1 @c -*- mode: texinfo; coding: utf-8 -*-
2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2017 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
8 This chapter describes a number of features related to the display
9 that Emacs presents to the user.
12 * Refresh Screen:: Clearing the screen and redrawing everything on it.
13 * Forcing Redisplay:: Forcing redisplay.
14 * Truncation:: Folding or wrapping long text lines.
15 * The Echo Area:: Displaying messages at the bottom of the screen.
16 * Warnings:: Displaying warning messages for the user.
17 * Invisible Text:: Hiding part of the buffer text.
18 * Selective Display:: Hiding part of the buffer text (the old way).
19 * Temporary Displays:: Displays that go away automatically.
20 * Overlays:: Use overlays to highlight parts of the buffer.
21 * Size of Displayed Text:: How large displayed text is.
22 * Line Height:: Controlling the height of lines.
23 * Faces:: A face defines a graphics style for text characters:
25 * Fringes:: Controlling window fringes.
26 * Scroll Bars:: Controlling scroll bars.
27 * Window Dividers:: Separating windows visually.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Xwidgets:: Displaying native widgets in Emacs buffers.
31 * Buttons:: Adding clickable buttons to Emacs buffers.
32 * Abstract Display:: Emacs's Widget for Object Collections.
33 * Blinking:: How Emacs shows the matching open parenthesis.
34 * Character Display:: How Emacs displays individual characters.
35 * Beeping:: Audible signal to the user.
36 * Window Systems:: Which window system is being used.
37 * Tooltips:: Tooltip display in Emacs.
38 * Bidirectional Display:: Display of bidirectional scripts, such as
43 @section Refreshing the Screen
44 @cindex refresh the screen
45 @cindex screen refresh
47 The function @code{redraw-frame} clears and redisplays the entire
48 contents of a given frame (@pxref{Frames}). This is useful if the
51 @defun redraw-frame &optional frame
52 This function clears and redisplays frame @var{frame}. If @var{frame}
53 is omitted or nil, it redraws the selected frame.
56 Even more powerful is @code{redraw-display}:
58 @deffn Command redraw-display
59 This function clears and redisplays all visible frames.
62 In Emacs, processing user input takes priority over redisplay. If
63 you call these functions when input is available, they don't redisplay
64 immediately, but the requested redisplay does happen
65 eventually---after all the input has been processed.
67 On text terminals, suspending and resuming Emacs normally also
68 refreshes the screen. Some terminal emulators record separate
69 contents for display-oriented programs such as Emacs and for ordinary
70 sequential display. If you are using such a terminal, you might want
71 to inhibit the redisplay on resumption.
73 @defopt no-redraw-on-reenter
74 @cindex suspend (cf. @code{no-redraw-on-reenter})
75 @cindex resume (cf. @code{no-redraw-on-reenter})
76 This variable controls whether Emacs redraws the entire screen after it
77 has been suspended and resumed. Non-@code{nil} means there is no need
78 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
81 @node Forcing Redisplay
82 @section Forcing Redisplay
83 @cindex forcing redisplay
85 Emacs normally tries to redisplay the screen whenever it waits for
86 input. With the following function, you can request an immediate
87 attempt to redisplay, in the middle of Lisp code, without actually
90 @defun redisplay &optional force
91 This function tries immediately to redisplay. The optional argument
92 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
93 instead of being preempted if input is pending.
95 The function returns @code{t} if it actually tried to redisplay, and
96 @code{nil} otherwise. A value of @code{t} does not mean that
97 redisplay proceeded to completion; it could have been preempted by
101 Although @code{redisplay} tries immediately to redisplay, it does
102 not change how Emacs decides which parts of its frame(s) to redisplay.
103 By contrast, the following function adds certain windows to the
104 pending redisplay work (as if their contents had completely changed),
105 but does not immediately try to perform redisplay.
107 @defun force-window-update &optional object
108 This function forces some or all windows to be updated the next time
109 Emacs does a redisplay. If @var{object} is a window, that window is
110 to be updated. If @var{object} is a buffer or buffer name, all
111 windows displaying that buffer are to be updated. If @var{object} is
112 @code{nil} (or omitted), all windows are to be updated.
114 This function does not do a redisplay immediately; Emacs does that as
115 it waits for input, or when the function @code{redisplay} is called.
118 @defvar pre-redisplay-function
119 A function run just before redisplay. It is called with one argument,
120 the set of windows to be redisplayed. The set can be @code{nil},
121 meaning only the selected window, or @code{t}, meaning all the
125 @defvar pre-redisplay-functions
126 This hook is run just before redisplay. It is called once in each
127 window that is about to be redisplayed, with @code{current-buffer} set
128 to the buffer displayed in that window.
133 @cindex line wrapping
134 @cindex line truncation
135 @cindex continuation lines
136 @cindex @samp{$} in display
137 @cindex @samp{\} in display
139 When a line of text extends beyond the right edge of a window, Emacs
140 can @dfn{continue} the line (make it wrap to the next screen
141 line), or @dfn{truncate} the line (limit it to one screen line). The
142 additional screen lines used to display a long text line are called
143 @dfn{continuation} lines. Continuation is not the same as filling;
144 continuation happens on the screen only, not in the buffer contents,
145 and it breaks a line precisely at the right margin, not at a word
146 boundary. @xref{Filling}.
148 On a graphical display, tiny arrow images in the window fringes
149 indicate truncated and continued lines (@pxref{Fringes}). On a text
150 terminal, a @samp{$} in the rightmost column of the window indicates
151 truncation; a @samp{\} on the rightmost column indicates a line that
152 wraps. (The display table can specify alternate characters to use
153 for this; @pxref{Display Tables}).
155 @defopt truncate-lines
156 If this buffer-local variable is non-@code{nil}, lines that extend
157 beyond the right edge of the window are truncated; otherwise, they are
158 continued. As a special exception, the variable
159 @code{truncate-partial-width-windows} takes precedence in
160 @dfn{partial-width} windows (i.e., windows that do not occupy the
164 @defopt truncate-partial-width-windows
165 @cindex partial-width windows
166 This variable controls line truncation in @dfn{partial-width} windows.
167 A partial-width window is one that does not occupy the entire frame
168 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
169 truncation is determined by the variable @code{truncate-lines} (see
170 above). If the value is an integer @var{n}, lines are truncated if
171 the partial-width window has fewer than @var{n} columns, regardless of
172 the value of @code{truncate-lines}; if the partial-width window has
173 @var{n} or more columns, line truncation is determined by
174 @code{truncate-lines}. For any other non-@code{nil} value, lines are
175 truncated in every partial-width window, regardless of the value of
176 @code{truncate-lines}.
179 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
180 a window, that forces truncation.
183 If this buffer-local variable is non-@code{nil}, it defines a
184 @dfn{wrap prefix} which Emacs displays at the start of every
185 continuation line. (If lines are truncated, @code{wrap-prefix} is
186 never used.) Its value may be a string or an image (@pxref{Other
187 Display Specs}), or a stretch of whitespace such as specified by the
188 @code{:width} or @code{:align-to} display properties (@pxref{Specified
189 Space}). The value is interpreted in the same way as a @code{display}
190 text property. @xref{Display Property}.
192 A wrap prefix may also be specified for regions of text, using the
193 @code{wrap-prefix} text or overlay property. This takes precedence
194 over the @code{wrap-prefix} variable. @xref{Special Properties}.
198 If this buffer-local variable is non-@code{nil}, it defines a
199 @dfn{line prefix} which Emacs displays at the start of every
200 non-continuation line. Its value may be a string or an image
201 (@pxref{Other Display Specs}), or a stretch of whitespace such as
202 specified by the @code{:width} or @code{:align-to} display properties
203 (@pxref{Specified Space}). The value is interpreted in the same way
204 as a @code{display} text property. @xref{Display Property}.
206 A line prefix may also be specified for regions of text using the
207 @code{line-prefix} text or overlay property. This takes precedence
208 over the @code{line-prefix} variable. @xref{Special Properties}.
212 If your buffer contains only very short lines, you might find it
213 advisable to set @code{cache-long-scans} to @code{nil}.
215 @defvar cache-long-scans
216 If this variable is non-@code{nil} (the default), various indentation
217 and motion functions, and Emacs redisplay, cache the results of
218 scanning the buffer, and consult the cache to avoid rescanning regions
219 of the buffer unless they are modified.
221 Turning off the cache speeds up processing of short lines somewhat.
223 This variable is automatically buffer-local in every buffer.
228 @section The Echo Area
229 @cindex error display
232 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
233 The @dfn{echo area} is used for displaying error messages
234 (@pxref{Errors}), for messages made with the @code{message} primitive,
235 and for echoing keystrokes. It is not the same as the minibuffer,
236 despite the fact that the minibuffer appears (when active) in the same
237 place on the screen as the echo area. @xref{Minibuffer,, The
238 Minibuffer, emacs, The GNU Emacs Manual}.
240 Apart from the functions documented in this section, you can print
241 Lisp objects to the echo area by specifying @code{t} as the output
242 stream. @xref{Output Streams}.
245 * Displaying Messages:: Explicitly displaying text in the echo area.
246 * Progress:: Informing user about progress of a long operation.
247 * Logging Messages:: Echo area messages are logged for the user.
248 * Echo Area Customization:: Controlling the echo area.
251 @node Displaying Messages
252 @subsection Displaying Messages in the Echo Area
253 @cindex display message in echo area
255 This section describes the standard functions for displaying
256 messages in the echo area.
258 @defun message format-string &rest arguments
259 This function displays a message in the echo area.
260 @var{format-string} is a format string, and @var{arguments} are the
261 objects for its format specifications, like in the @code{format-message}
262 function (@pxref{Formatting Strings}). The resulting formatted string
263 is displayed in the echo area; if it contains @code{face} text
264 properties, it is displayed with the specified faces (@pxref{Faces}).
265 The string is also added to the @file{*Messages*} buffer, but without
266 text properties (@pxref{Logging Messages}).
268 The @code{text-quoting-style} variable controls what quotes are
269 generated; @xref{Keys in Documentation}. A call using a format like
270 @t{"Missing `%s'"} with grave accents and apostrophes typically
271 generates a message like @t{"Missing ‘foo’"} with matching curved
272 quotes. In contrast, a call using a format like @t{"Missing '%s'"}
273 with only apostrophes typically generates a message like @t{"Missing
274 ’foo’"} with only closing curved quotes, an unusual style in English.
276 In batch mode, the message is printed to the standard error stream,
277 followed by a newline.
279 When @code{inhibit-message} is non-@code{nil}, no message will be displayed
280 in the echo area, it will only be logged to @samp{*Messages*}.
282 If @var{format-string} is @code{nil} or the empty string,
283 @code{message} clears the echo area; if the echo area has been
284 expanded automatically, this brings it back to its normal size. If
285 the minibuffer is active, this brings the minibuffer contents back
286 onto the screen immediately.
290 (message "Reverting `%s'..." (buffer-name))
291 @print{} Reverting ‘subr.el’...
292 @result{} "Reverting ‘subr.el’..."
296 ---------- Echo Area ----------
297 Reverting ‘subr.el’...
298 ---------- Echo Area ----------
302 To automatically display a message in the echo area or in a pop-buffer,
303 depending on its size, use @code{display-message-or-buffer} (see below).
305 @strong{Warning:} If you want to use your own string as a message
306 verbatim, don't just write @code{(message @var{string})}. If
307 @var{string} contains @samp{%}, @samp{`}, or @samp{'} it may be
308 reformatted, with undesirable results. Instead, use @code{(message
312 @defvar inhibit-message
313 When this variable is non-@code{nil}, @code{message} and related functions
314 will not use the Echo Area to display messages.
317 @defmac with-temp-message message &rest body
318 This construct displays a message in the echo area temporarily, during
319 the execution of @var{body}. It displays @var{message}, executes
320 @var{body}, then returns the value of the last body form while restoring
321 the previous echo area contents.
324 @defun message-or-box format-string &rest arguments
325 This function displays a message like @code{message}, but may display it
326 in a dialog box instead of the echo area. If this function is called in
327 a command that was invoked using the mouse---more precisely, if
328 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
329 @code{nil} or a list---then it uses a dialog box or pop-up menu to
330 display the message. Otherwise, it uses the echo area. (This is the
331 same criterion that @code{y-or-n-p} uses to make a similar decision; see
332 @ref{Yes-or-No Queries}.)
334 You can force use of the mouse or of the echo area by binding
335 @code{last-nonmenu-event} to a suitable value around the call.
338 @defun message-box format-string &rest arguments
340 This function displays a message like @code{message}, but uses a dialog
341 box (or a pop-up menu) whenever that is possible. If it is impossible
342 to use a dialog box or pop-up menu, because the terminal does not
343 support them, then @code{message-box} uses the echo area, like
347 @defun display-message-or-buffer message &optional buffer-name action frame
348 This function displays the message @var{message}, which may be either a
349 string or a buffer. If it is shorter than the maximum height of the
350 echo area, as defined by @code{max-mini-window-height}, it is displayed
351 in the echo area, using @code{message}. Otherwise,
352 @code{display-buffer} is used to show it in a pop-up buffer.
354 Returns either the string shown in the echo area, or when a pop-up
355 buffer is used, the window used to display it.
357 If @var{message} is a string, then the optional argument
358 @var{buffer-name} is the name of the buffer used to display it when a
359 pop-up buffer is used, defaulting to @file{*Message*}. In the case
360 where @var{message} is a string and displayed in the echo area, it is
361 not specified whether the contents are inserted into the buffer anyway.
363 The optional arguments @var{action} and @var{frame} are as for
364 @code{display-buffer}, and only used if a buffer is displayed.
367 @defun current-message
368 This function returns the message currently being displayed in the
369 echo area, or @code{nil} if there is none.
373 @subsection Reporting Operation Progress
374 @cindex progress reporting
376 When an operation can take a while to finish, you should inform the
377 user about the progress it makes. This way the user can estimate
378 remaining time and clearly see that Emacs is busy working, not hung.
379 A convenient way to do this is to use a @dfn{progress reporter}.
381 Here is a working example that does nothing useful:
384 (let ((progress-reporter
385 (make-progress-reporter "Collecting mana for Emacs..."
389 (progress-reporter-update progress-reporter k))
390 (progress-reporter-done progress-reporter))
393 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
394 This function creates and returns a progress reporter object, which
395 you will use as an argument for the other functions listed below. The
396 idea is to precompute as much data as possible to make progress
399 When this progress reporter is subsequently used, it will display
400 @var{message} in the echo area, followed by progress percentage.
401 @var{message} is treated as a simple string. If you need it to depend
402 on a filename, for instance, use @code{format-message} before calling this
405 The arguments @var{min-value} and @var{max-value} should be numbers
406 standing for the starting and final states of the operation. For
407 instance, an operation that scans a buffer should set these to the
408 results of @code{point-min} and @code{point-max} correspondingly.
409 @var{max-value} should be greater than @var{min-value}.
411 Alternatively, you can set @var{min-value} and @var{max-value} to
412 @code{nil}. In that case, the progress reporter does not report
413 process percentages; it instead displays a ``spinner'' that rotates a
414 notch each time you update the progress reporter.
416 If @var{min-value} and @var{max-value} are numbers, you can give the
417 argument @var{current-value} a numerical value specifying the initial
418 progress; if omitted, this defaults to @var{min-value}.
420 The remaining arguments control the rate of echo area updates. The
421 progress reporter will wait for at least @var{min-change} more
422 percents of the operation to be completed before printing next
423 message; the default is one percent. @var{min-time} specifies the
424 minimum time in seconds to pass between successive prints; the default
425 is 0.2 seconds. (On some operating systems, the progress reporter may
426 handle fractions of seconds with varying precision).
428 This function calls @code{progress-reporter-update}, so the first
429 message is printed immediately.
432 @defun progress-reporter-update reporter &optional value
433 This function does the main work of reporting progress of your
434 operation. It displays the message of @var{reporter}, followed by
435 progress percentage determined by @var{value}. If percentage is zero,
436 or close enough according to the @var{min-change} and @var{min-time}
437 arguments, then it is omitted from the output.
439 @var{reporter} must be the result of a call to
440 @code{make-progress-reporter}. @var{value} specifies the current
441 state of your operation and must be between @var{min-value} and
442 @var{max-value} (inclusive) as passed to
443 @code{make-progress-reporter}. For instance, if you scan a buffer,
444 then @var{value} should be the result of a call to @code{point}.
446 This function respects @var{min-change} and @var{min-time} as passed
447 to @code{make-progress-reporter} and so does not output new messages
448 on every invocation. It is thus very fast and normally you should not
449 try to reduce the number of calls to it: resulting overhead will most
450 likely negate your effort.
453 @defun progress-reporter-force-update reporter &optional value new-message
454 This function is similar to @code{progress-reporter-update} except
455 that it prints a message in the echo area unconditionally.
457 The first two arguments have the same meaning as for
458 @code{progress-reporter-update}. Optional @var{new-message} allows
459 you to change the message of the @var{reporter}. Since this function
460 always updates the echo area, such a change will be immediately
461 presented to the user.
464 @defun progress-reporter-done reporter
465 This function should be called when the operation is finished. It
466 prints the message of @var{reporter} followed by word @samp{done} in the
469 You should always call this function and not hope for
470 @code{progress-reporter-update} to print @samp{100%}. Firstly, it may
471 never print it, there are many good reasons for this not to happen.
472 Secondly, @samp{done} is more explicit.
475 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
476 This is a convenience macro that works the same way as @code{dotimes}
477 does, but also reports loop progress using the functions described
478 above. It allows you to save some typing.
480 You can rewrite the example in the beginning of this node using
484 (dotimes-with-progress-reporter
486 "Collecting some mana for Emacs..."
491 @node Logging Messages
492 @subsection Logging Messages in @file{*Messages*}
493 @cindex logging echo-area messages
495 Almost all the messages displayed in the echo area are also recorded
496 in the @file{*Messages*} buffer so that the user can refer back to
497 them. This includes all the messages that are output with
498 @code{message}. By default, this buffer is read-only and uses the major
499 mode @code{messages-buffer-mode}. Nothing prevents the user from
500 killing the @file{*Messages*} buffer, but the next display of a message
501 recreates it. Any Lisp code that needs to access the
502 @file{*Messages*} buffer directly and wants to ensure that it exists
503 should use the function @code{messages-buffer}.
505 @defun messages-buffer
506 This function returns the @file{*Messages*} buffer. If it does not
507 exist, it creates it, and switches it to @code{messages-buffer-mode}.
510 @defopt message-log-max
511 This variable specifies how many lines to keep in the @file{*Messages*}
512 buffer. The value @code{t} means there is no limit on how many lines to
513 keep. The value @code{nil} disables message logging entirely. Here's
514 how to display a message and prevent it from being logged:
517 (let (message-log-max)
522 To make @file{*Messages*} more convenient for the user, the logging
523 facility combines successive identical messages. It also combines
524 successive related messages for the sake of two cases: question
525 followed by answer, and a series of progress messages.
527 A question followed by an answer has two messages like the
528 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
529 and the second is @samp{@var{question}...@var{answer}}. The first
530 message conveys no additional information beyond what's in the second,
531 so logging the second message discards the first from the log.
533 A series of progress messages has successive messages like
534 those produced by @code{make-progress-reporter}. They have the form
535 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
536 time, while @var{how-far} varies. Logging each message in the series
537 discards the previous one, provided they are consecutive.
539 The functions @code{make-progress-reporter} and @code{y-or-n-p}
540 don't have to do anything special to activate the message log
541 combination feature. It operates whenever two consecutive messages
542 are logged that share a common prefix ending in @samp{...}.
544 @node Echo Area Customization
545 @subsection Echo Area Customization
546 @cindex echo area customization
548 These variables control details of how the echo area works.
550 @defvar cursor-in-echo-area
551 This variable controls where the cursor appears when a message is
552 displayed in the echo area. If it is non-@code{nil}, then the cursor
553 appears at the end of the message. Otherwise, the cursor appears at
554 point---not in the echo area at all.
556 The value is normally @code{nil}; Lisp programs bind it to @code{t}
557 for brief periods of time.
560 @defvar echo-area-clear-hook
561 This normal hook is run whenever the echo area is cleared---either by
562 @code{(message nil)} or for any other reason.
565 @defopt echo-keystrokes
566 This variable determines how much time should elapse before command
567 characters echo. Its value must be a number, and specifies the
568 number of seconds to wait before echoing. If the user types a prefix
569 key (such as @kbd{C-x}) and then delays this many seconds before
570 continuing, the prefix key is echoed in the echo area. (Once echoing
571 begins in a key sequence, all subsequent characters in the same key
572 sequence are echoed immediately.)
574 If the value is zero, then command input is not echoed.
577 @defvar message-truncate-lines
578 Normally, displaying a long message resizes the echo area to display
579 the entire message. But if the variable @code{message-truncate-lines}
580 is non-@code{nil}, the echo area does not resize, and the message is
584 The variable @code{max-mini-window-height}, which specifies the
585 maximum height for resizing minibuffer windows, also applies to the
586 echo area (which is really a special use of the minibuffer window;
587 @pxref{Minibuffer Misc}).
590 @section Reporting Warnings
593 @dfn{Warnings} are a facility for a program to inform the user of a
594 possible problem, but continue running.
597 * Warning Basics:: Warnings concepts and functions to report them.
598 * Warning Variables:: Variables programs bind to customize their warnings.
599 * Warning Options:: Variables users set to control display of warnings.
600 * Delayed Warnings:: Deferring a warning until the end of a command.
604 @subsection Warning Basics
605 @cindex severity level
607 Every warning has a textual message, which explains the problem for
608 the user, and a @dfn{severity level} which is a symbol. Here are the
609 possible severity levels, in order of decreasing severity, and their
614 A problem that will seriously impair Emacs operation soon
615 if you do not attend to it promptly.
617 A report of data or circumstances that are inherently wrong.
619 A report of data or circumstances that are not inherently wrong, but
620 raise suspicion of a possible problem.
622 A report of information that may be useful if you are debugging.
625 When your program encounters invalid input data, it can either
626 signal a Lisp error by calling @code{error} or @code{signal} or report
627 a warning with severity @code{:error}. Signaling a Lisp error is the
628 easiest thing to do, but it means the program cannot continue
629 processing. If you want to take the trouble to implement a way to
630 continue processing despite the bad data, then reporting a warning of
631 severity @code{:error} is the right way to inform the user of the
632 problem. For instance, the Emacs Lisp byte compiler can report an
633 error that way and continue compiling other functions. (If the
634 program signals a Lisp error and then handles it with
635 @code{condition-case}, the user won't see the error message; it could
636 show the message to the user by reporting it as a warning.)
638 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
639 @c "bytecomp" here? The parens are part of warning-type-format but
640 @c not part of the warning type. --xfq
642 Each warning has a @dfn{warning type} to classify it. The type is a
643 list of symbols. The first symbol should be the custom group that you
644 use for the program's user options. For example, byte compiler
645 warnings use the warning type @code{(bytecomp)}. You can also
646 subcategorize the warnings, if you wish, by using more symbols in the
649 @defun display-warning type message &optional level buffer-name
650 This function reports a warning, using @var{message} as the message
651 and @var{type} as the warning type. @var{level} should be the
652 severity level, with @code{:warning} being the default.
654 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
655 for logging the warning. By default, it is @file{*Warnings*}.
658 @defun lwarn type level message &rest args
659 This function reports a warning using the value of @code{(format-message
660 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
661 buffer. In other respects it is equivalent to @code{display-warning}.
664 @defun warn message &rest args
665 This function reports a warning using the value of @code{(format-message
666 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
667 type, and @code{:warning} as the severity level. It exists for
668 compatibility only; we recommend not using it, because you should
669 specify a specific warning type.
672 @node Warning Variables
673 @subsection Warning Variables
674 @cindex warning variables
676 Programs can customize how their warnings appear by binding
677 the variables described in this section.
679 @defvar warning-levels
680 This list defines the meaning and severity order of the warning
681 severity levels. Each element defines one severity level,
682 and they are arranged in order of decreasing severity.
684 Each element has the form @code{(@var{level} @var{string}
685 @var{function})}, where @var{level} is the severity level it defines.
686 @var{string} specifies the textual description of this level.
687 @var{string} should use @samp{%s} to specify where to put the warning
688 type information, or it can omit the @samp{%s} so as not to include
691 The optional @var{function}, if non-@code{nil}, is a function to call
692 with no arguments, to get the user's attention.
694 Normally you should not change the value of this variable.
697 @defvar warning-prefix-function
698 If non-@code{nil}, the value is a function to generate prefix text for
699 warnings. Programs can bind the variable to a suitable function.
700 @code{display-warning} calls this function with the warnings buffer
701 current, and the function can insert text in it. That text becomes
702 the beginning of the warning message.
704 The function is called with two arguments, the severity level and its
705 entry in @code{warning-levels}. It should return a list to use as the
706 entry (this value need not be an actual member of
707 @code{warning-levels}). By constructing this value, the function can
708 change the severity of the warning, or specify different handling for
709 a given severity level.
711 If the variable's value is @code{nil} then there is no function
715 @defvar warning-series
716 Programs can bind this variable to @code{t} to say that the next
717 warning should begin a series. When several warnings form a series,
718 that means to leave point on the first warning of the series, rather
719 than keep moving it for each warning so that it appears on the last one.
720 The series ends when the local binding is unbound and
721 @code{warning-series} becomes @code{nil} again.
723 The value can also be a symbol with a function definition. That is
724 equivalent to @code{t}, except that the next warning will also call
725 the function with no arguments with the warnings buffer current. The
726 function can insert text which will serve as a header for the series
729 Once a series has begun, the value is a marker which points to the
730 buffer position in the warnings buffer of the start of the series.
732 The variable's normal value is @code{nil}, which means to handle
733 each warning separately.
736 @defvar warning-fill-prefix
737 When this variable is non-@code{nil}, it specifies a fill prefix to
738 use for filling each warning's text.
741 @defvar warning-type-format
742 This variable specifies the format for displaying the warning type
743 in the warning message. The result of formatting the type this way
744 gets included in the message under the control of the string in the
745 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
746 If you bind it to @code{""} then the warning type won't appear at
750 @node Warning Options
751 @subsection Warning Options
752 @cindex warning options
754 These variables are used by users to control what happens
755 when a Lisp program reports a warning.
757 @defopt warning-minimum-level
758 This user option specifies the minimum severity level that should be
759 shown immediately to the user. The default is @code{:warning}, which
760 means to immediately display all warnings except @code{:debug}
764 @defopt warning-minimum-log-level
765 This user option specifies the minimum severity level that should be
766 logged in the warnings buffer. The default is @code{:warning}, which
767 means to log all warnings except @code{:debug} warnings.
770 @defopt warning-suppress-types
771 This list specifies which warning types should not be displayed
772 immediately for the user. Each element of the list should be a list
773 of symbols. If its elements match the first elements in a warning
774 type, then that warning is not displayed immediately.
777 @defopt warning-suppress-log-types
778 This list specifies which warning types should not be logged in the
779 warnings buffer. Each element of the list should be a list of
780 symbols. If it matches the first few elements in a warning type, then
781 that warning is not logged.
784 @node Delayed Warnings
785 @subsection Delayed Warnings
786 @cindex delayed warnings
788 Sometimes, you may wish to avoid showing a warning while a command is
789 running, and only show it only after the end of the command. You can
790 use the variable @code{delayed-warnings-list} for this.
792 @defvar delayed-warnings-list
793 The value of this variable is a list of warnings to be displayed after
794 the current command has finished. Each element must be a list
797 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
801 with the same form, and the same meanings, as the argument list of
802 @code{display-warning} (@pxref{Warning Basics}). Immediately after
803 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
804 command loop displays all the warnings specified by this variable,
805 then resets it to @code{nil}.
808 Programs which need to further customize the delayed warnings
809 mechanism can change the variable @code{delayed-warnings-hook}:
811 @defvar delayed-warnings-hook
812 This is a normal hook which is run by the Emacs command loop, after
813 @code{post-command-hook}, in order to to process and display delayed
816 Its default value is a list of two functions:
819 (collapse-delayed-warnings display-delayed-warnings)
822 @findex collapse-delayed-warnings
823 @findex display-delayed-warnings
825 The function @code{collapse-delayed-warnings} removes repeated entries
826 from @code{delayed-warnings-list}. The function
827 @code{display-delayed-warnings} calls @code{display-warning} on each
828 of the entries in @code{delayed-warnings-list}, in turn, and then sets
829 @code{delayed-warnings-list} to @code{nil}.
833 @section Invisible Text
835 @cindex invisible text
836 You can make characters @dfn{invisible}, so that they do not appear on
837 the screen, with the @code{invisible} property. This can be either a
838 text property (@pxref{Text Properties}) or an overlay property
839 (@pxref{Overlays}). Cursor motion also partly ignores these
840 characters; if the command loop finds that point is inside a range of
841 invisible text after a command, it relocates point to the other side
844 In the simplest case, any non-@code{nil} @code{invisible} property makes
845 a character invisible. This is the default case---if you don't alter
846 the default value of @code{buffer-invisibility-spec}, this is how the
847 @code{invisible} property works. You should normally use @code{t}
848 as the value of the @code{invisible} property if you don't plan
849 to set @code{buffer-invisibility-spec} yourself.
851 More generally, you can use the variable @code{buffer-invisibility-spec}
852 to control which values of the @code{invisible} property make text
853 invisible. This permits you to classify the text into different subsets
854 in advance, by giving them different @code{invisible} values, and
855 subsequently make various subsets visible or invisible by changing the
856 value of @code{buffer-invisibility-spec}.
858 Controlling visibility with @code{buffer-invisibility-spec} is
859 especially useful in a program to display the list of entries in a
860 database. It permits the implementation of convenient filtering
861 commands to view just a part of the entries in the database. Setting
862 this variable is very fast, much faster than scanning all the text in
863 the buffer looking for properties to change.
865 @defvar buffer-invisibility-spec
866 This variable specifies which kinds of @code{invisible} properties
867 actually make a character invisible. Setting this variable makes it
872 A character is invisible if its @code{invisible} property is
873 non-@code{nil}. This is the default.
876 Each element of the list specifies a criterion for invisibility; if a
877 character's @code{invisible} property fits any one of these criteria,
878 the character is invisible. The list can have two kinds of elements:
882 A character is invisible if its @code{invisible} property value is
883 @var{atom} or if it is a list with @var{atom} as a member; comparison
884 is done with @code{eq}.
886 @item (@var{atom} . t)
887 A character is invisible if its @code{invisible} property value is
888 @var{atom} or if it is a list with @var{atom} as a member; comparison
889 is done with @code{eq}. Moreover, a sequence of such characters
890 displays as an ellipsis.
895 Two functions are specifically provided for adding elements to
896 @code{buffer-invisibility-spec} and removing elements from it.
898 @defun add-to-invisibility-spec element
899 This function adds the element @var{element} to
900 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
901 was @code{t}, it changes to a list, @code{(t)}, so that text whose
902 @code{invisible} property is @code{t} remains invisible.
905 @defun remove-from-invisibility-spec element
906 This removes the element @var{element} from
907 @code{buffer-invisibility-spec}. This does nothing if @var{element}
911 A convention for use of @code{buffer-invisibility-spec} is that a
912 major mode should use the mode's own name as an element of
913 @code{buffer-invisibility-spec} and as the value of the
914 @code{invisible} property:
917 ;; @r{If you want to display an ellipsis:}
918 (add-to-invisibility-spec '(my-symbol . t))
919 ;; @r{If you don't want ellipsis:}
920 (add-to-invisibility-spec 'my-symbol)
922 (overlay-put (make-overlay beginning end)
923 'invisible 'my-symbol)
925 ;; @r{When done with the invisibility:}
926 (remove-from-invisibility-spec '(my-symbol . t))
927 ;; @r{Or respectively:}
928 (remove-from-invisibility-spec 'my-symbol)
931 You can check for invisibility using the following function:
933 @defun invisible-p pos-or-prop
934 If @var{pos-or-prop} is a marker or number, this function returns a
935 non-@code{nil} value if the text at that position is invisible.
