(x_clear_frame_selections): Don't call redisplay_preserve_echo_area here.

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

@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. 
@c See the file elisp.texi for copying conditions.
@setfilename ../info/keymaps
@node Keymaps, Modes, Command Loop, Top
@chapter Keymaps
@cindex keymap

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

@menu
* Keymap Terminology::          Definitions of terms pertaining to 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::              Each buffer has a local keymap
                                   to override the standard (global) bindings.
                                   A minor mode can also override them.
* Key Lookup::                  How extracting elements from keymaps works.
* Functions for Key Lookup::    How to request key lookup.
* Changing Key Bindings::       Redefining a key in a keymap.
* Key Binding Commands::        Interactive interfaces for redefining keys.
* Scanning Keymaps::            Looking through all keymaps, for printing help.
* Menu Keymaps::                A keymap can define a menu.
@end menu

@node Keymap Terminology
@section Keymap Terminology
@cindex key
@cindex keystroke
@cindex key binding
@cindex binding of a key
@cindex complete key
@cindex undefined key

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

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

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

  If the binding of a key sequence is a keymap, we call the key sequence
a @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 a key sequence.  In other words, removing one or
more events from the end of any valid key must always yield a prefix
key.  For example, @kbd{C-f C-n} is not a key; @kbd{C-f} is not a prefix
key, so a longer sequence starting with @kbd{C-f} cannot be a key.

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

  At any time, several primary keymaps are @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

  A 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.
Use the function @code{keymapp} (see below) to test whether an object is
a keymap.

  Each ordinary binding applies to events of a particular @dfn{event
type}, which is always a character or a symbol.  @xref{Classifying
Events}.

  An ordinary element of a keymap is a cons cell of the form
@code{(@var{type} .@: @var{binding})}.  This specifies one binding, for
events of type @var{type}.

@cindex default key binding
@c Emacs 19 feature
  A cons cell whose @sc{car} is @code{t} is 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.

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

  When a keymap contains a vector, it always defines a binding for every
@sc{ASCII} character even if the vector element is @code{nil}.  Such a
binding of @code{nil} overrides any default binding in the keymap.
However, default bindings are still meaningful for events that are not
@sc{ASCII} characters.  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 keymap prompt string
@cindex overall prompt string
@cindex prompt string of keymap
  Aside from bindings, 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{Menu Keymaps}.

@cindex meta characters lookup
  Keymaps do not directly record bindings for the meta characters, whose
codes are from 128 to 255.  Instead, meta characters are regarded for
purposes of key lookup as sequences of two characters, the first of
which is @key{ESC} (or whatever is currently the value of
@code{meta-prefix-char}).  Thus, the key @kbd{M-a} is really 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}).

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

@example
@group
lisp-mode-map
@result{} 
@end group
@group
(keymap 
 ;; @key{TAB}
 (9 . lisp-indent-line)                 
@end group
@group
 ;; @key{DEL}
 (127 . backward-delete-char-untabify)  
@end group
@group
 (3 keymap 
    ;; @kbd{C-c C-l}
    (12 . run-lisp))                    
@end group
@group
 (27 keymap 
     ;; @r{@kbd{M-C-q}, treated as @kbd{@key{ESC} C-q}}
     (17 . indent-sexp)                 
     ;; @r{@kbd{M-C-x}, treated as @kbd{@key{ESC} C-x}}
     (24 . lisp-send-defun)))           
@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}.

@example
@group
(keymapp '(keymap))
    @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.

@c ??? This should come after makr-sparse-keymap
@defun make-keymap &optional prompt
This function creates and returns a new full keymap (i.e., one
containing a vector of length 128 for defining all the @sc{ASCII}
characters).  The new keymap initially binds all @sc{ASCII} characters
to @code{nil}, and does not bind any other kind of event.

@example
@group
(make-keymap)
    @result{} (keymap [nil nil nil @dots{} nil nil])
@end group
@end example

If you specify @var{prompt}, that becomes the overall prompt string for
the keymap.  The prompt string is useful for menu keymaps (@pxref{Menu
Keymaps}).
@end defun

@defun make-sparse-keymap &optional prompt
This function creates and returns a new sparse keymap with no entries.
The new keymap does not bind any events.  The argument @var{prompt}
specifies a prompt string, as in @code{make-keymap}.

