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, 2006, 2007, 2008, 2009 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
67 @cindex text near point
69 Many functions are provided to look at the characters around point.
70 Several simple functions are described here. See also @code{looking-at}
71 in @ref{Regexp Search}.
73 In the following four functions, ``beginning'' or ``end'' of buffer
74 refers to the beginning or end of the accessible portion.
76 @defun char-after &optional position
77 This function returns the character in the current buffer at (i.e.,
78 immediately after) position @var{position}. If @var{position} is out of
79 range for this purpose, either before the beginning of the buffer, or at
80 or beyond the end, then the value is @code{nil}. The default for
81 @var{position} is point.
83 In the following example, assume that the first character in the
88 (char-to-string (char-after 1))
94 @defun char-before &optional position
95 This function returns the character in the current buffer immediately
96 before position @var{position}. If @var{position} is out of range for
97 this purpose, either at or before the beginning of the buffer, or beyond
98 the end, then the value is @code{nil}. The default for
99 @var{position} is point.
102 @defun following-char
103 This function returns the character following point in the current
104 buffer. This is similar to @code{(char-after (point))}. However, if
105 point is at the end of the buffer, then @code{following-char} returns 0.
107 Remember that point is always between characters, and the cursor
108 normally appears over the character following point. Therefore, the
109 character returned by @code{following-char} is the character the
112 In this example, point is between the @samp{a} and the @samp{c}.
116 ---------- Buffer: foo ----------
117 Gentlemen may cry ``Pea@point{}ce! Peace!,''
118 but there is no peace.
119 ---------- Buffer: foo ----------
123 (char-to-string (preceding-char))
125 (char-to-string (following-char))
131 @defun preceding-char
132 This function returns the character preceding point in the current
133 buffer. See above, under @code{following-char}, for an example. If
134 point is at the beginning of the buffer, @code{preceding-char} returns
139 This function returns @code{t} if point is at the beginning of the
140 buffer. If narrowing is in effect, this means the beginning of the
141 accessible portion of the text. See also @code{point-min} in
146 This function returns @code{t} if point is at the end of the buffer.
147 If narrowing is in effect, this means the end of accessible portion of
148 the text. See also @code{point-max} in @xref{Point}.
152 This function returns @code{t} if point is at the beginning of a line.
153 @xref{Text Lines}. The beginning of the buffer (or of its accessible
154 portion) always counts as the beginning of a line.
158 This function returns @code{t} if point is at the end of a line. The
159 end of the buffer (or of its accessible portion) is always considered
163 @node Buffer Contents
164 @section Examining Buffer Contents
166 This section describes functions that allow a Lisp program to
167 convert any portion of the text in the buffer into a string.
169 @defun buffer-substring start end
170 This function returns a string containing a copy of the text of the
171 region defined by positions @var{start} and @var{end} in the current
172 buffer. If the arguments are not positions in the accessible portion of
173 the buffer, @code{buffer-substring} signals an @code{args-out-of-range}
176 It is not necessary for @var{start} to be less than @var{end}; the
177 arguments can be given in either order. But most often the smaller
178 argument is written first.
180 Here's an example which assumes Font-Lock mode is not enabled:
184 ---------- Buffer: foo ----------
185 This is the contents of buffer foo
187 ---------- Buffer: foo ----------
191 (buffer-substring 1 10)
192 @result{} "This is t"
195 (buffer-substring (point-max) 10)
196 @result{} "he contents of buffer foo\n"
200 If the text being copied has any text properties, these are copied into
201 the string along with the characters they belong to. @xref{Text
202 Properties}. However, overlays (@pxref{Overlays}) in the buffer and
203 their properties are ignored, not copied.
205 For example, if Font-Lock mode is enabled, you might get results like
210 (buffer-substring 1 10)
211 @result{} #("This is t" 0 1 (fontified t) 1 9 (fontified t))
216 @defun buffer-substring-no-properties start end
217 This is like @code{buffer-substring}, except that it does not copy text
218 properties, just the characters themselves. @xref{Text Properties}.
221 @defun filter-buffer-substring start end &optional delete noprops
222 This function passes the buffer text between @var{start} and @var{end}
223 through the filter functions specified by the variable
224 @code{buffer-substring-filters}, and returns the value from the last
225 filter function. If @code{buffer-substring-filters} is @code{nil},
226 the value is the unaltered text from the buffer, what
227 @code{buffer-substring} would return.
229 If @var{delete} is non-@code{nil}, this function deletes the text
230 between @var{start} and @var{end} after copying it, like
231 @code{delete-and-extract-region}.
233 If @var{noprops} is non-@code{nil}, the final string returned does not
234 include text properties, while the string passed through the filters
235 still includes text properties from the buffer text.
237 Lisp code should use this function instead of @code{buffer-substring},
238 @code{buffer-substring-no-properties},
239 or @code{delete-and-extract-region} when copying into user-accessible
240 data structures such as the kill-ring, X clipboard, and registers.
241 Major and minor modes can add functions to
242 @code{buffer-substring-filters} to alter such text as it is copied out
246 @defvar buffer-substring-filters
247 This variable should be a list of functions that accept a single
248 argument, a string, and return a string.
249 @code{filter-buffer-substring} passes the buffer substring to the
250 first function in this list, and the return value of each function is
251 passed to the next function. The return value of the last function is
252 used as the return value of @code{filter-buffer-substring}.
254 As a special convention, point is set to the start of the buffer text
255 being operated on (i.e., the @var{start} argument for
256 @code{filter-buffer-substring}) before these functions are called.
258 If this variable is @code{nil}, no filtering is performed.
262 This function returns the contents of the entire accessible portion of
263 the current buffer as a string. It is equivalent to
266 (buffer-substring (point-min) (point-max))
271 ---------- Buffer: foo ----------
272 This is the contents of buffer foo
274 ---------- Buffer: foo ----------
277 @result{} "This is the contents of buffer foo\n"
282 @defun current-word &optional strict really-word
283 This function returns the symbol (or word) at or near point, as a string.
284 The return value includes no text properties.
286 If the optional argument @var{really-word} is non-@code{nil}, it finds a
287 word; otherwise, it finds a symbol (which includes both word
288 characters and symbol constituent characters).
290 If the optional argument @var{strict} is non-@code{nil}, then point
291 must be in or next to the symbol or word---if no symbol or word is
292 there, the function returns @code{nil}. Otherwise, a nearby symbol or
293 word on the same line is acceptable.
296 @defun thing-at-point thing
297 Return the @var{thing} around or next to point, as a string.
299 The argument @var{thing} is a symbol which specifies a kind of syntactic
300 entity. Possibilities include @code{symbol}, @code{list}, @code{sexp},
301 @code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
302 @code{whitespace}, @code{line}, @code{page}, and others.
305 ---------- Buffer: foo ----------
306 Gentlemen may cry ``Pea@point{}ce! Peace!,''
307 but there is no peace.
308 ---------- Buffer: foo ----------
310 (thing-at-point 'word)
312 (thing-at-point 'line)
313 @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
314 (thing-at-point 'whitespace)
320 @section Comparing Text
321 @cindex comparing buffer text
323 This function lets you compare portions of the text in a buffer, without
324 copying them into strings first.
326 @defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
327 This function lets you compare two substrings of the same buffer or two
328 different buffers. The first three arguments specify one substring,
329 giving a buffer (or a buffer name) and two positions within the
330 buffer. The last three arguments specify the other substring in the
331 same way. You can use @code{nil} for @var{buffer1}, @var{buffer2}, or
332 both to stand for the current buffer.
334 The value is negative if the first substring is less, positive if the
335 first is greater, and zero if they are equal. The absolute value of
336 the result is one plus the index of the first differing characters
337 within the substrings.
339 This function ignores case when comparing characters
340 if @code{case-fold-search} is non-@code{nil}. It always ignores
343 Suppose the current buffer contains the text @samp{foobarbar
344 haha!rara!}; then in this example the two substrings are @samp{rbar }
345 and @samp{rara!}. The value is 2 because the first substring is greater
346 at the second character.
349 (compare-buffer-substrings nil 6 11 nil 16 21)
355 @section Inserting Text
356 @cindex insertion of text
357 @cindex text insertion
359 @cindex insertion before point
360 @cindex before point, insertion
361 @dfn{Insertion} means adding new text to a buffer. The inserted text
362 goes at point---between the character before point and the character
363 after point. Some insertion functions leave point before the inserted
364 text, while other functions leave it after. We call the former
365 insertion @dfn{after point} and the latter insertion @dfn{before point}.
367 Insertion relocates markers that point at positions after the
368 insertion point, so that they stay with the surrounding text
369 (@pxref{Markers}). When a marker points at the place of insertion,
370 insertion may or may not relocate the marker, depending on the marker's
371 insertion type (@pxref{Marker Insertion Types}). Certain special
372 functions such as @code{insert-before-markers} relocate all such markers
373 to point after the inserted text, regardless of the markers' insertion
376 Insertion functions signal an error if the current buffer is
377 read-only or if they insert within read-only text.
379 These functions copy text characters from strings and buffers along
380 with their properties. The inserted characters have exactly the same
381 properties as the characters they were copied from. By contrast,
382 characters specified as separate arguments, not part of a string or
383 buffer, inherit their text properties from the neighboring text.
385 The insertion functions convert text from unibyte to multibyte in
386 order to insert in a multibyte buffer, and vice versa---if the text
387 comes from a string or from a buffer. However, they do not convert
388 unibyte character codes 128 through 255 to multibyte characters, not
389 even if the current buffer is a multibyte buffer. @xref{Converting
392 @defun insert &rest args
393 This function inserts the strings and/or characters @var{args} into the
394 current buffer, at point, moving point forward. In other words, it
395 inserts the text before point. An error is signaled unless all
396 @var{args} are either strings or characters. The value is @code{nil}.
399 @defun insert-before-markers &rest args
400 This function inserts the strings and/or characters @var{args} into the
401 current buffer, at point, moving point forward. An error is signaled
402 unless all @var{args} are either strings or characters. The value is
405 This function is unlike the other insertion functions in that it
406 relocates markers initially pointing at the insertion point, to point
407 after the inserted text. If an overlay begins at the insertion point,
408 the inserted text falls outside the overlay; if a nonempty overlay
409 ends at the insertion point, the inserted text falls inside that
413 @defun insert-char character count &optional inherit
414 This function inserts @var{count} instances of @var{character} into the
415 current buffer before point. The argument @var{count} should be an
416 integer, and @var{character} must be a character. The value is @code{nil}.
418 This function does not convert unibyte character codes 128 through 255
419 to multibyte characters, not even if the current buffer is a multibyte
420 buffer. @xref{Converting Representations}.
422 If @var{inherit} is non-@code{nil}, then the inserted characters inherit
423 sticky text properties from the two characters before and after the
424 insertion point. @xref{Sticky Properties}.
427 @defun insert-buffer-substring from-buffer-or-name &optional start end
428 This function inserts a portion of buffer @var{from-buffer-or-name}
429 (which must already exist) into the current buffer before point. The
430 text inserted is the region between @var{start} and @var{end}. (These
431 arguments default to the beginning and end of the accessible portion of
432 that buffer.) This function returns @code{nil}.
434 In this example, the form is executed with buffer @samp{bar} as the
435 current buffer. We assume that buffer @samp{bar} is initially empty.
439 ---------- Buffer: foo ----------
440 We hold these truths to be self-evident, that all
441 ---------- Buffer: foo ----------
445 (insert-buffer-substring "foo" 1 20)
448 ---------- Buffer: bar ----------
449 We hold these truth@point{}
450 ---------- Buffer: bar ----------
455 @defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
456 This is like @code{insert-buffer-substring} except that it does not
457 copy any text properties.
460 @xref{Sticky Properties}, for other insertion functions that inherit
461 text properties from the nearby text in addition to inserting it.
462 Whitespace inserted by indentation functions also inherits text
465 @node Commands for Insertion
466 @section User-Level Insertion Commands
468 This section describes higher-level commands for inserting text,
469 commands intended primarily for the user but useful also in Lisp
472 @deffn Command insert-buffer from-buffer-or-name
473 This command inserts the entire accessible contents of
474 @var{from-buffer-or-name} (which must exist) into the current buffer
475 after point. It leaves the mark after the inserted text. The value
479 @deffn Command self-insert-command count
480 @cindex character insertion
481 @cindex self-insertion
482 This command inserts the last character typed; it does so @var{count}
483 times, before point, and returns @code{nil}. Most printing characters
484 are bound to this command. In routine use, @code{self-insert-command}
485 is the most frequently called function in Emacs, but programs rarely use
486 it except to install it on a keymap.
488 In an interactive call, @var{count} is the numeric prefix argument.
490 Self-insertion translates the input character through
491 @code{translation-table-for-input}. @xref{Translation of Characters}.
493 This command calls @code{auto-fill-function} whenever that is
494 non-@code{nil} and the character inserted is in the table
495 @code{auto-fill-chars} (@pxref{Auto Filling}).
497 @c Cross refs reworded to prevent overfull hbox. --rjc 15mar92
498 This command performs abbrev expansion if Abbrev mode is enabled and
499 the inserted character does not have word-constituent
500 syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.) It is also
501 responsible for calling @code{blink-paren-function} when the inserted
502 character has close parenthesis syntax (@pxref{Blinking}).
504 Do not try substituting your own definition of
505 @code{self-insert-command} for the standard one. The editor command
506 loop handles this function specially.
509 @deffn Command newline &optional number-of-newlines
510 This command inserts newlines into the current buffer before point.
511 If @var{number-of-newlines} is supplied, that many newline characters
514 @cindex newline and Auto Fill mode
515 This function calls @code{auto-fill-function} if the current column
516 number is greater than the value of @code{fill-column} and
517 @var{number-of-newlines} is @code{nil}. Typically what
518 @code{auto-fill-function} does is insert a newline; thus, the overall
519 result in this case is to insert two newlines at different places: one
520 at point, and another earlier in the line. @code{newline} does not
521 auto-fill if @var{number-of-newlines} is non-@code{nil}.
523 This command indents to the left margin if that is not zero.
526 The value returned is @code{nil}. In an interactive call, @var{count}
527 is the numeric prefix argument.
530 @defvar overwrite-mode
531 This variable controls whether overwrite mode is in effect. The value
532 should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
533 or @code{nil}. @code{overwrite-mode-textual} specifies textual
534 overwrite mode (treats newlines and tabs specially), and
535 @code{overwrite-mode-binary} specifies binary overwrite mode (treats
536 newlines and tabs like any other characters).
540 @section Deleting Text
541 @cindex text deletion
543 @cindex deleting text vs killing
544 Deletion means removing part of the text in a buffer, without saving
545 it in the kill ring (@pxref{The Kill Ring}). Deleted text can't be
546 yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
547 Some deletion functions do save text in the kill ring in some special
550 All of the deletion functions operate on the current buffer.
552 @deffn Command erase-buffer
553 This function deletes the entire text of the current buffer
554 (@emph{not} just the accessible portion), leaving it
555 empty. If the buffer is read-only, it signals a @code{buffer-read-only}
556 error; if some of the text in it is read-only, it signals a
557 @code{text-read-only} error. Otherwise, it deletes the text without
558 asking for any confirmation. It returns @code{nil}.
560 Normally, deleting a large amount of text from a buffer inhibits further
561 auto-saving of that buffer ``because it has shrunk.'' However,
562 @code{erase-buffer} does not do this, the idea being that the future
563 text is not really related to the former text, and its size should not
564 be compared with that of the former text.
567 @deffn Command delete-region start end
568 This command deletes the text between positions @var{start} and
569 @var{end} in the current buffer, and returns @code{nil}. If point was
570 inside the deleted region, its value afterward is @var{start}.
571 Otherwise, point relocates with the surrounding text, as markers do.
574 @defun delete-and-extract-region start end
575 This function deletes the text between positions @var{start} and
576 @var{end} in the current buffer, and returns a string containing the
579 If point was inside the deleted region, its value afterward is
580 @var{start}. Otherwise, point relocates with the surrounding text, as
584 @deffn Command delete-char count &optional killp
585 This command deletes @var{count} characters directly after point, or
586 before point if @var{count} is negative. If @var{killp} is
587 non-@code{nil}, then it saves the deleted characters in the kill ring.
589 In an interactive call, @var{count} is the numeric prefix argument, and
590 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
591 argument is supplied, the text is saved in the kill ring. If no prefix
592 argument is supplied, then one character is deleted, but not saved in
595 The value returned is always @code{nil}.
598 @deffn Command delete-backward-char count &optional killp
599 @cindex deleting previous char
600 This command deletes @var{count} characters directly before point, or
601 after point if @var{count} is negative. If @var{killp} is
602 non-@code{nil}, then it saves the deleted characters in the kill ring.
604 In an interactive call, @var{count} is the numeric prefix argument, and
605 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
606 argument is supplied, the text is saved in the kill ring. If no prefix
607 argument is supplied, then one character is deleted, but not saved in
610 The value returned is always @code{nil}.
613 @deffn Command backward-delete-char-untabify count &optional killp
615 This command deletes @var{count} characters backward, changing tabs
616 into spaces. When the next character to be deleted is a tab, it is
617 first replaced with the proper number of spaces to preserve alignment
618 and then one of those spaces is deleted instead of the tab. If
619 @var{killp} is non-@code{nil}, then the command saves the deleted
620 characters in the kill ring.
622 Conversion of tabs to spaces happens only if @var{count} is positive.
623 If it is negative, exactly @minus{}@var{count} characters after point
626 In an interactive call, @var{count} is the numeric prefix argument, and
627 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
628 argument is supplied, the text is saved in the kill ring. If no prefix
629 argument is supplied, then one character is deleted, but not saved in
632 The value returned is always @code{nil}.
635 @defopt backward-delete-char-untabify-method
636 This option specifies how @code{backward-delete-char-untabify} should
637 deal with whitespace. Possible values include @code{untabify}, the
638 default, meaning convert a tab to many spaces and delete one;
639 @code{hungry}, meaning delete all tabs and spaces before point with
640 one command; @code{all} meaning delete all tabs, spaces and newlines
641 before point, and @code{nil}, meaning do nothing special for
642 whitespace characters.