937 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
938 to mean a possible value of the @code{invisible} text or overlay
939 property. In that case, this function returns a non-@code{nil} value
940 if that value would cause text to become invisible, based on the
941 current value of @code{buffer-invisibility-spec}.
944 @vindex line-move-ignore-invisible
945 Ordinarily, functions that operate on text or move point do not care
946 whether the text is invisible, they process invisible characters and
947 visible characters alike. The user-level line motion commands,
948 such as @code{next-line}, @code{previous-line}, ignore invisible
949 newlines if @code{line-move-ignore-invisible} is non-@code{nil} (the
950 default), i.e., behave like these invisible newlines didn't exist in
951 the buffer, but only because they are explicitly programmed to do so.
953 If a command ends with point inside or at the boundary of
954 invisible text, the main editing loop relocates point to one of the
955 two ends of the invisible text. Emacs chooses the direction of
956 relocation so that it is the same as the overall movement direction of
957 the command; if in doubt, it prefers a position where an inserted char
958 would not inherit the @code{invisible} property. Additionally, if the
959 text is not replaced by an ellipsis and the command only moved within
960 the invisible text, then point is moved one extra character so as to
961 try and reflect the command's movement by a visible movement of the
964 Thus, if the command moved point back to an invisible range (with the usual
965 stickiness), Emacs moves point back to the beginning of that range. If the
966 command moved point forward into an invisible range, Emacs moves point forward
967 to the first visible character that follows the invisible text and then forward
970 These @dfn{adjustments} of point that ended up in the middle of
971 invisible text can be disabled by setting @code{disable-point-adjustment}
972 to a non-@code{nil} value. @xref{Adjusting Point}.
974 Incremental search can make invisible overlays visible temporarily
975 and/or permanently when a match includes invisible text. To enable
976 this, the overlay should have a non-@code{nil}
977 @code{isearch-open-invisible} property. The property value should be a
978 function to be called with the overlay as an argument. This function
979 should make the overlay visible permanently; it is used when the match
980 overlaps the overlay on exit from the search.
982 During the search, such overlays are made temporarily visible by
983 temporarily modifying their invisible and intangible properties. If you
984 want this to be done differently for a certain overlay, give it an
985 @code{isearch-open-invisible-temporary} property which is a function.
986 The function is called with two arguments: the first is the overlay, and
987 the second is @code{nil} to make the overlay visible, or @code{t} to
988 make it invisible again.
990 @node Selective Display
991 @section Selective Display
992 @c @cindex selective display Duplicates selective-display
994 @dfn{Selective display} refers to a pair of related features for
995 hiding certain lines on the screen.
997 @cindex explicit selective display
998 The first variant, explicit selective display, was designed for use in a Lisp
999 program: it controls which lines are hidden by altering the text. This kind of
1000 hiding is now obsolete; instead you can get the same effect with the
1001 @code{invisible} property (@pxref{Invisible Text}).
1003 In the second variant, the choice of lines to hide is made
1004 automatically based on indentation. This variant is designed to be a
1007 The way you control explicit selective display is by replacing a
1008 newline (control-j) with a carriage return (control-m). The text that
1009 was formerly a line following that newline is now hidden. Strictly
1010 speaking, it is temporarily no longer a line at all, since only
1011 newlines can separate lines; it is now part of the previous line.
1013 Selective display does not directly affect editing commands. For
1014 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
1015 into hidden text. However, the replacement of newline characters with
1016 carriage return characters affects some editing commands. For
1017 example, @code{next-line} skips hidden lines, since it searches only
1018 for newlines. Modes that use selective display can also define
1019 commands that take account of the newlines, or that control which
1020 parts of the text are hidden.
1022 When you write a selectively displayed buffer into a file, all the
1023 control-m's are output as newlines. This means that when you next read
1024 in the file, it looks OK, with nothing hidden. The selective display
1025 effect is seen only within Emacs.
1027 @defvar selective-display
1028 This buffer-local variable enables selective display. This means that
1029 lines, or portions of lines, may be made hidden.
1033 If the value of @code{selective-display} is @code{t}, then the character
1034 control-m marks the start of hidden text; the control-m, and the rest
1035 of the line following it, are not displayed. This is explicit selective
1039 If the value of @code{selective-display} is a positive integer, then
1040 lines that start with more than that many columns of indentation are not
1044 When some portion of a buffer is hidden, the vertical movement
1045 commands operate as if that portion did not exist, allowing a single
1046 @code{next-line} command to skip any number of hidden lines.
1047 However, character movement commands (such as @code{forward-char}) do
1048 not skip the hidden portion, and it is possible (if tricky) to insert
1049 or delete text in an hidden portion.
1051 In the examples below, we show the @emph{display appearance} of the
1052 buffer @code{foo}, which changes with the value of
1053 @code{selective-display}. The @emph{contents} of the buffer do not
1058 (setq selective-display nil)
1061 ---------- Buffer: foo ----------
1068 ---------- Buffer: foo ----------
1072 (setq selective-display 2)
1075 ---------- Buffer: foo ----------
1080 ---------- Buffer: foo ----------
1085 @defopt selective-display-ellipses
1086 If this buffer-local variable is non-@code{nil}, then Emacs displays
1087 @samp{@dots{}} at the end of a line that is followed by hidden text.
1088 This example is a continuation of the previous one.
1092 (setq selective-display-ellipses t)
1095 ---------- Buffer: foo ----------
1100 ---------- Buffer: foo ----------
1104 You can use a display table to substitute other text for the ellipsis
1105 (@samp{@dots{}}). @xref{Display Tables}.
1108 @node Temporary Displays
1109 @section Temporary Displays
1110 @cindex temporary display
1111 @cindex temporary buffer display
1113 Temporary displays are used by Lisp programs to put output into a
1114 buffer and then present it to the user for perusal rather than for
1115 editing. Many help commands use this feature.
1117 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1118 This function executes the forms in @var{body} while arranging to insert
1119 any output they print into the buffer named @var{buffer-name}, which is
1120 first created if necessary, and put into Help mode. (See the similar
1121 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1122 displayed in some window, but that window is not selected.
1124 If the forms in @var{body} do not change the major mode in the output
1125 buffer, so that it is still Help mode at the end of their execution,
1126 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1127 the end, and also scans it for function and variable names to make them
1128 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1129 Documentation Strings}, in particular the item on hyperlinks in
1130 documentation strings, for more details.
1132 The string @var{buffer-name} specifies the temporary buffer, which need
1133 not already exist. The argument must be a string, not a buffer. The
1134 buffer is erased initially (with no questions asked), and it is marked
1135 as unmodified after @code{with-output-to-temp-buffer} exits.
1137 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1138 temporary buffer, then it evaluates the forms in @var{body}. Output
1139 using the Lisp output functions within @var{body} goes by default to
1140 that buffer (but screen display and messages in the echo area, although
1141 they are ``output'' in the general sense of the word, are not affected).
1142 @xref{Output Functions}.
1144 Several hooks are available for customizing the behavior
1145 of this construct; they are listed below.
1147 The value of the last form in @var{body} is returned.
1151 ---------- Buffer: foo ----------
1152 This is the contents of foo.
1153 ---------- Buffer: foo ----------
1157 (with-output-to-temp-buffer "foo"
1159 (print standard-output))
1160 @result{} #<buffer foo>
1162 ---------- Buffer: foo ----------
1168 ---------- Buffer: foo ----------
1173 @defopt temp-buffer-show-function
1174 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1175 calls it as a function to do the job of displaying a help buffer. The
1176 function gets one argument, which is the buffer it should display.
1178 It is a good idea for this function to run @code{temp-buffer-show-hook}
1179 just as @code{with-output-to-temp-buffer} normally would, inside of
1180 @code{save-selected-window} and with the chosen window and buffer
1184 @defvar temp-buffer-setup-hook
1185 This normal hook is run by @code{with-output-to-temp-buffer} before
1186 evaluating @var{body}. When the hook runs, the temporary buffer is
1187 current. This hook is normally set up with a function to put the
1188 buffer in Help mode.
1191 @defvar temp-buffer-show-hook
1192 This normal hook is run by @code{with-output-to-temp-buffer} after
1193 displaying the temporary buffer. When the hook runs, the temporary buffer
1194 is current, and the window it was displayed in is selected.
1197 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1198 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1199 construct, it executes @var{body} while arranging to insert any output
1200 it prints into the buffer named @var{buffer-or-name} and displays that
1201 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1202 however, it does not automatically switch that buffer to Help mode.
1204 The argument @var{buffer-or-name} specifies the temporary buffer. It
1205 can be either a buffer, which must already exist, or a string, in which
1206 case a buffer of that name is created, if necessary. The buffer is
1207 marked as unmodified and read-only when @code{with-temp-buffer-window}
1210 This macro does not call @code{temp-buffer-show-function}. Rather, it
1211 passes the @var{action} argument to @code{display-buffer}
1212 (@pxref{Choosing Window}) in order to display the buffer.
1214 The value of the last form in @var{body} is returned, unless the
1215 argument @var{quit-function} is specified. In that case, it is called
1216 with two arguments: the window showing the buffer and the result of
1217 @var{body}. The final return value is then whatever @var{quit-function}
1220 @vindex temp-buffer-window-setup-hook
1221 @vindex temp-buffer-window-show-hook
1222 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1223 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1224 run by @code{with-output-to-temp-buffer}.
1227 The two constructs described next are mostly identical to
1228 @code{with-temp-buffer-window} but differ from it as specified:
1230 @defmac with-current-buffer-window buffer-or-name action quit-function &rest body
1231 This macro is like @code{with-temp-buffer-window} but unlike that makes
1232 the buffer specified by @var{buffer-or-name} current for running
1236 @defmac with-displayed-buffer-window buffer-or-name action quit-function &rest body
1237 This macro is like @code{with-current-buffer-window} but unlike that
1238 displays the buffer specified by @var{buffer-or-name} @emph{before}
1242 A window showing a temporary buffer can be fit to the size of that
1243 buffer using the following mode:
1245 @defopt temp-buffer-resize-mode
1246 When this minor mode is enabled, windows showing a temporary buffer are
1247 automatically resized to fit their buffer's contents.
1249 A window is resized if and only if it has been specially created for the
1250 buffer. In particular, windows that have shown another buffer before
1251 are not resized. By default, this mode uses @code{fit-window-to-buffer}
1252 (@pxref{Resizing Windows}) for resizing. You can specify a different
1253 function by customizing the options @code{temp-buffer-max-height} and
1254 @code{temp-buffer-max-width} below.
1257 @defopt temp-buffer-max-height
1258 This option specifies the maximum height (in lines) of a window
1259 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1260 enabled. It can also be a function to be called to choose the height
1261 for such a buffer. It gets one argument, the buffer, and should return
1262 a positive integer. At the time the function is called, the window to
1263 be resized is selected.
1266 @defopt temp-buffer-max-width
1267 This option specifies the maximum width of a window (in columns)
1268 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1269 enabled. It can also be a function to be called to choose the width for
1270 such a buffer. It gets one argument, the buffer, and should return a
1271 positive integer. At the time the function is called, the window to be
1272 resized is selected.
1275 The following function uses the current buffer for temporal display:
1277 @defun momentary-string-display string position &optional char message
1278 This function momentarily displays @var{string} in the current buffer at
1279 @var{position}. It has no effect on the undo list or on the buffer's
1280 modification status.
1282 The momentary display remains until the next input event. If the next
1283 input event is @var{char}, @code{momentary-string-display} ignores it
1284 and returns. Otherwise, that event remains buffered for subsequent use
1285 as input. Thus, typing @var{char} will simply remove the string from
1286 the display, while typing (say) @kbd{C-f} will remove the string from
1287 the display and later (presumably) move point forward. The argument
1288 @var{char} is a space by default.
1290 The return value of @code{momentary-string-display} is not meaningful.
1292 If the string @var{string} does not contain control characters, you can
1293 do the same job in a more general way by creating (and then subsequently
1294 deleting) an overlay with a @code{before-string} property.
1295 @xref{Overlay Properties}.
1297 If @var{message} is non-@code{nil}, it is displayed in the echo area
1298 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1299 default message says to type @var{char} to continue.
1301 In this example, point is initially located at the beginning of the
1306 ---------- Buffer: foo ----------
1307 This is the contents of foo.
1308 @point{}Second line.
1309 ---------- Buffer: foo ----------
1313 (momentary-string-display
1314 "**** Important Message! ****"
1316 "Type RET when done reading")
1321 ---------- Buffer: foo ----------
1322 This is the contents of foo.
1323 **** Important Message! ****Second line.
1324 ---------- Buffer: foo ----------
1326 ---------- Echo Area ----------
1327 Type RET when done reading
1328 ---------- Echo Area ----------
1336 @c FIXME: mention intervals in this section?
1338 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1339 the screen, for the sake of presentation features. An overlay is an
1340 object that belongs to a particular buffer, and has a specified
1341 beginning and end. It also has properties that you can examine and set;
1342 these affect the display of the text within the overlay.
1344 @cindex scalability of overlays
1345 @cindex overlays, scalability
1346 The visual effect of an overlay is the same as of the corresponding
1347 text property (@pxref{Text Properties}). However, due to a different
1348 implementation, overlays generally don't scale well (many operations
1349 take a time that is proportional to the number of overlays in the
1350 buffer). If you need to affect the visual appearance of many portions
1351 in the buffer, we recommend using text properties.
1353 An overlay uses markers to record its beginning and end; thus,
1354 editing the text of the buffer adjusts the beginning and end of each
1355 overlay so that it stays with the text. When you create the overlay,
1356 you can specify whether text inserted at the beginning should be
1357 inside the overlay or outside, and likewise for the end of the overlay.
1360 * Managing Overlays:: Creating and moving overlays.
1361 * Overlay Properties:: How to read and set properties.
1362 What properties do to the screen display.
1363 * Finding Overlays:: Searching for overlays.
1366 @node Managing Overlays
1367 @subsection Managing Overlays
1368 @cindex managing overlays
1369 @cindex overlays, managing
1371 This section describes the functions to create, delete and move
1372 overlays, and to examine their contents. Overlay changes are not
1373 recorded in the buffer's undo list, since the overlays are not
1374 part of the buffer's contents.
1376 @defun overlayp object
1377 This function returns @code{t} if @var{object} is an overlay.
1380 @defun make-overlay start end &optional buffer front-advance rear-advance
1381 This function creates and returns an overlay that belongs to
1382 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1383 and @var{end} must specify buffer positions; they may be integers or
1384 markers. If @var{buffer} is omitted, the overlay is created in the
1387 @cindex empty overlay
1388 @cindex overlay, empty
1389 An overlay whose @var{start} and @var{end} specify the same buffer
1390 position is known as @dfn{empty}. A non-empty overlay can become
1391 empty if the text between its @var{start} and @var{end} is deleted.
1392 When that happens, the overlay is by default not deleted, but you can
1393 cause it to be deleted by giving it the @samp{evaporate} property
1394 (@pxref{Overlay Properties, evaporate property}).
1396 The arguments @var{front-advance} and @var{rear-advance} specify the
1397 marker insertion type for the start of the overlay and for the end of
1398 the overlay, respectively. @xref{Marker Insertion Types}. If they
1399 are both @code{nil}, the default, then the overlay extends to include
1400 any text inserted at the beginning, but not text inserted at the end.
1401 If @var{front-advance} is non-@code{nil}, text inserted at the
1402 beginning of the overlay is excluded from the overlay. If
1403 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1404 overlay is included in the overlay.
1407 @defun overlay-start overlay
1408 This function returns the position at which @var{overlay} starts,
1412 @defun overlay-end overlay
1413 This function returns the position at which @var{overlay} ends,
1417 @defun overlay-buffer overlay
1418 This function returns the buffer that @var{overlay} belongs to. It
1419 returns @code{nil} if @var{overlay} has been deleted.
1422 @defun delete-overlay overlay
1423 This function deletes @var{overlay}. The overlay continues to exist as
1424 a Lisp object, and its property list is unchanged, but it ceases to be
1425 attached to the buffer it belonged to, and ceases to have any effect on
1428 A deleted overlay is not permanently disconnected. You can give it a
1429 position in a buffer again by calling @code{move-overlay}.
1432 @defun move-overlay overlay start end &optional buffer
1433 This function moves @var{overlay} to @var{buffer}, and places its bounds
1434 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1435 must specify buffer positions; they may be integers or markers.
1437 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1438 was already associated with; if @var{overlay} was deleted, it goes into
1441 The return value is @var{overlay}.
1443 This is the only valid way to change the endpoints of an overlay. Do
1444 not try modifying the markers in the overlay by hand, as that fails to
1445 update other vital data structures and can cause some overlays to be
1449 @defun remove-overlays &optional start end name value
1450 This function removes all the overlays between @var{start} and
1451 @var{end} whose property @var{name} has the value @var{value}. It can
1452 move the endpoints of the overlays in the region, or split them.
1454 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1455 the specified region. If @var{start} and/or @var{end} are omitted or
1456 @code{nil}, that means the beginning and end of the buffer respectively.
1457 Therefore, @code{(remove-overlays)} removes all the overlays in the
1461 @defun copy-overlay overlay
1462 This function returns a copy of @var{overlay}. The copy has the same
1463 endpoints and properties as @var{overlay}. However, the marker
1464 insertion type for the start of the overlay and for the end of the
1465 overlay are set to their default values (@pxref{Marker Insertion
1469 Here are some examples:
1472 ;; @r{Create an overlay.}
1473 (setq foo (make-overlay 1 10))
1474 @result{} #<overlay from 1 to 10 in display.texi>
1479 (overlay-buffer foo)
1480 @result{} #<buffer display.texi>
1481 ;; @r{Give it a property we can check later.}
1482 (overlay-put foo 'happy t)
1484 ;; @r{Verify the property is present.}
1485 (overlay-get foo 'happy)
1487 ;; @r{Move the overlay.}
1488 (move-overlay foo 5 20)
1489 @result{} #<overlay from 5 to 20 in display.texi>
1494 ;; @r{Delete the overlay.}
1495 (delete-overlay foo)
1497 ;; @r{Verify it is deleted.}
1499 @result{} #<overlay in no buffer>
1500 ;; @r{A deleted overlay has no position.}
1505 (overlay-buffer foo)
1507 ;; @r{Undelete the overlay.}
1508 (move-overlay foo 1 20)
1509 @result{} #<overlay from 1 to 20 in display.texi>
1510 ;; @r{Verify the results.}
1515 (overlay-buffer foo)
1516 @result{} #<buffer display.texi>
1517 ;; @r{Moving and deleting the overlay does not change its properties.}
1518 (overlay-get foo 'happy)
1522 Emacs stores the overlays of each buffer in two lists, divided
1523 around an arbitrary center position. One list extends backwards
1524 through the buffer from that center position, and the other extends
1525 forwards from that center position. The center position can be anywhere
1528 @defun overlay-recenter pos
1529 This function recenters the overlays of the current buffer around
1530 position @var{pos}. That makes overlay lookup faster for positions
1531 near @var{pos}, but slower for positions far away from @var{pos}.
1534 A loop that scans the buffer forwards, creating overlays, can run
1535 faster if you do @code{(overlay-recenter (point-max))} first.
1537 @node Overlay Properties
1538 @subsection Overlay Properties
1539 @cindex overlay properties
1541 Overlay properties are like text properties in that the properties that
1542 alter how a character is displayed can come from either source. But in
1543 most respects they are different. @xref{Text Properties}, for comparison.
1545 Text properties are considered a part of the text; overlays and
1546 their properties are specifically considered not to be part of the
1547 text. Thus, copying text between various buffers and strings
1548 preserves text properties, but does not try to preserve overlays.
1549 Changing a buffer's text properties marks the buffer as modified,
1550 while moving an overlay or changing its properties does not. Unlike
1551 text property changes, overlay property changes are not recorded in
1552 the buffer's undo list.
1554 Since more than one overlay can specify a property value for the
1555 same character, Emacs lets you specify a priority value of each
1556 overlay. The priority value is used to decide which of the
1557 overlapping overlays will ``win''.
1559 These functions read and set the properties of an overlay:
1561 @defun overlay-get overlay prop
1562 This function returns the value of property @var{prop} recorded in
1563 @var{overlay}, if any. If @var{overlay} does not record any value for
1564 that property, but it does have a @code{category} property which is a
1565 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1569 @defun overlay-put overlay prop value
1570 This function sets the value of property @var{prop} recorded in
1571 @var{overlay} to @var{value}. It returns @var{value}.
1574 @defun overlay-properties overlay
1575 This returns a copy of the property list of @var{overlay}.
1578 See also the function @code{get-char-property} which checks both
1579 overlay properties and text properties for a given character.
1580 @xref{Examining Properties}.
1582 Many overlay properties have special meanings; here is a table
1587 @kindex priority @r{(overlay property)}
1588 This property's value determines the priority of the overlay.
1589 If you want to specify a priority value, use either @code{nil}
1590 (or zero), or a positive integer. Any other value has undefined behavior.
1592 The priority matters when two or more overlays cover the same
1593 character and both specify the same property; the one whose
1594 @code{priority} value is larger overrides the other. (For the
1595 @code{face} property, the higher priority overlay's value does not
1596 completely override the other value; instead, its face attributes
1597 override the face attributes of the lower priority @code{face}
1598 property.) If two overlays have the same priority value, and one is
1599 nested in the other, then the inner one will prevail over the outer
1600 one. If neither is nested in the other then you should not make
1601 assumptions about which overlay will prevail.
1603 Currently, all overlays take priority over text properties.
1605 Note that Emacs sometimes uses non-numeric priority values for some of
1606 its internal overlays, so do not try to do arithmetic on the priority
1607 of an overlay (unless it is one that you created). In particular, the
1608 overlay used for showing the region uses a priority value of the form
1609 @w{@code{(@var{primary} . @var{secondary})}}, where the @var{primary}
1610 value is used as described above, and @var{secondary} is the fallback
1611 value used when @var{primary} and the nesting considerations fail to
1612 resolve the precedence between overlays. However, you are advised not
1613 to design Lisp programs based on this implementation detail; if you
1614 need to put overlays in priority order, use the @var{sorted} argument
1615 of @code{overlays-at}. @xref{Finding Overlays}.
1618 @kindex window @r{(overlay property)}
1619 If the @code{window} property is non-@code{nil}, then the overlay
1620 applies only on that window.
1623 @kindex category @r{(overlay property)}
1624 If an overlay has a @code{category} property, we call it the
1625 @dfn{category} of the overlay. It should be a symbol. The properties
1626 of the symbol serve as defaults for the properties of the overlay.
1629 @kindex face @r{(overlay property)}
1630 This property controls the appearance of the text (@pxref{Faces}).
1631 The value of the property can be the following:
1635 A face name (a symbol or string).
1638 An anonymous face: a property list of the form @code{(@var{keyword}
1639 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1640 name and @var{value} is a value for that attribute.
1643 A list of faces. Each list element should be either a face name or an
1644 anonymous face. This specifies a face which is an aggregate of the
1645 attributes of each of the listed faces. Faces occurring earlier in
1646 the list have higher priority.
1649 A cons cell of the form @code{(foreground-color . @var{color-name})}
1650 or @code{(background-color . @var{color-name})}. This specifies the
1651 foreground or background color, similar to @code{(:foreground
1652 @var{color-name})} or @code{(:background @var{color-name})}. This
1653 form is supported for backward compatibility only, and should be
1658 @kindex mouse-face @r{(overlay property)}
1659 This property is used instead of @code{face} when the mouse is within
1660 the range of the overlay. However, Emacs ignores all face attributes
1661 from this property that alter the text size (e.g., @code{:height},
1662 @code{:weight}, and @code{:slant}). Those attributes are always the
1663 same as in the unhighlighted text.
1666 @kindex display @r{(overlay property)}
1667 This property activates various features that change the
1668 way text is displayed. For example, it can make text appear taller
1669 or shorter, higher or lower, wider or narrower, or replaced with an image.
1670 @xref{Display Property}.
1673 @kindex help-echo @r{(overlay property)}
1674 If an overlay has a @code{help-echo} property, then when you move the
1675 mouse onto the text in the overlay, Emacs displays a help string in the
1676 echo area, or in the tooltip window. For details see @ref{Text
1680 @kindex field @r{(overlay property)}
1681 @c Copied from Special Properties.
1682 Consecutive characters with the same @code{field} property constitute a
1683 @emph{field}. Some motion functions including @code{forward-word} and
1684 @code{beginning-of-line} stop moving at a field boundary.
1687 @item modification-hooks
1688 @kindex modification-hooks @r{(overlay property)}
1689 This property's value is a list of functions to be called if any
1690 character within the overlay is changed or if text is inserted strictly
1693 The hook functions are called both before and after each change.
1694 If the functions save the information they receive, and compare notes
1695 between calls, they can determine exactly what change has been made
1698 When called before a change, each function receives four arguments: the
1699 overlay, @code{nil}, and the beginning and end of the text range to be
1702 When called after a change, each function receives five arguments: the
1703 overlay, @code{t}, the beginning and end of the text range just
1704 modified, and the length of the pre-change text replaced by that range.
1705 (For an insertion, the pre-change length is zero; for a deletion, that
1706 length is the number of characters deleted, and the post-change
1707 beginning and end are equal.)
1709 If these functions modify the buffer, they should bind
1710 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1711 avoid confusing the internal mechanism that calls these hooks.
1713 Text properties also support the @code{modification-hooks} property,
1714 but the details are somewhat different (@pxref{Special Properties}).
1716 @item insert-in-front-hooks
1717 @kindex insert-in-front-hooks @r{(overlay property)}
1718 This property's value is a list of functions to be called before and
1719 after inserting text right at the beginning of the overlay. The calling
1720 conventions are the same as for the @code{modification-hooks} functions.
1722 @item insert-behind-hooks
1723 @kindex insert-behind-hooks @r{(overlay property)}
1724 This property's value is a list of functions to be called before and
1725 after inserting text right at the end of the overlay. The calling
1726 conventions are the same as for the @code{modification-hooks} functions.
1729 @kindex invisible @r{(overlay property)}
1730 The @code{invisible} property can make the text in the overlay
1731 invisible, which means that it does not appear on the screen.
1732 @xref{Invisible Text}, for details.
1735 @kindex intangible @r{(overlay property)}
1736 The @code{intangible} property on an overlay works just like the
1737 @code{intangible} text property. It is obsolete. @xref{Special
1738 Properties}, for details.
1740 @item isearch-open-invisible
1741 This property tells incremental search how to make an invisible overlay
1742 visible, permanently, if the final match overlaps it. @xref{Invisible
1745 @item isearch-open-invisible-temporary
1746 This property tells incremental search how to make an invisible overlay
1747 visible, temporarily, during the search. @xref{Invisible Text}.
1750 @kindex before-string @r{(overlay property)}
1751 This property's value is a string to add to the display at the beginning
1752 of the overlay. The string does not appear in the buffer in any
1753 sense---only on the screen.
1756 @kindex after-string @r{(overlay property)}
1757 This property's value is a string to add to the display at the end of
1758 the overlay. The string does not appear in the buffer in any
1759 sense---only on the screen.
1762 This property specifies a display spec to prepend to each
1763 non-continuation line at display-time. @xref{Truncation}.
1766 This property specifies a display spec to prepend to each continuation
1767 line at display-time. @xref{Truncation}.
1770 @kindex evaporate @r{(overlay property)}
1771 If this property is non-@code{nil}, the overlay is deleted automatically
1772 if it becomes empty (i.e., if its length becomes zero). If you give
1773 an empty overlay (@pxref{Managing Overlays, empty overlay}) a
1774 non-@code{nil} @code{evaporate} property, that deletes it immediately.
1775 Note that, unless an overlay has this property, it will not be deleted
1776 when the text between its starting and ending positions is deleted
1780 @cindex keymap of character (and overlays)
1781 @kindex keymap @r{(overlay property)}
1782 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1783 text. This keymap is used when the character after point is within the
1784 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1787 @kindex local-map @r{(overlay property)}
1788 The @code{local-map} property is similar to @code{keymap} but replaces the
1789 buffer's local map rather than augmenting existing keymaps. This also means it
1790 has lower precedence than minor mode keymaps.
1793 The @code{keymap} and @code{local-map} properties do not affect a
1794 string displayed by the @code{before-string}, @code{after-string}, or
1795 @code{display} properties. This is only relevant for mouse clicks and
1796 other mouse events that fall on the string, since point is never on
1797 the string. To bind special mouse events for the string, assign it a
1798 @code{keymap} or @code{local-map} text property. @xref{Special
1801 @node Finding Overlays
1802 @subsection Searching for Overlays
1803 @cindex searching for overlays
1804 @cindex overlays, searching for
1806 @defun overlays-at pos &optional sorted
1807 This function returns a list of all the overlays that cover the character at
1808 position @var{pos} in the current buffer. If @var{sorted} is non-@code{nil},
1809 the list is in decreasing order of priority, otherwise it is in no particular
1810 order. An overlay contains position @var{pos} if it begins at or before
1811 @var{pos}, and ends after @var{pos}.
1813 To illustrate usage, here is a Lisp function that returns a list of the
1814 overlays that specify property @var{prop} for the character at point:
1817 (defun find-overlays-specifying (prop)
1818 (let ((overlays (overlays-at (point)))
1821 (let ((overlay (car overlays)))
1822 (if (overlay-get overlay prop)
1823 (setq found (cons overlay found))))
1824 (setq overlays (cdr overlays)))
1829 @defun overlays-in beg end
1830 This function returns a list of the overlays that overlap the region
1831 @var{beg} through @var{end}. An overlay overlaps with a region if it
1832 contains one or more characters in the region; empty overlays
1833 (@pxref{Managing Overlays, empty overlay}) overlap if they are at
1834 @var{beg}, strictly between @var{beg} and @var{end}, or at @var{end}
1835 when @var{end} denotes the position at the end of the buffer.
1838 @defun next-overlay-change pos
1839 This function returns the buffer position of the next beginning or end
1840 of an overlay, after @var{pos}. If there is none, it returns
1844 @defun previous-overlay-change pos
1845 This function returns the buffer position of the previous beginning or
1846 end of an overlay, before @var{pos}. If there is none, it returns
1850 As an example, here's a simplified (and inefficient) version of the
1851 primitive function @code{next-single-char-property-change}
1852 (@pxref{Property Search}). It searches forward from position
1853 @var{pos} for the next position where the value of a given property
1854 @code{prop}, as obtained from either overlays or text properties,
1858 (defun next-single-char-property-change (position prop)
1860 (goto-char position)
1861 (let ((propval (get-char-property (point) prop)))
1862 (while (and (not (eobp))
1863 (eq (get-char-property (point) prop) propval))
1864 (goto-char (min (next-overlay-change (point))
1865 (next-single-property-change (point) prop)))))
1869 @node Size of Displayed Text
1870 @section Size of Displayed Text
1871 @cindex size of text on display
1872 @cindex character width on display
1874 Since not all characters have the same width, these functions let you
1875 check the width of a character. @xref{Primitive Indent}, and
1876 @ref{Screen Lines}, for related functions.
1878 @defun char-width char
1879 This function returns the width in columns of the character
1880 @var{char}, if it were displayed in the current buffer (i.e., taking
1881 into account the buffer's display table, if any; @pxref{Display
1882 Tables}). The width of a tab character is usually @code{tab-width}
1883 (@pxref{Usual Display}).
1886 @defun string-width string
1887 This function returns the width in columns of the string @var{string},
1888 if it were displayed in the current buffer and the selected window.
