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@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
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@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. 
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@c See the file elisp.texi for copying conditions.
@setfilename ../info/commands
@node Command Loop, Keymaps, Minibuffers, Top
@chapter Command Loop
@cindex editor command loop
@cindex command loop

  When you run Emacs, it enters the @dfn{editor command loop} almost
immediately.  This loop reads key sequences, executes their definitions,
and displays the results.  In this chapter, we describe how these things
are done, and the subroutines that allow Lisp programs to do them.  

@menu
* Command Overview::    How the command loop reads commands.
* Defining Commands::   Specifying how a function should read arguments.
* Interactive Call::    Calling a command, so that it will read arguments.
* Command Loop Info::   Variables set by the command loop for you to examine.
* Input Events::	What input looks like when you read it.
* Reading Input::       How to read input events from the keyboard or mouse.
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* Special Events::      Events processed immediately and individually.
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* Waiting::             Waiting for user input or elapsed time.
* Quitting::            How @kbd{C-g} works.  How to catch or defer quitting.
* Prefix Command Arguments::    How the commands to set prefix args work.
* Recursive Editing::   Entering a recursive edit,
                          and why you usually shouldn't.
* Disabling Commands::  How the command loop handles disabled commands.
* Command History::     How the command history is set up, and how accessed.
* Keyboard Macros::     How keyboard macros are implemented.
@end menu

@node Command Overview
@section Command Loop Overview

  The first thing the command loop must do is read a key sequence, which
is a sequence of events that translates into a command.  It does this by
calling the function @code{read-key-sequence}.  Your Lisp code can also
call this function (@pxref{Key Sequence Input}).  Lisp programs can also
do input at a lower level with @code{read-event} (@pxref{Reading One
Event}) or discard pending input with @code{discard-input}
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(@pxref{Event Input Misc}).
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  The key sequence is translated into a command through the currently
active keymaps.  @xref{Key Lookup}, for information on how this is done.
The result should be a keyboard macro or an interactively callable
function.  If the key is @kbd{M-x}, then it reads the name of another
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command, which it then calls.  This is done by the command
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@code{execute-extended-command} (@pxref{Interactive Call}).

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  To execute a command requires first reading the arguments for it.
This is done by calling @code{command-execute} (@pxref{Interactive
Call}).  For commands written in Lisp, the @code{interactive}
specification says how to read the arguments.  This may use the prefix
argument (@pxref{Prefix Command Arguments}) or may read with prompting
in the minibuffer (@pxref{Minibuffers}).  For example, the command
@code{find-file} has an @code{interactive} specification which says to
read a file name using the minibuffer.  The command's function body does
not use the minibuffer; if you call this command from Lisp code as a
function, you must supply the file name string as an ordinary Lisp
function argument.
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  If the command is a string or vector (i.e., a keyboard macro) then
@code{execute-kbd-macro} is used to execute it.  You can call this
function yourself (@pxref{Keyboard Macros}).

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  To terminate the execution of a running command, type @kbd{C-g}.  This
character causes @dfn{quitting} (@pxref{Quitting}).
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@defvar pre-command-hook
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The editor command loop runs this normal hook before each command.  At
that time, @code{this-command} contains the command that is about to
run, and @code{last-command} describes the previous command.
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@xref{Hooks}.
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@end defvar

@defvar post-command-hook
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The editor command loop runs this normal hook after each command
(including commands terminated prematurely by quitting or by errors),
and also when the command loop is first entered.  At that time,
@code{this-command} describes the command that just ran, and
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@code{last-command} describes the command before that.  @xref{Hooks}.
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@end defvar

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  Quitting is suppressed while running @code{pre-command-hook} and
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@code{post-command-hook}.  If an error happens while executing one of
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these hooks, it terminates execution of the hook, and clears the hook
variable to @code{nil} so as to prevent an infinite loop of errors.
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@node Defining Commands
@section Defining Commands
@cindex defining commands
@cindex commands, defining
@cindex functions, making them interactive
@cindex interactive function

  A Lisp function becomes a command when its body contains, at top
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level, a form that calls the special form @code{interactive}.  This
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form does nothing when actually executed, but its presence serves as a
flag to indicate that interactive calling is permitted.  Its argument
controls the reading of arguments for an interactive call.

@menu
* Using Interactive::     General rules for @code{interactive}.
* Interactive Codes::     The standard letter-codes for reading arguments
                             in various ways.
* Interactive Examples::  Examples of how to read interactive arguments.
@end menu

@node Using Interactive
@subsection Using @code{interactive}

  This section describes how to write the @code{interactive} form that
makes a Lisp function an interactively-callable command.

@defspec interactive arg-descriptor
@cindex argument descriptors
This special form declares that the function in which it appears is a
command, and that it may therefore be called interactively (via
@kbd{M-x} or by entering a key sequence bound to it).  The argument
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@var{arg-descriptor} declares how to compute the arguments to the
command when the command is called interactively.
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A command may be called from Lisp programs like any other function, but
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then the caller supplies the arguments and @var{arg-descriptor} has no
effect.
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The @code{interactive} form has its effect because the command loop
(actually, its subroutine @code{call-interactively}) scans through the
function definition looking for it, before calling the function.  Once
the function is called, all its body forms including the
@code{interactive} form are executed, but at this time
@code{interactive} simply returns @code{nil} without even evaluating its
argument.
@end defspec

There are three possibilities for the argument @var{arg-descriptor}:

@itemize @bullet
@item
It may be omitted or @code{nil}; then the command is called with no
arguments.  This leads quickly to an error if the command requires one
or more arguments.

@item
It may be a Lisp expression that is not a string; then it should be a
form that is evaluated to get a list of arguments to pass to the
command.
@cindex argument evaluation form

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If this expression reads keyboard input (this includes using the
minibuffer), keep in mind that the integer value of point or the mark
before reading input may be incorrect after reading input.  This is
because the current buffer may be receiving subprocess output;
if subprocess output arrives while the command is waiting for input,
it could relocate point and the mark.

