2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000, 2001,
4 @c 2002, 2005 Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/display
7 @node Display, System Interface, Processes, Top
10 This chapter describes a number of features related to the display
11 that Emacs presents to the user.
14 * Refresh Screen:: Clearing the screen and redrawing everything on it.
15 * Forcing Redisplay:: Forcing redisplay.
16 * Truncation:: Folding or wrapping long text lines.
17 * The Echo Area:: Displaying messages at the bottom of the screen.
18 * Warnings:: Displaying warning messages for the user.
19 * Invisible Text:: Hiding part of the buffer text.
20 * Selective Display:: Hiding part of the buffer text (the old way).
21 * Temporary Displays:: Displays that go away automatically.
22 * Overlays:: Use overlays to highlight parts of the buffer.
23 * Width:: How wide a character or string is on the screen.
24 * Line Height:: Controlling the height of lines.
25 * Faces:: A face defines a graphics style for text characters:
27 * Fringes:: Controlling window fringes.
28 * Scroll Bars:: Controlling vertical scroll bars.
29 * Pointer Shape:: Controlling the mouse pointer shape.
30 * Display Property:: Enabling special display features.
31 * Images:: Displaying images in Emacs buffers.
32 * Buttons:: Adding clickable buttons to Emacs buffers.
33 * Blinking:: How Emacs shows the matching open parenthesis.
34 * Inverse Video:: Specifying how the screen looks.
35 * Usual Display:: The usual conventions for displaying nonprinting chars.
36 * Display Tables:: How to specify other conventions.
37 * Beeping:: Audible signal to the user.
38 * Window Systems:: Which window system is being used.
42 @section Refreshing the Screen
44 The function @code{redraw-frame} clears and redisplays the entire
45 contents of a given frame (@pxref{Frames}). This is useful if the
49 @defun redraw-frame frame
50 This function clears and redisplays frame @var{frame}.
53 Even more powerful is @code{redraw-display}:
55 @deffn Command redraw-display
56 This function clears and redisplays all visible frames.
59 This function calls for redisplay of certain windows, the next time
60 redisplay is done, but does not clear them first.
62 @defun force-window-update &optional object
63 This function forces redisplay of some or all windows. If
64 @var{object} is a window, it forces redisplay of that window. If
65 @var{object} is a buffer or buffer name, it forces redisplay of all
66 windows displaying that buffer. If @var{object} is @code{nil} (or
67 omitted), it forces redisplay of all windows.
70 Processing user input takes absolute priority over redisplay. If you
71 call these functions when input is available, they do nothing
72 immediately, but a full redisplay does happen eventually---after all the
73 input has been processed.
75 Normally, suspending and resuming Emacs also refreshes the screen.
76 Some terminal emulators record separate contents for display-oriented
77 programs such as Emacs and for ordinary sequential display. If you are
78 using such a terminal, you might want to inhibit the redisplay on
81 @defvar no-redraw-on-reenter
82 @cindex suspend (cf. @code{no-redraw-on-reenter})
83 @cindex resume (cf. @code{no-redraw-on-reenter})
84 This variable controls whether Emacs redraws the entire screen after it
85 has been suspended and resumed. Non-@code{nil} means there is no need
86 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
89 @node Forcing Redisplay
90 @section Forcing Redisplay
91 @cindex forcing redisplay
93 Emacs redisplay normally stops if input arrives, and does not happen
94 at all if input is available before it starts. Most of the time, this
95 is exactly what you want. However, you can prevent preemption by
96 binding @code{redisplay-dont-pause} to a non-@code{nil} value.
98 @tindex redisplay-dont-pause
99 @defvar redisplay-dont-pause
100 If this variable is non-@code{nil}, pending input does not
101 prevent or halt redisplay; redisplay occurs, and finishes,
102 regardless of whether input is available.
105 You can request a display update, but only if no input is pending,
106 with @code{(sit-for 0)}. To force a display update even when input is
110 (let ((redisplay-dont-pause t))
116 @cindex line wrapping
117 @cindex continuation lines
118 @cindex @samp{$} in display
119 @cindex @samp{\} in display
121 When a line of text extends beyond the right edge of a window, the
122 line can either be continued on the next screen line, or truncated to
123 one screen line. The additional screen lines used to display a long
124 text line are called @dfn{continuation} lines. Normally, a @samp{$} in
125 the rightmost column of the window indicates truncation; a @samp{\} on
126 the rightmost column indicates a line that ``wraps'' onto the next line,
127 which is also called @dfn{continuing} the line. (The display table can
128 specify alternative indicators; see @ref{Display Tables}.)
130 On a window system display, the @samp{$} and @samp{\} indicators are
131 replaced with arrow images displayed in the window fringes
134 Note that continuation is different from filling; continuation happens
135 on the screen only, not in the buffer contents, and it breaks a line
136 precisely at the right margin, not at a word boundary. @xref{Filling}.
138 @defopt truncate-lines
139 This buffer-local variable controls how Emacs displays lines that extend
140 beyond the right edge of the window. The default is @code{nil}, which
141 specifies continuation. If the value is non-@code{nil}, then these
144 If the variable @code{truncate-partial-width-windows} is non-@code{nil},
145 then truncation is always used for side-by-side windows (within one
146 frame) regardless of the value of @code{truncate-lines}.
149 @defopt default-truncate-lines
150 This variable is the default value for @code{truncate-lines}, for
151 buffers that do not have buffer-local values for it.
154 @defopt truncate-partial-width-windows
155 This variable controls display of lines that extend beyond the right
156 edge of the window, in side-by-side windows (@pxref{Splitting Windows}).
157 If it is non-@code{nil}, these lines are truncated; otherwise,
158 @code{truncate-lines} says what to do with them.
161 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
162 a window, that forces truncation.
164 If your buffer contains @emph{very} long lines, and you use
165 continuation to display them, just thinking about them can make Emacs
166 redisplay slow. The column computation and indentation functions also
167 become slow. Then you might find it advisable to set
168 @code{cache-long-line-scans} to @code{t}.
170 @defvar cache-long-line-scans
171 If this variable is non-@code{nil}, various indentation and motion
172 functions, and Emacs redisplay, cache the results of scanning the
173 buffer, and consult the cache to avoid rescanning regions of the buffer
174 unless they are modified.
176 Turning on the cache slows down processing of short lines somewhat.
178 This variable is automatically buffer-local in every buffer.
182 @section The Echo Area
183 @cindex error display
186 The @dfn{echo area} is used for displaying error messages
187 (@pxref{Errors}), for messages made with the @code{message} primitive,
188 and for echoing keystrokes. It is not the same as the minibuffer,
189 despite the fact that the minibuffer appears (when active) in the same
190 place on the screen as the echo area. The @cite{GNU Emacs Manual}
191 specifies the rules for resolving conflicts between the echo area and
192 the minibuffer for use of that screen space (@pxref{Minibuffer,, The
193 Minibuffer, emacs, The GNU Emacs Manual}).
195 You can write output in the echo area by using the Lisp printing
196 functions with @code{t} as the stream (@pxref{Output Functions}), or
200 * Displaying Messages:: Explicitly displaying text in the echo area.
201 * Progress:: Informing user about progress of a long operation.
202 * Logging Messages:: Echo area messages are logged for the user.
203 * Echo Area Customization:: Controlling the echo area.
206 @node Displaying Messages
207 @subsection Displaying Messages in the Echo Area
209 This section describes the functions for explicitly producing echo
210 area messages. Many other Emacs features display messages there, too.
212 @defun message string &rest arguments
213 This function displays a message in the echo area. The
214 argument @var{string} is similar to a C language @code{printf} control
215 string. See @code{format} in @ref{Formatting Strings}, for the details
216 on the conversion specifications. @code{message} returns the
219 In batch mode, @code{message} prints the message text on the standard
220 error stream, followed by a newline.
222 If @var{string}, or strings among the @var{arguments}, have @code{face}
223 text properties, these affect the way the message is displayed.
226 If @var{string} is @code{nil}, @code{message} clears the echo area; if
227 the echo area has been expanded automatically, this brings it back to
228 its normal size. If the minibuffer is active, this brings the
229 minibuffer contents back onto the screen immediately.
233 (message "Minibuffer depth is %d."
235 @print{} Minibuffer depth is 0.
236 @result{} "Minibuffer depth is 0."
240 ---------- Echo Area ----------
241 Minibuffer depth is 0.
242 ---------- Echo Area ----------
246 To automatically display a message in the echo area or in a pop-buffer,
247 depending on its size, use @code{display-message-or-buffer} (see below).
250 @tindex with-temp-message
251 @defmac with-temp-message message &rest body
252 This construct displays a message in the echo area temporarily, during
253 the execution of @var{body}. It displays @var{message}, executes
254 @var{body}, then returns the value of the last body form while restoring
255 the previous echo area contents.
258 @defun message-or-box string &rest arguments
259 This function displays a message like @code{message}, but may display it
260 in a dialog box instead of the echo area. If this function is called in
261 a command that was invoked using the mouse---more precisely, if
262 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
263 @code{nil} or a list---then it uses a dialog box or pop-up menu to
264 display the message. Otherwise, it uses the echo area. (This is the
265 same criterion that @code{y-or-n-p} uses to make a similar decision; see
266 @ref{Yes-or-No Queries}.)
268 You can force use of the mouse or of the echo area by binding
269 @code{last-nonmenu-event} to a suitable value around the call.
272 @defun message-box string &rest arguments
273 This function displays a message like @code{message}, but uses a dialog
274 box (or a pop-up menu) whenever that is possible. If it is impossible
275 to use a dialog box or pop-up menu, because the terminal does not
276 support them, then @code{message-box} uses the echo area, like
280 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
281 @tindex display-message-or-buffer
282 This function displays the message @var{message}, which may be either a
283 string or a buffer. If it is shorter than the maximum height of the
284 echo area, as defined by @code{max-mini-window-height}, it is displayed
285 in the echo area, using @code{message}. Otherwise,
286 @code{display-buffer} is used to show it in a pop-up buffer.
288 Returns either the string shown in the echo area, or when a pop-up
289 buffer is used, the window used to display it.
291 If @var{message} is a string, then the optional argument
292 @var{buffer-name} is the name of the buffer used to display it when a
293 pop-up buffer is used, defaulting to @samp{*Message*}. In the case
294 where @var{message} is a string and displayed in the echo area, it is
295 not specified whether the contents are inserted into the buffer anyway.
297 The optional arguments @var{not-this-window} and @var{frame} are as for
298 @code{display-buffer}, and only used if a buffer is displayed.
301 @defun current-message
302 This function returns the message currently being displayed in the
303 echo area, or @code{nil} if there is none.
307 @subsection Reporting Operation Progress
308 @cindex progress reporting
310 When an operation can take a while to finish, you should inform the
311 user about the progress it makes. This way the user can estimate
312 remaining time and clearly see that Emacs is busy working, not hung.
314 Functions listed in this section provide simple and efficient way of
315 reporting operation progress. Here is a working example that does
319 (let ((progress-reporter
320 (make-progress-reporter "Collecting mana for Emacs..."
324 (progress-reporter-update progress-reporter k))
325 (progress-reporter-done progress-reporter))
328 @defun make-progress-reporter message min-value max-value &optional current-value min-change min-time
329 This function creates and returns a @dfn{progress reporter}---an
330 object you will use as an argument for all other functions listed
331 here. The idea is to precompute as much data as possible to make
332 progress reporting very fast.
334 When this progress reporter is subsequently used, it will display
335 @var{message} in the echo area, followed by progress percentage.
336 @var{message} is treated as a simple string. If you need it to depend
337 on a filename, for instance, use @code{format} before calling this
340 @var{min-value} and @var{max-value} arguments stand for starting and
341 final states of your operation. For instance, if you scan a buffer,
342 they should be the results of @code{point-min} and @code{point-max}
343 correspondingly. It is required that @var{max-value} is greater than
344 @var{min-value}. If you create progress reporter when some part of
345 the operation has already been completed, then specify
346 @var{current-value} argument. But normally you should omit it or set
347 it to @code{nil}---it will default to @var{min-value} then.
349 Remaining arguments control the rate of echo area updates. Progress
350 reporter will wait for at least @var{min-change} more percents of the
351 operation to be completed before printing next message.
352 @var{min-time} specifies the minimum time in seconds to pass between
353 successive prints. It can be fractional. Depending on Emacs and
354 system capabilities, progress reporter may or may not respect this
355 last argument or do it with varying precision. Default value for
356 @var{min-change} is 1 (one percent), for @var{min-time}---0.2
359 This function calls @code{progress-reporter-update}, so the first
360 message is printed immediately.
363 @defun progress-reporter-update reporter value
364 This function does the main work of reporting progress of your
365 operation. It displays the message of @var{reporter}, followed by
366 progress percentage determined by @var{value}. If percentage is zero,
367 or close enough according to the @var{min-change} and @var{min-time}
368 arguments, then it is omitted from the output.
370 @var{reporter} must be the result of a call to
371 @code{make-progress-reporter}. @var{value} specifies the current
372 state of your operation and must be between @var{min-value} and
373 @var{max-value} (inclusive) as passed to
374 @code{make-progress-reporter}. For instance, if you scan a buffer,
375 then @var{value} should be the result of a call to @code{point}.
377 This function respects @var{min-change} and @var{min-time} as passed
378 to @code{make-progress-reporter} and so does not output new messages
379 on every invocation. It is thus very fast and normally you should not
380 try to reduce the number of calls to it: resulting overhead will most
381 likely negate your effort.
384 @defun progress-reporter-force-update reporter value &optional new-message
385 This function is similar to @code{progress-reporter-update} except
386 that it prints a message in the echo area unconditionally.
388 The first two arguments have the same meaning as for
389 @code{progress-reporter-update}. Optional @var{new-message} allows
390 you to change the message of the @var{reporter}. Since this functions
391 always updates the echo area, such a change will be immediately
392 presented to the user.
395 @defun progress-reporter-done reporter
396 This function should be called when the operation is finished. It
397 prints the message of @var{reporter} followed by word ``done'' in the
400 You should always call this function and not hope for
401 @code{progress-reporter-update} to print ``100%.'' Firstly, it may
402 never print it, there are many good reasons for this not to happen.
403 Secondly, ``done'' is more explicit.
406 @defmac dotimes-with-progress-reporter (var count [result]) message body...
407 This is a convenience macro that works the same way as @code{dotimes}
408 does, but also reports loop progress using the functions described
409 above. It allows you to save some typing.
411 You can rewrite the example in the beginning of this node using
415 (dotimes-with-progress-reporter
417 "Collecting some mana for Emacs..."
422 @node Logging Messages
423 @subsection Logging Messages in @samp{*Messages*}
424 @cindex logging echo-area messages
426 Almost all the messages displayed in the echo area are also recorded
427 in the @samp{*Messages*} buffer so that the user can refer back to
428 them. This includes all the messages that are output with
431 @defopt message-log-max
432 This variable specifies how many lines to keep in the @samp{*Messages*}
433 buffer. The value @code{t} means there is no limit on how many lines to
434 keep. The value @code{nil} disables message logging entirely. Here's
435 how to display a message and prevent it from being logged:
438 (let (message-log-max)
443 To make @samp{*Messages*} more convenient for the user, the logging
444 facility combines successive identical messages. It also combines
445 successive related messages for the sake of two cases: question
446 followed by answer, and a series of progress messages.
448 A ``question followed by an answer'' means two messages like the
449 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
450 and the second is @samp{@var{question}...@var{answer}}. The first
451 message conveys no additional information beyond what's in the second,
452 so logging the second message discards the first from the log.
454 A ``series of progress messages'' means successive messages like
455 those produced by @code{make-progress-reporter}. They have the form
456 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
457 time, while @var{how-far} varies. Logging each message in the series
458 discards the previous one, provided they are consecutive.
460 The functions @code{make-progress-reporter} and @code{y-or-n-p}
461 don't have to do anything special to activate the message log
462 combination feature. It operates whenever two consecutive messages
463 are logged that share a common prefix ending in @samp{...}.
465 @node Echo Area Customization
466 @subsection Echo Area Customization
468 These variables control details of how the echo area works.
470 @defvar cursor-in-echo-area
471 This variable controls where the cursor appears when a message is
472 displayed in the echo area. If it is non-@code{nil}, then the cursor
473 appears at the end of the message. Otherwise, the cursor appears at
474 point---not in the echo area at all.
476 The value is normally @code{nil}; Lisp programs bind it to @code{t}
477 for brief periods of time.
480 @defvar echo-area-clear-hook
481 This normal hook is run whenever the echo area is cleared---either by
482 @code{(message nil)} or for any other reason.
485 @defvar echo-keystrokes
486 This variable determines how much time should elapse before command
487 characters echo. Its value must be an integer or floating point number,
489 number of seconds to wait before echoing. If the user types a prefix
490 key (such as @kbd{C-x}) and then delays this many seconds before
491 continuing, the prefix key is echoed in the echo area. (Once echoing
492 begins in a key sequence, all subsequent characters in the same key
493 sequence are echoed immediately.)
495 If the value is zero, then command input is not echoed.
498 @defopt max-mini-window-height
499 This variable specifies the maximum height for resizing minibuffer
500 windows. If a float, it specifies a fraction of the height of the
501 frame. If an integer, it specifies a number of lines.
504 @defvar message-truncate-lines
505 Normally, displaying a long message resizes the echo area to display
506 the entire message. But if the variable @code{message-truncate-lines}
507 is non-@code{nil}, the echo area does not resize, and the message is
508 truncated to fit it, as in Emacs 20 and before.
512 @section Reporting Warnings
515 @dfn{Warnings} are a facility for a program to inform the user of a
516 possible problem, but continue running.
519 * Warning Basics:: Warnings concepts and functions to report them.
520 * Warning Variables:: Variables programs bind to customize their warnings.
521 * Warning Options:: Variables users set to control display of warnings.
525 @subsection Warning Basics
526 @cindex severity level
528 Every warning has a textual message, which explains the problem for
529 the user, and a @dfn{severity level} which is a symbol. Here are the
530 possible severity levels, in order of decreasing severity, and their
535 A problem that will seriously impair Emacs operation soon
536 if you do not attend to it promptly.
538 A report of data or circumstances that are inherently wrong.
540 A report of data or circumstances that are not inherently wrong, but
541 raise suspicion of a possible problem.
543 A report of information that may be useful if you are debugging.
546 When your program encounters invalid input data, it can either
547 signal a Lisp error by calling @code{error} or @code{signal} or report
548 a warning with severity @code{:error}. Signaling a Lisp error is the
549 easiest thing to do, but it means the program cannot continue
550 processing. If you want to take the trouble to implement a way to
551 continue processing despite the bad data, then reporting a warning of
552 severity @code{:error} is the right way to inform the user of the
553 problem. For instance, the Emacs Lisp byte compiler can report an
554 error that way and continue compiling other functions. (If the
555 program signals a Lisp error and then handles it with
556 @code{condition-case}, the user won't see the error message; it could
557 show the message to the user by reporting it as a warning.)
560 Each warning has a @dfn{warning type} to classify it. The type is a
561 list of symbols. The first symbol should be the custom group that you
562 use for the program's user options. For example, byte compiler
563 warnings use the warning type @code{(bytecomp)}. You can also
564 subcategorize the warnings, if you wish, by using more symbols in the
567 @defun display-warning type message &optional level buffer-name
568 This function reports a warning, using @var{message} as the message
569 and @var{type} as the warning type. @var{level} should be the
570 severity level, with @code{:warning} being the default.
572 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
573 for logging the warning. By default, it is @samp{*Warnings*}.
576 @defun lwarn type level message &rest args
577 This function reports a warning using the value of @code{(format
578 @var{message} @var{args}...)} as the message. In other respects it is
579 equivalent to @code{display-warning}.
582 @defun warn message &rest args
583 This function reports a warning using the value of @code{(format
584 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
585 type, and @code{:warning} as the severity level. It exists for
586 compatibility only; we recommend not using it, because you should
587 specify a specific warning type.
590 @node Warning Variables
591 @subsection Warning Variables
593 Programs can customize how their warnings appear by binding
594 the variables described in this section.
596 @defvar warning-levels
597 This list defines the meaning and severity order of the warning
598 severity levels. Each element defines one severity level,
599 and they are arranged in order of decreasing severity.
601 Each element has the form @code{(@var{level} @var{string}
602 @var{function})}, where @var{level} is the severity level it defines.
603 @var{string} specifies the textual description of this level.
604 @var{string} should use @samp{%s} to specify where to put the warning
605 type information, or it can omit the @samp{%s} so as not to include
608 The optional @var{function}, if non-@code{nil}, is a function to call
609 with no arguments, to get the user's attention.
611 Normally you should not change the value of this variable.
614 @defvar warning-prefix-function
615 If non-@code{nil}, the value is a function to generate prefix text for
616 warnings. Programs can bind the variable to a suitable function.