1891 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1892 This function returns the part of @var{string} that fits within
1893 @var{width} columns, as a new string.
1895 If @var{string} does not reach @var{width}, then the result ends where
1896 @var{string} ends. If one multi-column character in @var{string}
1897 extends across the column @var{width}, that character is not included in
1898 the result. Thus, the result can fall short of @var{width} but cannot
1901 The optional argument @var{start-column} specifies the starting column.
1902 If this is non-@code{nil}, then the first @var{start-column} columns of
1903 the string are omitted from the value. If one multi-column character in
1904 @var{string} extends across the column @var{start-column}, that
1905 character is not included.
1907 The optional argument @var{padding}, if non-@code{nil}, is a padding
1908 character added at the beginning and end of the result string, to extend
1909 it to exactly @var{width} columns. The padding character is used at the
1910 end of the result if it falls short of @var{width}. It is also used at
1911 the beginning of the result if one multi-column character in
1912 @var{string} extends across the column @var{start-column}.
1914 @vindex truncate-string-ellipsis
1915 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1916 replace the end of @var{string} (including any padding) if it extends
1917 beyond @var{width}, unless the display width of @var{string} is equal
1918 to or less than the display width of @var{ellipsis}. If
1919 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1920 the value of the variable @code{truncate-string-ellipsis}.
1923 (truncate-string-to-width "\tab\t" 12 4)
1925 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1930 The following function returns the size in pixels of text as if it were
1931 displayed in a given window. This function is used by
1932 @code{fit-window-to-buffer} and @code{fit-frame-to-buffer}
1933 (@pxref{Resizing Windows}) to make a window exactly as large as the text
1936 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1937 This function returns the size of the text of @var{window}'s buffer in
1938 pixels. @var{window} must be a live window and defaults to the selected
1939 one. The return value is a cons of the maximum pixel-width of any text
1940 line and the maximum pixel-height of all text lines.
1942 The optional argument @var{from}, if non-@code{nil}, specifies the first
1943 text position to consider and defaults to the minimum accessible
1944 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1945 accessible position that is not a newline character. The optional
1946 argument @var{to}, if non-@code{nil}, specifies the last text position
1947 to consider and defaults to the maximum accessible position of the
1948 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1949 position that is not a newline character.
1951 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1952 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1953 omitted, means to use the pixel-width of @var{window}'s body
1954 (@pxref{Window Sizes}); this is useful when the caller does not intend
1955 to change the width of @var{window}. Otherwise, the caller should
1956 specify here the maximum width @var{window}'s body may assume. Text
1957 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1958 calculating the width of long lines can take some time, it's always a
1959 good idea to make this argument as small as needed; in particular, if
1960 the buffer might contain long lines that will be truncated anyway.
1962 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1963 maximum pixel-height that can be returned. Text lines whose
1964 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1965 pixel-height of a large buffer can take some time, it makes sense to
1966 specify this argument; in particular, if the caller does not know the
1969 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1970 means to not include the height of the mode- or header-line of
1971 @var{window} in the return value. If it is either the symbol
1972 @code{mode-line} or @code{header-line}, include only the height of that
1973 line, if present, in the return value. If it is @code{t}, include the
1974 height of both, if present, in the return value.
1977 @defun line-pixel-height
1978 This function returns the height in pixels of the line at point in the
1979 selected window. The value includes the line spacing of the line
1980 (@pxref{Line Height}).
1985 @section Line Height
1987 @cindex height of a line
1989 The total height of each display line consists of the height of the
1990 contents of the line, plus optional additional vertical line spacing
1991 above or below the display line.
1993 The height of the line contents is the maximum height of any character
1994 or image on that display line, including the final newline if there is
1995 one. (A display line that is continued doesn't include a final
1996 newline.) That is the default line height, if you do nothing to specify
1997 a greater height. (In the most common case, this equals the height of
1998 the corresponding frame's default font, see @ref{Frame Font}.)
2000 There are several ways to explicitly specify a larger line height,
2001 either by specifying an absolute height for the display line, or by
2002 specifying vertical space. However, no matter what you specify, the
2003 actual line height can never be less than the default.
2005 @kindex line-height @r{(text property)}
2006 A newline can have a @code{line-height} text or overlay property
2007 that controls the total height of the display line ending in that
2010 If the property value is @code{t}, the newline character has no
2011 effect on the displayed height of the line---the visible contents
2012 alone determine the height. The @code{line-spacing} property,
2013 described below, is also ignored in this case. This is useful for
2014 tiling small images (or image slices) without adding blank areas
2017 If the property value is a list of the form @code{(@var{height}
2018 @var{total})}, that adds extra space @emph{below} the display line.
2019 First Emacs uses @var{height} as a height spec to control extra space
2020 @emph{above} the line; then it adds enough space @emph{below} the line
2021 to bring the total line height up to @var{total}. In this case, any
2022 value of @code{line-spacing} property for the newline is ignored.
2025 Any other kind of property value is a height spec, which translates
2026 into a number---the specified line height. There are several ways to
2027 write a height spec; here's how each of them translates into a number:
2031 If the height spec is a positive integer, the height value is that integer.
2033 If the height spec is a float, @var{float}, the numeric height value
2034 is @var{float} times the frame's default line height.
2035 @item (@var{face} . @var{ratio})
2036 If the height spec is a cons of the format shown, the numeric height
2037 is @var{ratio} times the height of face @var{face}. @var{ratio} can
2038 be any type of number, or @code{nil} which means a ratio of 1.
2039 If @var{face} is @code{t}, it refers to the current face.
2040 @item (nil . @var{ratio})
2041 If the height spec is a cons of the format shown, the numeric height
2042 is @var{ratio} times the height of the contents of the line.
2045 Thus, any valid height spec determines the height in pixels, one way
2046 or another. If the line contents' height is less than that, Emacs
2047 adds extra vertical space above the line to achieve the specified
2050 If you don't specify the @code{line-height} property, the line's
2051 height consists of the contents' height plus the line spacing.
2052 There are several ways to specify the line spacing for different
2053 parts of Emacs text.
2055 On graphical terminals, you can specify the line spacing for all
2056 lines in a frame, using the @code{line-spacing} frame parameter
2057 (@pxref{Layout Parameters}). However, if the default value of
2058 @code{line-spacing} is non-@code{nil}, it overrides the
2059 frame's @code{line-spacing} parameter. An integer specifies the
2060 number of pixels put below lines. A floating-point number specifies
2061 the spacing relative to the frame's default line height.
2063 @vindex line-spacing
2064 You can specify the line spacing for all lines in a buffer via the
2065 buffer-local @code{line-spacing} variable. An integer specifies
2066 the number of pixels put below lines. A floating-point number
2067 specifies the spacing relative to the default frame line height. This
2068 overrides line spacings specified for the frame.
2070 @kindex line-spacing @r{(text property)}
2071 Finally, a newline can have a @code{line-spacing} text or overlay
2072 property that can enlarge the default frame line spacing and the
2073 buffer local @code{line-spacing} variable: if its value is larger than
2074 the buffer or frame defaults, that larger value is used instead, for
2075 the display line ending in that newline.
2077 One way or another, these mechanisms specify a Lisp value for the
2078 spacing of each line. The value is a height spec, and it translates
2079 into a Lisp value as described above. However, in this case the
2080 numeric height value specifies the line spacing, rather than the line
2083 On text terminals, the line spacing cannot be altered.
2089 A @dfn{face} is a collection of graphical attributes for displaying
2090 text: font, foreground color, background color, optional underlining,
2091 etc. Faces control how Emacs displays text in buffers, as well as
2092 other parts of the frame such as the mode line.
2094 @cindex anonymous face
2095 One way to represent a face is as a property list of attributes,
2096 like @code{(:foreground "red" :weight bold)}. Such a list is called
2097 an @dfn{anonymous face}. For example, you can assign an anonymous
2098 face as the value of the @code{face} text property, and Emacs will
2099 display the underlying text with the specified attributes.
2100 @xref{Special Properties}.
2103 More commonly, a face is referred to via a @dfn{face name}: a Lisp
2104 symbol associated with a set of face attributes@footnote{For backward
2105 compatibility, you can also use a string to specify a face name; that
2106 is equivalent to a Lisp symbol with the same name.}. Named faces are
2107 defined using the @code{defface} macro (@pxref{Defining Faces}).
2108 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2110 Many parts of Emacs require named faces, and do not accept
2111 anonymous faces. These include the functions documented in
2112 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2113 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2114 will use the term @dfn{face} to refer only to named faces.
2117 This function returns a non-@code{nil} value if @var{object} is a
2118 named face: a Lisp symbol or string which serves as a face name.
2119 Otherwise, it returns @code{nil}.
2123 * Face Attributes:: What is in a face?
2124 * Defining Faces:: How to define a face.
2125 * Attribute Functions:: Functions to examine and set face attributes.
2126 * Displaying Faces:: How Emacs combines the faces specified for a character.
2127 * Face Remapping:: Remapping faces to alternative definitions.
2128 * Face Functions:: How to define and examine faces.
2129 * Auto Faces:: Hook for automatic face assignment.
2130 * Basic Faces:: Faces that are defined by default.
2131 * Font Selection:: Finding the best available font for a face.
2132 * Font Lookup:: Looking up the names of available fonts
2133 and information about them.
2134 * Fontsets:: A fontset is a collection of fonts
2135 that handle a range of character sets.
2136 * Low-Level Font:: Lisp representation for character display fonts.
2139 @node Face Attributes
2140 @subsection Face Attributes
2141 @cindex face attributes
2143 @dfn{Face attributes} determine the visual appearance of a face.
2144 The following table lists all the face attributes, their possible
2145 values, and their effects.
2147 Apart from the values given below, each face attribute can have the
2148 value @code{unspecified}. This special value means that the face
2149 doesn't specify that attribute directly. An @code{unspecified}
2150 attribute tells Emacs to refer instead to a parent face (see the
2151 description @code{:inherit} attribute below); or, failing that, to an
2152 underlying face (@pxref{Displaying Faces}). The @code{default} face
2153 must specify all attributes.
2155 Some of these attributes are meaningful only on certain kinds of
2156 displays. If your display cannot handle a certain attribute, the
2157 attribute is ignored.
2161 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2162 Emacs Manual}, for more information about font families. The function
2163 @code{font-family-list} (see below) returns a list of available family
2164 names. @xref{Fontsets}, for information about fontsets.
2167 The name of the @dfn{font foundry} for the font family specified by
2168 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2172 Relative character width. This should be one of the symbols
2173 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2174 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2175 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2178 The height of the font. In the simplest case, this is an integer in
2179 units of 1/10 point.
2181 The value can also be floating point or a function, which
2182 specifies the height relative to an @dfn{underlying face}
2183 (@pxref{Displaying Faces}). A floating-point value
2184 specifies the amount by which to scale the height of the
2185 underlying face. A function value is called
2186 with one argument, the height of the underlying face, and returns the
2187 height of the new face. If the function is passed an integer
2188 argument, it must return an integer.
2190 The height of the default face must be specified using an integer;
2191 floating point and function values are not allowed.
2194 Font weight---one of the symbols (from densest to faintest)
2195 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2196 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2197 @code{ultra-light}. On text terminals which support
2198 variable-brightness text, any weight greater than normal is displayed
2199 as extra bright, and any weight less than normal is displayed as
2204 Font slant---one of the symbols @code{italic}, @code{oblique},
2205 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2206 text terminals that support variable-brightness text, slanted text is
2207 displayed as half-bright.
2210 Foreground color, a string. The value can be a system-defined color
2211 name, or a hexadecimal color specification. @xref{Color Names}. On
2212 black-and-white displays, certain shades of gray are implemented by
2215 @item :distant-foreground
2216 Alternative foreground color, a string. This is like @code{:foreground}
2217 but the color is only used as a foreground when the background color is
2218 near to the foreground that would have been used. This is useful for
2219 example when marking text (i.e., the region face). If the text has a foreground
2220 that is visible with the region face, that foreground is used.
2221 If the foreground is near the region face background,
2222 @code{:distant-foreground} is used instead so the text is readable.
2225 Background color, a string. The value can be a system-defined color
2226 name, or a hexadecimal color specification. @xref{Color Names}.
2228 @cindex underlined text
2230 Whether or not characters should be underlined, and in what
2231 way. The possible values of the @code{:underline} attribute are:
2238 Underline with the foreground color of the face.
2241 Underline in color @var{color}, a string specifying a color.
2243 @item @code{(:color @var{color} :style @var{style})}
2244 @var{color} is either a string, or the symbol @code{foreground-color},
2245 meaning the foreground color of the face. Omitting the attribute
2246 @code{:color} means to use the foreground color of the face.
2247 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2248 use a straight or wavy line. Omitting the attribute @code{:style}
2249 means to use a straight line.
2252 @cindex overlined text
2254 Whether or not characters should be overlined, and in what color.
2255 If the value is @code{t}, overlining uses the foreground color of the
2256 face. If the value is a string, overlining uses that color. The
2257 value @code{nil} means do not overline.
2259 @cindex strike-through text
2260 @item :strike-through
2261 Whether or not characters should be strike-through, and in what
2262 color. The value is used like that of @code{:overline}.
2267 Whether or not a box should be drawn around characters, its color, the
2268 width of the box lines, and 3D appearance. Here are the possible
2269 values of the @code{:box} attribute, and what they mean:
2276 Draw a box with lines of width 1, in the foreground color.
2279 Draw a box with lines of width 1, in color @var{color}.
2281 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2282 This way you can explicitly specify all aspects of the box. The value
2283 @var{width} specifies the width of the lines to draw; it defaults to
2284 1. A negative width @var{-n} means to draw a line of width @var{n}
2285 that occupies the space of the underlying text, thus avoiding any
2286 increase in the character height or width.
2288 The value @var{color} specifies the color to draw with. The default is
2289 the foreground color of the face for simple boxes, and the background
2290 color of the face for 3D boxes.
2292 The value @var{style} specifies whether to draw a 3D box. If it is
2293 @code{released-button}, the box looks like a 3D button that is not being
2294 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2295 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2299 @item :inverse-video
2300 Whether or not characters should be displayed in inverse video. The
2301 value should be @code{t} (yes) or @code{nil} (no).
2304 The background stipple, a bitmap.
2306 The value can be a string; that should be the name of a file containing
2307 external-format X bitmap data. The file is found in the directories
2308 listed in the variable @code{x-bitmap-file-path}.
2310 Alternatively, the value can specify the bitmap directly, with a list
2311 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2312 @var{width} and @var{height} specify the size in pixels, and
2313 @var{data} is a string containing the raw bits of the bitmap, row by
2314 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2315 in the string (which should be a unibyte string for best results).
2316 This means that each row always occupies at least one whole byte.
2318 If the value is @code{nil}, that means use no stipple pattern.
2320 Normally you do not need to set the stipple attribute, because it is
2321 used automatically to handle certain shades of gray.
2324 The font used to display the face. Its value should be a font object.
2325 @xref{Low-Level Font}, for information about font objects, font specs,
2328 When specifying this attribute using @code{set-face-attribute}
2329 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2330 entity, or a string. Emacs converts such values to an appropriate
2331 font object, and stores that font object as the actual attribute
2332 value. If you specify a string, the contents of the string should be
2333 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2334 font name is an XLFD containing wildcards, Emacs chooses the first
2335 font matching those wildcards. Specifying this attribute also changes
2336 the values of the @code{:family}, @code{:foundry}, @code{:width},
2337 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2339 @cindex inheritance, for faces
2341 The name of a face from which to inherit attributes, or a list of face
2342 names. Attributes from inherited faces are merged into the face like
2343 an underlying face would be, with higher priority than underlying
2344 faces (@pxref{Displaying Faces}). If a list of faces is used,
2345 attributes from faces earlier in the list override those from later
2349 @defun font-family-list &optional frame
2350 This function returns a list of available font family names. The
2351 optional argument @var{frame} specifies the frame on which the text is
2352 to be displayed; if it is @code{nil}, the selected frame is used.
2355 @defopt underline-minimum-offset
2356 This variable specifies the minimum distance between the baseline and
2357 the underline, in pixels, when displaying underlined text.
2360 @defopt x-bitmap-file-path
2361 This variable specifies a list of directories for searching
2362 for bitmap files, for the @code{:stipple} attribute.
2365 @defun bitmap-spec-p object
2366 This returns @code{t} if @var{object} is a valid bitmap specification,
2367 suitable for use with @code{:stipple} (see above). It returns
2368 @code{nil} otherwise.
2371 @node Defining Faces
2372 @subsection Defining Faces
2373 @cindex defining faces
2376 The usual way to define a face is through the @code{defface} macro.
2377 This macro associates a face name (a symbol) with a default @dfn{face
2378 spec}. A face spec is a construct which specifies what attributes a
2379 face should have on any given terminal; for example, a face spec might
2380 specify one foreground color on high-color terminals, and a different
2381 foreground color on low-color terminals.
2383 People are sometimes tempted to create a variable whose value is a
2384 face name. In the vast majority of cases, this is not necessary; the
2385 usual procedure is to define a face with @code{defface}, and then use
2388 @defmac defface face spec doc [keyword value]@dots{}
2389 This macro declares @var{face} as a named face whose default face spec
2390 is given by @var{spec}. You should not quote the symbol @var{face},
2391 and it should not end in @samp{-face} (that would be redundant). The
2392 argument @var{doc} is a documentation string for the face. The
2393 additional @var{keyword} arguments have the same meanings as in
2394 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2396 If @var{face} already has a default face spec, this macro does
2399 The default face spec determines @var{face}'s appearance when no
2400 customizations are in effect (@pxref{Customization}). If @var{face}
2401 has already been customized (via Custom themes or via customizations
2402 read from the init file), its appearance is determined by the custom
2403 face spec(s), which override the default face spec @var{spec}.
2404 However, if the customizations are subsequently removed, the
2405 appearance of @var{face} will again be determined by its default face
2408 As an exception, if you evaluate a @code{defface} form with
2409 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2410 of @code{eval-defun} overrides any custom face specs on the face,
2411 causing the face to reflect exactly what the @code{defface} says.
2413 The @var{spec} argument is a @dfn{face spec}, which states how the
2414 face should appear on different kinds of terminals. It should be an
2415 alist whose elements each have the form
2418 (@var{display} . @var{plist})
2422 @var{display} specifies a class of terminals (see below). @var{plist}
2423 is a property list of face attributes and their values, specifying how
2424 the face appears on such terminals. For backward compatibility, you
2425 can also write an element as @code{(@var{display} @var{plist})}.
2427 The @var{display} part of an element of @var{spec} determines which
2428 terminals the element matches. If more than one element of @var{spec}
2429 matches a given terminal, the first element that matches is the one
2430 used for that terminal. There are three possibilities for
2434 @item @code{default}
2435 This element of @var{spec} doesn't match any terminal; instead, it
2436 specifies defaults that apply to all terminals. This element, if
2437 used, must be the first element of @var{spec}. Each of the following
2438 elements can override any or all of these defaults.
2441 This element of @var{spec} matches all terminals. Therefore, any
2442 subsequent elements of @var{spec} are never used. Normally @code{t}
2443 is used in the last (or only) element of @var{spec}.
2446 If @var{display} is a list, each element should have the form
2447 @code{(@var{characteristic} @var{value}@dots{})}. Here
2448 @var{characteristic} specifies a way of classifying terminals, and the
2449 @var{value}s are possible classifications which @var{display} should
2450 apply to. Here are the possible values of @var{characteristic}:
2454 The kind of window system the terminal uses---either @code{graphic}
2455 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2456 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2457 non-graphics-capable display). @xref{Window Systems, window-system}.
2460 What kinds of colors the terminal supports---either @code{color},
2461 @code{grayscale}, or @code{mono}.
2464 The kind of background---either @code{light} or @code{dark}.
2467 An integer that represents the minimum number of colors the terminal
2468 should support. This matches a terminal if its
2469 @code{display-color-cells} value is at least the specified integer.
2472 Whether or not the terminal can display the face attributes given in
2473 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2474 Attribute Testing}, for more information on exactly how this testing
2478 If an element of @var{display} specifies more than one @var{value} for
2479 a given @var{characteristic}, any of those values is acceptable. If
2480 @var{display} has more than one element, each element should specify a
2481 different @var{characteristic}; then @emph{each} characteristic of the
2482 terminal must match one of the @var{value}s specified for it in
2487 For example, here's the definition of the standard face
2492 '((((class color) (min-colors 88) (background light))
2493 :background "darkseagreen2")
2494 (((class color) (min-colors 88) (background dark))
2495 :background "darkolivegreen")
2496 (((class color) (min-colors 16) (background light))
2497 :background "darkseagreen2")
2498 (((class color) (min-colors 16) (background dark))
2499 :background "darkolivegreen")
2500 (((class color) (min-colors 8))
2501 :background "green" :foreground "black")
2502 (t :inverse-video t))
2503 "Basic face for highlighting."
2504 :group 'basic-faces)
2507 Internally, Emacs stores each face's default spec in its
2508 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2509 The @code{saved-face} property stores any face spec saved by the user
2510 using the customization buffer; the @code{customized-face} property
2511 stores the face spec customized for the current session, but not
2512 saved; and the @code{theme-face} property stores an alist associating
2513 the active customization settings and Custom themes with the face
2514 specs for that face. The face's documentation string is stored in the
2515 @code{face-documentation} property.
2517 Normally, a face is declared just once, using @code{defface}, and
2518 any further changes to its appearance are applied using the Customize
2519 framework (e.g., via the Customize user interface or via the
2520 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2521 by face remapping (@pxref{Face Remapping}). In the rare event that
2522 you need to change a face spec directly from Lisp, you can use the
2523 @code{face-spec-set} function.
2525 @defun face-spec-set face spec &optional spec-type
2526 This function applies @var{spec} as a face spec for @code{face}.
2527 @var{spec} should be a face spec, as described in the above
2528 documentation for @code{defface}.
2530 This function also defines @var{face} as a valid face name if it is
2531 not already one, and (re)calculates its attributes on existing frames.
2533 @cindex override spec @r{(for a face)}
2534 The argument @var{spec-type} determines which spec to set. If it is
2535 @code{nil} or @code{face-override-spec}, this function sets the
2536 @dfn{override spec}, which overrides over all other face specs on
2537 @var{face}. If it is @code{customized-face} or @code{saved-face},
2538 this function sets the customized spec or the saved custom spec. If
2539 it is @code{face-defface-spec}, this function sets the default face
2540 spec (the same one set by @code{defface}). If it is @code{reset},
2541 this function clears out all customization specs and override specs
2542 from @var{face} (in this case, the value of @var{spec} is ignored).
2543 Any other value of @var{spec-type} is reserved for internal use.
2546 @node Attribute Functions
2547 @subsection Face Attribute Functions
2548 @cindex face attributes, access and modification
2550 This section describes functions for directly accessing and
2551 modifying the attributes of a named face.
2553 @defun face-attribute face attribute &optional frame inherit
2554 This function returns the value of the @var{attribute} attribute for
2555 @var{face} on @var{frame}.
2557 If @var{frame} is omitted or @code{nil}, that means the selected frame
2558 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2559 returns the value of the specified attribute for newly-created frames
2560 (this is normally @code{unspecified}, unless you have specified some
2561 value using @code{set-face-attribute}; see below).
2563 If @var{inherit} is @code{nil}, only attributes directly defined by
2564 @var{face} are considered, so the return value may be
2565 @code{unspecified}, or a relative value. If @var{inherit} is
2566 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2567 with the faces specified by its @code{:inherit} attribute; however the
2568 return value may still be @code{unspecified} or relative. If
2569 @var{inherit} is a face or a list of faces, then the result is further
2570 merged with that face (or faces), until it becomes specified and
2573 To ensure that the return value is always specified and absolute, use
2574 a value of @code{default} for @var{inherit}; this will resolve any
2575 unspecified or relative values by merging with the @code{default} face
2576 (which is always completely specified).
2581 (face-attribute 'bold :weight)
2586 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2587 @defun face-attribute-relative-p attribute value
2588 This function returns non-@code{nil} if @var{value}, when used as the
2589 value of the face attribute @var{attribute}, is relative. This means
2590 it would modify, rather than completely override, any value that comes
2591 from a subsequent face in the face list or that is inherited from
2594 @code{unspecified} is a relative value for all attributes. For
2595 @code{:height}, floating point and function values are also relative.
2600 (face-attribute-relative-p :height 2.0)
2605 @defun face-all-attributes face &optional frame
2606 This function returns an alist of attributes of @var{face}. The
2607 elements of the result are name-value pairs of the form
2608 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2609 @var{frame} specifies the frame whose definition of @var{face} to
2610 return; if omitted or @code{nil}, the returned value describes the
2611 default attributes of @var{face} for newly created frames.
2614 @defun merge-face-attribute attribute value1 value2
2615 If @var{value1} is a relative value for the face attribute
2616 @var{attribute}, returns it merged with the underlying value
2617 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2618 face attribute @var{attribute}, returns @var{value1} unchanged.
2621 Normally, Emacs uses the face specs of each face to automatically
2622 calculate its attributes on each frame (@pxref{Defining Faces}). The
2623 function @code{set-face-attribute} can override this calculation by
2624 directly assigning attributes to a face, either on a specific frame or
2625 for all frames. This function is mostly intended for internal usage.
2627 @defun set-face-attribute face frame &rest arguments
2628 This function sets one or more attributes of @var{face} for
2629 @var{frame}. The attributes specifies in this way override the face
2630 spec(s) belonging to @var{face}.
2632 The extra arguments @var{arguments} specify the attributes to set, and
2633 the values for them. They should consist of alternating attribute
2634 names (such as @code{:family} or @code{:underline}) and values. Thus,
2637 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2641 sets the attribute @code{:weight} to @code{bold} and the attribute
2642 @code{:slant} to @code{italic}.
2645 If @var{frame} is @code{t}, this function sets the default attributes
2646 for newly created frames. If @var{frame} is @code{nil}, this function
2647 sets the attributes for all existing frames, as well as for newly
2651 The following commands and functions mostly provide compatibility
2652 with old versions of Emacs. They work by calling
2653 @code{set-face-attribute}. Values of @code{t} and @code{nil} (or
2654 omitted) for their @var{frame} argument are handled just like
2655 @code{set-face-attribute} and @code{face-attribute}. The commands
2656 read their arguments using the minibuffer, if called interactively.
2658 @deffn Command set-face-foreground face color &optional frame
2659 @deffnx Command set-face-background face color &optional frame
2660 These set the @code{:foreground} attribute (or @code{:background}
2661 attribute, respectively) of @var{face} to @var{color}.
2664 @deffn Command set-face-stipple face pattern &optional frame
2665 This sets the @code{:stipple} attribute of @var{face} to
2669 @deffn Command set-face-font face font &optional frame
2670 This sets the @code{:font} attribute of @var{face} to @var{font}.
2673 @defun set-face-bold face bold-p &optional frame
2674 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2675 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2678 @defun set-face-italic face italic-p &optional frame
2679 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2680 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2683 @defun set-face-underline face underline &optional frame
2684 This sets the @code{:underline} attribute of @var{face} to
2688 @defun set-face-inverse-video face inverse-video-p &optional frame
2689 This sets the @code{:inverse-video} attribute of @var{face} to
2690 @var{inverse-video-p}.
2693 @deffn Command invert-face face &optional frame
2694 This swaps the foreground and background colors of face @var{face}.
2697 The following functions examine the attributes of a face. They
2698 mostly provide compatibility with old versions of Emacs. If you don't
2699 specify @var{frame}, they refer to the selected frame; @code{t} refers
2700 to the default data for new frames. They return @code{unspecified} if
2701 the face doesn't define any value for that attribute. If
2702 @var{inherit} is @code{nil}, only an attribute directly defined by the
2703 face is returned. If @var{inherit} is non-@code{nil}, any faces
2704 specified by its @code{:inherit} attribute are considered as well, and
2705 if @var{inherit} is a face or a list of faces, then they are also
2706 considered, until a specified attribute is found. To ensure that the
2707 return value is always specified, use a value of @code{default} for
2710 @defun face-font face &optional frame character
2711 This function returns the name of the font of face @var{face}.
2713 If the optional argument @var{frame} is specified, it returns the name
2714 of the font of @var{face} for that frame. If @var{frame} is omitted or
2715 @code{nil}, the selected frame is used. And, in this case, if the
2716 optional third argument @var{character} is supplied, it returns the font
2717 name used for @var{character}.
2720 @defun face-foreground face &optional frame inherit
2721 @defunx face-background face &optional frame inherit
2722 These functions return the foreground color (or background color,
2723 respectively) of face @var{face}, as a string. If the color is
2724 unspecified, they return @code{nil}.
2727 @defun face-stipple face &optional frame inherit
2728 This function returns the name of the background stipple pattern of face
2729 @var{face}, or @code{nil} if it doesn't have one.
2732 @defun face-bold-p face &optional frame inherit
2733 This function returns a non-@code{nil} value if the @code{:weight}
2734 attribute of @var{face} is bolder than normal (i.e., one of
2735 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2736 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2739 @defun face-italic-p face &optional frame inherit
2740 This function returns a non-@code{nil} value if the @code{:slant}
2741 attribute of @var{face} is @code{italic} or @code{oblique}, and
2742 @code{nil} otherwise.
2745 @defun face-underline-p face &optional frame inherit
2746 This function returns non-@code{nil} if face @var{face} specifies
2747 a non-@code{nil} @code{:underline} attribute.
2750 @defun face-inverse-video-p face &optional frame inherit
2751 This function returns non-@code{nil} if face @var{face} specifies
2752 a non-@code{nil} @code{:inverse-video} attribute.
2755 @node Displaying Faces
2756 @subsection Displaying Faces
2757 @cindex displaying faces
2758 @cindex face merging
2760 When Emacs displays a given piece of text, the visual appearance of
2761 the text may be determined by faces drawn from different sources. If
2762 these various sources together specify more than one face for a
2763 particular character, Emacs merges the attributes of the various
2764 faces. Here is the order in which Emacs merges the faces, from
2765 highest to lowest priority:
2769 If the text consists of a special glyph, the glyph can specify a
2770 particular face. @xref{Glyphs}.
2773 If the text lies within an active region, Emacs highlights it using
2774 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2778 If the text lies within an overlay with a non-@code{nil} @code{face}
2779 property, Emacs applies the face(s) specified by that property. If
2780 the overlay has a @code{mouse-face} property and the mouse is near
2781 enough to the overlay, Emacs applies the face or face attributes
2782 specified by the @code{mouse-face} property instead. @xref{Overlay
2785 When multiple overlays cover one character, an overlay with higher
2786 priority overrides those with lower priority. @xref{Overlays}.
2789 If the text contains a @code{face} or @code{mouse-face} property,
2790 Emacs applies the specified faces and face attributes. @xref{Special
2791 Properties}. (This is how Font Lock mode faces are applied.
2792 @xref{Font Lock Mode}.)
2795 If the text lies within the mode line of the selected window, Emacs
2796 applies the @code{mode-line} face. For the mode line of a
2797 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2798 For a header line, Emacs applies the @code{header-line} face.
2801 If any given attribute has not been specified during the preceding
2802 steps, Emacs applies the attribute of the @code{default} face.
2805 At each stage, if a face has a valid @code{:inherit} attribute,
2806 Emacs treats any attribute with an @code{unspecified} value as having
2807 the corresponding value drawn from the parent face(s). @pxref{Face
2808 Attributes}. Note that the parent face(s) may also leave the
2809 attribute unspecified; in that case, the attribute remains unspecified
2810 at the next level of face merging.