645 @node User-Level Deletion
646 @section User-Level Deletion Commands
648 This section describes higher-level commands for deleting text,
649 commands intended primarily for the user but useful also in Lisp
652 @deffn Command delete-horizontal-space &optional backward-only
653 @cindex deleting whitespace
654 This function deletes all spaces and tabs around point. It returns
657 If @var{backward-only} is non-@code{nil}, the function deletes
658 spaces and tabs before point, but not after point.
660 In the following examples, we call @code{delete-horizontal-space} four
661 times, once on each line, with point between the second and third
662 characters on the line each time.
666 ---------- Buffer: foo ----------
671 ---------- Buffer: foo ----------
675 (delete-horizontal-space) ; @r{Four times.}
678 ---------- Buffer: foo ----------
683 ---------- Buffer: foo ----------
688 @deffn Command delete-indentation &optional join-following-p
689 This function joins the line point is on to the previous line, deleting
690 any whitespace at the join and in some cases replacing it with one
691 space. If @var{join-following-p} is non-@code{nil},
692 @code{delete-indentation} joins this line to the following line
693 instead. The function returns @code{nil}.
695 If there is a fill prefix, and the second of the lines being joined
696 starts with the prefix, then @code{delete-indentation} deletes the
697 fill prefix before joining the lines. @xref{Margins}.
699 In the example below, point is located on the line starting
700 @samp{events}, and it makes no difference if there are trailing spaces
701 in the preceding line.
705 ---------- Buffer: foo ----------
706 When in the course of human
707 @point{} events, it becomes necessary
708 ---------- Buffer: foo ----------
715 ---------- Buffer: foo ----------
716 When in the course of human@point{} events, it becomes necessary
717 ---------- Buffer: foo ----------
721 After the lines are joined, the function @code{fixup-whitespace} is
722 responsible for deciding whether to leave a space at the junction.
725 @deffn Command fixup-whitespace
726 This function replaces all the horizontal whitespace surrounding point
727 with either one space or no space, according to the context. It
730 At the beginning or end of a line, the appropriate amount of space is
731 none. Before a character with close parenthesis syntax, or after a
732 character with open parenthesis or expression-prefix syntax, no space is
733 also appropriate. Otherwise, one space is appropriate. @xref{Syntax
736 In the example below, @code{fixup-whitespace} is called the first time
737 with point before the word @samp{spaces} in the first line. For the
738 second invocation, point is directly after the @samp{(}.
742 ---------- Buffer: foo ----------
743 This has too many @point{}spaces
744 This has too many spaces at the start of (@point{} this list)
745 ---------- Buffer: foo ----------
756 ---------- Buffer: foo ----------
757 This has too many spaces
758 This has too many spaces at the start of (this list)
759 ---------- Buffer: foo ----------
764 @deffn Command just-one-space &optional n
765 @comment !!SourceFile simple.el
766 This command replaces any spaces and tabs around point with a single
767 space, or @var{n} spaces if @var{n} is specified. It returns
771 @deffn Command delete-blank-lines
772 This function deletes blank lines surrounding point. If point is on a
773 blank line with one or more blank lines before or after it, then all but
774 one of them are deleted. If point is on an isolated blank line, then it
775 is deleted. If point is on a nonblank line, the command deletes all
776 blank lines immediately following it.
778 A blank line is defined as a line containing only tabs and spaces.
780 @code{delete-blank-lines} returns @code{nil}.
784 @section The Kill Ring
787 @dfn{Kill functions} delete text like the deletion functions, but save
788 it so that the user can reinsert it by @dfn{yanking}. Most of these
789 functions have @samp{kill-} in their name. By contrast, the functions
790 whose names start with @samp{delete-} normally do not save text for
791 yanking (though they can still be undone); these are ``deletion''
794 Most of the kill commands are primarily for interactive use, and are
795 not described here. What we do describe are the functions provided for
796 use in writing such commands. You can use these functions to write
797 commands for killing text. When you need to delete text for internal
798 purposes within a Lisp function, you should normally use deletion
799 functions, so as not to disturb the kill ring contents.
802 Killed text is saved for later yanking in the @dfn{kill ring}. This
803 is a list that holds a number of recent kills, not just the last text
804 kill. We call this a ``ring'' because yanking treats it as having
805 elements in a cyclic order. The list is kept in the variable
806 @code{kill-ring}, and can be operated on with the usual functions for
807 lists; there are also specialized functions, described in this section,
808 that treat it as a ring.
810 Some people think this use of the word ``kill'' is unfortunate, since
811 it refers to operations that specifically @emph{do not} destroy the
812 entities ``killed.'' This is in sharp contrast to ordinary life, in
813 which death is permanent and ``killed'' entities do not come back to
814 life. Therefore, other metaphors have been proposed. For example, the
815 term ``cut ring'' makes sense to people who, in pre-computer days, used
816 scissors and paste to cut up and rearrange manuscripts. However, it
817 would be difficult to change the terminology now.
820 * Kill Ring Concepts:: What text looks like in the kill ring.
821 * Kill Functions:: Functions that kill text.
822 * Yanking:: How yanking is done.
823 * Yank Commands:: Commands that access the kill ring.
824 * Low-Level Kill Ring:: Functions and variables for kill ring access.
825 * Internals of Kill Ring:: Variables that hold kill ring data.
828 @node Kill Ring Concepts
829 @comment node-name, next, previous, up
830 @subsection Kill Ring Concepts
832 The kill ring records killed text as strings in a list, most recent
833 first. A short kill ring, for example, might look like this:
836 ("some text" "a different piece of text" "even older text")
840 When the list reaches @code{kill-ring-max} entries in length, adding a
841 new entry automatically deletes the last entry.
843 When kill commands are interwoven with other commands, each kill
844 command makes a new entry in the kill ring. Multiple kill commands in
845 succession build up a single kill ring entry, which would be yanked as a
846 unit; the second and subsequent consecutive kill commands add text to
847 the entry made by the first one.
849 For yanking, one entry in the kill ring is designated the ``front'' of
850 the ring. Some yank commands ``rotate'' the ring by designating a
851 different element as the ``front.'' But this virtual rotation doesn't
852 change the list itself---the most recent entry always comes first in the
856 @comment node-name, next, previous, up
857 @subsection Functions for Killing
859 @code{kill-region} is the usual subroutine for killing text. Any
860 command that calls this function is a ``kill command'' (and should
861 probably have @samp{kill} in its name). @code{kill-region} puts the
862 newly killed text in a new element at the beginning of the kill ring or
863 adds it to the most recent element. It determines automatically (using
864 @code{last-command}) whether the previous command was a kill command,
865 and if so appends the killed text to the most recent entry.
867 @deffn Command kill-region start end &optional yank-handler
868 This function kills the text in the region defined by @var{start} and
869 @var{end}. The text is deleted but saved in the kill ring, along with
870 its text properties. The value is always @code{nil}.
872 In an interactive call, @var{start} and @var{end} are point and
876 If the buffer or text is read-only, @code{kill-region} modifies the kill
877 ring just the same, then signals an error without modifying the buffer.
878 This is convenient because it lets the user use a series of kill
879 commands to copy text from a read-only buffer into the kill ring.
881 If @var{yank-handler} is non-@code{nil}, this puts that value onto
882 the string of killed text, as a @code{yank-handler} text property.
883 @xref{Yanking}. Note that if @var{yank-handler} is @code{nil}, any
884 @code{yank-handler} properties present on the killed text are copied
885 onto the kill ring, like other text properties.
888 @defopt kill-read-only-ok
889 If this option is non-@code{nil}, @code{kill-region} does not signal an
890 error if the buffer or text is read-only. Instead, it simply returns,
891 updating the kill ring but not changing the buffer.
894 @deffn Command copy-region-as-kill start end
895 This command saves the region defined by @var{start} and @var{end} on
896 the kill ring (including text properties), but does not delete the text
897 from the buffer. It returns @code{nil}.
899 The command does not set @code{this-command} to @code{kill-region}, so a
900 subsequent kill command does not append to the same kill ring entry.
902 Don't call @code{copy-region-as-kill} in Lisp programs unless you aim to
903 support Emacs 18. For newer Emacs versions, it is better to use
904 @code{kill-new} or @code{kill-append} instead. @xref{Low-Level Kill
911 Yanking means inserting text from the kill ring, but it does
912 not insert the text blindly. Yank commands and some other commands
913 use @code{insert-for-yank} to perform special processing on the
914 text that they copy into the buffer.
916 @defun insert-for-yank string
917 This function normally works like @code{insert} except that it doesn't
918 insert the text properties in the @code{yank-excluded-properties}
919 list. However, if any part of @var{string} has a non-@code{nil}
920 @code{yank-handler} text property, that property can do various
921 special processing on that part of the text being inserted.
924 @defun insert-buffer-substring-as-yank buf &optional start end
925 This function resembles @code{insert-buffer-substring} except that it
926 doesn't insert the text properties in the
927 @code{yank-excluded-properties} list.
930 You can put a @code{yank-handler} text property on all or part of
931 the text to control how it will be inserted if it is yanked. The
932 @code{insert-for-yank} function looks for that property. The property
933 value must be a list of one to four elements, with the following
934 format (where elements after the first may be omitted):
937 (@var{function} @var{param} @var{noexclude} @var{undo})
940 Here is what the elements do:
944 When @var{function} is present and non-@code{nil}, it is called instead of
945 @code{insert} to insert the string. @var{function} takes one
946 argument---the string to insert.
949 If @var{param} is present and non-@code{nil}, it replaces @var{string}
950 (or the part of @var{string} being processed) as the object passed to
951 @var{function} (or @code{insert}); for example, if @var{function} is
952 @code{yank-rectangle}, @var{param} should be a list of strings to
953 insert as a rectangle.
956 If @var{noexclude} is present and non-@code{nil}, the normal removal of the
957 yank-excluded-properties is not performed; instead @var{function} is
958 responsible for removing those properties. This may be necessary
959 if @var{function} adjusts point before or after inserting the object.
962 If @var{undo} is present and non-@code{nil}, it is a function that will be
963 called by @code{yank-pop} to undo the insertion of the current object.
964 It is called with two arguments, the start and end of the current
965 region. @var{function} can set @code{yank-undo-function} to override
966 the @var{undo} value.
970 @comment node-name, next, previous, up
971 @subsection Functions for Yanking
973 This section describes higher-level commands for yanking, which are
974 intended primarily for the user but useful also in Lisp programs.
975 Both @code{yank} and @code{yank-pop} honor the
976 @code{yank-excluded-properties} variable and @code{yank-handler} text
977 property (@pxref{Yanking}).
979 @deffn Command yank &optional arg
980 @cindex inserting killed text
981 This command inserts before point the text at the front of the kill
982 ring. It sets the mark at the beginning of that text, using
983 @code{push-mark} (@pxref{The Mark}), and puts point at the end.
985 If @var{arg} is a non-@code{nil} list (which occurs interactively when
986 the user types @kbd{C-u} with no digits), then @code{yank} inserts the
987 text as described above, but puts point before the yanked text and
988 sets the mark after it.
990 If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
991 most recently killed text---the @var{arg}th element of the kill ring
992 list, counted cyclically from the front, which is considered the
993 first element for this purpose.
995 @code{yank} does not alter the contents of the kill ring, unless it
996 used text provided by another program, in which case it pushes that text
997 onto the kill ring. However if @var{arg} is an integer different from
998 one, it rotates the kill ring to place the yanked string at the front.
1000 @code{yank} returns @code{nil}.
1003 @deffn Command yank-pop &optional arg
1004 This command replaces the just-yanked entry from the kill ring with a
1005 different entry from the kill ring.
1007 This is allowed only immediately after a @code{yank} or another
1008 @code{yank-pop}. At such a time, the region contains text that was just
1009 inserted by yanking. @code{yank-pop} deletes that text and inserts in
1010 its place a different piece of killed text. It does not add the deleted
1011 text to the kill ring, since it is already in the kill ring somewhere.
1012 It does however rotate the kill ring to place the newly yanked string at
1015 If @var{arg} is @code{nil}, then the replacement text is the previous
1016 element of the kill ring. If @var{arg} is numeric, the replacement is
1017 the @var{arg}th previous kill. If @var{arg} is negative, a more recent
1018 kill is the replacement.
1020 The sequence of kills in the kill ring wraps around, so that after the
1021 oldest one comes the newest one, and before the newest one goes the
1024 The return value is always @code{nil}.
1027 @defvar yank-undo-function
1028 If this variable is non-@code{nil}, the function @code{yank-pop} uses
1029 its value instead of @code{delete-region} to delete the text
1030 inserted by the previous @code{yank} or
1031 @code{yank-pop} command. The value must be a function of two
1032 arguments, the start and end of the current region.
1034 The function @code{insert-for-yank} automatically sets this variable
1035 according to the @var{undo} element of the @code{yank-handler}
1036 text property, if there is one.
1039 @node Low-Level Kill Ring
1040 @subsection Low-Level Kill Ring
1042 These functions and variables provide access to the kill ring at a
1043 lower level, but still convenient for use in Lisp programs, because they
1044 take care of interaction with window system selections
1045 (@pxref{Window System Selections}).
1047 @defun current-kill n &optional do-not-move
1048 The function @code{current-kill} rotates the yanking pointer, which
1049 designates the ``front'' of the kill ring, by @var{n} places (from newer
1050 kills to older ones), and returns the text at that place in the ring.
1052 If the optional second argument @var{do-not-move} is non-@code{nil},
1053 then @code{current-kill} doesn't alter the yanking pointer; it just
1054 returns the @var{n}th kill, counting from the current yanking pointer.
1056 If @var{n} is zero, indicating a request for the latest kill,
1057 @code{current-kill} calls the value of
1058 @code{interprogram-paste-function} (documented below) before
1059 consulting the kill ring. If that value is a function and calling it
1060 returns a string or a list of several string, @code{current-kill}
1061 pushes the strings onto the kill ring and returns the first string.
1062 It also sets the yanking pointer to point to the kill-ring entry of
1063 the first string returned by @code{interprogram-paste-function},
1064 regardless of the value of @var{do-not-move}. Otherwise,
1065 @code{current-kill} does not treat a zero value for @var{n} specially:
1066 it returns the entry pointed at by the yanking pointer and does not
1067 move the yanking pointer.
1070 @defun kill-new string &optional replace yank-handler
1071 This function pushes the text @var{string} onto the kill ring and
1072 makes the yanking pointer point to it. It discards the oldest entry
1073 if appropriate. It also invokes the value of
1074 @code{interprogram-cut-function} (see below).
1076 If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
1077 first element of the kill ring with @var{string}, rather than pushing
1078 @var{string} onto the kill ring.
1080 If @var{yank-handler} is non-@code{nil}, this puts that value onto
1081 the string of killed text, as a @code{yank-handler} property.
1082 @xref{Yanking}. Note that if @var{yank-handler} is @code{nil}, then
1083 @code{kill-new} copies any @code{yank-handler} properties present on
1084 @var{string} onto the kill ring, as it does with other text properties.
1087 @defun kill-append string before-p &optional yank-handler
1088 This function appends the text @var{string} to the first entry in the
1089 kill ring and makes the yanking pointer point to the combined entry.
1090 Normally @var{string} goes at the end of the entry, but if
1091 @var{before-p} is non-@code{nil}, it goes at the beginning. This
1092 function also invokes the value of @code{interprogram-cut-function}
1093 (see below). This handles @var{yank-handler} just like
1094 @code{kill-new}, except that if @var{yank-handler} is different from
1095 the @code{yank-handler} property of the first entry of the kill ring,
1096 @code{kill-append} pushes the concatenated string onto the kill ring,
1097 instead of replacing the original first entry with it.
1100 @defvar interprogram-paste-function
1101 This variable provides a way of transferring killed text from other
1102 programs, when you are using a window system. Its value should be
1103 @code{nil} or a function of no arguments.
1105 If the value is a function, @code{current-kill} calls it to get the
1106 ``most recent kill.'' If the function returns a non-@code{nil} value,
1107 then that value is used as the ``most recent kill.'' If it returns
1108 @code{nil}, then the front of the kill ring is used.
1110 To facilitate support for window systems that support multiple
1111 selections, this function may also return a list of strings. In that
1112 case, the first string is used as the ``most recent kill'', and all
1113 the other strings are pushed onto the kill ring, for easy access by
1116 The normal use of this function is to get the window system's primary
1117 selection as the most recent kill, even if the selection belongs to
1118 another application. @xref{Window System Selections}. However, if
1119 the selection was provided by the current Emacs session, this function
1120 should return @code{nil}. (If it is hard to tell whether Emacs or
1121 some other program provided the selection, it should be good enough to
1122 use @code{string=} to compare it with the last text Emacs provided.)
1125 @defvar interprogram-cut-function
1126 This variable provides a way of communicating killed text to other
1127 programs, when you are using a window system. Its value should be
1128 @code{nil} or a function of one required and one optional argument.
1130 If the value is a function, @code{kill-new} and @code{kill-append} call
1131 it with the new first element of the kill ring as the first argument.
1132 The second, optional, argument has the same meaning as the @var{push}
1133 argument to @code{x-set-cut-buffer} (@pxref{Definition of
1134 x-set-cut-buffer}) and only affects the second and later cut buffers.
1136 The normal use of this function is to set the window system's primary
1137 selection (and first cut buffer) from the newly killed text.
1138 @xref{Window System Selections}.
1141 @node Internals of Kill Ring
1142 @comment node-name, next, previous, up
1143 @subsection Internals of the Kill Ring
1145 The variable @code{kill-ring} holds the kill ring contents, in the
1146 form of a list of strings. The most recent kill is always at the front
1149 The @code{kill-ring-yank-pointer} variable points to a link in the
1150 kill ring list, whose @sc{car} is the text to yank next. We say it
1151 identifies the ``front'' of the ring. Moving
1152 @code{kill-ring-yank-pointer} to a different link is called
1153 @dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
1154 the functions that move the yank pointer wrap around from the end of the
1155 list to the beginning, or vice-versa. Rotation of the kill ring is
1156 virtual; it does not change the value of @code{kill-ring}.
1158 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
1159 variables whose values are normally lists. The word ``pointer'' in the
1160 name of the @code{kill-ring-yank-pointer} indicates that the variable's
1161 purpose is to identify one element of the list for use by the next yank
1164 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
1165 of the links in the kill ring list. The element it identifies is the
1166 @sc{car} of that link. Kill commands, which change the kill ring, also
1167 set this variable to the value of @code{kill-ring}. The effect is to
1168 rotate the ring so that the newly killed text is at the front.
