2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000, 2001,
4 @c 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/text
7 @node Text, Non-ASCII Characters, Markers, Top
11 This chapter describes the functions that deal with the text in a
12 buffer. Most examine, insert, or delete text in the current buffer,
13 often operating at point or on text adjacent to point. Many are
14 interactive. All the functions that change the text provide for undoing
15 the changes (@pxref{Undo}).
17 Many text-related functions operate on a region of text defined by two
18 buffer positions passed in arguments named @var{start} and @var{end}.
19 These arguments should be either markers (@pxref{Markers}) or numeric
20 character positions (@pxref{Positions}). The order of these arguments
21 does not matter; it is all right for @var{start} to be the end of the
22 region and @var{end} the beginning. For example, @code{(delete-region 1
23 10)} and @code{(delete-region 10 1)} are equivalent. An
24 @code{args-out-of-range} error is signaled if either @var{start} or
25 @var{end} is outside the accessible portion of the buffer. In an
26 interactive call, point and the mark are used for these arguments.
28 @cindex buffer contents
29 Throughout this chapter, ``text'' refers to the characters in the
30 buffer, together with their properties (when relevant). Keep in mind
31 that point is always between two characters, and the cursor appears on
32 the character after point.
35 * Near Point:: Examining text in the vicinity of point.
36 * Buffer Contents:: Examining text in a general fashion.
37 * Comparing Text:: Comparing substrings of buffers.
38 * Insertion:: Adding new text to a buffer.
39 * Commands for Insertion:: User-level commands to insert text.
40 * Deletion:: Removing text from a buffer.
41 * User-Level Deletion:: User-level commands to delete text.
42 * The Kill Ring:: Where removed text sometimes is saved for later use.
43 * Undo:: Undoing changes to the text of a buffer.
44 * Maintaining Undo:: How to enable and disable undo information.
45 How to control how much information is kept.
46 * Filling:: Functions for explicit filling.
47 * Margins:: How to specify margins for filling commands.
48 * Adaptive Fill:: Adaptive Fill mode chooses a fill prefix from context.
49 * Auto Filling:: How auto-fill mode is implemented to break lines.
50 * Sorting:: Functions for sorting parts of the buffer.
51 * Columns:: Computing horizontal positions, and using them.
52 * Indentation:: Functions to insert or adjust indentation.
53 * Case Changes:: Case conversion of parts of the buffer.
54 * Text Properties:: Assigning Lisp property lists to text characters.
55 * Substitution:: Replacing a given character wherever it appears.
56 * Transposition:: Swapping two portions of a buffer.
57 * Registers:: How registers are implemented. Accessing the text or
58 position stored in a register.
59 * Base 64:: Conversion to or from base 64 encoding.
60 * MD5 Checksum:: Compute the MD5 ``message digest''/``checksum''.
61 * Atomic Changes:: Installing several buffer changes ``atomically''.
62 * Change Hooks:: Supplying functions to be run when text is changed.
66 @section Examining Text Near Point
68 Many functions are provided to look at the characters around point.
69 Several simple functions are described here. See also @code{looking-at}
70 in @ref{Regexp Search}.
72 In the following four functions, ``beginning'' or ``end'' of buffer
73 refers to the beginning or end of the accessible portion.
75 @defun char-after &optional position
76 This function returns the character in the current buffer at (i.e.,
77 immediately after) position @var{position}. If @var{position} is out of
78 range for this purpose, either before the beginning of the buffer, or at
79 or beyond the end, then the value is @code{nil}. The default for
80 @var{position} is point.
82 In the following example, assume that the first character in the
87 (char-to-string (char-after 1))
93 @defun char-before &optional position
94 This function returns the character in the current buffer immediately
95 before position @var{position}. If @var{position} is out of range for
96 this purpose, either at or before the beginning of the buffer, or beyond
97 the end, then the value is @code{nil}. The default for
98 @var{position} is point.
101 @defun following-char
102 This function returns the character following point in the current
103 buffer. This is similar to @code{(char-after (point))}. However, if
104 point is at the end of the buffer, then @code{following-char} returns 0.
106 Remember that point is always between characters, and the terminal
107 cursor normally appears over the character following point. Therefore,
108 the character returned by @code{following-char} is the character the
111 In this example, point is between the @samp{a} and the @samp{c}.
115 ---------- Buffer: foo ----------
116 Gentlemen may cry ``Pea@point{}ce! Peace!,''
117 but there is no peace.
118 ---------- Buffer: foo ----------
122 (char-to-string (preceding-char))
124 (char-to-string (following-char))
130 @defun preceding-char
131 This function returns the character preceding point in the current
132 buffer. See above, under @code{following-char}, for an example. If
133 point is at the beginning of the buffer, @code{preceding-char} returns
138 This function returns @code{t} if point is at the beginning of the
139 buffer. If narrowing is in effect, this means the beginning of the
140 accessible portion of the text. See also @code{point-min} in
145 This function returns @code{t} if point is at the end of the buffer.
146 If narrowing is in effect, this means the end of accessible portion of
147 the text. See also @code{point-max} in @xref{Point}.
151 This function returns @code{t} if point is at the beginning of a line.
152 @xref{Text Lines}. The beginning of the buffer (or of its accessible
153 portion) always counts as the beginning of a line.
157 This function returns @code{t} if point is at the end of a line. The
158 end of the buffer (or of its accessible portion) is always considered
162 @node Buffer Contents
163 @section Examining Buffer Contents
165 This section describes functions that allow a Lisp program to
166 convert any portion of the text in the buffer into a string.
168 @defun buffer-substring start end
169 This function returns a string containing a copy of the text of the
170 region defined by positions @var{start} and @var{end} in the current
171 buffer. If the arguments are not positions in the accessible portion of
172 the buffer, @code{buffer-substring} signals an @code{args-out-of-range}
175 It is not necessary for @var{start} to be less than @var{end}; the
176 arguments can be given in either order. But most often the smaller
177 argument is written first.
179 If the text being copied has any text properties, these are copied into
180 the string along with the characters they belong to. @xref{Text
181 Properties}. However, overlays (@pxref{Overlays}) in the buffer and
182 their properties are ignored, not copied.
186 ---------- Buffer: foo ----------
187 This is the contents of buffer foo
189 ---------- Buffer: foo ----------
193 (buffer-substring 1 10)
194 @result{} "This is t"
197 (buffer-substring (point-max) 10)
198 @result{} "he contents of buffer foo
204 @defun buffer-substring-no-properties start end
205 This is like @code{buffer-substring}, except that it does not copy text
206 properties, just the characters themselves. @xref{Text Properties}.
209 @defun filter-buffer-substring start end &optional delete
210 This function passes the buffer text between @var{start} and @var{end}
211 through the filter functions specified by the variable
212 @code{buffer-substring-filters}, and returns the value from the last
213 filter function. If @code{buffer-substring-filters} is @code{nil},
214 the value is the unaltered text from the buffer, what
215 @code{buffer-substring} would return.
217 If @var{delete} is non-@code{nil}, this function deletes the text
218 between @var{start} and @var{end} after copying it, like
219 @code{delete-and-extract-region}.
221 Lisp code should use this function instead of @code{buffer-substring}
222 or @code{delete-and-extract-region} when copying into user-accessible
223 data structures such as the kill-ring, X clipboard, and registers.
224 Major and minor modes can add functions to
225 @code{buffer-substring-filters} to alter such text as it is copied out
229 @defvar buffer-substring-filters
230 This variable should be a list of functions that accept a single
231 argument, a string, and return a string.
232 @code{filter-buffer-substring} passes the buffer substring to the
233 first function in this list, and the return value of each function is
234 passed to the next function. The return value of the last function is
235 used as the return value of @code{filter-buffer-substring}.
237 As a special convention, point is set to the start of the buffer text
238 being operated on (i.e., the @var{start} argument for
239 @code{filter-buffer-substring}) before these functions are called.
241 If this variable is @code{nil}, no filtering is performed.
245 This function returns the contents of the entire accessible portion of
246 the current buffer as a string. It is equivalent to
249 (buffer-substring (point-min) (point-max))
254 ---------- Buffer: foo ----------
255 This is the contents of buffer foo
257 ---------- Buffer: foo ----------
260 @result{} "This is the contents of buffer foo
267 @defun current-word &optional strict really-word
268 This function returns the symbol (or word) at or near point, as a string.
269 The return value includes no text properties.
271 If the optional argument @var{really-word} is non-@code{nil}, it finds a
272 word; otherwise, it finds a symbol (which includes both word
273 characters and symbol constituent characters).
275 If the optional argument @var{strict} is non-@code{nil}, then point
276 must be in or next to the symbol or word---if no symbol or word is
277 there, the function returns @code{nil}. Otherwise, a nearby symbol or
278 word on the same line is acceptable.
281 @defun thing-at-point thing
282 Return the @var{thing} around or next to point, as a string.
284 The argument @var{thing} is a symbol which specifies a kind of syntactic
285 entity. Possibilities include @code{symbol}, @code{list}, @code{sexp},
286 @code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
287 @code{whitespace}, @code{line}, @code{page}, and others.
290 ---------- Buffer: foo ----------
291 Gentlemen may cry ``Pea@point{}ce! Peace!,''
292 but there is no peace.
293 ---------- Buffer: foo ----------
295 (thing-at-point 'word)
297 (thing-at-point 'line)
298 @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
299 (thing-at-point 'whitespace)
305 @section Comparing Text
306 @cindex comparing buffer text
308 This function lets you compare portions of the text in a buffer, without
309 copying them into strings first.
311 @defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
312 This function lets you compare two substrings of the same buffer or two
313 different buffers. The first three arguments specify one substring,
314 giving a buffer (or a buffer name) and two positions within the
315 buffer. The last three arguments specify the other substring in the
316 same way. You can use @code{nil} for @var{buffer1}, @var{buffer2}, or
317 both to stand for the current buffer.
319 The value is negative if the first substring is less, positive if the
320 first is greater, and zero if they are equal. The absolute value of
321 the result is one plus the index of the first differing characters
322 within the substrings.
324 This function ignores case when comparing characters
325 if @code{case-fold-search} is non-@code{nil}. It always ignores
328 Suppose the current buffer contains the text @samp{foobarbar
329 haha!rara!}; then in this example the two substrings are @samp{rbar }
330 and @samp{rara!}. The value is 2 because the first substring is greater
331 at the second character.
334 (compare-buffer-substrings nil 6 11 nil 16 21)
340 @section Inserting Text
341 @cindex insertion of text
342 @cindex text insertion
344 @cindex insertion before point
345 @cindex before point, insertion
346 @dfn{Insertion} means adding new text to a buffer. The inserted text
347 goes at point---between the character before point and the character
348 after point. Some insertion functions leave point before the inserted
349 text, while other functions leave it after. We call the former
350 insertion @dfn{after point} and the latter insertion @dfn{before point}.
352 Insertion relocates markers that point at positions after the
353 insertion point, so that they stay with the surrounding text
354 (@pxref{Markers}). When a marker points at the place of insertion,
355 insertion may or may not relocate the marker, depending on the marker's
356 insertion type (@pxref{Marker Insertion Types}). Certain special
357 functions such as @code{insert-before-markers} relocate all such markers
358 to point after the inserted text, regardless of the markers' insertion
361 Insertion functions signal an error if the current buffer is
362 read-only or if they insert within read-only text.
364 These functions copy text characters from strings and buffers along
365 with their properties. The inserted characters have exactly the same
366 properties as the characters they were copied from. By contrast,
367 characters specified as separate arguments, not part of a string or
368 buffer, inherit their text properties from the neighboring text.
370 The insertion functions convert text from unibyte to multibyte in
371 order to insert in a multibyte buffer, and vice versa---if the text
372 comes from a string or from a buffer. However, they do not convert
373 unibyte character codes 128 through 255 to multibyte characters, not
374 even if the current buffer is a multibyte buffer. @xref{Converting
377 @defun insert &rest args
378 This function inserts the strings and/or characters @var{args} into the
379 current buffer, at point, moving point forward. In other words, it
380 inserts the text before point. An error is signaled unless all
381 @var{args} are either strings or characters. The value is @code{nil}.
384 @defun insert-before-markers &rest args
385 This function inserts the strings and/or characters @var{args} into the
386 current buffer, at point, moving point forward. An error is signaled
387 unless all @var{args} are either strings or characters. The value is
390 This function is unlike the other insertion functions in that it
391 relocates markers initially pointing at the insertion point, to point
392 after the inserted text. If an overlay begins at the insertion point,
393 the inserted text falls outside the overlay; if a nonempty overlay
394 ends at the insertion point, the inserted text falls inside that
398 @defun insert-char character count &optional inherit
399 This function inserts @var{count} instances of @var{character} into the
400 current buffer before point. The argument @var{count} should be a
401 number, and @var{character} must be a character. The value is @code{nil}.
403 This function does not convert unibyte character codes 128 through 255
404 to multibyte characters, not even if the current buffer is a multibyte
405 buffer. @xref{Converting Representations}.
407 If @var{inherit} is non-@code{nil}, then the inserted characters inherit
408 sticky text properties from the two characters before and after the
409 insertion point. @xref{Sticky Properties}.
412 @defun insert-buffer-substring from-buffer-or-name &optional start end
413 This function inserts a portion of buffer @var{from-buffer-or-name}
414 (which must already exist) into the current buffer before point. The
415 text inserted is the region between @var{start} and @var{end}. (These
416 arguments default to the beginning and end of the accessible portion of
417 that buffer.) This function returns @code{nil}.
419 In this example, the form is executed with buffer @samp{bar} as the
420 current buffer. We assume that buffer @samp{bar} is initially empty.
424 ---------- Buffer: foo ----------
425 We hold these truths to be self-evident, that all
426 ---------- Buffer: foo ----------
430 (insert-buffer-substring "foo" 1 20)
433 ---------- Buffer: bar ----------
434 We hold these truth@point{}
435 ---------- Buffer: bar ----------
440 @defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
441 This is like @code{insert-buffer-substring} except that it does not
442 copy any text properties.
445 @xref{Sticky Properties}, for other insertion functions that inherit
446 text properties from the nearby text in addition to inserting it.
447 Whitespace inserted by indentation functions also inherits text
450 @node Commands for Insertion
451 @section User-Level Insertion Commands
453 This section describes higher-level commands for inserting text,
454 commands intended primarily for the user but useful also in Lisp
457 @deffn Command insert-buffer from-buffer-or-name
458 This command inserts the entire accessible contents of
459 @var{from-buffer-or-name} (which must exist) into the current buffer
460 after point. It leaves the mark after the inserted text. The value
464 @deffn Command self-insert-command count
465 @cindex character insertion
466 @cindex self-insertion
467 This command inserts the last character typed; it does so @var{count}
468 times, before point, and returns @code{nil}. Most printing characters
469 are bound to this command. In routine use, @code{self-insert-command}
470 is the most frequently called function in Emacs, but programs rarely use
471 it except to install it on a keymap.
473 In an interactive call, @var{count} is the numeric prefix argument.
475 This command calls @code{auto-fill-function} whenever that is
476 non-@code{nil} and the character inserted is in the table
477 @code{auto-fill-chars} (@pxref{Auto Filling}).
479 @c Cross refs reworded to prevent overfull hbox. --rjc 15mar92
480 This command performs abbrev expansion if Abbrev mode is enabled and
481 the inserted character does not have word-constituent
482 syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.)
484 This is also responsible for calling @code{blink-paren-function} when
485 the inserted character has close parenthesis syntax (@pxref{Blinking}).
487 Do not try substituting your own definition of
488 @code{self-insert-command} for the standard one. The editor command
489 loop handles this function specially.
492 @deffn Command newline &optional number-of-newlines
493 This command inserts newlines into the current buffer before point.
494 If @var{number-of-newlines} is supplied, that many newline characters
497 @cindex newline and Auto Fill mode
498 This function calls @code{auto-fill-function} if the current column
499 number is greater than the value of @code{fill-column} and
500 @var{number-of-newlines} is @code{nil}. Typically what
501 @code{auto-fill-function} does is insert a newline; thus, the overall
502 result in this case is to insert two newlines at different places: one
503 at point, and another earlier in the line. @code{newline} does not
504 auto-fill if @var{number-of-newlines} is non-@code{nil}.
506 This command indents to the left margin if that is not zero.
509 The value returned is @code{nil}. In an interactive call, @var{count}
510 is the numeric prefix argument.
513 @deffn Command split-line
514 This command splits the current line, moving the portion of the line
515 after point down vertically so that it is on the next line directly
516 below where it was before. Whitespace is inserted as needed at the
517 beginning of the lower line, using the @code{indent-to} function.
518 @code{split-line} returns the position of point.
520 Programs hardly ever use this function.
523 @defvar overwrite-mode
524 This variable controls whether overwrite mode is in effect. The value
525 should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
526 or @code{nil}. @code{overwrite-mode-textual} specifies textual
527 overwrite mode (treats newlines and tabs specially), and
528 @code{overwrite-mode-binary} specifies binary overwrite mode (treats
529 newlines and tabs like any other characters).
533 @section Deleting Text
535 @cindex deletion vs killing
536 Deletion means removing part of the text in a buffer, without saving
537 it in the kill ring (@pxref{The Kill Ring}). Deleted text can't be
538 yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
539 Some deletion functions do save text in the kill ring in some special
542 All of the deletion functions operate on the current buffer.
544 @deffn Command erase-buffer
545 This function deletes the entire text of the current buffer
546 (@emph{not} just the accessible portion), leaving it
547 empty. If the buffer is read-only, it signals a @code{buffer-read-only}
548 error; if some of the text in it is read-only, it signals a
549 @code{text-read-only} error. Otherwise, it deletes the text without
550 asking for any confirmation. It returns @code{nil}.
552 Normally, deleting a large amount of text from a buffer inhibits further
553 auto-saving of that buffer ``because it has shrunk''. However,
554 @code{erase-buffer} does not do this, the idea being that the future
555 text is not really related to the former text, and its size should not
556 be compared with that of the former text.
559 @deffn Command delete-region start end
560 This command deletes the text between positions @var{start} and
561 @var{end} in the current buffer, and returns @code{nil}. If point was
562 inside the deleted region, its value afterward is @var{start}.
563 Otherwise, point relocates with the surrounding text, as markers do.
566 @defun delete-and-extract-region start end
567 @tindex delete-and-extract-region
568 This function deletes the text between positions @var{start} and
569 @var{end} in the current buffer, and returns a string containing the
572 If point was inside the deleted region, its value afterward is
573 @var{start}. Otherwise, point relocates with the surrounding text, as
577 @deffn Command delete-char count &optional killp
578 This command deletes @var{count} characters directly after point, or
579 before point if @var{count} is negative. If @var{killp} is
580 non-@code{nil}, then it saves the deleted characters in the kill ring.