617 @code{display-warning} calls this function with the warnings buffer
618 current, and the function can insert text in it. That text becomes
619 the beginning of the warning message.
621 The function is called with two arguments, the severity level and its
622 entry in @code{warning-levels}. It should return a list to use as the
623 entry (this value need not be an actual member of
624 @code{warning-levels}). By constructing this value, the function can
625 change the severity of the warning, or specify different handling for
626 a given severity level.
628 If the variable's value is @code{nil} then there is no function
632 @defvar warning-series
633 Programs can bind this variable to @code{t} to say that the next
634 warning should begin a series. When several warnings form a series,
635 that means to leave point on the first warning of the series, rather
636 than keep moving it for each warning so that it appears on the last one.
637 The series ends when the local binding is unbound and
638 @code{warning-series} becomes @code{nil} again.
640 The value can also be a symbol with a function definition. That is
641 equivalent to @code{t}, except that the next warning will also call
642 the function with no arguments with the warnings buffer current. The
643 function can insert text which will serve as a header for the series
646 Once a series has begun, the value is a marker which points to the
647 buffer position in the warnings buffer of the start of the series.
649 The variable's normal value is @code{nil}, which means to handle
650 each warning separately.
653 @defvar warning-fill-prefix
654 When this variable is non-@code{nil}, it specifies a fill prefix to
655 use for filling each warning's text.
658 @defvar warning-type-format
659 This variable specifies the format for displaying the warning type
660 in the warning message. The result of formatting the type this way
661 gets included in the message under the control of the string in the
662 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
663 If you bind it to @code{""} then the warning type won't appear at
667 @node Warning Options
668 @subsection Warning Options
670 These variables are used by users to control what happens
671 when a Lisp program reports a warning.
673 @defopt warning-minimum-level
674 This user option specifies the minimum severity level that should be
675 shown immediately to the user. The default is @code{:warning}, which
676 means to immediately display all warnings except @code{:debug}
680 @defopt warning-minimum-log-level
681 This user option specifies the minimum severity level that should be
682 logged in the warnings buffer. The default is @code{:warning}, which
683 means to log all warnings except @code{:debug} warnings.
686 @defopt warning-suppress-types
687 This list specifies which warning types should not be displayed
688 immediately for the user. Each element of the list should be a list
689 of symbols. If its elements match the first elements in a warning
690 type, then that warning is not displayed immediately.
693 @defopt warning-suppress-log-types
694 This list specifies which warning types should not be logged in the
695 warnings buffer. Each element of the list should be a list of
696 symbols. If it matches the first few elements in a warning type, then
697 that warning is not logged.
701 @section Invisible Text
703 @cindex invisible text
704 You can make characters @dfn{invisible}, so that they do not appear on
705 the screen, with the @code{invisible} property. This can be either a
706 text property (@pxref{Text Properties}) or a property of an overlay
707 (@pxref{Overlays}). Cursor motion also partly ignores these
708 characters; if the command loop finds point within them, it moves
709 point to the other side of them.
711 In the simplest case, any non-@code{nil} @code{invisible} property makes
712 a character invisible. This is the default case---if you don't alter
713 the default value of @code{buffer-invisibility-spec}, this is how the
714 @code{invisible} property works. You should normally use @code{t}
715 as the value of the @code{invisible} property if you don't plan
716 to set @code{buffer-invisibility-spec} yourself.
718 More generally, you can use the variable @code{buffer-invisibility-spec}
719 to control which values of the @code{invisible} property make text
720 invisible. This permits you to classify the text into different subsets
721 in advance, by giving them different @code{invisible} values, and
722 subsequently make various subsets visible or invisible by changing the
723 value of @code{buffer-invisibility-spec}.
725 Controlling visibility with @code{buffer-invisibility-spec} is
726 especially useful in a program to display the list of entries in a
727 database. It permits the implementation of convenient filtering
728 commands to view just a part of the entries in the database. Setting
729 this variable is very fast, much faster than scanning all the text in
730 the buffer looking for properties to change.
732 @defvar buffer-invisibility-spec
733 This variable specifies which kinds of @code{invisible} properties
734 actually make a character invisible. Setting this variable makes it
739 A character is invisible if its @code{invisible} property is
740 non-@code{nil}. This is the default.
743 Each element of the list specifies a criterion for invisibility; if a
744 character's @code{invisible} property fits any one of these criteria,
745 the character is invisible. The list can have two kinds of elements:
749 A character is invisible if its @code{invisible} property value
750 is @var{atom} or if it is a list with @var{atom} as a member.
752 @item (@var{atom} . t)
753 A character is invisible if its @code{invisible} property value
754 is @var{atom} or if it is a list with @var{atom} as a member.
755 Moreover, if this character is at the end of a line and is followed
756 by a visible newline, it displays an ellipsis.
761 Two functions are specifically provided for adding elements to
762 @code{buffer-invisibility-spec} and removing elements from it.
764 @defun add-to-invisibility-spec element
765 This function adds the element @var{element} to
766 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
767 was @code{t}, it changes to a list, @code{(t)}, so that text whose
768 @code{invisible} property is @code{t} remains invisible.
771 @defun remove-from-invisibility-spec element
772 This removes the element @var{element} from
773 @code{buffer-invisibility-spec}. This does nothing if @var{element}
777 A convention for use of @code{buffer-invisibility-spec} is that a
778 major mode should use the mode's own name as an element of
779 @code{buffer-invisibility-spec} and as the value of the
780 @code{invisible} property:
783 ;; @r{If you want to display an ellipsis:}
784 (add-to-invisibility-spec '(my-symbol . t))
785 ;; @r{If you don't want ellipsis:}
786 (add-to-invisibility-spec 'my-symbol)
788 (overlay-put (make-overlay beginning end)
789 'invisible 'my-symbol)
791 ;; @r{When done with the overlays:}
792 (remove-from-invisibility-spec '(my-symbol . t))
793 ;; @r{Or respectively:}
794 (remove-from-invisibility-spec 'my-symbol)
797 @vindex line-move-ignore-invisible
798 Ordinarily, functions that operate on text or move point do not care
799 whether the text is invisible. The user-level line motion commands
800 explicitly ignore invisible newlines if
801 @code{line-move-ignore-invisible} is non-@code{nil} (the default), but
802 only because they are explicitly programmed to do so.
804 However, if a command ends with point inside or immediately after
805 invisible text, the main editing loop moves point further forward or
806 further backward (in the same direction that the command already moved
807 it) until that condition is no longer true. Thus, if the command
808 moved point back into an invisible range, Emacs moves point back to
809 the beginning of that range, following the previous visible character.
810 If the command moved point forward into an invisible range, Emacs
811 moves point forward past the first visible character that follows the
814 Incremental search can make invisible overlays visible temporarily
815 and/or permanently when a match includes invisible text. To enable
816 this, the overlay should have a non-@code{nil}
817 @code{isearch-open-invisible} property. The property value should be a
818 function to be called with the overlay as an argument. This function
819 should make the overlay visible permanently; it is used when the match
820 overlaps the overlay on exit from the search.
822 During the search, such overlays are made temporarily visible by
823 temporarily modifying their invisible and intangible properties. If you
824 want this to be done differently for a certain overlay, give it an
825 @code{isearch-open-invisible-temporary} property which is a function.
826 The function is called with two arguments: the first is the overlay, and
827 the second is @code{nil} to make the overlay visible, or @code{t} to
828 make it invisible again.
830 @node Selective Display
831 @section Selective Display
832 @cindex selective display
834 @dfn{Selective display} refers to a pair of related features for
835 hiding certain lines on the screen.
837 The first variant, explicit selective display, is designed for use
838 in a Lisp program: it controls which lines are hidden by altering the
839 text. This kind of hiding in some ways resembles the effect of the
840 @code{invisible} property (@pxref{Invisible Text}), but the two
841 features are different and do not work the same way.
843 In the second variant, the choice of lines to hide is made
844 automatically based on indentation. This variant is designed to be a
847 The way you control explicit selective display is by replacing a
848 newline (control-j) with a carriage return (control-m). The text that
849 was formerly a line following that newline is now hidden. Strictly
850 speaking, it is temporarily no longer a line at all, since only
851 newlines can separate lines; it is now part of the previous line.
853 Selective display does not directly affect editing commands. For
854 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
855 into hidden text. However, the replacement of newline characters with
856 carriage return characters affects some editing commands. For
857 example, @code{next-line} skips hidden lines, since it searches only
858 for newlines. Modes that use selective display can also define
859 commands that take account of the newlines, or that control which
860 parts of the text are hidden.
862 When you write a selectively displayed buffer into a file, all the
863 control-m's are output as newlines. This means that when you next read
864 in the file, it looks OK, with nothing hidden. The selective display
865 effect is seen only within Emacs.
867 @defvar selective-display
868 This buffer-local variable enables selective display. This means that
869 lines, or portions of lines, may be made hidden.
873 If the value of @code{selective-display} is @code{t}, then the character
874 control-m marks the start of hidden text; the control-m, and the rest
875 of the line following it, are not displayed. This is explicit selective
879 If the value of @code{selective-display} is a positive integer, then
880 lines that start with more than that many columns of indentation are not
884 When some portion of a buffer is hidden, the vertical movement
885 commands operate as if that portion did not exist, allowing a single
886 @code{next-line} command to skip any number of hidden lines.
887 However, character movement commands (such as @code{forward-char}) do
888 not skip the hidden portion, and it is possible (if tricky) to insert
889 or delete text in an hidden portion.
891 In the examples below, we show the @emph{display appearance} of the
892 buffer @code{foo}, which changes with the value of
893 @code{selective-display}. The @emph{contents} of the buffer do not
898 (setq selective-display nil)
901 ---------- Buffer: foo ----------
908 ---------- Buffer: foo ----------
912 (setq selective-display 2)
915 ---------- Buffer: foo ----------
920 ---------- Buffer: foo ----------
925 @defvar selective-display-ellipses
926 If this buffer-local variable is non-@code{nil}, then Emacs displays
927 @samp{@dots{}} at the end of a line that is followed by hidden text.
928 This example is a continuation of the previous one.
932 (setq selective-display-ellipses t)
935 ---------- Buffer: foo ----------
940 ---------- Buffer: foo ----------
944 You can use a display table to substitute other text for the ellipsis
945 (@samp{@dots{}}). @xref{Display Tables}.
948 @node Temporary Displays
949 @section Temporary Displays
951 Temporary displays are used by Lisp programs to put output into a
952 buffer and then present it to the user for perusal rather than for
953 editing. Many help commands use this feature.
955 @defspec with-output-to-temp-buffer buffer-name forms@dots{}
956 This function executes @var{forms} while arranging to insert any output
957 they print into the buffer named @var{buffer-name}, which is first
958 created if necessary, and put into Help mode. Finally, the buffer is
959 displayed in some window, but not selected.
961 If the @var{forms} do not change the major mode in the output buffer,
962 so that it is still Help mode at the end of their execution, then
963 @code{with-output-to-temp-buffer} makes this buffer read-only at the
964 end, and also scans it for function and variable names to make them
965 into clickable cross-references. @xref{Docstring hyperlinks, , Tips
966 for Documentation Strings}, in particular the item on hyperlinks in
967 documentation strings, for more details.
969 The string @var{buffer-name} specifies the temporary buffer, which
970 need not already exist. The argument must be a string, not a buffer.
971 The buffer is erased initially (with no questions asked), and it is
972 marked as unmodified after @code{with-output-to-temp-buffer} exits.
974 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
975 temporary buffer, then it evaluates the forms in @var{forms}. Output
976 using the Lisp output functions within @var{forms} goes by default to
977 that buffer (but screen display and messages in the echo area, although
978 they are ``output'' in the general sense of the word, are not affected).
979 @xref{Output Functions}.
981 Several hooks are available for customizing the behavior
982 of this construct; they are listed below.
984 The value of the last form in @var{forms} is returned.
988 ---------- Buffer: foo ----------
989 This is the contents of foo.
990 ---------- Buffer: foo ----------
994 (with-output-to-temp-buffer "foo"
996 (print standard-output))
997 @result{} #<buffer foo>
999 ---------- Buffer: foo ----------
1004 ---------- Buffer: foo ----------
1009 @defvar temp-buffer-show-function
1010 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1011 calls it as a function to do the job of displaying a help buffer. The
1012 function gets one argument, which is the buffer it should display.
1014 It is a good idea for this function to run @code{temp-buffer-show-hook}
1015 just as @code{with-output-to-temp-buffer} normally would, inside of
1016 @code{save-selected-window} and with the chosen window and buffer
1020 @defvar temp-buffer-setup-hook
1021 @tindex temp-buffer-setup-hook
1022 This normal hook is run by @code{with-output-to-temp-buffer} before
1023 evaluating @var{body}. When the hook runs, the temporary buffer is
1024 current. This hook is normally set up with a function to put the
1025 buffer in Help mode.
1028 @defvar temp-buffer-show-hook
1029 This normal hook is run by @code{with-output-to-temp-buffer} after
1030 displaying the temporary buffer. When the hook runs, the temporary buffer
1031 is current, and the window it was displayed in is selected. This hook
1032 is normally set up with a function to make the buffer read only, and
1033 find function names and variable names in it, provided the major mode
1037 @defun momentary-string-display string position &optional char message
1038 This function momentarily displays @var{string} in the current buffer at
1039 @var{position}. It has no effect on the undo list or on the buffer's
1040 modification status.
1042 The momentary display remains until the next input event. If the next
1043 input event is @var{char}, @code{momentary-string-display} ignores it
1044 and returns. Otherwise, that event remains buffered for subsequent use
1045 as input. Thus, typing @var{char} will simply remove the string from
1046 the display, while typing (say) @kbd{C-f} will remove the string from
1047 the display and later (presumably) move point forward. The argument
1048 @var{char} is a space by default.
1050 The return value of @code{momentary-string-display} is not meaningful.
1052 If the string @var{string} does not contain control characters, you can
1053 do the same job in a more general way by creating (and then subsequently
1054 deleting) an overlay with a @code{before-string} property.
1055 @xref{Overlay Properties}.
1057 If @var{message} is non-@code{nil}, it is displayed in the echo area
1058 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1059 default message says to type @var{char} to continue.
1061 In this example, point is initially located at the beginning of the
1066 ---------- Buffer: foo ----------
1067 This is the contents of foo.
1068 @point{}Second line.
1069 ---------- Buffer: foo ----------
1073 (momentary-string-display
1074 "**** Important Message! ****"
1076 "Type RET when done reading")
1081 ---------- Buffer: foo ----------
1082 This is the contents of foo.
1083 **** Important Message! ****Second line.
1084 ---------- Buffer: foo ----------
1086 ---------- Echo Area ----------
1087 Type RET when done reading
1088 ---------- Echo Area ----------
1097 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1098 the screen, for the sake of presentation features. An overlay is an
1099 object that belongs to a particular buffer, and has a specified
1100 beginning and end. It also has properties that you can examine and set;
1101 these affect the display of the text within the overlay.
1103 An overlays uses markers to record its beginning and end; thus,
1104 editing the text of the buffer adjusts the beginning and end of each
1105 overlay so that it stays with the text. When you create the overlay,
1106 you can specify whether text inserted at the beginning should be
1107 inside the overlay or outside, and likewise for the end of the overlay.
1110 * Managing Overlays:: Creating and moving overlays.
1111 * Overlay Properties:: How to read and set properties.
1112 What properties do to the screen display.
1113 * Finding Overlays:: Searching for overlays.
1116 @node Managing Overlays
1117 @subsection Managing Overlays
1119 This section describes the functions to create, delete and move
1120 overlays, and to examine their contents. Overlay changes are not
1121 recorded in the buffer's undo list, since the overlays are not
1122 part of the buffer's contents.
1124 @defun overlayp object
1125 This function returns @code{t} if @var{object} is an overlay.
1128 @defun make-overlay start end &optional buffer front-advance rear-advance
1129 This function creates and returns an overlay that belongs to
1130 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1131 and @var{end} must specify buffer positions; they may be integers or
1132 markers. If @var{buffer} is omitted, the overlay is created in the
1135 The arguments @var{front-advance} and @var{rear-advance} specify the
1136 insertion type for the start of the overlay and for the end of the
1137 overlay, respectively. @xref{Marker Insertion Types}. If
1138 @var{front-advance} is non-@code{nil}, text inserted at the beginning
1139 of the overlay is excluded from the overlay. If @var{read-advance} is
1140 non-@code{nil}, text inserted at the beginning of the overlay is
1141 included in the overlay.
1144 @defun overlay-start overlay
1145 This function returns the position at which @var{overlay} starts,
1149 @defun overlay-end overlay
1150 This function returns the position at which @var{overlay} ends,
1154 @defun overlay-buffer overlay
1155 This function returns the buffer that @var{overlay} belongs to. It
1156 returns @code{nil} if @var{overlay} has been deleted.
1159 @defun delete-overlay overlay
1160 This function deletes @var{overlay}. The overlay continues to exist as
1161 a Lisp object, and its property list is unchanged, but it ceases to be
1162 attached to the buffer it belonged to, and ceases to have any effect on
1165 A deleted overlay is not permanently disconnected. You can give it a
1166 position in a buffer again by calling @code{move-overlay}.
1169 @defun move-overlay overlay start end &optional buffer
1170 This function moves @var{overlay} to @var{buffer}, and places its bounds
1171 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1172 must specify buffer positions; they may be integers or markers.
1174 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1175 was already associated with; if @var{overlay} was deleted, it goes into
1178 The return value is @var{overlay}.
1180 This is the only valid way to change the endpoints of an overlay. Do
1181 not try modifying the markers in the overlay by hand, as that fails to
1182 update other vital data structures and can cause some overlays to be
1186 @defun remove-overlays &optional start end name value
1187 This function removes all the overlays between @var{start} and
1188 @var{end} whose property @var{name} has the value @var{value}. It can
1189 move the endpoints of the overlays in the region, or split them.
1191 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1192 the specified region. If @var{start} and/or @var{end} are omitted or
1193 @code{nil}, that means the beginning and end of the buffer respectively.
1194 Therefore, @code{(remove-overlays)} removes all the overlays in the
1198 Here are some examples:
1201 ;; @r{Create an overlay.}
1202 (setq foo (make-overlay 1 10))
1203 @result{} #<overlay from 1 to 10 in display.texi>
1208 (overlay-buffer foo)
1209 @result{} #<buffer display.texi>
1210 ;; @r{Give it a property we can check later.}
1211 (overlay-put foo 'happy t)
1213 ;; @r{Verify the property is present.}
1214 (overlay-get foo 'happy)
1216 ;; @r{Move the overlay.}
1217 (move-overlay foo 5 20)
1218 @result{} #<overlay from 5 to 20 in display.texi>
1223 ;; @r{Delete the overlay.}
1224 (delete-overlay foo)
1226 ;; @r{Verify it is deleted.}
1228 @result{} #<overlay in no buffer>
1229 ;; @r{A deleted overlay has no position.}
1234 (overlay-buffer foo)
1236 ;; @r{Undelete the overlay.}
1237 (move-overlay foo 1 20)
1238 @result{} #<overlay from 1 to 20 in display.texi>
1239 ;; @r{Verify the results.}
1244 (overlay-buffer foo)
1245 @result{} #<buffer display.texi>
1246 ;; @r{Moving and deleting the overlay does not change its properties.}
1247 (overlay-get foo 'happy)
1251 @node Overlay Properties
1252 @subsection Overlay Properties
1254 Overlay properties are like text properties in that the properties that
1255 alter how a character is displayed can come from either source. But in
1256 most respects they are different. @xref{Text Properties}, for comparison.
1258 Text properties are considered a part of the text; overlays and
1259 their properties are specifically considered not to be part of the
1260 text. Thus, copying text between various buffers and strings
1261 preserves text properties, but does not try to preserve overlays.
1262 Changing a buffer's text properties marks the buffer as modified,
1263 while moving an overlay or changing its properties does not. Unlike
1264 text property changes, overlay property changes are not recorded in
1265 the buffer's undo list.
1267 These functions read and set the properties of an overlay:
1269 @defun overlay-get overlay prop
1270 This function returns the value of property @var{prop} recorded in
1271 @var{overlay}, if any. If @var{overlay} does not record any value for
1272 that property, but it does have a @code{category} property which is a
1273 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1277 @defun overlay-put overlay prop value
1278 This function sets the value of property @var{prop} recorded in
1279 @var{overlay} to @var{value}. It returns @var{value}.
1282 @defun overlay-properties overlay
1283 This returns a copy of the property list of @var{overlay}.
1286 See also the function @code{get-char-property} which checks both
1287 overlay properties and text properties for a given character.
1288 @xref{Examining Properties}.
1290 Many overlay properties have special meanings; here is a table
1295 @kindex priority @r{(overlay property)}
1296 This property's value (which should be a nonnegative integer number)
1297 determines the priority of the overlay. The priority matters when two
1298 or more overlays cover the same character and both specify the same
1299 property; the one whose @code{priority} value is larger takes priority
1300 over the other. For the @code{face} property, the higher priority
1301 value does not completely replace the other; instead, its face
1302 attributes override the face attributes of the lower priority
1303 @code{face} property.