1170 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
1171 pointing to the second entry in the kill ring @code{("some text" "a
1172 different piece of text" "yet older text")}.
1176 kill-ring ---- kill-ring-yank-pointer
1179 | --- --- --- --- --- ---
1180 --> | | |------> | | |--> | | |--> nil
1181 --- --- --- --- --- ---
1184 | | -->"yet older text"
1186 | --> "a different piece of text"
1193 This state of affairs might occur after @kbd{C-y} (@code{yank})
1194 immediately followed by @kbd{M-y} (@code{yank-pop}).
1197 This variable holds the list of killed text sequences, most recently
1201 @defvar kill-ring-yank-pointer
1202 This variable's value indicates which element of the kill ring is at the
1203 ``front'' of the ring for yanking. More precisely, the value is a tail
1204 of the value of @code{kill-ring}, and its @sc{car} is the kill string
1205 that @kbd{C-y} should yank.
1208 @defopt kill-ring-max
1209 The value of this variable is the maximum length to which the kill
1210 ring can grow, before elements are thrown away at the end. The default
1211 value for @code{kill-ring-max} is 60.
1215 @comment node-name, next, previous, up
1219 Most buffers have an @dfn{undo list}, which records all changes made
1220 to the buffer's text so that they can be undone. (The buffers that
1221 don't have one are usually special-purpose buffers for which Emacs
1222 assumes that undoing is not useful. In particular, any buffer whose
1223 name begins with a space has its undo recording off by default;
1224 see @ref{Buffer Names}.) All the primitives that modify the
1225 text in the buffer automatically add elements to the front of the undo
1226 list, which is in the variable @code{buffer-undo-list}.
1228 @defvar buffer-undo-list
1229 This buffer-local variable's value is the undo list of the current
1230 buffer. A value of @code{t} disables the recording of undo information.
1233 Here are the kinds of elements an undo list can have:
1236 @item @var{position}
1237 This kind of element records a previous value of point; undoing this
1238 element moves point to @var{position}. Ordinary cursor motion does not
1239 make any sort of undo record, but deletion operations use these entries
1240 to record where point was before the command.
1242 @item (@var{beg} . @var{end})
1243 This kind of element indicates how to delete text that was inserted.
1244 Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1247 @item (@var{text} . @var{position})
1248 This kind of element indicates how to reinsert text that was deleted.
1249 The deleted text itself is the string @var{text}. The place to
1250 reinsert it is @code{(abs @var{position})}. If @var{position} is
1251 positive, point was at the beginning of the deleted text, otherwise it
1254 @item (t @var{high} . @var{low})
1255 This kind of element indicates that an unmodified buffer became
1256 modified. The elements @var{high} and @var{low} are two integers, each
1257 recording 16 bits of the visited file's modification time as of when it
1258 was previously visited or saved. @code{primitive-undo} uses those
1259 values to determine whether to mark the buffer as unmodified once again;
1260 it does so only if the file's modification time matches those numbers.
1262 @item (nil @var{property} @var{value} @var{beg} . @var{end})
1263 This kind of element records a change in a text property.
1264 Here's how you might undo the change:
1267 (put-text-property @var{beg} @var{end} @var{property} @var{value})
1270 @item (@var{marker} . @var{adjustment})
1271 This kind of element records the fact that the marker @var{marker} was
1272 relocated due to deletion of surrounding text, and that it moved
1273 @var{adjustment} character positions. Undoing this element moves
1274 @var{marker} @minus{} @var{adjustment} characters.
1276 @item (apply @var{funname} . @var{args})
1277 This is an extensible undo item, which is undone by calling
1278 @var{funname} with arguments @var{args}.
1280 @item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1281 This is an extensible undo item, which records a change limited to the
1282 range @var{beg} to @var{end}, which increased the size of the buffer
1283 by @var{delta}. It is undone by calling @var{funname} with arguments
1286 This kind of element enables undo limited to a region to determine
1287 whether the element pertains to that region.
1290 This element is a boundary. The elements between two boundaries are
1291 called a @dfn{change group}; normally, each change group corresponds to
1292 one keyboard command, and undo commands normally undo an entire group as
1296 @defun undo-boundary
1297 This function places a boundary element in the undo list. The undo
1298 command stops at such a boundary, and successive undo commands undo
1299 to earlier and earlier boundaries. This function returns @code{nil}.
1301 The editor command loop automatically creates an undo boundary before
1302 each key sequence is executed. Thus, each undo normally undoes the
1303 effects of one command. Self-inserting input characters are an
1304 exception. The command loop makes a boundary for the first such
1305 character; the next 19 consecutive self-inserting input characters do
1306 not make boundaries, and then the 20th does, and so on as long as
1307 self-inserting characters continue.
1309 All buffer modifications add a boundary whenever the previous undoable
1310 change was made in some other buffer. This is to ensure that
1311 each command makes a boundary in each buffer where it makes changes.
1313 Calling this function explicitly is useful for splitting the effects of
1314 a command into more than one unit. For example, @code{query-replace}
1315 calls @code{undo-boundary} after each replacement, so that the user can
1316 undo individual replacements one by one.
1319 @defvar undo-in-progress
1320 This variable is normally @code{nil}, but the undo commands bind it to
1321 @code{t}. This is so that various kinds of change hooks can tell when
1322 they're being called for the sake of undoing.
1325 @defun primitive-undo count list
1326 This is the basic function for undoing elements of an undo list.
1327 It undoes the first @var{count} elements of @var{list}, returning
1328 the rest of @var{list}.
1330 @code{primitive-undo} adds elements to the buffer's undo list when it
1331 changes the buffer. Undo commands avoid confusion by saving the undo
1332 list value at the beginning of a sequence of undo operations. Then the
1333 undo operations use and update the saved value. The new elements added
1334 by undoing are not part of this saved value, so they don't interfere with
1337 This function does not bind @code{undo-in-progress}.
1340 @node Maintaining Undo
1341 @section Maintaining Undo Lists
1343 This section describes how to enable and disable undo information for
1344 a given buffer. It also explains how the undo list is truncated
1345 automatically so it doesn't get too big.
1347 Recording of undo information in a newly created buffer is normally
1348 enabled to start with; but if the buffer name starts with a space, the
1349 undo recording is initially disabled. You can explicitly enable or
1350 disable undo recording with the following two functions, or by setting
1351 @code{buffer-undo-list} yourself.
1353 @deffn Command buffer-enable-undo &optional buffer-or-name
1354 This command enables recording undo information for buffer
1355 @var{buffer-or-name}, so that subsequent changes can be undone. If no
1356 argument is supplied, then the current buffer is used. This function
1357 does nothing if undo recording is already enabled in the buffer. It
1360 In an interactive call, @var{buffer-or-name} is the current buffer.
1361 You cannot specify any other buffer.
1364 @deffn Command buffer-disable-undo &optional buffer-or-name
1365 @cindex disabling undo
1366 This function discards the undo list of @var{buffer-or-name}, and disables
1367 further recording of undo information. As a result, it is no longer
1368 possible to undo either previous changes or any subsequent changes. If
1369 the undo list of @var{buffer-or-name} is already disabled, this function
1372 This function returns @code{nil}.
1375 As editing continues, undo lists get longer and longer. To prevent
1376 them from using up all available memory space, garbage collection trims
1377 them back to size limits you can set. (For this purpose, the ``size''
1378 of an undo list measures the cons cells that make up the list, plus the
1379 strings of deleted text.) Three variables control the range of acceptable
1380 sizes: @code{undo-limit}, @code{undo-strong-limit} and
1381 @code{undo-outer-limit}. In these variables, size is counted as the
1382 number of bytes occupied, which includes both saved text and other
1386 This is the soft limit for the acceptable size of an undo list. The
1387 change group at which this size is exceeded is the last one kept.
1390 @defopt undo-strong-limit
1391 This is the upper limit for the acceptable size of an undo list. The
1392 change group at which this size is exceeded is discarded itself (along
1393 with all older change groups). There is one exception: the very latest
1394 change group is only discarded if it exceeds @code{undo-outer-limit}.
1397 @defopt undo-outer-limit
1398 If at garbage collection time the undo info for the current command
1399 exceeds this limit, Emacs discards the info and displays a warning.
1400 This is a last ditch limit to prevent memory overflow.
1403 @defopt undo-ask-before-discard
1404 If this variable is non-@code{nil}, when the undo info exceeds
1405 @code{undo-outer-limit}, Emacs asks in the echo area whether to
1406 discard the info. The default value is @code{nil}, which means to
1407 discard it automatically.
1409 This option is mainly intended for debugging. Garbage collection is
1410 inhibited while the question is asked, which means that Emacs might
1411 leak memory if the user waits too long before answering the question.
1415 @comment node-name, next, previous, up
1417 @cindex filling text
1419 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1420 breaks) so that they are nearly (but no greater than) a specified
1421 maximum width. Additionally, lines can be @dfn{justified}, which means
1422 inserting spaces to make the left and/or right margins line up
1423 precisely. The width is controlled by the variable @code{fill-column}.
1424 For ease of reading, lines should be no longer than 70 or so columns.
1426 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1427 automatically as you insert it, but changes to existing text may leave
1428 it improperly filled. Then you must fill the text explicitly.
1430 Most of the commands in this section return values that are not
1431 meaningful. All the functions that do filling take note of the current
1432 left margin, current right margin, and current justification style
1433 (@pxref{Margins}). If the current justification style is
1434 @code{none}, the filling functions don't actually do anything.
1436 Several of the filling functions have an argument @var{justify}.
1437 If it is non-@code{nil}, that requests some kind of justification. It
1438 can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1439 request a specific style of justification. If it is @code{t}, that
1440 means to use the current justification style for this part of the text
1441 (see @code{current-justification}, below). Any other value is treated
1444 When you call the filling functions interactively, using a prefix
1445 argument implies the value @code{full} for @var{justify}.
1447 @deffn Command fill-paragraph &optional justify region
1448 This command fills the paragraph at or after point. If
1449 @var{justify} is non-@code{nil}, each line is justified as well.
1450 It uses the ordinary paragraph motion commands to find paragraph
1451 boundaries. @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
1453 When @var{region} is non-@code{nil}, then if Transient Mark mode is
1454 enabled and the mark is active, this command calls @code{fill-region}
1455 to fill all the paragraphs in the region, instead of filling only the
1456 current paragraph. When this command is called interactively,
1457 @var{region} is @code{t}.
1460 @deffn Command fill-region start end &optional justify nosqueeze to-eop
1461 This command fills each of the paragraphs in the region from @var{start}
1462 to @var{end}. It justifies as well if @var{justify} is
1465 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1466 other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1467 that means to keep filling to the end of the paragraph---or the next hard
1468 newline, if @code{use-hard-newlines} is enabled (see below).
1470 The variable @code{paragraph-separate} controls how to distinguish
1471 paragraphs. @xref{Standard Regexps}.
1474 @deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
1475 This command fills each paragraph in the region according to its
1476 individual fill prefix. Thus, if the lines of a paragraph were indented
1477 with spaces, the filled paragraph will remain indented in the same
1480 The first two arguments, @var{start} and @var{end}, are the beginning
1481 and end of the region to be filled. The third and fourth arguments,
1482 @var{justify} and @var{citation-regexp}, are optional. If
1483 @var{justify} is non-@code{nil}, the paragraphs are justified as
1484 well as filled. If @var{citation-regexp} is non-@code{nil}, it means the
1485 function is operating on a mail message and therefore should not fill
1486 the header lines. If @var{citation-regexp} is a string, it is used as
1487 a regular expression; if it matches the beginning of a line, that line
1488 is treated as a citation marker.
1490 Ordinarily, @code{fill-individual-paragraphs} regards each change in
1491 indentation as starting a new paragraph. If
1492 @code{fill-individual-varying-indent} is non-@code{nil}, then only
1493 separator lines separate paragraphs. That mode can handle indented
1494 paragraphs with additional indentation on the first line.
1497 @defopt fill-individual-varying-indent
1498 This variable alters the action of @code{fill-individual-paragraphs} as
1502 @deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1503 This command considers a region of text as a single paragraph and fills
1504 it. If the region was made up of many paragraphs, the blank lines
1505 between paragraphs are removed. This function justifies as well as
1506 filling when @var{justify} is non-@code{nil}.
1508 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1509 other than line breaks untouched. If @var{squeeze-after} is
1510 non-@code{nil}, it specifies a position in the region, and means don't
1511 canonicalize spaces before that position.
1513 In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1514 choose a fill prefix by default. @xref{Adaptive Fill}.
1517 @deffn Command justify-current-line &optional how eop nosqueeze
1518 This command inserts spaces between the words of the current line so
1519 that the line ends exactly at @code{fill-column}. It returns
1522 The argument @var{how}, if non-@code{nil} specifies explicitly the style
1523 of justification. It can be @code{left}, @code{right}, @code{full},
1524 @code{center}, or @code{none}. If it is @code{t}, that means to do
1525 follow specified justification style (see @code{current-justification},
1526 below). @code{nil} means to do full justification.
1528 If @var{eop} is non-@code{nil}, that means do only left-justification
1529 if @code{current-justification} specifies full justification. This is
1530 used for the last line of a paragraph; even if the paragraph as a
1531 whole is fully justified, the last line should not be.
1533 If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1537 @defopt default-justification
1538 This variable's value specifies the style of justification to use for
1539 text that doesn't specify a style with a text property. The possible
1540 values are @code{left}, @code{right}, @code{full}, @code{center}, or
1541 @code{none}. The default value is @code{left}.
1544 @defun current-justification
1545 This function returns the proper justification style to use for filling
1546 the text around point.
1548 This returns the value of the @code{justification} text property at
1549 point, or the variable @var{default-justification} if there is no such
1550 text property. However, it returns @code{nil} rather than @code{none}
1551 to mean ``don't justify''.
1554 @defopt sentence-end-double-space
1555 @anchor{Definition of sentence-end-double-space}
1556 If this variable is non-@code{nil}, a period followed by just one space
1557 does not count as the end of a sentence, and the filling functions
1558 avoid breaking the line at such a place.
1561 @defopt sentence-end-without-period
1562 If this variable is non-@code{nil}, a sentence can end without a
1563 period. This is used for languages like Thai, where sentences end
1564 with a double space but without a period.
1567 @defopt sentence-end-without-space
1568 If this variable is non-@code{nil}, it should be a string of
1569 characters that can end a sentence without following spaces.
1572 @defvar fill-paragraph-function
1573 This variable provides a way to override the filling of paragraphs.
1574 If its value is non-@code{nil}, @code{fill-paragraph} calls this
1575 function to do the work. If the function returns a non-@code{nil}
1576 value, @code{fill-paragraph} assumes the job is done, and immediately
1579 The usual use of this feature is to fill comments in programming
1580 language modes. If the function needs to fill a paragraph in the usual
1581 way, it can do so as follows:
1584 (let ((fill-paragraph-function nil))
1585 (fill-paragraph arg))
1589 @defvar fill-forward-paragraph-function
1590 This variable provides a way to override how the filling functions,
1591 such as @code{fill-region} and @code{fill-paragraph}, move forward to
1592 the next paragraph. Its value should be a function, which is called
1593 with a single argument @var{n}, the number of paragraphs to move, and
1594 should return the difference between @var{n} and the number of
1595 paragraphs actually moved. The default value of this variable is
1596 @code{forward-paragraph}. @xref{Paragraphs,,, emacs, The GNU Emacs
1600 @defvar use-hard-newlines
1601 If this variable is non-@code{nil}, the filling functions do not delete
1602 newlines that have the @code{hard} text property. These ``hard
1603 newlines'' act as paragraph separators.
1607 @section Margins for Filling
1610 This buffer-local variable, if non-@code{nil}, specifies a string of
1611 text that appears at the beginning of normal text lines and should be
1612 disregarded when filling them. Any line that fails to start with the
1613 fill prefix is considered the start of a paragraph; so is any line
1614 that starts with the fill prefix followed by additional whitespace.
1615 Lines that start with the fill prefix but no additional whitespace are
1616 ordinary text lines that can be filled together. The resulting filled
1617 lines also start with the fill prefix.
1619 The fill prefix follows the left margin whitespace, if any.
1623 This buffer-local variable specifies the maximum width of filled lines.
1624 Its value should be an integer, which is a number of columns. All the
1625 filling, justification, and centering commands are affected by this
1626 variable, including Auto Fill mode (@pxref{Auto Filling}).
1628 As a practical matter, if you are writing text for other people to
1629 read, you should set @code{fill-column} to no more than 70. Otherwise
1630 the line will be too long for people to read comfortably, and this can
1631 make the text seem clumsy.
1634 @defvar default-fill-column
1635 The value of this variable is the default value for @code{fill-column} in
1636 buffers that do not override it. This is the same as
1637 @code{(default-value 'fill-column)}.
1639 The default value for @code{default-fill-column} is 70.
1642 @deffn Command set-left-margin from to margin
1643 This sets the @code{left-margin} property on the text from @var{from} to
1644 @var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1645 command also refills the region to fit the new margin.
1648 @deffn Command set-right-margin from to margin
1649 This sets the @code{right-margin} property on the text from @var{from}
1650 to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1651 this command also refills the region to fit the new margin.
1654 @defun current-left-margin
1655 This function returns the proper left margin value to use for filling
1656 the text around point. The value is the sum of the @code{left-margin}
1657 property of the character at the start of the current line (or zero if
1658 none), and the value of the variable @code{left-margin}.
1661 @defun current-fill-column
1662 This function returns the proper fill column value to use for filling
1663 the text around point. The value is the value of the @code{fill-column}
1664 variable, minus the value of the @code{right-margin} property of the
1665 character after point.
1668 @deffn Command move-to-left-margin &optional n force
1669 This function moves point to the left margin of the current line. The
1670 column moved to is determined by calling the function
1671 @code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1672 @code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1674 If @var{force} is non-@code{nil}, that says to fix the line's
1675 indentation if that doesn't match the left margin value.
1678 @defun delete-to-left-margin &optional from to
1679 This function removes left margin indentation from the text between
1680 @var{from} and @var{to}. The amount of indentation to delete is
1681 determined by calling @code{current-left-margin}. In no case does this
1682 function delete non-whitespace. If @var{from} and @var{to} are omitted,
1683 they default to the whole buffer.