582 In an interactive call, @var{count} is the numeric prefix argument, and
583 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
584 argument is supplied, the text is saved in the kill ring. If no prefix
585 argument is supplied, then one character is deleted, but not saved in
588 The value returned is always @code{nil}.
591 @deffn Command delete-backward-char count &optional killp
592 @cindex delete previous char
593 This command deletes @var{count} characters directly before point, or
594 after point if @var{count} is negative. If @var{killp} is
595 non-@code{nil}, then it saves the deleted characters in the kill ring.
597 In an interactive call, @var{count} is the numeric prefix argument, and
598 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
599 argument is supplied, the text is saved in the kill ring. If no prefix
600 argument is supplied, then one character is deleted, but not saved in
603 The value returned is always @code{nil}.
606 @deffn Command backward-delete-char-untabify count &optional killp
608 This command deletes @var{count} characters backward, changing tabs
609 into spaces. When the next character to be deleted is a tab, it is
610 first replaced with the proper number of spaces to preserve alignment
611 and then one of those spaces is deleted instead of the tab. If
612 @var{killp} is non-@code{nil}, then the command saves the deleted
613 characters in the kill ring.
615 Conversion of tabs to spaces happens only if @var{count} is positive.
616 If it is negative, exactly @minus{}@var{count} characters after point
619 In an interactive call, @var{count} is the numeric prefix argument, and
620 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
621 argument is supplied, the text is saved in the kill ring. If no prefix
622 argument is supplied, then one character is deleted, but not saved in
625 The value returned is always @code{nil}.
628 @defopt backward-delete-char-untabify-method
629 This option specifies how @code{backward-delete-char-untabify} should
630 deal with whitespace. Possible values include @code{untabify}, the
631 default, meaning convert a tab to many spaces and delete one;
632 @code{hungry}, meaning delete all tabs and spaces before point with
633 one command; @code{all} meaning delete all tabs, spaces and newlines
634 before point, and @code{nil}, meaning do nothing special for
635 whitespace characters.
638 @node User-Level Deletion
639 @section User-Level Deletion Commands
641 This section describes higher-level commands for deleting text,
642 commands intended primarily for the user but useful also in Lisp
645 @deffn Command delete-horizontal-space &optional backward-only
646 @cindex deleting whitespace
647 This function deletes all spaces and tabs around point. It returns
650 If @var{backward-only} is non-@code{nil}, the function deletes
651 spaces and tabs before point, but not after point.
653 In the following examples, we call @code{delete-horizontal-space} four
654 times, once on each line, with point between the second and third
655 characters on the line each time.
659 ---------- Buffer: foo ----------
664 ---------- Buffer: foo ----------
668 (delete-horizontal-space) ; @r{Four times.}
671 ---------- Buffer: foo ----------
676 ---------- Buffer: foo ----------
681 @deffn Command delete-indentation &optional join-following-p
682 This function joins the line point is on to the previous line, deleting
683 any whitespace at the join and in some cases replacing it with one
684 space. If @var{join-following-p} is non-@code{nil},
685 @code{delete-indentation} joins this line to the following line
686 instead. The function returns @code{nil}.
688 If there is a fill prefix, and the second of the lines being joined
689 starts with the prefix, then @code{delete-indentation} deletes the
690 fill prefix before joining the lines. @xref{Margins}.
692 In the example below, point is located on the line starting
693 @samp{events}, and it makes no difference if there are trailing spaces
694 in the preceding line.
698 ---------- Buffer: foo ----------
699 When in the course of human
700 @point{} events, it becomes necessary
701 ---------- Buffer: foo ----------
708 ---------- Buffer: foo ----------
709 When in the course of human@point{} events, it becomes necessary
710 ---------- Buffer: foo ----------
714 After the lines are joined, the function @code{fixup-whitespace} is
715 responsible for deciding whether to leave a space at the junction.
718 @deffn Command fixup-whitespace
719 This function replaces all the horizontal whitespace surrounding point
720 with either one space or no space, according to the context. It
723 At the beginning or end of a line, the appropriate amount of space is
724 none. Before a character with close parenthesis syntax, or after a
725 character with open parenthesis or expression-prefix syntax, no space is
726 also appropriate. Otherwise, one space is appropriate. @xref{Syntax
729 In the example below, @code{fixup-whitespace} is called the first time
730 with point before the word @samp{spaces} in the first line. For the
731 second invocation, point is directly after the @samp{(}.
735 ---------- Buffer: foo ----------
736 This has too many @point{}spaces
737 This has too many spaces at the start of (@point{} this list)
738 ---------- Buffer: foo ----------
749 ---------- Buffer: foo ----------
750 This has too many spaces
751 This has too many spaces at the start of (this list)
752 ---------- Buffer: foo ----------
757 @deffn Command just-one-space &optional n
758 @comment !!SourceFile simple.el
759 This command replaces any spaces and tabs around point with a single
760 space, or @var{n} spaces if @var{n} is specified. It returns
764 @deffn Command delete-blank-lines
765 This function deletes blank lines surrounding point. If point is on a
766 blank line with one or more blank lines before or after it, then all but
767 one of them are deleted. If point is on an isolated blank line, then it
768 is deleted. If point is on a nonblank line, the command deletes all
769 blank lines immediately following it.
771 A blank line is defined as a line containing only tabs and spaces.
773 @code{delete-blank-lines} returns @code{nil}.
777 @section The Kill Ring
780 @dfn{Kill functions} delete text like the deletion functions, but save
781 it so that the user can reinsert it by @dfn{yanking}. Most of these
782 functions have @samp{kill-} in their name. By contrast, the functions
783 whose names start with @samp{delete-} normally do not save text for
784 yanking (though they can still be undone); these are ``deletion''
787 Most of the kill commands are primarily for interactive use, and are
788 not described here. What we do describe are the functions provided for
789 use in writing such commands. You can use these functions to write
790 commands for killing text. When you need to delete text for internal
791 purposes within a Lisp function, you should normally use deletion
792 functions, so as not to disturb the kill ring contents.
795 Killed text is saved for later yanking in the @dfn{kill ring}. This
796 is a list that holds a number of recent kills, not just the last text
797 kill. We call this a ``ring'' because yanking treats it as having
798 elements in a cyclic order. The list is kept in the variable
799 @code{kill-ring}, and can be operated on with the usual functions for
800 lists; there are also specialized functions, described in this section,
801 that treat it as a ring.
803 Some people think this use of the word ``kill'' is unfortunate, since
804 it refers to operations that specifically @emph{do not} destroy the
805 entities ``killed''. This is in sharp contrast to ordinary life, in
806 which death is permanent and ``killed'' entities do not come back to
807 life. Therefore, other metaphors have been proposed. For example, the
808 term ``cut ring'' makes sense to people who, in pre-computer days, used
809 scissors and paste to cut up and rearrange manuscripts. However, it
810 would be difficult to change the terminology now.
813 * Kill Ring Concepts:: What text looks like in the kill ring.
814 * Kill Functions:: Functions that kill text.
815 * Yanking:: How yanking is done.
816 * Yank Commands:: Commands that access the kill ring.
817 * Low-Level Kill Ring:: Functions and variables for kill ring access.
818 * Internals of Kill Ring:: Variables that hold kill ring data.
821 @node Kill Ring Concepts
822 @comment node-name, next, previous, up
823 @subsection Kill Ring Concepts
825 The kill ring records killed text as strings in a list, most recent
826 first. A short kill ring, for example, might look like this:
829 ("some text" "a different piece of text" "even older text")
833 When the list reaches @code{kill-ring-max} entries in length, adding a
834 new entry automatically deletes the last entry.
836 When kill commands are interwoven with other commands, each kill
837 command makes a new entry in the kill ring. Multiple kill commands in
838 succession build up a single kill ring entry, which would be yanked as a
839 unit; the second and subsequent consecutive kill commands add text to
840 the entry made by the first one.
842 For yanking, one entry in the kill ring is designated the ``front'' of
843 the ring. Some yank commands ``rotate'' the ring by designating a
844 different element as the ``front.'' But this virtual rotation doesn't
845 change the list itself---the most recent entry always comes first in the
849 @comment node-name, next, previous, up
850 @subsection Functions for Killing
852 @code{kill-region} is the usual subroutine for killing text. Any
853 command that calls this function is a ``kill command'' (and should
854 probably have @samp{kill} in its name). @code{kill-region} puts the
855 newly killed text in a new element at the beginning of the kill ring or
856 adds it to the most recent element. It determines automatically (using
857 @code{last-command}) whether the previous command was a kill command,
858 and if so appends the killed text to the most recent entry.
860 @deffn Command kill-region start end &optional yank-handler
861 This function kills the text in the region defined by @var{start} and
862 @var{end}. The text is deleted but saved in the kill ring, along with
863 its text properties. The value is always @code{nil}.
865 In an interactive call, @var{start} and @var{end} are point and
869 If the buffer or text is read-only, @code{kill-region} modifies the kill
870 ring just the same, then signals an error without modifying the buffer.
871 This is convenient because it lets the user use a series of kill
872 commands to copy text from a read-only buffer into the kill ring.
874 If @var{yank-handler} is non-@code{nil}, this puts that value onto
875 the string of killed text, as a @code{yank-handler} text property.
876 @xref{Yanking}. Note that if @var{yank-handler} is @code{nil}, any
877 @code{yank-handler} properties present on the killed text are copied
878 onto the kill ring, like other text properties.
881 @defopt kill-read-only-ok
882 If this option is non-@code{nil}, @code{kill-region} does not signal an
883 error if the buffer or text is read-only. Instead, it simply returns,
884 updating the kill ring but not changing the buffer.
887 @deffn Command copy-region-as-kill start end
888 This command saves the region defined by @var{start} and @var{end} on
889 the kill ring (including text properties), but does not delete the text
890 from the buffer. It returns @code{nil}.
892 The command does not set @code{this-command} to @code{kill-region}, so a
893 subsequent kill command does not append to the same kill ring entry.
895 Don't call @code{copy-region-as-kill} in Lisp programs unless you aim to
896 support Emacs 18. For newer Emacs versions, it is better to use
897 @code{kill-new} or @code{kill-append} instead. @xref{Low-Level Kill
904 Yanking means inserting text from the kill ring, but it does
905 not insert the text blindly. Yank commands and some other commands
906 use @code{insert-for-yank} to perform special processing on the
907 text that they copy into the buffer.
909 @defun insert-for-yank string
910 This function normally works like @code{insert} except that it doesn't
911 insert the text properties in the @code{yank-excluded-properties}
912 list. However, if any part of @var{string} has a non-@code{nil}
913 @code{yank-handler} text property, that property can do various
914 special processing on that part of the text being inserted.
917 @defun insert-buffer-substring-as-yank buf &optional start end
918 This function resembles @code{insert-buffer-substring} except that it
919 doesn't insert the text properties in the
920 @code{yank-excluded-properties} list.
923 You can put a @code{yank-handler} text property on all or part of
924 the text to control how it will be inserted if it is yanked. The
925 @code{insert-for-yank} function looks for that property. The property
926 value must be a list of one to four elements, with the following
927 format (where elements after the first may be omitted):
930 (@var{function} @var{param} @var{noexclude} @var{undo})
933 Here is what the elements do:
937 When @var{function} is present and non-@code{nil}, it is called instead of
938 @code{insert} to insert the string. @var{function} takes one
939 argument---the string to insert.
942 If @var{param} is present and non-@code{nil}, it replaces @var{string}
943 (or the part of @var{string} being processed) as the object passed to
944 @var{function} (or @code{insert}); for example, if @var{function} is
945 @code{yank-rectangle}, @var{param} should be a list of strings to
946 insert as a rectangle.
949 If @var{noexclude} is present and non-@code{nil}, the normal removal of the
950 yank-excluded-properties is not performed; instead @var{function} is
951 responsible for removing those properties. This may be necessary
952 if @var{function} adjusts point before or after inserting the object.
955 If @var{undo} is present and non-@code{nil}, it is a function that will be
956 called by @code{yank-pop} to undo the insertion of the current object.
957 It is called with two arguments, the start and end of the current
958 region. @var{function} can set @code{yank-undo-function} to override
959 the @var{undo} value.
963 @comment node-name, next, previous, up
964 @subsection Functions for Yanking
966 @dfn{Yanking} means reinserting an entry of previously killed text
967 from the kill ring. The text properties are copied too.
969 @deffn Command yank &optional arg
970 @cindex inserting killed text
971 This command inserts before point the text at the front of the
972 kill ring. It positions the mark at the beginning of that text, and
975 If @var{arg} is a non-@code{nil} list (which occurs interactively when
976 the user types @kbd{C-u} with no digits), then @code{yank} inserts the
977 text as described above, but puts point before the yanked text and
978 puts the mark after it.
980 If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
981 most recently killed text---the @var{arg}th element of the kill ring
982 list, counted cyclically from the front, which is considered the
983 first element for this purpose.
985 @code{yank} does not alter the contents of the kill ring, unless it
986 used text provided by another program, in which case it pushes that text
987 onto the kill ring. However if @var{arg} is an integer different from
988 one, it rotates the kill ring to place the yanked string at the front.
990 @code{yank} returns @code{nil}.
993 @deffn Command yank-pop &optional arg
994 This command replaces the just-yanked entry from the kill ring with a
995 different entry from the kill ring.
997 This is allowed only immediately after a @code{yank} or another
998 @code{yank-pop}. At such a time, the region contains text that was just
999 inserted by yanking. @code{yank-pop} deletes that text and inserts in
1000 its place a different piece of killed text. It does not add the deleted
1001 text to the kill ring, since it is already in the kill ring somewhere.
1002 It does however rotate the kill ring to place the newly yanked string at
1005 If @var{arg} is @code{nil}, then the replacement text is the previous
1006 element of the kill ring. If @var{arg} is numeric, the replacement is
1007 the @var{arg}th previous kill. If @var{arg} is negative, a more recent
1008 kill is the replacement.
1010 The sequence of kills in the kill ring wraps around, so that after the
1011 oldest one comes the newest one, and before the newest one goes the
1014 The return value is always @code{nil}.
1017 @defvar yank-undo-function
1018 If this variable is non-@code{nil}, the function @code{yank-pop} uses
1019 its value instead of @code{delete-region} to delete the text
1020 inserted by the previous @code{yank} or
1021 @code{yank-pop} command. The value must be a function of two
1022 arguments, the start and end of the current region.
1024 The function @code{insert-for-yank} automatically sets this variable
1025 according to the @var{undo} element of the @code{yank-handler}
1026 text property, if there is one.
1029 @node Low-Level Kill Ring
1030 @subsection Low-Level Kill Ring
1032 These functions and variables provide access to the kill ring at a
1033 lower level, but still convenient for use in Lisp programs, because they
1034 take care of interaction with window system selections
1035 (@pxref{Window System Selections}).
1037 @defun current-kill n &optional do-not-move
1038 The function @code{current-kill} rotates the yanking pointer, which
1039 designates the ``front'' of the kill ring, by @var{n} places (from newer
1040 kills to older ones), and returns the text at that place in the ring.
1042 If the optional second argument @var{do-not-move} is non-@code{nil},
1043 then @code{current-kill} doesn't alter the yanking pointer; it just
1044 returns the @var{n}th kill, counting from the current yanking pointer.
1046 If @var{n} is zero, indicating a request for the latest kill,
1047 @code{current-kill} calls the value of
1048 @code{interprogram-paste-function} (documented below) before
1049 consulting the kill ring. If that value is a function and calling it
1050 returns a string, @code{current-kill} pushes that string onto the kill
1051 ring and returns it. It also sets the yanking pointer to point to
1052 that new entry, regardless of the value of @var{do-not-move}.
1053 Otherwise, @code{current-kill} does not treat a zero value for @var{n}
1054 specially: it returns the entry pointed at by the yanking pointer and
1055 does not move the yanking pointer.
1058 @defun kill-new string &optional replace yank-handler
1059 This function pushes the text @var{string} onto the kill ring and
1060 makes the yanking pointer point to it. It discards the oldest entry
1061 if appropriate. It also invokes the value of
1062 @code{interprogram-cut-function} (see below).
1064 If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
1065 first element of the kill ring with @var{string}, rather than pushing
1066 @var{string} onto the kill ring.
1068 If @var{yank-handler} is non-@code{nil}, this puts that value onto
1069 the string of killed text, as a @code{yank-handler} property.
1070 @xref{Yanking}. Note that if @var{yank-handler} is @code{nil}, then
1071 @code{kill-new} copies any @code{yank-handler} properties present on
1072 @var{string} onto the kill ring, as it does with other text properties.
1075 @defun kill-append string before-p &optional yank-handler
1076 This function appends the text @var{string} to the first entry in the
1077 kill ring and makes the yanking pointer point to the combined entry.
1078 Normally @var{string} goes at the end of the entry, but if
1079 @var{before-p} is non-@code{nil}, it goes at the beginning. This
1080 function also invokes the value of @code{interprogram-cut-function}
1081 (see below). This handles @var{yank-handler} just like
1082 @code{kill-new}, except that if @var{yank-handler} is different from
1083 the @code{yank-handler} property of the first entry of the kill ring,
1084 @code{kill-append} pushes the concatenated string onto the kill ring,
1085 instead of replacing the original first entry with it.
1088 @defvar interprogram-paste-function
1089 This variable provides a way of transferring killed text from other
1090 programs, when you are using a window system. Its value should be
1091 @code{nil} or a function of no arguments.
1093 If the value is a function, @code{current-kill} calls it to get the
1094 ``most recent kill''. If the function returns a non-@code{nil} value,
1095 then that value is used as the ``most recent kill''. If it returns
1096 @code{nil}, then the front of the kill ring is used.
1098 The normal use of this hook is to get the window system's primary
1099 selection as the most recent kill, even if the selection belongs to
1100 another application. @xref{Window System Selections}.
1103 @defvar interprogram-cut-function
1104 This variable provides a way of communicating killed text to other
1105 programs, when you are using a window system. Its value should be
1106 @code{nil} or a function of one required and one optional argument.
1108 If the value is a function, @code{kill-new} and @code{kill-append} call
1109 it with the new first element of the kill ring as the first argument.
1110 The second, optional, argument has the same meaning as the @var{push}
1111 argument to @code{x-set-cut-buffer} (@pxref{Definition of
1112 x-set-cut-buffer}) and only affects the second and later cut buffers.
1114 The normal use of this hook is to set the window system's primary
1115 selection (and first cut buffer) from the newly killed text.