Here's an example of what @emph{not} to do:

@smallexample
(interactive
 (list (region-beginning) (region-end)
       (read-string "Foo: " nil 'my-history)))
@end smallexample

@noindent
Here's how to avoid the problem, by examining point and the mark only
after reading the keyboard input:

@smallexample
(interactive
 (let ((string (read-string "Foo: " nil 'my-history)))
   (list (region-beginning) (region-end) string)))
@end smallexample

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@item
@cindex argument prompt
It may be a string; then its contents should consist of a code character
followed by a prompt (which some code characters use and some ignore).
The prompt ends either with the end of the string or with a newline.
Here is a simple example:

@smallexample
(interactive "bFrobnicate buffer: ")
@end smallexample

@noindent
The code letter @samp{b} says to read the name of an existing buffer,
with completion.  The buffer name is the sole argument passed to the
command.  The rest of the string is a prompt.

If there is a newline character in the string, it terminates the prompt.
If the string does not end there, then the rest of the string should
contain another code character and prompt, specifying another argument.
You can specify any number of arguments in this way.

@c Emacs 19 feature
The prompt string can use @samp{%} to include previous argument values
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(starting with the first argument) in the prompt.  This is done using
@code{format} (@pxref{Formatting Strings}).  For example, here is how
you could read the name of an existing buffer followed by a new name to
give to that buffer:
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@smallexample
@group
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
@end group
@end smallexample

@cindex @samp{*} in interactive
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@cindex read-only buffers in interactive
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If the first character in the string is @samp{*}, then an error is
signaled if the buffer is read-only.

@cindex @samp{@@} in interactive
@c Emacs 19 feature
If the first character in the string is @samp{@@}, and if the key
sequence used to invoke the command includes any mouse events, then
the window associated with the first of those events is selected
before the command is run.

You can use @samp{*} and @samp{@@} together; the order does not matter.
Actual reading of arguments is controlled by the rest of the prompt
string (starting with the first character that is not @samp{*} or
@samp{@@}).
@end itemize

@node Interactive Codes
@comment  node-name,  next,  previous,  up
@subsection Code Characters for @code{interactive}
@cindex interactive code description
@cindex description for interactive codes
@cindex codes, interactive, description of
@cindex characters for interactive codes

  The code character descriptions below contain a number of key words,
defined here as follows:

@table @b
@item Completion
@cindex interactive completion
Provide completion.  @key{TAB}, @key{SPC}, and @key{RET} perform name
completion because the argument is read using @code{completing-read}
(@pxref{Completion}).  @kbd{?} displays a list of possible completions.

@item Existing
Require the name of an existing object.  An invalid name is not
accepted; the commands to exit the minibuffer do not exit if the current
input is not valid.

@item Default
@cindex default argument string
A default value of some sort is used if the user enters no text in the
minibuffer.  The default depends on the code character.

@item No I/O
This code letter computes an argument without reading any input.
Therefore, it does not use a prompt string, and any prompt string you
supply is ignored.

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Even though the code letter doesn't use a prompt string, you must follow
it with a newline if it is not the last code character in the string.

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@item Prompt
A prompt immediately follows the code character.  The prompt ends either
with the end of the string or with a newline.

@item Special
This code character is meaningful only at the beginning of the
interactive string, and it does not look for a prompt or a newline.
It is a single, isolated character.
@end table

@cindex reading interactive arguments
  Here are the code character descriptions for use with @code{interactive}:

@table @samp
@item *
Signal an error if the current buffer is read-only.  Special.

@item @@
Select the window mentioned in the first mouse event in the key
sequence that invoked this command.  Special.

@item a
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A function name (i.e., a symbol satisfying @code{fboundp}).  Existing,
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Completion, Prompt.

@item b
The name of an existing buffer.  By default, uses the name of the
current buffer (@pxref{Buffers}).  Existing, Completion, Default,
Prompt.

@item B
A buffer name.  The buffer need not exist.  By default, uses the name of
a recently used buffer other than the current buffer.  Completion,
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Default, Prompt.
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@item c
A character.  The cursor does not move into the echo area.  Prompt.

@item C
A command name (i.e., a symbol satisfying @code{commandp}).  Existing,
Completion, Prompt.

@item d
@cindex position argument
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The position of point, as an integer (@pxref{Point}).  No I/O.
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@item D
A directory name.  The default is the current default directory of the
current buffer, @code{default-directory} (@pxref{System Environment}).
Existing, Completion, Default, Prompt.

@item e
The first or next mouse event in the key sequence that invoked the command.
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More precisely, @samp{e} gets events that are lists, so you can look at
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the data in the lists.  @xref{Input Events}.  No I/O.

You can use @samp{e} more than once in a single command's interactive
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specification.  If the key sequence that invoked the command has
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@var{n} events that are lists, the @var{n}th @samp{e} provides the
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@var{n}th such event.  Events that are not lists, such as function keys
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and @sc{ASCII} characters, do not count where @samp{e} is concerned.

@item f
A file name of an existing file (@pxref{File Names}).  The default
directory is @code{default-directory}.  Existing, Completion, Default,
Prompt.

@item F
A file name.  The file need not exist.  Completion, Default, Prompt.

@item k
A key sequence (@pxref{Keymap Terminology}).  This keeps reading events
until a command (or undefined command) is found in the current key
maps.  The key sequence argument is represented as a string or vector.
The cursor does not move into the echo area.  Prompt.

This kind of input is used by commands such as @code{describe-key} and
@code{global-set-key}.

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@item K
A key sequence, whose definition you intend to change.  This works like
@samp{k}, except that it suppresses, for the last input event in the key
sequence, the conversions that are normally used (when necessary) to
convert an undefined key into a defined one.

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@item m
@cindex marker argument
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The position of the mark, as an integer.  No I/O.
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@item M
Arbitrary text, read in the minibuffer using the current buffer's input
method, and returned as a string (@pxref{Input Methods,,, emacs, The GNU
Emacs Manual}).  Prompt.

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@item n
A number read with the minibuffer.  If the input is not a number, the
user is asked to try again.  The prefix argument, if any, is not used.
Prompt.