2812 @node Face Remapping
2813 @subsection Face Remapping
2814 @cindex face remapping
2816 The variable @code{face-remapping-alist} is used for buffer-local or
2817 global changes in the appearance of a face. For instance, it is used
2818 to implement the @code{text-scale-adjust} command (@pxref{Text
2819 Scale,,, emacs, The GNU Emacs Manual}).
2821 @defvar face-remapping-alist
2822 The value of this variable is an alist whose elements have the form
2823 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2824 any text having the face @var{face} with @var{remapping}, rather than
2825 the ordinary definition of @var{face}.
2827 @var{remapping} may be any face spec suitable for a @code{face} text
2828 property: either a face (i.e., a face name or a property list of
2829 attribute/value pairs), or a list of faces. For details, see the
2830 description of the @code{face} text property in @ref{Special
2831 Properties}. @var{remapping} serves as the complete specification for
2832 the remapped face---it replaces the normal definition of @var{face},
2833 instead of modifying it.
2835 If @code{face-remapping-alist} is buffer-local, its local value takes
2836 effect only within that buffer.
2838 Note: face remapping is non-recursive. If @var{remapping} references
2839 the same face name @var{face}, either directly or via the
2840 @code{:inherit} attribute of some other face in @var{remapping}, that
2841 reference uses the normal definition of @var{face}. For instance, if
2842 the @code{mode-line} face is remapped using this entry in
2843 @code{face-remapping-alist}:
2846 (mode-line italic mode-line)
2850 then the new definition of the @code{mode-line} face inherits from the
2851 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2852 @code{mode-line} face.
2855 @cindex relative remapping, faces
2856 @cindex base remapping, faces
2857 The following functions implement a higher-level interface to
2858 @code{face-remapping-alist}. Most Lisp code should use these
2859 functions instead of setting @code{face-remapping-alist} directly, to
2860 avoid trampling on remappings applied elsewhere. These functions are
2861 intended for buffer-local remappings, so they all make
2862 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2863 @code{face-remapping-alist} entries of the form
2866 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2870 where, as explained above, each of the @var{relative-spec-N} and
2871 @var{base-spec} is either a face name, or a property list of
2872 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2873 @var{relative-spec-N}, is managed by the
2874 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2875 functions; these are intended for simple modifications like changing
2876 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2877 the lowest priority and is managed by the @code{face-remap-set-base}
2878 and @code{face-remap-reset-base} functions; it is intended for major
2879 modes to remap faces in the buffers they control.
2881 @defun face-remap-add-relative face &rest specs
2882 This function adds the face spec in @var{specs} as relative
2883 remappings for face @var{face} in the current buffer. The remaining
2884 arguments, @var{specs}, should form either a list of face names, or a
2885 property list of attribute/value pairs.
2887 The return value is a Lisp object that serves as a cookie; you can
2888 pass this object as an argument to @code{face-remap-remove-relative}
2889 if you need to remove the remapping later.
2892 ;; Remap the 'escape-glyph' face into a combination
2893 ;; of the 'highlight' and 'italic' faces:
2894 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2896 ;; Increase the size of the 'default' face by 50%:
2897 (face-remap-add-relative 'default :height 1.5)
2901 @defun face-remap-remove-relative cookie
2902 This function removes a relative remapping previously added by
2903 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2904 object returned by @code{face-remap-add-relative} when the remapping
2908 @defun face-remap-set-base face &rest specs
2909 This function sets the base remapping of @var{face} in the current
2910 buffer to @var{specs}. If @var{specs} is empty, the default base
2911 remapping is restored, similar to calling @code{face-remap-reset-base}
2912 (see below); note that this is different from @var{specs} containing a
2913 single value @code{nil}, which has the opposite result (the global
2914 definition of @var{face} is ignored).
2916 This overwrites the default @var{base-spec}, which inherits the global
2917 face definition, so it is up to the caller to add such inheritance if
2921 @defun face-remap-reset-base face
2922 This function sets the base remapping of @var{face} to its default
2923 value, which inherits from @var{face}'s global definition.
2926 @node Face Functions
2927 @subsection Functions for Working with Faces
2929 Here are additional functions for creating and working with faces.
2932 This function returns a list of all defined face names.
2936 This function returns the @dfn{face number} of face @var{face}. This
2937 is a number that uniquely identifies a face at low levels within
2938 Emacs. It is seldom necessary to refer to a face by its face number.
2941 @defun face-documentation face
2942 This function returns the documentation string of face @var{face}, or
2943 @code{nil} if none was specified for it.
2946 @defun face-equal face1 face2 &optional frame
2947 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2948 same attributes for display.
2951 @defun face-differs-from-default-p face &optional frame
2952 This returns non-@code{nil} if the face @var{face} displays
2953 differently from the default face.
2957 @cindex alias, for faces
2958 A @dfn{face alias} provides an equivalent name for a face. You can
2959 define a face alias by giving the alias symbol the @code{face-alias}
2960 property, with a value of the target face name. The following example
2961 makes @code{modeline} an alias for the @code{mode-line} face.
2964 (put 'modeline 'face-alias 'mode-line)
2967 @defmac define-obsolete-face-alias obsolete-face current-face when
2968 This macro defines @code{obsolete-face} as an alias for
2969 @var{current-face}, and also marks it as obsolete, indicating that it
2970 may be removed in future. @var{when} should be a string indicating
2971 when @code{obsolete-face} was made obsolete (usually a version number
2976 @subsection Automatic Face Assignment
2977 @cindex automatic face assignment
2978 @cindex faces, automatic choice
2980 This hook is used for automatically assigning faces to text in the
2981 buffer. It is part of the implementation of Jit-Lock mode, used by
2984 @defvar fontification-functions
2985 This variable holds a list of functions that are called by Emacs
2986 redisplay as needed, just before doing redisplay. They are called even
2987 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2988 variable usually holds just one function, @code{jit-lock-function}.
2990 The functions are called in the order listed, with one argument, a
2991 buffer position @var{pos}. Collectively they should attempt to assign
2992 faces to the text in the current buffer starting at @var{pos}.
2994 The functions should record the faces they assign by setting the
2995 @code{face} property. They should also add a non-@code{nil}
2996 @code{fontified} property to all the text they have assigned faces to.
2997 That property tells redisplay that faces have been assigned to that text
3000 It is probably a good idea for the functions to do nothing if the
3001 character after @var{pos} already has a non-@code{nil} @code{fontified}
3002 property, but this is not required. If one function overrides the
3003 assignments made by a previous one, the properties after the last
3004 function finishes are the ones that really matter.
3006 For efficiency, we recommend writing these functions so that they
3007 usually assign faces to around 400 to 600 characters at each call.
3011 @subsection Basic Faces
3014 If your Emacs Lisp program needs to assign some faces to text, it is
3015 often a good idea to use certain existing faces or inherit from them,
3016 rather than defining entirely new faces. This way, if other users
3017 have customized the basic faces to give Emacs a certain look, your
3018 program will fit in without additional customization.
3020 Some of the basic faces defined in Emacs are listed below. In
3021 addition to these, you might want to make use of the Font Lock faces
3022 for syntactic highlighting, if highlighting is not already handled by
3023 Font Lock mode, or if some Font Lock faces are not in use.
3024 @xref{Faces for Font Lock}.
3028 The default face, whose attributes are all specified. All other faces
3029 implicitly inherit from it: any unspecified attribute defaults to the
3030 attribute on this face (@pxref{Face Attributes}).
3037 @itemx fixed-pitch-serif
3038 @itemx variable-pitch
3039 These have the attributes indicated by their names (e.g., @code{bold}
3040 has a bold @code{:weight} attribute), with all other attributes
3041 unspecified (and so given by @code{default}).
3044 For dimmed-out text. For example, it is used for the ignored
3045 part of a filename in the minibuffer (@pxref{Minibuffer File,,
3046 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
3050 For clickable text buttons that send the user to a different
3054 For stretches of text that should temporarily stand out. For example,
3055 it is commonly assigned to the @code{mouse-face} property for cursor
3056 highlighting (@pxref{Special Properties}).
3060 @itemx lazy-highlight
3061 For text matching (respectively) permanent search matches, interactive
3062 search matches, and lazy highlighting other matches than the current
3068 For text concerning errors, warnings, or successes. For example,
3069 these are used for messages in @file{*Compilation*} buffers.
3072 @node Font Selection
3073 @subsection Font Selection
3074 @cindex font selection
3075 @cindex selecting a font
3077 Before Emacs can draw a character on a graphical display, it must
3078 select a @dfn{font} for that character@footnote{In this context, the
3079 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
3080 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
3081 Emacs automatically chooses a font based on the faces assigned to that
3082 character---specifically, the face attributes @code{:family},
3083 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
3084 Attributes}). The choice of font also depends on the character to be
3085 displayed; some fonts can only display a limited set of characters.
3086 If no available font exactly fits the requirements, Emacs looks for
3087 the @dfn{closest matching font}. The variables in this section
3088 control how Emacs makes this selection.
3090 @defopt face-font-family-alternatives
3091 If a given family is specified but does not exist, this variable
3092 specifies alternative font families to try. Each element should have
3096 (@var{family} @var{alternate-families}@dots{})
3099 If @var{family} is specified but not available, Emacs will try the other
3100 families given in @var{alternate-families}, one by one, until it finds a
3101 family that does exist.
3104 @defopt face-font-selection-order
3105 If there is no font that exactly matches all desired face attributes
3106 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
3107 this variable specifies the order in which these attributes should be
3108 considered when selecting the closest matching font. The value should
3109 be a list containing those four attribute symbols, in order of
3110 decreasing importance. The default is @code{(:width :height :weight
3113 Font selection first finds the best available matches for the first
3114 attribute in the list; then, among the fonts which are best in that
3115 way, it searches for the best matches in the second attribute, and so
3118 The attributes @code{:weight} and @code{:width} have symbolic values in
3119 a range centered around @code{normal}. Matches that are more extreme
3120 (farther from @code{normal}) are somewhat preferred to matches that are
3121 less extreme (closer to @code{normal}); this is designed to ensure that
3122 non-normal faces contrast with normal ones, whenever possible.
3124 One example of a case where this variable makes a difference is when the
3125 default font has no italic equivalent. With the default ordering, the
3126 @code{italic} face will use a non-italic font that is similar to the
3127 default one. But if you put @code{:slant} before @code{:height}, the
3128 @code{italic} face will use an italic font, even if its height is not
3132 @defopt face-font-registry-alternatives
3133 This variable lets you specify alternative font registries to try, if a
3134 given registry is specified and doesn't exist. Each element should have
3138 (@var{registry} @var{alternate-registries}@dots{})
3141 If @var{registry} is specified but not available, Emacs will try the
3142 other registries given in @var{alternate-registries}, one by one,
3143 until it finds a registry that does exist.
3146 @cindex scalable fonts
3147 Emacs can make use of scalable fonts, but by default it does not use
3150 @defopt scalable-fonts-allowed
3151 This variable controls which scalable fonts to use. A value of
3152 @code{nil}, the default, means do not use scalable fonts. @code{t}
3153 means to use any scalable font that seems appropriate for the text.
3155 Otherwise, the value must be a list of regular expressions. Then a
3156 scalable font is enabled for use if its name matches any regular
3157 expression in the list. For example,
3160 (setq scalable-fonts-allowed '("iso10646-1$"))
3164 allows the use of scalable fonts with registry @code{iso10646-1}.
3167 @defvar face-font-rescale-alist
3168 This variable specifies scaling for certain faces. Its value should
3169 be a list of elements of the form
3172 (@var{fontname-regexp} . @var{scale-factor})
3175 If @var{fontname-regexp} matches the font name that is about to be
3176 used, this says to choose a larger similar font according to the
3177 factor @var{scale-factor}. You would use this feature to normalize
3178 the font size if certain fonts are bigger or smaller than their
3179 nominal heights and widths would suggest.
3183 @subsection Looking Up Fonts
3185 @cindex looking up fonts
3187 @defun x-list-fonts name &optional reference-face frame maximum width
3188 This function returns a list of available font names that match
3189 @var{name}. @var{name} should be a string containing a font name in
3190 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3191 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3192 used: the @samp{*} character matches any substring, and the @samp{?}
3193 character matches any single character. Case is ignored when matching
3196 If the optional arguments @var{reference-face} and @var{frame} are
3197 specified, the returned list includes only fonts that are the same
3198 size as @var{reference-face} (a face name) currently is on the frame
3201 The optional argument @var{maximum} sets a limit on how many fonts to
3202 return. If it is non-@code{nil}, then the return value is truncated
3203 after the first @var{maximum} matching fonts. Specifying a small
3204 value for @var{maximum} can make this function much faster, in cases
3205 where many fonts match the pattern.
3207 The optional argument @var{width} specifies a desired font width. If
3208 it is non-@code{nil}, the function only returns those fonts whose
3209 characters are (on average) @var{width} times as wide as
3210 @var{reference-face}.
3213 @defun x-family-fonts &optional family frame
3214 This function returns a list describing the available fonts for family
3215 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3216 this list applies to all families, and therefore, it contains all
3217 available fonts. Otherwise, @var{family} must be a string; it may
3218 contain the wildcards @samp{?} and @samp{*}.
3220 The list describes the display that @var{frame} is on; if @var{frame} is
3221 omitted or @code{nil}, it applies to the selected frame's display
3222 (@pxref{Input Focus}).
3224 Each element in the list is a vector of the following form:
3227 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3228 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3231 The first five elements correspond to face attributes; if you
3232 specify these attributes for a face, it will use this font.
3234 The last three elements give additional information about the font.
3235 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3236 @var{full} is the full name of the font, and
3237 @var{registry-and-encoding} is a string giving the registry and
3238 encoding of the font.
3242 @subsection Fontsets
3245 A @dfn{fontset} is a list of fonts, each assigned to a range of
3246 character codes. An individual font cannot display the whole range of
3247 characters that Emacs supports, but a fontset can. Fontsets have names,
3248 just as fonts do, and you can use a fontset name in place of a font name
3249 when you specify the font for a frame or a face. Here is
3250 information about defining a fontset under Lisp program control.
3252 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3253 This function defines a new fontset according to the specification
3254 string @var{fontset-spec}. The string should have this format:
3257 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3261 Whitespace characters before and after the commas are ignored.
3263 The first part of the string, @var{fontpattern}, should have the form of
3264 a standard X font name, except that the last two fields should be
3265 @samp{fontset-@var{alias}}.
3267 The new fontset has two names, one long and one short. The long name is
3268 @var{fontpattern} in its entirety. The short name is
3269 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3270 name. If a fontset with the same name already exists, an error is
3271 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3272 function does nothing.
3274 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3275 to create bold, italic and bold-italic variants of the fontset as well.
3276 These variant fontsets do not have a short name, only a long one, which
3277 is made by altering @var{fontpattern} to indicate the bold and/or italic
3280 The specification string also says which fonts to use in the fontset.
3281 See below for the details.
3284 The construct @samp{@var{charset}:@var{font}} specifies which font to
3285 use (in this fontset) for one particular character set. Here,
3286 @var{charset} is the name of a character set, and @var{font} is the font
3287 to use for that character set. You can use this construct any number of
3288 times in the specification string.
3290 For the remaining character sets, those that you don't specify
3291 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3292 @samp{fontset-@var{alias}} with a value that names one character set.
3293 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3294 with @samp{ISO8859-1}.
3296 In addition, when several consecutive fields are wildcards, Emacs
3297 collapses them into a single wildcard. This is to prevent use of
3298 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3299 for editing, and scaling a smaller font is not useful because it is
3300 better to use the smaller font in its own size, which Emacs does.
3302 Thus if @var{fontpattern} is this,
3305 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3309 the font specification for @acronym{ASCII} characters would be this:
3312 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3316 and the font specification for Chinese GB2312 characters would be this:
3319 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3322 You may not have any Chinese font matching the above font
3323 specification. Most X distributions include only Chinese fonts that
3324 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3325 such a case, @samp{Fontset-@var{n}} can be specified as below:
3328 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3329 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3333 Then, the font specifications for all but Chinese GB2312 characters have
3334 @samp{fixed} in the @var{family} field, and the font specification for
3335 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3338 @defun set-fontset-font name character font-spec &optional frame add
3339 This function modifies the existing fontset @var{name} to use the font
3340 matching with @var{font-spec} for the specified @var{character}.
3342 If @var{name} is @code{nil}, this function modifies the fontset of the
3343 selected frame or that of @var{frame} if @var{frame} is not
3346 If @var{name} is @code{t}, this function modifies the default
3347 fontset, whose short name is @samp{fontset-default}.
3349 In addition to specifying a single codepoint, @var{character} may be a
3350 cons @code{(@var{from} . @var{to})}, where @var{from} and @var{to} are
3351 character codepoints. In that case, use @var{font-spec} for all the
3352 characters in the range @var{from} and @var{to} (inclusive).
3354 @var{character} may be a charset. In that case, use
3355 @var{font-spec} for all character in the charsets.
3357 @var{character} may be a script name. In that case, use
3358 @var{font-spec} for all character in the charsets.
3360 @var{font-spec} may be a font-spec object created by the function
3361 @code{font-spec} (@pxref{Low-Level Font}).
3363 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3364 where @var{family} is a family name of a font (possibly including a
3365 foundry name at the head), @var{registry} is a registry name of a font
3366 (possibly including an encoding name at the tail).
3368 @var{font-spec} may be a font name string.
3370 @var{font-spec} may be @code{nil}, which explicitly specifies that
3371 there's no font for the specified @var{character}. This is useful,
3372 for example, to avoid expensive system-wide search for fonts for
3373 characters that have no glyphs, like those from the Unicode Private
3376 The optional argument @var{add}, if non-@code{nil}, specifies how to
3377 add @var{font-spec} to the font specifications previously set. If it
3378 is @code{prepend}, @var{font-spec} is prepended. If it is
3379 @code{append}, @var{font-spec} is appended. By default,
3380 @var{font-spec} overrides the previous settings.
3382 For instance, this changes the default fontset to use a font of which
3383 family name is @samp{Kochi Gothic} for all characters belonging to
3384 the charset @code{japanese-jisx0208}.
3387 (set-fontset-font t 'japanese-jisx0208
3388 (font-spec :family "Kochi Gothic"))
3392 @defun char-displayable-p char
3393 This function returns @code{t} if Emacs ought to be able to display
3394 @var{char}. More precisely, if the selected frame's fontset has a
3395 font to display the character set that @var{char} belongs to.
3397 Fontsets can specify a font on a per-character basis; when the fontset
3398 does that, this function's value may not be accurate.
3401 @node Low-Level Font
3402 @subsection Low-Level Font Representation
3403 @cindex font property
3405 Normally, it is not necessary to manipulate fonts directly. In case
3406 you need to do so, this section explains how.
3408 In Emacs Lisp, fonts are represented using three different Lisp
3409 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3412 @defun fontp object &optional type
3413 Return @code{t} if @var{object} is a font object, font spec, or font
3414 entity. Otherwise, return @code{nil}.
3416 The optional argument @var{type}, if non-@code{nil}, determines the
3417 exact type of Lisp object to check for. In that case, @var{type}
3418 should be one of @code{font-object}, @code{font-spec}, or
3423 A font object is a Lisp object that represents a font that Emacs has
3424 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3427 @defun font-at position &optional window string
3428 Return the font object that is being used to display the character at
3429 position @var{position} in the window @var{window}. If @var{window}
3430 is @code{nil}, it defaults to the selected window. If @var{string} is
3431 @code{nil}, @var{position} specifies a position in the current buffer;
3432 otherwise, @var{string} should be a string, and @var{position}
3433 specifies a position in that string.
3437 A font spec is a Lisp object that contains a set of specifications
3438 that can be used to find a font. More than one font may match the
3439 specifications in a font spec.
3441 @defun font-spec &rest arguments
3442 Return a new font spec using the specifications in @var{arguments},
3443 which should come in @code{property}-@code{value} pairs. The possible
3444 specifications are as follows:
3448 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3449 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3456 These have the same meanings as the face attributes of the same name.
3457 @xref{Face Attributes}.
3460 The font size---either a non-negative integer that specifies the pixel
3461 size, or a floating-point number that specifies the point size.
3464 Additional typographic style information for the font, such as
3465 @samp{sans}. The value should be a string or a symbol.
3467 @cindex font registry
3469 The charset registry and encoding of the font, such as
3470 @samp{iso8859-1}. The value should be a string or a symbol.
3473 The script that the font must support (a symbol).
3476 The language that the font should support. The value should be a
3477 symbol whose name is a two-letter ISO-639 language name. On X, the
3478 value is matched against the ``Additional Style'' field of the XLFD
3479 name of a font, if it is non-empty. On MS-Windows, fonts matching the
3480 spec are required to support codepages needed for the language.
3481 Currently, only a small set of CJK languages is supported with this
3482 property: @samp{ja}, @samp{ko}, and @samp{zh}.
3485 @cindex OpenType font
3486 The font must be an OpenType font that supports these OpenType
3487 features, provided Emacs is compiled with a library, such as
3488 @samp{libotf} on GNU/Linux, that supports complex text layout for
3489 scripts which need that. The value must be a list of the form
3492 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3495 where @var{script-tag} is the OpenType script tag symbol;
3496 @var{langsys-tag} is the OpenType language system tag symbol, or
3497 @code{nil} to use the default language system; @code{gsub} is a list
3498 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3499 required; and @code{gpos} is a list of OpenType GPOS feature tag
3500 symbols, or @code{nil} if none is required. If @code{gsub} or
3501 @code{gpos} is a list, a @code{nil} element in that list means that
3502 the font must not match any of the remaining tag symbols. The
3503 @code{gpos} element may be omitted.
3507 @defun font-put font-spec property value
3508 Set the font property @var{property} in the font-spec @var{font-spec}
3513 A font entity is a reference to a font that need not be open. Its
3514 properties are intermediate between a font object and a font spec:
3515 like a font object, and unlike a font spec, it refers to a single,
3516 specific font. Unlike a font object, creating a font entity does not
3517 load the contents of that font into computer memory. Emacs may open
3518 multiple font objects of different sizes from a single font entity
3519 referring to a scalable font.
3521 @defun find-font font-spec &optional frame
3522 This function returns a font entity that best matches the font spec
3523 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3524 it defaults to the selected frame.
3527 @defun list-fonts font-spec &optional frame num prefer
3528 This function returns a list of all font entities that match the font
3529 spec @var{font-spec}.
3531 The optional argument @var{frame}, if non-@code{nil}, specifies the
3532 frame on which the fonts are to be displayed. The optional argument
3533 @var{num}, if non-@code{nil}, should be an integer that specifies the
3534 maximum length of the returned list. The optional argument
3535 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3536 used to control the order of the returned list; the returned font
3537 entities are sorted in order of decreasing closeness to that font
3541 If you call @code{set-face-attribute} and pass a font spec, font
3542 entity, or font name string as the value of the @code{:font}
3543 attribute, Emacs opens the best matching font that is available
3544 for display. It then stores the corresponding font object as the
3545 actual value of the @code{:font} attribute for that face.
3547 The following functions can be used to obtain information about a
3548 font. For these functions, the @var{font} argument can be a font
3549 object, a font entity, or a font spec.
3551 @defun font-get font property
3552 This function returns the value of the font property @var{property}
3555 If @var{font} is a font spec and the font spec does not specify
3556 @var{property}, the return value is @code{nil}. If @var{font} is a
3557 font object or font entity, the value for the @var{:script} property
3558 may be a list of scripts supported by the font.
3561 @defun font-face-attributes font &optional frame
3562 This function returns a list of face attributes corresponding to
3563 @var{font}. The optional argument @var{frame} specifies the frame on
3564 which the font is to be displayed. If it is @code{nil}, the selected
3565 frame is used. The return value has the form
3568 (:family @var{family} :height @var{height} :weight @var{weight}
3569 :slant @var{slant} :width @var{width})
3572 where the values of @var{family}, @var{height}, @var{weight},
3573 @var{slant}, and @var{width} are face attribute values. Some of these
3574 key-attribute pairs may be omitted from the list if they are not
3575 specified by @var{font}.
3578 @defun font-xlfd-name font &optional fold-wildcards
3579 This function returns the XLFD (X Logical Font Descriptor), a string,
3580 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3581 information about XLFDs. If the name is too long for an XLFD (which
3582 can contain at most 255 characters), the function returns @code{nil}.
3584 If the optional argument @var{fold-wildcards} is non-@code{nil},
3585 consecutive wildcards in the XLFD are folded into one.
3588 The following two functions return important information about a font.
3590 @defun font-info name &optional frame
3591 This function returns information about a font specified by its
3592 @var{name}, a string, as it is used on @var{frame}. If @var{frame} is
3593 omitted or @code{nil}, it defaults to the selected frame.
3595 The value returned by the function is a vector of the form
3596 @code{[@var{opened-name} @var{full-name} @var{size} @var{height}
3597 @var{baseline-offset} @var{relative-compose} @var{default-ascent}
3598 @var{max-width} @var{ascent} @var{descent} @var{space-width}
3599 @var{average-width} @var{filename} @var{capability}]}. Here's the
3600 description of each components of this vector:
3604 The name used to open the font, a string.
3607 The full name of the font, a string.
3610 The pixel size of the font.
3613 The height of the font in pixels.
3615 @item baseline-offset
3616 The offset in pixels from the @acronym{ASCII} baseline, positive
3619 @item relative-compose
3620 @itemx default-ascent
3621 Numbers controlling how to compose characters.
3625 The ascent and descent of this font. The sum of these two numbers
3626 should be equal to the value of @var{height} above.
3629 The width, in pixels, of the font's space character.
3632 The average width of the font characters. If this is zero, Emacs uses
3633 the value of @var{space-width} instead, when it calculates text layout
3637 The file name of the font as a string. This can be @code{nil} if the
3638 font back-end does not provide a way to find out the font's file name.
3641 A list whose first element is a symbol representing the font type, one
3642 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3643 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3644 additional elements describing the @sc{gsub} and @sc{gpos} features
3645 supported by the font. Each of these elements is a list of the form
3646 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3647 @dots{})}, where @var{script} is a symbol representing an OpenType
3648 script tag, @var{langsys} is a symbol representing an OpenType langsys
3649 tag (or @code{nil}, which stands for the default langsys), and each
3650 @var{feature} is a symbol representing an OpenType feature tag.
3654 @defun query-font font-object
3655 This function returns information about a @var{font-object}. (This is
3656 in contrast to @code{font-info}, which takes the font name, a string,
3659 The value returned by the function is a vector of the form
3660 @code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
3661 @var{ascent} @var{descent} @var{space-width} @var{average-width}
3662 @var{capability}]}. Here's the description of each components of this
3667 The font name, a string.
3670 The file name of the font as a string. This can be @code{nil} if the
3671 font back-end does not provide a way to find out the font's file name.
3674 The pixel size of the font used to open the font.
3677 The maximum advance width of the font.
3681 The ascent and descent of this font. The sum of these two numbers
3682 gives the font height.
3685 The width, in pixels, of the font's space character.
3688 The average width of the font characters. If this is zero, Emacs uses
3689 the value of @var{space-width} instead, when it calculates text layout
3693 A list whose first element is a symbol representing the font type, one
3694 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3695 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3696 additional elements describing the @sc{gsub} and @sc{gpos} features
3697 supported by the font. Each of these elements is a list of the form
3698 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3699 @dots{})}, where @var{script} is a symbol representing an OpenType
3700 script tag, @var{langsys} is a symbol representing an OpenType langsys
3701 tag (or @code{nil}, which stands for the default langsys), and each
3702 @var{feature} is a symbol representing an OpenType feature tag.
3706 @cindex font information for layout
3707 The following four functions return size information about fonts used
3708 by various faces, allowing various layout considerations in Lisp
3709 programs. These functions take face remapping into consideration,
3710 returning information about the remapped face, if the face in question
3711 was remapped. @xref{Face Remapping}.
3713 @defun default-font-width
3714 This function returns the average width in pixels of the font used by
3715 the current buffer's default face.
3718 @defun default-font-height
3719 This function returns the height in pixels of the font used by the
3720 current buffer's default face.
3723 @defun window-font-width &optional window face
3724 This function returns the average width in pixels for the font used by
3725 @var{face} in @var{window}. The specified @var{window} must be a live
3726 window. If @code{nil} or omitted, @var{window} defaults to the
3727 selected window, and @var{face} defaults to the default face in
3731 @defun window-font-height &optional window face
3732 This function returns the height in pixels for the font used by
3733 @var{face} in @var{window}. The specified @var{window} must be a live
3734 window. If @code{nil} or omitted, @var{window} defaults to the
3735 selected window, and @var{face} defaults to the default face in
3743 On graphical displays, Emacs draws @dfn{fringes} next to each
3744 window: thin vertical strips down the sides which can display bitmaps
3745 indicating truncation, continuation, horizontal scrolling, and so on.
3748 * Fringe Size/Pos:: Specifying where to put the window fringes.
3749 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3750 * Fringe Cursors:: Displaying cursors in the right fringe.
3751 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3752 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3753 * Overlay Arrow:: Display of an arrow to indicate position.
3756 @node Fringe Size/Pos
3757 @subsection Fringe Size and Position
3759 The following buffer-local variables control the position and width
3760 of fringes in windows showing that buffer.
3762 @defvar fringes-outside-margins
3763 The fringes normally appear between the display margins and the window
3764 text. If the value is non-@code{nil}, they appear outside the display
3765 margins. @xref{Display Margins}.
3768 @defvar left-fringe-width
3769 This variable, if non-@code{nil}, specifies the width of the left
3770 fringe in pixels. A value of @code{nil} means to use the left fringe
3771 width from the window's frame.
3774 @defvar right-fringe-width
3775 This variable, if non-@code{nil}, specifies the width of the right
3776 fringe in pixels. A value of @code{nil} means to use the right fringe
3777 width from the window's frame.
3780 Any buffer which does not specify values for these variables uses
3781 the values specified by the @code{left-fringe} and @code{right-fringe}
3782 frame parameters (@pxref{Layout Parameters}).
3784 The above variables actually take effect via the function
3785 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3786 @code{set-window-fringes} as a subroutine. If you change one of these
3787 variables, the fringe display is not updated in existing windows
3788 showing the buffer, unless you call @code{set-window-buffer} again in
3789 each affected window. You can also use @code{set-window-fringes} to
3790 control the fringe display in individual windows.
3792 @defun set-window-fringes window left &optional right outside-margins
3793 This function sets the fringe widths of window @var{window}.
3794 If @var{window} is @code{nil}, the selected window is used.
3796 The argument @var{left} specifies the width in pixels of the left
3797 fringe, and likewise @var{right} for the right fringe. A value of
3798 @code{nil} for either one stands for the default width. If
3799 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3800 should appear outside of the display margins.
3803 @defun window-fringes &optional window
3804 This function returns information about the fringes of a window
3805 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3806 window is used. The value has the form @code{(@var{left-width}
3807 @var{right-width} @var{outside-margins})}.
3811 @node Fringe Indicators
3812 @subsection Fringe Indicators
3813 @cindex fringe indicators
3814 @cindex indicators, fringe
3816 @dfn{Fringe indicators} are tiny icons displayed in the window
3817 fringe to indicate truncated or continued lines, buffer boundaries,
3820 @defopt indicate-empty-lines
3821 @cindex fringes, and empty line indication
3822 @cindex empty lines, indicating
3823 When this is non-@code{nil}, Emacs displays a special glyph in the
3824 fringe of each empty line at the end of the buffer, on graphical
3825 displays. @xref{Fringes}. This variable is automatically
3826 buffer-local in every buffer.
3829 @defopt indicate-buffer-boundaries
3830 @cindex buffer boundaries, indicating
3831 This buffer-local variable controls how the buffer boundaries and
3832 window scrolling are indicated in the window fringes.
3834 Emacs can indicate the buffer boundaries---that is, the first and last
3835 line in the buffer---with angle icons when they appear on the screen.
3836 In addition, Emacs can display an up-arrow in the fringe to show
3837 that there is text above the screen, and a down-arrow to show
3838 there is text below the screen.