1116 @xref{Window System Selections}.
1119 @node Internals of Kill Ring
1120 @comment node-name, next, previous, up
1121 @subsection Internals of the Kill Ring
1123 The variable @code{kill-ring} holds the kill ring contents, in the
1124 form of a list of strings. The most recent kill is always at the front
1127 The @code{kill-ring-yank-pointer} variable points to a link in the
1128 kill ring list, whose @sc{car} is the text to yank next. We say it
1129 identifies the ``front'' of the ring. Moving
1130 @code{kill-ring-yank-pointer} to a different link is called
1131 @dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
1132 the functions that move the yank pointer wrap around from the end of the
1133 list to the beginning, or vice-versa. Rotation of the kill ring is
1134 virtual; it does not change the value of @code{kill-ring}.
1136 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
1137 variables whose values are normally lists. The word ``pointer'' in the
1138 name of the @code{kill-ring-yank-pointer} indicates that the variable's
1139 purpose is to identify one element of the list for use by the next yank
1142 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
1143 of the links in the kill ring list. The element it identifies is the
1144 @sc{car} of that link. Kill commands, which change the kill ring, also
1145 set this variable to the value of @code{kill-ring}. The effect is to
1146 rotate the ring so that the newly killed text is at the front.
1148 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
1149 pointing to the second entry in the kill ring @code{("some text" "a
1150 different piece of text" "yet older text")}.
1154 kill-ring ---- kill-ring-yank-pointer
1157 | --- --- --- --- --- ---
1158 --> | | |------> | | |--> | | |--> nil
1159 --- --- --- --- --- ---
1162 | | -->"yet older text"
1164 | --> "a different piece of text"
1171 This state of affairs might occur after @kbd{C-y} (@code{yank})
1172 immediately followed by @kbd{M-y} (@code{yank-pop}).
1175 This variable holds the list of killed text sequences, most recently
1179 @defvar kill-ring-yank-pointer
1180 This variable's value indicates which element of the kill ring is at the
1181 ``front'' of the ring for yanking. More precisely, the value is a tail
1182 of the value of @code{kill-ring}, and its @sc{car} is the kill string
1183 that @kbd{C-y} should yank.
1186 @defopt kill-ring-max
1187 The value of this variable is the maximum length to which the kill
1188 ring can grow, before elements are thrown away at the end. The default
1189 value for @code{kill-ring-max} is 60.
1193 @comment node-name, next, previous, up
1197 Most buffers have an @dfn{undo list}, which records all changes made
1198 to the buffer's text so that they can be undone. (The buffers that
1199 don't have one are usually special-purpose buffers for which Emacs
1200 assumes that undoing is not useful.) All the primitives that modify the
1201 text in the buffer automatically add elements to the front of the undo
1202 list, which is in the variable @code{buffer-undo-list}.
1204 @defvar buffer-undo-list
1205 This variable's value is the undo list of the current buffer.
1206 A value of @code{t} disables the recording of undo information.
1209 Here are the kinds of elements an undo list can have:
1212 @item @var{position}
1213 This kind of element records a previous value of point; undoing this
1214 element moves point to @var{position}. Ordinary cursor motion does not
1215 make any sort of undo record, but deletion operations use these entries
1216 to record where point was before the command.
1218 @item (@var{beg} . @var{end})
1219 This kind of element indicates how to delete text that was inserted.
1220 Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1223 @item (@var{text} . @var{position})
1224 This kind of element indicates how to reinsert text that was deleted.
1225 The deleted text itself is the string @var{text}. The place to
1226 reinsert it is @code{(abs @var{position})}. If @var{position} is
1227 positive, point was at the beginning of the deleted text, otherwise it
1230 @item (t @var{high} . @var{low})
1231 This kind of element indicates that an unmodified buffer became
1232 modified. The elements @var{high} and @var{low} are two integers, each
1233 recording 16 bits of the visited file's modification time as of when it
1234 was previously visited or saved. @code{primitive-undo} uses those
1235 values to determine whether to mark the buffer as unmodified once again;
1236 it does so only if the file's modification time matches those numbers.
1238 @item (nil @var{property} @var{value} @var{beg} . @var{end})
1239 This kind of element records a change in a text property.
1240 Here's how you might undo the change:
1243 (put-text-property @var{beg} @var{end} @var{property} @var{value})
1246 @item (apply @var{funname} . @var{args})
1247 This kind of element records a change that can be undone by evaluating
1248 (@code{apply} @var{funname} @var{args}).
1250 @item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1251 This kind of element records a change that can be undone by evaluating
1252 (@code{apply} @var{funname} @var{args}). The integer values @var{beg}
1253 and @var{end} is buffer positions of the range affected by this change
1254 and @var{delta} is an integer value which is the number of bytes added
1255 or deleted in that range by this change. This kind of element
1256 enables undo limited to a region to determine whether the element
1257 pertains to that region.
1259 @item (@var{marker} . @var{adjustment})
1260 This kind of element records the fact that the marker @var{marker} was
1261 relocated due to deletion of surrounding text, and that it moved
1262 @var{adjustment} character positions. Undoing this element moves
1263 @var{marker} @minus{} @var{adjustment} characters.
1265 @item (apply @var{funname} . @var{args})
1266 This is an extensible undo item, which is undone by calling
1267 @var{funname} with arguments @var{args}.
1269 @item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1270 This is an extensible undo item, which records a change limited to the
1271 range @var{beg} to @var{end}, which increased the size of the buffer
1272 by @var{delta}. It is undone by calling @var{funname} with arguments
1276 This element is a boundary. The elements between two boundaries are
1277 called a @dfn{change group}; normally, each change group corresponds to
1278 one keyboard command, and undo commands normally undo an entire group as
1282 @defun undo-boundary
1283 This function places a boundary element in the undo list. The undo
1284 command stops at such a boundary, and successive undo commands undo
1285 to earlier and earlier boundaries. This function returns @code{nil}.
1287 The editor command loop automatically creates an undo boundary before
1288 each key sequence is executed. Thus, each undo normally undoes the
1289 effects of one command. Self-inserting input characters are an
1290 exception. The command loop makes a boundary for the first such
1291 character; the next 19 consecutive self-inserting input characters do
1292 not make boundaries, and then the 20th does, and so on as long as
1293 self-inserting characters continue.
1295 All buffer modifications add a boundary whenever the previous undoable
1296 change was made in some other buffer. This is to ensure that
1297 each command makes a boundary in each buffer where it makes changes.
1299 Calling this function explicitly is useful for splitting the effects of
1300 a command into more than one unit. For example, @code{query-replace}
1301 calls @code{undo-boundary} after each replacement, so that the user can
1302 undo individual replacements one by one.
1305 @defvar undo-in-progress
1306 This variable is normally @code{nil}, but the undo commands bind it to
1307 @code{t}. This is so that various kinds of change hooks can tell when
1308 they're being called for the sake of undoing.
1311 @defun primitive-undo count list
1312 This is the basic function for undoing elements of an undo list.
1313 It undoes the first @var{count} elements of @var{list}, returning
1314 the rest of @var{list}. You could write this function in Lisp,
1315 but it is convenient to have it in C.
1317 @code{primitive-undo} adds elements to the buffer's undo list when it
1318 changes the buffer. Undo commands avoid confusion by saving the undo
1319 list value at the beginning of a sequence of undo operations. Then the
1320 undo operations use and update the saved value. The new elements added
1321 by undoing are not part of this saved value, so they don't interfere with
1324 This function does not bind @code{undo-in-progress}.
1327 @node Maintaining Undo
1328 @section Maintaining Undo Lists
1330 This section describes how to enable and disable undo information for
1331 a given buffer. It also explains how the undo list is truncated
1332 automatically so it doesn't get too big.
1334 Recording of undo information in a newly created buffer is normally
1335 enabled to start with; but if the buffer name starts with a space, the
1336 undo recording is initially disabled. You can explicitly enable or
1337 disable undo recording with the following two functions, or by setting
1338 @code{buffer-undo-list} yourself.
1340 @deffn Command buffer-enable-undo &optional buffer-or-name
1341 This command enables recording undo information for buffer
1342 @var{buffer-or-name}, so that subsequent changes can be undone. If no
1343 argument is supplied, then the current buffer is used. This function
1344 does nothing if undo recording is already enabled in the buffer. It
1347 In an interactive call, @var{buffer-or-name} is the current buffer.
1348 You cannot specify any other buffer.
1351 @deffn Command buffer-disable-undo &optional buffer-or-name
1352 @cindex disable undo
1353 This function discards the undo list of @var{buffer-or-name}, and disables
1354 further recording of undo information. As a result, it is no longer
1355 possible to undo either previous changes or any subsequent changes. If
1356 the undo list of @var{buffer-or-name} is already disabled, this function
1359 This function returns @code{nil}.
1362 As editing continues, undo lists get longer and longer. To prevent
1363 them from using up all available memory space, garbage collection trims
1364 them back to size limits you can set. (For this purpose, the ``size''
1365 of an undo list measures the cons cells that make up the list, plus the
1366 strings of deleted text.) Three variables control the range of acceptable
1367 sizes: @code{undo-limit}, @code{undo-strong-limit} and
1368 @code{undo-outer-limit}.
1371 This is the soft limit for the acceptable size of an undo list. The
1372 change group at which this size is exceeded is the last one kept.
1375 @defopt undo-strong-limit
1376 This is the upper limit for the acceptable size of an undo list. The
1377 change group at which this size is exceeded is discarded itself (along
1378 with all older change groups). There is one exception: the very latest
1379 change group is only discarded if it exceeds @code{undo-outer-limit}.
1382 @defopt undo-outer-limit
1383 If at garbage collection time the undo info for the current command
1384 exceeds this limit, Emacs discards the info and displays a warning.
1385 This is a last ditch limit to prevent memory overflow.
1389 @comment node-name, next, previous, up
1391 @cindex filling, explicit
1393 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1394 breaks) so that they are nearly (but no greater than) a specified
1395 maximum width. Additionally, lines can be @dfn{justified}, which means
1396 inserting spaces to make the left and/or right margins line up
1397 precisely. The width is controlled by the variable @code{fill-column}.
1398 For ease of reading, lines should be no longer than 70 or so columns.
1400 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1401 automatically as you insert it, but changes to existing text may leave
1402 it improperly filled. Then you must fill the text explicitly.
1404 Most of the commands in this section return values that are not
1405 meaningful. All the functions that do filling take note of the current
1406 left margin, current right margin, and current justification style
1407 (@pxref{Margins}). If the current justification style is
1408 @code{none}, the filling functions don't actually do anything.
1410 Several of the filling functions have an argument @var{justify}.
1411 If it is non-@code{nil}, that requests some kind of justification. It
1412 can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1413 request a specific style of justification. If it is @code{t}, that
1414 means to use the current justification style for this part of the text
1415 (see @code{current-justification}, below). Any other value is treated
1418 When you call the filling functions interactively, using a prefix
1419 argument implies the value @code{full} for @var{justify}.
1421 @deffn Command fill-paragraph justify
1422 @cindex filling a paragraph
1423 This command fills the paragraph at or after point. If
1424 @var{justify} is non-@code{nil}, each line is justified as well.
1425 It uses the ordinary paragraph motion commands to find paragraph
1426 boundaries. @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
1429 @deffn Command fill-region start end &optional justify nosqueeze to-eop
1430 This command fills each of the paragraphs in the region from @var{start}
1431 to @var{end}. It justifies as well if @var{justify} is
1434 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1435 other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1436 that means to keep filling to the end of the paragraph---or the next hard
1437 newline, if @code{use-hard-newlines} is enabled (see below).
1439 The variable @code{paragraph-separate} controls how to distinguish
1440 paragraphs. @xref{Standard Regexps}.
1443 @deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
1444 This command fills each paragraph in the region according to its
1445 individual fill prefix. Thus, if the lines of a paragraph were indented
1446 with spaces, the filled paragraph will remain indented in the same
1449 The first two arguments, @var{start} and @var{end}, are the beginning
1450 and end of the region to be filled. The third and fourth arguments,
1451 @var{justify} and @var{citation-regexp}, are optional. If
1452 @var{justify} is non-@code{nil}, the paragraphs are justified as
1453 well as filled. If @var{citation-regexp} is non-@code{nil}, it means the
1454 function is operating on a mail message and therefore should not fill
1455 the header lines. If @var{citation-regexp} is a string, it is used as
1456 a regular expression; if it matches the beginning of a line, that line
1457 is treated as a citation marker.
1459 Ordinarily, @code{fill-individual-paragraphs} regards each change in
1460 indentation as starting a new paragraph. If
1461 @code{fill-individual-varying-indent} is non-@code{nil}, then only
1462 separator lines separate paragraphs. That mode can handle indented
1463 paragraphs with additional indentation on the first line.
1466 @defopt fill-individual-varying-indent
1467 This variable alters the action of @code{fill-individual-paragraphs} as
1471 @deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1472 This command considers a region of text as a single paragraph and fills
1473 it. If the region was made up of many paragraphs, the blank lines
1474 between paragraphs are removed. This function justifies as well as
1475 filling when @var{justify} is non-@code{nil}.
1477 In an interactive call, any prefix argument requests justification.
1479 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1480 other than line breaks untouched. If @var{squeeze-after} is
1481 non-@code{nil}, it specifies a position in the region, and means don't
1482 canonicalize spaces before that position.
1484 In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1485 choose a fill prefix by default. @xref{Adaptive Fill}.
1488 @deffn Command justify-current-line &optional how eop nosqueeze
1489 This command inserts spaces between the words of the current line so
1490 that the line ends exactly at @code{fill-column}. It returns
1493 The argument @var{how}, if non-@code{nil} specifies explicitly the style
1494 of justification. It can be @code{left}, @code{right}, @code{full},
1495 @code{center}, or @code{none}. If it is @code{t}, that means to do
1496 follow specified justification style (see @code{current-justification},
1497 below). @code{nil} means to do full justification.
1499 If @var{eop} is non-@code{nil}, that means do only left-justification
1500 if @code{current-justification} specifies full justification. This is
1501 used for the last line of a paragraph; even if the paragraph as a
1502 whole is fully justified, the last line should not be.
1504 If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1508 @defopt default-justification
1509 This variable's value specifies the style of justification to use for
1510 text that doesn't specify a style with a text property. The possible
1511 values are @code{left}, @code{right}, @code{full}, @code{center}, or
1512 @code{none}. The default value is @code{left}.
1515 @defun current-justification
1516 This function returns the proper justification style to use for filling
1517 the text around point.
1520 @defopt sentence-end-double-space
1521 @anchor{Definition of sentence-end-double-space}
1522 If this variable is non-@code{nil}, a period followed by just one space
1523 does not count as the end of a sentence, and the filling functions
1524 avoid breaking the line at such a place.
1527 @defopt sentence-end-without-period
1528 If this variable is non-@code{nil}, a sentence can end without a
1529 period. This is used for languages like Thai, where sentences end
1530 with a double space but without a period.
1533 @defopt sentence-end-without-space
1534 If this variable is non-@code{nil}, it should be a string of
1535 characters that can end a sentence without following spaces.
1538 @defvar fill-paragraph-function
1539 This variable provides a way for major modes to override the filling of
1540 paragraphs. If the value is non-@code{nil}, @code{fill-paragraph} calls
1541 this function to do the work. If the function returns a non-@code{nil}
1542 value, @code{fill-paragraph} assumes the job is done, and immediately
1545 The usual use of this feature is to fill comments in programming
1546 language modes. If the function needs to fill a paragraph in the usual
1547 way, it can do so as follows:
1550 (let ((fill-paragraph-function nil))
1551 (fill-paragraph arg))
1555 @defvar use-hard-newlines
1556 If this variable is non-@code{nil}, the filling functions do not delete
1557 newlines that have the @code{hard} text property. These ``hard
1558 newlines'' act as paragraph separators.
1562 @section Margins for Filling
1565 This buffer-local variable specifies a string of text that appears at
1567 of normal text lines and should be disregarded when filling them. Any
1568 line that fails to start with the fill prefix is considered the start of
1569 a paragraph; so is any line that starts with the fill prefix followed by
1570 additional whitespace. Lines that start with the fill prefix but no
1571 additional whitespace are ordinary text lines that can be filled
1572 together. The resulting filled lines also start with the fill prefix.
1574 The fill prefix follows the left margin whitespace, if any.
1578 This buffer-local variable specifies the maximum width of filled lines.
1579 Its value should be an integer, which is a number of columns. All the
1580 filling, justification, and centering commands are affected by this
1581 variable, including Auto Fill mode (@pxref{Auto Filling}).
1583 As a practical matter, if you are writing text for other people to
1584 read, you should set @code{fill-column} to no more than 70. Otherwise
1585 the line will be too long for people to read comfortably, and this can
1586 make the text seem clumsy.
1589 @defvar default-fill-column
1590 The value of this variable is the default value for @code{fill-column} in
1591 buffers that do not override it. This is the same as
1592 @code{(default-value 'fill-column)}.
1594 The default value for @code{default-fill-column} is 70.
1597 @deffn Command set-left-margin from to margin
1598 This sets the @code{left-margin} property on the text from @var{from} to
1599 @var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1600 command also refills the region to fit the new margin.
1603 @deffn Command set-right-margin from to margin
1604 This sets the @code{right-margin} property on the text from @var{from}
1605 to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1606 this command also refills the region to fit the new margin.
1609 @defun current-left-margin
1610 This function returns the proper left margin value to use for filling
1611 the text around point. The value is the sum of the @code{left-margin}
1612 property of the character at the start of the current line (or zero if
1613 none), and the value of the variable @code{left-margin}.
1616 @defun current-fill-column
1617 This function returns the proper fill column value to use for filling
1618 the text around point. The value is the value of the @code{fill-column}
1619 variable, minus the value of the @code{right-margin} property of the
1620 character after point.
1623 @deffn Command move-to-left-margin &optional n force
1624 This function moves point to the left margin of the current line. The
1625 column moved to is determined by calling the function
1626 @code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1627 @code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1629 If @var{force} is non-@code{nil}, that says to fix the line's
1630 indentation if that doesn't match the left margin value.
1633 @defun delete-to-left-margin &optional from to
1634 This function removes left margin indentation from the text between
1635 @var{from} and @var{to}. The amount of indentation to delete is
1636 determined by calling @code{current-left-margin}. In no case does this
1637 function delete non-whitespace. If @var{from} and @var{to} are omitted,
1638 they default to the whole buffer.