1305 Currently, all overlays take priority over text properties. Please
1306 avoid using negative priority values, as we have not yet decided just
1307 what they should mean.
1310 @kindex window @r{(overlay property)}
1311 If the @code{window} property is non-@code{nil}, then the overlay
1312 applies only on that window.
1315 @kindex category @r{(overlay property)}
1316 If an overlay has a @code{category} property, we call it the
1317 @dfn{category} of the overlay. It should be a symbol. The properties
1318 of the symbol serve as defaults for the properties of the overlay.
1321 @kindex face @r{(overlay property)}
1322 This property controls the way text is displayed---for example, which
1323 font and which colors. @xref{Faces}, for more information.
1325 In the simplest case, the value is a face name. It can also be a list;
1326 then each element can be any of these possibilities:
1330 A face name (a symbol or string).
1333 A property list of face attributes. This has the form (@var{keyword}
1334 @var{value} @dots{}), where each @var{keyword} is a face attribute
1335 name and @var{value} is a meaningful value for that attribute. With
1336 this feature, you do not need to create a face each time you want to
1337 specify a particular attribute for certain text. @xref{Face
1341 A cons cell of the form @code{(foreground-color . @var{color-name})} or
1342 @code{(background-color . @var{color-name})}. These elements specify
1343 just the foreground color or just the background color.
1345 @code{(foreground-color . @var{color-name})} has the same effect as
1346 @code{(:foreground @var{color-name})}; likewise for the background.
1350 @kindex mouse-face @r{(overlay property)}
1351 This property is used instead of @code{face} when the mouse is within
1352 the range of the overlay.
1355 @kindex display @r{(overlay property)}
1356 This property activates various features that change the
1357 way text is displayed. For example, it can make text appear taller
1358 or shorter, higher or lower, wider or narrower, or replaced with an image.
1359 @xref{Display Property}.
1362 @kindex help-echo @r{(overlay property)}
1363 If an overlay has a @code{help-echo} property, then when you move the
1364 mouse onto the text in the overlay, Emacs displays a help string in the
1365 echo area, or in the tooltip window. For details see @ref{Text
1368 @item modification-hooks
1369 @kindex modification-hooks @r{(overlay property)}
1370 This property's value is a list of functions to be called if any
1371 character within the overlay is changed or if text is inserted strictly
1374 The hook functions are called both before and after each change.
1375 If the functions save the information they receive, and compare notes
1376 between calls, they can determine exactly what change has been made
1379 When called before a change, each function receives four arguments: the
1380 overlay, @code{nil}, and the beginning and end of the text range to be
1383 When called after a change, each function receives five arguments: the
1384 overlay, @code{t}, the beginning and end of the text range just
1385 modified, and the length of the pre-change text replaced by that range.
1386 (For an insertion, the pre-change length is zero; for a deletion, that
1387 length is the number of characters deleted, and the post-change
1388 beginning and end are equal.)
1390 If these functions modify the buffer, they should bind
1391 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1392 avoid confusing the internal mechanism that calls these hooks.
1394 @item insert-in-front-hooks
1395 @kindex insert-in-front-hooks @r{(overlay property)}
1396 This property's value is a list of functions to be called before and
1397 after inserting text right at the beginning of the overlay. The calling
1398 conventions are the same as for the @code{modification-hooks} functions.
1400 @item insert-behind-hooks
1401 @kindex insert-behind-hooks @r{(overlay property)}
1402 This property's value is a list of functions to be called before and
1403 after inserting text right at the end of the overlay. The calling
1404 conventions are the same as for the @code{modification-hooks} functions.
1407 @kindex invisible @r{(overlay property)}
1408 The @code{invisible} property can make the text in the overlay
1409 invisible, which means that it does not appear on the screen.
1410 @xref{Invisible Text}, for details.
1413 @kindex intangible @r{(overlay property)}
1414 The @code{intangible} property on an overlay works just like the
1415 @code{intangible} text property. @xref{Special Properties}, for details.
1417 @item isearch-open-invisible
1418 This property tells incremental search how to make an invisible overlay
1419 visible, permanently, if the final match overlaps it. @xref{Invisible
1422 @item isearch-open-invisible-temporary
1423 This property tells incremental search how to make an invisible overlay
1424 visible, temporarily, during the search. @xref{Invisible Text}.
1427 @kindex before-string @r{(overlay property)}
1428 This property's value is a string to add to the display at the beginning
1429 of the overlay. The string does not appear in the buffer in any
1430 sense---only on the screen.
1433 @kindex after-string @r{(overlay property)}
1434 This property's value is a string to add to the display at the end of
1435 the overlay. The string does not appear in the buffer in any
1436 sense---only on the screen.
1439 @kindex evaporate @r{(overlay property)}
1440 If this property is non-@code{nil}, the overlay is deleted automatically
1441 if it becomes empty (i.e., if its length becomes zero). If you give
1442 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1446 @cindex keymap of character (and overlays)
1447 @kindex local-map @r{(overlay property)}
1448 If this property is non-@code{nil}, it specifies a keymap for a portion
1449 of the text. The property's value replaces the buffer's local map, when
1450 the character after point is within the overlay. @xref{Active Keymaps}.
1453 @kindex keymap @r{(overlay property)}
1454 The @code{keymap} property is similar to @code{local-map} but overrides the
1455 buffer's local map (and the map specified by the @code{local-map}
1456 property) rather than replacing it.
1459 @node Finding Overlays
1460 @subsection Searching for Overlays
1462 @defun overlays-at pos
1463 This function returns a list of all the overlays that cover the
1464 character at position @var{pos} in the current buffer. The list is in
1465 no particular order. An overlay contains position @var{pos} if it
1466 begins at or before @var{pos}, and ends after @var{pos}.
1468 To illustrate usage, here is a Lisp function that returns a list of the
1469 overlays that specify property @var{prop} for the character at point:
1472 (defun find-overlays-specifying (prop)
1473 (let ((overlays (overlays-at (point)))
1476 (let ((overlay (car overlays)))
1477 (if (overlay-get overlay prop)
1478 (setq found (cons overlay found))))
1479 (setq overlays (cdr overlays)))
1484 @defun overlays-in beg end
1485 This function returns a list of the overlays that overlap the region
1486 @var{beg} through @var{end}. ``Overlap'' means that at least one
1487 character is contained within the overlay and also contained within the
1488 specified region; however, empty overlays are included in the result if
1489 they are located at @var{beg}, or strictly between @var{beg} and @var{end}.
1492 @defun next-overlay-change pos
1493 This function returns the buffer position of the next beginning or end
1494 of an overlay, after @var{pos}. If there is none, it returns
1498 @defun previous-overlay-change pos
1499 This function returns the buffer position of the previous beginning or
1500 end of an overlay, before @var{pos}. If there is none, it returns
1504 Here's an easy way to use @code{next-overlay-change} to search for the
1505 next character which gets a non-@code{nil} @code{happy} property from
1506 either its overlays or its text properties (@pxref{Property Search}):
1509 (defun find-overlay-prop (prop)
1511 (while (and (not (eobp))
1512 (not (get-char-property (point) 'happy)))
1513 (goto-char (min (next-overlay-change (point))
1514 (next-single-property-change (point) 'happy))))
1521 Since not all characters have the same width, these functions let you
1522 check the width of a character. @xref{Primitive Indent}, and
1523 @ref{Screen Lines}, for related functions.
1525 @defun char-width char
1526 This function returns the width in columns of the character @var{char},
1527 if it were displayed in the current buffer and the selected window.
1530 @defun string-width string
1531 This function returns the width in columns of the string @var{string},
1532 if it were displayed in the current buffer and the selected window.
1535 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1536 This function returns the part of @var{string} that fits within
1537 @var{width} columns, as a new string.
1539 If @var{string} does not reach @var{width}, then the result ends where
1540 @var{string} ends. If one multi-column character in @var{string}
1541 extends across the column @var{width}, that character is not included in
1542 the result. Thus, the result can fall short of @var{width} but cannot
1545 The optional argument @var{start-column} specifies the starting column.
1546 If this is non-@code{nil}, then the first @var{start-column} columns of
1547 the string are omitted from the value. If one multi-column character in
1548 @var{string} extends across the column @var{start-column}, that
1549 character is not included.
1551 The optional argument @var{padding}, if non-@code{nil}, is a padding
1552 character added at the beginning and end of the result string, to extend
1553 it to exactly @var{width} columns. The padding character is used at the
1554 end of the result if it falls short of @var{width}. It is also used at
1555 the beginning of the result if one multi-column character in
1556 @var{string} extends across the column @var{start-column}.
1558 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1559 replace the end of @var{str} (including any padding) if it extends
1560 beyond @var{end-column}, unless the display width of @var{str} is
1561 equal to or less than the display width of @var{ellipsis}. If
1562 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1566 (truncate-string-to-width "\tab\t" 12 4)
1568 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1574 @section Line Height
1577 The total height of each display line consists of the height of the
1578 contents of the line, and additional vertical line spacing below the
1581 The height of the line contents is normally determined from the
1582 maximum height of any character or image on that display line,
1583 including the final newline if there is one. (A line that is
1584 continued doesn't include a final newline.) In the most common case,
1585 the line height equals the height of the default frame font.
1587 There are several ways to explicitly control or change the line
1588 height, either by specifying an absolute height for the display line,
1589 or by adding additional vertical space below one or all lines.
1591 @kindex line-height @r{(text property)}
1592 A newline can have a @code{line-height} text or overlay property
1593 that controls the total height of the display line ending in that
1596 If the property value is a list @code{(@var{height} @var{total})},
1597 then @var{height} is used as the actual property value for the
1598 @code{line-height}, and @var{total} specifies the total displayed
1599 height of the line, so the line spacing added below the line equals
1600 the @var{total} height minus the actual line height. In this case,
1601 the other ways to specify the line spacing are ignored.
1603 If the property value is @code{t}, the displayed height of the
1604 line is exactly what its contents demand; no line-spacing is added.
1605 This case is useful for tiling small images or image slices without
1606 adding blank areas between the images.
1608 If the property value is not @code{t}, it is a height spec. A height
1609 spec stands for a numeric height value; this height spec specifies the
1610 actual line height, @var{line-height}. There are several ways to
1611 write a height spec; here's how each of them translates into a numeric
1616 If the height spec is a positive integer, the height value is that integer.
1618 If the height spec is a float, @var{float}, the numeric height value
1619 is @var{float} times the frame's default line height.
1620 @item (@var{face} . @var{ratio})
1621 If the height spec is a cons of the format shown, the numeric height
1622 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1623 be any type of number, or @code{nil} which means a ratio of 1.
1624 If @var{face} is @code{t}, it refers to the current face.
1625 @item (nil . @var{ratio})
1626 If the height spec is a cons of the format shown, the numeric height
1627 is @var{ratio} times the height of the contents of the line.
1630 Thus, any valid non-@code{t} property value specifies a height in pixels,
1631 @var{line-height}, one way or another. If the line contents' height
1632 is less than @var{line-height}, Emacs adds extra vertical space above
1633 the line to achieve the total height @var{line-height}. Otherwise,
1634 @var{line-height} has no effect.
1636 If you don't specify the @code{line-height} property, the line's
1637 height consists of the contents' height plus the line spacing.
1638 There are several ways to specify the line spacing for different
1639 parts of Emacs text.
1641 @vindex default-line-spacing
1642 You can specify the line spacing for all lines in a frame with the
1643 @code{line-spacing} frame parameter, @xref{Window Frame Parameters}.
1644 However, if the variable @code{default-line-spacing} is
1645 non-@code{nil}, it overrides the frame's @code{line-spacing}
1646 parameter. An integer value specifies the number of pixels put below
1647 lines on window systems. A floating point number specifies the
1648 spacing relative to the frame's default line height.
1650 @vindex line-spacing
1651 You can specify the line spacing for all lines in a buffer via the
1652 buffer-local @code{line-spacing} variable. An integer value specifies
1653 the number of pixels put below lines on window systems. A floating
1654 point number specifies the spacing relative to the default frame line
1655 height. This overrides line spacings specified for the frame.
1657 @kindex line-spacing @r{(text property)}
1658 Finally, a newline can have a @code{line-spacing} text or overlay
1659 property that controls the height of the display line ending with that
1660 newline. The property value overrides the default frame line spacing
1661 and the buffer local @code{line-spacing} variable.
1663 One way or another, these mechanisms specify a Lisp value for the
1664 spacing of each line. The value is a height spec, and it translates
1665 into a Lisp value as described above. However, in this case the
1666 numeric height value specifies the line spacing, rather than the line
1673 A @dfn{face} is a named collection of graphical attributes: font
1674 family, foreground color, background color, optional underlining, and
1675 many others. Faces are used in Emacs to control the style of display of
1676 particular parts of the text or the frame.
1679 Each face has its own @dfn{face number}, which distinguishes faces at
1680 low levels within Emacs. However, for most purposes, you refer to
1681 faces in Lisp programs by the symbols that name them.
1684 This function returns @code{t} if @var{object} is a face name string
1685 or symbol (or if it is a vector of the kind used internally to record
1686 face data). It returns @code{nil} otherwise.
1689 Each face name is meaningful for all frames, and by default it has the
1690 same meaning in all frames. But you can arrange to give a particular
1691 face name a special meaning in one frame if you wish.
1694 * Standard Faces:: The faces Emacs normally comes with.
1695 * Defining Faces:: How to define a face with @code{defface}.
1696 * Face Attributes:: What is in a face?
1697 * Attribute Functions:: Functions to examine and set face attributes.
1698 * Displaying Faces:: How Emacs combines the faces specified for a character.
1699 * Font Selection:: Finding the best available font for a face.
1700 * Face Functions:: How to define and examine faces.
1701 * Auto Faces:: Hook for automatic face assignment.
1702 * Font Lookup:: Looking up the names of available fonts
1703 and information about them.
1704 * Fontsets:: A fontset is a collection of fonts
1705 that handle a range of character sets.
1708 @node Standard Faces
1709 @subsection Standard Faces
1711 This table lists all the standard faces and their uses. Most of them
1712 are used for displaying certain parts of the frames or certain kinds of
1713 text; you can control how those places look by customizing these faces.
1717 @kindex default @r{(face name)}
1718 This face is used for ordinary text.
1721 @kindex mode-line @r{(face name)}
1722 This face is used for the mode line of the selected window, and for
1723 menu bars when toolkit menus are not used.
1726 @kindex modeline @r{(face name)}
1727 This is an alias for the @code{mode-line} face, for compatibility with
1730 @item mode-line-inactive
1731 @kindex mode-line-inactive @r{(face name)}
1732 This face is used for mode lines of non-selected windows.
1733 This face inherits from @code{mode-line}, so changes
1734 in that face affect all windows.
1737 @kindex header-line @r{(face name)}
1738 This face is used for the header lines of windows that have them.
1741 This face controls the display of menus, both their colors and their
1742 font. (This works only on certain systems.)
1745 @kindex fringe @r{(face name)}
1746 This face controls the default colors of window fringes, the thin
1747 areas on either side that are used to display continuation and
1748 truncation glyphs. Other faces used to display bitmaps in the fringe
1749 are implicitly merged with this face.
1751 @item minibuffer-prompt
1752 @kindex minibuffer-prompt @r{(face name)}
1753 @vindex minibuffer-prompt-properties
1754 This face is used for the text of minibuffer prompts. By default,
1755 Emacs automatically adds this face to the value of
1756 @code{minibuffer-prompt-properties}, which is a list of text
1757 properties used to display the prompt text.
1760 @kindex scroll-bar @r{(face name)}
1761 This face controls the colors for display of scroll bars.
1764 @kindex tool-bar @r{(face name)}
1765 This face is used for display of the tool bar, if any.
1768 @kindex region @r{(face name)}
1769 This face is used for highlighting the region in Transient Mark mode.
1771 @item secondary-selection
1772 @kindex secondary-selection @r{(face name)}
1773 This face is used to show any secondary selection you have made.
1776 @kindex highlight @r{(face name)}
1777 This face is meant to be used for highlighting for various purposes.
1779 @item mode-line-highlight
1780 @kindex mode-line-highlight @r{(face name)}
1781 This face is used for highlighting something on @code{mode-line} or
1782 @code{header-line} for various purposes.
1784 @item trailing-whitespace
1785 @kindex trailing-whitespace @r{(face name)}
1786 This face is used to display excess whitespace at the end of a line,
1787 if @code{show-trailing-whitespace} is non-@code{nil}.
1790 @kindex escape-glyph @r{(face name)}
1791 This face is used to display control characters and escape glyphs.
1794 In contrast, these faces are provided to change the appearance of text
1795 in specific ways. You can use them on specific text, when you want
1796 the effects they produce.
1800 @kindex bold @r{(face name)}
1801 This face uses a bold font, if possible. It uses the bold variant of
1802 the frame's font, if it has one. It's up to you to choose a default
1803 font that has a bold variant, if you want to use one.
1806 @kindex italic @r{(face name)}
1807 This face uses the italic variant of the frame's font, if it has one.
1810 @kindex bold-italic @r{(face name)}
1811 This face uses the bold italic variant of the frame's font, if it has
1815 @kindex underline @r{(face name)}
1816 This face underlines text.
1819 @kindex fixed-pitch @r{(face name)}
1820 This face forces use of a particular fixed-width font.
1822 @item variable-pitch
1823 @kindex variable-pitch @r{(face name)}
1824 This face forces use of a particular variable-width font. It's
1825 reasonable to customize this to use a different variable-width font, if
1826 you like, but you should not make it a fixed-width font.
1829 @kindex shadow @r{(face name)}
1830 This face is used for making the text less noticeable than the
1831 surrounding ordinary text.
1834 @defvar show-trailing-whitespace
1835 @tindex show-trailing-whitespace
1836 If this variable is non-@code{nil}, Emacs uses the
1837 @code{trailing-whitespace} face to display any spaces and tabs at the
1841 @node Defining Faces
1842 @subsection Defining Faces
1844 The way to define a new face is with @code{defface}. This creates a
1845 kind of customization item (@pxref{Customization}) which the user can
1846 customize using the Customization buffer (@pxref{Easy Customization,,,
1847 emacs, The GNU Emacs Manual}).
1849 @defmac defface face spec doc [keyword value]...
1850 This declares @var{face} as a customizable face that defaults
1851 according to @var{spec}. You should not quote the symbol @var{face},
1852 and it should not end in @samp{-face} (that would be redundant). The
1853 argument @var{doc} specifies the face documentation. The keywords you
1854 can use in @code{defface} are the same as in @code{defgroup} and
1855 @code{defcustom} (@pxref{Common Keywords}).
1857 When @code{defface} executes, it defines the face according to
1858 @var{spec}, then uses any customizations that were read from the
1859 init file (@pxref{Init File}) to override that specification.
1861 The purpose of @var{spec} is to specify how the face should appear on
1862 different kinds of terminals. It should be an alist whose elements
1863 have the form @code{(@var{display} @var{atts})}. Each element's
1864 @sc{car}, @var{display}, specifies a class of terminals. (The first
1865 element, if it s @sc{car} is @code{default}, is special---it specifies
1866 defaults for the remaining elements). The element's @sc{cadr},
1867 @var{atts}, is a list of face attributes and their values; it
1868 specifies what the face should look like on that kind of terminal.
1869 The possible attributes are defined in the value of
1870 @code{custom-face-attributes}.
1872 The @var{display} part of an element of @var{spec} determines which
1873 frames the element matches. If more than one element of @var{spec}
1874 matches a given frame, the first element that matches is the one used
1875 for that frame. There are three possibilities for @var{display}:
1878 @item @code{default}
1879 This element of @var{spec} doesn't match any frames; instead, it
1880 specifies defaults that apply to all frames. This kind of element, if
1881 used, must be the first element of @var{spec}. Each of the following
1882 elements can override any or all of these defaults.
1885 This element of @var{spec} matches all frames. Therefore, any
1886 subsequent elements of @var{spec} are never used. Normally
1887 @code{t} is used in the last (or only) element of @var{spec}.
1890 If @var{display} is a list, each element should have the form
1891 @code{(@var{characteristic} @var{value}@dots{})}. Here
1892 @var{characteristic} specifies a way of classifying frames, and the
1893 @var{value}s are possible classifications which @var{display} should
1894 apply to. Here are the possible values of @var{characteristic}:
1898 The kind of window system the frame uses---either @code{graphic} (any
1899 graphics-capable display), @code{x}, @code{pc} (for the MS-DOS console),
1900 @code{w32} (for MS Windows 9X/NT), or @code{tty} (a non-graphics-capable
1904 What kinds of colors the frame supports---either @code{color},
1905 @code{grayscale}, or @code{mono}.