3840 There are three kinds of basic values:
3844 Don't display any of these fringe icons.
3846 Display the angle icons and arrows in the left fringe.
3848 Display the angle icons and arrows in the right fringe.
3850 Display the angle icons in the left fringe
3851 and don't display the arrows.
3854 Otherwise the value should be an alist that specifies which fringe
3855 indicators to display and where. Each element of the alist should
3856 have the form @code{(@var{indicator} . @var{position})}. Here,
3857 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3858 @code{down}, and @code{t} (which covers all the icons not yet
3859 specified), while @var{position} is one of @code{left}, @code{right}
3862 For example, @code{((top . left) (t . right))} places the top angle
3863 bitmap in left fringe, and the bottom angle bitmap as well as both
3864 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3865 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3868 @defvar fringe-indicator-alist
3869 This buffer-local variable specifies the mapping from logical fringe
3870 indicators to the actual bitmaps displayed in the window fringes. The
3871 value is an alist of elements @code{(@var{indicator}
3872 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3873 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3876 Each @var{indicator} should be one of the following symbols:
3879 @item @code{truncation}, @code{continuation}.
3880 Used for truncation and continuation lines.
3882 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3883 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3884 @code{up} and @code{down} indicate a buffer boundary lying above or
3885 below the window edge; @code{top} and @code{bottom} indicate the
3886 topmost and bottommost buffer text line; and @code{top-bottom}
3887 indicates where there is just one line of text in the buffer.
3889 @item @code{empty-line}
3890 Used to indicate empty lines when @code{indicate-empty-lines} is
3893 @item @code{overlay-arrow}
3894 Used for overlay arrows (@pxref{Overlay Arrow}).
3895 @c Is this used anywhere?
3896 @c @item Unknown bitmap indicator:
3900 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3901 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3902 @var{right} symbols specify the bitmaps shown in the left and/or right
3903 fringe, for the specific indicator. @var{left1} and @var{right1} are
3904 specific to the @code{bottom} and @code{top-bottom} indicators, and
3905 are used to indicate that the last text line has no final newline.
3906 Alternatively, @var{bitmaps} may be a single symbol which is used in
3907 both left and right fringes.
3909 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3910 to define your own. In addition, @code{nil} represents the empty
3911 bitmap (i.e., an indicator that is not shown).
3913 When @code{fringe-indicator-alist} has a buffer-local value, and
3914 there is no bitmap defined for a logical indicator, or the bitmap is
3915 @code{t}, the corresponding value from the default value of
3916 @code{fringe-indicator-alist} is used.
3919 @node Fringe Cursors
3920 @subsection Fringe Cursors
3921 @cindex fringe cursors
3922 @cindex cursor, fringe
3924 When a line is exactly as wide as the window, Emacs displays the
3925 cursor in the right fringe instead of using two lines. Different
3926 bitmaps are used to represent the cursor in the fringe depending on
3927 the current buffer's cursor type.
3929 @defopt overflow-newline-into-fringe
3930 If this is non-@code{nil}, lines exactly as wide as the window (not
3931 counting the final newline character) are not continued. Instead,
3932 when point is at the end of the line, the cursor appears in the right
3936 @defvar fringe-cursor-alist
3937 This variable specifies the mapping from logical cursor type to the
3938 actual fringe bitmaps displayed in the right fringe. The value is an
3939 alist where each element has the form @code{(@var{cursor-type}
3940 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3941 display cursors of type @var{cursor-type}.
3943 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3944 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3945 the same meanings as in the @code{cursor-type} frame parameter
3946 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3947 instead of @code{hollow} when the normal @code{hollow-rectangle}
3948 bitmap is too tall to fit on a specific display line.
3950 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3951 be displayed for that logical cursor type.
3953 See the next subsection for details.
3956 @xref{Fringe Bitmaps}.
3959 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3960 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3961 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3962 no bitmap defined for a cursor type, the corresponding value from the
3963 default value of @code{fringes-indicator-alist} is used.
3966 @node Fringe Bitmaps
3967 @subsection Fringe Bitmaps
3968 @cindex fringe bitmaps
3969 @cindex bitmaps, fringe
3971 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3972 logical fringe indicators for truncated or continued lines, buffer
3973 boundaries, overlay arrows, etc. Each bitmap is represented by a
3976 These symbols are referred to by the variables
3977 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3978 described in the previous subsections.
3981 These symbols are referred to by the variable
3982 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3983 (@pxref{Fringe Indicators}), and the variable
3984 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3985 (@pxref{Fringe Cursors}).
3988 Lisp programs can also directly display a bitmap in the left or
3989 right fringe, by using a @code{display} property for one of the
3990 characters appearing in the line (@pxref{Other Display Specs}). Such
3991 a display specification has the form
3994 (@var{fringe} @var{bitmap} [@var{face}])
3998 @var{fringe} is either the symbol @code{left-fringe} or
3999 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
4000 to display. The optional @var{face} names a face whose foreground
4001 color is used to display the bitmap; this face is automatically merged
4002 with the @code{fringe} face.
4004 Here is a list of the standard fringe bitmaps defined in Emacs, and
4005 how they are currently used in Emacs (via
4006 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
4009 @item @code{left-arrow}, @code{right-arrow}
4010 Used to indicate truncated lines.
4012 @item @code{left-curly-arrow}, @code{right-curly-arrow}
4013 Used to indicate continued lines.
4015 @item @code{right-triangle}, @code{left-triangle}
4016 The former is used by overlay arrows. The latter is unused.
4018 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
4019 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
4020 @itemx @code{top-right-angle}, @code{top-left-angle}
4021 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
4022 Used to indicate buffer boundaries.
4024 @item @code{filled-rectangle}, @code{hollow-rectangle}
4025 @itemx @code{filled-square}, @code{hollow-square}
4026 @itemx @code{vertical-bar}, @code{horizontal-bar}
4027 Used for different types of fringe cursors.
4029 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
4030 Not used by core Emacs features.
4034 The next subsection describes how to define your own fringe bitmaps.
4036 @defun fringe-bitmaps-at-pos &optional pos window
4037 This function returns the fringe bitmaps of the display line
4038 containing position @var{pos} in window @var{window}. The return
4039 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
4040 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
4041 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
4042 is non-@code{nil} if there is an overlay arrow in the left fringe.
4044 The value is @code{nil} if @var{pos} is not visible in @var{window}.
4045 If @var{window} is @code{nil}, that stands for the selected window.
4046 If @var{pos} is @code{nil}, that stands for the value of point in
4050 @node Customizing Bitmaps
4051 @subsection Customizing Fringe Bitmaps
4052 @cindex fringe bitmaps, customizing
4054 @defun define-fringe-bitmap bitmap bits &optional height width align
4055 This function defines the symbol @var{bitmap} as a new fringe bitmap,
4056 or replaces an existing bitmap with that name.
4058 The argument @var{bits} specifies the image to use. It should be
4059 either a string or a vector of integers, where each element (an
4060 integer) corresponds to one row of the bitmap. Each bit of an integer
4061 corresponds to one pixel of the bitmap, where the low bit corresponds
4062 to the rightmost pixel of the bitmap.
4064 The height is normally the length of @var{bits}. However, you
4065 can specify a different height with non-@code{nil} @var{height}. The width
4066 is normally 8, but you can specify a different width with non-@code{nil}
4067 @var{width}. The width must be an integer between 1 and 16.
4069 The argument @var{align} specifies the positioning of the bitmap
4070 relative to the range of rows where it is used; the default is to
4071 center the bitmap. The allowed values are @code{top}, @code{center},
4074 The @var{align} argument may also be a list @code{(@var{align}
4075 @var{periodic})} where @var{align} is interpreted as described above.
4076 If @var{periodic} is non-@code{nil}, it specifies that the rows in
4077 @code{bits} should be repeated enough times to reach the specified
4081 @defun destroy-fringe-bitmap bitmap
4082 This function destroy the fringe bitmap identified by @var{bitmap}.
4083 If @var{bitmap} identifies a standard fringe bitmap, it actually
4084 restores the standard definition of that bitmap, instead of
4085 eliminating it entirely.
4088 @defun set-fringe-bitmap-face bitmap &optional face
4089 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
4090 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
4091 bitmap's face controls the color to draw it in.
4093 @var{face} is merged with the @code{fringe} face, so normally
4094 @var{face} should specify only the foreground color.
4098 @subsection The Overlay Arrow
4099 @c @cindex overlay arrow Duplicates variable names
4101 The @dfn{overlay arrow} is useful for directing the user's attention
4102 to a particular line in a buffer. For example, in the modes used for
4103 interface to debuggers, the overlay arrow indicates the line of code
4104 about to be executed. This feature has nothing to do with
4105 @dfn{overlays} (@pxref{Overlays}).
4107 @defvar overlay-arrow-string
4108 This variable holds the string to display to call attention to a
4109 particular line, or @code{nil} if the arrow feature is not in use.
4110 On a graphical display the contents of the string are ignored; instead a
4111 glyph is displayed in the fringe area to the left of the display area.
4114 @defvar overlay-arrow-position
4115 This variable holds a marker that indicates where to display the overlay
4116 arrow. It should point at the beginning of a line. On a non-graphical
4117 display the arrow text
4118 appears at the beginning of that line, overlaying any text that would
4119 otherwise appear. Since the arrow is usually short, and the line
4120 usually begins with indentation, normally nothing significant is
4123 The overlay-arrow string is displayed in any given buffer if the value
4124 of @code{overlay-arrow-position} in that buffer points into that
4125 buffer. Thus, it is possible to display multiple overlay arrow strings
4126 by creating buffer-local bindings of @code{overlay-arrow-position}.
4127 However, it is usually cleaner to use
4128 @code{overlay-arrow-variable-list} to achieve this result.
4129 @c !!! overlay-arrow-position: but the overlay string may remain in the display
4130 @c of some other buffer until an update is required. This should be fixed
4134 You can do a similar job by creating an overlay with a
4135 @code{before-string} property. @xref{Overlay Properties}.
4137 You can define multiple overlay arrows via the variable
4138 @code{overlay-arrow-variable-list}.
4140 @defvar overlay-arrow-variable-list
4141 This variable's value is a list of variables, each of which specifies
4142 the position of an overlay arrow. The variable
4143 @code{overlay-arrow-position} has its normal meaning because it is on
4147 Each variable on this list can have properties
4148 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
4149 specify an overlay arrow string (for text terminals) or fringe bitmap
4150 (for graphical terminals) to display at the corresponding overlay
4151 arrow position. If either property is not set, the default
4152 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
4157 @section Scroll Bars
4160 Normally the frame parameter @code{vertical-scroll-bars} controls
4161 whether the windows in the frame have vertical scroll bars, and whether
4162 they are on the left or right. The frame parameter
4163 @code{scroll-bar-width} specifies how wide they are (@code{nil} meaning
4166 The frame parameter @code{horizontal-scroll-bars} controls whether
4167 the windows in the frame have horizontal scroll bars. The frame
4168 parameter @code{scroll-bar-height} specifies how high they are
4169 (@code{nil} meaning the default). @xref{Layout Parameters}.
4171 @vindex horizontal-scroll-bars-available-p
4172 Horizontal scroll bars are not available on all platforms. The
4173 function @code{horizontal-scroll-bars-available-p} which takes no
4174 argument returns non-@code{nil} if they are available on your system.
4176 The following three functions take as argument a live frame which
4177 defaults to the selected one.
4179 @defun frame-current-scroll-bars &optional frame
4180 This function reports the scroll bar types for frame @var{frame}. The
4181 value is a cons cell @code{(@var{vertical-type} .@:
4182 @var{horizontal-type})}, where @var{vertical-type} is either
4183 @code{left}, @code{right}, or @code{nil} (which means no vertical scroll
4184 bar.) @var{horizontal-type} is either @code{bottom} or @code{nil}
4185 (which means no horizontal scroll bar).
4188 @defun frame-scroll-bar-width &optional frame
4189 This function returns the width of vertical scroll bars of @var{frame}
4193 @defun frame-scroll-bar-height &optional frame
4194 This function returns the height of horizontal scroll bars of
4195 @var{frame} in pixels.
4198 You can override the frame specific settings for individual windows by
4199 using the following function:
4201 @defun set-window-scroll-bars window &optional width vertical-type height horizontal-type
4202 This function sets the width and/or height and the types of scroll bars
4203 for window @var{window}.
4205 @var{width} specifies the width of the vertical scroll bar in pixels
4206 (@code{nil} means use the width specified for the frame).
4207 @var{vertical-type} specifies whether to have a vertical scroll bar and,
4208 if so, where. The possible values are @code{left}, @code{right},
4209 @code{t}, which means to use the frame's default, and @code{nil} for no
4210 vertical scroll bar.
4212 @var{height} specifies the height of the horizontal scroll bar in pixels
4213 (@code{nil} means use the height specified for the frame).
4214 @var{horizontal-type} specifies whether to have a horizontal scroll bar.
4215 The possible values are @code{bottom}, @code{t}, which means to use the
4216 frame's default, and @code{nil} for no horizontal scroll bar.
4218 If @var{window} is @code{nil}, the selected window is used.
4221 The following four functions take as argument a live window which
4222 defaults to the selected one.
4224 @defun window-scroll-bars &optional window
4225 This function returns a list of the form @code{(@var{width}
4226 @var{columns} @var{vertical-type} @var{height} @var{lines}
4227 @var{horizontal-type})}.
4229 The value @var{width} is the value that was specified for the width of
4230 the vertical scroll bar (which may be @code{nil}); @var{columns} is the
4231 (possibly rounded) number of columns that the vertical scroll bar
4234 The value @var{height} is the value that was specified for the height of
4235 the horizontal scroll bar (which may be @code{nil}); @var{lines} is the
4236 (possibly rounded) number of lines that the horizontally scroll bar
4240 @defun window-current-scroll-bars &optional window
4241 This function reports the scroll bar type for window @var{window}. The
4242 value is a cons cell @code{(@var{vertical-type} .@:
4243 @var{horizontal-type})}. Unlike @code{window-scroll-bars}, this reports
4244 the scroll bar type actually used, once frame defaults and
4245 @code{scroll-bar-mode} are taken into account.
4248 @defun window-scroll-bar-width &optional window
4249 This function returns the width in pixels of @var{window}'s vertical
4253 @defun window-scroll-bar-height &optional window
4254 This function returns the height in pixels of @var{window}'s horizontal
4258 If you don't specify these values for a window with
4259 @code{set-window-scroll-bars}, the buffer-local variables
4260 @code{vertical-scroll-bar}, @code{horizontal-scroll-bar},
4261 @code{scroll-bar-width} and @code{scroll-bar-height} in the buffer being
4262 displayed control the window's scroll bars. The function
4263 @code{set-window-buffer} examines these variables. If you change them
4264 in a buffer that is already visible in a window, you can make the window
4265 take note of the new values by calling @code{set-window-buffer}
4266 specifying the same buffer that is already displayed.
4268 You can control the appearance of scroll bars for a particular buffer by
4269 setting the following variables which automatically become buffer-local
4272 @defvar vertical-scroll-bar
4273 This variable specifies the location of the vertical scroll bar. The
4274 possible values are @code{left}, @code{right}, @code{t}, which means to
4275 use the frame's default, and @code{nil} for no scroll bar.
4278 @defvar horizontal-scroll-bar
4279 This variable specifies the location of the horizontal scroll bar. The
4280 possible values are @code{bottom}, @code{t}, which means to use the
4281 frame's default, and @code{nil} for no scroll bar.
4284 @defvar scroll-bar-width
4285 This variable specifies the width of the buffer's vertical scroll bars,
4286 measured in pixels. A value of @code{nil} means to use the value
4287 specified by the frame.
4290 @defvar scroll-bar-height
4291 This variable specifies the height of the buffer's horizontal scroll
4292 bar, measured in pixels. A value of @code{nil} means to use the value
4293 specified by the frame.
4296 Finally you can toggle the display of scroll bars on all frames by
4297 customizing the variables @code{scroll-bar-mode} and
4298 @code{horizontal-scroll-bar-mode}.
4300 @defopt scroll-bar-mode
4301 This variable controls whether and where to put vertical scroll bars in
4302 all frames. The possible values are @code{nil} for no scroll bars,
4303 @code{left} to put scroll bars on the left and @code{right} to put
4304 scroll bars on the right.
4307 @defopt horizontal-scroll-bar-mode
4308 This variable controls whether to display horizontal scroll bars on all
4313 @node Window Dividers
4314 @section Window Dividers
4315 @cindex window dividers
4316 @cindex right dividers
4317 @cindex bottom dividers
4319 Window dividers are bars drawn between a frame's windows. A right
4320 divider is drawn between a window and any adjacent windows on the right.
4321 Its width (thickness) is specified by the frame parameter
4322 @code{right-divider-width}. A bottom divider is drawn between a
4323 window and adjacent windows on the bottom or the echo area. Its width
4324 is specified by the frame parameter @code{bottom-divider-width}. In
4325 either case, specifying a width of zero means to not draw such dividers.
4326 @xref{Layout Parameters}.
4328 Technically, a right divider belongs to the window on its left,
4329 which means that its width contributes to the total width of that
4330 window. A bottom divider belongs to the window above it, which
4331 means that its width contributes to the total height of that window.
4332 @xref{Window Sizes}. When a window has both, a right and a bottom
4333 divider, the bottom divider prevails. This means that a bottom
4334 divider is drawn over the full total width of its window while the right
4335 divider ends above the bottom divider.
4337 Dividers can be dragged with the mouse and are therefore useful for
4338 adjusting the sizes of adjacent windows with the mouse. They also serve
4339 to visually set apart adjacent windows when no scroll bars or mode lines
4340 are present. The following three faces allow the customization of the
4341 appearance of dividers:
4344 @item window-divider
4345 When a divider is less than three pixels wide, it is drawn solidly with
4346 the foreground of this face. For larger dividers this face is used for
4347 the inner part only, excluding the first and last pixel.
4349 @item window-divider-first-pixel
4350 This is the face used for drawing the first pixel of a divider that is
4351 at least three pixels wide. To obtain a solid appearance, set this to
4352 the same value used for the @code{window-divider} face.
4354 @item window-divider-last-pixel
4355 This is the face used for drawing the last pixel of a divider that is at
4356 least three pixels wide. To obtain a solid appearance, set this to the
4357 same value used for the @code{window-divider} face.
4360 You can get the sizes of the dividers of a specific window with the
4361 following two functions.
4363 @defun window-right-divider-width &optional window
4364 Return the width (thickness) in pixels of @var{window}'s right divider.
4365 @var{window} must be a live window and defaults to the selected one.
4366 The return value is always zero for a rightmost window.
4369 @defun window-bottom-divider-width &optional window
4370 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4371 @var{window} must be a live window and defaults to the selected one.
4372 The return value is zero for the minibuffer window or a bottommost
4373 window on a minibuffer-less frame.
4377 @node Display Property
4378 @section The @code{display} Property
4379 @cindex display specification
4380 @kindex display @r{(text property)}
4382 The @code{display} text property (or overlay property) is used to
4383 insert images into text, and to control other aspects of how text
4384 displays. The value of the @code{display} property should be a
4385 display specification, or a list or vector containing several display
4386 specifications. Display specifications in the same @code{display}
4387 property value generally apply in parallel to the text they cover.
4389 If several sources (overlays and/or a text property) specify values
4390 for the @code{display} property, only one of the values takes effect,
4391 following the rules of @code{get-char-property}. @xref{Examining
4394 The rest of this section describes several kinds of
4395 display specifications and what they mean.
4398 * Replacing Specs:: Display specs that replace the text.
4399 * Specified Space:: Displaying one space with a specified width.
4400 * Pixel Specification:: Specifying space width or height in pixels.
4401 * Other Display Specs:: Displaying an image; adjusting the height,
4402 spacing, and other properties of text.
4403 * Display Margins:: Displaying text or images to the side of the main text.
4406 @node Replacing Specs
4407 @subsection Display Specs That Replace The Text
4408 @cindex replacing display specs
4410 Some kinds of display specifications specify something to display
4411 instead of the text that has the property. These are called
4412 @dfn{replacing} display specifications. Emacs does not allow the user
4413 to interactively move point into the middle of buffer text that is
4414 replaced in this way.
4416 If a list of display specifications includes more than one replacing
4417 display specification, the first overrides the rest. Replacing
4418 display specifications make most other display specifications
4419 irrelevant, since those don't apply to the replacement.
4421 For replacing display specifications, @dfn{the text that has the
4422 property} means all the consecutive characters that have the same
4423 Lisp object as their @code{display} property; these characters are
4424 replaced as a single unit. If two characters have different Lisp
4425 objects as their @code{display} properties (i.e., objects which are
4426 not @code{eq}), they are handled separately.
4428 Here is an example which illustrates this point. A string serves as
4429 a replacing display specification, which replaces the text that has
4430 the property with the specified string (@pxref{Other Display Specs}).
4431 Consider the following function:
4436 (let ((string (concat "A"))
4437 (start (+ i i (point-min))))
4438 (put-text-property start (1+ start) 'display string)
4439 (put-text-property start (+ 2 start) 'display string))))
4443 This function gives each of the first ten characters in the buffer a
4444 @code{display} property which is a string @code{"A"}, but they don't
4445 all get the same string object. The first two characters get the same
4446 string object, so they are replaced with one @samp{A}; the fact that
4447 the display property was assigned in two separate calls to
4448 @code{put-text-property} is irrelevant. Similarly, the next two
4449 characters get a second string (@code{concat} creates a new string
4450 object), so they are replaced with one @samp{A}; and so on. Thus, the
4451 ten characters appear as five A's.
4453 @node Specified Space
4454 @subsection Specified Spaces
4455 @cindex spaces, specified height or width
4456 @cindex variable-width spaces
4458 To display a space of specified width and/or height, use a display
4459 specification of the form @code{(space . @var{props})}, where
4460 @var{props} is a property list (a list of alternating properties and
4461 values). You can put this property on one or more consecutive
4462 characters; a space of the specified height and width is displayed in
4463 place of @emph{all} of those characters. These are the properties you
4464 can use in @var{props} to specify the weight of the space:
4467 @item :width @var{width}
4468 If @var{width} is a number, it specifies
4469 that the space width should be @var{width} times the normal character
4470 width. @var{width} can also be a @dfn{pixel width} specification
4471 (@pxref{Pixel Specification}).
4473 @item :relative-width @var{factor}
4474 Specifies that the width of the stretch should be computed from the
4475 first character in the group of consecutive characters that have the
4476 same @code{display} property. The space width is the pixel width of
4477 that character, multiplied by @var{factor}. (On text-mode terminals,
4478 the ``pixel width'' of a character is usually 1, but it could be more
4479 for TABs and double-width CJK characters.)
4481 @item :align-to @var{hpos}
4482 Specifies that the space should be wide enough to reach @var{hpos}.
4483 If @var{hpos} is a number, it is measured in units of the normal
4484 character width. @var{hpos} can also be a @dfn{pixel width}
4485 specification (@pxref{Pixel Specification}).
4488 You should use one and only one of the above properties. You can
4489 also specify the height of the space, with these properties:
4492 @item :height @var{height}
4493 Specifies the height of the space.
4494 If @var{height} is a number, it specifies
4495 that the space height should be @var{height} times the normal character
4496 height. The @var{height} may also be a @dfn{pixel height} specification
4497 (@pxref{Pixel Specification}).
4499 @item :relative-height @var{factor}
4500 Specifies the height of the space, multiplying the ordinary height
4501 of the text having this display specification by @var{factor}.
4503 @item :ascent @var{ascent}
4504 If the value of @var{ascent} is a non-negative number no greater than
4505 100, it specifies that @var{ascent} percent of the height of the space
4506 should be considered as the ascent of the space---that is, the part
4507 above the baseline. The ascent may also be specified in pixel units
4508 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4512 Don't use both @code{:height} and @code{:relative-height} together.
4514 The @code{:width} and @code{:align-to} properties are supported on
4515 non-graphic terminals, but the other space properties in this section
4518 Note that space properties are treated as paragraph separators for
4519 the purposes of reordering bidirectional text for display.
4520 @xref{Bidirectional Display}, for the details.
4522 @node Pixel Specification
4523 @subsection Pixel Specification for Spaces
4524 @cindex spaces, pixel specification
4526 The value of the @code{:width}, @code{:align-to}, @code{:height},
4527 and @code{:ascent} properties can be a special kind of expression that
4528 is evaluated during redisplay. The result of the evaluation is used
4529 as an absolute number of pixels.
4531 The following expressions are supported:
4535 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4536 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4537 @var{unit} ::= in | mm | cm | width | height
4540 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4542 @var{pos} ::= left | center | right
4543 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4548 The form @var{num} specifies a fraction of the default frame font
4549 height or width. The form @code{(@var{num})} specifies an absolute
4550 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4551 buffer-local variable binding is used.
4553 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4554 pixels per inch, millimeter, and centimeter, respectively. The
4555 @code{width} and @code{height} units correspond to the default width
4556 and height of the current face. An image specification @code{image}
4557 corresponds to the width or height of the image.
4559 The elements @code{left-fringe}, @code{right-fringe},
4560 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4561 @code{text} specify to the width of the corresponding area of the
4564 The @code{left}, @code{center}, and @code{right} positions can be
4565 used with @code{:align-to} to specify a position relative to the left
4566 edge, center, or right edge of the text area.
4568 Any of the above window elements (except @code{text}) can also be
4569 used with @code{:align-to} to specify that the position is relative to
4570 the left edge of the given area. Once the base offset for a relative
4571 position has been set (by the first occurrence of one of these
4572 symbols), further occurrences of these symbols are interpreted as the
4573 width of the specified area. For example, to align to the center of
4574 the left-margin, use
4577 :align-to (+ left-margin (0.5 . left-margin))
4580 If no specific base offset is set for alignment, it is always relative
4581 to the left edge of the text area. For example, @samp{:align-to 0} in a
4582 header-line aligns with the first text column in the text area.
4584 A value of the form @code{(@var{num} . @var{expr})} stands for the
4585 product of the values of @var{num} and @var{expr}. For example,
4586 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4587 @var{image})} specifies half the width (or height) of the specified
4590 The form @code{(+ @var{expr} ...)} adds up the value of the
4591 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4592 the value of the expressions.
4594 @node Other Display Specs
4595 @subsection Other Display Specifications
4597 Here are the other sorts of display specifications that you can use
4598 in the @code{display} text property.
4602 Display @var{string} instead of the text that has this property.
4604 Recursive display specifications are not supported---@var{string}'s
4605 @code{display} properties, if any, are not used.
4607 @item (image . @var{image-props})
4608 This kind of display specification is an image descriptor (@pxref{Images}).
4609 When used as a display specification, it means to display the image
4610 instead of the text that has the display specification.
4612 @item (slice @var{x} @var{y} @var{width} @var{height})
4613 This specification together with @code{image} specifies a @dfn{slice}
4614 (a partial area) of the image to display. The elements @var{y} and
4615 @var{x} specify the top left corner of the slice, within the image;
4616 @var{width} and @var{height} specify the width and height of the
4617 slice. Integers are numbers of pixels. A floating-point number
4618 in the range 0.0--1.0 stands for that fraction of the width or height
4619 of the entire image.
4621 @item ((margin nil) @var{string})
4622 A display specification of this form means to display @var{string}
4623 instead of the text that has the display specification, at the same
4624 position as that text. It is equivalent to using just @var{string},
4625 but it is done as a special case of marginal display (@pxref{Display
4628 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4629 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4630 This display specification on any character of a line of text causes
4631 the specified @var{bitmap} be displayed in the left or right fringes
4632 for that line, instead of the characters that have the display
4633 specification. The optional @var{face} specifies the colors to be
4634 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4636 @item (space-width @var{factor})
4637 This display specification affects all the space characters within the
4638 text that has the specification. It displays all of these spaces
4639 @var{factor} times as wide as normal. The element @var{factor} should
4640 be an integer or float. Characters other than spaces are not affected
4641 at all; in particular, this has no effect on tab characters.
4643 @item (height @var{height})
4644 This display specification makes the text taller or shorter.
4645 Here are the possibilities for @var{height}:
4648 @item @code{(+ @var{n})}
4649 @c FIXME: Add an index for "step"? --xfq
4650 This means to use a font that is @var{n} steps larger. A @dfn{step} is
4651 defined by the set of available fonts---specifically, those that match
4652 what was otherwise specified for this text, in all attributes except
4653 height. Each size for which a suitable font is available counts as
4654 another step. @var{n} should be an integer.
4656 @item @code{(- @var{n})}
4657 This means to use a font that is @var{n} steps smaller.
4659 @item a number, @var{factor}
4660 A number, @var{factor}, means to use a font that is @var{factor} times
4661 as tall as the default font.
4663 @item a symbol, @var{function}
4664 A symbol is a function to compute the height. It is called with the
4665 current height as argument, and should return the new height to use.
4667 @item anything else, @var{form}
4668 If the @var{height} value doesn't fit the previous possibilities, it is
4669 a form. Emacs evaluates it to get the new height, with the symbol
4670 @code{height} bound to the current specified font height.
4673 @item (raise @var{factor})
4674 This kind of display specification raises or lowers the text
4675 it applies to, relative to the baseline of the line. It is mainly
4676 meant to support display of subscripts and superscripts.
4678 The @var{factor} must be a number, which is interpreted as a multiple
4679 of the height of the affected text. If it is positive, that means to
4680 display the characters raised. If it is negative, that means to
4681 display them lower down.
4683 Note that if the text also has a @code{height} display specification,
4684 which was specified before (i.e.@: to the left of) @code{raise}, the
4685 latter will affect the amount of raising or lowering in pixels,
4686 because that is based on the height of the text being raised.
4687 Therefore, if you want to display a sub- or superscript that is
4688 smaller than the normal text height, consider specifying @code{raise}
4689 before @code{height}.
4692 @c We put all the '@code{(when ...)}' on one line to encourage
4693 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4694 @c was at eol; the info file ended up w/ two spaces rendered after it.
4695 You can make any display specification conditional. To do that,
4696 package it in another list of the form
4697 @code{(when @var{condition} . @var{spec})}.
4698 Then the specification @var{spec} applies only when
4699 @var{condition} evaluates to a non-@code{nil} value. During the
4700 evaluation, @code{object} is bound to the string or buffer having the
4701 conditional @code{display} property. @code{position} and
4702 @code{buffer-position} are bound to the position within @code{object}
4703 and the buffer position where the @code{display} property was found,
4704 respectively. Both positions can be different when @code{object} is a
4707 @node Display Margins
4708 @subsection Displaying in the Margins
4709 @cindex display margins
4710 @cindex margins, display
4712 A buffer can have blank areas called @dfn{display margins} on the
4713 left and on the right. Ordinary text never appears in these areas,
4714 but you can put things into the display margins using the
4715 @code{display} property. There is currently no way to make text or
4716 images in the margin mouse-sensitive.
4718 The way to display something in the margins is to specify it in a
4719 margin display specification in the @code{display} property of some
4720 text. This is a replacing display specification, meaning that the
4721 text you put it on does not get displayed; the margin display appears,
4722 but that text does not.
4724 A margin display specification looks like @code{((margin
4725 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4726 Here, @var{spec} is another display specification that says what to
4727 display in the margin. Typically it is a string of text to display,
4728 or an image descriptor.
4730 To display something in the margin @emph{in association with}
4731 certain buffer text, without altering or preventing the display of
4732 that text, put a @code{before-string} property on the text and put the
4733 margin display specification on the contents of the before-string.
4735 Before the display margins can display anything, you must give
4736 them a nonzero width. The usual way to do that is to set these
4739 @defvar left-margin-width
4740 This variable specifies the width of the left margin, in character
4741 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4742 A value of @code{nil} means no left marginal area.