1641 @defun indent-to-left-margin
1642 This is the default @code{indent-line-function}, used in Fundamental
1643 mode, Text mode, etc. Its effect is to adjust the indentation at the
1644 beginning of the current line to the value specified by the variable
1645 @code{left-margin}. This may involve either inserting or deleting
1650 This variable specifies the base left margin column. In Fundamental
1651 mode, @kbd{C-j} indents to this column. This variable automatically
1652 becomes buffer-local when set in any fashion.
1655 @defvar fill-nobreak-predicate
1656 This variable gives major modes a way to specify not to break a line
1657 at certain places. Its value should be a list of functions, but a
1658 single function is also supported for compatibility. Whenever filling
1659 considers breaking the line at a certain place in the buffer, it calls
1660 each of these functions with no arguments and with point located at
1661 that place. If any of the functions returns non-@code{nil}, then the
1662 line won't be broken there.
1666 @section Adaptive Fill Mode
1667 @cindex Adaptive Fill mode
1669 When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
1670 prefix automatically from the text in each paragraph being filled
1671 rather than using a predetermined value. During filling, this fill
1672 prefix gets inserted at the start of the second and subsequent lines
1673 of the paragraph as described in @ref{Filling}, and in @ref{Auto
1676 @defopt adaptive-fill-mode
1677 Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1678 It is @code{t} by default.
1681 @defun fill-context-prefix from to
1682 This function implements the heart of Adaptive Fill mode; it chooses a
1683 fill prefix based on the text between @var{from} and @var{to},
1684 typically the start and end of a paragraph. It does this by looking
1685 at the first two lines of the paragraph, based on the variables
1687 @c The optional argument first-line-regexp is not documented
1688 @c because it exists for internal purposes and might be eliminated
1691 Usually, this function returns the fill prefix, a string. However,
1692 before doing this, the function makes a final check (not specially
1693 mentioned in the following) that a line starting with this prefix
1694 wouldn't look like the start of a paragraph. Should this happen, the
1695 function signals the anomaly by returning @code{nil} instead.
1697 In detail, @code{fill-context-prefix} does this:
1701 It takes a candidate for the fill prefix from the first line---it
1702 tries first the function in @code{adaptive-fill-function} (if any),
1703 then the regular expression @code{adaptive-fill-regexp} (see below).
1704 The first non-@code{nil} result of these, or the empty string if
1705 they're both @code{nil}, becomes the first line's candidate.
1707 If the paragraph has as yet only one line, the function tests the
1708 validity of the prefix candidate just found. The function then
1709 returns the candidate if it's valid, or a string of spaces otherwise.
1710 (see the description of @code{adaptive-fill-first-line-regexp} below).
1712 When the paragraph already has two lines, the function next looks for
1713 a prefix candidate on the second line, in just the same way it did for
1714 the first line. If it doesn't find one, it returns @code{nil}.
1716 The function now compares the two candidate prefixes heuristically: if
1717 the non-whitespace characters in the line 2 candidate occur in the
1718 same order in the line 1 candidate, the function returns the line 2
1719 candidate. Otherwise, it returns the largest initial substring which
1720 is common to both candidates (which might be the empty string).
1724 @defopt adaptive-fill-regexp
1725 Adaptive Fill mode matches this regular expression against the text
1726 starting after the left margin whitespace (if any) on a line; the
1727 characters it matches are that line's candidate for the fill prefix.
1729 @w{@samp{"[ \t]*\\([-|#;>*]+[ \t]*\\|(?[0-9]+[.)][ \t]*\\)*"}} is the
1730 default value. This matches a number enclosed in parentheses or
1731 followed by a period, or certain punctuation characters, or any
1732 sequence of these intermingled with whitespace. In particular, it
1733 matches a sequence of whitespace, possibly empty.
1736 @defopt adaptive-fill-first-line-regexp
1737 Used only in one-line paragraphs, this regular expression acts as an
1738 additional check of the validity of the one available candidate fill
1739 prefix: the candidate must match this regular expression, or match
1740 @code{comment-start-skip}. If it doesn't, @code{fill-context-prefix}
1741 replaces the candidate with a string of spaces ``of the same width''
1744 The default value of this variable is @w{@samp{"\\`[ \t]*\\'"}}, which
1745 matches only a string of whitespace. The effect of this default is to
1746 force the fill prefixes found in one-line paragraphs always to be pure
1750 @defopt adaptive-fill-function
1751 You can specify more complex ways of choosing a fill prefix
1752 automatically by setting this variable to a function. The function is
1753 called with point after the left margin (if any) of a line, and it
1754 must preserve point. It should return either ``that line's'' fill
1755 prefix or @code{nil}, meaning it has failed to determine a prefix.
1759 @comment node-name, next, previous, up
1760 @section Auto Filling
1761 @cindex filling, automatic
1762 @cindex Auto Fill mode
1764 Auto Fill mode is a minor mode that fills lines automatically as text
1765 is inserted. This section describes the hook used by Auto Fill mode.
1766 For a description of functions that you can call explicitly to fill and
1767 justify existing text, see @ref{Filling}.
1769 Auto Fill mode also enables the functions that change the margins and
1770 justification style to refill portions of the text. @xref{Margins}.
1772 @defvar auto-fill-function
1773 The value of this variable should be a function (of no arguments) to be
1774 called after self-inserting a character from the table
1775 @code{auto-fill-chars}. It may be @code{nil}, in which case nothing
1776 special is done in that case.
1778 The value of @code{auto-fill-function} is @code{do-auto-fill} when
1779 Auto-Fill mode is enabled. That is a function whose sole purpose is to
1780 implement the usual strategy for breaking a line.
1783 In older Emacs versions, this variable was named @code{auto-fill-hook},
1784 but since it is not called with the standard convention for hooks, it
1785 was renamed to @code{auto-fill-function} in version 19.
1789 @defvar normal-auto-fill-function
1790 This variable specifies the function to use for
1791 @code{auto-fill-function}, if and when Auto Fill is turned on. Major
1792 modes can set buffer-local values for this variable to alter how Auto
1796 @defvar auto-fill-chars
1797 A char table of characters which invoke @code{auto-fill-function} when
1798 self-inserted---space and newline in most language environments. They
1799 have an entry @code{t} in the table.
1803 @section Sorting Text
1804 @cindex sorting text
1806 The sorting functions described in this section all rearrange text in
1807 a buffer. This is in contrast to the function @code{sort}, which
1808 rearranges the order of the elements of a list (@pxref{Rearrangement}).
1809 The values returned by these functions are not meaningful.
1811 @defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun
1812 This function is the general text-sorting routine that subdivides a
1813 buffer into records and then sorts them. Most of the commands in this
1814 section use this function.
1816 To understand how @code{sort-subr} works, consider the whole accessible
1817 portion of the buffer as being divided into disjoint pieces called
1818 @dfn{sort records}. The records may or may not be contiguous, but they
1819 must not overlap. A portion of each sort record (perhaps all of it) is
1820 designated as the sort key. Sorting rearranges the records in order by
1823 Usually, the records are rearranged in order of ascending sort key.
1824 If the first argument to the @code{sort-subr} function, @var{reverse},
1825 is non-@code{nil}, the sort records are rearranged in order of
1826 descending sort key.
1828 The next four arguments to @code{sort-subr} are functions that are
1829 called to move point across a sort record. They are called many times
1830 from within @code{sort-subr}.
1834 @var{nextrecfun} is called with point at the end of a record. This
1835 function moves point to the start of the next record. The first record
1836 is assumed to start at the position of point when @code{sort-subr} is
1837 called. Therefore, you should usually move point to the beginning of
1838 the buffer before calling @code{sort-subr}.
1840 This function can indicate there are no more sort records by leaving
1841 point at the end of the buffer.
1844 @var{endrecfun} is called with point within a record. It moves point to
1845 the end of the record.
1848 @var{startkeyfun} is called to move point from the start of a record to
1849 the start of the sort key. This argument is optional; if it is omitted,
1850 the whole record is the sort key. If supplied, the function should
1851 either return a non-@code{nil} value to be used as the sort key, or
1852 return @code{nil} to indicate that the sort key is in the buffer
1853 starting at point. In the latter case, @var{endkeyfun} is called to
1854 find the end of the sort key.
1857 @var{endkeyfun} is called to move point from the start of the sort key
1858 to the end of the sort key. This argument is optional. If
1859 @var{startkeyfun} returns @code{nil} and this argument is omitted (or
1860 @code{nil}), then the sort key extends to the end of the record. There
1861 is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1862 non-@code{nil} value.
1865 As an example of @code{sort-subr}, here is the complete function
1866 definition for @code{sort-lines}:
1870 ;; @r{Note that the first two lines of doc string}
1871 ;; @r{are effectively one line when viewed by a user.}
1872 (defun sort-lines (reverse beg end)
1873 "Sort lines in region alphabetically;\
1874 argument means descending order.
1875 Called from a program, there are three arguments:
1878 REVERSE (non-nil means reverse order),\
1879 BEG and END (region to sort).
1880 The variable `sort-fold-case' determines\
1881 whether alphabetic case affects
1885 (interactive "P\nr")
1888 (narrow-to-region beg end)
1889 (goto-char (point-min))
1890 (sort-subr reverse 'forward-line 'end-of-line))))
1894 Here @code{forward-line} moves point to the start of the next record,
1895 and @code{end-of-line} moves point to the end of record. We do not pass
1896 the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
1897 record is used as the sort key.
1899 The @code{sort-paragraphs} function is very much the same, except that
1900 its @code{sort-subr} call looks like this:
1907 (while (and (not (eobp))
1908 (looking-at paragraph-separate))
1914 Markers pointing into any sort records are left with no useful
1915 position after @code{sort-subr} returns.
1918 @defopt sort-fold-case
1919 If this variable is non-@code{nil}, @code{sort-subr} and the other
1920 buffer sorting functions ignore case when comparing strings.
1923 @deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
1924 This command sorts the region between @var{start} and @var{end}
1925 alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
1926 If @var{reverse} is a negative integer, then sorting is in reverse
1929 Alphabetical sorting means that two sort keys are compared by
1930 comparing the first characters of each, the second characters of each,
1931 and so on. If a mismatch is found, it means that the sort keys are
1932 unequal; the sort key whose character is less at the point of first
1933 mismatch is the lesser sort key. The individual characters are compared
1934 according to their numerical character codes in the Emacs character set.
1936 The value of the @var{record-regexp} argument specifies how to divide
1937 the buffer into sort records. At the end of each record, a search is
1938 done for this regular expression, and the text that matches it is taken
1939 as the next record. For example, the regular expression @samp{^.+$},
1940 which matches lines with at least one character besides a newline, would
1941 make each such line into a sort record. @xref{Regular Expressions}, for
1942 a description of the syntax and meaning of regular expressions.
1944 The value of the @var{key-regexp} argument specifies what part of each
1945 record is the sort key. The @var{key-regexp} could match the whole
1946 record, or only a part. In the latter case, the rest of the record has
1947 no effect on the sorted order of records, but it is carried along when
1948 the record moves to its new position.
1950 The @var{key-regexp} argument can refer to the text matched by a
1951 subexpression of @var{record-regexp}, or it can be a regular expression
1954 If @var{key-regexp} is:
1957 @item @samp{\@var{digit}}
1958 then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
1959 grouping in @var{record-regexp} is the sort key.
1962 then the whole record is the sort key.
1964 @item a regular expression
1965 then @code{sort-regexp-fields} searches for a match for the regular
1966 expression within the record. If such a match is found, it is the sort
1967 key. If there is no match for @var{key-regexp} within a record then
1968 that record is ignored, which means its position in the buffer is not
1969 changed. (The other records may move around it.)
1972 For example, if you plan to sort all the lines in the region by the
1973 first word on each line starting with the letter @samp{f}, you should
1974 set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
1975 @samp{\<f\w*\>}. The resulting expression looks like this:
1979 (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
1985 If you call @code{sort-regexp-fields} interactively, it prompts for
1986 @var{record-regexp} and @var{key-regexp} in the minibuffer.
1989 @deffn Command sort-lines reverse start end
1990 This command alphabetically sorts lines in the region between
1991 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
1992 is in reverse order.
1995 @deffn Command sort-paragraphs reverse start end
1996 This command alphabetically sorts paragraphs in the region between
1997 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
1998 is in reverse order.
2001 @deffn Command sort-pages reverse start end
2002 This command alphabetically sorts pages in the region between
2003 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2004 is in reverse order.
2007 @deffn Command sort-fields field start end
2008 This command sorts lines in the region between @var{start} and
2009 @var{end}, comparing them alphabetically by the @var{field}th field
2010 of each line. Fields are separated by whitespace and numbered starting
2011 from 1. If @var{field} is negative, sorting is by the
2012 @w{@minus{}@var{field}th} field from the end of the line. This command
2013 is useful for sorting tables.
2016 @deffn Command sort-numeric-fields field start end
2017 This command sorts lines in the region between @var{start} and
2018 @var{end}, comparing them numerically by the @var{field}th field of
2019 each line. Fields are separated by whitespace and numbered starting
2020 from 1. The specified field must contain a number in each line of the
2021 region. Numbers starting with 0 are treated as octal, and numbers
2022 starting with @samp{0x} are treated as hexadecimal.
2024 If @var{field} is negative, sorting is by the
2025 @w{@minus{}@var{field}th} field from the end of the line. This
2026 command is useful for sorting tables.
2029 @defopt sort-numeric-base
2030 This variable specifies the default radix for
2031 @code{sort-numeric-fields} to parse numbers.
2034 @deffn Command sort-columns reverse &optional beg end
2035 This command sorts the lines in the region between @var{beg} and
2036 @var{end}, comparing them alphabetically by a certain range of
2037 columns. The column positions of @var{beg} and @var{end} bound the
2038 range of columns to sort on.
2040 If @var{reverse} is non-@code{nil}, the sort is in reverse order.
2042 One unusual thing about this command is that the entire line
2043 containing position @var{beg}, and the entire line containing position
2044 @var{end}, are included in the region sorted.
2046 Note that @code{sort-columns} uses the @code{sort} utility program,
2047 and so cannot work properly on text containing tab characters. Use
2048 @kbd{M-x untabify} to convert tabs to spaces before sorting.
2052 @comment node-name, next, previous, up
2053 @section Counting Columns
2055 @cindex counting columns
2056 @cindex horizontal position
2058 The column functions convert between a character position (counting
2059 characters from the beginning of the buffer) and a column position
2060 (counting screen characters from the beginning of a line).
2062 These functions count each character according to the number of
2063 columns it occupies on the screen. This means control characters count
2064 as occupying 2 or 4 columns, depending upon the value of
2065 @code{ctl-arrow}, and tabs count as occupying a number of columns that
2066 depends on the value of @code{tab-width} and on the column where the tab
2067 begins. @xref{Usual Display}.
2069 Column number computations ignore the width of the window and the
2070 amount of horizontal scrolling. Consequently, a column value can be
2071 arbitrarily high. The first (or leftmost) column is numbered 0. They
2072 also ignore overlays and text properties, aside from invisibility.
2074 @defun current-column
2075 This function returns the horizontal position of point, measured in
2076 columns, counting from 0 at the left margin. The column position is the
2077 sum of the widths of all the displayed representations of the characters
2078 between the start of the current line and point.
2080 For an example of using @code{current-column}, see the description of
2081 @code{count-lines} in @ref{Text Lines}.
2084 @defun move-to-column column &optional force
2085 This function moves point to @var{column} in the current line. The
2086 calculation of @var{column} takes into account the widths of the
2087 displayed representations of the characters between the start of the
2090 If column @var{column} is beyond the end of the line, point moves to the
2091 end of the line. If @var{column} is negative, point moves to the
2092 beginning of the line.
2094 If it is impossible to move to column @var{column} because that is in
2095 the middle of a multicolumn character such as a tab, point moves to the
2096 end of that character. However, if @var{force} is non-@code{nil}, and
2097 @var{column} is in the middle of a tab, then @code{move-to-column}
2098 converts the tab into spaces so that it can move precisely to column
2099 @var{column}. Other multicolumn characters can cause anomalies despite
2100 @var{force}, since there is no way to split them.
2102 The argument @var{force} also has an effect if the line isn't long
2103 enough to reach column @var{column}; if it is @code{t}, that means to
2104 add whitespace at the end of the line to reach that column.
2106 If @var{column} is not an integer, an error is signaled.
2108 The return value is the column number actually moved to.
2112 @section Indentation
2115 The indentation functions are used to examine, move to, and change
2116 whitespace that is at the beginning of a line. Some of the functions
2117 can also change whitespace elsewhere on a line. Columns and indentation
2118 count from zero at the left margin.
2121 * Primitive Indent:: Functions used to count and insert indentation.
2122 * Mode-Specific Indent:: Customize indentation for different modes.
2123 * Region Indent:: Indent all the lines in a region.
2124 * Relative Indent:: Indent the current line based on previous lines.
2125 * Indent Tabs:: Adjustable, typewriter-like tab stops.
2126 * Motion by Indent:: Move to first non-blank character.
2129 @node Primitive Indent
2130 @subsection Indentation Primitives
2132 This section describes the primitive functions used to count and
2133 insert indentation. The functions in the following sections use these
2134 primitives. @xref{Width}, for related functions.
2136 @defun current-indentation
2137 @comment !!Type Primitive Function
2138 @comment !!SourceFile indent.c
2139 This function returns the indentation of the current line, which is
2140 the horizontal position of the first nonblank character. If the
2141 contents are entirely blank, then this is the horizontal position of the
2145 @deffn Command indent-to column &optional minimum
2146 @comment !!Type Primitive Function
2147 @comment !!SourceFile indent.c
2148 This function indents from point with tabs and spaces until @var{column}
2149 is reached. If @var{minimum} is specified and non-@code{nil}, then at
2150 least that many spaces are inserted even if this requires going beyond
2151 @var{column}. Otherwise the function does nothing if point is already
2152 beyond @var{column}. The value is the column at which the inserted
2155 The inserted whitespace characters inherit text properties from the
2156 surrounding text (usually, from the preceding text only). @xref{Sticky
2160 @defopt indent-tabs-mode
2161 @comment !!SourceFile indent.c
2162 If this variable is non-@code{nil}, indentation functions can insert
2163 tabs as well as spaces. Otherwise, they insert only spaces. Setting
2164 this variable automatically makes it buffer-local in the current buffer.
2167 @node Mode-Specific Indent
2168 @subsection Indentation Controlled by Major Mode
2170 An important function of each major mode is to customize the @key{TAB}
2171 key to indent properly for the language being edited. This section
2172 describes the mechanism of the @key{TAB} key and how to control it.
2173 The functions in this section return unpredictable values.
2175 @defvar indent-line-function
2176 This variable's value is the function to be used by @key{TAB} (and
2177 various commands) to indent the current line. The command
2178 @code{indent-according-to-mode} does no more than call this function.