1908 The kind of background---either @code{light} or @code{dark}.
1911 An integer that represents the minimum number of colors the frame
1912 should support. This matches a frame if its
1913 @code{display-color-cells} value is at least the specified integer.
1916 Whether or not the frame can display the face attributes given in
1917 @var{value}@dots{} (@pxref{Face Attributes}). See the documentation
1918 for the function @code{display-supports-face-attributes-p} for more
1919 information on exactly how this testing is done. @xref{Display Face
1923 If an element of @var{display} specifies more than one @var{value} for a
1924 given @var{characteristic}, any of those values is acceptable. If
1925 @var{display} has more than one element, each element should specify a
1926 different @var{characteristic}; then @emph{each} characteristic of the
1927 frame must match one of the @var{value}s specified for it in
1932 Here's how the standard face @code{region} is defined:
1936 '((((class color) (min-colors 88) (background dark))
1937 :background "blue3")
1939 (((class color) (min-colors 88) (background light))
1940 :background "lightgoldenrod2")
1941 (((class color) (min-colors 16) (background dark))
1942 :background "blue3")
1943 (((class color) (min-colors 16) (background light))
1944 :background "lightgoldenrod2")
1945 (((class color) (min-colors 8))
1946 :background "blue" :foreground "white")
1947 (((type tty) (class mono))
1949 (t :background "gray"))
1951 "Basic face for highlighting the region."
1952 :group 'basic-faces)
1956 Internally, @code{defface} uses the symbol property
1957 @code{face-defface-spec} to record the face attributes specified in
1958 @code{defface}, @code{saved-face} for the attributes saved by the user
1959 with the customization buffer, @code{customized-face} for the
1960 attributes customized by the user for the current session, but not
1961 saved, and @code{face-documentation} for the documentation string.
1963 @defopt frame-background-mode
1964 This option, if non-@code{nil}, specifies the background type to use for
1965 interpreting face definitions. If it is @code{dark}, then Emacs treats
1966 all frames as if they had a dark background, regardless of their actual
1967 background colors. If it is @code{light}, then Emacs treats all frames
1968 as if they had a light background.
1971 @node Face Attributes
1972 @subsection Face Attributes
1973 @cindex face attributes
1975 The effect of using a face is determined by a fixed set of @dfn{face
1976 attributes}. This table lists all the face attributes, and what they
1977 mean. Note that in general, more than one face can be specified for a
1978 given piece of text; when that happens, the attributes of all the faces
1979 are merged to specify how to display the text. @xref{Displaying Faces}.
1981 Any attribute in a face can have the value @code{unspecified}. This
1982 means the face doesn't specify that attribute. In face merging, when
1983 the first face fails to specify a particular attribute, that means the
1984 next face gets a chance. However, the @code{default} face must
1985 specify all attributes.
1987 Some of these font attributes are meaningful only on certain kinds of
1988 displays---if your display cannot handle a certain attribute, the
1989 attribute is ignored. (The attributes @code{:family}, @code{:width},
1990 @code{:height}, @code{:weight}, and @code{:slant} correspond to parts of
1991 an X Logical Font Descriptor.)
1995 Font family name, or fontset name (@pxref{Fontsets}). If you specify a
1996 font family name, the wild-card characters @samp{*} and @samp{?} are
2000 Relative proportionate width, also known as the character set width or
2001 set width. This should be one of the symbols @code{ultra-condensed},
2002 @code{extra-condensed}, @code{condensed}, @code{semi-condensed},
2003 @code{normal}, @code{semi-expanded}, @code{expanded},
2004 @code{extra-expanded}, or @code{ultra-expanded}.
2007 Either the font height, an integer in units of 1/10 point, a floating
2008 point number specifying the amount by which to scale the height of any
2009 underlying face, or a function, which is called with the old height
2010 (from the underlying face), and should return the new height.
2013 Font weight---a symbol from this series (from most dense to most faint):
2014 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2015 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light},
2016 or @code{ultra-light}.
2018 On a text-only terminal, any weight greater than normal is displayed as
2019 extra bright, and any weight less than normal is displayed as
2020 half-bright (provided the terminal supports the feature).
2023 Font slant---one of the symbols @code{italic}, @code{oblique}, @code{normal},
2024 @code{reverse-italic}, or @code{reverse-oblique}.
2026 On a text-only terminal, slanted text is displayed as half-bright, if
2027 the terminal supports the feature.
2030 Foreground color, a string. The value can be a system-defined color
2031 name, or a hexadecimal color specification of the form
2032 @samp{#@var{rr}@var{gg}@var{bb}}. (@samp{#000000} is black,
2033 @samp{#ff0000} is red, @samp{#00ff00} is green, @samp{#0000ff} is
2034 blue, and @samp{#ffffff} is white.)
2037 Background color, a string, like the foreground color.
2039 @item :inverse-video
2040 Whether or not characters should be displayed in inverse video. The
2041 value should be @code{t} (yes) or @code{nil} (no).
2044 The background stipple, a bitmap.
2046 The value can be a string; that should be the name of a file containing
2047 external-format X bitmap data. The file is found in the directories
2048 listed in the variable @code{x-bitmap-file-path}.
2050 Alternatively, the value can specify the bitmap directly, with a list
2051 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2052 @var{width} and @var{height} specify the size in pixels, and
2053 @var{data} is a string containing the raw bits of the bitmap, row by
2054 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2055 in the string (which should be a unibyte string for best results).
2056 This means that each row always occupies at least one whole byte.
2058 If the value is @code{nil}, that means use no stipple pattern.
2060 Normally you do not need to set the stipple attribute, because it is
2061 used automatically to handle certain shades of gray.
2064 Whether or not characters should be underlined, and in what color. If
2065 the value is @code{t}, underlining uses the foreground color of the
2066 face. If the value is a string, underlining uses that color. The
2067 value @code{nil} means do not underline.
2070 Whether or not characters should be overlined, and in what color.
2071 The value is used like that of @code{:underline}.
2073 @item :strike-through
2074 Whether or not characters should be strike-through, and in what
2075 color. The value is used like that of @code{:underline}.
2078 The name of a face from which to inherit attributes, or a list of face
2079 names. Attributes from inherited faces are merged into the face like an
2080 underlying face would be, with higher priority than underlying faces.
2081 If a list of faces is used, attributes from faces earlier in the list
2082 override those from later faces.
2085 Whether or not a box should be drawn around characters, its color, the
2086 width of the box lines, and 3D appearance.
2089 Here are the possible values of the @code{:box} attribute, and what
2097 Draw a box with lines of width 1, in the foreground color.
2100 Draw a box with lines of width 1, in color @var{color}.
2102 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2103 This way you can explicitly specify all aspects of the box. The value
2104 @var{width} specifies the width of the lines to draw; it defaults to 1.
2106 The value @var{color} specifies the color to draw with. The default is
2107 the foreground color of the face for simple boxes, and the background
2108 color of the face for 3D boxes.
2110 The value @var{style} specifies whether to draw a 3D box. If it is
2111 @code{released-button}, the box looks like a 3D button that is not being
2112 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2113 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2117 In older versions of Emacs, before @code{:family}, @code{:height},
2118 @code{:width}, @code{:weight}, and @code{:slant} existed, these
2119 attributes were used to specify the type face. They are now
2120 semi-obsolete, but they still work:
2124 This attribute specifies the font name.
2127 A non-@code{nil} value specifies a bold font.
2130 A non-@code{nil} value specifies an italic font.
2133 For compatibility, you can still set these ``attributes'', even
2134 though they are not real face attributes. Here is what that does:
2138 You can specify an X font name as the ``value'' of this ``attribute'';
2139 that sets the @code{:family}, @code{:width}, @code{:height},
2140 @code{:weight}, and @code{:slant} attributes according to the font name.
2142 If the value is a pattern with wildcards, the first font that matches
2143 the pattern is used to set these attributes.
2146 A non-@code{nil} makes the face bold; @code{nil} makes it normal.
2147 This actually works by setting the @code{:weight} attribute.
2150 A non-@code{nil} makes the face italic; @code{nil} makes it normal.
2151 This actually works by setting the @code{:slant} attribute.
2154 @defvar x-bitmap-file-path
2155 This variable specifies a list of directories for searching
2156 for bitmap files, for the @code{:stipple} attribute.
2159 @defun bitmap-spec-p object
2160 This returns @code{t} if @var{object} is a valid bitmap specification,
2161 suitable for use with @code{:stipple} (see above). It returns
2162 @code{nil} otherwise.
2165 @node Attribute Functions
2166 @subsection Face Attribute Functions
2168 You can modify the attributes of an existing face with the following
2169 functions. If you specify @var{frame}, they affect just that frame;
2170 otherwise, they affect all frames as well as the defaults that apply to
2173 @tindex set-face-attribute
2174 @defun set-face-attribute face frame &rest arguments
2175 This function sets one or more attributes of face @var{face}
2176 for frame @var{frame}. If @var{frame} is @code{nil}, it sets
2177 the attribute for all frames, and the defaults for new frames.
2179 The extra arguments @var{arguments} specify the attributes to set, and
2180 the values for them. They should consist of alternating attribute names
2181 (such as @code{:family} or @code{:underline}) and corresponding values.
2185 (set-face-attribute 'foo nil
2192 sets the attributes @code{:width}, @code{:weight} and @code{:underline}
2193 to the corresponding values.
2196 @tindex face-attribute
2197 @defun face-attribute face attribute &optional frame inherit
2198 This returns the value of the @var{attribute} attribute of face
2199 @var{face} on @var{frame}. If @var{frame} is @code{nil},
2200 that means the selected frame (@pxref{Input Focus}).
2202 If @var{frame} is @code{t}, the value is the default for
2203 @var{face} for new frames.
2205 If @var{inherit} is @code{nil}, only attributes directly defined by
2206 @var{face} are considered, so the return value may be
2207 @code{unspecified}, or a relative value. If @var{inherit} is
2208 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2209 with the faces specified by its @code{:inherit} attribute; however the
2210 return value may still be @code{unspecified} or relative. If
2211 @var{inherit} is a face or a list of faces, then the result is further
2212 merged with that face (or faces), until it becomes specified and
2215 To ensure that the return value is always specified and absolute, use
2216 a value of @code{default} for @var{inherit}; this will resolve any
2217 unspecified or relative values by merging with the @code{default} face
2218 (which is always completely specified).
2223 (face-attribute 'bold :weight)
2228 The functions above did not exist before Emacs 21. For compatibility
2229 with older Emacs versions, you can use the following functions to set
2230 and examine the face attributes which existed in those versions.
2232 @tindex face-attribute-relative-p
2233 @defun face-attribute-relative-p attribute value
2234 This function returns non-@code{nil} if @var{value}, when used as
2235 the value of the face attribute @var{attribute}, is relative (that is,
2236 if it modifies an underlying or inherited value of @var{attribute}).
2239 @tindex merge-face-attribute
2240 @defun merge-face-attribute attribute value1 value2
2241 If @var{value1} is a relative value for the face attribute
2242 @var{attribute}, returns it merged with the underlying value
2243 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2244 face attribute @var{attribute}, returns @var{value1} unchanged.
2247 @defun set-face-foreground face color &optional frame
2248 @defunx set-face-background face color &optional frame
2249 These functions set the foreground (or background, respectively) color
2250 of face @var{face} to @var{color}. The argument @var{color} should be a
2251 string, the name of a color.
2253 Certain shades of gray are implemented by stipple patterns on
2254 black-and-white screens.
2257 @defun set-face-stipple face pattern &optional frame
2258 This function sets the background stipple pattern of face @var{face}
2259 to @var{pattern}. The argument @var{pattern} should be the name of a
2260 stipple pattern defined by the X server, or actual bitmap data
2261 (@pxref{Face Attributes}), or @code{nil} meaning don't use stipple.
2263 Normally there is no need to pay attention to stipple patterns, because
2264 they are used automatically to handle certain shades of gray.
2267 @defun set-face-font face font &optional frame
2268 This function sets the font of face @var{face}. This actually sets
2269 the attributes @code{:family}, @code{:width}, @code{:height},
2270 @code{:weight}, and @code{:slant} according to the font name
2274 @defun set-face-bold-p face bold-p &optional frame
2275 This function specifies whether @var{face} should be bold. If
2276 @var{bold-p} is non-@code{nil}, that means yes; @code{nil} means no.
2277 This actually sets the @code{:weight} attribute.
2280 @defun set-face-italic-p face italic-p &optional frame
2281 This function specifies whether @var{face} should be italic. If
2282 @var{italic-p} is non-@code{nil}, that means yes; @code{nil} means no.
2283 This actually sets the @code{:slant} attribute.
2286 @defun set-face-underline-p face underline-p &optional frame
2287 This function sets the underline attribute of face @var{face}.
2288 Non-@code{nil} means do underline; @code{nil} means don't.
2291 @defun invert-face face &optional frame
2292 This function inverts the @code{:inverse-video} attribute of face
2293 @var{face}. If the attribute is @code{nil}, this function sets it to
2294 @code{t}, and vice versa.
2297 These functions examine the attributes of a face. If you don't
2298 specify @var{frame}, they refer to the default data for new frames.
2299 They return the symbol @code{unspecified} if the face doesn't define any
2300 value for that attribute.
2302 @defun face-foreground face &optional frame inherit
2303 @defunx face-background face &optional frame
2304 These functions return the foreground color (or background color,
2305 respectively) of face @var{face}, as a string.
2307 If @var{inherit} is @code{nil}, only a color directly defined by the face is
2308 returned. If @var{inherit} is non-@code{nil}, any faces specified by its
2309 @code{:inherit} attribute are considered as well, and if @var{inherit}
2310 is a face or a list of faces, then they are also considered, until a
2311 specified color is found. To ensure that the return value is always
2312 specified, use a value of @code{default} for @var{inherit}.
2315 @defun face-stipple face &optional frame inherit
2316 This function returns the name of the background stipple pattern of face
2317 @var{face}, or @code{nil} if it doesn't have one.
2319 If @var{inherit} is @code{nil}, only a stipple directly defined by the
2320 face is returned. If @var{inherit} is non-@code{nil}, any faces
2321 specified by its @code{:inherit} attribute are considered as well, and
2322 if @var{inherit} is a face or a list of faces, then they are also
2323 considered, until a specified stipple is found. To ensure that the
2324 return value is always specified, use a value of @code{default} for
2328 @defun face-font face &optional frame
2329 This function returns the name of the font of face @var{face}.
2332 @defun face-bold-p face &optional frame
2333 This function returns @code{t} if @var{face} is bold---that is, if it is
2334 bolder than normal. It returns @code{nil} otherwise.
2337 @defun face-italic-p face &optional frame
2338 This function returns @code{t} if @var{face} is italic or oblique,
2339 @code{nil} otherwise.
2342 @defun face-underline-p face &optional frame
2343 This function returns the @code{:underline} attribute of face @var{face}.
2346 @defun face-inverse-video-p face &optional frame
2347 This function returns the @code{:inverse-video} attribute of face @var{face}.
2350 @node Displaying Faces
2351 @subsection Displaying Faces
2353 Here are the ways to specify which faces to use for display of text:
2357 With defaults. The @code{default} face is used as the ultimate
2358 default for all text. (In Emacs 19 and 20, the @code{default}
2359 face is used only when no other face is specified.)
2362 For a mode line or header line, the face @code{mode-line} or
2363 @code{mode-line-inactive}, or @code{header-line}, is merged in just
2364 before @code{default}.
2367 With text properties. A character can have a @code{face} property; if
2368 so, the faces and face attributes specified there apply. @xref{Special
2371 If the character has a @code{mouse-face} property, that is used instead
2372 of the @code{face} property when the mouse is ``near enough'' to the
2376 With overlays. An overlay can have @code{face} and @code{mouse-face}
2377 properties too; they apply to all the text covered by the overlay.
2380 With a region that is active. In Transient Mark mode, the region is
2381 highlighted with the face @code{region} (@pxref{Standard Faces}).
2384 With special glyphs. Each glyph can specify a particular face
2385 number. @xref{Glyphs}.
2388 If these various sources together specify more than one face for a
2389 particular character, Emacs merges the attributes of the various faces
2390 specified. For each attribute, Emacs tries first the face of any
2391 special glyph; then the face for region highlighting, if appropriate;
2392 then the faces specified by overlays, followed by those specified by
2393 text properties, then the @code{mode-line} or
2394 @code{mode-line-inactive} or @code{header-line} face (if in a mode
2395 line or a header line), and last the @code{default} face.
2397 When multiple overlays cover one character, an overlay with higher
2398 priority overrides those with lower priority. @xref{Overlays}.
2400 @node Font Selection
2401 @subsection Font Selection
2403 @dfn{Selecting a font} means mapping the specified face attributes for
2404 a character to a font that is available on a particular display. The
2405 face attributes, as determined by face merging, specify most of the
2406 font choice, but not all. Part of the choice depends on what character
2409 If the face specifies a fontset name, that fontset determines a
2410 pattern for fonts of the given charset. If the face specifies a font
2411 family, a font pattern is constructed.
2413 Emacs tries to find an available font for the given face attributes
2414 and character's registry and encoding. If there is a font that matches
2415 exactly, it is used, of course. The hard case is when no available font
2416 exactly fits the specification. Then Emacs looks for one that is
2417 ``close''---one attribute at a time. You can specify the order to
2418 consider the attributes. In the case where a specified font family is
2419 not available, you can specify a set of mappings for alternatives to
2422 @defvar face-font-selection-order
2423 @tindex face-font-selection-order
2424 This variable specifies the order of importance of the face attributes
2425 @code{:width}, @code{:height}, @code{:weight}, and @code{:slant}. The
2426 value should be a list containing those four symbols, in order of
2427 decreasing importance.
2429 Font selection first finds the best available matches for the first
2430 attribute listed; then, among the fonts which are best in that way, it
2431 searches for the best matches in the second attribute, and so on.
2433 The attributes @code{:weight} and @code{:width} have symbolic values in
2434 a range centered around @code{normal}. Matches that are more extreme
2435 (farther from @code{normal}) are somewhat preferred to matches that are
2436 less extreme (closer to @code{normal}); this is designed to ensure that
2437 non-normal faces contrast with normal ones, whenever possible.
2439 The default is @code{(:width :height :weight :slant)}, which means first
2440 find the fonts closest to the specified @code{:width}, then---among the
2441 fonts with that width---find a best match for the specified font height,
2444 One example of a case where this variable makes a difference is when the
2445 default font has no italic equivalent. With the default ordering, the
2446 @code{italic} face will use a non-italic font that is similar to the
2447 default one. But if you put @code{:slant} before @code{:height}, the
2448 @code{italic} face will use an italic font, even if its height is not
2452 @defvar face-font-family-alternatives
2453 @tindex face-font-family-alternatives
2454 This variable lets you specify alternative font families to try, if a
2455 given family is specified and doesn't exist. Each element should have
2459 (@var{family} @var{alternate-families}@dots{})
2462 If @var{family} is specified but not available, Emacs will try the other
2463 families given in @var{alternate-families}, one by one, until it finds a
2464 family that does exist.
2467 @defvar face-font-registry-alternatives
2468 @tindex face-font-registry-alternatives
2469 This variable lets you specify alternative font registries to try, if a
2470 given registry is specified and doesn't exist. Each element should have
2474 (@var{registry} @var{alternate-registries}@dots{})
2477 If @var{registry} is specified but not available, Emacs will try the
2478 other registries given in @var{alternate-registries}, one by one,
2479 until it finds a registry that does exist.
2482 Emacs can make use of scalable fonts, but by default it does not use
2483 them, since the use of too many or too big scalable fonts can crash
2486 @defvar scalable-fonts-allowed
2487 @tindex scalable-fonts-allowed
2488 This variable controls which scalable fonts to use. A value of
2489 @code{nil}, the default, means do not use scalable fonts. @code{t}
2490 means to use any scalable font that seems appropriate for the text.
2492 Otherwise, the value must be a list of regular expressions. Then a
2493 scalable font is enabled for use if its name matches any regular
2494 expression in the list. For example,
2497 (setq scalable-fonts-allowed '("muleindian-2$"))
2501 allows the use of scalable fonts with registry @code{muleindian-2}.
2504 @defun clear-face-cache &optional unload-p
2505 @tindex clear-face-cache
2506 This function clears the face cache for all frames.
2507 If @var{unload-p} is non-@code{nil}, that means to unload
2508 all unused fonts as well.
2511 @defvar face-font-rescale-alist
2512 This variable specifies scaling for certain faces. Its value should
2513 be a list of elements of the form
2516 (@var{fontname-regexp} . @var{scale-factor})
2519 If @var{fontname-regexp} matches the font name that is about to be
2520 used, this says to choose a larger similar font according to the
2521 factor @var{scale-factor}. You would use this feature to normalize
2522 the font size if certain fonts are bigger or smaller than their
2523 nominal heights and widths would suggest.