4745 @defvar right-margin-width
4746 This variable specifies the width of the right margin, in character
4747 cell units. It is buffer-local in all buffers. A value of @code{nil}
4748 means no right marginal area.
4751 Setting these variables does not immediately affect the window. These
4752 variables are checked when a new buffer is displayed in the window.
4753 Thus, you can make changes take effect by calling
4754 @code{set-window-buffer}.
4756 You can also set the margin widths immediately.
4758 @defun set-window-margins window left &optional right
4759 This function specifies the margin widths for window @var{window}, in
4760 character cell units. The argument @var{left} controls the left
4761 margin, and @var{right} controls the right margin (default @code{0}).
4764 @defun window-margins &optional window
4765 This function returns the width of the left and right margins of
4766 @var{window} as a cons cell of the form @w{@code{(@var{left}
4767 . @var{right})}}. If one of the two marginal areas does not exist,
4768 its width is returned as @code{nil}; if neither of the two margins exist,
4769 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4770 selected window is used.
4775 @cindex images in buffers
4777 To display an image in an Emacs buffer, you must first create an image
4778 descriptor, then use it as a display specifier in the @code{display}
4779 property of text that is displayed (@pxref{Display Property}).
4781 Emacs is usually able to display images when it is run on a
4782 graphical terminal. Images cannot be displayed in a text terminal, on
4783 certain graphical terminals that lack the support for this, or if
4784 Emacs is compiled without image support. You can use the function
4785 @code{display-images-p} to determine if images can in principle be
4786 displayed (@pxref{Display Feature Testing}).
4789 * Image Formats:: Supported image formats.
4790 * Image Descriptors:: How to specify an image for use in @code{:display}.
4791 * XBM Images:: Special features for XBM format.
4792 * XPM Images:: Special features for XPM format.
4793 * ImageMagick Images:: Special features available through ImageMagick.
4794 * SVG Images:: Creating and manipulating SVG images.
4795 * Other Image Types:: Various other formats are supported.
4796 * Defining Images:: Convenient ways to define an image for later use.
4797 * Showing Images:: Convenient ways to display an image once it is defined.
4798 * Multi-Frame Images:: Some images contain more than one frame.
4799 * Image Cache:: Internal mechanisms of image display.
4803 @subsection Image Formats
4804 @cindex image formats
4807 Emacs can display a number of different image formats. Some of
4808 these image formats are supported only if particular support libraries
4809 are installed. On some platforms, Emacs can load support libraries on
4810 demand; if so, the variable @code{dynamic-library-alist} can be used
4811 to modify the set of known names for these dynamic libraries.
4812 @xref{Dynamic Libraries}.
4814 Supported image formats (and the required support libraries) include
4815 PBM and XBM (which do not depend on support libraries and are always
4816 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4817 @code{libungif}), JPEG (@code{libjpeg}), TIFF
4818 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4820 Each of these image formats is associated with an @dfn{image type
4821 symbol}. The symbols for the above formats are, respectively,
4822 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif},
4823 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4825 Furthermore, if you build Emacs with ImageMagick
4826 (@code{libMagickWand}) support, Emacs can display any image format
4827 that ImageMagick can. @xref{ImageMagick Images}. All images
4828 displayed via ImageMagick have type symbol @code{imagemagick}.
4831 This variable contains a list of type symbols for image formats which
4832 are potentially supported in the current configuration.
4834 ``Potentially'' means that Emacs knows about the image types, not
4835 necessarily that they can be used (for example, they could depend on
4836 unavailable dynamic libraries). To know which image types are really
4837 available, use @code{image-type-available-p}.
4840 @defun image-type-available-p type
4841 This function returns non-@code{nil} if images of type @var{type} can
4842 be loaded and displayed. @var{type} must be an image type symbol.
4844 For image types whose support libraries are statically linked, this
4845 function always returns @code{t}. For image types whose support
4846 libraries are dynamically loaded, it returns @code{t} if the library
4847 could be loaded and @code{nil} otherwise.
4850 @node Image Descriptors
4851 @subsection Image Descriptors
4852 @cindex image descriptor
4854 An @dfn{image descriptor} is a list which specifies the underlying
4855 data for an image, and how to display it. It is typically used as the
4856 value of a @code{display} overlay or text property (@pxref{Other
4857 Display Specs}); but @xref{Showing Images}, for convenient helper
4858 functions to insert images into buffers.
4860 Each image descriptor has the form @code{(image . @var{props})},
4861 where @var{props} is a property list of alternating keyword symbols
4862 and values, including at least the pair @code{:type @var{type}} that
4863 specifies the image type.
4865 The following is a list of properties that are meaningful for all
4866 image types (there are also properties which are meaningful only for
4867 certain image types, as documented in the following subsections):
4870 @item :type @var{type}
4873 @xref{Image Formats}.
4875 Every image descriptor must include this property.
4877 @item :file @var{file}
4878 This says to load the image from file @var{file}. If @var{file} is
4879 not an absolute file name, it is expanded in @code{data-directory}.
4881 @item :data @var{data}
4882 This specifies the raw image data. Each image descriptor must have
4883 either @code{:data} or @code{:file}, but not both.
4885 For most image types, the value of a @code{:data} property should be a
4886 string containing the image data. Some image types do not support
4887 @code{:data}; for some others, @code{:data} alone is not enough, so
4888 you need to use other image properties along with @code{:data}. See
4889 the following subsections for details.
4891 @item :margin @var{margin}
4892 This specifies how many pixels to add as an extra margin around the
4893 image. The value, @var{margin}, must be a non-negative number, or a
4894 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4895 @var{x} specifies how many pixels to add horizontally, and @var{y}
4896 specifies how many pixels to add vertically. If @code{:margin} is not
4897 specified, the default is zero.
4899 @item :ascent @var{ascent}
4900 This specifies the amount of the image's height to use for its
4901 ascent---that is, the part above the baseline. The value,
4902 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4905 If @var{ascent} is a number, that percentage of the image's height is
4906 used for its ascent.
4908 If @var{ascent} is @code{center}, the image is vertically centered
4909 around a centerline which would be the vertical centerline of text drawn
4910 at the position of the image, in the manner specified by the text
4911 properties and overlays that apply to the image.
4913 If this property is omitted, it defaults to 50.
4915 @item :relief @var{relief}
4916 This adds a shadow rectangle around the image. The value,
4917 @var{relief}, specifies the width of the shadow lines, in pixels. If
4918 @var{relief} is negative, shadows are drawn so that the image appears
4919 as a pressed button; otherwise, it appears as an unpressed button.
4921 @item :conversion @var{algorithm}
4922 This specifies a conversion algorithm that should be applied to the
4923 image before it is displayed; the value, @var{algorithm}, specifies
4929 Specifies the Laplace edge detection algorithm, which blurs out small
4930 differences in color while highlighting larger differences. People
4931 sometimes consider this useful for displaying the image for a
4934 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4935 @cindex edge detection, images
4936 Specifies a general edge-detection algorithm. @var{matrix} must be
4937 either a nine-element list or a nine-element vector of numbers. A pixel
4938 at position @math{x/y} in the transformed image is computed from
4939 original pixels around that position. @var{matrix} specifies, for each
4940 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4941 will influence the transformed pixel; element @math{0} specifies the
4942 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4943 the pixel at @math{x/y-1} etc., as shown below:
4946 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4947 x-1/y & x/y & x+1/y \cr
4948 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4953 (x-1/y-1 x/y-1 x+1/y-1
4955 x-1/y+1 x/y+1 x+1/y+1)
4959 The resulting pixel is computed from the color intensity of the color
4960 resulting from summing up the RGB values of surrounding pixels,
4961 multiplied by the specified factors, and dividing that sum by the sum
4962 of the factors' absolute values.
4964 Laplace edge-detection currently uses a matrix of
4967 $$\pmatrix{1 & 0 & 0 \cr
4980 Emboss edge-detection uses a matrix of
4983 $$\pmatrix{ 2 & -1 & 0 \cr
4997 Specifies transforming the image so that it looks disabled.
5000 @item :mask @var{mask}
5001 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
5002 a clipping mask for the image, so that the background of a frame is
5003 visible behind the image. If @var{bg} is not specified, or if @var{bg}
5004 is @code{t}, determine the background color of the image by looking at
5005 the four corners of the image, assuming the most frequently occurring
5006 color from the corners is the background color of the image. Otherwise,
5007 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
5008 specifying the color to assume for the background of the image.
5010 If @var{mask} is @code{nil}, remove a mask from the image, if it has
5011 one. Images in some formats include a mask which can be removed by
5012 specifying @code{:mask nil}.
5014 @item :pointer @var{shape}
5015 This specifies the pointer shape when the mouse pointer is over this
5016 image. @xref{Pointer Shape}, for available pointer shapes.
5018 @item :map @var{map}
5020 This associates an image map of @dfn{hot spots} with this image.
5022 An image map is an alist where each element has the format
5023 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
5024 as either a rectangle, a circle, or a polygon.
5026 A rectangle is a cons
5027 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
5028 which specifies the pixel coordinates of the upper left and bottom right
5029 corners of the rectangle area.
5032 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
5033 which specifies the center and the radius of the circle; @var{r} may
5034 be a float or integer.
5037 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
5038 where each pair in the vector describes one corner in the polygon.
5040 When the mouse pointer lies on a hot-spot area of an image, the
5041 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
5042 property, that defines a tool-tip for the hot-spot, and if it contains
5043 a @code{pointer} property, that defines the shape of the mouse cursor when
5044 it is on the hot-spot.
5045 @xref{Pointer Shape}, for available pointer shapes.
5047 When you click the mouse when the mouse pointer is over a hot-spot, an
5048 event is composed by combining the @var{id} of the hot-spot with the
5049 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
5050 @var{id} is @code{area4}.
5053 @defun image-mask-p spec &optional frame
5054 This function returns @code{t} if image @var{spec} has a mask bitmap.
5055 @var{frame} is the frame on which the image will be displayed.
5056 @var{frame} @code{nil} or omitted means to use the selected frame
5057 (@pxref{Input Focus}).
5061 @subsection XBM Images
5064 To use XBM format, specify @code{xbm} as the image type. This image
5065 format doesn't require an external library, so images of this type are
5068 Additional image properties supported for the @code{xbm} image type are:
5071 @item :foreground @var{foreground}
5072 The value, @var{foreground}, should be a string specifying the image
5073 foreground color, or @code{nil} for the default color. This color is
5074 used for each pixel in the XBM that is 1. The default is the frame's
5077 @item :background @var{background}
5078 The value, @var{background}, should be a string specifying the image
5079 background color, or @code{nil} for the default color. This color is
5080 used for each pixel in the XBM that is 0. The default is the frame's
5084 If you specify an XBM image using data within Emacs instead of an
5085 external file, use the following three properties:
5088 @item :data @var{data}
5089 The value, @var{data}, specifies the contents of the image.
5090 There are three formats you can use for @var{data}:
5094 A vector of strings or bool-vectors, each specifying one line of the
5095 image. Do specify @code{:height} and @code{:width}.
5098 A string containing the same byte sequence as an XBM file would contain.
5099 You must not specify @code{:height} and @code{:width} in this case,
5100 because omitting them is what indicates the data has the format of an
5101 XBM file. The file contents specify the height and width of the image.
5104 A string or a bool-vector containing the bits of the image (plus perhaps
5105 some extra bits at the end that will not be used). It should contain at
5106 least @var{width} * @code{height} bits. In this case, you must specify
5107 @code{:height} and @code{:width}, both to indicate that the string
5108 contains just the bits rather than a whole XBM file, and to specify the
5112 @item :width @var{width}
5113 The value, @var{width}, specifies the width of the image, in pixels.
5115 @item :height @var{height}
5116 The value, @var{height}, specifies the height of the image, in pixels.
5120 @subsection XPM Images
5123 To use XPM format, specify @code{xpm} as the image type. The
5124 additional image property @code{:color-symbols} is also meaningful with
5125 the @code{xpm} image type:
5128 @item :color-symbols @var{symbols}
5129 The value, @var{symbols}, should be an alist whose elements have the
5130 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
5131 the name of a color as it appears in the image file, and @var{color}
5132 specifies the actual color to use for displaying that name.
5135 @node ImageMagick Images
5136 @subsection ImageMagick Images
5137 @cindex ImageMagick images
5138 @cindex images, support for more formats
5140 If your Emacs build has ImageMagick support, you can use the
5141 ImageMagick library to load many image formats (@pxref{File
5142 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
5143 for images loaded via ImageMagick is @code{imagemagick}, regardless of
5144 the actual underlying image format.
5146 To check for ImageMagick support, use the following:
5149 (image-type-available-p 'imagemagick)
5152 @defun imagemagick-types
5153 This function returns a list of image file extensions supported by the
5154 current ImageMagick installation. Each list element is a symbol
5155 representing an internal ImageMagick name for an image type, such as
5156 @code{BMP} for @file{.bmp} images.
5159 @defopt imagemagick-enabled-types
5160 The value of this variable is a list of ImageMagick image types which
5161 Emacs may attempt to render using ImageMagick. Each list element
5162 should be one of the symbols in the list returned by
5163 @code{imagemagick-types}, or an equivalent string. Alternatively, a
5164 value of @code{t} enables ImageMagick for all possible image types.
5165 Regardless of the value of this variable,
5166 @code{imagemagick-types-inhibit} (see below) takes precedence.
5169 @defopt imagemagick-types-inhibit
5170 The value of this variable lists the ImageMagick image types which
5171 should never be rendered using ImageMagick, regardless of the value of
5172 @code{imagemagick-enabled-types}. A value of @code{t} disables
5173 ImageMagick entirely.
5176 @defvar image-format-suffixes
5177 This variable is an alist mapping image types to file name extensions.
5178 Emacs uses this in conjunction with the @code{:format} image property
5179 (see below) to give a hint to the ImageMagick library as to the type
5180 of an image. Each element has the form @code{(@var{type}
5181 @var{extension})}, where @var{type} is a symbol specifying an image
5182 content-type, and @var{extension} is a string that specifies the
5183 associated file name extension.
5186 Images loaded with ImageMagick support the following additional
5187 image descriptor properties:
5190 @item :background @var{background}
5191 @var{background}, if non-@code{nil}, should be a string specifying a
5192 color, which is used as the image's background color if the image
5193 supports transparency. If the value is @code{nil}, it defaults to the
5194 frame's background color.
5196 @item :width @var{width}, :height @var{height}
5197 The @code{:width} and @code{:height} keywords are used for scaling the
5198 image. If only one of them is specified, the other one will be
5199 calculated so as to preserve the aspect ratio. If both are specified,
5200 aspect ratio may not be preserved.
5202 @item :max-width @var{max-width}, :max-height @var{max-height}
5203 The @code{:max-width} and @code{:max-height} keywords are used for
5204 scaling if the size of the image of the image exceeds these values.
5205 If @code{:width} is set it will have precedence over @code{max-width},
5206 and if @code{:height} is set it will have precedence over
5207 @code{max-height}, but you can otherwise mix these keywords as you
5208 wish. @code{:max-width} and @code{:max-height} will always preserve
5211 @item :scale @var{scale}
5212 This should be a number, where values higher than 1 means to increase
5213 the size, and lower means to decrease the size. For instance, a value
5214 of 0.25 will make the image a quarter size of what it originally was.
5215 If the scaling makes the image larger than specified by
5216 @code{:max-width} or @code{:max-height}, the resulting size will not
5217 exceed those two values. If both @code{:scale} and
5218 @code{:height}/@code{:width} are specified, the height/width will be
5219 adjusted by the specified scaling factor.
5221 @item :format @var{type}
5222 The value, @var{type}, should be a symbol specifying the type of the
5223 image data, as found in @code{image-format-suffixes}. This is used
5224 when the image does not have an associated file name, to provide a
5225 hint to ImageMagick to help it detect the image type.
5227 @item :rotation @var{angle}
5228 Specifies a rotation angle in degrees.
5230 @item :index @var{frame}
5231 @c Doesn't work: http://debbugs.gnu.org/7978
5232 @xref{Multi-Frame Images}.
5236 @subsection SVG Images
5239 SVG (Scalable Vector Graphics) is an XML format for specifying images.
5240 If your Emacs build has with SVG support, you can create and manipulate
5241 these images with the following commands.
5243 @defun svg-create width height &rest args
5244 Create a new, empty SVG image with the specified dimensions.
5245 @var{args} is an argument plist with you can specify following:
5249 The default width (in pixels) of any lines created.
5252 The default stroke color on any lines created.
5255 This function returns an SVG structure, and all the following commands
5256 work on that structure.
5259 @defun svg-gradient svg id type stops
5260 Create a gradient in @var{svg} with identifier @var{id}. @var{type}
5261 specifies the gradient type, and can be either @code{linear} or
5262 @code{radial}. @var{stops} is a list of percentage/color pairs.
5264 The following will create a linear gradient that goes from red at the
5265 start, to green 25% of the way, to blue at the end:
5268 (svg-gradient svg "gradient1" 'linear
5269 '((0 . "red") (25 . "green") (100 . "blue")))
5272 The gradient created (and inserted into the SVG object) can later be
5273 used by all functions that create shapes.
5276 All the following functions take an optional list of keyword
5277 parameters that alter the various attributes from their default
5278 values. Valid attributes include:
5282 The width (in pixels) of lines drawn, and outlines around solid
5286 The color of lines drawn, and outlines around solid shapes.
5289 The color used for solid shapes.
5292 The identified of the shape.
5295 If given, this should be the identifier of a previously defined
5299 @defun svg-rectangle svg x y width height &rest args
5300 Add a rectangle to @var{svg} where the upper left corner is at
5301 position @var{x}/@var{y} and is of size @var{width}/@var{height}.
5304 (svg-rectangle svg 100 100 500 500 :gradient "gradient1")
5308 @defun svg-circle svg x y radius &rest args
5309 Add a circle to @var{svg} where the center is at @var{x}/@var{y}
5310 and the radius is @var{radius}.
5313 @defun svg-ellipse svg x y x-radius y-radius &rest args
5314 Add a circle to @var{svg} where the center is at @var{x}/@var{y} and
5315 the horizontal radius is @var{x-radius} and the vertical radius is
5319 @defun svg-line svg x1 y1 x2 y2 &rest args
5320 Add a line to @var{svg} that starts at @var{x1}/@var{y1} and extends
5321 to @var{x2}/@var{y2}.
5324 @defun svg-polyline svg points &rest args
5325 Add a multiple segment line to @var{svg} that goes through
5326 @var{points}, which is a list of X/Y position pairs.
5329 (svg-polyline svg '((200 . 100) (500 . 450) (80 . 100))
5330 :stroke-color "green")
5334 @defun svg-polygon svg points &rest args
5335 Add a polygon to @var{svg} where @var{points} is a list of X/Y pairs
5336 that describe the outer circumference of the polygon.
5339 (svg-polygon svg '((100 . 100) (200 . 150) (150 . 90))
5340 :stroke-color "blue" :fill-color "red"")
5344 @defun svg-text svg text &rest args
5345 Add a text to @var{svg}.
5349 svg "This is a text"
5354 :font-family "impact"
5355 :letter-spacing "4pt"
5362 @defun svg-embed svg image image-type datap &rest args
5363 Add an embedded (raster) image to @var{svg}. If @var{datap} is
5364 @code{nil}, @var{IMAGE} should be a file name; if not, it should be a
5365 binary string containing the image data. @var{image-type} should be a
5366 @acronym{MIME} image type, for instance @samp{"image/jpeg"}.
5369 (svg-embed svg "~/rms.jpg" "image/jpeg" nil
5370 :width "100px" :height "100px"
5371 :x "50px" :y "75px")
5375 @defun svg-remove svg id
5376 Remove the element with identifier @code{id} from the @code{svg}.
5379 Finally, the @code{svg-image} takes an SVG object as its parameter and
5380 returns an image object suitable for use in functions like
5381 @code{insert-image}. Here's a complete example that creates and
5382 inserts an image with a circle:
5385 (let ((svg (svg-create 400 400 :stroke-width 10)))
5386 (svg-gradient svg "gradient1" 'linear '((0 . "red") (100 . "blue")))
5387 (svg-circle svg 200 200 100 :gradient "gradient1" :stroke-color "green")
5388 (insert-image (svg-image svg)))
5392 @node Other Image Types
5393 @subsection Other Image Types
5396 For PBM images, specify image type @code{pbm}. Color, gray-scale and
5397 monochromatic images are supported. For mono PBM images, two additional
5398 image properties are supported.
5401 @item :foreground @var{foreground}
5402 The value, @var{foreground}, should be a string specifying the image
5403 foreground color, or @code{nil} for the default color. This color is
5404 used for each pixel in the PBM that is 1. The default is the frame's
5407 @item :background @var{background}
5408 The value, @var{background}, should be a string specifying the image
5409 background color, or @code{nil} for the default color. This color is
5410 used for each pixel in the PBM that is 0. The default is the frame's
5415 The remaining image types that Emacs can support are:
5419 Image type @code{gif}.
5420 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5423 Image type @code{jpeg}.
5426 Image type @code{png}.
5429 Image type @code{tiff}.
5430 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5433 @node Defining Images
5434 @subsection Defining Images
5435 @cindex define image
5437 The functions @code{create-image}, @code{defimage} and
5438 @code{find-image} provide convenient ways to create image descriptors.
5440 @defun create-image file-or-data &optional type data-p &rest props
5441 This function creates and returns an image descriptor which uses the
5442 data in @var{file-or-data}. @var{file-or-data} can be a file name or
5443 a string containing the image data; @var{data-p} should be @code{nil}
5444 for the former case, non-@code{nil} for the latter case.
5446 The optional argument @var{type} is a symbol specifying the image type.
5447 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
5448 determine the image type from the file's first few bytes, or else
5449 from the file's name.
5451 The remaining arguments, @var{props}, specify additional image
5452 properties---for example,
5454 @c ':heuristic-mask' is not documented?
5456 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
5459 The function returns @code{nil} if images of this type are not
5460 supported. Otherwise it returns an image descriptor.
5463 @defmac defimage symbol specs &optional doc
5464 This macro defines @var{symbol} as an image name. The arguments
5465 @var{specs} is a list which specifies how to display the image.
5466 The third argument, @var{doc}, is an optional documentation string.
5468 Each argument in @var{specs} has the form of a property list, and each
5469 one should specify at least the @code{:type} property and either the
5470 @code{:file} or the @code{:data} property. The value of @code{:type}
5471 should be a symbol specifying the image type, the value of
5472 @code{:file} is the file to load the image from, and the value of
5473 @code{:data} is a string containing the actual image data. Here is an
5477 (defimage test-image
5478 ((:type xpm :file "~/test1.xpm")
5479 (:type xbm :file "~/test1.xbm")))
5482 @code{defimage} tests each argument, one by one, to see if it is
5483 usable---that is, if the type is supported and the file exists. The
5484 first usable argument is used to make an image descriptor which is
5485 stored in @var{symbol}.
5487 If none of the alternatives will work, then @var{symbol} is defined
5491 @defun image-property image property
5492 Return the value of @var{property} in @var{image}. Properties can be
5493 set by using @code{setf}. Setting a property to @code{nil} will
5494 remove the property from the image.
5497 @defun find-image specs
5498 This function provides a convenient way to find an image satisfying one
5499 of a list of image specifications @var{specs}.
5501 Each specification in @var{specs} is a property list with contents
5502 depending on image type. All specifications must at least contain the
5503 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
5504 or @w{@code{:data @var{data}}}, where @var{type} is a symbol specifying
5505 the image type, e.g., @code{xbm}, @var{file} is the file to load the
5506 image from, and @var{data} is a string containing the actual image data.
5507 The first specification in the list whose @var{type} is supported, and
5508 @var{file} exists, is used to construct the image specification to be
5509 returned. If no specification is satisfied, @code{nil} is returned.
5511 The image is looked for in @code{image-load-path}.
5514 @defopt image-load-path
5515 This variable's value is a list of locations in which to search for
5516 image files. If an element is a string or a variable symbol whose
5517 value is a string, the string is taken to be the name of a directory
5518 to search. If an element is a variable symbol whose value is a list,
5519 that is taken to be a list of directory names to search.
5521 The default is to search in the @file{images} subdirectory of the
5522 directory specified by @code{data-directory}, then the directory
5523 specified by @code{data-directory}, and finally in the directories in
5524 @code{load-path}. Subdirectories are not automatically included in
5525 the search, so if you put an image file in a subdirectory, you have to
5526 supply the subdirectory name explicitly. For example, to find the
5527 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5528 should specify the image as follows:
5531 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5535 @defun image-load-path-for-library library image &optional path no-error
5536 This function returns a suitable search path for images used by the
5537 Lisp package @var{library}.
5539 The function searches for @var{image} first using @code{image-load-path},
5540 excluding @file{@code{data-directory}/images}, and then in
5541 @code{load-path}, followed by a path suitable for @var{library}, which
5542 includes @file{../../etc/images} and @file{../etc/images} relative to
5543 the library file itself, and finally in
5544 @file{@code{data-directory}/images}.
5546 Then this function returns a list of directories which contains first
5547 the directory in which @var{image} was found, followed by the value of
5548 @code{load-path}. If @var{path} is given, it is used instead of
5551 If @var{no-error} is non-@code{nil} and a suitable path can't be
5552 found, don't signal an error. Instead, return a list of directories as
5553 before, except that @code{nil} appears in place of the image directory.
5555 Here is an example of using @code{image-load-path-for-library}:
5558 (defvar image-load-path) ; shush compiler
5559 (let* ((load-path (image-load-path-for-library
5560 "mh-e" "mh-logo.xpm"))
5561 (image-load-path (cons (car load-path)
5563 (mh-tool-bar-folder-buttons-init))
5567 @vindex image-scaling-factor
5568 Images are automatically scaled when created based on the
5569 @code{image-scaling-factor} variable. The value is either a floating
5570 point number (where numbers higher than 1 means to increase the size
5571 and lower means to shrink the size), or the symbol @code{auto}, which
5572 will compute a scaling factor based on the font pixel size.
5574 @node Showing Images
5575 @subsection Showing Images
5578 You can use an image descriptor by setting up the @code{display}
5579 property yourself, but it is easier to use the functions in this
5582 @defun insert-image image &optional string area slice
5583 This function inserts @var{image} in the current buffer at point. The
5584 value @var{image} should be an image descriptor; it could be a value
5585 returned by @code{create-image}, or the value of a symbol defined with
5586 @code{defimage}. The argument @var{string} specifies the text to put
5587 in the buffer to hold the image. If it is omitted or @code{nil},
5588 @code{insert-image} uses @code{" "} by default.
5590 The argument @var{area} specifies whether to put the image in a margin.
5591 If it is @code{left-margin}, the image appears in the left margin;
5592 @code{right-margin} specifies the right margin. If @var{area} is
5593 @code{nil} or omitted, the image is displayed at point within the
5596 The argument @var{slice} specifies a slice of the image to insert. If
5597 @var{slice} is @code{nil} or omitted the whole image is inserted.
5598 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5599 @var{height})} which specifies the @var{x} and @var{y} positions and
5600 @var{width} and @var{height} of the image area to insert. Integer
5601 values are in units of pixels. A floating-point number in the range
5602 0.0--1.0 stands for that fraction of the width or height of the entire
5605 Internally, this function inserts @var{string} in the buffer, and gives
5606 it a @code{display} property which specifies @var{image}. @xref{Display
5610 @cindex slice, image
5612 @defun insert-sliced-image image &optional string area rows cols
5613 This function inserts @var{image} in the current buffer at point, like
5614 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5615 equally sized slices.
5617 Emacs displays each slice as a
5618 separate image, and allows more intuitive scrolling up/down, instead of
5619 jumping up/down the entire image when paging through a buffer that
5620 displays (large) images.
5623 @defun put-image image pos &optional string area
5624 This function puts image @var{image} in front of @var{pos} in the
5625 current buffer. The argument @var{pos} should be an integer or a
5626 marker. It specifies the buffer position where the image should appear.
5627 The argument @var{string} specifies the text that should hold the image
5628 as an alternative to the default.
5630 The argument @var{image} must be an image descriptor, perhaps returned
5631 by @code{create-image} or stored by @code{defimage}.
5633 The argument @var{area} specifies whether to put the image in a margin.
5634 If it is @code{left-margin}, the image appears in the left margin;
5635 @code{right-margin} specifies the right margin. If @var{area} is
5636 @code{nil} or omitted, the image is displayed at point within the
5639 Internally, this function creates an overlay, and gives it a
5640 @code{before-string} property containing text that has a @code{display}
5641 property whose value is the image. (Whew!)
5644 @defun remove-images start end &optional buffer
5645 This function removes images in @var{buffer} between positions
5646 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5647 images are removed from the current buffer.
5649 This removes only images that were put into @var{buffer} the way
5650 @code{put-image} does it, not images that were inserted with
5651 @code{insert-image} or in other ways.
5654 @defun image-size spec &optional pixels frame
5655 @cindex size of image
5656 This function returns the size of an image as a pair
5657 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5658 specification. @var{pixels} non-@code{nil} means return sizes measured
5659 in pixels, otherwise return sizes measured in the default character size
5660 of @var{frame} (@pxref{Frame Font}). @var{frame} is the frame on which
5661 the image will be displayed. @var{frame} null or omitted means use the
5662 selected frame (@pxref{Input Focus}).
5665 @defvar max-image-size
5666 This variable is used to define the maximum size of image that Emacs
5667 will load. Emacs will refuse to load (and display) any image that is
5668 larger than this limit.
5670 If the value is an integer, it directly specifies the maximum
5671 image height and width, measured in pixels. If it is floating
5672 point, it specifies the maximum image height and width
5673 as a ratio to the frame height and width. If the value is
5674 non-numeric, there is no explicit limit on the size of images.
5676 The purpose of this variable is to prevent unreasonably large images
5677 from accidentally being loaded into Emacs. It only takes effect the
5678 first time an image is loaded. Once an image is placed in the image
5679 cache, it can always be displayed, even if the value of
5680 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5683 Images inserted with the insertion functions above also get a local
5684 keymap installed in the text properties (or overlays) that span the
5685 displayed image. This keymap defines the following commands:
5689 Increase the image size (@code{image-increase-size}). A prefix value
5690 of @samp{4} means to increase the size by 40%. The default is 20%.
5693 Decrease the image size (@code{image-increase-size}). A prefix value
5694 of @samp{4} means to decrease the size by 40%. The default is 20%.
5697 Rotate the image by 90 degrees (@code{image-rotate}).
5700 Save the image to a file (@code{image-save}).
5703 @node Multi-Frame Images
5704 @subsection Multi-Frame Images
5705 @cindex multi-frame images
5708 @cindex image animation
5709 @cindex image frames
5710 Some image files can contain more than one image. We say that there
5711 are multiple ``frames'' in the image. At present, Emacs supports
5712 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5715 The frames can be used either to represent multiple pages (this is
5716 usually the case with multi-frame TIFF files, for example), or to
5717 create animation (usually the case with multi-frame GIF files).
5719 A multi-frame image has a property @code{:index}, whose value is an
5720 integer (counting from 0) that specifies which frame is being displayed.
5722 @defun image-multi-frame-p image
5723 This function returns non-@code{nil} if @var{image} contains more than
5724 one frame. The actual return value is a cons @code{(@var{nimages}
5725 . @var{delay})}, where @var{nimages} is the number of frames and
5726 @var{delay} is the delay in seconds between them, or @code{nil}
5727 if the image does not specify a delay. Images that are intended to be
5728 animated usually specify a frame delay, whereas ones that are intended
5729 to be treated as multiple pages do not.
5732 @defun image-current-frame image
5733 This function returns the index of the current frame number for
5734 @var{image}, counting from 0.
