2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../info/text
6 @node Text, Non-ASCII Characters, Markers, Top
10 This chapter describes the functions that deal with the text in a
11 buffer. Most examine, insert, or delete text in the current buffer,
12 often in the vicinity of point. Many are interactive. All the
13 functions that change the text provide for undoing the changes
16 Many text-related functions operate on a region of text defined by two
17 buffer positions passed in arguments named @var{start} and @var{end}.
18 These arguments should be either markers (@pxref{Markers}) or numeric
19 character positions (@pxref{Positions}). The order of these arguments
20 does not matter; it is all right for @var{start} to be the end of the
21 region and @var{end} the beginning. For example, @code{(delete-region 1
22 10)} and @code{(delete-region 10 1)} are equivalent. An
23 @code{args-out-of-range} error is signaled if either @var{start} or
24 @var{end} is outside the accessible portion of the buffer. In an
25 interactive call, point and the mark are used for these arguments.
27 @cindex buffer contents
28 Throughout this chapter, ``text'' refers to the characters in the
29 buffer, together with their properties (when relevant).
32 * Near Point:: Examining text in the vicinity of point.
33 * Buffer Contents:: Examining text in a general fashion.
34 * Comparing Text:: Comparing substrings of buffers.
35 * Insertion:: Adding new text to a buffer.
36 * Commands for Insertion:: User-level commands to insert text.
37 * Deletion:: Removing text from a buffer.
38 * User-Level Deletion:: User-level commands to delete text.
39 * The Kill Ring:: Where removed text sometimes is saved for later use.
40 * Undo:: Undoing changes to the text of a buffer.
41 * Maintaining Undo:: How to enable and disable undo information.
42 How to control how much information is kept.
43 * Filling:: Functions for explicit filling.
44 * Margins:: How to specify margins for filling commands.
45 * Adaptive Fill:: Adaptive Fill mode chooses a fill prefix from context.
46 * Auto Filling:: How auto-fill mode is implemented to break lines.
47 * Sorting:: Functions for sorting parts of the buffer.
48 * Columns:: Computing horizontal positions, and using them.
49 * Indentation:: Functions to insert or adjust indentation.
50 * Case Changes:: Case conversion of parts of the buffer.
51 * Text Properties:: Assigning Lisp property lists to text characters.
52 * Substitution:: Replacing a given character wherever it appears.
53 * Transposition:: Swapping two portions of a buffer.
54 * Registers:: How registers are implemented. Accessing the text or
55 position stored in a register.
56 * Change Hooks:: Supplying functions to be run when text is changed.
60 @section Examining Text Near Point
62 Many functions are provided to look at the characters around point.
63 Several simple functions are described here. See also @code{looking-at}
64 in @ref{Regexp Search}.
66 @defun char-after &optional position
67 This function returns the character in the current buffer at (i.e.,
68 immediately after) position @var{position}. If @var{position} is out of
69 range for this purpose, either before the beginning of the buffer, or at
70 or beyond the end, then the value is @code{nil}. The default for
71 @var{position} is point.
73 In the following example, assume that the first character in the
78 (char-to-string (char-after 1))
84 @defun char-before &optional position
85 This function returns the character in the current buffer immediately
86 before position @var{position}. If @var{position} is out of range for
87 this purpose, either before the beginning of the buffer, or at or beyond
88 the end, then the value is @code{nil}. The default for
89 @var{position} is point.
93 This function returns the character following point in the current
94 buffer. This is similar to @code{(char-after (point))}. However, if
95 point is at the end of the buffer, then @code{following-char} returns 0.
97 Remember that point is always between characters, and the terminal
98 cursor normally appears over the character following point. Therefore,
99 the character returned by @code{following-char} is the character the
102 In this example, point is between the @samp{a} and the @samp{c}.
106 ---------- Buffer: foo ----------
107 Gentlemen may cry ``Pea@point{}ce! Peace!,''
108 but there is no peace.