@item N
@cindex raw prefix argument usage
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The numeric prefix argument; but if there is no prefix argument, read a
number as with @kbd{n}.  Requires a number.  @xref{Prefix Command
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Arguments}.  Prompt.
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@item p
@cindex numeric prefix argument usage
The numeric prefix argument.  (Note that this @samp{p} is lower case.)
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No I/O.
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@item P
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The raw prefix argument.  (Note that this @samp{P} is upper case.)  No
I/O.
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@item r
@cindex region argument
Point and the mark, as two numeric arguments, smallest first.  This is
the only code letter that specifies two successive arguments rather than
one.  No I/O.

@item s
Arbitrary text, read in the minibuffer and returned as a string
(@pxref{Text from Minibuffer}).  Terminate the input with either
@key{LFD} or @key{RET}.  (@kbd{C-q} may be used to include either of
these characters in the input.)  Prompt.

@item S
An interned symbol whose name is read in the minibuffer.  Any whitespace
character terminates the input.  (Use @kbd{C-q} to include whitespace in
the string.)  Other characters that normally terminate a symbol (e.g.,
parentheses and brackets) do not do so here.  Prompt.

@item v
A variable declared to be a user option (i.e., satisfying the predicate
@code{user-variable-p}).  @xref{High-Level Completion}.  Existing,
Completion, Prompt.

@item x
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A Lisp object, specified with its read syntax, terminated with a
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@key{LFD} or @key{RET}.  The object is not evaluated.  @xref{Object from
Minibuffer}.  Prompt.

@item X
@cindex evaluated expression argument
A Lisp form is read as with @kbd{x}, but then evaluated so that its
value becomes the argument for the command.  Prompt.
@end table

@node Interactive Examples
@comment  node-name,  next,  previous,  up
@subsection Examples of Using @code{interactive}
@cindex examples of using @code{interactive}
@cindex @code{interactive}, examples of using 

  Here are some examples of @code{interactive}:

@example
@group
(defun foo1 ()              ; @r{@code{foo1} takes no arguments,}
    (interactive)           ;   @r{just moves forward two words.}
    (forward-word 2))
     @result{} foo1
@end group

@group
(defun foo2 (n)             ; @r{@code{foo2} takes one argument,}
    (interactive "p")       ;   @r{which is the numeric prefix.}
    (forward-word (* 2 n)))
     @result{} foo2
@end group

@group
(defun foo3 (n)             ; @r{@code{foo3} takes one argument,}
    (interactive "nCount:") ;   @r{which is read with the Minibuffer.}
    (forward-word (* 2 n)))
     @result{} foo3
@end group

@group
(defun three-b (b1 b2 b3)
  "Select three existing buffers.
Put them into three windows, selecting the last one."
@end group
    (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:")
    (delete-other-windows)
    (split-window (selected-window) 8)
    (switch-to-buffer b1)
    (other-window 1)
    (split-window (selected-window) 8)
    (switch-to-buffer b2)
    (other-window 1)
    (switch-to-buffer b3))
     @result{} three-b
@group
(three-b "*scratch*" "declarations.texi" "*mail*")
     @result{} nil
@end group
@end example

@node Interactive Call
@section Interactive Call
@cindex interactive call

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  After the command loop has translated a key sequence into a command it
invokes that command using the function @code{command-execute}.  If the
command is a function, @code{command-execute} calls
@code{call-interactively}, which reads the arguments and calls the
command.  You can also call these functions yourself.
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@defun commandp object
Returns @code{t} if @var{object} is suitable for calling interactively;
that is, if @var{object} is a command.  Otherwise, returns @code{nil}.  

The interactively callable objects include strings and vectors (treated
as keyboard macros), lambda expressions that contain a top-level call to
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@code{interactive}, byte-code function objects made from such lambda
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expressions, autoload objects that are declared as interactive
(non-@code{nil} fourth argument to @code{autoload}), and some of the
primitive functions.
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A symbol is @code{commandp} if its function definition is
@code{commandp}.

Keys and keymaps are not commands.  Rather, they are used to look up
commands (@pxref{Keymaps}).

See @code{documentation} in @ref{Accessing Documentation}, for a
realistic example of using @code{commandp}.
@end defun

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@defun call-interactively command &optional record-flag keys
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This function calls the interactively callable function @var{command},
reading arguments according to its interactive calling specifications.
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An error is signaled if @var{command} is not a function or if it cannot
be called interactively (i.e., is not a command).  Note that keyboard
macros (strings and vectors) are not accepted, even though they are
considered commands, because they are not functions.
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@cindex record command history
If @var{record-flag} is non-@code{nil}, then this command and its
arguments are unconditionally added to the list @code{command-history}.
Otherwise, the command is added only if it uses the minibuffer to read
an argument.  @xref{Command History}.
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The argument @var{keys}, if given, specifies the sequence of events to
use if the command inquires which events were used to invoke it.
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@end defun

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@defun command-execute command &optional record-flag keys
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@cindex keyboard macro execution
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This function executes @var{command}.  The argument @var{command} must
satisfy the @code{commandp} predicate; i.e., it must be an interactively
callable function or a keyboard macro.
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A string or vector as @var{command} is executed with
@code{execute-kbd-macro}.  A function is passed to
@code{call-interactively}, along with the optional @var{record-flag}.

A symbol is handled by using its function definition in its place.  A
symbol with an @code{autoload} definition counts as a command if it was
declared to stand for an interactively callable function.  Such a
definition is handled by loading the specified library and then
rechecking the definition of the symbol.
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The argument @var{keys}, if given, specifies the sequence of events to
use if the command inquires which events were used to invoke it.
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@end defun

@deffn Command execute-extended-command prefix-argument
@cindex read command name
This function reads a command name from the minibuffer using
@code{completing-read} (@pxref{Completion}).  Then it uses
@code{command-execute} to call the specified command.  Whatever that
command returns becomes the value of @code{execute-extended-command}.

@cindex execute with prefix argument
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If the command asks for a prefix argument, it receives the value
@var{prefix-argument}.  If @code{execute-extended-command} is called
interactively, the current raw prefix argument is used for
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@var{prefix-argument}, and thus passed on to whatever command is run.

@c !!! Should this be @kindex?
@cindex @kbd{M-x}
@code{execute-extended-command} is the normal definition of @kbd{M-x},
so it uses the string @w{@samp{M-x }} as a prompt.  (It would be better
to take the prompt from the events used to invoke
@code{execute-extended-command}, but that is painful to implement.)  A
description of the value of the prefix argument, if any, also becomes
part of the prompt.