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

@defun copy-keymap keymap
This function returns a copy of @var{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 inheriting a keymap's bindings

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

@example
(keymap @var{bindings}@dots{} . @var{other-keymap})
@end example

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

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

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

@example
(setq my-mode-map (cons 'keymap text-mode-map))
@end example

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

  A @dfn{prefix key} has an associated keymap that defines what to do
with key sequences that start with 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}.  Here is a list of the standard prefix
keys of Emacs and their keymaps:

@itemize @bullet
@item
@vindex esc-map
@findex ESC-prefix
@code{esc-map} is used for events that follow @key{ESC}.  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 used for events that follow @kbd{C-h}.

@item
@cindex @kbd{C-c}
@vindex mode-specific-map
@code{mode-specific-map} is for events that follow @kbd{C-c}.  This
map is not actually mode specific; its name was chosen to be informative
for the user in @kbd{C-h b} (@code{display-bindings}), where it
describes the main use of the @kbd{C-c} prefix key.

@item
@cindex @kbd{C-x}
@vindex ctl-x-map
@findex Control-X-prefix
@code{ctl-x-map} is the map used for events that follow @kbd{C-x}.  This
map is also the function definition of @code{Control-X-prefix}.

@item
@cindex @kbd{C-x 4}
@vindex ctl-x-4-map
@code{ctl-x-4-map} is used for events that follow @kbd{C-x 4}.

@c Emacs 19 feature
@item
@cindex @kbd{C-x 5}
@vindex ctl-x-5-map
@code{ctl-x-5-map} is used for events that follow @kbd{C-x 5}.

@c Emacs 19 feature
@item
@cindex @kbd{C-x n}
@cindex @kbd{C-x r}
@cindex @kbd{C-x a}
The prefix keys @kbd{C-x n}, @kbd{C-x r} and @kbd{C-x a} use keymaps
that have no special name.
@end itemize

  The binding of a prefix key is the keymap to use for looking up the
events that follow the prefix key.  (It may instead be a symbol whose
function definition is a keymap.  The effect is the same, but the symbol
serves as a name for the prefix key.)  Thus, the binding of @kbd{C-x} is
the symbol @code{Control-X-prefix}, whose function definition is 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
@cindex prefix command
This function defines @var{symbol} as a prefix command: it creates a
full keymap and stores it as @var{symbol}'s function definition.
Storing the symbol as the binding of a key makes the key a prefix key
that has a name.  The function also sets @var{symbol} as a variable, to
have the keymap as its value.  It returns @var{symbol}.

  In Emacs version 18, only the function definition of @var{symbol} was
set, not the value as a variable.
@end defun

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

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

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

  Each buffer may have another keymap, its @dfn{local keymap}, which may
contain new or overriding definitions for keys.  The current buffer's
local keymap is always active except when @code{overriding-local-map}
overrides it.  Text properties can specify an alternative local map for
certain parts of the buffer; see @ref{Special Properties}.

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

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

  All the active keymaps are used together to determine what command to
execute when a key is entered.  Emacs searches these maps one by one, in
order of decreasing precedence, until it finds a binding in one of the maps.

  Normally, Emacs @emph{first} searches for the key in the minor mode
maps (one map at a time); if they do not supply a binding for the key,
Emacs searches the local map; if that too has no binding, Emacs then
searches the global map.  However, if @code{overriding-local-map} is
non-@code{nil}, Emacs searches that map first, followed by the global
map.

  The procedure for searching a single keymap is called
@dfn{key lookup}; see @ref{Key Lookup}.

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

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

  The minibuffer has local keymaps, too; they contain various completion
and exit commands.  @xref{Intro to Minibuffers}.

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

@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 map, 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.

@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
@samp{*scratch*} buffer (using Lisp Interaction mode) is a sparse keymap
in which the entry for @key{ESC}, @sc{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

@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

@c Emacs 19 feature
@defvar 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.

What's more, the keymap itself must appear in the @sc{cdr}.  It does not
work to store a variable in the @sc{cdr} and make the map the value of
that variable.

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

See also @code{minor-mode-key-binding}, above.  See @ref{Keymaps and
Minor Modes}, for more information about minor modes.
@end defvar

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

This variable is always local to the current terminal and cannot be
buffer-local.  @xref{Multiple Displays}.  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

@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.  Actual execution of the binding is not
part of key lookup.

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

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

  Let's use the term @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 menu key bindings 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 list of
the meaningful kinds 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{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{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{list}
@cindex list in keymap
The meaning of a list depends on the types of the elements of the list.

@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 command, and is treated as
such (see above).