1686 @defun indent-to-left-margin
1687 This function adjusts the indentation at the beginning of the current
1688 line to the value specified by the variable @code{left-margin}. (That
1689 may involve either inserting or deleting whitespace.) This function
1690 is value of @code{indent-line-function} in Paragraph-Indent Text mode.
1694 This variable specifies the base left margin column. In Fundamental
1695 mode, @kbd{C-j} indents to this column. This variable automatically
1696 becomes buffer-local when set in any fashion.
1699 @defopt fill-nobreak-predicate
1700 This variable gives major modes a way to specify not to break a line
1701 at certain places. Its value should be a list of functions. Whenever
1702 filling considers breaking the line at a certain place in the buffer,
1703 it calls each of these functions with no arguments and with point
1704 located at that place. If any of the functions returns
1705 non-@code{nil}, then the line won't be broken there.
1709 @section Adaptive Fill Mode
1710 @c @cindex Adaptive Fill mode "adaptive-fill-mode" is adjacent.
1712 When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
1713 prefix automatically from the text in each paragraph being filled
1714 rather than using a predetermined value. During filling, this fill
1715 prefix gets inserted at the start of the second and subsequent lines
1716 of the paragraph as described in @ref{Filling}, and in @ref{Auto
1719 @defopt adaptive-fill-mode
1720 Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1721 It is @code{t} by default.
1724 @defun fill-context-prefix from to
1725 This function implements the heart of Adaptive Fill mode; it chooses a
1726 fill prefix based on the text between @var{from} and @var{to},
1727 typically the start and end of a paragraph. It does this by looking
1728 at the first two lines of the paragraph, based on the variables
1730 @c The optional argument first-line-regexp is not documented
1731 @c because it exists for internal purposes and might be eliminated
1734 Usually, this function returns the fill prefix, a string. However,
1735 before doing this, the function makes a final check (not specially
1736 mentioned in the following) that a line starting with this prefix
1737 wouldn't look like the start of a paragraph. Should this happen, the
1738 function signals the anomaly by returning @code{nil} instead.
1740 In detail, @code{fill-context-prefix} does this:
1744 It takes a candidate for the fill prefix from the first line---it
1745 tries first the function in @code{adaptive-fill-function} (if any),
1746 then the regular expression @code{adaptive-fill-regexp} (see below).
1747 The first non-@code{nil} result of these, or the empty string if
1748 they're both @code{nil}, becomes the first line's candidate.
1750 If the paragraph has as yet only one line, the function tests the
1751 validity of the prefix candidate just found. The function then
1752 returns the candidate if it's valid, or a string of spaces otherwise.
1753 (see the description of @code{adaptive-fill-first-line-regexp} below).
1755 When the paragraph already has two lines, the function next looks for
1756 a prefix candidate on the second line, in just the same way it did for
1757 the first line. If it doesn't find one, it returns @code{nil}.
1759 The function now compares the two candidate prefixes heuristically: if
1760 the non-whitespace characters in the line 2 candidate occur in the
1761 same order in the line 1 candidate, the function returns the line 2
1762 candidate. Otherwise, it returns the largest initial substring which
1763 is common to both candidates (which might be the empty string).
1767 @defopt adaptive-fill-regexp
1768 Adaptive Fill mode matches this regular expression against the text
1769 starting after the left margin whitespace (if any) on a line; the
1770 characters it matches are that line's candidate for the fill prefix.
1772 The default value matches whitespace with certain punctuation
1773 characters intermingled.
1776 @defopt adaptive-fill-first-line-regexp
1777 Used only in one-line paragraphs, this regular expression acts as an
1778 additional check of the validity of the one available candidate fill
1779 prefix: the candidate must match this regular expression, or match
1780 @code{comment-start-skip}. If it doesn't, @code{fill-context-prefix}
1781 replaces the candidate with a string of spaces ``of the same width''
1784 The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
1785 matches only a string of whitespace. The effect of this default is to
1786 force the fill prefixes found in one-line paragraphs always to be pure
1790 @defopt adaptive-fill-function
1791 You can specify more complex ways of choosing a fill prefix
1792 automatically by setting this variable to a function. The function is
1793 called with point after the left margin (if any) of a line, and it
1794 must preserve point. It should return either ``that line's'' fill
1795 prefix or @code{nil}, meaning it has failed to determine a prefix.
1799 @comment node-name, next, previous, up
1800 @section Auto Filling
1801 @cindex filling, automatic
1802 @cindex Auto Fill mode
1804 Auto Fill mode is a minor mode that fills lines automatically as text
1805 is inserted. This section describes the hook used by Auto Fill mode.
1806 For a description of functions that you can call explicitly to fill and
1807 justify existing text, see @ref{Filling}.
1809 Auto Fill mode also enables the functions that change the margins and
1810 justification style to refill portions of the text. @xref{Margins}.
1812 @defvar auto-fill-function
1813 The value of this buffer-local variable should be a function (of no
1814 arguments) to be called after self-inserting a character from the table
1815 @code{auto-fill-chars}. It may be @code{nil}, in which case nothing
1816 special is done in that case.
1818 The value of @code{auto-fill-function} is @code{do-auto-fill} when
1819 Auto-Fill mode is enabled. That is a function whose sole purpose is to
1820 implement the usual strategy for breaking a line.
1823 In older Emacs versions, this variable was named @code{auto-fill-hook},
1824 but since it is not called with the standard convention for hooks, it
1825 was renamed to @code{auto-fill-function} in version 19.
1829 @defvar normal-auto-fill-function
1830 This variable specifies the function to use for
1831 @code{auto-fill-function}, if and when Auto Fill is turned on. Major
1832 modes can set buffer-local values for this variable to alter how Auto
1836 @defvar auto-fill-chars
1837 A char table of characters which invoke @code{auto-fill-function} when
1838 self-inserted---space and newline in most language environments. They
1839 have an entry @code{t} in the table.
1843 @section Sorting Text
1844 @cindex sorting text
1846 The sorting functions described in this section all rearrange text in
1847 a buffer. This is in contrast to the function @code{sort}, which
1848 rearranges the order of the elements of a list (@pxref{Rearrangement}).
1849 The values returned by these functions are not meaningful.
1851 @defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
1852 This function is the general text-sorting routine that subdivides a
1853 buffer into records and then sorts them. Most of the commands in this
1854 section use this function.
1856 To understand how @code{sort-subr} works, consider the whole accessible
1857 portion of the buffer as being divided into disjoint pieces called
1858 @dfn{sort records}. The records may or may not be contiguous, but they
1859 must not overlap. A portion of each sort record (perhaps all of it) is
1860 designated as the sort key. Sorting rearranges the records in order by
1863 Usually, the records are rearranged in order of ascending sort key.
1864 If the first argument to the @code{sort-subr} function, @var{reverse},
1865 is non-@code{nil}, the sort records are rearranged in order of
1866 descending sort key.
1868 The next four arguments to @code{sort-subr} are functions that are
1869 called to move point across a sort record. They are called many times
1870 from within @code{sort-subr}.
1874 @var{nextrecfun} is called with point at the end of a record. This
1875 function moves point to the start of the next record. The first record
1876 is assumed to start at the position of point when @code{sort-subr} is
1877 called. Therefore, you should usually move point to the beginning of
1878 the buffer before calling @code{sort-subr}.
1880 This function can indicate there are no more sort records by leaving
1881 point at the end of the buffer.
1884 @var{endrecfun} is called with point within a record. It moves point to
1885 the end of the record.
1888 @var{startkeyfun} is called to move point from the start of a record to
1889 the start of the sort key. This argument is optional; if it is omitted,
1890 the whole record is the sort key. If supplied, the function should
1891 either return a non-@code{nil} value to be used as the sort key, or
1892 return @code{nil} to indicate that the sort key is in the buffer
1893 starting at point. In the latter case, @var{endkeyfun} is called to
1894 find the end of the sort key.
1897 @var{endkeyfun} is called to move point from the start of the sort key
1898 to the end of the sort key. This argument is optional. If
1899 @var{startkeyfun} returns @code{nil} and this argument is omitted (or
1900 @code{nil}), then the sort key extends to the end of the record. There
1901 is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1902 non-@code{nil} value.
1905 The argument @var{predicate} is the function to use to compare keys.
1906 If keys are numbers, it defaults to @code{<}; otherwise it defaults to
1909 As an example of @code{sort-subr}, here is the complete function
1910 definition for @code{sort-lines}:
1914 ;; @r{Note that the first two lines of doc string}
1915 ;; @r{are effectively one line when viewed by a user.}
1916 (defun sort-lines (reverse beg end)
1917 "Sort lines in region alphabetically;\
1918 argument means descending order.
1919 Called from a program, there are three arguments:
1922 REVERSE (non-nil means reverse order),\
1923 BEG and END (region to sort).
1924 The variable `sort-fold-case' determines\
1925 whether alphabetic case affects
1929 (interactive "P\nr")
1932 (narrow-to-region beg end)
1933 (goto-char (point-min))
1934 (let ((inhibit-field-text-motion t))
1935 (sort-subr reverse 'forward-line 'end-of-line)))))
1939 Here @code{forward-line} moves point to the start of the next record,
1940 and @code{end-of-line} moves point to the end of record. We do not pass
1941 the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
1942 record is used as the sort key.
1944 The @code{sort-paragraphs} function is very much the same, except that
1945 its @code{sort-subr} call looks like this:
1952 (while (and (not (eobp))
1953 (looking-at paragraph-separate))
1959 Markers pointing into any sort records are left with no useful
1960 position after @code{sort-subr} returns.
1963 @defopt sort-fold-case
1964 If this variable is non-@code{nil}, @code{sort-subr} and the other
1965 buffer sorting functions ignore case when comparing strings.
1968 @deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
1969 This command sorts the region between @var{start} and @var{end}
1970 alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
1971 If @var{reverse} is a negative integer, then sorting is in reverse
1974 Alphabetical sorting means that two sort keys are compared by
1975 comparing the first characters of each, the second characters of each,
1976 and so on. If a mismatch is found, it means that the sort keys are
1977 unequal; the sort key whose character is less at the point of first
1978 mismatch is the lesser sort key. The individual characters are compared
1979 according to their numerical character codes in the Emacs character set.
1981 The value of the @var{record-regexp} argument specifies how to divide
1982 the buffer into sort records. At the end of each record, a search is
1983 done for this regular expression, and the text that matches it is taken
1984 as the next record. For example, the regular expression @samp{^.+$},
1985 which matches lines with at least one character besides a newline, would
1986 make each such line into a sort record. @xref{Regular Expressions}, for
1987 a description of the syntax and meaning of regular expressions.
1989 The value of the @var{key-regexp} argument specifies what part of each
1990 record is the sort key. The @var{key-regexp} could match the whole
1991 record, or only a part. In the latter case, the rest of the record has
1992 no effect on the sorted order of records, but it is carried along when
1993 the record moves to its new position.
1995 The @var{key-regexp} argument can refer to the text matched by a
1996 subexpression of @var{record-regexp}, or it can be a regular expression
1999 If @var{key-regexp} is:
2002 @item @samp{\@var{digit}}
2003 then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
2004 grouping in @var{record-regexp} is the sort key.
2007 then the whole record is the sort key.
2009 @item a regular expression
2010 then @code{sort-regexp-fields} searches for a match for the regular
2011 expression within the record. If such a match is found, it is the sort
2012 key. If there is no match for @var{key-regexp} within a record then
2013 that record is ignored, which means its position in the buffer is not
2014 changed. (The other records may move around it.)
2017 For example, if you plan to sort all the lines in the region by the
2018 first word on each line starting with the letter @samp{f}, you should
2019 set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
2020 @samp{\<f\w*\>}. The resulting expression looks like this:
2024 (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
2030 If you call @code{sort-regexp-fields} interactively, it prompts for
2031 @var{record-regexp} and @var{key-regexp} in the minibuffer.
2034 @deffn Command sort-lines reverse start end
2035 This command alphabetically sorts lines in the region between
2036 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2037 is in reverse order.
2040 @deffn Command sort-paragraphs reverse start end
2041 This command alphabetically sorts paragraphs in the region between
2042 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2043 is in reverse order.
2046 @deffn Command sort-pages reverse start end
2047 This command alphabetically sorts pages in the region between
2048 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2049 is in reverse order.
2052 @deffn Command sort-fields field start end
2053 This command sorts lines in the region between @var{start} and
2054 @var{end}, comparing them alphabetically by the @var{field}th field
2055 of each line. Fields are separated by whitespace and numbered starting
2056 from 1. If @var{field} is negative, sorting is by the
2057 @w{@minus{}@var{field}th} field from the end of the line. This command
2058 is useful for sorting tables.
2061 @deffn Command sort-numeric-fields field start end
2062 This command sorts lines in the region between @var{start} and
2063 @var{end}, comparing them numerically by the @var{field}th field of
2064 each line. Fields are separated by whitespace and numbered starting
2065 from 1. The specified field must contain a number in each line of the
2066 region. Numbers starting with 0 are treated as octal, and numbers
2067 starting with @samp{0x} are treated as hexadecimal.
2069 If @var{field} is negative, sorting is by the
2070 @w{@minus{}@var{field}th} field from the end of the line. This
2071 command is useful for sorting tables.
2074 @defopt sort-numeric-base
2075 This variable specifies the default radix for
2076 @code{sort-numeric-fields} to parse numbers.
2079 @deffn Command sort-columns reverse &optional beg end
2080 This command sorts the lines in the region between @var{beg} and
2081 @var{end}, comparing them alphabetically by a certain range of
2082 columns. The column positions of @var{beg} and @var{end} bound the
2083 range of columns to sort on.
2085 If @var{reverse} is non-@code{nil}, the sort is in reverse order.
2087 One unusual thing about this command is that the entire line
2088 containing position @var{beg}, and the entire line containing position
2089 @var{end}, are included in the region sorted.
2091 Note that @code{sort-columns} rejects text that contains tabs, because
2092 tabs could be split across the specified columns. Use @kbd{M-x
2093 untabify} to convert tabs to spaces before sorting.
2095 When possible, this command actually works by calling the @code{sort}
2100 @comment node-name, next, previous, up
2101 @section Counting Columns
2103 @cindex counting columns
2104 @cindex horizontal position
2106 The column functions convert between a character position (counting
2107 characters from the beginning of the buffer) and a column position
2108 (counting screen characters from the beginning of a line).
2110 These functions count each character according to the number of
2111 columns it occupies on the screen. This means control characters count
2112 as occupying 2 or 4 columns, depending upon the value of
2113 @code{ctl-arrow}, and tabs count as occupying a number of columns that
2114 depends on the value of @code{tab-width} and on the column where the tab
2115 begins. @xref{Usual Display}.
2117 Column number computations ignore the width of the window and the
2118 amount of horizontal scrolling. Consequently, a column value can be
2119 arbitrarily high. The first (or leftmost) column is numbered 0. They
2120 also ignore overlays and text properties, aside from invisibility.
2122 @defun current-column
2123 This function returns the horizontal position of point, measured in
2124 columns, counting from 0 at the left margin. The column position is the
2125 sum of the widths of all the displayed representations of the characters
2126 between the start of the current line and point.
2128 For an example of using @code{current-column}, see the description of
2129 @code{count-lines} in @ref{Text Lines}.
2132 @deffn Command move-to-column column &optional force
2133 This function moves point to @var{column} in the current line. The
2134 calculation of @var{column} takes into account the widths of the
2135 displayed representations of the characters between the start of the
2138 When called interactively, @var{column} is the value of prefix numeric
2139 argument. If @var{column} is not an integer, an error is signaled.
2141 If column @var{column} is beyond the end of the line, point moves to
2142 the end of the line. If @var{column} is negative, point moves to the
2143 beginning of the line.
2145 If it is impossible to move to column @var{column} because that is in
2146 the middle of a multicolumn character such as a tab, point moves to the
2147 end of that character. However, if @var{force} is non-@code{nil}, and
2148 @var{column} is in the middle of a tab, then @code{move-to-column}
2149 converts the tab into spaces so that it can move precisely to column
2150 @var{column}. Other multicolumn characters can cause anomalies despite
2151 @var{force}, since there is no way to split them.
2153 The argument @var{force} also has an effect if the line isn't long
2154 enough to reach column @var{column}; if it is @code{t}, that means to
2155 add whitespace at the end of the line to reach that column.
2157 The return value is the column number actually moved to.
2161 @section Indentation
2164 The indentation functions are used to examine, move to, and change
2165 whitespace that is at the beginning of a line. Some of the functions
2166 can also change whitespace elsewhere on a line. Columns and indentation
2167 count from zero at the left margin.
2170 * Primitive Indent:: Functions used to count and insert indentation.
2171 * Mode-Specific Indent:: Customize indentation for different modes.
2172 * Region Indent:: Indent all the lines in a region.
2173 * Relative Indent:: Indent the current line based on previous lines.
2174 * Indent Tabs:: Adjustable, typewriter-like tab stops.
2175 * Motion by Indent:: Move to first non-blank character.
2178 @node Primitive Indent
2179 @subsection Indentation Primitives
2181 This section describes the primitive functions used to count and
2182 insert indentation. The functions in the following sections use these
2183 primitives. @xref{Width}, for related functions.
2185 @defun current-indentation
2186 @comment !!Type Primitive Function
2187 @comment !!SourceFile indent.c
2188 This function returns the indentation of the current line, which is
2189 the horizontal position of the first nonblank character. If the
2190 contents are entirely blank, then this is the horizontal position of the
2194 @deffn Command indent-to column &optional minimum
2195 @comment !!Type Primitive Function
2196 @comment !!SourceFile indent.c
2197 This function indents from point with tabs and spaces until @var{column}
2198 is reached. If @var{minimum} is specified and non-@code{nil}, then at
2199 least that many spaces are inserted even if this requires going beyond
2200 @var{column}. Otherwise the function does nothing if point is already
2201 beyond @var{column}. The value is the column at which the inserted
2204 The inserted whitespace characters inherit text properties from the
2205 surrounding text (usually, from the preceding text only). @xref{Sticky
2209 @defopt indent-tabs-mode
2210 @comment !!SourceFile indent.c
2211 If this variable is non-@code{nil}, indentation functions can insert
2212 tabs as well as spaces. Otherwise, they insert only spaces. Setting
2213 this variable automatically makes it buffer-local in the current buffer.