2180 In Lisp mode, the value is the symbol @code{lisp-indent-line}; in C
2181 mode, @code{c-indent-line}; in Fortran mode, @code{fortran-indent-line}.
2182 In Fundamental mode, Text mode, and many other modes with no standard
2183 for indentation, the value is @code{indent-to-left-margin} (which is the
2187 @deffn Command indent-according-to-mode
2188 This command calls the function in @code{indent-line-function} to
2189 indent the current line in a way appropriate for the current major mode.
2192 @deffn Command indent-for-tab-command
2193 This command calls the function in @code{indent-line-function} to indent
2194 the current line; however, if that function is
2195 @code{indent-to-left-margin}, @code{insert-tab} is called instead. (That
2196 is a trivial command that inserts a tab character.)
2199 @deffn Command newline-and-indent
2200 @comment !!SourceFile simple.el
2201 This function inserts a newline, then indents the new line (the one
2202 following the newline just inserted) according to the major mode.
2204 It does indentation by calling the current @code{indent-line-function}.
2205 In programming language modes, this is the same thing @key{TAB} does,
2206 but in some text modes, where @key{TAB} inserts a tab,
2207 @code{newline-and-indent} indents to the column specified by
2211 @deffn Command reindent-then-newline-and-indent
2212 @comment !!SourceFile simple.el
2213 This command reindents the current line, inserts a newline at point,
2214 and then indents the new line (the one following the newline just
2217 This command does indentation on both lines according to the current
2218 major mode, by calling the current value of @code{indent-line-function}.
2219 In programming language modes, this is the same thing @key{TAB} does,
2220 but in some text modes, where @key{TAB} inserts a tab,
2221 @code{reindent-then-newline-and-indent} indents to the column specified
2222 by @code{left-margin}.
2226 @subsection Indenting an Entire Region
2228 This section describes commands that indent all the lines in the
2229 region. They return unpredictable values.
2231 @deffn Command indent-region start end to-column
2232 This command indents each nonblank line starting between @var{start}
2233 (inclusive) and @var{end} (exclusive). If @var{to-column} is
2234 @code{nil}, @code{indent-region} indents each nonblank line by calling
2235 the current mode's indentation function, the value of
2236 @code{indent-line-function}.
2238 If @var{to-column} is non-@code{nil}, it should be an integer
2239 specifying the number of columns of indentation; then this function
2240 gives each line exactly that much indentation, by either adding or
2241 deleting whitespace.
2243 If there is a fill prefix, @code{indent-region} indents each line
2244 by making it start with the fill prefix.
2247 @defvar indent-region-function
2248 The value of this variable is a function that can be used by
2249 @code{indent-region} as a short cut. It should take two arguments, the
2250 start and end of the region. You should design the function so
2251 that it will produce the same results as indenting the lines of the
2252 region one by one, but presumably faster.
2254 If the value is @code{nil}, there is no short cut, and
2255 @code{indent-region} actually works line by line.
2257 A short-cut function is useful in modes such as C mode and Lisp mode,
2258 where the @code{indent-line-function} must scan from the beginning of
2259 the function definition: applying it to each line would be quadratic in
2260 time. The short cut can update the scan information as it moves through
2261 the lines indenting them; this takes linear time. In a mode where
2262 indenting a line individually is fast, there is no need for a short cut.
2264 @code{indent-region} with a non-@code{nil} argument @var{to-column} has
2265 a different meaning and does not use this variable.
2268 @deffn Command indent-rigidly start end count
2269 @comment !!SourceFile indent.el
2270 This command indents all lines starting between @var{start}
2271 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
2272 This ``preserves the shape'' of the affected region, moving it as a
2273 rigid unit. Consequently, this command is useful not only for indenting
2274 regions of unindented text, but also for indenting regions of formatted
2277 For example, if @var{count} is 3, this command adds 3 columns of
2278 indentation to each of the lines beginning in the region specified.
2280 In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses
2281 @code{indent-rigidly} to indent the text copied from the message being
2285 @defun indent-code-rigidly start end columns &optional nochange-regexp
2286 This is like @code{indent-rigidly}, except that it doesn't alter lines
2287 that start within strings or comments.
2289 In addition, it doesn't alter a line if @var{nochange-regexp} matches at
2290 the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
2293 @node Relative Indent
2294 @subsection Indentation Relative to Previous Lines
2296 This section describes two commands that indent the current line
2297 based on the contents of previous lines.
2299 @deffn Command indent-relative &optional unindented-ok
2300 This command inserts whitespace at point, extending to the same
2301 column as the next @dfn{indent point} of the previous nonblank line. An
2302 indent point is a non-whitespace character following whitespace. The
2303 next indent point is the first one at a column greater than the current
2304 column of point. For example, if point is underneath and to the left of
2305 the first non-blank character of a line of text, it moves to that column
2306 by inserting whitespace.
2308 If the previous nonblank line has no next indent point (i.e., none at a
2309 great enough column position), @code{indent-relative} either does
2310 nothing (if @var{unindented-ok} is non-@code{nil}) or calls
2311 @code{tab-to-tab-stop}. Thus, if point is underneath and to the right
2312 of the last column of a short line of text, this command ordinarily
2313 moves point to the next tab stop by inserting whitespace.
2315 The return value of @code{indent-relative} is unpredictable.
2317 In the following example, point is at the beginning of the second
2322 This line is indented twelve spaces.
2323 @point{}The quick brown fox jumped.
2328 Evaluation of the expression @code{(indent-relative nil)} produces the
2333 This line is indented twelve spaces.
2334 @point{}The quick brown fox jumped.
2338 In this next example, point is between the @samp{m} and @samp{p} of
2343 This line is indented twelve spaces.
2344 The quick brown fox jum@point{}ped.
2349 Evaluation of the expression @code{(indent-relative nil)} produces the
2354 This line is indented twelve spaces.
2355 The quick brown fox jum @point{}ped.
2360 @deffn Command indent-relative-maybe
2361 @comment !!SourceFile indent.el
2362 This command indents the current line like the previous nonblank line,
2363 by calling @code{indent-relative} with @code{t} as the
2364 @var{unindented-ok} argument. The return value is unpredictable.
2366 If the previous nonblank line has no indent points beyond the current
2367 column, this command does nothing.
2371 @comment node-name, next, previous, up
2372 @subsection Adjustable ``Tab Stops''
2373 @cindex tabs stops for indentation
2375 This section explains the mechanism for user-specified ``tab stops''
2376 and the mechanisms that use and set them. The name ``tab stops'' is
2377 used because the feature is similar to that of the tab stops on a
2378 typewriter. The feature works by inserting an appropriate number of
2379 spaces and tab characters to reach the next tab stop column; it does not
2380 affect the display of tab characters in the buffer (@pxref{Usual
2381 Display}). Note that the @key{TAB} character as input uses this tab
2382 stop feature only in a few major modes, such as Text mode.
2384 @deffn Command tab-to-tab-stop
2385 This command inserts spaces or tabs before point, up to the next tab
2386 stop column defined by @code{tab-stop-list}. It searches the list for
2387 an element greater than the current column number, and uses that element
2388 as the column to indent to. It does nothing if no such element is
2392 @defopt tab-stop-list
2393 This variable is the list of tab stop columns used by
2394 @code{tab-to-tab-stops}. The elements should be integers in increasing
2395 order. The tab stop columns need not be evenly spaced.
2397 Use @kbd{M-x edit-tab-stops} to edit the location of tab stops
2401 @node Motion by Indent
2402 @subsection Indentation-Based Motion Commands
2404 These commands, primarily for interactive use, act based on the
2405 indentation in the text.
2407 @deffn Command back-to-indentation
2408 @comment !!SourceFile simple.el
2409 This command moves point to the first non-whitespace character in the
2410 current line (which is the line in which point is located). It returns
2414 @deffn Command backward-to-indentation &optional arg
2415 @comment !!SourceFile simple.el
2416 This command moves point backward @var{arg} lines and then to the
2417 first nonblank character on that line. It returns @code{nil}.
2418 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2421 @deffn Command forward-to-indentation &optional arg
2422 @comment !!SourceFile simple.el
2423 This command moves point forward @var{arg} lines and then to the first
2424 nonblank character on that line. It returns @code{nil}.
2425 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2429 @comment node-name, next, previous, up
2430 @section Case Changes
2431 @cindex case conversion in buffers
2433 The case change commands described here work on text in the current
2434 buffer. @xref{Case Conversion}, for case conversion functions that work
2435 on strings and characters. @xref{Case Tables}, for how to customize
2436 which characters are upper or lower case and how to convert them.
2438 @deffn Command capitalize-region start end
2439 This function capitalizes all words in the region defined by
2440 @var{start} and @var{end}. To capitalize means to convert each word's
2441 first character to upper case and convert the rest of each word to lower
2442 case. The function returns @code{nil}.
2444 If one end of the region is in the middle of a word, the part of the
2445 word within the region is treated as an entire word.
2447 When @code{capitalize-region} is called interactively, @var{start} and
2448 @var{end} are point and the mark, with the smallest first.
2452 ---------- Buffer: foo ----------
2453 This is the contents of the 5th foo.
2454 ---------- Buffer: foo ----------
2458 (capitalize-region 1 44)
2461 ---------- Buffer: foo ----------
2462 This Is The Contents Of The 5th Foo.
2463 ---------- Buffer: foo ----------
2468 @deffn Command downcase-region start end
2469 This function converts all of the letters in the region defined by
2470 @var{start} and @var{end} to lower case. The function returns
2473 When @code{downcase-region} is called interactively, @var{start} and
2474 @var{end} are point and the mark, with the smallest first.
2477 @deffn Command upcase-region start end
2478 This function converts all of the letters in the region defined by
2479 @var{start} and @var{end} to upper case. The function returns
2482 When @code{upcase-region} is called interactively, @var{start} and
2483 @var{end} are point and the mark, with the smallest first.
2486 @deffn Command capitalize-word count
2487 This function capitalizes @var{count} words after point, moving point
2488 over as it does. To capitalize means to convert each word's first
2489 character to upper case and convert the rest of each word to lower case.
2490 If @var{count} is negative, the function capitalizes the
2491 @minus{}@var{count} previous words but does not move point. The value
2494 If point is in the middle of a word, the part of the word before point
2495 is ignored when moving forward. The rest is treated as an entire word.
2497 When @code{capitalize-word} is called interactively, @var{count} is
2498 set to the numeric prefix argument.
2501 @deffn Command downcase-word count
2502 This function converts the @var{count} words after point to all lower
2503 case, moving point over as it does. If @var{count} is negative, it
2504 converts the @minus{}@var{count} previous words but does not move point.
2505 The value is @code{nil}.
2507 When @code{downcase-word} is called interactively, @var{count} is set
2508 to the numeric prefix argument.
2511 @deffn Command upcase-word count
2512 This function converts the @var{count} words after point to all upper
2513 case, moving point over as it does. If @var{count} is negative, it
2514 converts the @minus{}@var{count} previous words but does not move point.
2515 The value is @code{nil}.
2517 When @code{upcase-word} is called interactively, @var{count} is set to
2518 the numeric prefix argument.
2521 @node Text Properties
2522 @section Text Properties
2523 @cindex text properties
2524 @cindex attributes of text
2525 @cindex properties of text
2527 Each character position in a buffer or a string can have a @dfn{text
2528 property list}, much like the property list of a symbol (@pxref{Property
2529 Lists}). The properties belong to a particular character at a
2530 particular place, such as, the letter @samp{T} at the beginning of this
2531 sentence or the first @samp{o} in @samp{foo}---if the same character
2532 occurs in two different places, the two occurrences generally have
2533 different properties.
2535 Each property has a name and a value. Both of these can be any Lisp
2536 object, but the name is normally a symbol. The usual way to access the
2537 property list is to specify a name and ask what value corresponds to it.
2539 If a character has a @code{category} property, we call it the
2540 @dfn{category} of the character. It should be a symbol. The properties
2541 of the symbol serve as defaults for the properties of the character.
2543 Copying text between strings and buffers preserves the properties
2544 along with the characters; this includes such diverse functions as
2545 @code{substring}, @code{insert}, and @code{buffer-substring}.
2548 * Examining Properties:: Looking at the properties of one character.
2549 * Changing Properties:: Setting the properties of a range of text.
2550 * Property Search:: Searching for where a property changes value.
2551 * Special Properties:: Particular properties with special meanings.
2552 * Format Properties:: Properties for representing formatting of text.
2553 * Sticky Properties:: How inserted text gets properties from
2555 * Saving Properties:: Saving text properties in files, and reading
2557 * Lazy Properties:: Computing text properties in a lazy fashion
2558 only when text is examined.
2559 * Clickable Text:: Using text properties to make regions of text
2560 do something when you click on them.
2561 * Links and Mouse-1:: How to make @key{Mouse-1} follow a link.
2562 * Fields:: The @code{field} property defines
2563 fields within the buffer.
2564 * Not Intervals:: Why text properties do not use
2565 Lisp-visible text intervals.
2568 @node Examining Properties
2569 @subsection Examining Text Properties
2571 The simplest way to examine text properties is to ask for the value of
2572 a particular property of a particular character. For that, use
2573 @code{get-text-property}. Use @code{text-properties-at} to get the
2574 entire property list of a character. @xref{Property Search}, for
2575 functions to examine the properties of a number of characters at once.
2577 These functions handle both strings and buffers. Keep in mind that
2578 positions in a string start from 0, whereas positions in a buffer start
2581 @defun get-text-property pos prop &optional object
2582 This function returns the value of the @var{prop} property of the
2583 character after position @var{pos} in @var{object} (a buffer or
2584 string). The argument @var{object} is optional and defaults to the
2587 If there is no @var{prop} property strictly speaking, but the character
2588 has a category that is a symbol, then @code{get-text-property} returns
2589 the @var{prop} property of that symbol.
2592 @defun get-char-property position prop &optional object
2593 This function is like @code{get-text-property}, except that it checks
2594 overlays first and then text properties. @xref{Overlays}.
2596 The argument @var{object} may be a string, a buffer, or a window. If it
2597 is a window, then the buffer displayed in that window is used for text
2598 properties and overlays, but only the overlays active for that window
2599 are considered. If @var{object} is a buffer, then all overlays in that
2600 buffer are considered, as well as text properties. If @var{object} is a
2601 string, only text properties are considered, since strings never have
2605 @defun get-char-property-and-overlay position prop &optional object
2606 This is like @code{get-char-property}, but gives extra information
2607 about the overlay that the property value comes from.
2609 Its value is a cons cell whose @sc{car} is the property value, the
2610 same value @code{get-char-property} would return with the same
2611 arguments. Its @sc{cdr} is the overlay in which the property was
2612 found, or @code{nil}, if it was found as a text property or not found
2615 If @var{position} is at the end of @var{object}, both the @sc{car} and
2616 the @sc{cdr} of the value are @code{nil}.
2619 @defvar char-property-alias-alist
2620 This variable holds an alist which maps property names to a list of
2621 alternative property names. If a character does not specify a direct
2622 value for a property, the alternative property names are consulted in
2623 order; the first non-@code{nil} value is used. This variable takes
2624 precedence over @code{default-text-properties}, and @code{category}
2625 properties take precedence over this variable.
2628 @defun text-properties-at position &optional object
2629 This function returns the entire property list of the character at
2630 @var{position} in the string or buffer @var{object}. If @var{object} is
2631 @code{nil}, it defaults to the current buffer.
2634 @defvar default-text-properties
2635 This variable holds a property list giving default values for text
2636 properties. Whenever a character does not specify a value for a
2637 property, neither directly, through a category symbol, or through
2638 @code{char-property-alias-alist}, the value stored in this list is
2639 used instead. Here is an example:
2642 (setq default-text-properties '(foo 69)
2643 char-property-alias-alist nil)
2644 ;; @r{Make sure character 1 has no properties of its own.}
2645 (set-text-properties 1 2 nil)
2646 ;; @r{What we get, when we ask, is the default value.}
2647 (get-text-property 1 'foo)
2652 @node Changing Properties
2653 @subsection Changing Text Properties
2655 The primitives for changing properties apply to a specified range of
2656 text in a buffer or string. The function @code{set-text-properties}
2657 (see end of section) sets the entire property list of the text in that
2658 range; more often, it is useful to add, change, or delete just certain
2659 properties specified by name.
2661 Since text properties are considered part of the contents of the
2662 buffer (or string), and can affect how a buffer looks on the screen,
2663 any change in buffer text properties marks the buffer as modified.
2664 Buffer text property changes are undoable also (@pxref{Undo}).
2665 Positions in a string start from 0, whereas positions in a buffer
2668 @defun put-text-property start end prop value &optional object
2669 This function sets the @var{prop} property to @var{value} for the text
2670 between @var{start} and @var{end} in the string or buffer @var{object}.
2671 If @var{object} is @code{nil}, it defaults to the current buffer.
2674 @defun add-text-properties start end props &optional object
2675 This function adds or overrides text properties for the text between
2676 @var{start} and @var{end} in the string or buffer @var{object}. If
2677 @var{object} is @code{nil}, it defaults to the current buffer.
2679 The argument @var{props} specifies which properties to add. It should
2680 have the form of a property list (@pxref{Property Lists}): a list whose
2681 elements include the property names followed alternately by the
2682 corresponding values.
2684 The return value is @code{t} if the function actually changed some
2685 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2686 its values agree with those in the text).
2688 For example, here is how to set the @code{comment} and @code{face}
2689 properties of a range of text:
2692 (add-text-properties @var{start} @var{end}
2693 '(comment t face highlight))
2697 @defun remove-text-properties start end props &optional object
2698 This function deletes specified text properties from the text between
2699 @var{start} and @var{end} in the string or buffer @var{object}. If
2700 @var{object} is @code{nil}, it defaults to the current buffer.
2702 The argument @var{props} specifies which properties to delete. It
2703 should have the form of a property list (@pxref{Property Lists}): a list
2704 whose elements are property names alternating with corresponding values.
2705 But only the names matter---the values that accompany them are ignored.
2706 For example, here's how to remove the @code{face} property.
2709 (remove-text-properties @var{start} @var{end} '(face nil))
2712 The return value is @code{t} if the function actually changed some
2713 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2714 if no character in the specified text had any of those properties).
2716 To remove all text properties from certain text, use
2717 @code{set-text-properties} and specify @code{nil} for the new property
2721 @defun remove-list-of-text-properties start end list-of-properties &optional object
2722 Like @code{remove-text-properties} except that
2723 @var{list-of-properties} is a list property names only, not an
2724 alternating list of property names and values.