2526 @node Face Functions
2527 @subsection Functions for Working with Faces
2529 Here are additional functions for creating and working with faces.
2531 @defun make-face name
2532 This function defines a new face named @var{name}, initially with all
2533 attributes @code{nil}. It does nothing if there is already a face named
2538 This function returns a list of all defined face names.
2541 @defun copy-face old-face new-name &optional frame new-frame
2542 This function defines a face named @var{new-name} as a copy of the existing
2543 face named @var{old-face}. It creates the face @var{new-name} if that
2544 doesn't already exist.
2546 If the optional argument @var{frame} is given, this function applies
2547 only to that frame. Otherwise it applies to each frame individually,
2548 copying attributes from @var{old-face} in each frame to @var{new-face}
2551 If the optional argument @var{new-frame} is given, then @code{copy-face}
2552 copies the attributes of @var{old-face} in @var{frame} to @var{new-name}
2557 This function returns the face number of face @var{face}.
2560 @defun face-documentation face
2561 This function returns the documentation string of face @var{face}, or
2562 @code{nil} if none was specified for it.
2565 @defun face-equal face1 face2 &optional frame
2566 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2567 same attributes for display.
2570 @defun face-differs-from-default-p face &optional frame
2571 This returns non-@code{nil} if the face @var{face} displays
2572 differently from the default face.
2576 A @dfn{face alias} provides an equivalent name for a face. You can
2577 define a face alias by giving the alias symbol the @code{face-alias}
2578 property, with a value of the target face name. The following example
2579 makes @code{modeline} an alias for the @code{mode-line} face.
2582 (put 'modeline 'face-alias 'mode-line)
2587 @subsection Automatic Face Assignment
2588 @cindex automatic face assignment
2589 @cindex faces, automatic choice
2591 @cindex Font-Lock mode
2592 This hook is used for automatically assigning faces to text in the
2593 buffer. It is part of the implementation of Font-Lock mode.
2595 @tindex fontification-functions
2596 @defvar fontification-functions
2597 This variable holds a list of functions that are called by Emacs
2598 redisplay as needed to assign faces automatically to text in the buffer.
2600 The functions are called in the order listed, with one argument, a
2601 buffer position @var{pos}. Each function should attempt to assign faces
2602 to the text in the current buffer starting at @var{pos}.
2604 Each function should record the faces they assign by setting the
2605 @code{face} property. It should also add a non-@code{nil}
2606 @code{fontified} property for all the text it has assigned faces to.
2607 That property tells redisplay that faces have been assigned to that text
2610 It is probably a good idea for each function to do nothing if the
2611 character after @var{pos} already has a non-@code{nil} @code{fontified}
2612 property, but this is not required. If one function overrides the
2613 assignments made by a previous one, the properties as they are
2614 after the last function finishes are the ones that really matter.
2616 For efficiency, we recommend writing these functions so that they
2617 usually assign faces to around 400 to 600 characters at each call.
2621 @subsection Looking Up Fonts
2623 @defun x-list-fonts pattern &optional face frame maximum
2624 This function returns a list of available font names that match
2625 @var{pattern}. If the optional arguments @var{face} and @var{frame} are
2626 specified, then the list is limited to fonts that are the same size as
2627 @var{face} currently is on @var{frame}.
2629 The argument @var{pattern} should be a string, perhaps with wildcard
2630 characters: the @samp{*} character matches any substring, and the
2631 @samp{?} character matches any single character. Pattern matching
2632 of font names ignores case.
2634 If you specify @var{face} and @var{frame}, @var{face} should be a face name
2635 (a symbol) and @var{frame} should be a frame.
2637 The optional argument @var{maximum} sets a limit on how many fonts to
2638 return. If this is non-@code{nil}, then the return value is truncated
2639 after the first @var{maximum} matching fonts. Specifying a small value
2640 for @var{maximum} can make this function much faster, in cases where
2641 many fonts match the pattern.
2644 @defun x-family-fonts &optional family frame
2645 @tindex x-family-fonts
2646 This function returns a list describing the available fonts for family
2647 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
2648 this list applies to all families, and therefore, it contains all
2649 available fonts. Otherwise, @var{family} must be a string; it may
2650 contain the wildcards @samp{?} and @samp{*}.
2652 The list describes the display that @var{frame} is on; if @var{frame} is
2653 omitted or @code{nil}, it applies to the selected frame's display
2654 (@pxref{Input Focus}).
2656 The list contains a vector of the following form for each font:
2659 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
2660 @var{fixed-p} @var{full} @var{registry-and-encoding}]
2663 The first five elements correspond to face attributes; if you
2664 specify these attributes for a face, it will use this font.
2666 The last three elements give additional information about the font.
2667 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
2668 @var{full} is the full name of the font, and
2669 @var{registry-and-encoding} is a string giving the registry and
2670 encoding of the font.
2672 The result list is sorted according to the current face font sort order.
2675 @defun x-font-family-list &optional frame
2676 @tindex x-font-family-list
2677 This function returns a list of the font families available for
2678 @var{frame}'s display. If @var{frame} is omitted or @code{nil}, it
2679 describes the selected frame's display (@pxref{Input Focus}).
2681 The value is a list of elements of this form:
2684 (@var{family} . @var{fixed-p})
2688 Here @var{family} is a font family, and @var{fixed-p} is
2689 non-@code{nil} if fonts of that family are fixed-pitch.
2692 @defvar font-list-limit
2693 @tindex font-list-limit
2694 This variable specifies maximum number of fonts to consider in font
2695 matching. The function @code{x-family-fonts} will not return more than
2696 that many fonts, and font selection will consider only that many fonts
2697 when searching a matching font for face attributes. The default is
2702 @subsection Fontsets
2704 A @dfn{fontset} is a list of fonts, each assigned to a range of
2705 character codes. An individual font cannot display the whole range of
2706 characters that Emacs supports, but a fontset can. Fontsets have names,
2707 just as fonts do, and you can use a fontset name in place of a font name
2708 when you specify the ``font'' for a frame or a face. Here is
2709 information about defining a fontset under Lisp program control.
2711 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
2712 This function defines a new fontset according to the specification
2713 string @var{fontset-spec}. The string should have this format:
2716 @var{fontpattern}, @r{[}@var{charsetname}:@var{fontname}@r{]@dots{}}
2720 Whitespace characters before and after the commas are ignored.
2722 The first part of the string, @var{fontpattern}, should have the form of
2723 a standard X font name, except that the last two fields should be
2724 @samp{fontset-@var{alias}}.
2726 The new fontset has two names, one long and one short. The long name is
2727 @var{fontpattern} in its entirety. The short name is
2728 @samp{fontset-@var{alias}}. You can refer to the fontset by either
2729 name. If a fontset with the same name already exists, an error is
2730 signaled, unless @var{noerror} is non-@code{nil}, in which case this
2731 function does nothing.
2733 If optional argument @var{style-variant-p} is non-@code{nil}, that says
2734 to create bold, italic and bold-italic variants of the fontset as well.
2735 These variant fontsets do not have a short name, only a long one, which
2736 is made by altering @var{fontpattern} to indicate the bold or italic
2739 The specification string also says which fonts to use in the fontset.
2740 See below for the details.
2743 The construct @samp{@var{charset}:@var{font}} specifies which font to
2744 use (in this fontset) for one particular character set. Here,
2745 @var{charset} is the name of a character set, and @var{font} is the font
2746 to use for that character set. You can use this construct any number of
2747 times in the specification string.
2749 For the remaining character sets, those that you don't specify
2750 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
2751 @samp{fontset-@var{alias}} with a value that names one character set.
2752 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
2753 with @samp{ISO8859-1}.
2755 In addition, when several consecutive fields are wildcards, Emacs
2756 collapses them into a single wildcard. This is to prevent use of
2757 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
2758 for editing, and scaling a smaller font is not useful because it is
2759 better to use the smaller font in its own size, which Emacs does.
2761 Thus if @var{fontpattern} is this,
2764 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
2768 the font specification for @acronym{ASCII} characters would be this:
2771 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
2775 and the font specification for Chinese GB2312 characters would be this:
2778 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
2781 You may not have any Chinese font matching the above font
2782 specification. Most X distributions include only Chinese fonts that
2783 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
2784 such a case, @samp{Fontset-@var{n}} can be specified as below:
2787 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
2788 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
2792 Then, the font specifications for all but Chinese GB2312 characters have
2793 @samp{fixed} in the @var{family} field, and the font specification for
2794 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
2797 @defun set-fontset-font name character fontname &optional frame
2798 This function modifies the existing fontset @var{name} to
2799 use the font name @var{fontname} for the character @var{character}.
2801 If @var{name} is @code{nil}, this function modifies the default
2802 fontset, whose short name is @samp{fontset-default}.
2804 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
2805 @var{from} and @var{to} are non-generic characters. In that case, use
2806 @var{fontname} for all characters in the range @var{from} and @var{to}
2809 @var{character} may be a charset. In that case, use
2810 @var{fontname} for all character in the charsets.
2812 @var{fontname} may be a cons; @code{(@var{family} . @var{registry})},
2813 where @var{family} is a family name of a font (possibly including a
2814 foundry name at the head), @var{registry} is a registry name of a font
2815 (possibly including an encoding name at the tail).
2817 For instance, this changes the default fontset to use a font of which
2818 registry name is @samp{JISX0208.1983} for all characters belonging to
2819 the charset @code{japanese-jisx0208}.
2822 (set-fontset-font nil 'japanese-jisx0208 '(nil . "JISX0208.1983"))
2826 @defun char-displayable-p char
2827 This function returns @code{t} if Emacs ought to be able to display
2828 @var{char}. More precisely, if the selected frame's fontset has a
2829 font to display the character set that @var{char} belongs to.
2831 Fontsets can specify a font on a per-character basis; when the fontset
2832 does that, this function's value may not be accurate.
2839 The @dfn{fringes} of a window are thin vertical strips down the
2840 sides that are used for displaying bitmaps that indicate truncation,
2841 continuation, horizontal scrolling, and the overlay arrow.
2844 * Fringe Size/Pos:: Specifying where to put the window fringes.
2845 * Fringe Bitmaps:: Displaying bitmaps in the window fringes.
2846 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
2847 * Overlay Arrow:: Display of an arrow to indicate position.
2850 @node Fringe Size/Pos
2851 @subsection Fringe Size and Position
2853 Here's how to control the position and width of the window fringes.
2855 @defvar fringes-outside-margins
2856 If the value is non-@code{nil}, the frames appear outside the display
2857 margins. The fringes normally appear between the display margins and
2858 the window text. It works to set @code{fringes-outside-margins}
2859 buffer-locally. @xref{Display Margins}.
2862 @defvar left-fringe-width
2863 This variable, if non-@code{nil}, specifies the width of the left
2867 @defvar right-fringe-width
2868 This variable, if non-@code{nil}, specifies the width of the right
2872 The values of these variables take effect when you display the
2873 buffer in a window. If you change them while the buffer is visible,
2874 you can call @code{set-window-buffer} to display it once again in the
2875 same window, to make the changes take effect.
2877 @defun set-window-fringes window left &optional right outside-margins
2878 This function sets the fringe widths of window @var{window}.
2879 If @var{window} is @code{nil}, the selected window is used.
2881 The argument @var{left} specifies the width in pixels of the left
2882 fringe, and likewise @var{right} for the right fringe. A value of
2883 @code{nil} for either one stands for the default width. If
2884 @var{outside-margins} is non-@code{nil}, that specifies that fringes
2885 should appear outside of the display margins.
2888 @defun window-fringes &optional window
2889 This function returns information about the fringes of a window
2890 @var{window}. If @var{window} is omitted or @code{nil}, the selected
2891 window is used. The value has the form @code{(@var{left-width}
2892 @var{right-width} @var{outside-margins})}.
2895 @defvar overflow-newline-into-fringe
2896 If this is non-@code{nil}, lines exactly as wide as the window (not
2897 counting the final newline character) are not continued. Instead,
2898 when point is at the end of the line, the cursor appears in the right
2902 @node Fringe Bitmaps
2903 @subsection Fringe Bitmaps
2904 @cindex fringe bitmaps
2905 @cindex bitmaps, fringe
2907 The @dfn{fringe bitmaps} are tiny icons Emacs displays in the window
2908 fringe (on a graphic display) to indicate truncated or continued
2909 lines, buffer boundaries, overlay arrow, etc. The fringe bitmaps are
2910 shared by all frames and windows. You can redefine the built-in
2911 fringe bitmaps, and you can define new fringe bitmaps.
2913 The way to display a bitmap in the left or right fringes for a given
2914 line in a window is by specifying the @code{display} property for one
2915 of the characters that appears in it. Use a display specification of
2916 the form @code{(left-fringe @var{bitmap} [@var{face}])} or
2917 @code{(right-fringe @var{bitmap} [@var{face}])} (@pxref{Display
2918 Property}). Here, @var{bitmap} is a symbol identifying the bitmap you
2919 want, and @var{face} (which is optional) is the name of the face whose
2920 colors should be used for displaying the bitmap, instead of the
2921 default @code{fringe} face. @var{face} is automatically merged with
2922 the @code{fringe} face, so normally @var{face} need only specify the
2923 foreground color for the bitmap.
2925 These symbols identify the standard fringe bitmaps. Evaluate
2926 @code{(require 'fringe)} to define them. Fringe bitmap symbols have
2927 their own name space.
2930 @item Truncation and continuation line bitmaps:
2931 @code{left-truncation}, @code{right-truncation},
2932 @code{continued-line}, @code{continuation-line}.
2934 @item Buffer indication bitmaps:
2935 @code{up-arrow}, @code{down-arrow},
2936 @code{top-left-angle}, @code{top-right-angle},
2937 @code{bottom-left-angle}, @code{bottom-right-angle},
2938 @code{left-bracket}, @code{right-bracket}.
2940 @item Empty line indication bitmap:
2943 @item Overlay arrow bitmap:
2944 @code{overlay-arrow}.
2946 @item Bitmaps for displaying the cursor in right fringe:
2947 @code{filled-box-cursor}, @code{hollow-box-cursor}, @code{hollow-square},
2948 @code{bar-cursor}, @code{hbar-cursor}.
2951 @defun fringe-bitmaps-at-pos &optional pos window
2952 This function returns the fringe bitmaps of the display line
2953 containing position @var{pos} in window @var{window}. The return
2954 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
2955 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
2956 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
2957 is non-@code{nil} if there is an overlay arrow in the left fringe.
2959 The value is @code{nil} if @var{pos} is not visible in @var{window}.
2960 If @var{window} is @code{nil}, that stands for the selected window.
2961 If @var{pos} is @code{nil}, that stands for the value of point in
2965 @node Customizing Bitmaps
2966 @subsection Customizing Fringe Bitmaps
2968 @defun define-fringe-bitmap bitmap bits &optional height width align
2969 This function defines the symbol @var{bitmap} as a new fringe bitmap,
2970 or replaces an existing bitmap with that name.
2972 The argument @var{bits} specifies the image to use. It should be
2973 either a string or a vector of integers, where each element (an
2974 integer) corresponds to one row of the bitmap. Each bit of an integer
2975 corresponds to one pixel of the bitmap, where the low bit corresponds
2976 to the rightmost pixel of the bitmap.
2978 The height is normally the length of @var{bits}. However, you
2979 can specify a different height with non-@code{nil} @var{height}. The width
2980 is normally 8, but you can specify a different width with non-@code{nil}
2981 @var{width}. The width must be an integer between 1 and 16.
2983 The argument @var{align} specifies the positioning of the bitmap
2984 relative to the range of rows where it is used; the default is to
2985 center the bitmap. The allowed values are @code{top}, @code{center},
2988 The @var{align} argument may also be a list @code{(@var{align}
2989 @var{periodic})} where @var{align} is interpreted as described above.
2990 If @var{periodic} is non-@code{nil}, it specifies that the rows in
2991 @code{bits} should be repeated enough times to reach the specified
2994 The return value on success is an integer identifying the new bitmap.
2995 You should save that integer in a variable so it can be used to select
2998 This function signals an error if there are no more free bitmap slots.
3001 @defun destroy-fringe-bitmap bitmap
3002 This function destroy the fringe bitmap identified by @var{bitmap}.
3003 If @var{bitmap} identifies a standard fringe bitmap, it actually
3004 restores the standard definition of that bitmap, instead of
3005 eliminating it entirely.
3008 @defun set-fringe-bitmap-face bitmap &optional face
3009 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3010 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3011 bitmap's face controls the color to draw it in.
3013 @var{face} is merged with the @code{fringe} face, so normally
3014 @var{face} should specify only the foreground color.
3018 @subsection The Overlay Arrow
3019 @cindex overlay arrow
3021 The @dfn{overlay arrow} is useful for directing the user's attention
3022 to a particular line in a buffer. For example, in the modes used for
3023 interface to debuggers, the overlay arrow indicates the line of code
3024 about to be executed. This feature has nothing to do with
3025 @dfn{overlays} (@pxref{Overlays}).
3027 @defvar overlay-arrow-string
3028 This variable holds the string to display to call attention to a
3029 particular line, or @code{nil} if the arrow feature is not in use.
3030 On a graphical display the contents of the string are ignored; instead a
3031 glyph is displayed in the fringe area to the left of the display area.
3034 @defvar overlay-arrow-position
3035 This variable holds a marker that indicates where to display the overlay
3036 arrow. It should point at the beginning of a line. On a non-graphical
3037 display the arrow text
3038 appears at the beginning of that line, overlaying any text that would
3039 otherwise appear. Since the arrow is usually short, and the line
3040 usually begins with indentation, normally nothing significant is
3043 The overlay string is displayed only in the buffer that this marker
3044 points into. Thus, only one buffer can have an overlay arrow at any
3046 @c !!! overlay-arrow-position: but the overlay string may remain in the display
3047 @c of some other buffer until an update is required. This should be fixed
3051 You can do a similar job by creating an overlay with a
3052 @code{before-string} property. @xref{Overlay Properties}.
3054 You can define multiple overlay arrows via the variable
3055 @code{overlay-arrow-variable-list}.
3057 @defvar overlay-arrow-variable-list
3058 This variable's value is a list of variables, each of which specifies
3059 the position of an overlay arrow. The variable
3060 @code{overlay-arrow-position} has its normal meaning because it is on
3064 Each variable on this list can have properties
3065 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3066 specify an overlay arrow string (for text-only terminals) or fringe
3067 bitmap (for graphical terminals) to display at the corresponding
3068 overlay arrow position. If either property is not set, the default
3069 (@code{overlay-arrow-string} or @code{overlay-arrow-fringe-bitmap}) is
3073 @section Scroll Bars
3075 Normally the frame parameter @code{vertical-scroll-bars} controls
3076 whether the windows in the frame have vertical scroll bars, and
3077 whether they are on the left or right. The frame parameter
3078 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3079 meaning the default). @xref{Window Frame Parameters}.
3081 @defun frame-current-scroll-bars &optional frame
3082 This function reports the scroll bar type settings for frame
3083 @var{frame}. The value is a cons cell
3084 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3085 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3086 (which means no scroll bar.) @var{horizontal-type} is meant to
3087 specify the horizontal scroll bar type, but since they are not
3088 implemented, it is always @code{nil}.
3091 @vindex vertical-scroll-bar
3092 You can enable or disable scroll bars for a particular buffer,
3093 by setting the variable @code{vertical-scroll-bar}. This variable
3094 automatically becomes buffer-local when set. The possible values are
3095 @code{left}, @code{right}, @code{t}, which means to use the
3096 frame's default, and @code{nil} for no scroll bar.
3098 You can also control this for individual windows. Call the function
3099 @code{set-window-scroll-bars} to specify what to do for a specific window:
3101 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3102 This function sets the width and type of scroll bars for window
3105 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3106 use the width specified for the frame). @var{vertical-type} specifies
3107 whether to have a vertical scroll bar and, if so, where. The possible
3108 values are @code{left}, @code{right} and @code{nil}, just like the
3109 values of the @code{vertical-scroll-bars} frame parameter.
3111 The argument @var{horizontal-type} is meant to specify whether and
3112 where to have horizontal scroll bars, but since they are not
3113 implemented, it has no effect. If @var{window} is @code{nil}, the
3114 selected window is used.
3117 @defun window-scroll-bars &optional window
3118 Report the width and type of scroll bars specified for @var{window}.
3119 If @var{window} is omitted or @code{nil}, the selected window is used.
3120 The value is a list of the form @code{(@var{width}
3121 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3122 @var{width} is the value that was specified for the width (which may
3123 be @code{nil}); @var{cols} is the number of columns that the scroll
3124 bar actually occupies.
3126 @var{horizontal-type} is not actually meaningful.
3129 If you don't specify these values for a window with
3130 @code{set-window-scroll-bars}, the buffer-local variables
3131 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3132 displayed control the window's vertical scroll bars. The function
3133 @code{set-window-buffer} examines these variables. If you change them
3134 in a buffer that is already visible in a window, you can make the
3135 window take note of the new values by calling @code{set-window-buffer}
3136 specifying the same buffer that is already displayed.