109 ---------- Buffer: foo ----------
113 (char-to-string (preceding-char))
115 (char-to-string (following-char))
121 @defun preceding-char
122 This function returns the character preceding point in the current
123 buffer. See above, under @code{following-char}, for an example. If
124 point is at the beginning of the buffer, @code{preceding-char} returns
129 This function returns @code{t} if point is at the beginning of the
130 buffer. If narrowing is in effect, this means the beginning of the
131 accessible portion of the text. See also @code{point-min} in
136 This function returns @code{t} if point is at the end of the buffer.
137 If narrowing is in effect, this means the end of accessible portion of
138 the text. See also @code{point-max} in @xref{Point}.
142 This function returns @code{t} if point is at the beginning of a line.
143 @xref{Text Lines}. The beginning of the buffer (or of its accessible
144 portion) always counts as the beginning of a line.
148 This function returns @code{t} if point is at the end of a line. The
149 end of the buffer (or of its accessible portion) is always considered
153 @node Buffer Contents
154 @section Examining Buffer Contents
156 This section describes two functions that allow a Lisp program to
157 convert any portion of the text in the buffer into a string.
159 @defun buffer-substring start end
160 This function returns a string containing a copy of the text of the
161 region defined by positions @var{start} and @var{end} in the current
162 buffer. If the arguments are not positions in the accessible portion of
163 the buffer, @code{buffer-substring} signals an @code{args-out-of-range}
166 It is not necessary for @var{start} to be less than @var{end}; the
167 arguments can be given in either order. But most often the smaller
168 argument is written first.
170 If the text being copied has any text properties, these are copied into
171 the string along with the characters they belong to. @xref{Text
172 Properties}. However, overlays (@pxref{Overlays}) in the buffer and
173 their properties are ignored, not copied.
177 ---------- Buffer: foo ----------
178 This is the contents of buffer foo
180 ---------- Buffer: foo ----------
184 (buffer-substring 1 10)
185 @result{} "This is t"
188 (buffer-substring (point-max) 10)
189 @result{} "he contents of buffer foo
195 @defun buffer-substring-no-properties start end
196 This is like @code{buffer-substring}, except that it does not copy text
197 properties, just the characters themselves. @xref{Text Properties}.
201 This function returns the contents of the entire accessible portion of
202 the current buffer as a string. It is equivalent to
205 (buffer-substring (point-min) (point-max))
210 ---------- Buffer: foo ----------
211 This is the contents of buffer foo
213 ---------- Buffer: foo ----------
216 @result{} "This is the contents of buffer foo
222 @defun thing-at-point thing
223 Return the @var{thing} around or next to point, as a string.
225 The argument @var{thing} is a symbol which specifies a kind of syntactic
226 entity. Possibilities include @code{symbol}, @code{list}, @code{sexp},
227 @code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
228 @code{whitespace}, @code{line}, @code{page}, and others.
231 ---------- Buffer: foo ----------
232 Gentlemen may cry ``Pea@point{}ce! Peace!,''
233 but there is no peace.
234 ---------- Buffer: foo ----------
236 (thing-at-point 'word)
238 (thing-at-point 'line)
239 @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
240 (thing-at-point 'whitespace)
246 @section Comparing Text
247 @cindex comparing buffer text
249 This function lets you compare portions of the text in a buffer, without
250 copying them into strings first.
252 @defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
253 This function lets you compare two substrings of the same buffer or two
254 different buffers. The first three arguments specify one substring,
255 giving a buffer and two positions within the buffer. The last three
256 arguments specify the other substring in the same way. You can use
257 @code{nil} for @var{buffer1}, @var{buffer2}, or both to stand for the
260 The value is negative if the first substring is less, positive if the
261 first is greater, and zero if they are equal. The absolute value of
262 the result is one plus the index of the first differing characters
263 within the substrings.
265 This function ignores case when comparing characters
266 if @code{case-fold-search} is non-@code{nil}. It always ignores
269 Suppose the current buffer contains the text @samp{foobarbar
270 haha!rara!}; then in this example the two substrings are @samp{rbar }
271 and @samp{rara!}. The value is 2 because the first substring is greater
272 at the second character.
275 (compare-buffer-substring nil 6 11 nil 16 21)
281 @section Inserting Text
282 @cindex insertion of text
283 @cindex text insertion
285 @cindex insertion before point
286 @cindex before point, insertion
287 @dfn{Insertion} means adding new text to a buffer. The inserted text
288 goes at point---between the character before point and the character
289 after point. Some insertion functions leave point before the inserted
290 text, while other functions leave it after. We call the former
291 insertion @dfn{after point} and the latter insertion @dfn{before point}.