@example
@group
(execute-extended-command 1)
---------- Buffer: Minibuffer ----------
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1 M-x forward-word RET
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---------- Buffer: Minibuffer ----------
     @result{} t
@end group
@end example
@end deffn

@defun interactive-p
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This function returns @code{t} if the containing function (the one whose
code includes the call to @code{interactive-p}) was called
interactively, with the function @code{call-interactively}.  (It makes
no difference whether @code{call-interactively} was called from Lisp or
directly from the editor command loop.)  If the containing function was
called by Lisp evaluation (or with @code{apply} or @code{funcall}), then
it was not called interactively.
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The most common use of @code{interactive-p} is for deciding whether to
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print an informative message.  As a special exception,
@code{interactive-p} returns @code{nil} whenever a keyboard macro is
being run.  This is to suppress the informative messages and speed
execution of the macro.

For example:

@example
@group
(defun foo ()
  (interactive)
  (and (interactive-p)
       (message "foo")))
     @result{} foo
@end group

@group
(defun bar ()
  (interactive)
  (setq foobar (list (foo) (interactive-p))))
     @result{} bar
@end group

@group
;; @r{Type @kbd{M-x foo}.}
     @print{} foo
@end group

@group
;; @r{Type @kbd{M-x bar}.}
;; @r{This does not print anything.}
@end group

@group
foobar
     @result{} (nil t)
@end group
@end example
@end defun

@node Command Loop Info
@comment  node-name,  next,  previous,  up
@section Information from the Command Loop

The editor command loop sets several Lisp variables to keep status
records for itself and for commands that are run.  

@defvar last-command
This variable records the name of the previous command executed by the
command loop (the one before the current command).  Normally the value
is a symbol with a function definition, but this is not guaranteed.

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The value is copied from @code{this-command} when a command returns to
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the command loop, except when the command has specified a prefix
argument for the following command.
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This variable is always local to the current terminal and cannot be
buffer-local.  @xref{Multiple Displays}.
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@end defvar

@defvar this-command
@cindex current command
This variable records the name of the command now being executed by
the editor command loop.  Like @code{last-command}, it is normally a symbol
with a function definition.

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The command loop sets this variable just before running a command, and
copies its value into @code{last-command} when the command finishes
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(unless the command specified a prefix argument for the following
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command).
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@cindex kill command repetition
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Some commands set this variable during their execution, as a flag for
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whatever command runs next.  In particular, the functions for killing text
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set @code{this-command} to @code{kill-region} so that any kill commands
immediately following will know to append the killed text to the
previous kill.
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@end defvar

If you do not want a particular command to be recognized as the previous
command in the case where it got an error, you must code that command to
prevent this.  One way is to set @code{this-command} to @code{t} at the
beginning of the command, and set @code{this-command} back to its proper
value at the end, like this:

@example
(defun foo (args@dots{})
  (interactive @dots{})
  (let ((old-this-command this-command))
    (setq this-command t)
    @r{@dots{}do the work@dots{}}
    (setq this-command old-this-command)))
@end example

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@noindent
We do not bind @code{this-command} with @code{let} because that would
restore the old value in case of error---a feature of @code{let} which
in this case does precisely what we want to avoid.

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@defun this-command-keys
This function returns a string or vector containing the key sequence
that invoked the present command, plus any previous commands that
generated the prefix argument for this command.  The value is a string
if all those events were characters.  @xref{Input Events}.

@example
@group
(this-command-keys)
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;; @r{Now use @kbd{C-u C-x C-e} to evaluate that.}
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     @result{} "^U^X^E"
@end group
@end example
@end defun

@defvar last-nonmenu-event
This variable holds the last input event read as part of a key
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sequence, not counting events resulting from mouse menus.
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One use of this variable is for telling @code{x-popup-menu} where to pop
up a menu.
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@end defvar

@defvar last-command-event
@defvarx last-command-char
This variable is set to the last input event that was read by the
command loop as part of a command.  The principal use of this variable
is in @code{self-insert-command}, which uses it to decide which
character to insert.

@example
@group
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last-command-event
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;; @r{Now use @kbd{C-u C-x C-e} to evaluate that.}
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     @result{} 5
@end group
@end example

@noindent
The value is 5 because that is the @sc{ASCII} code for @kbd{C-e}.

The alias @code{last-command-char} exists for compatibility with
Emacs version 18.
@end defvar

@c Emacs 19 feature
@defvar last-event-frame
This variable records which frame the last input event was directed to.
Usually this is the frame that was selected when the event was
generated, but if that frame has redirected input focus to another
frame, the value is the frame to which the event was redirected.
@xref{Input Focus}.
@end defvar

@node Input Events
@section Input Events
@cindex events
@cindex input events

The Emacs command loop reads a sequence of @dfn{input events} that
represent keyboard or mouse activity.  The events for keyboard activity
are characters or symbols; mouse events are always lists.  This section
describes the representation and meaning of input events in detail.

@defun eventp object
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This function returns non-@code{nil} if @var{object} is an input event.
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A symbol 
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@end defun

@menu
* Keyboard Events::		Ordinary characters--keys with symbols on them.
* Function Keys::		Function keys--keys with names, not symbols.
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* Mouse Events::                Overview of mouse events.
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* Click Events::		Pushing and releasing a mouse button.
* Drag Events::			Moving the mouse before releasing the button.
* Button-Down Events::		A button was pushed and not yet released.
* Repeat Events::               Double and triple click (or drag, or down).
* Motion Events::		Just moving the mouse, not pushing a button.
* Focus Events::		Moving the mouse between frames.
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* Misc Events::                 Other events window systems can generate.
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* Event Examples::		Examples of the lists for mouse events.
* Classifying Events::		Finding the modifier keys in an event symbol.
				Event types.
* Accessing Events::		Functions to extract info from events.
* Strings of Events::           Special considerations for putting
				  keyboard character events in a string.
@end menu

@node Keyboard Events
@subsection Keyboard Events

There are two kinds of input you can get from the keyboard: ordinary
keys, and function keys.  Ordinary keys correspond to characters; the
events they generate are represented in Lisp as characters.  In Emacs
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versions 18 and earlier, characters were the only events.  The event
type of a character event is the character itself (an integer); 
see @ref{Classifying Events}.
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@cindex modifier bits (of input character)
@cindex basic code (of input character)
An input character event consists of a @dfn{basic code} between 0 and
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524287, plus any or all of these @dfn{modifier bits}:
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@table @asis
@item meta
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The
@iftex
$2^{27}$
@end iftex
@ifinfo
2**27
@end ifinfo
bit in the character code indicates a character
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typed with the meta key held down.