2216 @node Mode-Specific Indent
2217 @subsection Indentation Controlled by Major Mode
2219 An important function of each major mode is to customize the @key{TAB}
2220 key to indent properly for the language being edited. This section
2221 describes the mechanism of the @key{TAB} key and how to control it.
2222 The functions in this section return unpredictable values.
2224 @defvar indent-line-function
2225 This variable's value is the function to be used by @key{TAB} (and
2226 various commands) to indent the current line. The command
2227 @code{indent-according-to-mode} does no more than call this function.
2229 In Lisp mode, the value is the symbol @code{lisp-indent-line}; in C
2230 mode, @code{c-indent-line}; in Fortran mode, @code{fortran-indent-line}.
2231 The default value is @code{indent-relative}.
2234 @deffn Command indent-according-to-mode
2235 This command calls the function in @code{indent-line-function} to
2236 indent the current line in a way appropriate for the current major mode.
2239 @deffn Command indent-for-tab-command &optional rigid
2240 This command calls the function in @code{indent-line-function} to
2241 indent the current line; however, if that function is
2242 @code{indent-to-left-margin}, @code{insert-tab} is called instead.
2243 (That is a trivial command that inserts a tab character.) If
2244 @var{rigid} is non-@code{nil}, this function also rigidly indents the
2245 entire balanced expression that starts at the beginning of the current
2246 line, to reflect change in indentation of the current line.
2249 @deffn Command newline-and-indent
2250 This function inserts a newline, then indents the new line (the one
2251 following the newline just inserted) according to the major mode.
2253 It does indentation by calling the current @code{indent-line-function}.
2254 In programming language modes, this is the same thing @key{TAB} does,
2255 but in some text modes, where @key{TAB} inserts a tab,
2256 @code{newline-and-indent} indents to the column specified by
2260 @deffn Command reindent-then-newline-and-indent
2261 @comment !!SourceFile simple.el
2262 This command reindents the current line, inserts a newline at point,
2263 and then indents the new line (the one following the newline just
2266 This command does indentation on both lines according to the current
2267 major mode, by calling the current value of @code{indent-line-function}.
2268 In programming language modes, this is the same thing @key{TAB} does,
2269 but in some text modes, where @key{TAB} inserts a tab,
2270 @code{reindent-then-newline-and-indent} indents to the column specified
2271 by @code{left-margin}.
2275 @subsection Indenting an Entire Region
2277 This section describes commands that indent all the lines in the
2278 region. They return unpredictable values.
2280 @deffn Command indent-region start end &optional to-column
2281 This command indents each nonblank line starting between @var{start}
2282 (inclusive) and @var{end} (exclusive). If @var{to-column} is
2283 @code{nil}, @code{indent-region} indents each nonblank line by calling
2284 the current mode's indentation function, the value of
2285 @code{indent-line-function}.
2287 If @var{to-column} is non-@code{nil}, it should be an integer
2288 specifying the number of columns of indentation; then this function
2289 gives each line exactly that much indentation, by either adding or
2290 deleting whitespace.
2292 If there is a fill prefix, @code{indent-region} indents each line
2293 by making it start with the fill prefix.
2296 @defvar indent-region-function
2297 The value of this variable is a function that can be used by
2298 @code{indent-region} as a short cut. It should take two arguments, the
2299 start and end of the region. You should design the function so
2300 that it will produce the same results as indenting the lines of the
2301 region one by one, but presumably faster.
2303 If the value is @code{nil}, there is no short cut, and
2304 @code{indent-region} actually works line by line.
2306 A short-cut function is useful in modes such as C mode and Lisp mode,
2307 where the @code{indent-line-function} must scan from the beginning of
2308 the function definition: applying it to each line would be quadratic in
2309 time. The short cut can update the scan information as it moves through
2310 the lines indenting them; this takes linear time. In a mode where
2311 indenting a line individually is fast, there is no need for a short cut.
2313 @code{indent-region} with a non-@code{nil} argument @var{to-column} has
2314 a different meaning and does not use this variable.
2317 @deffn Command indent-rigidly start end count
2318 This command indents all lines starting between @var{start}
2319 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
2320 This ``preserves the shape'' of the affected region, moving it as a
2321 rigid unit. Consequently, this command is useful not only for indenting
2322 regions of unindented text, but also for indenting regions of formatted
2325 For example, if @var{count} is 3, this command adds 3 columns of
2326 indentation to each of the lines beginning in the region specified.
2328 In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses
2329 @code{indent-rigidly} to indent the text copied from the message being
2333 @deffn Command indent-code-rigidly start end columns &optional nochange-regexp
2334 This is like @code{indent-rigidly}, except that it doesn't alter lines
2335 that start within strings or comments.
2337 In addition, it doesn't alter a line if @var{nochange-regexp} matches at
2338 the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
2341 @node Relative Indent
2342 @subsection Indentation Relative to Previous Lines
2344 This section describes two commands that indent the current line
2345 based on the contents of previous lines.
2347 @deffn Command indent-relative &optional unindented-ok
2348 This command inserts whitespace at point, extending to the same
2349 column as the next @dfn{indent point} of the previous nonblank line. An
2350 indent point is a non-whitespace character following whitespace. The
2351 next indent point is the first one at a column greater than the current
2352 column of point. For example, if point is underneath and to the left of
2353 the first non-blank character of a line of text, it moves to that column
2354 by inserting whitespace.
2356 If the previous nonblank line has no next indent point (i.e., none at a
2357 great enough column position), @code{indent-relative} either does
2358 nothing (if @var{unindented-ok} is non-@code{nil}) or calls
2359 @code{tab-to-tab-stop}. Thus, if point is underneath and to the right
2360 of the last column of a short line of text, this command ordinarily
2361 moves point to the next tab stop by inserting whitespace.
2363 The return value of @code{indent-relative} is unpredictable.
2365 In the following example, point is at the beginning of the second
2370 This line is indented twelve spaces.
2371 @point{}The quick brown fox jumped.
2376 Evaluation of the expression @code{(indent-relative nil)} produces the
2381 This line is indented twelve spaces.
2382 @point{}The quick brown fox jumped.
2386 In this next example, point is between the @samp{m} and @samp{p} of
2391 This line is indented twelve spaces.
2392 The quick brown fox jum@point{}ped.
2397 Evaluation of the expression @code{(indent-relative nil)} produces the
2402 This line is indented twelve spaces.
2403 The quick brown fox jum @point{}ped.
2408 @deffn Command indent-relative-maybe
2409 @comment !!SourceFile indent.el
2410 This command indents the current line like the previous nonblank line,
2411 by calling @code{indent-relative} with @code{t} as the
2412 @var{unindented-ok} argument. The return value is unpredictable.
2414 If the previous nonblank line has no indent points beyond the current
2415 column, this command does nothing.
2419 @comment node-name, next, previous, up
2420 @subsection Adjustable ``Tab Stops''
2421 @cindex tabs stops for indentation
2423 This section explains the mechanism for user-specified ``tab stops''
2424 and the mechanisms that use and set them. The name ``tab stops'' is
2425 used because the feature is similar to that of the tab stops on a
2426 typewriter. The feature works by inserting an appropriate number of
2427 spaces and tab characters to reach the next tab stop column; it does not
2428 affect the display of tab characters in the buffer (@pxref{Usual
2429 Display}). Note that the @key{TAB} character as input uses this tab
2430 stop feature only in a few major modes, such as Text mode.
2431 @xref{Tab Stops,,, emacs, The GNU Emacs Manual}.
2433 @deffn Command tab-to-tab-stop
2434 This command inserts spaces or tabs before point, up to the next tab
2435 stop column defined by @code{tab-stop-list}. It searches the list for
2436 an element greater than the current column number, and uses that element
2437 as the column to indent to. It does nothing if no such element is
2441 @defopt tab-stop-list
2442 This variable is the list of tab stop columns used by
2443 @code{tab-to-tab-stops}. The elements should be integers in increasing
2444 order. The tab stop columns need not be evenly spaced.
2446 Use @kbd{M-x edit-tab-stops} to edit the location of tab stops
2450 @node Motion by Indent
2451 @subsection Indentation-Based Motion Commands
2453 These commands, primarily for interactive use, act based on the
2454 indentation in the text.
2456 @deffn Command back-to-indentation
2457 @comment !!SourceFile simple.el
2458 This command moves point to the first non-whitespace character in the
2459 current line (which is the line in which point is located). It returns
2463 @deffn Command backward-to-indentation &optional arg
2464 @comment !!SourceFile simple.el
2465 This command moves point backward @var{arg} lines and then to the
2466 first nonblank character on that line. It returns @code{nil}.
2467 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2470 @deffn Command forward-to-indentation &optional arg
2471 @comment !!SourceFile simple.el
2472 This command moves point forward @var{arg} lines and then to the first
2473 nonblank character on that line. It returns @code{nil}.
2474 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2478 @comment node-name, next, previous, up
2479 @section Case Changes
2480 @cindex case conversion in buffers
2482 The case change commands described here work on text in the current
2483 buffer. @xref{Case Conversion}, for case conversion functions that work
2484 on strings and characters. @xref{Case Tables}, for how to customize
2485 which characters are upper or lower case and how to convert them.
2487 @deffn Command capitalize-region start end
2488 This function capitalizes all words in the region defined by
2489 @var{start} and @var{end}. To capitalize means to convert each word's
2490 first character to upper case and convert the rest of each word to lower
2491 case. The function returns @code{nil}.
2493 If one end of the region is in the middle of a word, the part of the
2494 word within the region is treated as an entire word.
2496 When @code{capitalize-region} is called interactively, @var{start} and
2497 @var{end} are point and the mark, with the smallest first.
2501 ---------- Buffer: foo ----------
2502 This is the contents of the 5th foo.
2503 ---------- Buffer: foo ----------
2507 (capitalize-region 1 44)
2510 ---------- Buffer: foo ----------
2511 This Is The Contents Of The 5th Foo.
2512 ---------- Buffer: foo ----------
2517 @deffn Command downcase-region start end
2518 This function converts all of the letters in the region defined by
2519 @var{start} and @var{end} to lower case. The function returns
2522 When @code{downcase-region} is called interactively, @var{start} and
2523 @var{end} are point and the mark, with the smallest first.
2526 @deffn Command upcase-region start end
2527 This function converts all of the letters in the region defined by
2528 @var{start} and @var{end} to upper case. The function returns
2531 When @code{upcase-region} is called interactively, @var{start} and
2532 @var{end} are point and the mark, with the smallest first.
2535 @deffn Command capitalize-word count
2536 This function capitalizes @var{count} words after point, moving point
2537 over as it does. To capitalize means to convert each word's first
2538 character to upper case and convert the rest of each word to lower case.
2539 If @var{count} is negative, the function capitalizes the
2540 @minus{}@var{count} previous words but does not move point. The value
2543 If point is in the middle of a word, the part of the word before point
2544 is ignored when moving forward. The rest is treated as an entire word.
2546 When @code{capitalize-word} is called interactively, @var{count} is
2547 set to the numeric prefix argument.
2550 @deffn Command downcase-word count
2551 This function converts the @var{count} words after point to all lower
2552 case, moving point over as it does. If @var{count} is negative, it
2553 converts the @minus{}@var{count} previous words but does not move point.
2554 The value is @code{nil}.
2556 When @code{downcase-word} is called interactively, @var{count} is set
2557 to the numeric prefix argument.
2560 @deffn Command upcase-word count
2561 This function converts the @var{count} words after point to all upper
2562 case, moving point over as it does. If @var{count} is negative, it
2563 converts the @minus{}@var{count} previous words but does not move point.
2564 The value is @code{nil}.
2566 When @code{upcase-word} is called interactively, @var{count} is set to
2567 the numeric prefix argument.
2570 @node Text Properties
2571 @section Text Properties
2572 @cindex text properties
2573 @cindex attributes of text
2574 @cindex properties of text
2576 Each character position in a buffer or a string can have a @dfn{text
2577 property list}, much like the property list of a symbol (@pxref{Property
2578 Lists}). The properties belong to a particular character at a
2579 particular place, such as, the letter @samp{T} at the beginning of this
2580 sentence or the first @samp{o} in @samp{foo}---if the same character
2581 occurs in two different places, the two occurrences in general have
2582 different properties.
2584 Each property has a name and a value. Both of these can be any Lisp
2585 object, but the name is normally a symbol. Typically each property
2586 name symbol is used for a particular purpose; for instance, the text
2587 property @code{face} specifies the faces for displaying the character
2588 (@pxref{Special Properties}). The usual way to access the property
2589 list is to specify a name and ask what value corresponds to it.
2591 If a character has a @code{category} property, we call it the
2592 @dfn{property category} of the character. It should be a symbol. The
2593 properties of the symbol serve as defaults for the properties of the
2596 Copying text between strings and buffers preserves the properties
2597 along with the characters; this includes such diverse functions as
2598 @code{substring}, @code{insert}, and @code{buffer-substring}.
2601 * Examining Properties:: Looking at the properties of one character.
2602 * Changing Properties:: Setting the properties of a range of text.
2603 * Property Search:: Searching for where a property changes value.
2604 * Special Properties:: Particular properties with special meanings.
2605 * Format Properties:: Properties for representing formatting of text.
2606 * Sticky Properties:: How inserted text gets properties from
2608 * Lazy Properties:: Computing text properties in a lazy fashion
2609 only when text is examined.
2610 * Clickable Text:: Using text properties to make regions of text
2611 do something when you click on them.
2612 * Fields:: The @code{field} property defines
2613 fields within the buffer.
2614 * Not Intervals:: Why text properties do not use
2615 Lisp-visible text intervals.
2618 @node Examining Properties
2619 @subsection Examining Text Properties
2621 The simplest way to examine text properties is to ask for the value of
2622 a particular property of a particular character. For that, use
2623 @code{get-text-property}. Use @code{text-properties-at} to get the
2624 entire property list of a character. @xref{Property Search}, for
2625 functions to examine the properties of a number of characters at once.
2627 These functions handle both strings and buffers. Keep in mind that
2628 positions in a string start from 0, whereas positions in a buffer start
2631 @defun get-text-property pos prop &optional object
2632 This function returns the value of the @var{prop} property of the
2633 character after position @var{pos} in @var{object} (a buffer or
2634 string). The argument @var{object} is optional and defaults to the
2637 If there is no @var{prop} property strictly speaking, but the character
2638 has a property category that is a symbol, then @code{get-text-property} returns
2639 the @var{prop} property of that symbol.
2642 @defun get-char-property position prop &optional object
2643 This function is like @code{get-text-property}, except that it checks
2644 overlays first and then text properties. @xref{Overlays}.
2646 The argument @var{object} may be a string, a buffer, or a window. If
2647 it is a window, then the buffer displayed in that window is used for
2648 text properties and overlays, but only the overlays active for that
2649 window are considered. If @var{object} is a buffer, then overlays in
2650 that buffer are considered first, in order of decreasing priority,
2651 followed by the text properties. If @var{object} is a string, only
2652 text properties are considered, since strings never have overlays.
2655 @defun get-char-property-and-overlay position prop &optional object
2656 This is like @code{get-char-property}, but gives extra information
2657 about the overlay that the property value comes from.
2659 Its value is a cons cell whose @sc{car} is the property value, the
2660 same value @code{get-char-property} would return with the same
2661 arguments. Its @sc{cdr} is the overlay in which the property was
2662 found, or @code{nil}, if it was found as a text property or not found
2665 If @var{position} is at the end of @var{object}, both the @sc{car} and
2666 the @sc{cdr} of the value are @code{nil}.
2669 @defvar char-property-alias-alist
2670 This variable holds an alist which maps property names to a list of
2671 alternative property names. If a character does not specify a direct
2672 value for a property, the alternative property names are consulted in
2673 order; the first non-@code{nil} value is used. This variable takes
2674 precedence over @code{default-text-properties}, and @code{category}
2675 properties take precedence over this variable.
2678 @defun text-properties-at position &optional object
2679 This function returns the entire property list of the character at
2680 @var{position} in the string or buffer @var{object}. If @var{object} is
2681 @code{nil}, it defaults to the current buffer.
2684 @defvar default-text-properties
2685 This variable holds a property list giving default values for text
2686 properties. Whenever a character does not specify a value for a
2687 property, neither directly, through a category symbol, or through
2688 @code{char-property-alias-alist}, the value stored in this list is
2689 used instead. Here is an example:
2692 (setq default-text-properties '(foo 69)
2693 char-property-alias-alist nil)
2694 ;; @r{Make sure character 1 has no properties of its own.}
2695 (set-text-properties 1 2 nil)
2696 ;; @r{What we get, when we ask, is the default value.}
2697 (get-text-property 1 'foo)
2702 @node Changing Properties
2703 @subsection Changing Text Properties
2705 The primitives for changing properties apply to a specified range of
2706 text in a buffer or string. The function @code{set-text-properties}
2707 (see end of section) sets the entire property list of the text in that
2708 range; more often, it is useful to add, change, or delete just certain
2709 properties specified by name.
2711 Since text properties are considered part of the contents of the
2712 buffer (or string), and can affect how a buffer looks on the screen,
2713 any change in buffer text properties marks the buffer as modified.
2714 Buffer text property changes are undoable also (@pxref{Undo}).
2715 Positions in a string start from 0, whereas positions in a buffer
2718 @defun put-text-property start end prop value &optional object
2719 This function sets the @var{prop} property to @var{value} for the text
2720 between @var{start} and @var{end} in the string or buffer @var{object}.
2721 If @var{object} is @code{nil}, it defaults to the current buffer.
2724 @defun add-text-properties start end props &optional object
2725 This function adds or overrides text properties for the text between
2726 @var{start} and @var{end} in the string or buffer @var{object}. If
2727 @var{object} is @code{nil}, it defaults to the current buffer.
2729 The argument @var{props} specifies which properties to add. It should
2730 have the form of a property list (@pxref{Property Lists}): a list whose
2731 elements include the property names followed alternately by the
2732 corresponding values.
2734 The return value is @code{t} if the function actually changed some
2735 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2736 its values agree with those in the text).