293 Insertion relocates markers that point at positions after the
294 insertion point, so that they stay with the surrounding text
295 (@pxref{Markers}). When a marker points at the place of insertion,
296 insertion may or may not relocate the marker, depending on the marker's
297 insertion type (@pxref{Marker Insertion Types}). Certain special
298 functions such as @code{insert-before-markers} relocate all such markers
299 to point after the inserted text, regardless of the markers' insertion
302 Insertion functions signal an error if the current buffer is
305 These functions copy text characters from strings and buffers along
306 with their properties. The inserted characters have exactly the same
307 properties as the characters they were copied from. By contrast,
308 characters specified as separate arguments, not part of a string or
309 buffer, inherit their text properties from the neighboring text.
311 The insertion functions convert text from unibyte to multibyte in
312 order to insert in a multibyte buffer, and vice versa---if the text
313 comes from a string or from a buffer. However, they do not convert
314 unibyte character codes 128 through 255 to multibyte characters, not
315 even if the current buffer is a multibyte buffer. @xref{Converting
318 @defun insert &rest args
319 This function inserts the strings and/or characters @var{args} into the
320 current buffer, at point, moving point forward. In other words, it
321 inserts the text before point. An error is signaled unless all
322 @var{args} are either strings or characters. The value is @code{nil}.
325 @defun insert-before-markers &rest args
326 This function inserts the strings and/or characters @var{args} into the
327 current buffer, at point, moving point forward. An error is signaled
328 unless all @var{args} are either strings or characters. The value is
331 This function is unlike the other insertion functions in that it
332 relocates markers initially pointing at the insertion point, to point
333 after the inserted text. If an overlay begins the insertion point, the
334 inserted text falls outside the overlay; if a nonempty overlay ends at
335 the insertion point, the inserted text falls inside that overlay.
338 @defun insert-char character &optional count inherit
339 This function inserts @var{count} instances of @var{character} into the
340 current buffer before point. The argument @var{count} should be a
341 number (@code{nil} means 1), and @var{character} must be a character.
342 The value is @code{nil}.
344 This function does not convert unibyte character codes 128 through 255
345 to multibyte characters, not even if the current buffer is a multibyte
346 buffer. @xref{Converting Representations}.
348 If @var{inherit} is non-@code{nil}, then the inserted characters inherit
349 sticky text properties from the two characters before and after the
350 insertion point. @xref{Sticky Properties}.
353 @defun insert-buffer-substring from-buffer-or-name &optional start end
354 This function inserts a portion of buffer @var{from-buffer-or-name}
355 (which must already exist) into the current buffer before point. The
356 text inserted is the region from @var{start} and @var{end}. (These
357 arguments default to the beginning and end of the accessible portion of
358 that buffer.) This function returns @code{nil}.
360 In this example, the form is executed with buffer @samp{bar} as the
361 current buffer. We assume that buffer @samp{bar} is initially empty.
365 ---------- Buffer: foo ----------
366 We hold these truths to be self-evident, that all
367 ---------- Buffer: foo ----------
371 (insert-buffer-substring "foo" 1 20)
374 ---------- Buffer: bar ----------
375 We hold these truth@point{}
376 ---------- Buffer: bar ----------
381 @xref{Sticky Properties}, for other insertion functions that inherit
382 text properties from the nearby text in addition to inserting it.
383 Whitespace inserted by indentation functions also inherits text
386 @node Commands for Insertion
387 @section User-Level Insertion Commands
389 This section describes higher-level commands for inserting text,
390 commands intended primarily for the user but useful also in Lisp
393 @deffn Command insert-buffer from-buffer-or-name
394 This command inserts the entire contents of @var{from-buffer-or-name}
395 (which must exist) into the current buffer after point. It leaves
396 the mark after the inserted text. The value is @code{nil}.
399 @deffn Command self-insert-command count
400 @cindex character insertion
401 @cindex self-insertion
402 This command inserts the last character typed; it does so @var{count}
403 times, before point, and returns @code{nil}. Most printing characters
404 are bound to this command. In routine use, @code{self-insert-command}
405 is the most frequently called function in Emacs, but programs rarely use
406 it except to install it on a keymap.