2727 @defun set-text-properties start end props &optional object
2728 This function completely replaces the text property list for the text
2729 between @var{start} and @var{end} in the string or buffer @var{object}.
2730 If @var{object} is @code{nil}, it defaults to the current buffer.
2732 The argument @var{props} is the new property list. It should be a list
2733 whose elements are property names alternating with corresponding values.
2735 After @code{set-text-properties} returns, all the characters in the
2736 specified range have identical properties.
2738 If @var{props} is @code{nil}, the effect is to get rid of all properties
2739 from the specified range of text. Here's an example:
2742 (set-text-properties @var{start} @var{end} nil)
2746 The easiest way to make a string with text properties
2747 is with @code{propertize}:
2749 @defun propertize string &rest properties
2751 This function returns a copy of @var{string} which has the text
2752 properties @var{properties}. These properties apply to all the
2753 characters in the string that is returned. Here is an example that
2754 constructs a string with a @code{face} property and a @code{mouse-face}
2758 (propertize "foo" 'face 'italic
2759 'mouse-face 'bold-italic)
2760 @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
2763 To put different properties on various parts of a string, you can
2764 construct each part with @code{propertize} and then combine them with
2769 (propertize "foo" 'face 'italic
2770 'mouse-face 'bold-italic)
2772 (propertize "bar" 'face 'italic
2773 'mouse-face 'bold-italic))
2774 @result{} #("foo and bar"
2775 0 3 (face italic mouse-face bold-italic)
2777 8 11 (face italic mouse-face bold-italic))
2781 See also the function @code{buffer-substring-no-properties}
2782 (@pxref{Buffer Contents}) which copies text from the buffer
2783 but does not copy its properties.
2785 @node Property Search
2786 @subsection Text Property Search Functions
2788 In typical use of text properties, most of the time several or many
2789 consecutive characters have the same value for a property. Rather than
2790 writing your programs to examine characters one by one, it is much
2791 faster to process chunks of text that have the same property value.
2793 Here are functions you can use to do this. They use @code{eq} for
2794 comparing property values. In all cases, @var{object} defaults to the
2797 For high performance, it's very important to use the @var{limit}
2798 argument to these functions, especially the ones that search for a
2799 single property---otherwise, they may spend a long time scanning to the
2800 end of the buffer, if the property you are interested in does not change.
2802 These functions do not move point; instead, they return a position (or
2803 @code{nil}). Remember that a position is always between two characters;
2804 the position returned by these functions is between two characters with
2805 different properties.
2807 @defun next-property-change pos &optional object limit
2808 The function scans the text forward from position @var{pos} in the
2809 string or buffer @var{object} till it finds a change in some text
2810 property, then returns the position of the change. In other words, it
2811 returns the position of the first character beyond @var{pos} whose
2812 properties are not identical to those of the character just after
2815 If @var{limit} is non-@code{nil}, then the scan ends at position
2816 @var{limit}. If there is no property change before that point,
2817 @code{next-property-change} returns @var{limit}.
2819 The value is @code{nil} if the properties remain unchanged all the way
2820 to the end of @var{object} and @var{limit} is @code{nil}. If the value
2821 is non-@code{nil}, it is a position greater than or equal to @var{pos}.
2822 The value equals @var{pos} only when @var{limit} equals @var{pos}.
2824 Here is an example of how to scan the buffer by chunks of text within
2825 which all properties are constant:
2829 (let ((plist (text-properties-at (point)))
2831 (or (next-property-change (point) (current-buffer))
2833 @r{Process text from point to @var{next-change}@dots{}}
2834 (goto-char next-change)))
2838 @defun next-single-property-change pos prop &optional object limit
2839 The function scans the text forward from position @var{pos} in the
2840 string or buffer @var{object} till it finds a change in the @var{prop}
2841 property, then returns the position of the change. In other words, it
2842 returns the position of the first character beyond @var{pos} whose
2843 @var{prop} property differs from that of the character just after
2846 If @var{limit} is non-@code{nil}, then the scan ends at position
2847 @var{limit}. If there is no property change before that point,
2848 @code{next-single-property-change} returns @var{limit}.
2850 The value is @code{nil} if the property remains unchanged all the way to
2851 the end of @var{object} and @var{limit} is @code{nil}. If the value is
2852 non-@code{nil}, it is a position greater than or equal to @var{pos}; it
2853 equals @var{pos} only if @var{limit} equals @var{pos}.
2856 @defun previous-property-change pos &optional object limit
2857 This is like @code{next-property-change}, but scans back from @var{pos}
2858 instead of forward. If the value is non-@code{nil}, it is a position
2859 less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
2863 @defun previous-single-property-change pos prop &optional object limit
2864 This is like @code{next-single-property-change}, but scans back from
2865 @var{pos} instead of forward. If the value is non-@code{nil}, it is a
2866 position less than or equal to @var{pos}; it equals @var{pos} only if
2867 @var{limit} equals @var{pos}.
2870 @defun next-char-property-change pos &optional limit
2871 This is like @code{next-property-change} except that it considers
2872 overlay properties as well as text properties, and if no change is
2873 found before the end of the buffer, it returns the maximum buffer
2874 position rather than @code{nil} (in this sense, it resembles the
2875 corresponding overlay function @code{next-overlay-change}, rather than
2876 @code{next-property-change}). There is no @var{object} operand
2877 because this function operates only on the current buffer. It returns
2878 the next address at which either kind of property changes.
2881 @defun previous-char-property-change pos &optional limit
2882 This is like @code{next-char-property-change}, but scans back from
2883 @var{pos} instead of forward, and returns the minimum buffer
2884 position if no change is found.
2887 @defun next-single-char-property-change pos prop &optional object limit
2888 @tindex next-single-char-property-change
2889 This is like @code{next-single-property-change} except that it
2890 considers overlay properties as well as text properties, and if no
2891 change is found before the end of the @var{object}, it returns the
2892 maximum valid position in @var{object} rather than @code{nil}. Unlike
2893 @code{next-char-property-change}, this function @emph{does} have an
2894 @var{object} operand; if @var{object} is not a buffer, only
2895 text-properties are considered.
2898 @defun previous-single-char-property-change pos prop &optional object limit
2899 @tindex previous-single-char-property-change
2900 This is like @code{next-single-char-property-change}, but scans back
2901 from @var{pos} instead of forward, and returns the minimum valid
2902 position in @var{object} if no change is found.
2905 @defun text-property-any start end prop value &optional object
2906 This function returns non-@code{nil} if at least one character between
2907 @var{start} and @var{end} has a property @var{prop} whose value is
2908 @var{value}. More precisely, it returns the position of the first such
2909 character. Otherwise, it returns @code{nil}.
2911 The optional fifth argument, @var{object}, specifies the string or
2912 buffer to scan. Positions are relative to @var{object}. The default
2913 for @var{object} is the current buffer.
2916 @defun text-property-not-all start end prop value &optional object
2917 This function returns non-@code{nil} if at least one character between
2918 @var{start} and @var{end} does not have a property @var{prop} with value
2919 @var{value}. More precisely, it returns the position of the first such
2920 character. Otherwise, it returns @code{nil}.
2922 The optional fifth argument, @var{object}, specifies the string or
2923 buffer to scan. Positions are relative to @var{object}. The default
2924 for @var{object} is the current buffer.
2927 @node Special Properties
2928 @subsection Properties with Special Meanings
2930 Here is a table of text property names that have special built-in
2931 meanings. The following sections list a few additional special property
2932 names that control filling and property inheritance. All other names
2933 have no standard meaning, and you can use them as you like.
2936 @cindex category of text character
2937 @kindex category @r{(text property)}
2939 If a character has a @code{category} property, we call it the
2940 @dfn{category} of the character. It should be a symbol. The properties
2941 of the symbol serve as defaults for the properties of the character.
2944 @cindex face codes of text
2945 @kindex face @r{(text property)}
2946 You can use the property @code{face} to control the font and color of
2947 text. @xref{Faces}, for more information.
2949 In the simplest case, the value is a face name. It can also be a list;
2950 then each element can be any of these possibilities;
2954 A face name (a symbol or string).
2957 A property list of face attributes. This has the
2958 form (@var{keyword} @var{value} @dots{}), where each @var{keyword} is a
2959 face attribute name and @var{value} is a meaningful value for that
2960 attribute. With this feature, you do not need to create a face each
2961 time you want to specify a particular attribute for certain text.
2962 @xref{Face Attributes}.
2965 A cons cell of the form @code{(foreground-color . @var{color-name})} or
2966 @code{(background-color . @var{color-name})}. These elements specify
2967 just the foreground color or just the background color.
2969 @code{(foreground-color . @var{color-name})} is equivalent to
2970 specifying @code{(:foreground @var{color-name})}, and likewise for the
2974 You can use Font Lock Mode (@pxref{Font Lock Mode}), to dynamically
2975 update @code{face} properties based on the contents of the text.
2977 @item font-lock-face
2978 @kindex font-lock-face @r{(text property)}
2979 The @code{font-lock-face} property is the same in all respects as the
2980 @code{face} property, but its state of activation is controlled by
2981 @code{font-lock-mode}. This can be advantageous for special buffers
2982 which are not intended to be user-editable, or for static areas of
2983 text which are always fontified in the same way.
2984 @xref{Precalculated Fontification}.
2986 Strictly speaking, @code{font-lock-face} is not a built-in text
2987 property; rather, it is implemented in Font Lock mode using
2988 @code{char-property-alias-alist}. @xref{Examining Properties}.
2990 This property is new in Emacs 22.1.
2993 @kindex mouse-face @r{(text property)}
2994 The property @code{mouse-face} is used instead of @code{face} when the
2995 mouse is on or near the character. For this purpose, ``near'' means
2996 that all text between the character and where the mouse is have the same
2997 @code{mouse-face} property value.
3000 @kindex fontified @r{(text property)}
3001 This property, if non-@code{nil}, says that text in the buffer has
3002 had faces assigned automatically by a feature such as Font-Lock mode.
3006 @kindex display @r{(text property)}
3007 This property activates various features that change the
3008 way text is displayed. For example, it can make text appear taller
3009 or shorter, higher or lower, wider or narrow, or replaced with an image.
3010 @xref{Display Property}.
3013 @kindex help-echo @r{(text property)}
3015 @anchor{Text help-echo}
3016 If text has a string as its @code{help-echo} property, then when you
3017 move the mouse onto that text, Emacs displays that string in the echo
3018 area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
3021 If the value of the @code{help-echo} property is a function, that
3022 function is called with three arguments, @var{window}, @var{object} and
3023 @var{pos} and should return a help string or @code{nil} for
3024 none. The first argument, @var{window} is the window in which
3025 the help was found. The second, @var{object}, is the buffer, overlay or
3026 string which had the @code{help-echo} property. The @var{pos}
3027 argument is as follows:
3031 If @var{object} is a buffer, @var{pos} is the position in the buffer
3032 where the @code{help-echo} text property was found.
3034 If @var{object} is an overlay, that overlay has a @code{help-echo}
3035 property, and @var{pos} is the position in the overlay's buffer under
3038 If @var{object} is a string (an overlay string or a string displayed
3039 with the @code{display} property), @var{pos} is the position in that
3040 string under the mouse.
3043 If the value of the @code{help-echo} property is neither a function nor
3044 a string, it is evaluated to obtain a help string.
3046 You can alter the way help text is displayed by setting the variable
3047 @code{show-help-function} (@pxref{Help display}).
3049 This feature is used in the mode line and for other active text.
3052 @cindex keymap of character
3053 @kindex keymap @r{(text property)}
3054 The @code{keymap} property specifies an additional keymap for
3055 commands. The property's value for the character before point applies
3056 if it is non-@code{nil} and rear-sticky, and the property's value for
3057 the character after point applies if it is non-@code{nil} and
3058 front-sticky. (For mouse clicks, the position of the click is used
3059 instead of the position of point.) If the property value is a symbol,
3060 the symbol's function definition is used as the keymap.
3062 When this keymap applies, it is used for key lookup before the minor
3063 mode keymaps and before the buffer's local map. @xref{Active
3067 @kindex local-map @r{(text property)}
3068 This property works like @code{keymap} except that it specifies a
3069 keymap to use @emph{instead of} the buffer's local map. For most
3070 purposes (perhaps all purposes), the @code{keymap} is superior.
3073 The @code{syntax-table} property overrides what the syntax table says
3074 about this particular character. @xref{Syntax Properties}.
3077 @cindex read-only character
3078 @kindex read-only @r{(text property)}
3079 If a character has the property @code{read-only}, then modifying that
3080 character is not allowed. Any command that would do so gets an error,
3081 @code{text-read-only}.
3083 Insertion next to a read-only character is an error if inserting
3084 ordinary text there would inherit the @code{read-only} property due to
3085 stickiness. Thus, you can control permission to insert next to
3086 read-only text by controlling the stickiness. @xref{Sticky Properties}.
3088 Since changing properties counts as modifying the buffer, it is not
3089 possible to remove a @code{read-only} property unless you know the
3090 special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
3091 and then remove the property. @xref{Read Only Buffers}.
3094 @kindex invisible @r{(text property)}
3095 A non-@code{nil} @code{invisible} property can make a character invisible
3096 on the screen. @xref{Invisible Text}, for details.
3099 @kindex intangible @r{(text property)}
3100 If a group of consecutive characters have equal and non-@code{nil}
3101 @code{intangible} properties, then you cannot place point between them.
3102 If you try to move point forward into the group, point actually moves to
3103 the end of the group. If you try to move point backward into the group,
3104 point actually moves to the start of the group.
3106 When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
3107 the @code{intangible} property is ignored.
3110 @kindex field @r{(text property)}
3111 Consecutive characters with the same @code{field} property constitute a
3112 @dfn{field}. Some motion functions including @code{forward-word} and
3113 @code{beginning-of-line} stop moving at a field boundary.
3117 @kindex cursor @r{(text property)}
3118 Normally, the cursor is displayed at the end of any overlay and text
3119 property strings present at the current window position. You can
3120 place the cursor on any desired character of these strings by giving
3121 that character a non-@code{nil} @var{cursor} text property.
3124 @kindex pointer @r{(text property)}
3125 This specifies a specific pointer shape when the mouse pointer is over
3126 this text or image. @xref{Pointer Shape}, for possible pointer
3130 @kindex line-spacing @r{(text property)}
3131 A newline can have a @code{line-spacing} text or overlay property that
3132 controls the height of the display line ending with that newline. The
3133 property value overrides the default frame line spacing and the buffer
3134 local @code{line-spacing} variable. @xref{Line Height}.
3137 @kindex line-height @r{(text property)}
3138 A newline can have a @code{line-height} text or overlay property that
3139 controls the total height of the display line ending in that newline.
3142 @item modification-hooks
3143 @cindex change hooks for a character
3144 @cindex hooks for changing a character
3145 @kindex modification-hooks @r{(text property)}
3146 If a character has the property @code{modification-hooks}, then its
3147 value should be a list of functions; modifying that character calls all
3148 of those functions. Each function receives two arguments: the beginning
3149 and end of the part of the buffer being modified. Note that if a
3150 particular modification hook function appears on several characters
3151 being modified by a single primitive, you can't predict how many times
3152 the function will be called.
3154 If these functions modify the buffer, they should bind
3155 @code{inhibit-modification-hooks} to @code{t} around doing so, to
3156 avoid confusing the internal mechanism that calls these hooks.
3158 @item insert-in-front-hooks
3159 @itemx insert-behind-hooks
3160 @kindex insert-in-front-hooks @r{(text property)}
3161 @kindex insert-behind-hooks @r{(text property)}
3162 The operation of inserting text in a buffer also calls the functions
3163 listed in the @code{insert-in-front-hooks} property of the following
3164 character and in the @code{insert-behind-hooks} property of the
3165 preceding character. These functions receive two arguments, the
3166 beginning and end of the inserted text. The functions are called
3167 @emph{after} the actual insertion takes place.
3169 See also @ref{Change Hooks}, for other hooks that are called
3170 when you change text in a buffer.
3174 @cindex hooks for motion of point
3175 @kindex point-entered @r{(text property)}
3176 @kindex point-left @r{(text property)}
3177 The special properties @code{point-entered} and @code{point-left}
3178 record hook functions that report motion of point. Each time point
3179 moves, Emacs compares these two property values:
3183 the @code{point-left} property of the character after the old location,
3186 the @code{point-entered} property of the character after the new
3191 If these two values differ, each of them is called (if not @code{nil})
3192 with two arguments: the old value of point, and the new one.
3194 The same comparison is made for the characters before the old and new
3195 locations. The result may be to execute two @code{point-left} functions
3196 (which may be the same function) and/or two @code{point-entered}
3197 functions (which may be the same function). In any case, all the
3198 @code{point-left} functions are called first, followed by all the
3199 @code{point-entered} functions.
3201 It is possible with @code{char-after} to examine characters at various
3202 buffer positions without moving point to those positions. Only an
3203 actual change in the value of point runs these hook functions.
3206 @defvar inhibit-point-motion-hooks
3207 When this variable is non-@code{nil}, @code{point-left} and
3208 @code{point-entered} hooks are not run, and the @code{intangible}
3209 property has no effect. Do not set this variable globally; bind it with
3213 @defvar show-help-function
3214 @tindex show-help-function
3215 @anchor{Help display} If this variable is non-@code{nil}, it specifies a
3216 function called to display help strings. These may be @code{help-echo}
3217 properties, menu help strings (@pxref{Simple Menu Items},
3218 @pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
3219 Bar}). The specified function is called with one argument, the help
3220 string to display. Tooltip mode (@pxref{Tooltips,,, emacs, The GNU Emacs
3221 Manual}) provides an example.
3224 @node Format Properties
3225 @subsection Formatted Text Properties
3227 These text properties affect the behavior of the fill commands. They
3228 are used for representing formatted text. @xref{Filling}, and
3233 If a newline character has this property, it is a ``hard'' newline.
3234 The fill commands do not alter hard newlines and do not move words
3235 across them. However, this property takes effect only if the
3236 @code{use-hard-newlines} minor mode is enabled. @xref{Hard and Soft
3237 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
3240 This property specifies an extra right margin for filling this part of the
3244 This property specifies an extra left margin for filling this part of the
3248 This property specifies the style of justification for filling this part
3252 @node Sticky Properties
3253 @subsection Stickiness of Text Properties
3254 @cindex sticky text properties
3255 @cindex inheritance of text properties
3257 Self-inserting characters normally take on the same properties as the
3258 preceding character. This is called @dfn{inheritance} of properties.