@item control
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The
@iftex
$2^{26}$
@end iftex
@ifinfo
2**26
@end ifinfo
bit in the character code indicates a non-@sc{ASCII}
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control character.

@sc{ASCII} control characters such as @kbd{C-a} have special basic
codes of their own, so Emacs needs no special bit to indicate them.
Thus, the code for @kbd{C-a} is just 1.

But if you type a control combination not in @sc{ASCII}, such as
@kbd{%} with the control key, the numeric value you get is the code
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for @kbd{%} plus
@iftex
$2^{26}$
@end iftex
@ifinfo
2**26
@end ifinfo
(assuming the terminal supports non-@sc{ASCII}
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control characters).

@item shift
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The
@iftex
$2^{25}$
@end iftex
@ifinfo
2**25
@end ifinfo
bit in the character code indicates an @sc{ASCII} control
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character typed with the shift key held down.

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For letters, the basic code itself indicates upper versus lower case;
for digits and punctuation, the shift key selects an entirely different
character with a different basic code.  In order to keep within the
@sc{ASCII} character set whenever possible, Emacs avoids using the
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@iftex
$2^{25}$
@end iftex
@ifinfo
2**25
@end ifinfo
bit for those characters.
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However, @sc{ASCII} provides no way to distinguish @kbd{C-A} from
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@kbd{C-a}, so Emacs uses the
@iftex
$2^{25}$
@end iftex
@ifinfo
2**25
@end ifinfo
bit in @kbd{C-A} and not in
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@kbd{C-a}.

@item hyper
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The
@iftex
$2^{24}$
@end iftex
@ifinfo
2**24
@end ifinfo
bit in the character code indicates a character
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typed with the hyper key held down.

@item super
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The
@iftex
$2^{23}$
@end iftex
@ifinfo
2**23
@end ifinfo
bit in the character code indicates a character
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typed with the super key held down.

@item alt
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The
@iftex
$2^{22}$
@end iftex
@ifinfo
2**22
@end ifinfo
bit in the character code indicates a character typed with
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the alt key held down.  (On some terminals, the key labeled @key{ALT}
is actually the meta key.)
@end table

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  It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
@code{event-modifiers} (@pxref{Classifying Events}).  When making key
bindings, you can use the read syntax for characters with modifier bits
(@samp{\C-}, @samp{\M-}, and so on).  For making key bindings with
@code{define-key}, you can use lists such as @code{(control hyper ?x)} to
specify the characters (@pxref{Changing Key Bindings}).  The function
@code{event-convert-list} converts such a list into an event type
(@pxref{Classifying Events}).
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@node Function Keys
@subsection Function Keys

@cindex function keys
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Most keyboards also have @dfn{function keys}---keys that have names or
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symbols that are not characters.  Function keys are represented in Emacs
Lisp as symbols; the symbol's name is the function key's label, in lower
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case.  For example, pressing a key labeled @key{F1} places the symbol
@code{f1} in the input stream.
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The event type of a function key event is the event symbol itself.
@xref{Classifying Events}.
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Here are a few special cases in the symbol-naming convention for
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function keys:

@table @asis
@item @code{backspace}, @code{tab}, @code{newline}, @code{return}, @code{delete}
These keys correspond to common @sc{ASCII} control characters that have
special keys on most keyboards.

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In @sc{ASCII}, @kbd{C-i} and @key{TAB} are the same character.  If the
terminal can distinguish between them, Emacs conveys the distinction to
Lisp programs by representing the former as the integer 9, and the
latter as the symbol @code{tab}.
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Most of the time, it's not useful to distinguish the two.  So normally
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@code{function-key-map} (@pxref{Translating Input}) is set up to map
@code{tab} into 9.  Thus, a key binding for character code 9 (the
character @kbd{C-i}) also applies to @code{tab}.  Likewise for the other
symbols in this group.  The function @code{read-char} likewise converts
these events into characters.
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In @sc{ASCII}, @key{BS} is really @kbd{C-h}.  But @code{backspace}
converts into the character code 127 (@key{DEL}), not into code 8
(@key{BS}).  This is what most users prefer.

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@item @code{left}, @code{up}, @code{right}, @code{down}
Cursor arrow keys
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@item @code{kp-add}, @code{kp-decimal}, @code{kp-divide}, @dots{}
Keypad keys (to the right of the regular keyboard).
@item @code{kp-0}, @code{kp-1}, @dots{}
Keypad keys with digits.
@item @code{kp-f1}, @code{kp-f2}, @code{kp-f3}, @code{kp-f4}
Keypad PF keys.
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@item @code{kp-home}, @code{kp-left}, @code{kp-up}, @code{kp-right}, @code{kp-down}
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Keypad arrow keys.  Emacs normally translates these into the
corresponding non-keypad keys @code{home}, @code{left}, @dots{}
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@item @code{kp-prior}, @code{kp-next}, @code{kp-end}, @code{kp-begin}, @code{kp-insert}, @code{kp-delete}
Additional keypad duplicates of keys ordinarily found elsewhere.  Emacs
normally translates these into the like-named non-keypad keys.
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@end table

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You can use the modifier keys @key{ALT}, @key{CTRL}, @key{HYPER},
@key{META}, @key{SHIFT}, and @key{SUPER} with function keys.  The way to
represent them is with prefixes in the symbol name:
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@table @samp
@item A-
The alt modifier.
@item C-
The control modifier.
@item H-
The hyper modifier.
@item M-
The meta modifier.
@item S-
The shift modifier.
@item s-
The super modifier.
@end table

Thus, the symbol for the key @key{F3} with @key{META} held down is
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@code{M-f3}.  When you use more than one prefix, we recommend you
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write them in alphabetical order; but the order does not matter in
arguments to the key-binding lookup and modification functions.