408 In an interactive call, @var{count} is the numeric prefix argument.
410 This command calls @code{auto-fill-function} whenever that is
411 non-@code{nil} and the character inserted is a space or a newline
412 (@pxref{Auto Filling}).
414 @c Cross refs reworded to prevent overfull hbox. --rjc 15mar92
415 This command performs abbrev expansion if Abbrev mode is enabled and
416 the inserted character does not have word-constituent
417 syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.)
419 This is also responsible for calling @code{blink-paren-function} when
420 the inserted character has close parenthesis syntax (@pxref{Blinking}).
423 @deffn Command newline &optional number-of-newlines
424 This command inserts newlines into the current buffer before point.
425 If @var{number-of-newlines} is supplied, that many newline characters
428 @cindex newline and Auto Fill mode
429 This function calls @code{auto-fill-function} if the current column
430 number is greater than the value of @code{fill-column} and
431 @var{number-of-newlines} is @code{nil}. Typically what
432 @code{auto-fill-function} does is insert a newline; thus, the overall
433 result in this case is to insert two newlines at different places: one
434 at point, and another earlier in the line. @code{newline} does not
435 auto-fill if @var{number-of-newlines} is non-@code{nil}.
437 This command indents to the left margin if that is not zero.
440 The value returned is @code{nil}. In an interactive call, @var{count}
441 is the numeric prefix argument.
444 @deffn Command split-line
445 This command splits the current line, moving the portion of the line
446 after point down vertically so that it is on the next line directly
447 below where it was before. Whitespace is inserted as needed at the
448 beginning of the lower line, using the @code{indent-to} function.
449 @code{split-line} returns the position of point.
451 Programs hardly ever use this function.
454 @defvar overwrite-mode
455 This variable controls whether overwrite mode is in effect. The value
456 should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
457 or @code{nil}. @code{overwrite-mode-textual} specifies textual
458 overwrite mode (treats newlines and tabs specially), and
459 @code{overwrite-mode-binary} specifies binary overwrite mode (treats
460 newlines and tabs like any other characters).
464 @section Deleting Text
466 @cindex deletion vs killing
467 Deletion means removing part of the text in a buffer, without saving
468 it in the kill ring (@pxref{The Kill Ring}). Deleted text can't be
469 yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
470 Some deletion functions do save text in the kill ring in some special
473 All of the deletion functions operate on the current buffer, and all
474 return a value of @code{nil}.
476 @deffn Command erase-buffer
477 This function deletes the entire text of the current buffer, leaving it
478 empty. If the buffer is read-only, it signals a @code{buffer-read-only}
479 error. Otherwise, it deletes the text without asking for any
480 confirmation. It returns @code{nil}.
482 Normally, deleting a large amount of text from a buffer inhibits further
483 auto-saving of that buffer ``because it has shrunk''. However,
484 @code{erase-buffer} does not do this, the idea being that the future
485 text is not really related to the former text, and its size should not
486 be compared with that of the former text.
489 @deffn Command delete-region start end
490 This command deletes the text in the current buffer in the region
491 defined by @var{start} and @var{end}. The value is @code{nil}. If
492 point was inside the deleted region, its value afterward is @var{start}.
493 Otherwise, point relocates with the surrounding text, as markers do.
496 @deffn Command delete-char count &optional killp
497 This command deletes @var{count} characters directly after point, or
498 before point if @var{count} is negative. If @var{killp} is
499 non-@code{nil}, then it saves the deleted characters in the kill ring.
501 In an interactive call, @var{count} is the numeric prefix argument, and
502 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
503 argument is supplied, the text is saved in the kill ring. If no prefix
504 argument is supplied, then one character is deleted, but not saved in
507 The value returned is always @code{nil}.
510 @deffn Command delete-backward-char count &optional killp
511 @cindex delete previous char
512 This command deletes @var{count} characters directly before point, or
513 after point if @var{count} is negative. If @var{killp} is
514 non-@code{nil}, then it saves the deleted characters in the kill ring.
