(quoted-printable-decode-region): Avoid invalid

[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, 1998, 1999, 2000
@c   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 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
* 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::		Defining a menu as a keymap.
@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
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 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

  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.

  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}.

@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.

@item @var{vector}
If an element of a keymap is a vector, the vector counts as bindings for
all the @sc{ascii} characters, codes 0 through 127; 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 each
@sc{ascii} character, even if the vector contains @code{nil} for that
character.  Such a binding of @code{nil} overrides any default key
binding in the keymap, for @sc{ascii} characters.  However, default
bindings are still meaningful for events other than @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.

@item @var{string}
@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{Defining Menus}.
@end table

@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 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 make-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 should be provided for menu keymaps
(@pxref{Defining Menus}).
@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, which we call the
@dfn{parent keymap}.  Such a keymap looks like this:

@example
(keymap @var{bindings}@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{bindings}.

If you change the bindings in @var{parent-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{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

@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.

@c Emacs 19 feature
@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.

@c Emacs 19 feature
@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 facemenu-keymap
@code{facemenu-keymap} is the global keymap used for the @kbd{M-g}
prefix key.

@c Emacs 19 feature
@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
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
@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 can 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.  The procedure for searching a single keymap is called @dfn{key
lookup}; see @ref{Key Lookup}.

  Normally, Emacs first searches for the key in the minor mode maps, in
the order specified by @code{minor-mode-map-alist}; if they do not
supply a binding for the key, Emacs searches the local map; if that too
has no binding, Emacs then searches the global map.  However, if
@code{overriding-local-map} is non-@code{nil}, Emacs searches that map
first, before the global map.

@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 and some other major
modes exist even if they have not yet been used.  These local maps are
the values of variables such as @code{lisp-mode-map}.  For most major
modes, which are less frequently used, the local keymap is constructed
only when the mode is used for the first time in a session.

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

  Emacs has other keymaps that are used in a different way---translating
events within @code{read-key-sequence}.  @xref{Translating Input}.

  @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.  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, 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 @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 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

@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

@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 ``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 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 table 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{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 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}.  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) "\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, 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 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

@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.  Here is an illustration:

@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 such lists is that the precise
numeric codes for the modifier bits don't appear in compiled files.

  For the functions below, an error is signaled if @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} 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 in most cases, but it does
matter for menu keymaps (@pxref{Menu Keymaps}).
@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}, 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.

@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
(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 init files
(@pxref{Init 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.

@cindex non-@sc{ascii} text in keybindings
  Be careful when using non-@sc{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 "@"o" 'my-function) ; bind o-umlaut
@end smallexample

@noindent
or

@smallexample
(global-set-key ?@"o '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 2294, not the unibyte
Latin-1 character with code 246 (@kbd{M-v}).  In order to use this
binding, you need to enter the multibyte Latin-1 character as keyboard
input.  One way to do this is by using an appropriate input method
(@pxref{Input Methods, , Input Methods, emacs,The GNU Emacs Manual}).

  If you want to use a unibyte character in the key binding, you can
construct the key sequence string using @code{multibyte-char-to-unibyte}
or @code{string-make-unibyte} (@pxref{Converting Representations}).

@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 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 where-is-internal command &optional keymap firstonly noindirect
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 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.

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

@deffn Command describe-bindings &optional prefix
This function creates a listing of all current key bindings, and
displays it in a buffer named @samp{*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}.

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.
* Tool Bar::                    A tool bar is a row of images.
* 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'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.@: under MS-DOS.}  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} or @code{define-prefix-command}
(@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}).

@menu
* Simple Menu Items::       A simple kind of menu key binding,
                              limited in capabilities.
* Extended Menu Items::     More powerful menu item definitions
                              let you specify keywords to enable
                              various features.
* 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 older way to define a menu keymap binding
looks 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.

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

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

@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}).

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{item-string} @r{[}@var{help-string}@r{]} (@var{key-binding-data}) . @var{real-binding})
@end example

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

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

  An extended-format menu item is a more flexible and also cleaner
alternative to the simple format.  It consists of a list that starts
with the symbol @code{menu-item}.  To define a non-selectable string,
the item 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
item 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.
@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.)

  Starting in Emacs 21, 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"}.

  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{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

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{toggle-read-only}.

@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.

  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 produce multiple panes or submenus from separate keymaps.
The full definition of a prefix key always comes from merging the
definitions supplied by the various active keymaps (minor mode, local,
and global).  When more than one of these keymaps is a menu, each of
them makes a separate pane or panes (when Emacs does not use an
X-toolkit) or a separate submenu (when using an X-toolkit).
@xref{Active Keymaps}.

@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's overall prompt string followed by the
alternatives (the item strings of the 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.

@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
@cindex menu definition example

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

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

@noindent
Next we define the menu items:

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

@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 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-ps-print}.  If one menu has two separators, they must
have two different key symbols.

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

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

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

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

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

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

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

  We could equally well use an extended menu item (@pxref{Extended Menu
Items}) for @code{print-region}, like this:

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

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

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

@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 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}.

  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{Window 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 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
@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 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 Tool Bar
@subsection Tool bars
@cindex tool bar

  A @dfn{tool bar} is a row of icons at the top of a frame, that execute
commands when you click on them---in effect, a kind of graphical menu
bar.  Emacs supports tool bars starting with version 21.

  The frame parameter @code{tool-bar-lines} (X resource @samp{toolBar})
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.

  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{images} is either a single image specification 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

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.

@tindex auto-resize-tool-bar
@defvar auto-resize-tool-bar
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.
@end defvar

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

@tindex tool-bar-item-margin
@defvar tool-bar-item-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 1.
@end defvar

@tindex tool-bar-item-relief
@defvar tool-bar-item-relief
This variable specifies the shadow width for tool bar items.
The value is an integer, a number of pixels.  The default is 3.
@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

  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