@node Mouse Events
@subsection Mouse Events

Emacs supports four kinds of mouse events: click events, drag events,
button-down events, and motion events.  All mouse events are represented
as lists.  The @sc{car} of the list is the event type; this says which
mouse button was involved, and which modifier keys were used with it.
The event type can also distinguish double or triple button presses
(@pxref{Repeat Events}).  The rest of the list elements give position
and time information.

For key lookup, only the event type matters: two events of the same type
necessarily run the same command.  The command can access the full
values of these events using the @samp{e} interactive code.
@xref{Interactive Codes}.

A key sequence that starts with a mouse event is read using the keymaps
of the buffer in the window that the mouse was in, not the current
buffer.  This does not imply that clicking in a window selects that
window or its buffer---that is entirely under the control of the command
binding of the key sequence.
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@node Click Events
@subsection Click Events
@cindex click event
@cindex mouse click event

When the user presses a mouse button and releases it at the same
location, that generates a @dfn{click} event.  Mouse click events have
this form:

@example
(@var{event-type}
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 (@var{window} @var{buffer-pos} (@var{x} . @var{y}) @var{timestamp})
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 @var{click-count})
@end example

Here is what the elements normally mean:

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@table @asis
@item @var{event-type}
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This is a symbol that indicates which mouse button was used.  It is
one of the symbols @code{mouse-1}, @code{mouse-2}, @dots{}, where the
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buttons are numbered left to right.
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You can also use prefixes @samp{A-}, @samp{C-}, @samp{H-}, @samp{M-},
@samp{S-} and @samp{s-} for modifiers alt, control, hyper, meta, shift
and super, just as you would with function keys.

This symbol also serves as the event type of the event.  Key bindings
describe events by their types; thus, if there is a key binding for
@code{mouse-1}, that binding would apply to all events whose
@var{event-type} is @code{mouse-1}.

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@item @var{window}
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This is the window in which the click occurred.

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@item @var{x}, @var{y}
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These are the pixel-denominated coordinates of the click, relative to
the top left corner of @var{window}, which is @code{(0 . 0)}.
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@item @var{buffer-pos}
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This is the buffer position of the character clicked on.

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@item @var{timestamp}
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This is the time at which the event occurred, in milliseconds.  (Since
this value wraps around the entire range of Emacs Lisp integers in about
five hours, it is useful only for relating the times of nearby events.)

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@item @var{click-count}
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This is the number of rapid repeated presses so far of the same mouse
button.  @xref{Repeat Events}.
@end table

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The meanings of @var{buffer-pos}, @var{x} and @var{y} are somewhat
different when the event location is in a special part of the screen,
such as the mode line or a scroll bar.
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If the location is in a scroll bar, then @var{buffer-pos} is the symbol
@code{vertical-scroll-bar} or @code{horizontal-scroll-bar}, and the pair
@code{(@var{x} . @var{y})} is replaced with a pair @code{(@var{portion}
. @var{whole})}, where @var{portion} is the distance of the click from
the top or left end of the scroll bar, and @var{whole} is the length of
the entire scroll bar.

If the position is on a mode line or the vertical line separating
@var{window} from its neighbor to the right, then @var{buffer-pos} is
the symbol @code{mode-line} or @code{vertical-line}.  For the mode line,
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@var{y} does not have meaningful data.  For the vertical line, @var{x}
does not have meaningful data.
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In one special case, @var{buffer-pos} is a list containing a symbol (one
of the symbols listed above) instead of just the symbol.  This happens
after the imaginary prefix keys for the event are inserted into the
input stream.  @xref{Key Sequence Input}.
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@node Drag Events
@subsection Drag Events
@cindex drag event
@cindex mouse drag event

With Emacs, you can have a drag event without even changing your
clothes.  A @dfn{drag event} happens every time the user presses a mouse
button and then moves the mouse to a different character position before
releasing the button.  Like all mouse events, drag events are
represented in Lisp as lists.  The lists record both the starting mouse
position and the final position, like this:

@example
(@var{event-type}
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 (@var{window1} @var{buffer-pos1} (@var{x1} . @var{y1}) @var{timestamp1})
 (@var{window2} @var{buffer-pos2} (@var{x2} . @var{y2}) @var{timestamp2})
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 @var{click-count})
@end example

For a drag event, the name of the symbol @var{event-type} contains the
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prefix @samp{drag-}.  For example, dragging the mouse with button 2 held
down generates a @code{drag-mouse-2} event.  The second and third
elements of the event give the starting and ending position of the drag.
Aside from that, the data have the same meanings as in a click event
(@pxref{Click Events}).  You can access the second element of any mouse
event in the same way, with no need to distinguish drag events from
others.
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The @samp{drag-} prefix follows the modifier key prefixes such as
@samp{C-} and @samp{M-}.

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If @code{read-key-sequence} receives a drag event that has no key
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binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position.  This means that you don't have to distinguish between click
and drag events unless you want to.

@node Button-Down Events
@subsection Button-Down Events
@cindex button-down event

Click and drag events happen when the user releases a mouse button.
They cannot happen earlier, because there is no way to distinguish a
click from a drag until the button is released.

If you want to take action as soon as a button is pressed, you need to
handle @dfn{button-down} events.@footnote{Button-down is the
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conservative antithesis of drag.}  These occur as soon as a button is
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pressed.  They are represented by lists that look exactly like click
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events (@pxref{Click Events}), except that the @var{event-type} symbol
name contains the prefix @samp{down-}.  The @samp{down-} prefix follows
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modifier key prefixes such as @samp{C-} and @samp{M-}.

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The function @code{read-key-sequence}, and therefore the Emacs command
loop as well, ignore any button-down events that don't have command
bindings.  This means that you need not worry about defining button-down
events unless you want them to do something.  The usual reason to define
a button-down event is so that you can track mouse motion (by reading
motion events) until the button is released.  @xref{Motion Events}.
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@node Repeat Events
@subsection Repeat Events
@cindex repeat events
@cindex double-click events
@cindex triple-click events

If you press the same mouse button more than once in quick succession
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without moving the mouse, Emacs generates special @dfn{repeat} mouse
events for the second and subsequent presses.
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The most common repeat events are @dfn{double-click} events.  Emacs
generates a double-click event when you click a button twice; the event
happens when you release the button (as is normal for all click
events).