5737 @defun image-show-frame image n &optional nocheck
5738 This function switches @var{image} to frame number @var{n}. It
5739 replaces a frame number outside the valid range with that of the end
5740 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5741 does not contain a frame with the specified number, the image displays
5745 @defun image-animate image &optional index limit
5746 This function animates @var{image}. The optional integer @var{index}
5747 specifies the frame from which to start (default 0). The optional
5748 argument @var{limit} controls the length of the animation. If omitted
5749 or @code{nil}, the image animates once only; if @code{t} it loops
5750 forever; if a number animation stops after that many seconds.
5753 @vindex image-minimum-frame-delay
5754 @vindex image-default-frame-delay
5755 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5756 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5757 If the image itself does not specify a delay, Emacs uses
5758 @code{image-default-frame-delay}.
5760 @defun image-animate-timer image
5761 This function returns the timer responsible for animating @var{image},
5767 @subsection Image Cache
5770 Emacs caches images so that it can display them again more
5771 efficiently. When Emacs displays an image, it searches the image
5772 cache for an existing image specification @code{equal} to the desired
5773 specification. If a match is found, the image is displayed from the
5774 cache. Otherwise, Emacs loads the image normally.
5776 @defun image-flush spec &optional frame
5777 This function removes the image with specification @var{spec} from the
5778 image cache of frame @var{frame}. Image specifications are compared
5779 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5780 selected frame. If @var{frame} is @code{t}, the image is flushed on
5781 all existing frames.
5783 In Emacs's current implementation, each graphical terminal possesses an
5784 image cache, which is shared by all the frames on that terminal
5785 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5786 also refreshes it in all other frames on the same terminal.
5789 One use for @code{image-flush} is to tell Emacs about a change in an
5790 image file. If an image specification contains a @code{:file}
5791 property, the image is cached based on the file's contents when the
5792 image is first displayed. Even if the file subsequently changes,
5793 Emacs continues displaying the old version of the image. Calling
5794 @code{image-flush} flushes the image from the cache, forcing Emacs to
5795 re-read the file the next time it needs to display that image.
5797 Another use for @code{image-flush} is for memory conservation. If
5798 your Lisp program creates a large number of temporary images over a
5799 period much shorter than @code{image-cache-eviction-delay} (see
5800 below), you can opt to flush unused images yourself, instead of
5801 waiting for Emacs to do it automatically.
5803 @defun clear-image-cache &optional filter
5804 This function clears an image cache, removing all the images stored in
5805 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5806 the selected frame. If @var{filter} is a frame, it clears the cache
5807 for that frame. If @var{filter} is @code{t}, all image caches are
5808 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5809 images associated with that file name are removed from all image
5813 If an image in the image cache has not been displayed for a specified
5814 period of time, Emacs removes it from the cache and frees the
5817 @defvar image-cache-eviction-delay
5818 This variable specifies the number of seconds an image can remain in
5819 the cache without being displayed. When an image is not displayed for
5820 this length of time, Emacs removes it from the image cache.
5822 Under some circumstances, if the number of images in the cache grows
5823 too large, the actual eviction delay may be shorter than this.
5825 If the value is @code{nil}, Emacs does not remove images from the cache
5826 except when you explicitly clear it. This mode can be useful for
5831 @section Embedded Native Widgets
5833 @cindex embedded widgets
5834 @cindex webkit browser widget
5836 Emacs is able to display native widgets, such as GTK WebKit widgets,
5837 in Emacs buffers when it was built with the necessary support
5838 libraries and is running on a graphical terminal. To test whether
5839 Emacs supports display of embedded widgets, check that the
5840 @code{xwidget-internal} feature is available (@pxref{Named Features}).
5842 To display an embedded widget in a buffer, you must first create an
5843 xwidget object, and then use that object as the display specifier
5844 in a @code{display} text or overlay property (@pxref{Display
5847 @defun make-xwidget type title width height arguments &optional buffer
5848 This creates and returns an xwidget object. If
5849 @var{buffer} is omitted or @code{nil}, it defaults to the current
5850 buffer. If @var{buffer} names a buffer that doesn't exist, it will be
5851 created. The @var{type} identifies the type of the xwidget component,
5852 it can be one of the following:
5856 The WebKit component.
5859 The @var{width} and @var{height} arguments specify the widget size in
5860 pixels, and @var{title}, a string, specifies its title.
5863 @defun xwidgetp object
5864 This function returns @code{t} if @var{object} is an xwidget,
5865 @code{nil} otherwise.
5868 @defun xwidget-plist xwidget
5869 This function returns the property list of @var{xwidget}.
5872 @defun set-xwidget-plist xwidget plist
5873 This function replaces the property list of @var{xwidget} with a new
5874 property list given by @var{plist}.
5877 @defun xwidget-buffer xwidget
5878 This function returns the buffer of @var{xwidget}.
5881 @defun get-buffer-xwidgets buffer
5882 This function returns a list of xwidget objects associated with the
5883 @var{buffer}, which can be specified as a buffer object or a name of
5884 an existing buffer, a string. The value is @code{nil} if @var{buffer}
5885 contains no xwidgets.
5888 @defun xwidget-webkit-goto-uri xwidget uri
5889 This function browses the specified @var{uri} in the given
5890 @var{xwidget}. The @var{uri} is a string that specifies the name of a
5891 file or a URL. @c FIXME: What else can a URI specify in this context?
5894 @defun xwidget-webkit-execute-script xwidget script
5895 This function causes the browser widget specified by @var{xwidget} to
5896 execute the specified JavaScript @code{script}.
5899 @defun xwidget-webkit-execute-script-rv xwidget script &optional default
5900 This function executes the specified @var{script} like
5901 @code{xwidget-webkit-execute-script} does, but it also returns the
5902 script's return value as a string. If @var{script} doesn't return a
5903 value, this function returns @var{default}, or @code{nil} if
5904 @var{default} was omitted.
5907 @defun xwidget-webkit-get-title xwidget
5908 This function returns the title of @var{xwidget} as a string.
5911 @defun xwidget-resize xwidget width height
5912 This function resizes the specified @var{xwidget} to the size
5913 @var{width}x@var{height} pixels.
5916 @defun xwidget-size-request xwidget
5917 This function returns the desired size of @var{xwidget} as a list of
5918 the form @code{(@var{width} @var{height})}. The dimensions are in
5922 @defun xwidget-info xwidget
5923 This function returns the attributes of @var{xwidget} as a vector of
5924 the form @code{[@var{type} @var{title} @var{width} @var{height}]}.
5925 The attributes are usually determined by @code{make-xwidget} when the
5929 @defun set-xwidget-query-on-exit-flag xwidget flag
5930 This function allows you to arrange that Emacs will ask the user for
5931 confirmation before exiting or before killing a buffer that has
5932 @var{xwidget} associated with it. If @var{flag} is non-@code{nil},
5933 Emacs will query the user, otherwise it will not.
5936 @defun xwidget-query-on-exit-flag xwidget
5937 This function returns the current setting of @var{xwidget}s
5938 query-on-exit flag, either @code{t} or @code{nil}.
5943 @cindex buttons in buffers
5944 @cindex clickable buttons in buffers
5946 The Button package defines functions for inserting and manipulating
5947 @dfn{buttons} that can be activated with the mouse or via keyboard
5948 commands. These buttons are typically used for various kinds of
5951 A button is essentially a set of text or overlay properties,
5952 attached to a stretch of text in a buffer. These properties are
5953 called @dfn{button properties}. One of these properties, the
5954 @dfn{action property}, specifies a function which is called when the
5955 user invokes the button using the keyboard or the mouse. The action
5956 function may examine the button and use its other properties as
5959 In some ways, the Button package duplicates the functionality in the
5960 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5961 Library}. The advantage of the Button package is that it is faster,
5962 smaller, and simpler to program. From the point of view of the user,
5963 the interfaces produced by the two packages are very similar.
5966 * Button Properties:: Button properties with special meanings.
5967 * Button Types:: Defining common properties for classes of buttons.
5968 * Making Buttons:: Adding buttons to Emacs buffers.
5969 * Manipulating Buttons:: Getting and setting properties of buttons.
5970 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5973 @node Button Properties
5974 @subsection Button Properties
5975 @cindex button properties
5977 Each button has an associated list of properties defining its
5978 appearance and behavior, and other arbitrary properties may be used
5979 for application specific purposes. The following properties have
5980 special meaning to the Button package:
5984 @kindex action @r{(button property)}
5985 The function to call when the user invokes the button, which is passed
5986 the single argument @var{button}. By default this is @code{ignore},
5990 @kindex mouse-action @r{(button property)}
5991 This is similar to @code{action}, and when present, will be used
5992 instead of @code{action} for button invocations resulting from
5993 mouse-clicks (instead of the user hitting @key{RET}). If not
5994 present, mouse-clicks use @code{action} instead.
5997 @kindex face @r{(button property)}
5998 This is an Emacs face controlling how buttons of this type are
5999 displayed; by default this is the @code{button} face.
6002 @kindex mouse-face @r{(button property)}
6003 This is an additional face which controls appearance during
6004 mouse-overs (merged with the usual button face); by default this is
6005 the usual Emacs @code{highlight} face.
6008 @kindex keymap @r{(button property)}
6009 The button's keymap, defining bindings active within the button
6010 region. By default this is the usual button region keymap, stored
6011 in the variable @code{button-map}, which defines @key{RET} and
6012 @key{mouse-2} to invoke the button.
6015 @kindex type @r{(button property)}
6016 The button type. @xref{Button Types}.
6019 @kindex help-index @r{(button property)}
6020 A string displayed by the Emacs tool-tip help system; by default,
6021 @code{"mouse-2, RET: Push this button"}.
6024 @kindex follow-link @r{(button property)}
6025 The follow-link property, defining how a @key{mouse-1} click behaves
6026 on this button, @xref{Clickable Text}.
6029 @kindex button @r{(button property)}
6030 All buttons have a non-@code{nil} @code{button} property, which may be useful
6031 in finding regions of text that comprise buttons (which is what the
6032 standard button functions do).
6035 There are other properties defined for the regions of text in a
6036 button, but these are not generally interesting for typical uses.
6039 @subsection Button Types
6040 @cindex button types
6042 Every button has a @dfn{button type}, which defines default values
6043 for the button's properties. Button types are arranged in a
6044 hierarchy, with specialized types inheriting from more general types,
6045 so that it's easy to define special-purpose types of buttons for
6048 @defun define-button-type name &rest properties
6049 Define a button type called @var{name} (a symbol).
6050 The remaining arguments
6051 form a sequence of @var{property value} pairs, specifying default
6052 property values for buttons with this type (a button's type may be set
6053 by giving it a @code{type} property when creating the button, using
6054 the @code{:type} keyword argument).
6056 In addition, the keyword argument @code{:supertype} may be used to
6057 specify a button-type from which @var{name} inherits its default
6058 property values. Note that this inheritance happens only when
6059 @var{name} is defined; subsequent changes to a supertype are not
6060 reflected in its subtypes.
6063 Using @code{define-button-type} to define default properties for
6064 buttons is not necessary---buttons without any specified type use the
6065 built-in button-type @code{button}---but it is encouraged, since
6066 doing so usually makes the resulting code clearer and more efficient.
6068 @node Making Buttons
6069 @subsection Making Buttons
6070 @cindex making buttons
6072 Buttons are associated with a region of text, using an overlay or
6073 text properties to hold button-specific information, all of which are
6074 initialized from the button's type (which defaults to the built-in
6075 button type @code{button}). Like all Emacs text, the appearance of
6076 the button is governed by the @code{face} property; by default (via
6077 the @code{face} property inherited from the @code{button} button-type)
6078 this is a simple underline, like a typical web-page link.
6080 For convenience, there are two sorts of button-creation functions,
6081 those that add button properties to an existing region of a buffer,
6082 called @code{make-...button}, and those that also insert the button
6083 text, called @code{insert-...button}.
6085 The button-creation functions all take the @code{&rest} argument
6086 @var{properties}, which should be a sequence of @var{property value}
6087 pairs, specifying properties to add to the button; see @ref{Button
6088 Properties}. In addition, the keyword argument @code{:type} may be
6089 used to specify a button-type from which to inherit other properties;
6090 see @ref{Button Types}. Any properties not explicitly specified
6091 during creation will be inherited from the button's type (if the type
6092 defines such a property).
6094 The following functions add a button using an overlay
6095 (@pxref{Overlays}) to hold the button properties:
6097 @defun make-button beg end &rest properties
6098 This makes a button from @var{beg} to @var{end} in the
6099 current buffer, and returns it.
6102 @defun insert-button label &rest properties
6103 This insert a button with the label @var{label} at point,
6107 The following functions are similar, but using text properties
6108 (@pxref{Text Properties}) to hold the button properties. Such buttons
6109 do not add markers to the buffer, so editing in the buffer does not
6110 slow down if there is an extremely large numbers of buttons. However,
6111 if there is an existing face text property on the text (e.g., a face
6112 assigned by Font Lock mode), the button face may not be visible. Both
6113 of these functions return the starting position of the new button.
6115 @defun make-text-button beg end &rest properties
6116 This makes a button from @var{beg} to @var{end} in the current buffer,
6117 using text properties.
6120 @defun insert-text-button label &rest properties
6121 This inserts a button with the label @var{label} at point, using text
6125 @node Manipulating Buttons
6126 @subsection Manipulating Buttons
6127 @cindex manipulating buttons
6129 These are functions for getting and setting properties of buttons.
6130 Often these are used by a button's invocation function to determine
6133 Where a @var{button} parameter is specified, it means an object
6134 referring to a specific button, either an overlay (for overlay
6135 buttons), or a buffer-position or marker (for text property buttons).
6136 Such an object is passed as the first argument to a button's
6137 invocation function when it is invoked.
6139 @defun button-start button
6140 Return the position at which @var{button} starts.
6143 @defun button-end button
6144 Return the position at which @var{button} ends.
6147 @defun button-get button prop
6148 Get the property of button @var{button} named @var{prop}.
6151 @defun button-put button prop val
6152 Set @var{button}'s @var{prop} property to @var{val}.
6155 @defun button-activate button &optional use-mouse-action
6156 Call @var{button}'s @code{action} property (i.e., invoke the function
6157 that is the value of that property, passing it the single argument
6158 @var{button}). If @var{use-mouse-action} is non-@code{nil}, try to
6159 invoke the button's @code{mouse-action} property instead of
6160 @code{action}; if the button has no @code{mouse-action} property, use
6161 @code{action} as normal.
6164 @defun button-label button
6165 Return @var{button}'s text label.
6168 @defun button-type button
6169 Return @var{button}'s button-type.
6172 @defun button-has-type-p button type
6173 Return @code{t} if @var{button} has button-type @var{type}, or one of
6174 @var{type}'s subtypes.
6177 @defun button-at pos
6178 Return the button at position @var{pos} in the current buffer, or
6179 @code{nil}. If the button at @var{pos} is a text property button, the
6180 return value is a marker pointing to @var{pos}.
6183 @defun button-type-put type prop val
6184 Set the button-type @var{type}'s @var{prop} property to @var{val}.
6187 @defun button-type-get type prop
6188 Get the property of button-type @var{type} named @var{prop}.
6191 @defun button-type-subtype-p type supertype
6192 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
6195 @node Button Buffer Commands
6196 @subsection Button Buffer Commands
6197 @cindex button buffer commands
6199 These are commands and functions for locating and operating on
6200 buttons in an Emacs buffer.
6202 @code{push-button} is the command that a user uses to actually push
6203 a button, and is bound by default in the button itself to @key{RET}
6204 and to @key{mouse-2} using a local keymap in the button's overlay or
6205 text properties. Commands that are useful outside the buttons itself,
6206 such as @code{forward-button} and @code{backward-button} are
6207 additionally available in the keymap stored in
6208 @code{button-buffer-map}; a mode which uses buttons may want to use
6209 @code{button-buffer-map} as a parent keymap for its keymap.
6211 If the button has a non-@code{nil} @code{follow-link} property, and
6212 @code{mouse-1-click-follows-link} is set, a quick @key{mouse-1} click
6213 will also activate the @code{push-button} command.
6214 @xref{Clickable Text}.
6216 @deffn Command push-button &optional pos use-mouse-action
6217 Perform the action specified by a button at location @var{pos}.
6218 @var{pos} may be either a buffer position or a mouse-event. If
6219 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
6220 mouse-event (@pxref{Mouse Events}), try to invoke the button's
6221 @code{mouse-action} property instead of @code{action}; if the button
6222 has no @code{mouse-action} property, use @code{action} as normal.
6223 @var{pos} defaults to point, except when @code{push-button} is invoked
6224 interactively as the result of a mouse-event, in which case, the mouse
6225 event's position is used. If there's no button at @var{pos}, do
6226 nothing and return @code{nil}, otherwise return @code{t}.
6229 @deffn Command forward-button n &optional wrap display-message
6230 Move to the @var{n}th next button, or @var{n}th previous button if
6231 @var{n} is negative. If @var{n} is zero, move to the start of any
6232 button at point. If @var{wrap} is non-@code{nil}, moving past either
6233 end of the buffer continues from the other end. If
6234 @var{display-message} is non-@code{nil}, the button's help-echo string
6235 is displayed. Any button with a non-@code{nil} @code{skip} property
6236 is skipped over. Returns the button found.
6239 @deffn Command backward-button n &optional wrap display-message
6240 Move to the @var{n}th previous button, or @var{n}th next button if
6241 @var{n} is negative. If @var{n} is zero, move to the start of any
6242 button at point. If @var{wrap} is non-@code{nil}, moving past either
6243 end of the buffer continues from the other end. If
6244 @var{display-message} is non-@code{nil}, the button's help-echo string
6245 is displayed. Any button with a non-@code{nil} @code{skip} property
6246 is skipped over. Returns the button found.
6249 @defun next-button pos &optional count-current
6250 @defunx previous-button pos &optional count-current
6251 Return the next button after (for @code{next-button}) or before (for
6252 @code{previous-button}) position @var{pos} in the current buffer. If
6253 @var{count-current} is non-@code{nil}, count any button at @var{pos}
6254 in the search, instead of starting at the next button.
6257 @node Abstract Display
6258 @section Abstract Display
6260 @cindex display, abstract
6261 @cindex display, arbitrary objects
6262 @cindex model/view/controller
6263 @cindex view part, model/view/controller
6265 The Ewoc package constructs buffer text that represents a structure
6266 of Lisp objects, and updates the text to follow changes in that
6267 structure. This is like the ``view'' component in the
6268 ``model--view--controller'' design paradigm. Ewoc means ``Emacs's
6269 Widget for Object Collections''.
6271 An @dfn{ewoc} is a structure that organizes information required to
6272 construct buffer text that represents certain Lisp data. The buffer
6273 text of the ewoc has three parts, in order: first, fixed @dfn{header}
6274 text; next, textual descriptions of a series of data elements (Lisp
6275 objects that you specify); and last, fixed @dfn{footer} text.
6276 Specifically, an ewoc contains information on:
6280 The buffer which its text is generated in.
6283 The text's start position in the buffer.
6286 The header and footer strings.
6290 @c or "@cindex node, abstract display"?
6291 A doubly-linked chain of @dfn{nodes}, each of which contains:
6295 A @dfn{data element}, a single Lisp object.
6298 Links to the preceding and following nodes in the chain.
6302 A @dfn{pretty-printer} function which is responsible for
6303 inserting the textual representation of a data
6304 element value into the current buffer.
6307 Typically, you define an ewoc with @code{ewoc-create}, and then pass
6308 the resulting ewoc structure to other functions in the Ewoc package to
6309 build nodes within it, and display it in the buffer. Once it is
6310 displayed in the buffer, other functions determine the correspondence
6311 between buffer positions and nodes, move point from one node's textual
6312 representation to another, and so forth. @xref{Abstract Display
6315 @cindex encapsulation, ewoc
6316 @c or "@cindex encapsulation, abstract display"?
6317 A node @dfn{encapsulates} a data element much the way a variable
6318 holds a value. Normally, encapsulation occurs as a part of adding a
6319 node to the ewoc. You can retrieve the data element value and place a
6320 new value in its place, like so:
6323 (ewoc-data @var{node})
6326 (ewoc-set-data @var{node} @var{new-value})
6327 @result{} @var{new-value}
6331 You can also use, as the data element value, a Lisp object (list or
6332 vector) that is a container for the real value, or an index into
6333 some other structure. The example (@pxref{Abstract Display Example})
6334 uses the latter approach.
6336 When the data changes, you will want to update the text in the
6337 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
6338 just specific nodes using @code{ewoc-invalidate}, or all nodes
6339 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
6340 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
6341 and add new nodes in their place. Deleting a node from an ewoc deletes
6342 its associated textual description from buffer, as well.
6345 * Abstract Display Functions:: Functions in the Ewoc package.
6346 * Abstract Display Example:: Example of using Ewoc.
6349 @node Abstract Display Functions
6350 @subsection Abstract Display Functions
6352 In this subsection, @var{ewoc} and @var{node} stand for the
6353 structures described above (@pxref{Abstract Display}), while
6354 @var{data} stands for an arbitrary Lisp object used as a data element.
6356 @defun ewoc-create pretty-printer &optional header footer nosep
6357 This constructs and returns a new ewoc, with no nodes (and thus no data
6358 elements). @var{pretty-printer} should be a function that takes one
6359 argument, a data element of the sort you plan to use in this ewoc, and
6360 inserts its textual description at point using @code{insert} (and never
6361 @code{insert-before-markers}, because that would interfere with the
6362 Ewoc package's internal mechanisms).
6364 Normally, a newline is automatically inserted after the header,
6365 the footer and every node's textual description. If @var{nosep}
6366 is non-@code{nil}, no newline is inserted. This may be useful for
6367 displaying an entire ewoc on a single line, for example, or for
6368 making nodes invisible by arranging for @var{pretty-printer}
6369 to do nothing for those nodes.
6371 An ewoc maintains its text in the buffer that is current when
6372 you create it, so switch to the intended buffer before calling
6376 @defun ewoc-buffer ewoc
6377 This returns the buffer where @var{ewoc} maintains its text.
6380 @defun ewoc-get-hf ewoc
6381 This returns a cons cell @code{(@var{header} . @var{footer})}
6382 made from @var{ewoc}'s header and footer.
6385 @defun ewoc-set-hf ewoc header footer
6386 This sets the header and footer of @var{ewoc} to the strings
6387 @var{header} and @var{footer}, respectively.
6390 @defun ewoc-enter-first ewoc data
6391 @defunx ewoc-enter-last ewoc data
6392 These add a new node encapsulating @var{data}, putting it, respectively,
6393 at the beginning or end of @var{ewoc}'s chain of nodes.
6396 @defun ewoc-enter-before ewoc node data
6397 @defunx ewoc-enter-after ewoc node data
6398 These add a new node encapsulating @var{data}, adding it to
6399 @var{ewoc} before or after @var{node}, respectively.
6402 @defun ewoc-prev ewoc node
6403 @defunx ewoc-next ewoc node
6404 These return, respectively, the previous node and the next node of @var{node}
6408 @defun ewoc-nth ewoc n
6409 This returns the node in @var{ewoc} found at zero-based index @var{n}.
6410 A negative @var{n} means count from the end. @code{ewoc-nth} returns
6411 @code{nil} if @var{n} is out of range.
6414 @defun ewoc-data node
6415 This extracts the data encapsulated by @var{node} and returns it.
6418 @defun ewoc-set-data node data
6419 This sets the data encapsulated by @var{node} to @var{data}.
6422 @defun ewoc-locate ewoc &optional pos guess
6423 This determines the node in @var{ewoc} which contains point (or
6424 @var{pos} if specified), and returns that node. If @var{ewoc} has no
6425 nodes, it returns @code{nil}. If @var{pos} is before the first node,
6426 it returns the first node; if @var{pos} is after the last node, it returns
6427 the last node. The optional third arg @var{guess}
6428 should be a node that is likely to be near @var{pos}; this doesn't
6429 alter the result, but makes the function run faster.
6432 @defun ewoc-location node
6433 This returns the start position of @var{node}.
6436 @defun ewoc-goto-prev ewoc arg
6437 @defunx ewoc-goto-next ewoc arg
6438 These move point to the previous or next, respectively, @var{arg}th node
6439 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
6440 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
6441 moves past the last node, returning @code{nil}. Excepting this special
6442 case, these functions return the node moved to.
6445 @defun ewoc-goto-node ewoc node
6446 This moves point to the start of @var{node} in @var{ewoc}.
6449 @defun ewoc-refresh ewoc
6450 This function regenerates the text of @var{ewoc}. It works by
6451 deleting the text between the header and the footer, i.e., all the
6452 data elements' representations, and then calling the pretty-printer
6453 function for each node, one by one, in order.
6456 @defun ewoc-invalidate ewoc &rest nodes
6457 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
6458 @var{ewoc} are updated instead of the entire set.
6461 @defun ewoc-delete ewoc &rest nodes
6462 This deletes each node in @var{nodes} from @var{ewoc}.
6465 @defun ewoc-filter ewoc predicate &rest args
6466 This calls @var{predicate} for each data element in @var{ewoc} and
6467 deletes those nodes for which @var{predicate} returns @code{nil}.
6468 Any @var{args} are passed to @var{predicate}.
6471 @defun ewoc-collect ewoc predicate &rest args
6472 This calls @var{predicate} for each data element in @var{ewoc}
6473 and returns a list of those elements for which @var{predicate}
6474 returns non-@code{nil}. The elements in the list are ordered
6475 as in the buffer. Any @var{args} are passed to @var{predicate}.
6478 @defun ewoc-map map-function ewoc &rest args
6479 This calls @var{map-function} for each data element in @var{ewoc} and
6480 updates those nodes for which @var{map-function} returns non-@code{nil}.
6481 Any @var{args} are passed to @var{map-function}.
6484 @node Abstract Display Example
6485 @subsection Abstract Display Example
6487 Here is a simple example using functions of the ewoc package to
6488 implement a @dfn{color components} display, an area in a buffer that
6489 represents a vector of three integers (itself representing a 24-bit RGB
6490 value) in various ways.
6493 (setq colorcomp-ewoc nil
6495 colorcomp-mode-map nil
6496 colorcomp-labels ["Red" "Green" "Blue"])
6498 (defun colorcomp-pp (data)
6500 (let ((comp (aref colorcomp-data data)))
6501 (insert (aref colorcomp-labels data) "\t: #x"
6502 (format "%02X" comp) " "
6503 (make-string (ash comp -2) ?#) "\n"))
6504 (let ((cstr (format "#%02X%02X%02X"
6505 (aref colorcomp-data 0)
6506 (aref colorcomp-data 1)
6507 (aref colorcomp-data 2)))
6508 (samp " (sample text) "))
6510 (propertize samp 'face
6511 `(foreground-color . ,cstr))
6512 (propertize samp 'face
6513 `(background-color . ,cstr))
6516 (defun colorcomp (color)
6517 "Allow fiddling with COLOR in a new buffer.
6518 The buffer is in Color Components mode."
6519 (interactive "sColor (name or #RGB or #RRGGBB): ")
6520 (when (string= "" color)
6521 (setq color "green"))
6522 (unless (color-values color)
6523 (error "No such color: %S" color))
6525 (generate-new-buffer (format "originally: %s" color)))
6526 (kill-all-local-variables)
6527 (setq major-mode 'colorcomp-mode
6528 mode-name "Color Components")
6529 (use-local-map colorcomp-mode-map)
6531 (buffer-disable-undo)
6532 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
6533 (color-values color))))
6534 (ewoc (ewoc-create 'colorcomp-pp
6535 "\nColor Components\n\n"
6536 (substitute-command-keys
6537 "\n\\@{colorcomp-mode-map@}"))))
6538 (set (make-local-variable 'colorcomp-data) data)
6539 (set (make-local-variable 'colorcomp-ewoc) ewoc)
6540 (ewoc-enter-last ewoc 0)
6541 (ewoc-enter-last ewoc 1)
6542 (ewoc-enter-last ewoc 2)
6543 (ewoc-enter-last ewoc nil)))
6546 @cindex controller part, model/view/controller
6547 This example can be extended to be a color selection widget (in
6548 other words, the ``controller'' part of the ``model--view--controller''
6549 design paradigm) by defining commands to modify @code{colorcomp-data}
6550 and to finish the selection process, and a keymap to tie it all
6551 together conveniently.
6554 (defun colorcomp-mod (index limit delta)
6555 (let ((cur (aref colorcomp-data index)))
6556 (unless (= limit cur)
6557 (aset colorcomp-data index (+ cur delta)))
6560 (ewoc-nth colorcomp-ewoc index)
6561 (ewoc-nth colorcomp-ewoc -1))))
6563 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
6564 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
6565 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
6566 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
6567 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
6568 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
6570 (defun colorcomp-copy-as-kill-and-exit ()
6571 "Copy the color components into the kill ring and kill the buffer.
6572 The string is formatted #RRGGBB (hash followed by six hex digits)."
6574 (kill-new (format "#%02X%02X%02X"
6575 (aref colorcomp-data 0)
6576 (aref colorcomp-data 1)
6577 (aref colorcomp-data 2)))
6580 (setq colorcomp-mode-map
6581 (let ((m (make-sparse-keymap)))
6583 (define-key m "i" 'colorcomp-R-less)
6584 (define-key m "o" 'colorcomp-R-more)
6585 (define-key m "k" 'colorcomp-G-less)
6586 (define-key m "l" 'colorcomp-G-more)
6587 (define-key m "," 'colorcomp-B-less)
6588 (define-key m "." 'colorcomp-B-more)
6589 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
6593 Note that we never modify the data in each node, which is fixed when the
6594 ewoc is created to be either @code{nil} or an index into the vector
6595 @code{colorcomp-data}, the actual color components.
6598 @section Blinking Parentheses
6599 @cindex parenthesis matching
6600 @cindex blinking parentheses
6601 @cindex balancing parentheses
6603 This section describes the mechanism by which Emacs shows a matching
6604 open parenthesis when the user inserts a close parenthesis.
6606 @defvar blink-paren-function
6607 The value of this variable should be a function (of no arguments) to
6608 be called whenever a character with close parenthesis syntax is inserted.
6609 The value of @code{blink-paren-function} may be @code{nil}, in which
6610 case nothing is done.
6613 @defopt blink-matching-paren
6614 If this variable is @code{nil}, then @code{blink-matching-open} does
6618 @defopt blink-matching-paren-distance
6619 This variable specifies the maximum distance to scan for a matching
6620 parenthesis before giving up.
6623 @defopt blink-matching-delay
6624 This variable specifies the number of seconds to keep indicating the
6625 matching parenthesis. A fraction of a second often gives good
6626 results, but the default is 1, which works on all systems.
6629 @deffn Command blink-matching-open
6630 This function is the default value of @code{blink-paren-function}. It
6631 assumes that point follows a character with close parenthesis syntax
6632 and applies the appropriate effect momentarily to the matching opening
6633 character. If that character is not already on the screen, it
6634 displays the character's context in the echo area. To avoid long
6635 delays, this function does not search farther than
6636 @code{blink-matching-paren-distance} characters.
6638 Here is an example of calling this function explicitly.
6642 (defun interactive-blink-matching-open ()
6643 "Indicate momentarily the start of parenthesized sexp before point."
6647 (let ((blink-matching-paren-distance
6649 (blink-matching-paren t))
6650 (blink-matching-open)))
6655 @node Character Display
6656 @section Character Display
6658 This section describes how characters are actually displayed by
6659 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6660 graphical symbol which occupies one character position on the screen),
6661 whose appearance corresponds to the character itself. For example,
6662 the character @samp{a} (character code 97) is displayed as @samp{a}.
6663 Some characters, however, are displayed specially. For example, the
6664 formfeed character (character code 12) is usually displayed as a
6665 sequence of two glyphs, @samp{^L}, while the newline character
6666 (character code 10) starts a new screen line.