3138 @defvar scroll-bar-mode
3139 This variable, always local in all buffers, controls whether and where
3140 to put scroll bars in windows displaying the buffer. The possible values
3141 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3142 the left, and @code{right} to put a scroll bar on the right.
3145 @defun window-current-scroll-bars &optional window
3146 This function reports the scroll bar type for window @var{window}.
3147 If @var{window} is omitted or @code{nil}, the selected window is used.
3148 The value is a cons cell
3149 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3150 @code{window-scroll-bars}, this reports the scroll bar type actually
3151 used, once frame defaults and @code{scroll-bar-mode} are taken into
3155 @defvar scroll-bar-width
3156 This variable, always local in all buffers, specifies the width of the
3157 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3158 to use the value specified by the frame.
3162 @section Pointer Shape
3164 Normally, the mouse pointer has the @code{text} shape over text and
3165 the @code{arrow} shape over window areas which do not correspond to
3166 any buffer text. You can specify the mouse pointer shape over text or
3167 images via the @code{pointer} text property, and for images with the
3168 @code{:pointer} and @code{:map} image properties.
3170 The available pointer shapes are: @code{text} (or @code{nil}),
3171 @code{arrow}, @code{hand}, @code{vdrag}, @code{hdrag},
3172 @code{modeline}, and @code{hourglass}.
3174 @defvar void-text-area-pointer
3175 @tindex void-text-area-pointer
3176 This variable specifies the mouse pointer shape in void text areas,
3177 i.e. the areas after the end of a line or below the last line in the
3178 buffer. The default is to use the @code{arrow} (non-text) pointer.
3181 @node Display Property
3182 @section The @code{display} Property
3183 @cindex display specification
3184 @kindex display @r{(text property)}
3186 The @code{display} text property (or overlay property) is used to
3187 insert images into text, and also control other aspects of how text
3188 displays. The value of the @code{display} property should be a
3189 display specification, or a list or vector containing several display
3192 Some kinds of @code{display} properties specify something to display
3193 instead of the text that has the property. In this case, ``the text''
3194 means all the consecutive characters that have the same Lisp object as
3195 their @code{display} property; these characters are replaced as a
3196 single unit. By contrast, characters that have similar but distinct
3197 Lisp objects as their @code{display} properties are handled
3198 separately. Here's a function that illustrates this point:
3202 (goto-char (point-min))
3204 (let ((string (concat "A")))
3205 (put-text-property (point) (1+ (point)) 'display string)
3207 (put-text-property (point) (1+ (point)) 'display string)
3212 It gives each of the first ten characters in the buffer string
3213 @code{"A"} as the @code{display} property, but they don't all get the
3214 same string. The first two characters get the same string, so they
3215 together are replaced with one @samp{A}. The next two characters get
3216 a second string, so they together are replaced with one @samp{A}.
3217 Likewise for each following pair of characters. Thus, the ten
3218 characters appear as five A's. This function would have the same
3223 (goto-char (point-min))
3225 (let ((string (concat "A")))
3226 (put-text-property (point) (2+ (point)) 'display string)
3227 (put-text-property (point) (1+ (point)) 'display string)
3232 This illustrates that what matters is the property value for
3233 each character. If two consecutive characters have the same
3234 object as the @code{display} property value, it's irrelevant
3235 whether they got this property from a single call to
3236 @code{put-text-property} or from two different calls.
3238 The rest of this section describes several kinds of
3239 display specifications and what they mean.
3242 * Specified Space:: Displaying one space with a specified width.
3243 * Pixel Specification:: Specifying space width or height in pixels.
3244 * Other Display Specs:: Displaying an image; magnifying text; moving it
3245 up or down on the page; adjusting the width
3246 of spaces within text.
3247 * Display Margins:: Displaying text or images to the side of the main text.
3250 @node Specified Space
3251 @subsection Specified Spaces
3252 @cindex spaces, specified height or width
3253 @cindex specified spaces
3254 @cindex variable-width spaces
3256 To display a space of specified width and/or height, use a display
3257 specification of the form @code{(space . @var{props})}, where
3258 @var{props} is a property list (a list of alternating properties and
3259 values). You can put this property on one or more consecutive
3260 characters; a space of the specified height and width is displayed in
3261 place of @emph{all} of those characters. These are the properties you
3262 can use in @var{props} to specify the weight of the space:
3265 @item :width @var{width}
3266 If @var{width} is an integer or floating point number, it specifies
3267 that the space width should be @var{width} times the normal character
3268 width. @var{width} can also be a @dfn{pixel width} specification
3269 (@pxref{Pixel Specification}).
3271 @item :relative-width @var{factor}
3272 Specifies that the width of the stretch should be computed from the
3273 first character in the group of consecutive characters that have the
3274 same @code{display} property. The space width is the width of that
3275 character, multiplied by @var{factor}.
3277 @item :align-to @var{hpos}
3278 Specifies that the space should be wide enough to reach @var{hpos}.
3279 If @var{hpos} is a number, it is measured in units of the normal
3280 character width. @var{hpos} can also be a @dfn{pixel width}
3281 specification (@pxref{Pixel Specification}).
3284 You should use one and only one of the above properties. You can
3285 also specify the height of the space, with these properties:
3288 @item :height @var{height}
3289 Specifies the height of the space.
3290 If @var{height} is an integer or floating point number, it specifies
3291 that the space height should be @var{height} times the normal character
3292 height. The @var{height} may also be a @dfn{pixel height} specification
3293 (@pxref{Pixel Specification}).
3295 @item :relative-height @var{factor}
3296 Specifies the height of the space, multiplying the ordinary height
3297 of the text having this display specification by @var{factor}.
3299 @item :ascent @var{ascent}
3300 If the value of @var{ascent} is a non-negative number no greater than
3301 100, it specifies that @var{ascent} percent of the height of the space
3302 should be considered as the ascent of the space---that is, the part
3303 above the baseline. The ascent may also be specified in pixel units
3304 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
3308 Don't use both @code{:height} and @code{:relative-height} together.
3310 The @code{:width} and @code{:align-to} properties are supported on
3311 non-graphic terminals, but the other space properties in this section
3314 @node Pixel Specification
3315 @subsection Pixel Specification for Spaces
3316 @cindex spaces, pixel specification
3318 The value of the @code{:width}, @code{:align-to}, @code{:height},
3319 and @code{:ascent} properties can be a special kind of expression that
3320 is evaluated during redisplay. The result of the evaluation is used
3321 as an absolute number of pixels.
3323 The following expressions are supported:
3327 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
3328 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
3329 @var{unit} ::= in | mm | cm | width | height
3332 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
3334 @var{pos} ::= left | center | right
3335 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
3340 The form @var{num} specifies a fraction of the default frame font
3341 height or width. The form @code{(@var{num})} specifies an absolute
3342 number of pixels. If @var{num} is a symbol, @var{symbol}, its
3343 buffer-local variable binding is used.
3345 The @code{in}, @code{mm}, and @code{cm} units specify the number of
3346 pixels per inch, millimeter, and centimeter, respectively. The
3347 @code{width} and @code{height} units correspond to the default width
3348 and height of the current face. An image specification @code{image}
3349 corresponds to the width or height of the image.
3351 The @code{left-fringe}, @code{right-fringe}, @code{left-margin},
3352 @code{right-margin}, @code{scroll-bar}, and @code{text} elements
3353 specify to the width of the corresponding area of the window.
3355 The @code{left}, @code{center}, and @code{right} positions can be
3356 used with @code{:align-to} to specify a position relative to the left
3357 edge, center, or right edge of the text area.
3359 Any of the above window elements (except @code{text}) can also be
3360 used with @code{:align-to} to specify that the position is relative to
3361 the left edge of the given area. Once the base offset for a relative
3362 position has been set (by the first occurrence of one of these
3363 symbols), further occurrences of these symbols are interpreted as the
3364 width of the specified area. For example, to align to the center of
3365 the left-margin, use
3368 :align-to (+ left-margin (0.5 . left-margin))
3371 If no specific base offset is set for alignment, it is always relative
3372 to the left edge of the text area. For example, @samp{:align-to 0} in a
3373 header-line aligns with the first text column in the text area.
3375 A value of the form @code{(@var{num} . @var{expr})} stands for the
3376 product of the values of @var{num} and @var{expr}. For example,
3377 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
3378 @var{image})} specifies half the width (or height) of the specified
3381 The form @code{(+ @var{expr} ...)} adds up the value of the
3382 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
3383 the value of the expressions.
3385 @node Other Display Specs
3386 @subsection Other Display Specifications
3388 Here are the other sorts of display specifications that you can use
3389 in the @code{display} text property.
3393 Display @var{string} instead of the text that has this property.
3395 @item (image . @var{image-props})
3396 This kind of display specification is an image descriptor (@pxref{Images}).
3397 When used as a display specification, it means to display the image
3398 instead of the text that has the display specification.
3400 @item (slice @var{x} @var{y} @var{width} @var{height})
3401 This specification together with @code{image} specifies a @dfn{slice}
3402 (a partial area) of the image to display. The elements @var{y} and
3403 @var{x} specify the top left corner of the slice, within the image;
3404 @var{width} and @var{height} specify the width and height of the
3405 slice. Integer values are numbers of pixels. A floating point number
3406 in the range 0.0--1.0 stands for that fraction of the width or height
3407 of the entire image.
3409 @item ((margin nil) @var{string})
3411 A display specification of this form means to display @var{string}
3412 instead of the text that has the display specification, at the same
3413 position as that text. This is a special case of marginal display
3414 (@pxref{Display Margins}).
3416 Recursive display specifications are not supported---string display
3417 specifications must not have @code{display} properties themselves.
3419 @item (space-width @var{factor})
3420 This display specification affects all the space characters within the
3421 text that has the specification. It displays all of these spaces
3422 @var{factor} times as wide as normal. The element @var{factor} should
3423 be an integer or float. Characters other than spaces are not affected
3424 at all; in particular, this has no effect on tab characters.
3426 @item (height @var{height})
3427 This display specification makes the text taller or shorter.
3428 Here are the possibilities for @var{height}:
3431 @item @code{(+ @var{n})}
3432 This means to use a font that is @var{n} steps larger. A ``step'' is
3433 defined by the set of available fonts---specifically, those that match
3434 what was otherwise specified for this text, in all attributes except
3435 height. Each size for which a suitable font is available counts as
3436 another step. @var{n} should be an integer.
3438 @item @code{(- @var{n})}
3439 This means to use a font that is @var{n} steps smaller.
3441 @item a number, @var{factor}
3442 A number, @var{factor}, means to use a font that is @var{factor} times
3443 as tall as the default font.
3445 @item a symbol, @var{function}
3446 A symbol is a function to compute the height. It is called with the
3447 current height as argument, and should return the new height to use.
3449 @item anything else, @var{form}
3450 If the @var{height} value doesn't fit the previous possibilities, it is
3451 a form. Emacs evaluates it to get the new height, with the symbol
3452 @code{height} bound to the current specified font height.
3455 @item (raise @var{factor})
3456 This kind of display specification raises or lowers the text
3457 it applies to, relative to the baseline of the line.
3459 @var{factor} must be a number, which is interpreted as a multiple of the
3460 height of the affected text. If it is positive, that means to display
3461 the characters raised. If it is negative, that means to display them
3464 If the text also has a @code{height} display specification, that does
3465 not affect the amount of raising or lowering, which is based on the
3466 faces used for the text.
3469 You can make any display specification conditional. To do that,
3470 package it in another list of the form @code{(when @var{condition} .
3471 @var{spec})}. Then the specification @var{spec} applies only when
3472 @var{condition} evaluates to a non-@code{nil} value. During the
3473 evaluation, @code{object} is bound to the string or buffer having the
3474 conditional @code{display} property. @code{position} and
3475 @code{buffer-position} are bound to the position within @code{object}
3476 and the buffer position where the @code{display} property was found,
3477 respectively. Both positions can be different when @code{object} is a
3480 @node Display Margins
3481 @subsection Displaying in the Margins
3482 @cindex display margins
3483 @cindex margins, display
3485 A buffer can have blank areas called @dfn{display margins} on the left
3486 and on the right. Ordinary text never appears in these areas, but you
3487 can put things into the display margins using the @code{display}
3490 To put text in the left or right display margin of the window, use a
3491 display specification of the form @code{(margin right-margin)} or
3492 @code{(margin left-margin)} on it. To put an image in a display margin,
3493 use that display specification along with the display specification for
3494 the image. Unfortunately, there is currently no way to make
3495 text or images in the margin mouse-sensitive.
3497 If you put such a display specification directly on text in the
3498 buffer, the specified margin display appears @emph{instead of} that
3499 buffer text itself. To put something in the margin @emph{in
3500 association with} certain buffer text without preventing or altering
3501 the display of that text, put a @code{before-string} property on the
3502 text and put the display specification on the contents of the
3505 Before the display margins can display anything, you must give
3506 them a nonzero width. The usual way to do that is to set these
3509 @defvar left-margin-width
3510 @tindex left-margin-width
3511 This variable specifies the width of the left margin.
3512 It is buffer-local in all buffers.
3515 @defvar right-margin-width
3516 @tindex right-margin-width
3517 This variable specifies the width of the right margin.
3518 It is buffer-local in all buffers.
3521 Setting these variables does not immediately affect the window. These
3522 variables are checked when a new buffer is displayed in the window.
3523 Thus, you can make changes take effect by calling
3524 @code{set-window-buffer}.
3526 You can also set the margin widths immediately.
3528 @defun set-window-margins window left &optional right
3529 @tindex set-window-margins
3530 This function specifies the margin widths for window @var{window}.
3531 The argument @var{left} controls the left margin and
3532 @var{right} controls the right margin (default @code{0}).
3535 @defun window-margins &optional window
3536 @tindex window-margins
3537 This function returns the left and right margins of @var{window}
3538 as a cons cell of the form @code{(@var{left} . @var{right})}.
3539 If @var{window} is @code{nil}, the selected window is used.
3544 @cindex images in buffers
3546 To display an image in an Emacs buffer, you must first create an image
3547 descriptor, then use it as a display specifier in the @code{display}
3548 property of text that is displayed (@pxref{Display Property}).
3550 Emacs can display a number of different image formats; some of them
3551 are supported only if particular support libraries are installed on
3552 your machine. In some environments, Emacs can load image
3553 libraries on demand; if so, the variable @code{image-library-alist}
3554 can be used to modify the set of known names for these dynamic
3555 libraries (though it is not possible to add new image formats).
3557 The supported image formats include XBM, XPM (this requires the
3558 libraries @code{libXpm} version 3.4k and @code{libz}), GIF (requiring
3559 @code{libungif} 4.1.0), Postscript, PBM, JPEG (requiring the
3560 @code{libjpeg} library version v6a), TIFF (requiring @code{libtiff}
3561 v3.4), and PNG (requiring @code{libpng} 1.0.2).
3563 You specify one of these formats with an image type symbol. The image
3564 type symbols are @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
3565 @code{pbm}, @code{jpeg}, @code{tiff}, and @code{png}.
3568 This variable contains a list of those image type symbols that are
3569 potentially supported in the current configuration.
3570 @emph{Potentially} here means that Emacs knows about the image types,
3571 not necessarily that they can be loaded (they could depend on
3572 unavailable dynamic libraries, for example).
3574 To know which image types are really available, use
3575 @code{image-type-available-p}.
3578 @defvar image-library-alist
3579 This in an alist of image types vs external libraries needed to
3582 Each element is a list @code{(@var{image-type} @var{library}...)},
3583 where the car is a supported image format from @code{image-types}, and
3584 the rest are strings giving alternate filenames for the corresponding
3585 external libraries to load.
3587 Emacs tries to load the libraries in the order they appear on the
3588 list; if none is loaded, the running session of Emacs won't support
3589 the image type. @code{pbm} and @code{xbm} don't need to be listed;
3590 they're always supported.
3592 This variable is ignored if the image libraries are statically linked
3596 @defun image-type-available-p type
3597 @findex image-type-available-p
3599 This function returns non-@code{nil} if image type @var{type} is
3600 available, i.e., if images of this type can be loaded and displayed in
3601 Emacs. @var{type} should be one of the types contained in
3604 For image types whose support libraries are statically linked, this
3605 function always returns @code{t}; for other image types, it returns
3606 @code{t} if the dynamic library could be loaded, @code{nil} otherwise.
3610 * Image Descriptors:: How to specify an image for use in @code{:display}.
3611 * XBM Images:: Special features for XBM format.
3612 * XPM Images:: Special features for XPM format.
3613 * GIF Images:: Special features for GIF format.
3614 * Postscript Images:: Special features for Postscript format.
3615 * Other Image Types:: Various other formats are supported.
3616 * Defining Images:: Convenient ways to define an image for later use.
3617 * Showing Images:: Convenient ways to display an image once it is defined.
3618 * Image Cache:: Internal mechanisms of image display.
3621 @node Image Descriptors
3622 @subsection Image Descriptors
3623 @cindex image descriptor
3625 An image description is a list of the form @code{(image
3626 . @var{props})}, where @var{props} is a property list containing
3627 alternating keyword symbols (symbols whose names start with a colon) and
3628 their values. You can use any Lisp object as a property, but the only
3629 properties that have any special meaning are certain symbols, all of
3632 Every image descriptor must contain the property @code{:type
3633 @var{type}} to specify the format of the image. The value of @var{type}
3634 should be an image type symbol; for example, @code{xpm} for an image in
3637 Here is a list of other properties that are meaningful for all image
3641 @item :file @var{file}
3642 The @code{:file} property says to load the image from file
3643 @var{file}. If @var{file} is not an absolute file name, it is expanded
3644 in @code{data-directory}.
3646 @item :data @var{data}
3647 The @code{:data} property says the actual contents of the image.
3648 Each image must use either @code{:data} or @code{:file}, but not both.
3649 For most image types, the value of the @code{:data} property should be a
3650 string containing the image data; we recommend using a unibyte string.
3652 Before using @code{:data}, look for further information in the section
3653 below describing the specific image format. For some image types,
3654 @code{:data} may not be supported; for some, it allows other data types;
3655 for some, @code{:data} alone is not enough, so you need to use other
3656 image properties along with @code{:data}.
3658 @item :margin @var{margin}
3659 The @code{:margin} property specifies how many pixels to add as an
3660 extra margin around the image. The value, @var{margin}, must be a
3661 non-negative number, or a pair @code{(@var{x} . @var{y})} of such
3662 numbers. If it is a pair, @var{x} specifies how many pixels to add
3663 horizontally, and @var{y} specifies how many pixels to add vertically.
3664 If @code{:margin} is not specified, the default is zero.
3666 @item :ascent @var{ascent}
3667 The @code{:ascent} property specifies the amount of the image's
3668 height to use for its ascent---that is, the part above the baseline.
3669 The value, @var{ascent}, must be a number in the range 0 to 100, or
3670 the symbol @code{center}.
3672 If @var{ascent} is a number, that percentage of the image's height is
3673 used for its ascent.
3675 If @var{ascent} is @code{center}, the image is vertically centered
3676 around a centerline which would be the vertical centerline of text drawn
3677 at the position of the image, in the manner specified by the text
3678 properties and overlays that apply to the image.
3680 If this property is omitted, it defaults to 50.
3682 @item :relief @var{relief}
3683 The @code{:relief} property, if non-@code{nil}, adds a shadow rectangle
3684 around the image. The value, @var{relief}, specifies the width of the
3685 shadow lines, in pixels. If @var{relief} is negative, shadows are drawn
3686 so that the image appears as a pressed button; otherwise, it appears as
3687 an unpressed button.
3689 @item :conversion @var{algorithm}
3690 The @code{:conversion} property, if non-@code{nil}, specifies a
3691 conversion algorithm that should be applied to the image before it is
3692 displayed; the value, @var{algorithm}, specifies which algorithm.
3697 Specifies the Laplace edge detection algorithm, which blurs out small
3698 differences in color while highlighting larger differences. People
3699 sometimes consider this useful for displaying the image for a
3700 ``disabled'' button.
3702 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
3703 Specifies a general edge-detection algorithm. @var{matrix} must be
3704 either a nine-element list or a nine-element vector of numbers. A pixel
3705 at position @math{x/y} in the transformed image is computed from
3706 original pixels around that position. @var{matrix} specifies, for each
3707 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
3708 will influence the transformed pixel; element @math{0} specifies the
3709 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
3710 the pixel at @math{x/y-1} etc., as shown below:
3713 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
3714 x-1/y & x/y & x+1/y \cr
3715 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
3720 (x-1/y-1 x/y-1 x+1/y-1
3722 x-1/y+1 x/y+1 x+1/y+1)
3726 The resulting pixel is computed from the color intensity of the color
3727 resulting from summing up the RGB values of surrounding pixels,
3728 multiplied by the specified factors, and dividing that sum by the sum
3729 of the factors' absolute values.