@item
If the @sc{car} of @var{list} is a keymap and the @sc{cdr} is an event
type, then this is an @dfn{indirect entry}:

@example
(@var{othermap} . @var{othertype})
@end example

When key lookup encounters an indirect entry, it looks up instead the
binding of @var{othertype} in @var{othermap} and uses that.

This feature permits you to define one key as an alias for another key.
For example, an entry whose @sc{car} is the keymap called @code{esc-map}
and whose @sc{cdr} is 32 (the code for @key{SPC}) means, ``Use the global
binding of @kbd{Meta-@key{SPC}}, whatever that may be.''
@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.  A list is allowed if it is a
keymap or a command, but indirect entries are not understood when found
via symbols.

Note that keymaps and keyboard macros (strings and vectors) are not
valid functions, so a symbol with a keymap, string, or vector as its
function definition is invalid as a function.  It is, however, valid as
a key binding.  If the definition is a keyboard macro, then the symbol
is also valid as an argument to @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 an indirection or @code{nil}.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap.  This map is the normal value
of @code{emacs-lisp-mode-map}.  Note that 9 is the code for @key{TAB},
127 for @key{DEL}, 27 for @key{ESC}, 17 for @kbd{C-q} and 24 for
@kbd{C-x}.

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

@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}.  If
the string or vector @var{key} is not a valid key sequence according to
the prefix keys specified in @var{keymap} (which means it is ``too
long'' and has extra events at the end), then the value is a number, the
number of events at the front of @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}.)

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

@example
@group
(lookup-key (current-global-map) "\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 @var{key} contains a meta character, 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 key-binding key &optional accept-defaults
This function returns the binding for @var{key} in the current
keymaps, trying all the active keymaps.  The result is @code{nil} if
@var{key} is undefined in the keymaps.

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

An error is signaled 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

@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 is not a prefix command, 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

@defvar meta-prefix-char
@cindex @key{ESC}
This variable is the meta-prefix character code.  It is used when
translating a meta character to a two-character sequence so it can be
looked up in a keymap.  For useful results, the value should be a prefix
event (@pxref{Prefix Keys}).  The default value is 27, which is the
@sc{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 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.

@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
@end defvar

@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 specify explicitly the map to change.

@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 using a list to represent the event type is that the
precise numeric codes for the modifier bits don't appear in compiled
files.

  For the functions below, an error is signaled if @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.

@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}.

@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} may be defined as
specified.
@end defun

  Here is an example that 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 "\C-xf" '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 "\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 "\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.

@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}, then its bindings 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.

@ignore
@c Emacs 18 only
Prefix keymaps that appear within @var{keymap} are not checked
recursively for keys bound to @var{olddef}; they are not changed at all.
Perhaps it would be better to check nested keymaps recursively.
@end ignore

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
making all the printing characters undefined.  More precisely, it binds
them to the command @code{undefined}.  This makes 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.

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

@smallexample
@group
  @dots{}
  (setq dired-mode-map (make-keymap))
  (suppress-keymap dired-mode-map)
  (define-key dired-mode-map "r" 'dired-rename-file)
  (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted)
  (define-key dired-mode-map "d" 'dired-flag-file-deleted)
  (define-key dired-mode-map "v" 'dired-view-file)
  (define-key dired-mode-map "e" 'dired-find-file)
  (define-key dired-mode-map "f" 'dired-find-file)
  @dots{}
@end group
@end smallexample
@end defun

@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 @file{.emacs} file for
simple customization.  For example,

@smallexample
(global-set-key "\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, typed with the Meta key, to
set point where you click.

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

@smallexample
@group
(global-set-key @var{key} @var{definition})
@equiv{}
(define-key (current-global-map) @var{key} @var{definition})
@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 implemented simply using @code{define-key}:

@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 definition
This function sets the binding of @var{key} in the current local
keymap to @var{definition}.

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

  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 accessed
(via 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 an actual case.
@end defun

@defun where-is-internal command &optional keymap firstonly noindirect
This function returns a list of 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 non-@code{nil}, then the
maps searched are @var{keymap} and the global keymap.

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
@code{(keymap)} (an empty keymap) as @var{keymap}.

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

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

This function is used by @code{where-is} (@pxref{Help, , Help, emacs,
The GNU Emacs Manual}).