6668 You can modify how each character is displayed by defining a
6669 @dfn{display table}, which maps each character code into a sequence of
6670 glyphs. @xref{Display Tables}.
6673 * Usual Display:: The usual conventions for displaying characters.
6674 * Display Tables:: What a display table consists of.
6675 * Active Display Table:: How Emacs selects a display table to use.
6676 * Glyphs:: How to define a glyph, and what glyphs mean.
6677 * Glyphless Chars:: How glyphless characters are drawn.
6681 @subsection Usual Display Conventions
6683 Here are the conventions for displaying each character code (in the
6684 absence of a display table, which can override these
6689 conventions; @pxref{Display Tables}).
6692 @cindex printable ASCII characters
6695 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6696 through 126 (consisting of numerals, English letters, and symbols like
6697 @samp{#}) are displayed literally.
6700 The tab character (character code 9) displays as whitespace stretching
6701 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6702 Emacs Manual}. The variable @code{tab-width} controls the number of
6703 spaces per tab stop (see below).
6706 The newline character (character code 10) has a special effect: it
6707 ends the preceding line and starts a new line.
6709 @cindex ASCII control characters
6711 The non-printable @dfn{@acronym{ASCII} control characters}---character
6712 codes 0 through 31, as well as the @key{DEL} character (character code
6713 127)---display in one of two ways according to the variable
6714 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6715 these characters are displayed as sequences of two glyphs, where the
6716 first glyph is @samp{^} (a display table can specify a glyph to use
6717 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6720 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6721 octal escapes (see below).
6723 This rule also applies to carriage return (character code 13), if that
6724 character appears in the buffer. But carriage returns usually do not
6725 appear in buffer text; they are eliminated as part of end-of-line
6726 conversion (@pxref{Coding System Basics}).
6728 @cindex octal escapes
6730 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6731 through 255 (@pxref{Text Representations}). These characters display
6732 as @dfn{octal escapes}: sequences of four glyphs, where the first
6733 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6734 digit characters representing the character code in octal. (A display
6735 table can specify a glyph to use instead of @samp{\}.)
6738 Each non-@acronym{ASCII} character with code above 255 is displayed
6739 literally, if the terminal supports it. If the terminal does not
6740 support it, the character is said to be @dfn{glyphless}, and it is
6741 usually displayed using a placeholder glyph. For example, if a
6742 graphical terminal has no font for a character, Emacs usually displays
6743 a box containing the character code in hexadecimal. @xref{Glyphless
6747 The above display conventions apply even when there is a display
6748 table, for any character whose entry in the active display table is
6749 @code{nil}. Thus, when you set up a display table, you need only
6750 specify the characters for which you want special behavior.
6752 The following variables affect how certain characters are displayed
6753 on the screen. Since they change the number of columns the characters
6754 occupy, they also affect the indentation functions. They also affect
6755 how the mode line is displayed; if you want to force redisplay of the
6756 mode line using the new values, call the function
6757 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6760 @cindex control characters in display
6761 This buffer-local variable controls how control characters are
6762 displayed. If it is non-@code{nil}, they are displayed as a caret
6763 followed by the character: @samp{^A}. If it is @code{nil}, they are
6764 displayed as octal escapes: a backslash followed by three octal
6765 digits, as in @samp{\001}.
6769 The value of this buffer-local variable is the spacing between tab
6770 stops used for displaying tab characters in Emacs buffers. The value
6771 is in units of columns, and the default is 8. Note that this feature
6772 is completely independent of the user-settable tab stops used by the
6773 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6776 @node Display Tables
6777 @subsection Display Tables
6779 @cindex display table
6780 A display table is a special-purpose char-table
6781 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6782 is used to override the usual character display conventions. This
6783 section describes how to make, inspect, and assign elements to a
6784 display table object.
6786 @defun make-display-table
6787 This creates and returns a display table. The table initially has
6788 @code{nil} in all elements.
6791 The ordinary elements of the display table are indexed by character
6792 codes; the element at index @var{c} says how to display the character
6793 code @var{c}. The value should be @code{nil} (which means to display
6794 the character @var{c} according to the usual display conventions;
6795 @pxref{Usual Display}), or a vector of glyph codes (which means to
6796 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6798 @strong{Warning:} if you use the display table to change the display
6799 of newline characters, the whole buffer will be displayed as one long
6802 The display table also has six @dfn{extra slots} which serve special
6803 purposes. Here is a table of their meanings; @code{nil} in any slot
6804 means to use the default for that slot, as stated below.
6808 The glyph for the end of a truncated screen line (the default for this
6809 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6810 arrows in the fringes to indicate truncation, so the display table has
6814 The glyph for the end of a continued line (the default is @samp{\}).
6815 On graphical terminals, Emacs uses curved arrows in the fringes to
6816 indicate continuation, so the display table has no effect.
6819 The glyph for indicating a character displayed as an octal character
6820 code (the default is @samp{\}).
6823 The glyph for indicating a control character (the default is @samp{^}).
6826 A vector of glyphs for indicating the presence of invisible lines (the
6827 default is @samp{...}). @xref{Selective Display}.
6830 The glyph used to draw the border between side-by-side windows (the
6831 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6832 when there are no scroll bars; if scroll bars are supported and in use,
6833 a scroll bar separates the two windows.
6836 For example, here is how to construct a display table that mimics
6837 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6838 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6841 (setq disptab (make-display-table))
6846 (vector (make-glyph-code ?^ 'escape-glyph)
6847 (make-glyph-code (+ i 64) 'escape-glyph)))))
6849 (vector (make-glyph-code ?^ 'escape-glyph)
6850 (make-glyph-code ?? 'escape-glyph)))))
6853 @defun display-table-slot display-table slot
6854 This function returns the value of the extra slot @var{slot} of
6855 @var{display-table}. The argument @var{slot} may be a number from 0 to
6856 5 inclusive, or a slot name (symbol). Valid symbols are
6857 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6858 @code{selective-display}, and @code{vertical-border}.
6861 @defun set-display-table-slot display-table slot value
6862 This function stores @var{value} in the extra slot @var{slot} of
6863 @var{display-table}. The argument @var{slot} may be a number from 0 to
6864 5 inclusive, or a slot name (symbol). Valid symbols are
6865 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6866 @code{selective-display}, and @code{vertical-border}.
6869 @defun describe-display-table display-table
6870 This function displays a description of the display table
6871 @var{display-table} in a help buffer.
6874 @deffn Command describe-current-display-table
6875 This command displays a description of the current display table in a
6879 @node Active Display Table
6880 @subsection Active Display Table
6881 @cindex active display table
6883 Each window can specify a display table, and so can each buffer.
6884 The window's display table, if there is one, takes precedence over the
6885 buffer's display table. If neither exists, Emacs tries to use the
6886 standard display table; if that is @code{nil}, Emacs uses the usual
6887 character display conventions (@pxref{Usual Display}).
6889 Note that display tables affect how the mode line is displayed, so
6890 if you want to force redisplay of the mode line using a new display
6891 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6893 @defun window-display-table &optional window
6894 This function returns @var{window}'s display table, or @code{nil} if
6895 there is none. The default for @var{window} is the selected window.
6898 @defun set-window-display-table window table
6899 This function sets the display table of @var{window} to @var{table}.
6900 The argument @var{table} should be either a display table or
6904 @defvar buffer-display-table
6905 This variable is automatically buffer-local in all buffers; its value
6906 specifies the buffer's display table. If it is @code{nil}, there is
6907 no buffer display table.
6910 @defvar standard-display-table
6911 The value of this variable is the standard display table, which is
6912 used when Emacs is displaying a buffer in a window with neither a
6913 window display table nor a buffer display table defined, or when Emacs
6914 is outputting text to the standard output or error streams. Although its
6915 default is typically @code{nil}, in an interactive session if the
6916 terminal cannot display curved quotes, its default maps curved quotes
6917 to ASCII approximations. @xref{Keys in Documentation}.
6920 The @file{disp-table} library defines several functions for changing
6921 the standard display table.
6928 A @dfn{glyph} is a graphical symbol which occupies a single
6929 character position on the screen. Each glyph is represented in Lisp
6930 as a @dfn{glyph code}, which specifies a character and optionally a
6931 face to display it in (@pxref{Faces}). The main use of glyph codes is
6932 as the entries of display tables (@pxref{Display Tables}). The
6933 following functions are used to manipulate glyph codes:
6935 @defun make-glyph-code char &optional face
6936 This function returns a glyph code representing char @var{char} with
6937 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6938 uses the default face; in that case, the glyph code is an integer. If
6939 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6943 @defun glyph-char glyph
6944 This function returns the character of glyph code @var{glyph}.
6947 @defun glyph-face glyph
6948 This function returns face of glyph code @var{glyph}, or @code{nil} if
6949 @var{glyph} uses the default face.
6953 You can set up a @dfn{glyph table} to change how glyph codes are
6954 actually displayed on text terminals. This feature is semi-obsolete;
6955 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6958 The value of this variable, if non-@code{nil}, is the current glyph
6959 table. It takes effect only on character terminals; on graphical
6960 displays, all glyphs are displayed literally. The glyph table should
6961 be a vector whose @var{g}th element specifies how to display glyph
6962 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6963 is unspecified. Each element should be one of the following:
6967 Display this glyph literally.
6970 Display this glyph by sending the specified string to the terminal.
6973 Display the specified glyph code instead.
6976 Any integer glyph code greater than or equal to the length of the
6977 glyph table is displayed literally.
6981 @node Glyphless Chars
6982 @subsection Glyphless Character Display
6983 @cindex glyphless characters
6985 @dfn{Glyphless characters} are characters which are displayed in a
6986 special way, e.g., as a box containing a hexadecimal code, instead of
6987 being displayed literally. These include characters which are
6988 explicitly defined to be glyphless, as well as characters for which
6989 there is no available font (on a graphical display), and characters
6990 which cannot be encoded by the terminal's coding system (on a text
6993 @defvar glyphless-char-display
6994 The value of this variable is a char-table which defines glyphless
6995 characters and how they are displayed. Each entry must be one of the
6996 following display methods:
7000 Display the character in the usual way.
7002 @item @code{zero-width}
7003 Don't display the character.
7005 @item @code{thin-space}
7006 Display a thin space, 1-pixel wide on graphical displays, or
7007 1-character wide on text terminals.
7009 @item @code{empty-box}
7010 Display an empty box.
7012 @item @code{hex-code}
7013 Display a box containing the Unicode codepoint of the character, in
7014 hexadecimal notation.
7016 @item an @acronym{ASCII} string
7017 Display a box containing that string. The string should contain at
7018 most 6 @acronym{ASCII} characters.
7020 @item a cons cell @code{(@var{graphical} . @var{text})}
7021 Display with @var{graphical} on graphical displays, and with
7022 @var{text} on text terminals. Both @var{graphical} and @var{text}
7023 must be one of the display methods described above.
7027 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
7028 @acronym{ASCII} string display methods are drawn with the
7029 @code{glyphless-char} face. On text terminals, a box is emulated by
7030 square brackets, @samp{[]}.
7032 The char-table has one extra slot, which determines how to display any
7033 character that cannot be displayed with any available font, or cannot
7034 be encoded by the terminal's coding system. Its value should be one
7035 of the above display methods, except @code{zero-width} or a cons cell.
7037 If a character has a non-@code{nil} entry in an active display table,
7038 the display table takes effect; in this case, Emacs does not consult
7039 @code{glyphless-char-display} at all.
7042 @defopt glyphless-char-display-control
7043 This user option provides a convenient way to set
7044 @code{glyphless-char-display} for groups of similar characters. Do
7045 not set its value directly from Lisp code; the value takes effect only
7046 via a custom @code{:set} function (@pxref{Variable Definitions}),
7047 which updates @code{glyphless-char-display}.
7049 Its value should be an alist of elements @code{(@var{group}
7050 . @var{method})}, where @var{group} is a symbol specifying a group of
7051 characters, and @var{method} is a symbol specifying how to display
7054 @var{group} should be one of the following:
7058 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
7059 excluding the newline and tab characters (normally displayed as escape
7060 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
7061 emacs, The GNU Emacs Manual}).
7064 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
7065 @code{U+009F} (normally displayed as octal escape sequences like
7068 @item format-control
7069 Characters of Unicode General Category [Cf], such as @samp{U+200E}
7070 (Left-to-Right Mark), but excluding characters that have graphic
7071 images, such as @samp{U+00AD} (Soft Hyphen).
7074 Characters for there is no suitable font, or which cannot be encoded
7075 by the terminal's coding system.
7078 @c FIXME: this can also be 'acronym', but that's not currently
7079 @c completely implemented; it applies only to the format-control
7080 @c group, and only works if the acronym is in 'char-acronym-table'.
7081 The @var{method} symbol should be one of @code{zero-width},
7082 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
7083 the same meanings as in @code{glyphless-char-display}, above.
7090 This section describes how to make Emacs ring the bell (or blink the
7091 screen) to attract the user's attention. Be conservative about how
7092 often you do this; frequent bells can become irritating. Also be
7093 careful not to use just beeping when signaling an error is more
7094 appropriate (@pxref{Errors}).
7096 @defun ding &optional do-not-terminate
7097 @cindex keyboard macro termination
7098 This function beeps, or flashes the screen (see @code{visible-bell} below).
7099 It also terminates any keyboard macro currently executing unless
7100 @var{do-not-terminate} is non-@code{nil}.
7103 @defun beep &optional do-not-terminate
7104 This is a synonym for @code{ding}.
7107 @defopt visible-bell
7108 This variable determines whether Emacs should flash the screen to
7109 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
7110 This is effective on graphical displays, and on text terminals
7111 provided the terminal's Termcap entry defines the visible bell
7112 capability (@samp{vb}).
7115 @defopt ring-bell-function
7116 If this is non-@code{nil}, it specifies how Emacs should ring the
7117 bell. Its value should be a function of no arguments. If this is
7118 non-@code{nil}, it takes precedence over the @code{visible-bell}
7122 @node Window Systems
7123 @section Window Systems
7125 Emacs works with several window systems, most notably the X Window
7126 System. Both Emacs and X use the term ``window'', but use it
7127 differently. An Emacs frame is a single window as far as X is
7128 concerned; the individual Emacs windows are not known to X at all.
7130 @defvar window-system
7131 This terminal-local variable tells Lisp programs what window system
7132 Emacs is using for displaying the frame. The possible values are
7136 @cindex X Window System
7137 Emacs is displaying the frame using X.
7139 Emacs is displaying the frame using native MS-Windows GUI.
7141 Emacs is displaying the frame using the Nextstep interface (used on
7144 Emacs is displaying the frame using MS-DOS direct screen writes.
7146 Emacs is displaying the frame on a character-based terminal.
7150 @defvar initial-window-system
7151 This variable holds the value of @code{window-system} used for the
7152 first frame created by Emacs during startup. (When Emacs is invoked
7153 as a daemon, it does not create any initial
7154 frames, so @code{initial-window-system} is @code{nil}, except on
7155 MS-Windows, where it is still @code{w32}. @xref{Initial Options,
7156 daemon,, emacs, The GNU Emacs Manual}.)
7159 @defun window-system &optional frame
7160 This function returns a symbol whose name tells what window system is
7161 used for displaying @var{frame} (which defaults to the currently
7162 selected frame). The list of possible symbols it returns is the same
7163 one documented for the variable @code{window-system} above.
7166 Do @emph{not} use @code{window-system} and
7167 @code{initial-window-system} as predicates or boolean flag variables,
7168 if you want to write code that works differently on text terminals and
7169 graphic displays. That is because @code{window-system} is not a good
7170 indicator of Emacs capabilities on a given display type. Instead, use
7171 @code{display-graphic-p} or any of the other @code{display-*-p}
7172 predicates described in @ref{Display Feature Testing}.
7177 @dfn{Tooltips} are special frames (@pxref{Frames}) that are used to
7178 display helpful hints (a.k.a.@: ``tips'') related to the current
7179 position of the mouse pointer. Emacs uses tooltips to display help
7180 strings about active portions of text (@pxref{Special Properties}) and
7181 about various UI elements, such as menu items (@pxref{Extended Menu
7182 Items}) and tool-bar buttons (@pxref{Tool Bar}).
7185 Tooltip Mode is a minor mode that enables display of tooltips.
7186 Turning off this mode causes the tooltips be displayed in the echo
7187 area. On text-mode (a.k.a.@: ``TTY'') frames, tooltips are always
7188 displayed in the echo area.
7191 @vindex x-gtk-use-system-tooltips
7192 When Emacs is built with GTK+ support, it by default displays tooltips
7193 using GTK+ functions, and the appearance of the tooltips is then
7194 controlled by GTK+ settings. GTK+ tooltips can be disabled by
7195 changing the value of the variable @code{x-gtk-use-system-tooltips} to
7196 @code{nil}. The rest of this subsection describes how to control
7197 non-GTK+ tooltips, which are presented by Emacs itself.
7199 @cindex tooltip frames
7200 Tooltips are displayed in special frames called tooltip frames, which
7201 have their own frame parameters (@pxref{Frame Parameters}). Unlike
7202 other frames, the default parameters for tooltip frames are stored in a
7205 @defvar tooltip-frame-parameters
7206 This customizable option holds the default frame parameters used for
7207 displaying tooltips. Any font and color parameters are ignored, and the
7208 corresponding attributes of the @code{tooltip} face are used instead.
7209 If @code{left} or @code{top} parameters are included, they are used as
7210 absolute frame-relative coordinates where the tooltip should be shown.
7211 (Mouse-relative position of the tooltip can be customized using the
7212 variables described in @ref{Tooltips,,, emacs, The GNU Emacs Manual}.)
7213 Note that the @code{left} and @code{top} parameters, if present,
7214 override the values of mouse-relative offsets.
7217 @vindex tooltip@r{ face}
7218 The @code{tooltip} face determines the appearance of text shown in
7219 tooltips. It should generally use a variable-pitch font of size that
7220 is preferably smaller than the default frame font.
7222 @findex tooltip-help-tips
7223 @defvar tooltip-functions
7224 This abnormal hook is a list of functions to call when Emacs needs to
7225 display a tooltip. Each function is called with a single argument
7226 @var{event} which is a copy of the last mouse movement event. If a
7227 function on this list actually displays the tooltip, it should return
7228 non-@code{nil}, and then the rest of the functions will not be
7229 called. The default value of this variable is a single function
7230 @code{tooltip-help-tips}.
7233 If you write your own function to be put on the
7234 @code{tooltip-functions} list, you may need to know the buffer of the
7235 mouse event that triggered the tooltip display. The following
7236 function provides that information.
7238 @defun tooltip-event-buffer event
7239 This function returns the buffer over which @var{event} occurred.
7240 Call it with the argument of the function from
7241 @code{tooltip-functions} to obtain the buffer whose text triggered the
7242 tooltip. Note that the event might occur not over a buffer (e.g.,
7243 over the tool bar), in which case this function will return
7247 Other aspects of tooltip display are controlled by several
7248 customizable settings; see @ref{Tooltips,,, emacs, The GNU Emacs
7251 @node Bidirectional Display
7252 @section Bidirectional Display
7253 @cindex bidirectional display
7254 @cindex right-to-left text
7256 Emacs can display text written in scripts, such as Arabic, Farsi,
7257 and Hebrew, whose natural ordering for horizontal text display runs
7258 from right to left. Furthermore, segments of Latin script and digits
7259 embedded in right-to-left text are displayed left-to-right, while
7260 segments of right-to-left script embedded in left-to-right text
7261 (e.g., Arabic or Hebrew text in comments or strings in a program
7262 source file) are appropriately displayed right-to-left. We call such
7263 mixtures of left-to-right and right-to-left text @dfn{bidirectional
7264 text}. This section describes the facilities and options for editing
7265 and displaying bidirectional text.
7267 @cindex logical order
7268 @cindex reading order
7269 @cindex visual order
7270 @cindex unicode bidirectional algorithm
7272 @cindex bidirectional reordering
7273 @cindex reordering, of bidirectional text
7274 Text is stored in Emacs buffers and strings in @dfn{logical} (or
7275 @dfn{reading}) order, i.e., the order in which a human would read
7276 each character. In right-to-left and bidirectional text, the order in
7277 which characters are displayed on the screen (called @dfn{visual
7278 order}) is not the same as logical order; the characters' screen
7279 positions do not increase monotonically with string or buffer
7280 position. In performing this @dfn{bidirectional reordering}, Emacs
7281 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
7282 which is described in Annex #9 of the Unicode standard
7283 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
7284 Bidirectionality'' class implementation of the @acronym{UBA},
7285 consistent with the requirements of the Unicode Standard v8.0.
7287 @defvar bidi-display-reordering
7288 If the value of this buffer-local variable is non-@code{nil} (the
7289 default), Emacs performs bidirectional reordering for display. The
7290 reordering affects buffer text, as well as display strings and overlay
7291 strings from text and overlay properties in the buffer (@pxref{Overlay
7292 Properties}, and @pxref{Display Property}). If the value is
7293 @code{nil}, Emacs does not perform bidirectional reordering in the
7296 The default value of @code{bidi-display-reordering} controls the
7297 reordering of strings which are not directly supplied by a buffer,
7298 including the text displayed in mode lines (@pxref{Mode Line Format})
7299 and header lines (@pxref{Header Lines}).
7302 @cindex unibyte buffers, and bidi reordering
7303 Emacs never reorders the text of a unibyte buffer, even if
7304 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
7305 is because unibyte buffers contain raw bytes, not characters, and thus
7306 lack the directionality properties required for reordering.
7307 Therefore, to test whether text in a buffer will be reordered for
7308 display, it is not enough to test the value of
7309 @code{bidi-display-reordering} alone. The correct test is this:
7312 (if (and enable-multibyte-characters
7313 bidi-display-reordering)
7314 ;; Buffer is being reordered for display
7318 However, unibyte display and overlay strings @emph{are} reordered if
7319 their parent buffer is reordered. This is because plain-@sc{ascii}
7320 strings are stored by Emacs as unibyte strings. If a unibyte display
7321 or overlay string includes non-@sc{ascii} characters, these characters
7322 are assumed to have left-to-right direction.
7324 @cindex display properties, and bidi reordering of text
7325 Text covered by @code{display} text properties, by overlays with
7326 @code{display} properties whose value is a string, and by any other
7327 properties that replace buffer text, is treated as a single unit when
7328 it is reordered for display. That is, the entire chunk of text
7329 covered by these properties is reordered together. Moreover, the
7330 bidirectional properties of the characters in such a chunk of text are
7331 ignored, and Emacs reorders them as if they were replaced with a
7332 single character @code{U+FFFC}, known as the @dfn{Object Replacement
7333 Character}. This means that placing a display property over a portion
7334 of text may change the way that the surrounding text is reordered for
7335 display. To prevent this unexpected effect, always place such
7336 properties on text whose directionality is identical with text that
7339 @cindex base direction of a paragraph
7340 Each paragraph of bidirectional text has a @dfn{base direction},
7341 either right-to-left or left-to-right. Left-to-right paragraphs are
7342 displayed beginning at the left margin of the window, and are
7343 truncated or continued when the text reaches the right margin.
7344 Right-to-left paragraphs are displayed beginning at the right margin,
7345 and are continued or truncated at the left margin.
7347 By default, Emacs determines the base direction of each paragraph by
7348 looking at the text at its beginning. The precise method of
7349 determining the base direction is specified by the @acronym{UBA}; in a
7350 nutshell, the first character in a paragraph that has an explicit
7351 directionality determines the base direction of the paragraph.
7352 However, sometimes a buffer may need to force a certain base direction
7353 for its paragraphs. For example, buffers containing program source
7354 code should force all paragraphs to be displayed left-to-right. You
7355 can use following variable to do this:
7357 @defvar bidi-paragraph-direction
7358 If the value of this buffer-local variable is the symbol
7359 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
7360 buffer are assumed to have that specified direction. Any other value
7361 is equivalent to @code{nil} (the default), which means to determine
7362 the base direction of each paragraph from its contents.
7364 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
7365 Modes for program source code should set this to @code{left-to-right}.
7366 Prog mode does this by default, so modes derived from Prog mode do not
7367 need to set this explicitly (@pxref{Basic Major Modes}).
7370 @defun current-bidi-paragraph-direction &optional buffer
7371 This function returns the paragraph direction at point in the named
7372 @var{buffer}. The returned value is a symbol, either
7373 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
7374 omitted or @code{nil}, it defaults to the current buffer. If the
7375 buffer-local value of the variable @code{bidi-paragraph-direction} is
7376 non-@code{nil}, the returned value will be identical to that value;
7377 otherwise, the returned value reflects the paragraph direction
7378 determined dynamically by Emacs. For buffers whose value of
7379 @code{bidi-display-reordering} is @code{nil} as well as unibyte
7380 buffers, this function always returns @code{left-to-right}.
7383 @cindex visual-order cursor motion
7384 Sometimes there's a need to move point in strict visual order,
7385 either to the left or to the right of its current screen position.
7386 Emacs provides a primitive to do that.
7388 @defun move-point-visually direction
7389 This function moves point of the currently selected window to the
7390 buffer position that appears immediately to the right or to the left
7391 of point on the screen. If @var{direction} is positive, point will
7392 move one screen position to the right, otherwise it will move one
7393 screen position to the left. Note that, depending on the surrounding
7394 bidirectional context, this could potentially move point many buffer
7395 positions away. If invoked at the end of a screen line, the function
7396 moves point to the rightmost or leftmost screen position of the next
7397 or previous screen line, as appropriate for the value of
7400 The function returns the new buffer position as its value.
7403 @cindex layout on display, and bidirectional text
7404 @cindex jumbled display of bidirectional text
7405 @cindex concatenating bidirectional strings
7406 Bidirectional reordering can have surprising and unpleasant effects
7407 when two strings with bidirectional content are juxtaposed in a
7408 buffer, or otherwise programmatically concatenated into a string of
7409 text. A typical problematic case is when a buffer consists of
7410 sequences of text fields separated by whitespace or punctuation
7411 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
7412 punctuation characters used as separators have @dfn{weak
7413 directionality}, they take on the directionality of surrounding text.
7414 As result, a numeric field that follows a field with bidirectional
7415 content can be displayed @emph{to the left} of the preceding field,
7416 messing up the expected layout. There are several ways to avoid this
7421 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
7422 @acronym{LRM}, to the end of each field that may have bidirectional
7423 content, or prepend it to the beginning of the following field. The
7424 function @code{bidi-string-mark-left-to-right}, described below, comes
7425 in handy for this purpose. (In a right-to-left paragraph, use
7426 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
7427 is one of the solutions recommended by the UBA.
7430 Include the tab character in the field separator. The tab character
7431 plays the role of @dfn{segment separator} in bidirectional reordering,
7432 causing the text on either side to be reordered separately.
7434 @cindex @code{space} display spec, and bidirectional text
7436 Separate fields with a @code{display} property or overlay with a
7437 property value of the form @code{(space . PROPS)} (@pxref{Specified
7438 Space}). Emacs treats this display specification as a @dfn{paragraph
7439 separator}, and reorders the text on either side separately.
7442 @defun bidi-string-mark-left-to-right string
7443 This function returns its argument @var{string}, possibly modified,
7444 such that the result can be safely concatenated with another string,
7445 or juxtaposed with another string in a buffer, without disrupting the
7446 relative layout of this string and the next one on display. If the
7447 string returned by this function is displayed as part of a
7448 left-to-right paragraph, it will always appear on display to the left
7449 of the text that follows it. The function works by examining the
7450 characters of its argument, and if any of those characters could cause
7451 reordering on display, the function appends the @acronym{LRM}
7452 character to the string. The appended @acronym{LRM} character is made
7453 invisible by giving it an @code{invisible} text property of @code{t}
7454 (@pxref{Invisible Text}).
7457 The reordering algorithm uses the bidirectional properties of the
7458 characters stored as their @code{bidi-class} property
7459 (@pxref{Character Properties}). Lisp programs can change these
7460 properties by calling the @code{put-char-code-property} function.
7461 However, doing this requires a thorough understanding of the
7462 @acronym{UBA}, and is therefore not recommended. Any changes to the
7463 bidirectional properties of a character have global effect: they
7464 affect all Emacs frames and windows.
7466 Similarly, the @code{mirroring} property is used to display the
7467 appropriate mirrored character in the reordered text. Lisp programs
7468 can affect the mirrored display by changing this property. Again, any
7469 such changes affect all of Emacs display.
7471 @cindex overriding bidirectional properties
7472 @cindex directional overrides
7475 The bidirectional properties of characters can be overridden by
7476 inserting into the text special directional control characters,
7477 LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
7478 (@acronym{RLO}). Any characters between a @acronym{RLO} and the
7479 following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
7480 control character, whichever comes first, will be displayed as if they
7481 were strong right-to-left characters, i.e.@: they will be reversed on
7482 display. Similarly, any characters between @acronym{LRO} and
7483 @acronym{PDF} or newline will display as if they were strong
7484 left-to-right, and will @emph{not} be reversed even if they are strong
7485 right-to-left characters.
7487 @cindex phishing using directional overrides
7488 @cindex malicious use of directional overrides
7489 These overrides are useful when you want to make some text
7490 unaffected by the reordering algorithm, and instead directly control
7491 the display order. But they can also be used for malicious purposes,
7492 known as @dfn{phishing}. Specifically, a URL on a Web page or a link
7493 in an email message can be manipulated to make its visual appearance
7494 unrecognizable, or similar to some popular benign location, while the
7495 real location, interpreted by a browser in the logical order, is very
7498 Emacs provides a primitive that applications can use to detect
7499 instances of text whose bidirectional properties were overridden so as
7500 to make a left-to-right character display as if it were a
7501 right-to-left character, or vise versa.
7503 @defun bidi-find-overridden-directionality from to &optional object
7504 This function looks at the text of the specified @var{object} between
7505 positions @var{from} (inclusive) and @var{to} (exclusive), and returns
7506 the first position where it finds a strong left-to-right character
7507 whose directional properties were forced to display the character as
7508 right-to-left, or for a strong right-to-left character that was forced
7509 to display as left-to-right. If it finds no such characters in the
7510 specified region of text, it returns @code{nil}.
7512 The optional argument @var{object} specifies which text to search, and
7513 defaults to the current buffer. If @var{object} is non-@code{nil}, it
7514 can be some other buffer, or it can be a string or a window. If it is
7515 a string, the function searches that string. If it is a window, the
7516 function searches the buffer displayed in that window. If a buffer
7517 whose text you want to examine is displayed in some window, we
7518 recommend to specify it by that window, rather than pass the buffer to
7519 the function. This is because telling the function about the window
7520 allows it to correctly account for window-specific overlays, which
7521 might change the result of the function if some text in the buffer is
7522 covered by overlays.
7525 @cindex copying bidirectional text, preserve visual order
7526 @cindex visual order, preserve when copying bidirectional text
7527 When text that includes mixed right-to-left and left-to-right
7528 characters and bidirectional controls is copied into a different
7529 location, it can change its visual appearance, and also can affect the
7530 visual appearance of the surrounding text at destination. This is
7531 because reordering of bidirectional text specified by the
7532 @acronym{UBA} has non-trivial context-dependent effects both on the
7533 copied text and on the text at copy destination that will surround it.
7535 Sometimes, a Lisp program may need to preserve the exact visual
7536 appearance of the copied text at destination, and of the text that
7537 surrounds the copy. Lisp programs can use the following function to
7538 achieve that effect.
7540 @defun buffer-substring-with-bidi-context start end &optional no-properties
7541 This function works similar to @code{buffer-substring} (@pxref{Buffer
7542 Contents}), but it prepends and appends to the copied text bidi
7543 directional control characters necessary to preserve the visual
7544 appearance of the text when it is inserted at another place. Optional
7545 argument @var{no-properties}, if non-@code{nil}, means remove the text
7546 properties from the copy of the text.