516 In an interactive call, @var{count} is the numeric prefix argument, and
517 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
518 argument is supplied, the text is saved in the kill ring. If no prefix
519 argument is supplied, then one character is deleted, but not saved in
522 The value returned is always @code{nil}.
525 @deffn Command backward-delete-char-untabify count &optional killp
527 This command deletes @var{count} characters backward, changing tabs
528 into spaces. When the next character to be deleted is a tab, it is
529 first replaced with the proper number of spaces to preserve alignment
530 and then one of those spaces is deleted instead of the tab. If
531 @var{killp} is non-@code{nil}, then the command saves the deleted
532 characters in the kill ring.
534 Conversion of tabs to spaces happens only if @var{count} is positive.
535 If it is negative, exactly @minus{}@var{count} characters after point
538 In an interactive call, @var{count} is the numeric prefix argument, and
539 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
540 argument is supplied, the text is saved in the kill ring. If no prefix
541 argument is supplied, then one character is deleted, but not saved in
544 The value returned is always @code{nil}.
547 @defopt backward-delete-char-untabify-method
548 @tindex backward-delete-char-untabify-method
549 This option specifies how @code{backward-delete-char-untabify} should
550 deal with whitespace. Possible values include @code{untabify}, the
551 default, meaning convert a tab to many spaces and delete one;
552 @code{hungry}, meaning delete all the whitespace characters before point
553 with one command, and @code{nil}, meaning do nothing special for
554 whitespace characters.
557 @node User-Level Deletion
558 @section User-Level Deletion Commands
560 This section describes higher-level commands for deleting text,
561 commands intended primarily for the user but useful also in Lisp
564 @deffn Command delete-horizontal-space
565 @cindex deleting whitespace
566 This function deletes all spaces and tabs around point. It returns
569 In the following examples, we call @code{delete-horizontal-space} four
570 times, once on each line, with point between the second and third
571 characters on the line each time.
575 ---------- Buffer: foo ----------
580 ---------- Buffer: foo ----------
584 (delete-horizontal-space) ; @r{Four times.}
587 ---------- Buffer: foo ----------
592 ---------- Buffer: foo ----------
597 @deffn Command delete-indentation &optional join-following-p
598 This function joins the line point is on to the previous line, deleting
599 any whitespace at the join and in some cases replacing it with one
600 space. If @var{join-following-p} is non-@code{nil},
601 @code{delete-indentation} joins this line to the following line
602 instead. The function returns @code{nil}.
604 If there is a fill prefix, and the second of the lines being joined
605 starts with the prefix, then @code{delete-indentation} deletes the
606 fill prefix before joining the lines. @xref{Margins}.
608 In the example below, point is located on the line starting
609 @samp{events}, and it makes no difference if there are trailing spaces
610 in the preceding line.
614 ---------- Buffer: foo ----------
615 When in the course of human
616 @point{} events, it becomes necessary
617 ---------- Buffer: foo ----------
624 ---------- Buffer: foo ----------
625 When in the course of human@point{} events, it becomes necessary
626 ---------- Buffer: foo ----------
630 After the lines are joined, the function @code{fixup-whitespace} is
631 responsible for deciding whether to leave a space at the junction.
634 @defun fixup-whitespace
635 This function replaces all the whitespace surrounding point with either
636 one space or no space, according to the context. It returns @code{nil}.
638 At the beginning or end of a line, the appropriate amount of space is
639 none. Before a character with close parenthesis syntax, or after a
640 character with open parenthesis or expression-prefix syntax, no space is
641 also appropriate. Otherwise, one space is appropriate. @xref{Syntax
644 In the example below, @code{fixup-whitespace} is called the first time
645 with point before the word @samp{spaces} in the first line. For the
646 second invocation, point is directly after the @samp{(}.
650 ---------- Buffer: foo ----------
651 This has too many @point{}spaces
652 This has too many spaces at the start of (@point{} this list)
653 ---------- Buffer: foo ----------
664 ---------- Buffer: foo ----------
665 This has too many spaces
666 This has too many spaces at the start of (this list)
667 ---------- Buffer: foo ----------
672 @deffn Command just-one-space
673 @comment !!SourceFile simple.el
674 This command replaces any spaces and tabs around point with a single
675 space. It returns @code{nil}.