@smallexample
@group
(where-is-internal 'describe-function)
    @result{} ("\^hf" "\^hd")
@end group
@end smallexample
@end defun

@deffn Command describe-bindings prefix
This function creates a listing of all defined keys and their
definitions.  It writes the listing in a buffer named @samp{*Help*} and
displays it in a window.

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

The listing describes meta characters as @key{ESC} followed by the
corresponding non-meta character.

When several characters with consecutive @sc{ASCII} codes have the
same definition, they are shown together, as
@samp{@var{firstchar}..@var{lastchar}}.  In this instance, you need to
know the @sc{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 @sc{ASCII} 32,
@kbd{~} is @sc{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}.
@end deffn

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

@c Emacs 19 feature
A keymap can define a menu as well as bindings for keyboard keys and
mouse button.  Menus are usually actuated with the mouse, but they can
work with the keyboard also.

@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 they actuate it with the keyboard.
* Menu Example::                Making a simple menu.
* Menu Bar::                    How to customize the menu bar.
* Modifying Menus::             How to add new items to a menu.
@end menu

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

A keymap is suitable for menu use 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.  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} or
@code{make-sparse-keymap} (@pxref{Creating Keymaps}).

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}).

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

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

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

As far as @code{define-key} is concerned, @var{string} is 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.

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

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

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

If @var{real-binding} is @code{nil}, then @var{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 with the mouse.

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}).

Sometimes it is useful to make menu items that use the ``same'' command
but with different enable conditions.  You can do this by defining alias
commands.  Here's an example that makes two aliases for
@code{toggle-read-only} and gives them different enable conditions:

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

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

@c This line is not too long--rms.
@example
(@var{string} @r{[}@var{help-string}@r{]} (@var{key-binding-data}) . @var{real-binding})
@end example

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

If an alias command has no keyboard equivalent itself, menus show the
keyboard equivalent of its underlying command.  In the example above,
menu items defined to run @code{make-read-only} or @code{make-writable}
would show the keyboard equivalents of @code{toggle-read-only}.

@node Mouse Menus
@subsection Menus and the Mouse

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

If the prefix key ends with a mouse event, Emacs handles the menu keymap
by popping up a visible menu, so that the user can select a choice with
the mouse.  When the user clicks on a menu item, the event generated is
whatever character or symbol has the binding that brought about that
menu item.  (A menu item may generate a series of events if the menu has
multiple levels or comes from the menu bar.)

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

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

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

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

In toolkit versions of Emacs, menus don't have panes, so submenus are
used to represent the separate keymaps.  Each keymap's contribution
becomes one submenu.

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

@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 user can use the
keyboard to choose a menu item.

Emacs displays the menu alternatives (the item strings of the bindings)
in the echo area.  If they don't all fit at once, the user can type
@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.

@ignore
In a menu intended for keyboard use, each menu item must clearly
indicate what character to type.  The best convention to use is to make
the character the first letter of the item string---that is something
users will understand without being told.  We plan to change this; by
the time you read this manual, keyboard menus may explicitly name the
key for each alternative.
@end ignore

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

@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

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

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

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

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

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

  However, if you want the menu to be usable from the keyboard as well,
you must bind real @sc{ASCII} characters as well as fictitious function
keys.

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

  Most window systems allow each frame to have a @dfn{menu bar}---a
permanently displayed menu stretching horizontally across the top of the
frame.  The items of the menu bar are the subcommands of the fake
``function key'' @code{menu-bar}, as defined by all the active keymaps.

  To add an item to the menu bar, invent a fake ``function key'' of your
own (let's call it @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 fake function key
for the menu bar, the item appears just once.  If the user clicks on
that menu bar item, it brings up a single, combined submenu containing
all the subcommands of that item---the global subcommands, the local
subcommands, and the minor mode subcommands, all together.

  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}.

  In order for a frame to display a menu bar, its @code{menu-bar-lines}
parameter must be greater than zero.  Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame.  We
recommend 1 or 2 as the value of @code{menu-bar-lines}.  @xref{X Frame
Parameters}.

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

@example
@group
(modify-frame-parameters (selected-frame)
                         '((menu-bar-lines . 2)))
@end group

@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 the item's 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
@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)}; 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 whenever the user clicks on the menu bar, before
displaying a submenu.  You can use it to update submenus whose contents
should vary.
@end defvar

@node Modifying Menus
@subsection Modifying Menus

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

@defun define-key-after map key binding 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.

For 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

Note that @var{key} is a sequence containing just one event type, but
@var{after} is just an event type (not a sequence).
@end defun