3731 Laplace edge-detection currently uses a matrix of
3734 $$\pmatrix{1 & 0 & 0 \cr
3747 Emboss edge-detection uses a matrix of
3750 $$\pmatrix{ 2 & -1 & 0 \cr
3764 Specifies transforming the image so that it looks ``disabled''.
3767 @item :mask @var{mask}
3768 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
3769 a clipping mask for the image, so that the background of a frame is
3770 visible behind the image. If @var{bg} is not specified, or if @var{bg}
3771 is @code{t}, determine the background color of the image by looking at
3772 the four corners of the image, assuming the most frequently occurring
3773 color from the corners is the background color of the image. Otherwise,
3774 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
3775 specifying the color to assume for the background of the image.
3777 If @var{mask} is @code{nil}, remove a mask from the image, if it has
3778 one. Images in some formats include a mask which can be removed by
3779 specifying @code{:mask nil}.
3781 @item :pointer @var{shape}
3782 This specifies the pointer shape when the mouse pointer is over this
3783 image. @xref{Pointer Shape}, for available pointer shapes.
3785 @item :map @var{map}
3786 This associates an image map of @dfn{hot spots} with this image.
3788 An image map is an alist where each element has the format
3789 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
3790 as either a rectangle, a circle, or a polygon.
3792 A rectangle is a cons
3793 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
3794 which specifies the pixel coordinates of the upper left and bottom right
3795 corners of the rectangle area.
3798 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
3799 which specifies the center and the radius of the circle; @var{r} may
3800 be a float or integer.
3803 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
3804 where each pair in the vector describes one corner in the polygon.
3806 When the mouse pointer is above a hot-spot area of an image, the
3807 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
3808 property it defines a tool-tip for the hot-spot, and if it contains
3809 a @code{pointer} property, it defines the shape of the mouse cursor when
3810 it is over the hot-spot.
3811 @xref{Pointer Shape}, for available pointer shapes.
3813 When you click the mouse when the mouse pointer is over a hot-spot, an
3814 event is composed by combining the @var{id} of the hot-spot with the
3815 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
3816 @var{id} is @code{area4}.
3819 @defun image-mask-p spec &optional frame
3820 @tindex image-mask-p
3821 This function returns @code{t} if image @var{spec} has a mask bitmap.
3822 @var{frame} is the frame on which the image will be displayed.
3823 @var{frame} @code{nil} or omitted means to use the selected frame
3824 (@pxref{Input Focus}).
3828 @subsection XBM Images
3831 To use XBM format, specify @code{xbm} as the image type. This image
3832 format doesn't require an external library, so images of this type are
3835 Additional image properties supported for the @code{xbm} image type are:
3838 @item :foreground @var{foreground}
3839 The value, @var{foreground}, should be a string specifying the image
3840 foreground color, or @code{nil} for the default color. This color is
3841 used for each pixel in the XBM that is 1. The default is the frame's
3844 @item :background @var{background}
3845 The value, @var{background}, should be a string specifying the image
3846 background color, or @code{nil} for the default color. This color is
3847 used for each pixel in the XBM that is 0. The default is the frame's
3851 If you specify an XBM image using data within Emacs instead of an
3852 external file, use the following three properties:
3855 @item :data @var{data}
3856 The value, @var{data}, specifies the contents of the image.
3857 There are three formats you can use for @var{data}:
3861 A vector of strings or bool-vectors, each specifying one line of the
3862 image. Do specify @code{:height} and @code{:width}.
3865 A string containing the same byte sequence as an XBM file would contain.
3866 You must not specify @code{:height} and @code{:width} in this case,
3867 because omitting them is what indicates the data has the format of an
3868 XBM file. The file contents specify the height and width of the image.
3871 A string or a bool-vector containing the bits of the image (plus perhaps
3872 some extra bits at the end that will not be used). It should contain at
3873 least @var{width} * @code{height} bits. In this case, you must specify
3874 @code{:height} and @code{:width}, both to indicate that the string
3875 contains just the bits rather than a whole XBM file, and to specify the
3879 @item :width @var{width}
3880 The value, @var{width}, specifies the width of the image, in pixels.
3882 @item :height @var{height}
3883 The value, @var{height}, specifies the height of the image, in pixels.
3887 @subsection XPM Images
3890 To use XPM format, specify @code{xpm} as the image type. The
3891 additional image property @code{:color-symbols} is also meaningful with
3892 the @code{xpm} image type:
3895 @item :color-symbols @var{symbols}
3896 The value, @var{symbols}, should be an alist whose elements have the
3897 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
3898 the name of a color as it appears in the image file, and @var{color}
3899 specifies the actual color to use for displaying that name.
3903 @subsection GIF Images
3906 For GIF images, specify image type @code{gif}.
3909 @item :index @var{index}
3910 You can use @code{:index} to specify one image from a GIF file that
3911 contains more than one image. This property specifies use of image
3912 number @var{index} from the file. If the GIF file doesn't contain an
3913 image with index @var{index}, the image displays as a hollow box.
3917 This could be used to implement limited support for animated GIFs.
3918 For example, the following function displays a multi-image GIF file
3919 at point-min in the current buffer, switching between sub-images
3922 (defun show-anim (file max)
3923 "Display multi-image GIF file FILE which contains MAX subimages."
3924 (display-anim (current-buffer) file 0 max t))
3926 (defun display-anim (buffer file idx max first-time)
3929 (let ((img (create-image file nil :image idx)))
3932 (goto-char (point-min))
3933 (unless first-time (delete-char 1))
3935 (run-with-timer 0.1 nil 'display-anim buffer file (1+ idx) max nil)))
3938 @node Postscript Images
3939 @subsection Postscript Images
3940 @cindex Postscript images
3942 To use Postscript for an image, specify image type @code{postscript}.
3943 This works only if you have Ghostscript installed. You must always use
3944 these three properties:
3947 @item :pt-width @var{width}
3948 The value, @var{width}, specifies the width of the image measured in
3949 points (1/72 inch). @var{width} must be an integer.
3951 @item :pt-height @var{height}
3952 The value, @var{height}, specifies the height of the image in points
3953 (1/72 inch). @var{height} must be an integer.
3955 @item :bounding-box @var{box}
3956 The value, @var{box}, must be a list or vector of four integers, which
3957 specifying the bounding box of the Postscript image, analogous to the
3958 @samp{BoundingBox} comment found in Postscript files.
3961 %%BoundingBox: 22 171 567 738
3965 Displaying Postscript images from Lisp data is not currently
3966 implemented, but it may be implemented by the time you read this.
3967 See the @file{etc/NEWS} file to make sure.
3969 @node Other Image Types
3970 @subsection Other Image Types
3973 For PBM images, specify image type @code{pbm}. Color, gray-scale and
3974 monochromatic images are supported. For mono PBM images, two additional
3975 image properties are supported.
3978 @item :foreground @var{foreground}
3979 The value, @var{foreground}, should be a string specifying the image
3980 foreground color, or @code{nil} for the default color. This color is
3981 used for each pixel in the XBM that is 1. The default is the frame's
3984 @item :background @var{background}
3985 The value, @var{background}, should be a string specifying the image
3986 background color, or @code{nil} for the default color. This color is
3987 used for each pixel in the XBM that is 0. The default is the frame's
3991 For JPEG images, specify image type @code{jpeg}.
3993 For TIFF images, specify image type @code{tiff}.
3995 For PNG images, specify image type @code{png}.
3997 @node Defining Images
3998 @subsection Defining Images
4000 The functions @code{create-image}, @code{defimage} and
4001 @code{find-image} provide convenient ways to create image descriptors.
4003 @defun create-image file-or-data &optional type data-p &rest props
4004 @tindex create-image
4005 This function creates and returns an image descriptor which uses the
4006 data in @var{file-or-data}. @var{file-or-data} can be a file name or
4007 a string containing the image data; @var{data-p} should be @code{nil}
4008 for the former case, non-@code{nil} for the latter case.
4010 The optional argument @var{type} is a symbol specifying the image type.
4011 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
4012 determine the image type from the file's first few bytes, or else
4013 from the file's name.
4015 The remaining arguments, @var{props}, specify additional image
4016 properties---for example,
4019 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
4022 The function returns @code{nil} if images of this type are not
4023 supported. Otherwise it returns an image descriptor.
4026 @defmac defimage symbol specs &optional doc
4028 This macro defines @var{symbol} as an image name. The arguments
4029 @var{specs} is a list which specifies how to display the image.
4030 The third argument, @var{doc}, is an optional documentation string.
4032 Each argument in @var{specs} has the form of a property list, and each
4033 one should specify at least the @code{:type} property and either the
4034 @code{:file} or the @code{:data} property. The value of @code{:type}
4035 should be a symbol specifying the image type, the value of
4036 @code{:file} is the file to load the image from, and the value of
4037 @code{:data} is a string containing the actual image data. Here is an
4041 (defimage test-image
4042 ((:type xpm :file "~/test1.xpm")
4043 (:type xbm :file "~/test1.xbm")))
4046 @code{defimage} tests each argument, one by one, to see if it is
4047 usable---that is, if the type is supported and the file exists. The
4048 first usable argument is used to make an image descriptor which is
4049 stored in @var{symbol}.
4051 If none of the alternatives will work, then @var{symbol} is defined
4055 @defun find-image specs
4057 This function provides a convenient way to find an image satisfying one
4058 of a list of image specifications @var{specs}.
4060 Each specification in @var{specs} is a property list with contents
4061 depending on image type. All specifications must at least contain the
4062 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4063 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4064 the image type, e.g.@: @code{xbm}, @var{file} is the file to load the
4065 image from, and @var{data} is a string containing the actual image data.
4066 The first specification in the list whose @var{type} is supported, and
4067 @var{file} exists, is used to construct the image specification to be
4068 returned. If no specification is satisfied, @code{nil} is returned.
4070 The image is looked for first on @code{load-path} and then in
4071 @code{data-directory}.
4074 @node Showing Images
4075 @subsection Showing Images
4077 You can use an image descriptor by setting up the @code{display}
4078 property yourself, but it is easier to use the functions in this
4081 @defun insert-image image &optional string area slice
4082 This function inserts @var{image} in the current buffer at point. The
4083 value @var{image} should be an image descriptor; it could be a value
4084 returned by @code{create-image}, or the value of a symbol defined with
4085 @code{defimage}. The argument @var{string} specifies the text to put
4086 in the buffer to hold the image. If it is omitted or @code{nil},
4087 @code{insert-image} uses @code{" "} by default.
4089 The argument @var{area} specifies whether to put the image in a margin.
4090 If it is @code{left-margin}, the image appears in the left margin;
4091 @code{right-margin} specifies the right margin. If @var{area} is
4092 @code{nil} or omitted, the image is displayed at point within the
4095 The argument @var{slice} specifies a slice of the image to insert. If
4096 @var{slice} is @code{nil} or omitted the whole image is inserted.
4097 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
4098 @var{height})} which specifies the @var{x} and @var{y} positions and
4099 @var{width} and @var{height} of the image area to insert. Integer
4100 values are in units of pixels. A floating point number in the range
4101 0.0--1.0 stands for that fraction of the width or height of the entire
4104 Internally, this function inserts @var{string} in the buffer, and gives
4105 it a @code{display} property which specifies @var{image}. @xref{Display
4109 @defun insert-sliced-image image &optional string area rows cols
4110 This function inserts @var{image} in the current buffer at point, like
4111 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
4112 equally sized slices.
4115 @defun put-image image pos &optional string area
4116 This function puts image @var{image} in front of @var{pos} in the
4117 current buffer. The argument @var{pos} should be an integer or a
4118 marker. It specifies the buffer position where the image should appear.
4119 The argument @var{string} specifies the text that should hold the image
4120 as an alternative to the default.
4122 The argument @var{image} must be an image descriptor, perhaps returned
4123 by @code{create-image} or stored by @code{defimage}.
4125 The argument @var{area} specifies whether to put the image in a margin.
4126 If it is @code{left-margin}, the image appears in the left margin;
4127 @code{right-margin} specifies the right margin. If @var{area} is
4128 @code{nil} or omitted, the image is displayed at point within the
4131 Internally, this function creates an overlay, and gives it a
4132 @code{before-string} property containing text that has a @code{display}
4133 property whose value is the image. (Whew!)
4136 @defun remove-images start end &optional buffer
4137 This function removes images in @var{buffer} between positions
4138 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
4139 images are removed from the current buffer.
4141 This removes only images that were put into @var{buffer} the way
4142 @code{put-image} does it, not images that were inserted with
4143 @code{insert-image} or in other ways.
4146 @defun image-size spec &optional pixels frame
4148 This function returns the size of an image as a pair
4149 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
4150 specification. @var{pixels} non-@code{nil} means return sizes
4151 measured in pixels, otherwise return sizes measured in canonical
4152 character units (fractions of the width/height of the frame's default
4153 font). @var{frame} is the frame on which the image will be displayed.
4154 @var{frame} null or omitted means use the selected frame (@pxref{Input
4159 @subsection Image Cache
4161 Emacs stores images in an image cache when it displays them, so it can
4162 display them again more efficiently. It removes an image from the cache
4163 when it hasn't been displayed for a specified period of time.
4165 When an image is looked up in the cache, its specification is compared
4166 with cached image specifications using @code{equal}. This means that
4167 all images with equal specifications share the same image in the cache.
4169 @defvar image-cache-eviction-delay
4170 @tindex image-cache-eviction-delay
4171 This variable specifies the number of seconds an image can remain in the
4172 cache without being displayed. When an image is not displayed for this
4173 length of time, Emacs removes it from the image cache.
4175 If the value is @code{nil}, Emacs does not remove images from the cache
4176 except when you explicitly clear it. This mode can be useful for
4180 @defun clear-image-cache &optional frame
4181 @tindex clear-image-cache
4182 This function clears the image cache. If @var{frame} is non-@code{nil},
4183 only the cache for that frame is cleared. Otherwise all frames' caches
4190 @cindex buttons in buffers
4191 @cindex clickable buttons in buffers
4193 The @emph{button} package defines functions for inserting and
4194 manipulating clickable (with the mouse, or via keyboard commands)
4195 buttons in Emacs buffers, such as might be used for help hyper-links,
4196 etc. Emacs uses buttons for the hyper-links in help text and the like.
4198 A button is essentially a set of properties attached (via text
4199 properties or overlays) to a region of text in an Emacs buffer. These
4200 properties are called @dfn{button properties}.
4202 One of the these properties (@code{action}) is a function, which will
4203 be called when the user invokes it using the keyboard or the mouse.
4204 The invoked function may then examine the button and use its other
4205 properties as desired.
4207 In some ways the Emacs button package duplicates functionality offered
4208 by the widget package (@pxref{Top, , Introduction, widget, The Emacs
4209 Widget Library}), but the button package has the advantage that it is
4210 much faster, much smaller, and much simpler to use (for elisp
4211 programmers---for users, the result is about the same). The extra
4212 speed and space savings are useful mainly if you need to create many
4213 buttons in a buffer (for instance an @code{*Apropos*} buffer uses
4214 buttons to make entries clickable, and may contain many thousands of
4218 * Button Properties:: Button properties with special meanings.
4219 * Button Types:: Defining common properties for classes of buttons.
4220 * Making Buttons:: Adding buttons to Emacs buffers.
4221 * Manipulating Buttons:: Getting and setting properties of buttons.
4222 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
4225 @node Button Properties
4226 @subsection Button Properties
4227 @cindex button properties
4229 Buttons have an associated list of properties defining their
4230 appearance and behavior, and other arbitrary properties may be used
4231 for application specific purposes. Some properties that have special
4232 meaning to the button package include:
4236 @kindex action @r{(button property)}
4237 The function to call when the user invokes the button, which is passed
4238 the single argument @var{button}. By default this is @code{ignore},
4242 @kindex mouse-action @r{(button property)}
4243 This is similar to @code{action}, and when present, will be used
4244 instead of @code{action} for button invocations resulting from
4245 mouse-clicks (instead of the user hitting @key{RET}). If not
4246 present, mouse-clicks use @code{action} instead.
4249 @kindex face @r{(button property)}
4250 This is an Emacs face controlling how buttons of this type are
4251 displayed; by default this is the @code{button} face.
4254 @kindex mouse-face @r{(button property)}
4255 This is an additional face which controls appearance during
4256 mouse-overs (merged with the usual button face); by default this is
4257 the usual Emacs @code{highlight} face.
4260 @kindex keymap @r{(button property)}
4261 The button's keymap, defining bindings active within the button
4262 region. By default this is the usual button region keymap, stored
4263 in the variable @code{button-map}, which defines @key{RET} and
4264 @key{mouse-2} to invoke the button.
4267 @kindex type @r{(button property)}
4268 The button-type of the button. When creating a button, this is
4269 usually specified using the @code{:type} keyword argument.
4270 @xref{Button Types}.
4273 @kindex help-index @r{(button property)}
4274 A string displayed by the Emacs tool-tip help system; by default,
4275 @code{"mouse-2, RET: Push this button"}.
4278 @kindex follow-link @r{(button property)}
4279 The follow-link property, defining how a @key{Mouse-1} click behaves
4280 on this button, @xref{Links and Mouse-1}.
4283 @kindex button @r{(button property)}
4284 All buttons have a non-@code{nil} @code{button} property, which may be useful
4285 in finding regions of text that comprise buttons (which is what the
4286 standard button functions do).
4289 There are other properties defined for the regions of text in a
4290 button, but these are not generally interesting for typical uses.
4293 @subsection Button Types
4294 @cindex button types
4296 Every button has a button @emph{type}, which defines default values
4297 for the button's properties. Button types are arranged in a
4298 hierarchy, with specialized types inheriting from more general types,
4299 so that it's easy to define special-purpose types of buttons for
4302 @defun define-button-type name &rest properties
4303 @tindex define-button-type
4304 Define a `button type' called @var{name}. The remaining arguments
4305 form a sequence of @var{property value} pairs, specifying default
4306 property values for buttons with this type (a button's type may be set
4307 by giving it a @code{type} property when creating the button, using
4308 the @code{:type} keyword argument).
4310 In addition, the keyword argument @code{:supertype} may be used to
4311 specify a button-type from which @var{name} inherits its default
4312 property values. Note that this inheritance happens only when
4313 @var{name} is defined; subsequent changes to a supertype are not
4314 reflected in its subtypes.
4317 Using @code{define-button-type} to define default properties for
4318 buttons is not necessary---buttons without any specified type use the
4319 built-in button-type @code{button}---but it is encouraged, since
4320 doing so usually makes the resulting code clearer and more efficient.
4322 @node Making Buttons
4323 @subsection Making Buttons
4324 @cindex making buttons
4326 Buttons are associated with a region of text, using an overlay or
4327 text properties to hold button-specific information, all of which are
4328 initialized from the button's type (which defaults to the built-in
4329 button type @code{button}). Like all Emacs text, the appearance of
4330 the button is governed by the @code{face} property; by default (via
4331 the @code{face} property inherited from the @code{button} button-type)
4332 this is a simple underline, like a typical web-page link.
4334 For convenience, there are two sorts of button-creation functions,
4335 those that add button properties to an existing region of a buffer,
4336 called @code{make-...button}, and those also insert the button text,
4337 called @code{insert-...button}.
4339 The button-creation functions all take the @code{&rest} argument
4340 @var{properties}, which should be a sequence of @var{property value}
4341 pairs, specifying properties to add to the button; see @ref{Button
4342 Properties}. In addition, the keyword argument @code{:type} may be
4343 used to specify a button-type from which to inherit other properties;
4344 see @ref{Button Types}. Any properties not explicitly specified
4345 during creation will be inherited from the button's type (if the type
4346 defines such a property).
4348 The following functions add a button using an overlay
4349 (@pxref{Overlays}) to hold the button properties:
4351 @defun make-button beg end &rest properties
4353 This makes a button from @var{beg} to @var{end} in the
4354 current buffer, and returns it.
4357 @defun insert-button label &rest properties
4358 @tindex insert-button
4359 This insert a button with the label @var{label} at point,
4363 The following functions are similar, but use Emacs text properties
4364 (@pxref{Text Properties}) to hold the button properties, making the
4365 button actually part of the text instead of being a property of the
4366 buffer. Buttons using text properties do not create markers into the
4367 buffer, which is important for speed when you use extremely large
4368 numbers of buttons. Both functions return the position of the start
4371 @defun make-text-button beg end &rest properties
4372 @tindex make-text-button
4373 This makes a button from @var{beg} to @var{end} in the current buffer, using
4377 @defun insert-text-button label &rest properties
4378 @tindex insert-text-button
4379 This inserts a button with the label @var{label} at point, using text
4383 @node Manipulating Buttons
4384 @subsection Manipulating Buttons
4385 @cindex manipulating buttons
4387 These are functions for getting and setting properties of buttons.
4388 Often these are used by a button's invocation function to determine
4391 Where a @var{button} parameter is specified, it means an object
4392 referring to a specific button, either an overlay (for overlay
4393 buttons), or a buffer-position or marker (for text property buttons).