678 @deffn Command delete-blank-lines
679 This function deletes blank lines surrounding point. If point is on a
680 blank line with one or more blank lines before or after it, then all but
681 one of them are deleted. If point is on an isolated blank line, then it
682 is deleted. If point is on a nonblank line, the command deletes all
683 blank lines following it.
685 A blank line is defined as a line containing only tabs and spaces.
687 @code{delete-blank-lines} returns @code{nil}.
691 @section The Kill Ring
694 @dfn{Kill functions} delete text like the deletion functions, but save
695 it so that the user can reinsert it by @dfn{yanking}. Most of these
696 functions have @samp{kill-} in their name. By contrast, the functions
697 whose names start with @samp{delete-} normally do not save text for
698 yanking (though they can still be undone); these are ``deletion''
701 Most of the kill commands are primarily for interactive use, and are
702 not described here. What we do describe are the functions provided for
703 use in writing such commands. You can use these functions to write
704 commands for killing text. When you need to delete text for internal
705 purposes within a Lisp function, you should normally use deletion
706 functions, so as not to disturb the kill ring contents.
709 Killed text is saved for later yanking in the @dfn{kill ring}. This
710 is a list that holds a number of recent kills, not just the last text
711 kill. We call this a ``ring'' because yanking treats it as having
712 elements in a cyclic order. The list is kept in the variable
713 @code{kill-ring}, and can be operated on with the usual functions for
714 lists; there are also specialized functions, described in this section,
715 that treat it as a ring.
717 Some people think this use of the word ``kill'' is unfortunate, since
718 it refers to operations that specifically @emph{do not} destroy the
719 entities ``killed''. This is in sharp contrast to ordinary life, in
720 which death is permanent and ``killed'' entities do not come back to
721 life. Therefore, other metaphors have been proposed. For example, the
722 term ``cut ring'' makes sense to people who, in pre-computer days, used
723 scissors and paste to cut up and rearrange manuscripts. However, it
724 would be difficult to change the terminology now.
727 * Kill Ring Concepts:: What text looks like in the kill ring.
728 * Kill Functions:: Functions that kill text.
729 * Yank Commands:: Commands that access the kill ring.
730 * Low-Level Kill Ring:: Functions and variables for kill ring access.
731 * Internals of Kill Ring:: Variables that hold kill-ring data.
734 @node Kill Ring Concepts
735 @comment node-name, next, previous, up
736 @subsection Kill Ring Concepts
738 The kill ring records killed text as strings in a list, most recent
739 first. A short kill ring, for example, might look like this:
742 ("some text" "a different piece of text" "even older text")
746 When the list reaches @code{kill-ring-max} entries in length, adding a
747 new entry automatically deletes the last entry.
749 When kill commands are interwoven with other commands, each kill
750 command makes a new entry in the kill ring. Multiple kill commands in
751 succession build up a single kill-ring entry, which would be yanked as a
752 unit; the second and subsequent consecutive kill commands add text to
753 the entry made by the first one.
755 For yanking, one entry in the kill ring is designated the ``front'' of
756 the ring. Some yank commands ``rotate'' the ring by designating a
757 different element as the ``front.'' But this virtual rotation doesn't
758 change the list itself---the most recent entry always comes first in the
762 @comment node-name, next, previous, up
763 @subsection Functions for Killing
765 @code{kill-region} is the usual subroutine for killing text. Any
766 command that calls this function is a ``kill command'' (and should
767 probably have @samp{kill} in its name). @code{kill-region} puts the
768 newly killed text in a new element at the beginning of the kill ring or
769 adds it to the most recent element. It determines automatically (using
770 @code{last-command}) whether the previous command was a kill command,
771 and if so appends the killed text to the most recent entry.
773 @deffn Command kill-region start end
774 This function kills the text in the region defined by @var{start} and
775 @var{end}. The text is deleted but saved in the kill ring, along with
776 its text properties. The value is always @code{nil}.
778 In an interactive call, @var{start} and @var{end} are point and
782 If the buffer is read-only, @code{kill-region} modifies the kill ring
783 just the same, then signals an error without modifying the buffer. This
784 is convenient because it lets the user use all the kill commands to copy
785 text into the kill ring from a read-only buffer.
788 @defopt kill-read-only-ok
789 If this option is non-@code{nil}, @code{kill-region} does not get an
790 error if the buffer is read-only. Instead, it simply returns, updating
791 the kill ring but not changing the buffer.