2738 For example, here is how to set the @code{comment} and @code{face}
2739 properties of a range of text:
2742 (add-text-properties @var{start} @var{end}
2743 '(comment t face highlight))
2747 @defun remove-text-properties start end props &optional object
2748 This function deletes specified text properties from the text between
2749 @var{start} and @var{end} in the string or buffer @var{object}. If
2750 @var{object} is @code{nil}, it defaults to the current buffer.
2752 The argument @var{props} specifies which properties to delete. It
2753 should have the form of a property list (@pxref{Property Lists}): a list
2754 whose elements are property names alternating with corresponding values.
2755 But only the names matter---the values that accompany them are ignored.
2756 For example, here's how to remove the @code{face} property.
2759 (remove-text-properties @var{start} @var{end} '(face nil))
2762 The return value is @code{t} if the function actually changed some
2763 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2764 if no character in the specified text had any of those properties).
2766 To remove all text properties from certain text, use
2767 @code{set-text-properties} and specify @code{nil} for the new property
2771 @defun remove-list-of-text-properties start end list-of-properties &optional object
2772 Like @code{remove-text-properties} except that
2773 @var{list-of-properties} is a list of property names only, not an
2774 alternating list of property names and values.
2777 @defun set-text-properties start end props &optional object
2778 This function completely replaces the text property list for the text
2779 between @var{start} and @var{end} in the string or buffer @var{object}.
2780 If @var{object} is @code{nil}, it defaults to the current buffer.
2782 The argument @var{props} is the new property list. It should be a list
2783 whose elements are property names alternating with corresponding values.
2785 After @code{set-text-properties} returns, all the characters in the
2786 specified range have identical properties.
2788 If @var{props} is @code{nil}, the effect is to get rid of all properties
2789 from the specified range of text. Here's an example:
2792 (set-text-properties @var{start} @var{end} nil)
2795 Do not rely on the return value of this function.
2798 The easiest way to make a string with text properties
2799 is with @code{propertize}:
2801 @defun propertize string &rest properties
2802 This function returns a copy of @var{string} which has the text
2803 properties @var{properties}. These properties apply to all the
2804 characters in the string that is returned. Here is an example that
2805 constructs a string with a @code{face} property and a @code{mouse-face}
2809 (propertize "foo" 'face 'italic
2810 'mouse-face 'bold-italic)
2811 @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
2814 To put different properties on various parts of a string, you can
2815 construct each part with @code{propertize} and then combine them with
2820 (propertize "foo" 'face 'italic
2821 'mouse-face 'bold-italic)
2823 (propertize "bar" 'face 'italic
2824 'mouse-face 'bold-italic))
2825 @result{} #("foo and bar"
2826 0 3 (face italic mouse-face bold-italic)
2828 8 11 (face italic mouse-face bold-italic))
2832 See also the function @code{buffer-substring-no-properties}
2833 (@pxref{Buffer Contents}) which copies text from the buffer
2834 but does not copy its properties.
2836 @node Property Search
2837 @subsection Text Property Search Functions
2839 In typical use of text properties, most of the time several or many
2840 consecutive characters have the same value for a property. Rather than
2841 writing your programs to examine characters one by one, it is much
2842 faster to process chunks of text that have the same property value.
2844 Here are functions you can use to do this. They use @code{eq} for
2845 comparing property values. In all cases, @var{object} defaults to the
2848 For high performance, it's very important to use the @var{limit}
2849 argument to these functions, especially the ones that search for a
2850 single property---otherwise, they may spend a long time scanning to the
2851 end of the buffer, if the property you are interested in does not change.
2853 These functions do not move point; instead, they return a position (or
2854 @code{nil}). Remember that a position is always between two characters;
2855 the position returned by these functions is between two characters with
2856 different properties.
2858 @defun next-property-change pos &optional object limit
2859 The function scans the text forward from position @var{pos} in the
2860 string or buffer @var{object} till it finds a change in some text
2861 property, then returns the position of the change. In other words, it
2862 returns the position of the first character beyond @var{pos} whose
2863 properties are not identical to those of the character just after
2866 If @var{limit} is non-@code{nil}, then the scan ends at position
2867 @var{limit}. If there is no property change before that point,
2868 @code{next-property-change} returns @var{limit}.
2870 The value is @code{nil} if the properties remain unchanged all the way
2871 to the end of @var{object} and @var{limit} is @code{nil}. If the value
2872 is non-@code{nil}, it is a position greater than or equal to @var{pos}.
2873 The value equals @var{pos} only when @var{limit} equals @var{pos}.
2875 Here is an example of how to scan the buffer by chunks of text within
2876 which all properties are constant:
2880 (let ((plist (text-properties-at (point)))
2882 (or (next-property-change (point) (current-buffer))
2884 @r{Process text from point to @var{next-change}@dots{}}
2885 (goto-char next-change)))
2889 @defun previous-property-change pos &optional object limit
2890 This is like @code{next-property-change}, but scans back from @var{pos}
2891 instead of forward. If the value is non-@code{nil}, it is a position
2892 less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
2896 @defun next-single-property-change pos prop &optional object limit
2897 The function scans text for a change in the @var{prop} property, then
2898 returns the position of the change. The scan goes forward from
2899 position @var{pos} in the string or buffer @var{object}. In other
2900 words, this function returns the position of the first character
2901 beyond @var{pos} whose @var{prop} property differs from that of the
2902 character just after @var{pos}.
2904 If @var{limit} is non-@code{nil}, then the scan ends at position
2905 @var{limit}. If there is no property change before that point,
2906 @code{next-single-property-change} returns @var{limit}.
2908 The value is @code{nil} if the property remains unchanged all the way to
2909 the end of @var{object} and @var{limit} is @code{nil}. If the value is
2910 non-@code{nil}, it is a position greater than or equal to @var{pos}; it
2911 equals @var{pos} only if @var{limit} equals @var{pos}.
2914 @defun previous-single-property-change pos prop &optional object limit
2915 This is like @code{next-single-property-change}, but scans back from
2916 @var{pos} instead of forward. If the value is non-@code{nil}, it is a
2917 position less than or equal to @var{pos}; it equals @var{pos} only if
2918 @var{limit} equals @var{pos}.
2921 @defun next-char-property-change pos &optional limit
2922 This is like @code{next-property-change} except that it considers
2923 overlay properties as well as text properties, and if no change is
2924 found before the end of the buffer, it returns the maximum buffer
2925 position rather than @code{nil} (in this sense, it resembles the
2926 corresponding overlay function @code{next-overlay-change}, rather than
2927 @code{next-property-change}). There is no @var{object} operand
2928 because this function operates only on the current buffer. It returns
2929 the next address at which either kind of property changes.
2932 @defun previous-char-property-change pos &optional limit
2933 This is like @code{next-char-property-change}, but scans back from
2934 @var{pos} instead of forward, and returns the minimum buffer
2935 position if no change is found.
2938 @defun next-single-char-property-change pos prop &optional object limit
2939 This is like @code{next-single-property-change} except that it
2940 considers overlay properties as well as text properties, and if no
2941 change is found before the end of the @var{object}, it returns the
2942 maximum valid position in @var{object} rather than @code{nil}. Unlike
2943 @code{next-char-property-change}, this function @emph{does} have an
2944 @var{object} operand; if @var{object} is not a buffer, only
2945 text-properties are considered.
2948 @defun previous-single-char-property-change pos prop &optional object limit
2949 This is like @code{next-single-char-property-change}, but scans back
2950 from @var{pos} instead of forward, and returns the minimum valid
2951 position in @var{object} if no change is found.
2954 @defun text-property-any start end prop value &optional object
2955 This function returns non-@code{nil} if at least one character between
2956 @var{start} and @var{end} has a property @var{prop} whose value is
2957 @var{value}. More precisely, it returns the position of the first such
2958 character. Otherwise, it returns @code{nil}.
2960 The optional fifth argument, @var{object}, specifies the string or
2961 buffer to scan. Positions are relative to @var{object}. The default
2962 for @var{object} is the current buffer.
2965 @defun text-property-not-all start end prop value &optional object
2966 This function returns non-@code{nil} if at least one character between
2967 @var{start} and @var{end} does not have a property @var{prop} with value
2968 @var{value}. More precisely, it returns the position of the first such
2969 character. Otherwise, it returns @code{nil}.
2971 The optional fifth argument, @var{object}, specifies the string or
2972 buffer to scan. Positions are relative to @var{object}. The default
2973 for @var{object} is the current buffer.
2976 @node Special Properties
2977 @subsection Properties with Special Meanings
2979 Here is a table of text property names that have special built-in
2980 meanings. The following sections list a few additional special property
2981 names that control filling and property inheritance. All other names
2982 have no standard meaning, and you can use them as you like.
2984 Note: the properties @code{composition}, @code{display},
2985 @code{invisible} and @code{intangible} can also cause point to move to
2986 an acceptable place, after each Emacs command. @xref{Adjusting
2990 @cindex property category of text character
2991 @kindex category @r{(text property)}
2993 If a character has a @code{category} property, we call it the
2994 @dfn{property category} of the character. It should be a symbol. The
2995 properties of this symbol serve as defaults for the properties of the
2999 @cindex face codes of text
3000 @kindex face @r{(text property)}
3001 You can use the property @code{face} to control the font and color of
3002 text. @xref{Faces}, for more information.
3004 In the simplest case, the value is a face name. It can also be a list;
3005 then each element can be any of these possibilities;
3009 A face name (a symbol or string).
3012 A property list of face attributes. This has the
3013 form (@var{keyword} @var{value} @dots{}), where each @var{keyword} is a
3014 face attribute name and @var{value} is a meaningful value for that
3015 attribute. With this feature, you do not need to create a face each
3016 time you want to specify a particular attribute for certain text.
3017 @xref{Face Attributes}.
3020 A cons cell with the form @code{(foreground-color . @var{color-name})}
3021 or @code{(background-color . @var{color-name})}. These are older,
3022 deprecated equivalents for @code{(:foreground @var{color-name})} and
3023 @code{(:background @var{color-name})}. Please convert code that uses
3027 It works to use the latter two forms directly as the value
3028 of the @code{face} property.
3030 Font Lock mode (@pxref{Font Lock Mode}) works in most buffers by
3031 dynamically updating the @code{face} property of characters based on
3034 @item font-lock-face
3035 @kindex font-lock-face @r{(text property)}
3036 The @code{font-lock-face} property is equivalent to the @code{face}
3037 property when Font Lock mode is enabled. When Font Lock mode is disabled,
3038 @code{font-lock-face} has no effect.
3040 The @code{font-lock-mode} property is useful for special modes that
3041 implement their own highlighting. @xref{Precalculated Fontification}.
3044 @kindex mouse-face @r{(text property)}
3045 The property @code{mouse-face} is used instead of @code{face} when the
3046 mouse is on or near the character. For this purpose, ``near'' means
3047 that all text between the character and where the mouse is have the same
3048 @code{mouse-face} property value.
3051 @kindex fontified @r{(text property)}
3052 This property says whether the text is ready for display. If
3053 @code{nil}, Emacs's redisplay routine calls the functions in
3054 @code{fontification-functions} (@pxref{Auto Faces}) to prepare this
3055 part of the buffer before it is displayed. It is used internally by
3056 the ``just in time'' font locking code.
3059 This property activates various features that change the
3060 way text is displayed. For example, it can make text appear taller
3061 or shorter, higher or lower, wider or narrow, or replaced with an image.
3062 @xref{Display Property}.
3065 @kindex help-echo @r{(text property)}
3067 @anchor{Text help-echo}
3068 If text has a string as its @code{help-echo} property, then when you
3069 move the mouse onto that text, Emacs displays that string in the echo
3070 area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
3073 If the value of the @code{help-echo} property is a function, that
3074 function is called with three arguments, @var{window}, @var{object} and
3075 @var{pos} and should return a help string or @code{nil} for
3076 none. The first argument, @var{window} is the window in which
3077 the help was found. The second, @var{object}, is the buffer, overlay or
3078 string which had the @code{help-echo} property. The @var{pos}
3079 argument is as follows:
3083 If @var{object} is a buffer, @var{pos} is the position in the buffer.
3085 If @var{object} is an overlay, that overlay has a @code{help-echo}
3086 property, and @var{pos} is the position in the overlay's buffer.
3088 If @var{object} is a string (an overlay string or a string displayed
3089 with the @code{display} property), @var{pos} is the position in that
3093 If the value of the @code{help-echo} property is neither a function nor
3094 a string, it is evaluated to obtain a help string.
3096 You can alter the way help text is displayed by setting the variable
3097 @code{show-help-function} (@pxref{Help display}).
3099 This feature is used in the mode line and for other active text.
3102 @cindex keymap of character
3103 @kindex keymap @r{(text property)}
3104 The @code{keymap} property specifies an additional keymap for
3105 commands. When this keymap applies, it is used for key lookup before
3106 the minor mode keymaps and before the buffer's local map.
3107 @xref{Active Keymaps}. If the property value is a symbol, the
3108 symbol's function definition is used as the keymap.
3110 The property's value for the character before point applies if it is
3111 non-@code{nil} and rear-sticky, and the property's value for the
3112 character after point applies if it is non-@code{nil} and
3113 front-sticky. (For mouse clicks, the position of the click is used
3114 instead of the position of point.)
3117 @kindex local-map @r{(text property)}
3118 This property works like @code{keymap} except that it specifies a
3119 keymap to use @emph{instead of} the buffer's local map. For most
3120 purposes (perhaps all purposes), it is better to use the @code{keymap}
3124 The @code{syntax-table} property overrides what the syntax table says
3125 about this particular character. @xref{Syntax Properties}.
3128 @cindex read-only character
3129 @kindex read-only @r{(text property)}
3130 If a character has the property @code{read-only}, then modifying that
3131 character is not allowed. Any command that would do so gets an error,
3132 @code{text-read-only}. If the property value is a string, that string
3133 is used as the error message.
3135 Insertion next to a read-only character is an error if inserting
3136 ordinary text there would inherit the @code{read-only} property due to
3137 stickiness. Thus, you can control permission to insert next to
3138 read-only text by controlling the stickiness. @xref{Sticky Properties}.
3140 Since changing properties counts as modifying the buffer, it is not
3141 possible to remove a @code{read-only} property unless you know the
3142 special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
3143 and then remove the property. @xref{Read Only Buffers}.
3146 @kindex invisible @r{(text property)}
3147 A non-@code{nil} @code{invisible} property can make a character invisible
3148 on the screen. @xref{Invisible Text}, for details.
3151 @kindex intangible @r{(text property)}
3152 If a group of consecutive characters have equal and non-@code{nil}
3153 @code{intangible} properties, then you cannot place point between them.
3154 If you try to move point forward into the group, point actually moves to
3155 the end of the group. If you try to move point backward into the group,
3156 point actually moves to the start of the group.
3158 If consecutive characters have unequal non-@code{nil}
3159 @code{intangible} properties, they belong to separate groups; each
3160 group is separately treated as described above.
3162 When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
3163 the @code{intangible} property is ignored.
3166 @kindex field @r{(text property)}
3167 Consecutive characters with the same @code{field} property constitute a
3168 @dfn{field}. Some motion functions including @code{forward-word} and
3169 @code{beginning-of-line} stop moving at a field boundary.
3173 @kindex cursor @r{(text property)}
3174 Normally, the cursor is displayed at the end of any overlay and text
3175 property strings present at the current window position. You can
3176 place the cursor on any desired character of these strings by giving
3177 that character a non-@code{nil} @var{cursor} text property.
3180 @kindex pointer @r{(text property)}
3181 This specifies a specific pointer shape when the mouse pointer is over
3182 this text or image. @xref{Pointer Shape}, for possible pointer
3186 @kindex line-spacing @r{(text property)}
3187 A newline can have a @code{line-spacing} text or overlay property that
3188 controls the height of the display line ending with that newline. The
3189 property value overrides the default frame line spacing and the buffer
3190 local @code{line-spacing} variable. @xref{Line Height}.
3193 @kindex line-height @r{(text property)}
3194 A newline can have a @code{line-height} text or overlay property that
3195 controls the total height of the display line ending in that newline.
3199 If text has a @code{wrap-prefix} property, the prefix it defines will
3200 be added at display-time to the beginning of every continuation line
3201 due to text wrapping (so if lines are truncated, the wrap-prefix is
3202 never used). It may be a string, an image, or a stretch-glyph such as
3203 used by the @code{display} text-property. @xref{Display Property}.
3205 A wrap-prefix may also be specified for an entire buffer using the
3206 @code{wrap-prefix} buffer-local variable (however, a
3207 @code{wrap-prefix} text-property takes precedence over the value of
3208 the @code{wrap-prefix} variable). @xref{Truncation}.
3211 If text has a @code{line-prefix} property, the prefix it defines will
3212 be added at display-time to the beginning of every non-continuation
3213 line. It may be a string, an image, or a stretch-glyph such as used
3214 by the @code{display} text-property. @xref{Display Property}.
3216 A line-prefix may also be specified for an entire buffer using the
3217 @code{line-prefix} buffer-local variable (however, a
3218 @code{line-prefix} text-property takes precedence over the value of
3219 the @code{line-prefix} variable). @xref{Truncation}.
3221 @item modification-hooks
3222 @cindex change hooks for a character
3223 @cindex hooks for changing a character
3224 @kindex modification-hooks @r{(text property)}
3225 If a character has the property @code{modification-hooks}, then its
3226 value should be a list of functions; modifying that character calls all
3227 of those functions. Each function receives two arguments: the beginning
3228 and end of the part of the buffer being modified. Note that if a
3229 particular modification hook function appears on several characters
3230 being modified by a single primitive, you can't predict how many times
3231 the function will be called.
3233 If these functions modify the buffer, they should bind
3234 @code{inhibit-modification-hooks} to @code{t} around doing so, to
3235 avoid confusing the internal mechanism that calls these hooks.
3237 Overlays also support the @code{modification-hooks} property, but the
3238 details are somewhat different (@pxref{Overlay Properties}).
3240 @item insert-in-front-hooks
3241 @itemx insert-behind-hooks
3242 @kindex insert-in-front-hooks @r{(text property)}
3243 @kindex insert-behind-hooks @r{(text property)}
3244 The operation of inserting text in a buffer also calls the functions
3245 listed in the @code{insert-in-front-hooks} property of the following
3246 character and in the @code{insert-behind-hooks} property of the
3247 preceding character. These functions receive two arguments, the
3248 beginning and end of the inserted text. The functions are called
3249 @emph{after} the actual insertion takes place.