4394 Such an object is passed as the first argument to a button's
4395 invocation function when it is invoked.
4397 @defun button-start button
4398 @tindex button-start
4399 Return the position at which @var{button} starts.
4402 @defun button-end button
4404 Return the position at which @var{button} ends.
4407 @defun button-get button prop
4409 Get the property of button @var{button} named @var{prop}.
4412 @defun button-put button prop val
4414 Set @var{button}'s @var{prop} property to @var{val}.
4417 @defun button-activate button &optional use-mouse-action
4418 @tindex button-activate
4419 Call @var{button}'s @code{action} property (i.e., invoke it). If
4420 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
4421 @code{mouse-action} property instead of @code{action}; if the button
4422 has no @code{mouse-action} property, use @code{action} as normal.
4425 @defun button-label button
4426 @tindex button-label
4427 Return @var{button}'s text label.
4430 @defun button-type button
4432 Return @var{button}'s button-type.
4435 @defun button-has-type-p button type
4436 @tindex button-has-type-p
4437 Return @code{t} if @var{button} has button-type @var{type}, or one of
4438 @var{type}'s subtypes.
4441 @defun button-at pos
4443 Return the button at position @var{pos} in the current buffer, or @code{nil}.
4446 @defun button-type-put type prop val
4447 @tindex button-type-put
4448 Set the button-type @var{type}'s @var{prop} property to @var{val}.
4451 @defun button-type-get type prop
4452 @tindex button-type-get
4453 Get the property of button-type @var{type} named @var{prop}.
4456 @defun button-type-subtype-p type supertype
4457 @tindex button-type-subtype-p
4458 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
4461 @node Button Buffer Commands
4462 @subsection Button Buffer Commands
4463 @cindex button buffer commands
4465 These are commands and functions for locating and operating on
4466 buttons in an Emacs buffer.
4468 @code{push-button} is the command that a user uses to actually `push'
4469 a button, and is bound by default in the button itself to @key{RET}
4470 and to @key{mouse-2} using a region-specific keymap. Commands
4471 that are useful outside the buttons itself, such as
4472 @code{forward-button} and @code{backward-button} are additionally
4473 available in the keymap stored in @code{button-buffer-map}; a mode
4474 which uses buttons may want to use @code{button-buffer-map} as a
4475 parent keymap for its keymap.
4477 If the button has a non-@code{nil} @code{follow-link} property, and
4478 @var{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
4479 will also activate the @code{push-button} command.
4480 @xref{Links and Mouse-1}.
4482 @deffn Command push-button &optional pos use-mouse-action
4484 Perform the action specified by a button at location @var{pos}.
4485 @var{pos} may be either a buffer position or a mouse-event. If
4486 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
4487 mouse-event (@pxref{Mouse Events}), try to invoke the button's
4488 @code{mouse-action} property instead of @code{action}; if the button
4489 has no @code{mouse-action} property, use @code{action} as normal.
4490 @var{pos} defaults to point, except when @code{push-button} is invoked
4491 interactively as the result of a mouse-event, in which case, the mouse
4492 event's position is used. If there's no button at @var{pos}, do
4493 nothing and return @code{nil}, otherwise return @code{t}.
4496 @deffn Command forward-button n &optional wrap display-message
4497 @tindex forward-button
4498 Move to the @var{n}th next button, or @var{n}th previous button if
4499 @var{n} is negative. If @var{n} is zero, move to the start of any
4500 button at point. If @var{wrap} is non-@code{nil}, moving past either
4501 end of the buffer continues from the other end. If
4502 @var{display-message} is non-@code{nil}, the button's help-echo string
4503 is displayed. Any button with a non-@code{nil} @code{skip} property
4504 is skipped over. Returns the button found.
4507 @deffn Command backward-button n &optional wrap display-message
4508 @tindex backward-button
4509 Move to the @var{n}th previous button, or @var{n}th next button if
4510 @var{n} is negative. If @var{n} is zero, move to the start of any
4511 button at point. If @var{wrap} is non-@code{nil}, moving past either
4512 end of the buffer continues from the other end. If
4513 @var{display-message} is non-@code{nil}, the button's help-echo string
4514 is displayed. Any button with a non-@code{nil} @code{skip} property
4515 is skipped over. Returns the button found.
4518 @defun next-button pos &optional count-current
4520 Return the next button after position @var{pos} in the current buffer.
4521 If @var{count-current} is non-@code{nil}, count any button at
4522 @var{pos} in the search, instead of starting at the next button.
4525 @defun previous-button pos &optional count-current
4526 @tindex previous-button
4527 Return the @var{n}th button before position @var{pos} in the current
4528 buffer. If @var{count-current} is non-@code{nil}, count any button at
4529 @var{pos} in the search, instead of starting at the next button.
4533 @section Blinking Parentheses
4534 @cindex parenthesis matching
4536 @cindex balancing parentheses
4537 @cindex close parenthesis
4539 This section describes the mechanism by which Emacs shows a matching
4540 open parenthesis when the user inserts a close parenthesis.
4542 @defvar blink-paren-function
4543 The value of this variable should be a function (of no arguments) to
4544 be called whenever a character with close parenthesis syntax is inserted.
4545 The value of @code{blink-paren-function} may be @code{nil}, in which
4546 case nothing is done.
4549 @defopt blink-matching-paren
4550 If this variable is @code{nil}, then @code{blink-matching-open} does
4554 @defopt blink-matching-paren-distance
4555 This variable specifies the maximum distance to scan for a matching
4556 parenthesis before giving up.
4559 @defopt blink-matching-delay
4560 This variable specifies the number of seconds for the cursor to remain
4561 at the matching parenthesis. A fraction of a second often gives
4562 good results, but the default is 1, which works on all systems.
4565 @deffn Command blink-matching-open
4566 This function is the default value of @code{blink-paren-function}. It
4567 assumes that point follows a character with close parenthesis syntax and
4568 moves the cursor momentarily to the matching opening character. If that
4569 character is not already on the screen, it displays the character's
4570 context in the echo area. To avoid long delays, this function does not
4571 search farther than @code{blink-matching-paren-distance} characters.
4573 Here is an example of calling this function explicitly.
4577 (defun interactive-blink-matching-open ()
4578 @c Do not break this line! -- rms.
4579 @c The first line of a doc string
4580 @c must stand alone.
4581 "Indicate momentarily the start of sexp before point."
4585 (let ((blink-matching-paren-distance
4587 (blink-matching-paren t))
4588 (blink-matching-open)))
4594 @section Inverse Video
4595 @cindex Inverse Video
4597 @defopt inverse-video
4598 @cindex highlighting
4599 This variable controls whether Emacs uses inverse video for all text
4600 on the screen. Non-@code{nil} means yes, @code{nil} means no. The
4601 default is @code{nil}.
4605 @section Usual Display Conventions
4607 The usual display conventions define how to display each character
4608 code. You can override these conventions by setting up a display table
4609 (@pxref{Display Tables}). Here are the usual display conventions:
4613 Character codes 32 through 126 map to glyph codes 32 through 126.
4614 Normally this means they display as themselves.
4617 Character code 9 is a horizontal tab. It displays as whitespace
4618 up to a position determined by @code{tab-width}.
4621 Character code 10 is a newline.
4624 All other codes in the range 0 through 31, and code 127, display in one
4625 of two ways according to the value of @code{ctl-arrow}. If it is
4626 non-@code{nil}, these codes map to sequences of two glyphs, where the
4627 first glyph is the @acronym{ASCII} code for @samp{^}. (A display table can
4628 specify a glyph to use instead of @samp{^}.) Otherwise, these codes map
4629 just like the codes in the range 128 to 255.
4631 On MS-DOS terminals, Emacs arranges by default for the character code
4632 127 to be mapped to the glyph code 127, which normally displays as an
4633 empty polygon. This glyph is used to display non-@acronym{ASCII} characters
4634 that the MS-DOS terminal doesn't support. @xref{MS-DOS and MULE,,,
4635 emacs, The GNU Emacs Manual}.
4638 Character codes 128 through 255 map to sequences of four glyphs, where
4639 the first glyph is the @acronym{ASCII} code for @samp{\}, and the others are
4640 digit characters representing the character code in octal. (A display
4641 table can specify a glyph to use instead of @samp{\}.)
4644 Multibyte character codes above 256 are displayed as themselves, or as a
4645 question mark or empty box if the terminal cannot display that
4649 The usual display conventions apply even when there is a display
4650 table, for any character whose entry in the active display table is
4651 @code{nil}. Thus, when you set up a display table, you need only
4652 specify the characters for which you want special behavior.
4654 These display rules apply to carriage return (character code 13), when
4655 it appears in the buffer. But that character may not appear in the
4656 buffer where you expect it, if it was eliminated as part of end-of-line
4657 conversion (@pxref{Coding System Basics}).
4659 These variables affect the way certain characters are displayed on the
4660 screen. Since they change the number of columns the characters occupy,
4661 they also affect the indentation functions. These variables also affect
4662 how the mode line is displayed; if you want to force redisplay of the
4663 mode line using the new values, call the function
4664 @code{force-mode-line-update} (@pxref{Mode Line Format}).
4667 @cindex control characters in display
4668 This buffer-local variable controls how control characters are
4669 displayed. If it is non-@code{nil}, they are displayed as a caret
4670 followed by the character: @samp{^A}. If it is @code{nil}, they are
4671 displayed as a backslash followed by three octal digits: @samp{\001}.
4674 @c Following may have overfull hbox.
4675 @defvar default-ctl-arrow
4676 The value of this variable is the default value for @code{ctl-arrow} in
4677 buffers that do not override it. @xref{Default Value}.
4681 The value of this variable is the spacing between tab stops used for
4682 displaying tab characters in Emacs buffers. The value is in units of
4683 columns, and the default is 8. Note that this feature is completely
4684 independent of the user-settable tab stops used by the command
4685 @code{tab-to-tab-stop}. @xref{Indent Tabs}.
4688 @defopt indicate-empty-lines
4689 @tindex indicate-empty-lines
4690 @cindex fringes, and empty line indication
4691 When this is non-@code{nil}, Emacs displays a special glyph in the
4692 fringe of each empty line at the end of the buffer, on terminals that
4693 support it (window systems). @xref{Fringes}.
4696 @defvar indicate-buffer-boundaries
4697 This buffer-local variable controls how the buffer boundaries and
4698 window scrolling are indicated in the window fringes.
4700 Emacs can indicate the buffer boundaries---that is, the first and last
4701 line in the buffer---with angle icons when they appear on the screen.
4702 In addition, Emacs can display an up-arrow in the fringe to show
4703 that there is text above the screen, and a down-arrow to show
4704 there is text below the screen.
4706 There are four kinds of basic values:
4710 Don't display the icons.
4712 Display them in the left fringe.
4714 Display them in the right fringe.
4715 @item @var{anything-else}
4716 Display the icon at the top of the window top in the left fringe, and other
4717 in the right fringe.
4720 If value is a cons @code{(@var{angles} . @var{arrows})}, @var{angles}
4721 controls the angle icons, and @var{arrows} controls the arrows. Both
4722 @var{angles} and @var{arrows} work according to the table above.
4723 Thus, @code{(t . right)} places the top angle icon in the left
4724 fringe, the bottom angle icon in the right fringe, and both arrows in
4728 @defvar default-indicate-buffer-boundaries
4729 The value of this variable is the default value for
4730 @code{indicate-buffer-boundaries} in buffers that do not override it.
4733 @node Display Tables
4734 @section Display Tables
4736 @cindex display table
4737 You can use the @dfn{display table} feature to control how all possible
4738 character codes display on the screen. This is useful for displaying
4739 European languages that have letters not in the @acronym{ASCII} character
4742 The display table maps each character code into a sequence of
4743 @dfn{glyphs}, each glyph being a graphic that takes up one character
4744 position on the screen. You can also define how to display each glyph
4745 on your terminal, using the @dfn{glyph table}.
4747 Display tables affect how the mode line is displayed; if you want to
4748 force redisplay of the mode line using a new display table, call
4749 @code{force-mode-line-update} (@pxref{Mode Line Format}).
4752 * Display Table Format:: What a display table consists of.
4753 * Active Display Table:: How Emacs selects a display table to use.
4754 * Glyphs:: How to define a glyph, and what glyphs mean.
4757 @node Display Table Format
4758 @subsection Display Table Format
4760 A display table is actually a char-table (@pxref{Char-Tables}) with
4761 @code{display-table} as its subtype.
4763 @defun make-display-table
4764 This creates and returns a display table. The table initially has
4765 @code{nil} in all elements.
4768 The ordinary elements of the display table are indexed by character
4769 codes; the element at index @var{c} says how to display the character
4770 code @var{c}. The value should be @code{nil} or a vector of glyph
4771 values (@pxref{Glyphs}). If an element is @code{nil}, it says to
4772 display that character according to the usual display conventions
4773 (@pxref{Usual Display}).
4775 If you use the display table to change the display of newline
4776 characters, the whole buffer will be displayed as one long ``line.''
4778 The display table also has six ``extra slots'' which serve special
4779 purposes. Here is a table of their meanings; @code{nil} in any slot
4780 means to use the default for that slot, as stated below.
4784 The glyph for the end of a truncated screen line (the default for this
4785 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
4786 arrows in the fringes to indicate truncation, so the display table has
4790 The glyph for the end of a continued line (the default is @samp{\}).
4791 On graphical terminals, Emacs uses curved arrows in the fringes to
4792 indicate continuation, so the display table has no effect.
4795 The glyph for indicating a character displayed as an octal character
4796 code (the default is @samp{\}).
4799 The glyph for indicating a control character (the default is @samp{^}).
4802 A vector of glyphs for indicating the presence of invisible lines (the
4803 default is @samp{...}). @xref{Selective Display}.
4806 The glyph used to draw the border between side-by-side windows (the
4807 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
4808 when there are no scroll bars; if scroll bars are supported and in use,
4809 a scroll bar separates the two windows.
4812 For example, here is how to construct a display table that mimics the
4813 effect of setting @code{ctl-arrow} to a non-@code{nil} value:
4816 (setq disptab (make-display-table))
4819 (or (= i ?\t) (= i ?\n)
4820 (aset disptab i (vector ?^ (+ i 64))))
4822 (aset disptab 127 (vector ?^ ??)))
4825 @defun display-table-slot display-table slot
4826 This function returns the value of the extra slot @var{slot} of
4827 @var{display-table}. The argument @var{slot} may be a number from 0 to
4828 5 inclusive, or a slot name (symbol). Valid symbols are
4829 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
4830 @code{selective-display}, and @code{vertical-border}.
4833 @defun set-display-table-slot display-table slot value
4834 This function stores @var{value} in the extra slot @var{slot} of
4835 @var{display-table}. The argument @var{slot} may be a number from 0 to
4836 5 inclusive, or a slot name (symbol). Valid symbols are
4837 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
4838 @code{selective-display}, and @code{vertical-border}.
4841 @defun describe-display-table display-table
4842 @tindex describe-display-table
4843 This function displays a description of the display table
4844 @var{display-table} in a help buffer.
4847 @deffn Command describe-current-display-table
4848 @tindex describe-current-display-table
4849 This command displays a description of the current display table in a
4853 @node Active Display Table
4854 @subsection Active Display Table
4855 @cindex active display table
4857 Each window can specify a display table, and so can each buffer. When
4858 a buffer @var{b} is displayed in window @var{w}, display uses the
4859 display table for window @var{w} if it has one; otherwise, the display
4860 table for buffer @var{b} if it has one; otherwise, the standard display
4861 table if any. The display table chosen is called the @dfn{active}
4864 @defun window-display-table &optional window
4865 This function returns @var{window}'s display table, or @code{nil}
4866 if @var{window} does not have an assigned display table. The default
4867 for @var{window} is the selected window.
4870 @defun set-window-display-table window table
4871 This function sets the display table of @var{window} to @var{table}.
4872 The argument @var{table} should be either a display table or
4876 @defvar buffer-display-table
4877 This variable is automatically buffer-local in all buffers; its value in
4878 a particular buffer specifies the display table for that buffer. If it
4879 is @code{nil}, that means the buffer does not have an assigned display
4883 @defvar standard-display-table
4884 This variable's value is the default display table, used whenever a
4885 window has no display table and neither does the buffer displayed in
4886 that window. This variable is @code{nil} by default.
4889 If there is no display table to use for a particular window---that is,
4890 if the window specifies none, its buffer specifies none, and
4891 @code{standard-display-table} is @code{nil}---then Emacs uses the usual
4892 display conventions for all character codes in that window. @xref{Usual
4895 A number of functions for changing the standard display table
4896 are defined in the library @file{disp-table}.
4902 A @dfn{glyph} is a generalization of a character; it stands for an
4903 image that takes up a single character position on the screen. Glyphs
4904 are represented in Lisp as integers, just as characters are. Normally
4905 Emacs finds glyphs in the display table (@pxref{Display Tables}).
4907 A glyph can be @dfn{simple} or it can be defined by the @dfn{glyph
4908 table}. A simple glyph is just a way of specifying a character and a
4909 face to output it in. The glyph code for a simple glyph, mod 524288,
4910 is the character to output, and the glyph code divided by 524288
4911 specifies the face number (@pxref{Face Functions}) to use while
4912 outputting it. (524288 is
4921 On character terminals, you can set up a @dfn{glyph table} to define
4922 the meaning of glyph codes. The glyph codes is the value of the
4923 variable @code{glyph-table}.
4926 The value of this variable is the current glyph table. It should be a
4927 vector; the @var{g}th element defines glyph code @var{g}.
4929 If a glyph code is greater than or equal to the length of the glyph
4930 table, that code is automatically simple. If the value of
4931 @code{glyph-table} is @code{nil} instead of a vector, then all glyphs
4932 are simple. The glyph table is not used on graphical displays, only
4933 on character terminals. On graphical displays, all glyphs are simple.
4936 Here are the possible types of elements in the glyph table:
4940 Send the characters in @var{string} to the terminal to output
4941 this glyph. This alternative is available on character terminals,
4942 but not under a window system.
4945 Define this glyph code as an alias for glyph code @var{integer}. You
4946 can use an alias to specify a face code for the glyph and use a small
4950 This glyph is simple.
4953 @defun create-glyph string
4954 @tindex create-glyph
4955 This function returns a newly-allocated glyph code which is set up to
4956 display by sending @var{string} to the terminal.
4964 This section describes how to make Emacs ring the bell (or blink the
4965 screen) to attract the user's attention. Be conservative about how
4966 often you do this; frequent bells can become irritating. Also be
4967 careful not to use just beeping when signaling an error is more
4968 appropriate. (@xref{Errors}.)
4970 @defun ding &optional do-not-terminate
4971 @cindex keyboard macro termination
4972 This function beeps, or flashes the screen (see @code{visible-bell} below).
4973 It also terminates any keyboard macro currently executing unless
4974 @var{do-not-terminate} is non-@code{nil}.
4977 @defun beep &optional do-not-terminate
4978 This is a synonym for @code{ding}.
4981 @defopt visible-bell
4982 This variable determines whether Emacs should flash the screen to
4983 represent a bell. Non-@code{nil} means yes, @code{nil} means no. This
4984 is effective on a window system, and on a character-only terminal
4985 provided the terminal's Termcap entry defines the visible bell
4986 capability (@samp{vb}).
4989 @defvar ring-bell-function
4990 If this is non-@code{nil}, it specifies how Emacs should ``ring the
4991 bell.'' Its value should be a function of no arguments. If this is
4992 non-@code{nil}, it takes precedence over the @code{visible-bell}
4996 @node Window Systems
4997 @section Window Systems
4999 Emacs works with several window systems, most notably the X Window
5000 System. Both Emacs and X use the term ``window'', but use it
5001 differently. An Emacs frame is a single window as far as X is
5002 concerned; the individual Emacs windows are not known to X at all.
5004 @defvar window-system
5005 This variable tells Lisp programs what window system Emacs is running
5006 under. The possible values are
5010 @cindex X Window System
5011 Emacs is displaying using X.
5013 Emacs is displaying using MS-DOS.
5015 Emacs is displaying using Windows.
5017 Emacs is displaying using a Macintosh.
5019 Emacs is using a character-based terminal.
5023 @defvar window-setup-hook
5024 This variable is a normal hook which Emacs runs after handling the
5025 initialization files. Emacs runs this hook after it has completed
5026 loading your init file, the default initialization file (if
5027 any), and the terminal-specific Lisp code, and running the hook
5028 @code{term-setup-hook}.
5030 This hook is used for internal purposes: setting up communication with
5031 the window system, and creating the initial window. Users should not
5036 arch-tag: ffdf5714-7ecf-415b-9023-fbc6b409c2c6