3260 In a Lisp program, you can do insertion with inheritance or without,
3261 depending on your choice of insertion primitive. The ordinary text
3262 insertion functions such as @code{insert} do not inherit any properties.
3263 They insert text with precisely the properties of the string being
3264 inserted, and no others. This is correct for programs that copy text
3265 from one context to another---for example, into or out of the kill ring.
3266 To insert with inheritance, use the special primitives described in this
3267 section. Self-inserting characters inherit properties because they work
3268 using these primitives.
3270 When you do insertion with inheritance, @emph{which} properties are
3271 inherited, and from where, depends on which properties are @dfn{sticky}.
3272 Insertion after a character inherits those of its properties that are
3273 @dfn{rear-sticky}. Insertion before a character inherits those of its
3274 properties that are @dfn{front-sticky}. When both sides offer different
3275 sticky values for the same property, the previous character's value
3278 By default, a text property is rear-sticky but not front-sticky; thus,
3279 the default is to inherit all the properties of the preceding character,
3280 and nothing from the following character.
3282 You can control the stickiness of various text properties with two
3283 specific text properties, @code{front-sticky} and @code{rear-nonsticky},
3284 and with the variable @code{text-property-default-nonsticky}. You can
3285 use the variable to specify a different default for a given property.
3286 You can use those two text properties to make any specific properties
3287 sticky or nonsticky in any particular part of the text.
3289 If a character's @code{front-sticky} property is @code{t}, then all
3290 its properties are front-sticky. If the @code{front-sticky} property is
3291 a list, then the sticky properties of the character are those whose
3292 names are in the list. For example, if a character has a
3293 @code{front-sticky} property whose value is @code{(face read-only)},
3294 then insertion before the character can inherit its @code{face} property
3295 and its @code{read-only} property, but no others.
3297 The @code{rear-nonsticky} property works the opposite way. Most
3298 properties are rear-sticky by default, so the @code{rear-nonsticky}
3299 property says which properties are @emph{not} rear-sticky. If a
3300 character's @code{rear-nonsticky} property is @code{t}, then none of its
3301 properties are rear-sticky. If the @code{rear-nonsticky} property is a
3302 list, properties are rear-sticky @emph{unless} their names are in the
3305 @defvar text-property-default-nonsticky
3306 @tindex text-property-default-nonsticky
3307 This variable holds an alist which defines the default rear-stickiness
3308 of various text properties. Each element has the form
3309 @code{(@var{property} . @var{nonstickiness})}, and it defines the
3310 stickiness of a particular text property, @var{property}.
3312 If @var{nonstickiness} is non-@code{nil}, this means that the property
3313 @var{property} is rear-nonsticky by default. Since all properties are
3314 front-nonsticky by default, this makes @var{property} nonsticky in both
3315 directions by default.
3317 The text properties @code{front-sticky} and @code{rear-nonsticky}, when
3318 used, take precedence over the default @var{nonstickiness} specified in
3319 @code{text-property-default-nonsticky}.
3322 Here are the functions that insert text with inheritance of properties:
3324 @defun insert-and-inherit &rest strings
3325 Insert the strings @var{strings}, just like the function @code{insert},
3326 but inherit any sticky properties from the adjoining text.
3329 @defun insert-before-markers-and-inherit &rest strings
3330 Insert the strings @var{strings}, just like the function
3331 @code{insert-before-markers}, but inherit any sticky properties from the
3335 @xref{Insertion}, for the ordinary insertion functions which do not
3338 @node Saving Properties
3339 @subsection Saving Text Properties in Files
3340 @cindex text properties in files
3341 @cindex saving text properties
3343 You can save text properties in files (along with the text itself),
3344 and restore the same text properties when visiting or inserting the
3345 files, using these two hooks:
3347 @defvar write-region-annotate-functions
3348 This variable's value is a list of functions for @code{write-region} to
3349 run to encode text properties in some fashion as annotations to the text
3350 being written in the file. @xref{Writing to Files}.
3352 Each function in the list is called with two arguments: the start and
3353 end of the region to be written. These functions should not alter the
3354 contents of the buffer. Instead, they should return lists indicating
3355 annotations to write in the file in addition to the text in the
3358 Each function should return a list of elements of the form
3359 @code{(@var{position} . @var{string})}, where @var{position} is an
3360 integer specifying the relative position within the text to be written,
3361 and @var{string} is the annotation to add there.
3363 Each list returned by one of these functions must be already sorted in
3364 increasing order by @var{position}. If there is more than one function,
3365 @code{write-region} merges the lists destructively into one sorted list.
3367 When @code{write-region} actually writes the text from the buffer to the
3368 file, it intermixes the specified annotations at the corresponding
3369 positions. All this takes place without modifying the buffer.
3372 @defvar after-insert-file-functions
3373 This variable holds a list of functions for @code{insert-file-contents}
3374 to call after inserting a file's contents. These functions should scan
3375 the inserted text for annotations, and convert them to the text
3376 properties they stand for.
3378 Each function receives one argument, the length of the inserted text;
3379 point indicates the start of that text. The function should scan that
3380 text for annotations, delete them, and create the text properties that
3381 the annotations specify. The function should return the updated length
3382 of the inserted text, as it stands after those changes. The value
3383 returned by one function becomes the argument to the next function.
3385 These functions should always return with point at the beginning of
3388 The intended use of @code{after-insert-file-functions} is for converting
3389 some sort of textual annotations into actual text properties. But other
3390 uses may be possible.
3393 We invite users to write Lisp programs to store and retrieve text
3394 properties in files, using these hooks, and thus to experiment with
3395 various data formats and find good ones. Eventually we hope users
3396 will produce good, general extensions we can install in Emacs.
3398 We suggest not trying to handle arbitrary Lisp objects as text property
3399 names or values---because a program that general is probably difficult
3400 to write, and slow. Instead, choose a set of possible data types that
3401 are reasonably flexible, and not too hard to encode.
3403 @xref{Format Conversion}, for a related feature.
3405 @c ??? In next edition, merge this info Format Conversion.
3407 @node Lazy Properties
3408 @subsection Lazy Computation of Text Properties
3410 Instead of computing text properties for all the text in the buffer,
3411 you can arrange to compute the text properties for parts of the text
3412 when and if something depends on them.
3414 The primitive that extracts text from the buffer along with its
3415 properties is @code{buffer-substring}. Before examining the properties,
3416 this function runs the abnormal hook @code{buffer-access-fontify-functions}.
3418 @defvar buffer-access-fontify-functions
3419 This variable holds a list of functions for computing text properties.
3420 Before @code{buffer-substring} copies the text and text properties for a
3421 portion of the buffer, it calls all the functions in this list. Each of
3422 the functions receives two arguments that specify the range of the
3423 buffer being accessed. (The buffer itself is always the current
3427 The function @code{buffer-substring-no-properties} does not call these
3428 functions, since it ignores text properties anyway.
3430 In order to prevent the hook functions from being called more than
3431 once for the same part of the buffer, you can use the variable
3432 @code{buffer-access-fontified-property}.
3434 @defvar buffer-access-fontified-property
3435 If this value's variable is non-@code{nil}, it is a symbol which is used
3436 as a text property name. A non-@code{nil} value for that text property
3437 means, ``the other text properties for this character have already been
3440 If all the characters in the range specified for @code{buffer-substring}
3441 have a non-@code{nil} value for this property, @code{buffer-substring}
3442 does not call the @code{buffer-access-fontify-functions} functions. It
3443 assumes these characters already have the right text properties, and
3444 just copies the properties they already have.
3446 The normal way to use this feature is that the
3447 @code{buffer-access-fontify-functions} functions add this property, as
3448 well as others, to the characters they operate on. That way, they avoid
3449 being called over and over for the same text.
3452 @node Clickable Text
3453 @subsection Defining Clickable Text
3454 @cindex clickable text
3456 There are two ways to set up @dfn{clickable text} in a buffer.
3457 There are typically two parts of this: to make the text highlight
3458 when the mouse is over it, and to make a mouse button do something
3459 when you click it on that part of the text.
3461 Highlighting is done with the @code{mouse-face} text property.
3462 Here is an example of how Dired does it:
3466 (if (dired-move-to-filename)
3467 (put-text-property (point)
3469 (dired-move-to-end-of-filename)
3471 'mouse-face 'highlight))
3476 The first two arguments to @code{put-text-property} specify the
3477 beginning and end of the text.
3479 The usual way to make the mouse do something when you click it
3480 on this text is to define @code{mouse-2} in the major mode's
3481 keymap. The job of checking whether the click was on clickable text
3482 is done by the command definition. Here is how Dired does it:
3485 (defun dired-mouse-find-file-other-window (event)
3486 "In dired, visit the file or directory name you click on."
3490 (set-buffer (window-buffer (posn-window (event-end event))))
3492 (goto-char (posn-point (event-end event)))
3493 (setq file (dired-get-filename))))
3494 (select-window (posn-window (event-end event)))
3495 (find-file-other-window (file-name-sans-versions file t))))
3499 The reason for the outer @code{save-excursion} construct is to avoid
3500 changing the current buffer; the reason for the inner one is to avoid
3501 permanently altering point in the buffer you click on. In this case,
3502 Dired uses the function @code{dired-get-filename} to determine which
3503 file to visit, based on the position found in the event.
3505 Instead of defining a mouse command for the major mode, you can define
3506 a key binding for the clickable text itself, using the @code{keymap}
3510 (let ((map (make-sparse-keymap)))
3511 (define-key map [mouse-2] 'operate-this-button)
3512 (put-text-property (point)
3514 (dired-move-to-end-of-filename)
3520 This method makes it possible to define different commands for various
3521 clickable pieces of text. Also, the major mode definition (or the
3522 global definition) remains available for the rest of the text in the
3525 @node Links and Mouse-1
3526 @subsection Links and Mouse-1
3527 @cindex follow links
3530 The normal Emacs command for activating text in read-only buffers is
3531 @key{Mouse-2}, which includes following textual links. However, most
3532 graphical applications use @key{Mouse-1} for following links. For
3533 compatibility, @key{Mouse-1} follows links in Emacs too, when you
3534 click on a link quickly without moving the mouse. The user can
3535 customize this behavior through the variable
3536 @code{mouse-1-click-follows-link}.
3538 To define text as a link at the Lisp level, you should bind the
3539 @code{mouse-2} event to a command to follow the link. Then, to indicate that
3540 @key{Mouse-1} should also follow the link, you should specify a
3541 @code{follow-link} condition either as a text property or as a key
3545 @item @code{follow-link} property
3546 If the clickable text has a non-@code{nil} @code{follow-link} text or overlay
3547 property, that specifies the condition.
3549 @item @code{follow-link} event
3550 If there is a binding for the @code{follow-link} event, either on the
3551 clickable text or in the local keymap, the binding is the condition.
3554 Regardless of how you set the @code{follow-link} condition, its
3555 value is used as follows to determine whether the given position is
3556 inside a link, and (if so) to compute an @dfn{action code} saying how
3557 @key{Mouse-1} should handle the link.
3560 @item @code{mouse-face}
3561 If the condition is @code{mouse-face}, a position is inside a link if
3562 there is a non-@code{nil} @code{mouse-face} property at that position.
3563 The action code is always @code{t}.
3565 For example, here is how Info mode handles @key{Mouse-1}:
3568 (define-key Info-mode-map [follow-link] 'mouse-face)
3572 If the condition is a valid function, @var{func}, then a position
3573 @var{pos} is inside a link if @code{(@var{func} @var{pos})} evaluates
3574 to non-@code{nil}. The value returned by @var{func} serves as the
3577 For example, here is how pcvs enables @key{Mouse-1} to follow links on
3581 (define-key map [follow-link]
3583 (eq (get-char-property pos 'face) 'cvs-filename-face)))
3587 If the condition value is anything else, then the position is inside a
3588 link and the condition itself is the action code. Clearly you should
3589 only specify this kind of condition on the text that constitutes a
3594 The action code tells @key{Mouse-1} how to follow the link:
3597 @item a string or vector
3598 If the action code is a string or vector, the @key{Mouse-1} event is
3599 translated into the first element of the string or vector; i.e., the
3600 action of the @key{Mouse-1} click is the local or global binding of
3601 that character or symbol. Thus, if the action code is @code{"foo"},
3602 @key{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
3603 @key{Mouse-1} translates into @key{foo}.
3606 For any other non-@code{nil} action code, the @code{mouse-1} event is
3607 translated into a @code{mouse-2} event at the same position.
3610 To define @key{Mouse-1} to activate a button defined with
3611 @code{define-button-type}, give the button a @code{follow-link}
3612 property with a value as specified above to determine how to follow
3613 the link. For example, here is how Help mode handles @key{Mouse-1}:
3616 (define-button-type 'help-xref
3618 'action #'help-button-action)
3621 To define @key{Mouse-1} on a widget defined with
3622 @code{define-widget}, give the widget a @code{:follow-link} property
3623 with a value as specified above to determine how to follow the link.
3625 For example, here is how the @code{link} widget specifies that
3626 a @key{Mouse-1} click shall be translated to @key{RET}:
3629 (define-widget 'link 'item
3631 :button-prefix 'widget-link-prefix
3632 :button-suffix 'widget-link-suffix
3634 :help-echo "Follow the link."
3638 @defun mouse-on-link-p pos
3639 @tindex mouse-on-link-p
3640 This function returns non-@code{nil} if position @var{pos} in the
3641 current buffer is on a link.
3645 @subsection Defining and Using Fields
3648 A field is a range of consecutive characters in the buffer that are
3649 identified by having the same value (comparing with @code{eq}) of the
3650 @code{field} property (either a text-property or an overlay property).
3651 This section describes special functions that are available for
3652 operating on fields.
3654 You specify a field with a buffer position, @var{pos}. We think of
3655 each field as containing a range of buffer positions, so the position
3656 you specify stands for the field containing that position.
3658 When the characters before and after @var{pos} are part of the same
3659 field, there is no doubt which field contains @var{pos}: the one those
3660 characters both belong to. When @var{pos} is at a boundary between
3661 fields, which field it belongs to depends on the stickiness of the
3662 @code{field} properties of the two surrounding characters (@pxref{Sticky
3663 Properties}). The field whose property would be inherited by text
3664 inserted at @var{pos} is the field that contains @var{pos}.
3666 There is an anomalous case where newly inserted text at @var{pos}
3667 would not inherit the @code{field} property from either side. This
3668 happens if the previous character's @code{field} property is not
3669 rear-sticky, and the following character's @code{field} property is not
3670 front-sticky. In this case, @var{pos} belongs to neither the preceding
3671 field nor the following field; the field functions treat it as belonging
3672 to an empty field whose beginning and end are both at @var{pos}.
3674 In all of these functions, if @var{pos} is omitted or @code{nil}, the
3675 value of point is used by default.
3677 @defun field-beginning &optional pos escape-from-edge limit
3678 @tindex field-beginning
3679 This function returns the beginning of the field specified by @var{pos}.
3681 If @var{pos} is at the beginning of its field, and
3682 @var{escape-from-edge} is non-@code{nil}, then the return value is
3683 always the beginning of the preceding field that @emph{ends} at @var{pos},
3684 regardless of the stickiness of the @code{field} properties around
3687 If @var{limit} is non-@code{nil}, it is a buffer position; if the
3688 beginning of the field is before @var{limit}, then @var{limit} will be
3692 @defun field-end &optional pos escape-from-edge limit
3694 This function returns the end of the field specified by @var{pos}.
3696 If @var{pos} is at the end of its field, and @var{escape-from-edge} is
3697 non-@code{nil}, then the return value is always the end of the following
3698 field that @emph{begins} at @var{pos}, regardless of the stickiness of
3699 the @code{field} properties around @var{pos}.
3701 If @var{limit} is non-@code{nil}, it is a buffer position; if the end
3702 of the field is after @var{limit}, then @var{limit} will be returned
3706 @defun field-string &optional pos
3707 @tindex field-string
3708 This function returns the contents of the field specified by @var{pos},
3712 @defun field-string-no-properties &optional pos
3713 @tindex field-string-no-properties
3714 This function returns the contents of the field specified by @var{pos},
3715 as a string, discarding text properties.
3718 @defun delete-field &optional pos
3719 @tindex delete-field
3720 This function deletes the text of the field specified by @var{pos}.
3723 @defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
3724 @tindex constrain-to-field
3725 This function ``constrains'' @var{new-pos} to the field that
3726 @var{old-pos} belongs to---in other words, it returns the position
3727 closest to @var{new-pos} that is in the same field as @var{old-pos}.
3729 If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
3730 the value of point instead, and moves point to the resulting position.
3732 If @var{old-pos} is at the boundary of two fields, then the acceptable
3733 positions for @var{new-pos} depend on the value of the optional argument
3734 @var{escape-from-edge}. If @var{escape-from-edge} is @code{nil}, then
3735 @var{new-pos} is constrained to the field that has the same @code{field}
3736 property (either a text-property or an overlay property) that new
3737 characters inserted at @var{old-pos} would get. (This depends on the
3738 stickiness of the @code{field} property for the characters before and
3739 after @var{old-pos}.) If @var{escape-from-edge} is non-@code{nil},
3740 @var{new-pos} is constrained to the union of the two adjacent fields.
3741 Additionally, if two fields are separated by another field with the
3742 special value @code{boundary}, then any point within this special field
3743 is also considered to be ``on the boundary.''
3745 If the optional argument @var{only-in-line} is non-@code{nil}, and
3746 constraining @var{new-pos} in the usual way would move it to a different
3747 line, @var{new-pos} is returned unconstrained. This used in commands
3748 that move by line, such as @code{next-line} and
3749 @code{beginning-of-line}, so that they respect field boundaries only in
3750 the case where they can still move to the right line.
3752 If the optional argument @var{inhibit-capture-property} is
3753 non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
3754 name, then any field boundaries are ignored.
3756 You can cause @code{constrain-to-field} to ignore all field boundaries
3757 (and so never constrain anything) by binding the variable
3758 @code{inhibit-field-text-motion} to a non-@code{nil} value.
3762 @subsection Why Text Properties are not Intervals
3765 Some editors that support adding attributes to text in the buffer do
3766 so by letting the user specify ``intervals'' within the text, and adding
3767 the properties to the intervals. Those editors permit the user or the
3768 programmer to determine where individual intervals start and end. We
3769 deliberately provided a different sort of interface in Emacs Lisp to
3770 avoid certain paradoxical behavior associated with text modification.
3772 If the actual subdivision into intervals is meaningful, that means you
3773 can distinguish between a buffer that is just one interval with a
3774 certain property, and a buffer containing the same text subdivided into
3775 two intervals, both of which have that property.