3251 See also @ref{Change Hooks}, for other hooks that are called
3252 when you change text in a buffer.
3256 @cindex hooks for motion of point
3257 @kindex point-entered @r{(text property)}
3258 @kindex point-left @r{(text property)}
3259 The special properties @code{point-entered} and @code{point-left}
3260 record hook functions that report motion of point. Each time point
3261 moves, Emacs compares these two property values:
3265 the @code{point-left} property of the character after the old location,
3268 the @code{point-entered} property of the character after the new
3273 If these two values differ, each of them is called (if not @code{nil})
3274 with two arguments: the old value of point, and the new one.
3276 The same comparison is made for the characters before the old and new
3277 locations. The result may be to execute two @code{point-left} functions
3278 (which may be the same function) and/or two @code{point-entered}
3279 functions (which may be the same function). In any case, all the
3280 @code{point-left} functions are called first, followed by all the
3281 @code{point-entered} functions.
3283 It is possible with @code{char-after} to examine characters at various
3284 buffer positions without moving point to those positions. Only an
3285 actual change in the value of point runs these hook functions.
3287 @defvar inhibit-point-motion-hooks
3288 When this variable is non-@code{nil}, @code{point-left} and
3289 @code{point-entered} hooks are not run, and the @code{intangible}
3290 property has no effect. Do not set this variable globally; bind it with
3294 @defvar show-help-function
3295 @anchor{Help display} If this variable is non-@code{nil}, it specifies a
3296 function called to display help strings. These may be @code{help-echo}
3297 properties, menu help strings (@pxref{Simple Menu Items},
3298 @pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
3299 Bar}). The specified function is called with one argument, the help
3300 string to display. Tooltip mode (@pxref{Tooltips,,, emacs, The GNU Emacs
3301 Manual}) provides an example.
3305 @kindex composition @r{(text property)}
3306 This text property is used to display a sequence of characters as a
3307 single glyph composed from components. But the value of the property
3308 itself is completely internal to Emacs and should not be manipulated
3309 directly by, for instance, @code{put-text-property}.
3313 @node Format Properties
3314 @subsection Formatted Text Properties
3316 These text properties affect the behavior of the fill commands. They
3317 are used for representing formatted text. @xref{Filling}, and
3322 If a newline character has this property, it is a ``hard'' newline.
3323 The fill commands do not alter hard newlines and do not move words
3324 across them. However, this property takes effect only if the
3325 @code{use-hard-newlines} minor mode is enabled. @xref{Hard and Soft
3326 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
3329 This property specifies an extra right margin for filling this part of the
3333 This property specifies an extra left margin for filling this part of the
3337 This property specifies the style of justification for filling this part
3341 @node Sticky Properties
3342 @subsection Stickiness of Text Properties
3343 @cindex sticky text properties
3344 @cindex inheritance of text properties
3346 Self-inserting characters normally take on the same properties as the
3347 preceding character. This is called @dfn{inheritance} of properties.
3349 In a Lisp program, you can do insertion with inheritance or without,
3350 depending on your choice of insertion primitive. The ordinary text
3351 insertion functions such as @code{insert} do not inherit any properties.
3352 They insert text with precisely the properties of the string being
3353 inserted, and no others. This is correct for programs that copy text
3354 from one context to another---for example, into or out of the kill ring.
3355 To insert with inheritance, use the special primitives described in this
3356 section. Self-inserting characters inherit properties because they work
3357 using these primitives.
3359 When you do insertion with inheritance, @emph{which} properties are
3360 inherited, and from where, depends on which properties are @dfn{sticky}.
3361 Insertion after a character inherits those of its properties that are
3362 @dfn{rear-sticky}. Insertion before a character inherits those of its
3363 properties that are @dfn{front-sticky}. When both sides offer different
3364 sticky values for the same property, the previous character's value
3367 By default, a text property is rear-sticky but not front-sticky; thus,
3368 the default is to inherit all the properties of the preceding character,
3369 and nothing from the following character.
3371 You can control the stickiness of various text properties with two
3372 specific text properties, @code{front-sticky} and @code{rear-nonsticky},
3373 and with the variable @code{text-property-default-nonsticky}. You can
3374 use the variable to specify a different default for a given property.
3375 You can use those two text properties to make any specific properties
3376 sticky or nonsticky in any particular part of the text.
3378 If a character's @code{front-sticky} property is @code{t}, then all
3379 its properties are front-sticky. If the @code{front-sticky} property is
3380 a list, then the sticky properties of the character are those whose
3381 names are in the list. For example, if a character has a
3382 @code{front-sticky} property whose value is @code{(face read-only)},
3383 then insertion before the character can inherit its @code{face} property
3384 and its @code{read-only} property, but no others.
3386 The @code{rear-nonsticky} property works the opposite way. Most
3387 properties are rear-sticky by default, so the @code{rear-nonsticky}
3388 property says which properties are @emph{not} rear-sticky. If a
3389 character's @code{rear-nonsticky} property is @code{t}, then none of its
3390 properties are rear-sticky. If the @code{rear-nonsticky} property is a
3391 list, properties are rear-sticky @emph{unless} their names are in the
3394 @defvar text-property-default-nonsticky
3395 This variable holds an alist which defines the default rear-stickiness
3396 of various text properties. Each element has the form
3397 @code{(@var{property} . @var{nonstickiness})}, and it defines the
3398 stickiness of a particular text property, @var{property}.
3400 If @var{nonstickiness} is non-@code{nil}, this means that the property
3401 @var{property} is rear-nonsticky by default. Since all properties are
3402 front-nonsticky by default, this makes @var{property} nonsticky in both
3403 directions by default.
3405 The text properties @code{front-sticky} and @code{rear-nonsticky}, when
3406 used, take precedence over the default @var{nonstickiness} specified in
3407 @code{text-property-default-nonsticky}.
3410 Here are the functions that insert text with inheritance of properties:
3412 @defun insert-and-inherit &rest strings
3413 Insert the strings @var{strings}, just like the function @code{insert},
3414 but inherit any sticky properties from the adjoining text.
3417 @defun insert-before-markers-and-inherit &rest strings
3418 Insert the strings @var{strings}, just like the function
3419 @code{insert-before-markers}, but inherit any sticky properties from the
3423 @xref{Insertion}, for the ordinary insertion functions which do not
3426 @node Lazy Properties
3427 @subsection Lazy Computation of Text Properties
3429 Instead of computing text properties for all the text in the buffer,
3430 you can arrange to compute the text properties for parts of the text
3431 when and if something depends on them.
3433 The primitive that extracts text from the buffer along with its
3434 properties is @code{buffer-substring}. Before examining the properties,
3435 this function runs the abnormal hook @code{buffer-access-fontify-functions}.
3437 @defvar buffer-access-fontify-functions
3438 This variable holds a list of functions for computing text properties.
3439 Before @code{buffer-substring} copies the text and text properties for a
3440 portion of the buffer, it calls all the functions in this list. Each of
3441 the functions receives two arguments that specify the range of the
3442 buffer being accessed. (The buffer itself is always the current
3446 The function @code{buffer-substring-no-properties} does not call these
3447 functions, since it ignores text properties anyway.
3449 In order to prevent the hook functions from being called more than
3450 once for the same part of the buffer, you can use the variable
3451 @code{buffer-access-fontified-property}.
3453 @defvar buffer-access-fontified-property
3454 If this variable's value is non-@code{nil}, it is a symbol which is used
3455 as a text property name. A non-@code{nil} value for that text property
3456 means, ``the other text properties for this character have already been
3459 If all the characters in the range specified for @code{buffer-substring}
3460 have a non-@code{nil} value for this property, @code{buffer-substring}
3461 does not call the @code{buffer-access-fontify-functions} functions. It
3462 assumes these characters already have the right text properties, and
3463 just copies the properties they already have.
3465 The normal way to use this feature is that the
3466 @code{buffer-access-fontify-functions} functions add this property, as
3467 well as others, to the characters they operate on. That way, they avoid
3468 being called over and over for the same text.
3471 @node Clickable Text
3472 @subsection Defining Clickable Text
3473 @cindex clickable text
3474 @cindex follow links
3477 @dfn{Clickable text} is text that can be clicked, with either the
3478 mouse or via a keyboard command, to produce some result. Many major
3479 modes use clickable text to implement textual hyper-links, or
3480 @dfn{links} for short.
3482 The easiest way to insert and manipulate links is to use the
3483 @code{button} package. @xref{Buttons}. In this section, we will
3484 explain how to manually set up clickable text in a buffer, using text
3485 properties. For simplicity, we will refer to the clickable text as a
3488 Implementing a link involves three separate steps: (1) indicating
3489 clickability when the mouse moves over the link; (2) making @kbd{RET}
3490 or @kbd{Mouse-2} on that link do something; and (3) setting up a
3491 @code{follow-link} condition so that the link obeys
3492 @code{mouse-1-click-follows-link}.
3494 To indicate clickability, add the @code{mouse-face} text property to
3495 the text of the link; then Emacs will highlight the link when the
3496 mouse moves over it. In addition, you should define a tooltip or echo
3497 area message, using the @code{help-echo} text property. @xref{Special
3498 Properties}. For instance, here is how Dired indicates that file
3499 names are clickable:
3502 (if (dired-move-to-filename)
3503 (add-text-properties
3506 (dired-move-to-end-of-filename)
3508 '(mouse-face highlight
3509 help-echo "mouse-2: visit this file in other window")))
3512 To make the link clickable, bind @key{RET} and @kbd{Mouse-2} to
3513 commands that perform the desired action. Each command should check
3514 to see whether it was called on a link, and act accordingly. For
3515 instance, Dired's major mode keymap binds @kbd{Mouse-2} to the
3519 (defun dired-mouse-find-file-other-window (event)
3520 "In Dired, visit the file or directory name you click on."
3522 (let (window pos file)
3524 (setq window (posn-window (event-end event))
3525 pos (posn-point (event-end event)))
3526 (if (not (windowp window))
3527 (error "No file chosen"))
3528 (set-buffer (window-buffer window))
3530 (setq file (dired-get-file-for-visit)))
3531 (if (file-directory-p file)
3532 (or (and (cdr dired-subdir-alist)
3533 (dired-goto-subdir file))
3535 (select-window window)
3536 (dired-other-window file)))
3537 (select-window window)
3538 (find-file-other-window (file-name-sans-versions file t)))))
3542 This command uses the functions @code{posn-window} and
3543 @code{posn-point} to determine where the click occurred, and
3544 @code{dired-get-file-for-visit} to determine which file to visit.
3546 Instead of binding the mouse command in a major mode keymap, you can
3547 bind it within the link text, using the @code{keymap} text property
3548 (@pxref{Special Properties}). For instance:
3551 (let ((map (make-sparse-keymap)))
3552 (define-key map [mouse-2] 'operate-this-button)
3553 (put-text-property link-start link-end 'keymap map))
3557 With this method, you can easily define different commands for
3558 different links. Furthermore, the global definition of @key{RET} and
3559 @kbd{Mouse-2} remain available for the rest of the text in the buffer.
3561 @vindex mouse-1-click-follows-link
3562 The basic Emacs command for clicking on links is @kbd{Mouse-2}.
3563 However, for compatibility with other graphical applications, Emacs
3564 also recognizes @kbd{Mouse-1} clicks on links, provided the user
3565 clicks on the link quickly without moving the mouse. This behavior is
3566 controlled by the user option @code{mouse-1-click-follows-link}.
3567 @xref{Mouse References,,, emacs, The GNU Emacs Manual}.
3569 To set up the link so that it obeys
3570 @code{mouse-1-click-follows-link}, you must either (1) apply a
3571 @code{follow-link} text or overlay property to the link text, or (2)
3572 bind the @code{follow-link} event to a keymap (which can be a major
3573 mode keymap or a local keymap specified via the @code{keymap} text
3574 property). The value of the @code{follow-link} property, or the
3575 binding for the @code{follow-link} event, acts as a ``condition'' for
3576 the link action. This condition tells Emacs two things: the
3577 circumstances under which a @kbd{Mouse-1} click should be regarded as
3578 occurring ``inside'' the link, and how to compute an ``action code''
3579 that says what to translate the @kbd{Mouse-1} click into. The link
3580 action condition can be one of the following:
3583 @item @code{mouse-face}
3584 If the condition is the symbol @code{mouse-face}, a position is inside
3585 a link if there is a non-@code{nil} @code{mouse-face} property at that
3586 position. The action code is always @code{t}.
3588 For example, here is how Info mode handles @key{Mouse-1}:
3591 (define-key Info-mode-map [follow-link] 'mouse-face)
3595 If the condition is a function, @var{func}, then a position @var{pos}
3596 is inside a link if @code{(@var{func} @var{pos})} evaluates to
3597 non-@code{nil}. The value returned by @var{func} serves as the action
3600 For example, here is how pcvs enables @kbd{Mouse-1} to follow links on
3604 (define-key map [follow-link]
3606 (eq (get-char-property pos 'face) 'cvs-filename-face)))
3610 If the condition value is anything else, then the position is inside a
3611 link and the condition itself is the action code. Clearly, you should
3612 specify this kind of condition only when applying the condition via a
3613 text or property overlay on the link text (so that it does not apply
3614 to the entire buffer).
3618 The action code tells @kbd{Mouse-1} how to follow the link:
3621 @item a string or vector
3622 If the action code is a string or vector, the @kbd{Mouse-1} event is
3623 translated into the first element of the string or vector; i.e., the
3624 action of the @kbd{Mouse-1} click is the local or global binding of
3625 that character or symbol. Thus, if the action code is @code{"foo"},
3626 @kbd{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
3627 @kbd{Mouse-1} translates into @key{foo}.
3630 For any other non-@code{nil} action code, the @kbd{Mouse-1} event is
3631 translated into a @kbd{Mouse-2} event at the same position.
3634 To define @kbd{Mouse-1} to activate a button defined with
3635 @code{define-button-type}, give the button a @code{follow-link}
3636 property. The property value should be a link action condition, as
3637 described above. @xref{Buttons}. For example, here is how Help mode
3638 handles @kbd{Mouse-1}:
3641 (define-button-type 'help-xref
3643 'action #'help-button-action)
3646 To define @kbd{Mouse-1} on a widget defined with
3647 @code{define-widget}, give the widget a @code{:follow-link} property.
3648 The property value should be a link action condition, as described
3649 above. For example, here is how the @code{link} widget specifies that
3650 a @key{Mouse-1} click shall be translated to @key{RET}:
3653 (define-widget 'link 'item
3655 :button-prefix 'widget-link-prefix
3656 :button-suffix 'widget-link-suffix
3658 :help-echo "Follow the link."
3662 @defun mouse-on-link-p pos
3663 This function returns non-@code{nil} if position @var{pos} in the
3664 current buffer is on a link. @var{pos} can also be a mouse event
3665 location, as returned by @code{event-start} (@pxref{Accessing Mouse}).
3669 @subsection Defining and Using Fields
3672 A field is a range of consecutive characters in the buffer that are
3673 identified by having the same value (comparing with @code{eq}) of the
3674 @code{field} property (either a text-property or an overlay property).
3675 This section describes special functions that are available for
3676 operating on fields.
3678 You specify a field with a buffer position, @var{pos}. We think of
3679 each field as containing a range of buffer positions, so the position
3680 you specify stands for the field containing that position.
3682 When the characters before and after @var{pos} are part of the same
3683 field, there is no doubt which field contains @var{pos}: the one those
3684 characters both belong to. When @var{pos} is at a boundary between
3685 fields, which field it belongs to depends on the stickiness of the
3686 @code{field} properties of the two surrounding characters (@pxref{Sticky
3687 Properties}). The field whose property would be inherited by text
3688 inserted at @var{pos} is the field that contains @var{pos}.
3690 There is an anomalous case where newly inserted text at @var{pos}
3691 would not inherit the @code{field} property from either side. This
3692 happens if the previous character's @code{field} property is not
3693 rear-sticky, and the following character's @code{field} property is not
3694 front-sticky. In this case, @var{pos} belongs to neither the preceding
3695 field nor the following field; the field functions treat it as belonging
3696 to an empty field whose beginning and end are both at @var{pos}.
3698 In all of these functions, if @var{pos} is omitted or @code{nil}, the
3699 value of point is used by default. If narrowing is in effect, then
3700 @var{pos} should fall within the accessible portion. @xref{Narrowing}.
3702 @defun field-beginning &optional pos escape-from-edge limit
3703 This function returns the beginning of the field specified by @var{pos}.
3705 If @var{pos} is at the beginning of its field, and
3706 @var{escape-from-edge} is non-@code{nil}, then the return value is
3707 always the beginning of the preceding field that @emph{ends} at @var{pos},
3708 regardless of the stickiness of the @code{field} properties around
3711 If @var{limit} is non-@code{nil}, it is a buffer position; if the
3712 beginning of the field is before @var{limit}, then @var{limit} will be
3716 @defun field-end &optional pos escape-from-edge limit
3717 This function returns the end of the field specified by @var{pos}.
3719 If @var{pos} is at the end of its field, and @var{escape-from-edge} is
3720 non-@code{nil}, then the return value is always the end of the following
3721 field that @emph{begins} at @var{pos}, regardless of the stickiness of
3722 the @code{field} properties around @var{pos}.
3724 If @var{limit} is non-@code{nil}, it is a buffer position; if the end
3725 of the field is after @var{limit}, then @var{limit} will be returned
3729 @defun field-string &optional pos
3730 This function returns the contents of the field specified by @var{pos},
3734 @defun field-string-no-properties &optional pos
3735 This function returns the contents of the field specified by @var{pos},
3736 as a string, discarding text properties.
3739 @defun delete-field &optional pos
3740 This function deletes the text of the field specified by @var{pos}.
3743 @defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
3744 This function ``constrains'' @var{new-pos} to the field that
3745 @var{old-pos} belongs to---in other words, it returns the position
3746 closest to @var{new-pos} that is in the same field as @var{old-pos}.
3748 If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
3749 the value of point instead, and moves point to the resulting position
3750 as well as returning it.