The event type of a double-click event contains the prefix
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@samp{double-}.  Thus, a double click on the second mouse button with
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@key{meta} held down comes to the Lisp program as
@code{M-double-mouse-2}.  If a double-click event has no binding, the
binding of the corresponding ordinary click event is used to execute
it.  Thus, you need not pay attention to the double click feature 
unless you really want to.

When the user performs a double click, Emacs generates first an ordinary
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click event, and then a double-click event.  Therefore, you must design
the command binding of the double click event to assume that the
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single-click command has already run.  It must produce the desired
results of a double click, starting from the results of a single click.

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This is convenient, if the meaning of a double click somehow ``builds
on'' the meaning of a single click---which is recommended user interface
design practice for double clicks.
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If you click a button, then press it down again and start moving the
mouse with the button held down, then you get a @dfn{double-drag} event
when you ultimately release the button.  Its event type contains
@samp{double-drag} instead of just @samp{drag}.  If a double-drag event
has no binding, Emacs looks for an alternate binding as if the event
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were an ordinary drag.
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Before the double-click or double-drag event, Emacs generates a
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@dfn{double-down} event when the user presses the button down for the
second time.  Its event type contains @samp{double-down} instead of just
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@samp{down}.  If a double-down event has no binding, Emacs looks for an
alternate binding as if the event were an ordinary button-down event.
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If it finds no binding that way either, the double-down event is
ignored.
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To summarize, when you click a button and then press it again right
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away, Emacs generates a down event and a click event for the first
click, a double-down event when you press the button again, and finally
either a double-click or a double-drag event.
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If you click a button twice and then press it again, all in quick
succession, Emacs generates a @dfn{triple-down} event, followed by
either a @dfn{triple-click} or a @dfn{triple-drag}.  The event types of
these events contain @samp{triple} instead of @samp{double}.  If any
triple event has no binding, Emacs uses the binding that it would use
for the corresponding double event.

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If you click a button three or more times and then press it again, the
events for the presses beyond the third are all triple events.  Emacs
does not have separate event types for quadruple, quintuple, etc.@:
events.  However, you can look at the event list to find out precisely
how many times the button was pressed.
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@defun event-click-count event
This function returns the number of consecutive button presses that led
up to @var{event}.  If @var{event} is a double-down, double-click or
double-drag event, the value is 2.  If @var{event} is a triple event,
the value is 3 or greater.  If @var{event} is an ordinary mouse event
(not a repeat event), the value is 1.
@end defun

@defvar double-click-time
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To generate repeat events, successive mouse button presses must be at
the same screen position, and the number of milliseconds between
successive button presses must be less than the value of
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@code{double-click-time}.  Setting @code{double-click-time} to
@code{nil} disables multi-click detection entirely.  Setting it to
@code{t} removes the time limit; Emacs then detects multi-clicks by
position only.
@end defvar

@node Motion Events
@subsection Motion Events
@cindex motion event
@cindex mouse motion events

Emacs sometimes generates @dfn{mouse motion} events to describe motion
of the mouse without any button activity.  Mouse motion events are
represented by lists that look like this:

@example
(mouse-movement
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 (@var{window} @var{buffer-pos} (@var{x} . @var{y}) @var{timestamp}))
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@end example

The second element of the list describes the current position of the
mouse, just as in a click event (@pxref{Click Events}).

The special form @code{track-mouse} enables generation of motion events
within its body.  Outside of @code{track-mouse} forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear.

@defspec track-mouse body@dots{}
This special form executes @var{body}, with generation of mouse motion
events enabled.  Typically @var{body} would use @code{read-event}
to read the motion events and modify the display accordingly.

When the user releases the button, that generates a click event.
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Typically, @var{body} should return when it sees the click event, and
discard that event.
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@end defspec

@node Focus Events
@subsection Focus Events
@cindex focus event

Window systems provide general ways for the user to control which window
gets keyboard input.  This choice of window is called the @dfn{focus}.
When the user does something to switch between Emacs frames, that
generates a @dfn{focus event}.  The normal definition of a focus event,
in the global keymap, is to select a new frame within Emacs, as the user
would expect.  @xref{Input Focus}.

Focus events are represented in Lisp as lists that look like this:

@example
(switch-frame @var{new-frame})
@end example

@noindent
where @var{new-frame} is the frame switched to.

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Most X window managers are set up so that just moving the mouse into a
window is enough to set the focus there.  Emacs appears to do this,
because it changes the cursor to solid in the new frame.  However, there
is no need for the Lisp program to know about the focus change until
some other kind of input arrives.  So Emacs generates a focus event only
when the user actually types a keyboard key or presses a mouse button in
the new frame; just moving the mouse between frames does not generate a
focus event.
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A focus event in the middle of a key sequence would garble the
sequence.  So Emacs never generates a focus event in the middle of a key
sequence.  If the user changes focus in the middle of a key
sequence---that is, after a prefix key---then Emacs reorders the events
so that the focus event comes either before or after the multi-event key
sequence, and not within it.

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@node Misc Events
@subsection Miscellaneous Window System Events

A few other event types represent occurrences within the window system.

@table @code
@cindex @code{delete-frame} event
@item (delete-frame (@var{frame}))
This kind of event indicates that the user gave the window manager
a command to delete a particular window, which happens to be an Emacs frame.

The standard definition of the @code{delete-frame} event is to delete @var{frame}.

@cindex @code{iconify-frame} event
@item (iconify-frame (@var{frame}))
This kind of event indicates that the user iconified @var{frame} using
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the window manager.  Its standard definition is @code{ignore}; since the
frame has already been iconified, Emacs has no work to do.  The purpose
of this event type is so that you can keep track of such events if you
want to.
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@cindex @code{make-frame-visible} event
@item (make-frame-visible (@var{frame}))
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This kind of event indicates that the user deiconified @var{frame} using
the window manager.  Its standard definition is @code{ignore}; since the
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frame has already been made visible, Emacs has no work to do.
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@end table

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  If one of these events arrives in the middle of a key sequence---that
is, after a prefix key---then Emacs reorders the events so that this
event comes either before or after the multi-event key sequence, not
within it.

