox), or @code{radio} (a radio button), or
anything else (meaning an ordinary menu item).

@item :selected @var{selected}
@var{selected} is an expression; the checkbox or radio button is
selected whenever the expression's value is non-@code{nil}.

@item :help @var{help}
@var{help} is a string describing the menu item.
@end table

Alternatively, a menu item can be a string.  Then that string appears
in the menu as unselectable text.  A string consisting of dashes is
displayed as a separator (@pxref{Menu Separators}).

Alternatively, a menu item can be a list with the same format as
@var{menu}.  This is a submenu.
@end defmac

Here is an example of using @code{easy-menu-define} to define a menu
similar to the one defined in the example in @ref{Menu Bar}:

@example
(easy-menu-define words-menu global-map
  "Menu for word navigation commands."
  '("Words"
     ["Forward word" forward-word]
     ["Backward word" backward-word]))
@end example