3752 If @var{old-pos} is at the boundary of two fields, then the acceptable
3753 final positions depend on the argument @var{escape-from-edge}. If
3754 @var{escape-from-edge} is @code{nil}, then @var{new-pos} must be in
3755 the field whose @code{field} property equals what new characters
3756 inserted at @var{old-pos} would inherit. (This depends on the
3757 stickiness of the @code{field} property for the characters before and
3758 after @var{old-pos}.) If @var{escape-from-edge} is non-@code{nil},
3759 @var{new-pos} can be anywhere in the two adjacent fields.
3760 Additionally, if two fields are separated by another field with the
3761 special value @code{boundary}, then any point within this special
3762 field is also considered to be ``on the boundary.''
3764 Commands like @kbd{C-a} with no argumemt, that normally move backward
3765 to a specific kind of location and stay there once there, probably
3766 should specify @code{nil} for @var{escape-from-edge}. Other motion
3767 commands that check fields should probably pass @code{t}.
3769 If the optional argument @var{only-in-line} is non-@code{nil}, and
3770 constraining @var{new-pos} in the usual way would move it to a different
3771 line, @var{new-pos} is returned unconstrained. This used in commands
3772 that move by line, such as @code{next-line} and
3773 @code{beginning-of-line}, so that they respect field boundaries only in
3774 the case where they can still move to the right line.
3776 If the optional argument @var{inhibit-capture-property} is
3777 non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
3778 name, then any field boundaries are ignored.
3780 You can cause @code{constrain-to-field} to ignore all field boundaries
3781 (and so never constrain anything) by binding the variable
3782 @code{inhibit-field-text-motion} to a non-@code{nil} value.
3786 @subsection Why Text Properties are not Intervals
3789 Some editors that support adding attributes to text in the buffer do
3790 so by letting the user specify ``intervals'' within the text, and adding
3791 the properties to the intervals. Those editors permit the user or the
3792 programmer to determine where individual intervals start and end. We
3793 deliberately provided a different sort of interface in Emacs Lisp to
3794 avoid certain paradoxical behavior associated with text modification.
3796 If the actual subdivision into intervals is meaningful, that means you
3797 can distinguish between a buffer that is just one interval with a
3798 certain property, and a buffer containing the same text subdivided into
3799 two intervals, both of which have that property.
3801 Suppose you take the buffer with just one interval and kill part of
3802 the text. The text remaining in the buffer is one interval, and the
3803 copy in the kill ring (and the undo list) becomes a separate interval.
3804 Then if you yank back the killed text, you get two intervals with the
3805 same properties. Thus, editing does not preserve the distinction
3806 between one interval and two.
3808 Suppose we ``fix'' this problem by coalescing the two intervals when
3809 the text is inserted. That works fine if the buffer originally was a
3810 single interval. But suppose instead that we have two adjacent
3811 intervals with the same properties, and we kill the text of one interval
3812 and yank it back. The same interval-coalescence feature that rescues
3813 the other case causes trouble in this one: after yanking, we have just
3814 one interval. One again, editing does not preserve the distinction
3815 between one interval and two.
3817 Insertion of text at the border between intervals also raises
3818 questions that have no satisfactory answer.
3820 However, it is easy to arrange for editing to behave consistently for
3821 questions of the form, ``What are the properties of this character?''
3822 So we have decided these are the only questions that make sense; we have
3823 not implemented asking questions about where intervals start or end.
3825 In practice, you can usually use the text property search functions in
3826 place of explicit interval boundaries. You can think of them as finding
3827 the boundaries of intervals, assuming that intervals are always
3828 coalesced whenever possible. @xref{Property Search}.
3830 Emacs also provides explicit intervals as a presentation feature; see
3834 @section Substituting for a Character Code
3836 The following functions replace characters within a specified region
3837 based on their character codes.
3839 @defun subst-char-in-region start end old-char new-char &optional noundo
3840 @cindex replace characters
3841 This function replaces all occurrences of the character @var{old-char}
3842 with the character @var{new-char} in the region of the current buffer
3843 defined by @var{start} and @var{end}.
3845 @cindex undo avoidance
3846 If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
3847 not record the change for undo and does not mark the buffer as modified.
3848 This was useful for controlling the old selective display feature
3849 (@pxref{Selective Display}).
3851 @code{subst-char-in-region} does not move point and returns
3856 ---------- Buffer: foo ----------
3857 This is the contents of the buffer before.
3858 ---------- Buffer: foo ----------
3862 (subst-char-in-region 1 20 ?i ?X)
3865 ---------- Buffer: foo ----------
3866 ThXs Xs the contents of the buffer before.
3867 ---------- Buffer: foo ----------
3872 @deffn Command translate-region start end table
3873 This function applies a translation table to the characters in the
3874 buffer between positions @var{start} and @var{end}.
3876 The translation table @var{table} is a string or a char-table;
3877 @code{(aref @var{table} @var{ochar})} gives the translated character
3878 corresponding to @var{ochar}. If @var{table} is a string, any
3879 characters with codes larger than the length of @var{table} are not
3880 altered by the translation.
3882 The return value of @code{translate-region} is the number of
3883 characters that were actually changed by the translation. This does
3884 not count characters that were mapped into themselves in the
3892 A register is a sort of variable used in Emacs editing that can hold a
3893 variety of different kinds of values. Each register is named by a
3894 single character. All @acronym{ASCII} characters and their meta variants
3895 (but with the exception of @kbd{C-g}) can be used to name registers.
3896 Thus, there are 255 possible registers. A register is designated in
3897 Emacs Lisp by the character that is its name.
3899 @defvar register-alist
3900 This variable is an alist of elements of the form @code{(@var{name} .
3901 @var{contents})}. Normally, there is one element for each Emacs
3902 register that has been used.
3904 The object @var{name} is a character (an integer) identifying the
3908 The @var{contents} of a register can have several possible types:
3912 A number stands for itself. If @code{insert-register} finds a number
3913 in the register, it converts the number to decimal.
3916 A marker represents a buffer position to jump to.
3919 A string is text saved in the register.
3922 A rectangle is represented by a list of strings.
3924 @item @code{(@var{window-configuration} @var{position})}
3925 This represents a window configuration to restore in one frame, and a
3926 position to jump to in the current buffer.
3928 @item @code{(@var{frame-configuration} @var{position})}
3929 This represents a frame configuration to restore, and a position
3930 to jump to in the current buffer.
3932 @item (file @var{filename})
3933 This represents a file to visit; jumping to this value visits file
3936 @item (file-query @var{filename} @var{position})
3937 This represents a file to visit and a position in it; jumping to this
3938 value visits file @var{filename} and goes to buffer position
3939 @var{position}. Restoring this type of position asks the user for
3943 The functions in this section return unpredictable values unless
3946 @defun get-register reg
3947 This function returns the contents of the register
3948 @var{reg}, or @code{nil} if it has no contents.
3951 @defun set-register reg value
3952 This function sets the contents of register @var{reg} to @var{value}.
3953 A register can be set to any value, but the other register functions
3954 expect only certain data types. The return value is @var{value}.
3957 @deffn Command view-register reg
3958 This command displays what is contained in register @var{reg}.
3961 @deffn Command insert-register reg &optional beforep
3962 This command inserts contents of register @var{reg} into the current
3965 Normally, this command puts point before the inserted text, and the
3966 mark after it. However, if the optional second argument @var{beforep}
3967 is non-@code{nil}, it puts the mark before and point after.
3968 You can pass a non-@code{nil} second argument @var{beforep} to this
3969 function interactively by supplying any prefix argument.
3971 If the register contains a rectangle, then the rectangle is inserted
3972 with its upper left corner at point. This means that text is inserted
3973 in the current line and underneath it on successive lines.
3975 If the register contains something other than saved text (a string) or
3976 a rectangle (a list), currently useless things happen. This may be
3977 changed in the future.
3981 @section Transposition of Text
3983 This subroutine is used by the transposition commands.
3985 @defun transpose-regions start1 end1 start2 end2 &optional leave-markers
3986 This function exchanges two nonoverlapping portions of the buffer.
3987 Arguments @var{start1} and @var{end1} specify the bounds of one portion
3988 and arguments @var{start2} and @var{end2} specify the bounds of the
3991 Normally, @code{transpose-regions} relocates markers with the transposed
3992 text; a marker previously positioned within one of the two transposed
3993 portions moves along with that portion, thus remaining between the same
3994 two characters in their new position. However, if @var{leave-markers}
3995 is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
3996 all markers unrelocated.
4000 @section Base 64 Encoding
4001 @cindex base 64 encoding
4003 Base 64 code is used in email to encode a sequence of 8-bit bytes as
4004 a longer sequence of @acronym{ASCII} graphic characters. It is defined in
4005 Internet RFC@footnote{
4006 An RFC, an acronym for @dfn{Request for Comments}, is a numbered
4007 Internet informational document describing a standard. RFCs are
4008 usually written by technical experts acting on their own initiative,
4009 and are traditionally written in a pragmatic, experience-driven
4011 }2045. This section describes the functions for
4012 converting to and from this code.
4014 @deffn Command base64-encode-region beg end &optional no-line-break
4015 This function converts the region from @var{beg} to @var{end} into base
4016 64 code. It returns the length of the encoded text. An error is
4017 signaled if a character in the region is multibyte, i.e.@: in a
4018 multibyte buffer the region must contain only characters from the
4019 charsets @code{ascii}, @code{eight-bit-control} and
4020 @code{eight-bit-graphic}.
4022 Normally, this function inserts newline characters into the encoded
4023 text, to avoid overlong lines. However, if the optional argument
4024 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4025 the output is just one long line.
4028 @deffn Command base64-encode-string string &optional no-line-break
4029 This function converts the string @var{string} into base 64 code. It
4030 returns a string containing the encoded text. As for
4031 @code{base64-encode-region}, an error is signaled if a character in the
4032 string is multibyte.
4034 Normally, this function inserts newline characters into the encoded
4035 text, to avoid overlong lines. However, if the optional argument
4036 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4037 the result string is just one long line.
4040 @defun base64-decode-region beg end
4041 This function converts the region from @var{beg} to @var{end} from base
4042 64 code into the corresponding decoded text. It returns the length of
4045 The decoding functions ignore newline characters in the encoded text.
4048 @defun base64-decode-string string
4049 This function converts the string @var{string} from base 64 code into
4050 the corresponding decoded text. It returns a unibyte string containing the
4053 The decoding functions ignore newline characters in the encoded text.
4057 @section MD5 Checksum
4058 @cindex MD5 checksum
4059 @cindex message digest computation
4061 MD5 cryptographic checksums, or @dfn{message digests}, are 128-bit
4062 ``fingerprints'' of a document or program. They are used to verify
4063 that you have an exact and unaltered copy of the data. The algorithm
4064 to calculate the MD5 message digest is defined in Internet
4066 For an explanation of what is an RFC, see the footnote in @ref{Base
4068 }1321. This section describes the Emacs facilities for computing
4071 @defun md5 object &optional start end coding-system noerror
4072 This function returns the MD5 message digest of @var{object}, which
4073 should be a buffer or a string.
4075 The two optional arguments @var{start} and @var{end} are character
4076 positions specifying the portion of @var{object} to compute the
4077 message digest for. If they are @code{nil} or omitted, the digest is
4078 computed for the whole of @var{object}.
4080 The function @code{md5} does not compute the message digest directly
4081 from the internal Emacs representation of the text (@pxref{Text
4082 Representations}). Instead, it encodes the text using a coding
4083 system, and computes the message digest from the encoded text. The
4084 optional fourth argument @var{coding-system} specifies which coding
4085 system to use for encoding the text. It should be the same coding
4086 system that you used to read the text, or that you used or will use
4087 when saving or sending the text. @xref{Coding Systems}, for more
4088 information about coding systems.
4090 If @var{coding-system} is @code{nil} or omitted, the default depends
4091 on @var{object}. If @var{object} is a buffer, the default for
4092 @var{coding-system} is whatever coding system would be chosen by
4093 default for writing this text into a file. If @var{object} is a
4094 string, the user's most preferred coding system (@pxref{Recognize
4095 Coding, prefer-coding-system, the description of
4096 @code{prefer-coding-system}, emacs, GNU Emacs Manual}) is used.
4098 Normally, @code{md5} signals an error if the text can't be encoded
4099 using the specified or chosen coding system. However, if
4100 @var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
4104 @node Atomic Changes
4105 @section Atomic Change Groups
4106 @cindex atomic changes
4108 In data base terminology, an @dfn{atomic} change is an indivisible
4109 change---it can succeed entirely or it can fail entirely, but it
4110 cannot partly succeed. A Lisp program can make a series of changes to
4111 one or several buffers as an @dfn{atomic change group}, meaning that
4112 either the entire series of changes will be installed in their buffers
4113 or, in case of an error, none of them will be.
4115 To do this for one buffer, the one already current, simply write a
4116 call to @code{atomic-change-group} around the code that makes the
4120 (atomic-change-group
4122 (delete-region x y))
4126 If an error (or other nonlocal exit) occurs inside the body of
4127 @code{atomic-change-group}, it unmakes all the changes in that buffer
4128 that were during the execution of the body. This kind of change group
4129 has no effect on any other buffers---any such changes remain.
4131 If you need something more sophisticated, such as to make changes in
4132 various buffers constitute one atomic group, you must directly call
4133 lower-level functions that @code{atomic-change-group} uses.
4135 @defun prepare-change-group &optional buffer
4136 This function sets up a change group for buffer @var{buffer}, which
4137 defaults to the current buffer. It returns a ``handle'' that
4138 represents the change group. You must use this handle to activate the
4139 change group and subsequently to finish it.
4142 To use the change group, you must @dfn{activate} it. You must do
4143 this before making any changes in the text of @var{buffer}.
4145 @defun activate-change-group handle
4146 This function activates the change group that @var{handle} designates.
4149 After you activate the change group, any changes you make in that
4150 buffer become part of it. Once you have made all the desired changes
4151 in the buffer, you must @dfn{finish} the change group. There are two
4152 ways to do this: you can either accept (and finalize) all the changes,
4155 @defun accept-change-group handle
4156 This function accepts all the changes in the change group specified by
4157 @var{handle}, making them final.
4160 @defun cancel-change-group handle
4161 This function cancels and undoes all the changes in the change group
4162 specified by @var{handle}.
4165 Your code should use @code{unwind-protect} to make sure the group is
4166 always finished. The call to @code{activate-change-group} should be
4167 inside the @code{unwind-protect}, in case the user types @kbd{C-g}
4168 just after it runs. (This is one reason why
4169 @code{prepare-change-group} and @code{activate-change-group} are
4170 separate functions, because normally you would call
4171 @code{prepare-change-group} before the start of that
4172 @code{unwind-protect}.) Once you finish the group, don't use the
4173 handle again---in particular, don't try to finish the same group
4176 To make a multibuffer change group, call @code{prepare-change-group}
4177 once for each buffer you want to cover, then use @code{nconc} to
4178 combine the returned values, like this:
4181 (nconc (prepare-change-group buffer-1)
4182 (prepare-change-group buffer-2))
4185 You can then activate the multibuffer change group with a single call
4186 to @code{activate-change-group}, and finish it with a single call to
4187 @code{accept-change-group} or @code{cancel-change-group}.
4189 Nested use of several change groups for the same buffer works as you
4190 would expect. Non-nested use of change groups for the same buffer
4191 will get Emacs confused, so don't let it happen; the first change
4192 group you start for any given buffer should be the last one finished.
4195 @section Change Hooks
4196 @cindex change hooks
4197 @cindex hooks for text changes
4199 These hook variables let you arrange to take notice of all changes in
4200 all buffers (or in a particular buffer, if you make them buffer-local).
4201 See also @ref{Special Properties}, for how to detect changes to specific
4204 The functions you use in these hooks should save and restore the match
4205 data if they do anything that uses regular expressions; otherwise, they
4206 will interfere in bizarre ways with the editing operations that call
4209 @defvar before-change-functions
4210 This variable holds a list of functions to call before any buffer
4211 modification. Each function gets two arguments, the beginning and end
4212 of the region that is about to change, represented as integers. The
4213 buffer that is about to change is always the current buffer.
4216 @defvar after-change-functions
4217 This variable holds a list of functions to call after any buffer
4218 modification. Each function receives three arguments: the beginning and
4219 end of the region just changed, and the length of the text that existed
4220 before the change. All three arguments are integers. The buffer that's
4221 about to change is always the current buffer.
4223 The length of the old text is the difference between the buffer positions
4224 before and after that text as it was before the change. As for the
4225 changed text, its length is simply the difference between the first two
4229 Output of messages into the @samp{*Messages*} buffer does not
4230 call these functions.
4232 @defmac combine-after-change-calls body@dots{}
4233 The macro executes @var{body} normally, but arranges to call the
4234 after-change functions just once for a series of several changes---if
4237 If a program makes several text changes in the same area of the buffer,
4238 using the macro @code{combine-after-change-calls} around that part of
4239 the program can make it run considerably faster when after-change hooks
4240 are in use. When the after-change hooks are ultimately called, the
4241 arguments specify a portion of the buffer including all of the changes
4242 made within the @code{combine-after-change-calls} body.
4244 @strong{Warning:} You must not alter the values of
4245 @code{after-change-functions} within
4246 the body of a @code{combine-after-change-calls} form.
4248 @strong{Warning:} if the changes you combine occur in widely scattered
4249 parts of the buffer, this will still work, but it is not advisable,
4250 because it may lead to inefficient behavior for some change hook
4254 @defvar first-change-hook
4255 This variable is a normal hook that is run whenever a buffer is changed
4256 that was previously in the unmodified state.
4259 @defvar inhibit-modification-hooks
4260 If this variable is non-@code{nil}, all of the change hooks are
4261 disabled; none of them run. This affects all the hook variables
4262 described above in this section, as well as the hooks attached to
4263 certain special text properties (@pxref{Special Properties}) and overlay
4264 properties (@pxref{Overlay Properties}).
4266 Also, this variable is bound to non-@code{nil} while running those
4267 same hook variables, so that by default modifying the buffer from
4268 a modification hook does not cause other modification hooks to be run.
4269 If you do want modification hooks to be run in a particular piece of
4270 code that is itself run from a modification hook, then rebind locally
4271 @code{inhibit-modification-hooks} to @code{nil}.
4275 arch-tag: 3721e738-a1cb-4085-bc1a-6cb8d8e1d32b