3777 Suppose you take the buffer with just one interval and kill part of
3778 the text. The text remaining in the buffer is one interval, and the
3779 copy in the kill ring (and the undo list) becomes a separate interval.
3780 Then if you yank back the killed text, you get two intervals with the
3781 same properties. Thus, editing does not preserve the distinction
3782 between one interval and two.
3784 Suppose we ``fix'' this problem by coalescing the two intervals when
3785 the text is inserted. That works fine if the buffer originally was a
3786 single interval. But suppose instead that we have two adjacent
3787 intervals with the same properties, and we kill the text of one interval
3788 and yank it back. The same interval-coalescence feature that rescues
3789 the other case causes trouble in this one: after yanking, we have just
3790 one interval. One again, editing does not preserve the distinction
3791 between one interval and two.
3793 Insertion of text at the border between intervals also raises
3794 questions that have no satisfactory answer.
3796 However, it is easy to arrange for editing to behave consistently for
3797 questions of the form, ``What are the properties of this character?''
3798 So we have decided these are the only questions that make sense; we have
3799 not implemented asking questions about where intervals start or end.
3801 In practice, you can usually use the text property search functions in
3802 place of explicit interval boundaries. You can think of them as finding
3803 the boundaries of intervals, assuming that intervals are always
3804 coalesced whenever possible. @xref{Property Search}.
3806 Emacs also provides explicit intervals as a presentation feature; see
3810 @section Substituting for a Character Code
3812 The following functions replace characters within a specified region
3813 based on their character codes.
3815 @defun subst-char-in-region start end old-char new-char &optional noundo
3816 @cindex replace characters
3817 This function replaces all occurrences of the character @var{old-char}
3818 with the character @var{new-char} in the region of the current buffer
3819 defined by @var{start} and @var{end}.
3821 @cindex undo avoidance
3822 If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
3823 not record the change for undo and does not mark the buffer as modified.
3824 This was useful for controlling the old selective display feature
3825 (@pxref{Selective Display}).
3827 @code{subst-char-in-region} does not move point and returns
3832 ---------- Buffer: foo ----------
3833 This is the contents of the buffer before.
3834 ---------- Buffer: foo ----------
3838 (subst-char-in-region 1 20 ?i ?X)
3841 ---------- Buffer: foo ----------
3842 ThXs Xs the contents of the buffer before.
3843 ---------- Buffer: foo ----------
3848 @defun translate-region start end table
3849 This function applies a translation table to the characters in the
3850 buffer between positions @var{start} and @var{end}.
3852 The translation table @var{table} is a string or a char-table;
3853 @code{(aref @var{table} @var{ochar})} gives the translated character
3854 corresponding to @var{ochar}. If @var{table} is a string, any
3855 characters with codes larger than the length of @var{table} are not
3856 altered by the translation.
3858 The return value of @code{translate-region} is the number of
3859 characters that were actually changed by the translation. This does
3860 not count characters that were mapped into themselves in the
3868 A register is a sort of variable used in Emacs editing that can hold a
3869 variety of different kinds of values. Each register is named by a
3870 single character. All @acronym{ASCII} characters and their meta variants
3871 (but with the exception of @kbd{C-g}) can be used to name registers.
3872 Thus, there are 255 possible registers. A register is designated in
3873 Emacs Lisp by the character that is its name.
3875 @defvar register-alist
3876 This variable is an alist of elements of the form @code{(@var{name} .
3877 @var{contents})}. Normally, there is one element for each Emacs
3878 register that has been used.
3880 The object @var{name} is a character (an integer) identifying the
3884 The @var{contents} of a register can have several possible types:
3888 A number stands for itself. If @code{insert-register} finds a number
3889 in the register, it converts the number to decimal.
3892 A marker represents a buffer position to jump to.
3895 A string is text saved in the register.
3898 A rectangle is represented by a list of strings.
3900 @item @code{(@var{window-configuration} @var{position})}
3901 This represents a window configuration to restore in one frame, and a
3902 position to jump to in the current buffer.
3904 @item @code{(@var{frame-configuration} @var{position})}
3905 This represents a frame configuration to restore, and a position
3906 to jump to in the current buffer.
3908 @item (file @var{filename})
3909 This represents a file to visit; jumping to this value visits file
3912 @item (file-query @var{filename} @var{position})
3913 This represents a file to visit and a position in it; jumping to this
3914 value visits file @var{filename} and goes to buffer position
3915 @var{position}. Restoring this type of position asks the user for
3919 The functions in this section return unpredictable values unless
3922 @defun get-register reg
3923 This function returns the contents of the register
3924 @var{reg}, or @code{nil} if it has no contents.
3927 @defun set-register reg value
3928 This function sets the contents of register @var{reg} to @var{value}.
3929 A register can be set to any value, but the other register functions
3930 expect only certain data types. The return value is @var{value}.
3933 @deffn Command view-register reg
3934 This command displays what is contained in register @var{reg}.
3938 @deffn Command point-to-register reg
3939 This command stores both the current location of point and the current
3940 buffer in register @var{reg} as a marker.
3943 @deffn Command jump-to-register reg
3944 @deffnx Command register-to-point reg
3945 @comment !!SourceFile register.el
3946 This command restores the status recorded in register @var{reg}.
3948 If @var{reg} contains a marker, it moves point to the position stored in
3949 the marker. Since both the buffer and the location within the buffer
3950 are stored by the @code{point-to-register} function, this command can
3951 switch you to another buffer.
3953 If @var{reg} contains a window configuration or a frame configuration.
3954 @code{jump-to-register} restores that configuration.
3958 @deffn Command insert-register reg &optional beforep
3959 This command inserts contents of register @var{reg} into the current
3962 Normally, this command puts point before the inserted text, and the
3963 mark after it. However, if the optional second argument @var{beforep}
3964 is non-@code{nil}, it puts the mark before and point after.
3965 You can pass a non-@code{nil} second argument @var{beforep} to this
3966 function interactively by supplying any prefix argument.
3968 If the register contains a rectangle, then the rectangle is inserted
3969 with its upper left corner at point. This means that text is inserted
3970 in the current line and underneath it on successive lines.
3972 If the register contains something other than saved text (a string) or
3973 a rectangle (a list), currently useless things happen. This may be
3974 changed in the future.
3978 @deffn Command copy-to-register reg start end &optional delete-flag
3979 This command copies the region from @var{start} to @var{end} into
3980 register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes
3981 the region from the buffer after copying it into the register.
3984 @deffn Command prepend-to-register reg start end &optional delete-flag
3985 This command prepends the region from @var{start} to @var{end} into
3986 register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes
3987 the region from the buffer after copying it to the register.
3990 @deffn Command append-to-register reg start end &optional delete-flag
3991 This command appends the region from @var{start} to @var{end} to the
3992 text already in register @var{reg}. If @var{delete-flag} is
3993 non-@code{nil}, it deletes the region from the buffer after copying it
3997 @deffn Command copy-rectangle-to-register reg start end &optional delete-flag
3998 This command copies a rectangular region from @var{start} to @var{end}
3999 into register @var{reg}. If @var{delete-flag} is non-@code{nil}, it
4000 deletes the region from the buffer after copying it to the register.
4003 @deffn Command window-configuration-to-register reg
4004 This function stores the window configuration of the selected frame in
4008 @deffn Command frame-configuration-to-register reg
4009 This function stores the current frame configuration in register
4015 @section Transposition of Text
4017 This subroutine is used by the transposition commands.
4019 @defun transpose-regions start1 end1 start2 end2 &optional leave-markers
4020 This function exchanges two nonoverlapping portions of the buffer.
4021 Arguments @var{start1} and @var{end1} specify the bounds of one portion
4022 and arguments @var{start2} and @var{end2} specify the bounds of the
4025 Normally, @code{transpose-regions} relocates markers with the transposed
4026 text; a marker previously positioned within one of the two transposed
4027 portions moves along with that portion, thus remaining between the same
4028 two characters in their new position. However, if @var{leave-markers}
4029 is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
4030 all markers unrelocated.
4034 @section Base 64 Encoding
4035 @cindex base 64 encoding
4037 Base 64 code is used in email to encode a sequence of 8-bit bytes as
4038 a longer sequence of @acronym{ASCII} graphic characters. It is defined in
4039 Internet RFC@footnote{
4040 An RFC, an acronym for @dfn{Request for Comments}, is a numbered
4041 Internet informational document describing a standard. RFCs are
4042 usually written by technical experts acting on their own initiative,
4043 and are traditionally written in a pragmatic, experience-driven
4045 }2045. This section describes the functions for
4046 converting to and from this code.
4048 @defun base64-encode-region beg end &optional no-line-break
4049 @tindex base64-encode-region
4050 This function converts the region from @var{beg} to @var{end} into base
4051 64 code. It returns the length of the encoded text. An error is
4052 signaled if a character in the region is multibyte, i.e.@: in a
4053 multibyte buffer the region must contain only characters from the
4054 charsets @code{ascii}, @code{eight-bit-control} and
4055 @code{eight-bit-graphic}.
4057 Normally, this function inserts newline characters into the encoded
4058 text, to avoid overlong lines. However, if the optional argument
4059 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4060 the output is just one long line.
4063 @defun base64-encode-string string &optional no-line-break
4064 @tindex base64-encode-string
4065 This function converts the string @var{string} into base 64 code. It
4066 returns a string containing the encoded text. As for
4067 @code{base64-encode-region}, an error is signaled if a character in the
4068 string is multibyte.
4070 Normally, this function inserts newline characters into the encoded
4071 text, to avoid overlong lines. However, if the optional argument
4072 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4073 the result string is just one long line.
4076 @defun base64-decode-region beg end
4077 @tindex base64-decode-region
4078 This function converts the region from @var{beg} to @var{end} from base
4079 64 code into the corresponding decoded text. It returns the length of
4082 The decoding functions ignore newline characters in the encoded text.
4085 @defun base64-decode-string string
4086 @tindex base64-decode-string
4087 This function converts the string @var{string} from base 64 code into
4088 the corresponding decoded text. It returns a unibyte string containing the
4091 The decoding functions ignore newline characters in the encoded text.
4095 @section MD5 Checksum
4096 @cindex MD5 checksum
4097 @cindex message digest computation
4099 MD5 cryptographic checksums, or @dfn{message digests}, are 128-bit
4100 ``fingerprints'' of a document or program. They are used to verify
4101 that you have an exact and unaltered copy of the data. The algorithm
4102 to calculate the MD5 message digest is defined in Internet
4104 For an explanation of what is an RFC, see the footnote in @ref{Base
4106 }1321. This section describes the Emacs facilities for computing
4109 @defun md5 object &optional start end coding-system noerror
4110 This function returns the MD5 message digest of @var{object}, which
4111 should be a buffer or a string.
4113 The two optional arguments @var{start} and @var{end} are character
4114 positions specifying the portion of @var{object} to compute the
4115 message digest for. If they are @code{nil} or omitted, the digest is
4116 computed for the whole of @var{object}.
4118 The function @code{md5} does not compute the message digest directly
4119 from the internal Emacs representation of the text (@pxref{Text
4120 Representations}). Instead, it encodes the text using a coding
4121 system, and computes the message digest from the encoded text. The
4122 optional fourth argument @var{coding-system} specifies which coding
4123 system to use for encoding the text. It should be the same coding
4124 system that you used to read the text, or that you used or will use
4125 when saving or sending the text. @xref{Coding Systems}, for more
4126 information about coding systems.
4128 If @var{coding-system} is @code{nil} or omitted, the default depends
4129 on @var{object}. If @var{object} is a buffer, the default for
4130 @var{coding-system} is whatever coding system would be chosen by
4131 default for writing this text into a file. If @var{object} is a
4132 string, the user's most preferred coding system (@pxref{Recognize
4133 Coding, prefer-coding-system, the description of
4134 @code{prefer-coding-system}, emacs, GNU Emacs Manual}) is used.
4136 Normally, @code{md5} signals an error if the text can't be encoded
4137 using the specified or chosen coding system. However, if
4138 @var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
4142 @node Atomic Changes
4143 @section Atomic Change Groups
4144 @cindex atomic changes
4146 In data base terminology, an @dfn{atomic} change is an indivisible
4147 change---it can succeed entirely or it can fail entirely, but it
4148 cannot partly succeed. A Lisp program can make a series of changes to
4149 one or several buffers as an @dfn{atomic change group}, meaning that
4150 either the entire series of changes will be installed in their buffers
4151 or, in case of an error, none of them will be.
4153 To do this for one buffer, the one already current, simply write a
4154 call to @code{atomic-change-group} around the code that makes the
4158 (atomic-change-group
4160 (delete-region x y))
4164 If an error (or other nonlocal exit) occurs inside the body of
4165 @code{atomic-change-group}, it unmakes all the changes in that buffer
4166 that were during the execution of the body. This kind of change group
4167 has no effect on any other buffers---any such changes remain.
4169 If you need something more sophisticated, such as to make changes in
4170 various buffers constitute one atomic group, you must directly call
4171 lower-level functions that @code{atomic-change-group} uses.
4173 @defun prepare-change-group &optional buffer
4174 This function sets up a change group for buffer @var{buffer}, which
4175 defaults to the current buffer. It returns a ``handle'' that
4176 represents the change group. You must use this handle to activate the
4177 change group and subsequently to finish it.
4180 To use the change group, you must @dfn{activate} it. You must do
4181 this before making any changes in the text of @var{buffer}.
4183 @defun activate-change-group handle
4184 This function activates the change group that @var{handle} designates.
4187 After you activate the change group, any changes you make in that
4188 buffer become part of it. Once you have made all the desired changes
4189 in the buffer, you must @dfn{finish} the change group. There are two
4190 ways to do this: you can either accept (and finalize) all the changes,
4193 @defun accept-change-group handle
4194 This function accepts all the changes in the change group specified by
4195 @var{handle}, making them final.
4198 @defun cancel-change-group handle
4199 This function cancels and undoes all the changes in the change group
4200 specified by @var{handle}.
4203 Your code should use @code{unwind-protect} to make sure the group is
4204 always finished. The call to @code{activate-change-group} should be
4205 inside the @code{unwind-protect}, in case the user types @kbd{C-g}
4206 just after it runs. (This is one reason why
4207 @code{prepare-change-group} and @code{activate-change-group} are
4208 separate functions, because normally you would call
4209 @code{prepare-change-group} before the start of that
4210 @code{unwind-protect}.) Once you finish the group, don't use the
4211 handle again---in particular, don't try to finish the same group
4214 To make a multibuffer change group, call @code{prepare-change-group}
4215 once for each buffer you want to cover, then use @code{nconc} to
4216 combine the returned values, like this:
4219 (nconc (prepare-change-group buffer-1)
4220 (prepare-change-group buffer-2))
4223 You can then activate the multibuffer change group with a single call
4224 to @code{activate-change-group}, and finish it with a single call to
4225 @code{accept-change-group} or @code{cancel-change-group}.
4227 Nested use of several change groups for the same buffer works as you
4228 would expect. Non-nested use of change groups for the same buffer
4229 will get Emacs confused, so don't let it happen; the first change
4230 group you start for any given buffer should be the last one finished.
4233 @section Change Hooks
4234 @cindex change hooks
4235 @cindex hooks for text changes
4237 These hook variables let you arrange to take notice of all changes in
4238 all buffers (or in a particular buffer, if you make them buffer-local).
4239 See also @ref{Special Properties}, for how to detect changes to specific
4242 The functions you use in these hooks should save and restore the match
4243 data if they do anything that uses regular expressions; otherwise, they
4244 will interfere in bizarre ways with the editing operations that call
4247 @defvar before-change-functions
4248 This variable holds a list of functions to call before any buffer
4249 modification. Each function gets two arguments, the beginning and end
4250 of the region that is about to change, represented as integers. The
4251 buffer that is about to change is always the current buffer.
4254 @defvar after-change-functions
4255 This variable holds a list of functions to call after any buffer
4256 modification. Each function receives three arguments: the beginning and
4257 end of the region just changed, and the length of the text that existed
4258 before the change. All three arguments are integers. The buffer that's
4259 about to change is always the current buffer.
4261 The length of the old text is the difference between the buffer positions
4262 before and after that text as it was before the change. As for the
4263 changed text, its length is simply the difference between the first two
4267 Output of messages into the @samp{*Messages*} buffer does not
4268 call these functions.
4270 @defmac combine-after-change-calls body...
4271 The macro executes @var{body} normally, but arranges to call the
4272 after-change functions just once for a series of several changes---if
4275 If a program makes several text changes in the same area of the buffer,
4276 using the macro @code{combine-after-change-calls} around that part of
4277 the program can make it run considerably faster when after-change hooks
4278 are in use. When the after-change hooks are ultimately called, the
4279 arguments specify a portion of the buffer including all of the changes
4280 made within the @code{combine-after-change-calls} body.
4282 @strong{Warning:} You must not alter the values of
4283 @code{after-change-functions} within
4284 the body of a @code{combine-after-change-calls} form.
4286 @strong{Warning:} if the changes you combine occur in widely scattered
4287 parts of the buffer, this will still work, but it is not advisable,
4288 because it may lead to inefficient behavior for some change hook
4292 The two variables above are temporarily bound to @code{nil} during the
4293 time that any of these functions is running. This means that if one of
4294 these functions changes the buffer, that change won't run these
4295 functions. If you do want a hook function to make changes that run
4296 these functions, make it bind these variables back to their usual
4299 One inconvenient result of this protective feature is that you cannot
4300 have a function in @code{after-change-functions} or
4301 @code{before-change-functions} which changes the value of that variable.
4302 But that's not a real limitation. If you want those functions to change
4303 the list of functions to run, simply add one fixed function to the hook,
4304 and code that function to look in another variable for other functions
4305 to call. Here is an example:
4308 (setq my-own-after-change-functions nil)
4309 (defun indirect-after-change-function (beg end len)
4310 (let ((list my-own-after-change-functions))
4312 (funcall (car list) beg end len)
4313 (setq list (cdr list)))))
4316 (add-hooks 'after-change-functions
4317 'indirect-after-change-function)
4321 @defvar first-change-hook
4322 This variable is a normal hook that is run whenever a buffer is changed
4323 that was previously in the unmodified state.
4326 @defvar inhibit-modification-hooks
4327 @tindex inhibit-modification-hooks
4328 If this variable is non-@code{nil}, all of the change hooks are
4329 disabled; none of them run. This affects all the hook variables
4330 described above in this section, as well as the hooks attached to
4331 certain special text properties (@pxref{Special Properties}) and overlay
4332 properties (@pxref{Overlay Properties}).
4336 arch-tag: 3721e738-a1cb-4085-bc1a-6cb8d8e1d32b