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@node Event Examples
@subsection Event Examples

If the user presses and releases the left mouse button over the same
location, that generates a sequence of events like this:

@smallexample
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
(mouse-1      (#<window 18 on NEWS> 2613 (0 . 38) -864180))
@end smallexample

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While holding the control key down, the user might hold down the
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second mouse button, and drag the mouse from one line to the next.
That produces two events, as shown here:

@smallexample
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
                (#<window 18 on NEWS> 3510 (0 . 28) -729648))
@end smallexample

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While holding down the meta and shift keys, the user might press the
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second mouse button on the window's mode line, and then drag the mouse
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into another window.  That produces a pair of events like these:
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@smallexample
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
                  (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
                   -453816))
@end smallexample

@node Classifying Events
@subsection Classifying Events
@cindex event type

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  Every event has an @dfn{event type}, which classifies the event for
key binding purposes.  For a keyboard event, the event type equals the
event value; thus, the event type for a character is the character, and
the event type for a function key symbol is the symbol itself.  For
events that are lists, the event type is the symbol in the @sc{car} of
the list.  Thus, the event type is always a symbol or a character.
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  Two events of the same type are equivalent where key bindings are
concerned; thus, they always run the same command.  That does not
necessarily mean they do the same things, however, as some commands look
at the whole event to decide what to do.  For example, some commands use
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the location of a mouse event to decide where in the buffer to act.
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  Sometimes broader classifications of events are useful.  For example,
you might want to ask whether an event involved the @key{META} key,
regardless of which other key or mouse button was used.

  The functions @code{event-modifiers} and @code{event-basic-type} are
provided to get such information conveniently.

@defun event-modifiers event
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This function returns a list of the modifiers that @var{event} has.  The
modifiers are symbols; they include @code{shift}, @code{control},
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@code{meta}, @code{alt}, @code{hyper} and @code{super}.  In addition,
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the modifiers list of a mouse event symbol always contains one of
@code{click}, @code{drag}, and @code{down}.

The argument @var{event} may be an entire event object, or just an event
type.

Here are some examples:
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@example
(event-modifiers ?a)
     @result{} nil
(event-modifiers ?\C-a)
     @result{} (control)
(event-modifiers ?\C-%)
     @result{} (control)
(event-modifiers ?\C-\S-a)
     @result{} (control shift)
(event-modifiers 'f5)
     @result{} nil
(event-modifiers 's-f5)
     @result{} (super)
(event-modifiers 'M-S-f5)
     @result{} (meta shift)
(event-modifiers 'mouse-1)
     @result{} (click)
(event-modifiers 'down-mouse-1)
     @result{} (down)
@end example

The modifiers list for a click event explicitly contains @code{click},
but the event symbol name itself does not contain @samp{click}.
@end defun

@defun event-basic-type event
This function returns the key or mouse button that @var{event}
describes, with all modifiers removed.  For example:

@example
(event-basic-type ?a)
     @result{} 97
(event-basic-type ?A)
     @result{} 97
(event-basic-type ?\C-a)
     @result{} 97
(event-basic-type ?\C-\S-a)
     @result{} 97
(event-basic-type 'f5)
     @result{} f5
(event-basic-type 's-f5)
     @result{} f5
(event-basic-type 'M-S-f5)
     @result{} f5
(event-basic-type 'down-mouse-1)
     @result{} mouse-1
@end example
@end defun

@defun mouse-movement-p object
This function returns non-@code{nil} if @var{object} is a mouse movement
event.
@end defun

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@defun event-convert-list list
This function converts a list of modifier names and a basic event type
to an event type which specifies all of them.  For example,

@example
(event-convert-list '(control ?a))
     @result{} 1
(event-convert-list '(control meta ?a))
     @result{} -134217727
(event-convert-list '(control super f1))
     @result{} C-s-f1
@end example
@end defun

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@node Accessing Events
@subsection Accessing Events

  This section describes convenient functions for accessing the data in
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a mouse button or motion event.
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  These two functions return the starting or ending position of a
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mouse-button event.  The position is a list of this form:

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@example
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(@var{window} @var{buffer-position} (@var{x} . @var{y}) @var{timestamp})
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@end example
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@defun event-start event
This returns the starting position of @var{event}.

If @var{event} is a click or button-down event, this returns the
location of the event.  If @var{event} is a drag event, this returns the
drag's starting position.
@end defun

@defun event-end event
This returns the ending position of @var{event}.

If @var{event} is a drag event, this returns the position where the user
released the mouse button.  If @var{event} is a click or button-down
event, the value is actually the starting position, which is the only
position such events have.
@end defun

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  These five functions take a position as described above, and return
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various parts of it.
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@defun posn-window position
Return the window that @var{position} is in.
@end defun

@defun posn-point position
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Return the buffer position in @var{position}.  This is an integer.
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@end defun

@defun posn-x-y position
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Return the pixel-based x and y coordinates in @var{position}, as a cons
cell @code{(@var{x} . @var{y})}.
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@end defun

@defun posn-col-row position
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Return the row and column (in units of characters) of @var{position}, as
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a cons cell @code{(@var{col} . @var{row})}.  These are computed from the
@var{x} and @var{y} values actually found in @var{position}.
@end defun

@defun posn-timestamp position
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Return the timestamp in @var{position}.
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@end defun

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@defun scroll-bar-event-ratio event
This function returns the fractional vertical position of a scroll bar
event within the scroll bar.  The value is a cons cell
@code{(@var{portion} . @var{whole})} containing two integers whose ratio
is the fractional position.
@end defun

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@defun scroll-bar-scale ratio total
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This function multiplies (in effect) @var{ratio} by @var{total},
rounding the result to an integer.  The argument @var{ratio} is not a
number, but rather a pair @code{(@var{num} . @var{denom})}---typically a
value returned by @code{scroll-bar-event-ratio}.
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This function is handy for scaling a position on a scroll bar into a
buffer position.  Here's how to do that:
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@example
(+ (point-min)
   (scroll-bar-scale
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      (posn-x-y (event-start event))
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      (- (point-max) (point-min))))
@end example
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