794 @deffn Command copy-region-as-kill start end
795 This command saves the region defined by @var{start} and @var{end} on
796 the kill ring (including text properties), but does not delete the text
797 from the buffer. It returns @code{nil}. It also indicates the extent
798 of the text copied by moving the cursor momentarily, or by displaying a
799 message in the echo area.
801 The command does not set @code{this-command} to @code{kill-region}, so a
802 subsequent kill command does not append to the same kill ring entry.
804 Don't call @code{copy-region-as-kill} in Lisp programs unless you aim to
805 support Emacs 18. For newer Emacs versions, it is better to use
806 @code{kill-new} or @code{kill-append} instead. @xref{Low-Level Kill
811 @comment node-name, next, previous, up
812 @subsection Functions for Yanking
814 @dfn{Yanking} means reinserting an entry of previously killed text
815 from the kill ring. The text properties are copied too.
817 @deffn Command yank &optional arg
818 @cindex inserting killed text
819 This command inserts before point the text in the first entry in the
820 kill ring. It positions the mark at the beginning of that text, and
823 If @var{arg} is a list (which occurs interactively when the user
824 types @kbd{C-u} with no digits), then @code{yank} inserts the text as
825 described above, but puts point before the yanked text and puts the mark
828 If @var{arg} is a number, then @code{yank} inserts the @var{arg}th most
829 recently killed text---the @var{arg}th element of the kill ring list.
831 @code{yank} does not alter the contents of the kill ring or rotate it.
832 It returns @code{nil}.
835 @deffn Command yank-pop arg
836 This command replaces the just-yanked entry from the kill ring with a
837 different entry from the kill ring.
839 This is allowed only immediately after a @code{yank} or another
840 @code{yank-pop}. At such a time, the region contains text that was just
841 inserted by yanking. @code{yank-pop} deletes that text and inserts in
842 its place a different piece of killed text. It does not add the deleted
843 text to the kill ring, since it is already in the kill ring somewhere.
845 If @var{arg} is @code{nil}, then the replacement text is the previous
846 element of the kill ring. If @var{arg} is numeric, the replacement is
847 the @var{arg}th previous kill. If @var{arg} is negative, a more recent
848 kill is the replacement.
850 The sequence of kills in the kill ring wraps around, so that after the
851 oldest one comes the newest one, and before the newest one goes the
854 The return value is always @code{nil}.
857 @node Low-Level Kill Ring
858 @subsection Low-Level Kill Ring
860 These functions and variables provide access to the kill ring at a
861 lower level, but still convenient for use in Lisp programs, because they
862 take care of interaction with window system selections
863 (@pxref{Window System Selections}).
865 @defun current-kill n &optional do-not-move
866 The function @code{current-kill} rotates the yanking pointer, which
867 designates the ``front'' of the kill ring, by @var{n} places (from newer
868 kills to older ones), and returns the text at that place in the ring.
870 If the optional second argument @var{do-not-move} is non-@code{nil},
871 then @code{current-kill} doesn't alter the yanking pointer; it just
872 returns the @var{n}th kill, counting from the current yanking pointer.
874 If @var{n} is zero, indicating a request for the latest kill,
875 @code{current-kill} calls the value of
876 @code{interprogram-paste-function} (documented below) before consulting
880 @defun kill-new string
881 This function puts the text @var{string} into the kill ring as a new
882 entry at the front of the ring. It discards the oldest entry if
883 appropriate. It also invokes the value of
884 @code{interprogram-cut-function} (see below).
887 @defun kill-append string before-p
888 This function appends the text @var{string} to the first entry in the
889 kill ring. Normally @var{string} goes at the end of the entry, but if
890 @var{before-p} is non-@code{nil}, it goes at the beginning. This
891 function also invokes the value of @code{interprogram-cut-function} (see
895 @defvar interprogram-paste-function
896 This variable provides a way of transferring killed text from other
897 programs, when you are using a window system. Its value should be
898 @code{nil} or a function of no arguments.
900 If the value is a function, @code{current-kill} calls it to get the
901 ``most recent kill''. If the function returns a non-@code{nil} value,
902 then that value is used as the ``most recent kill''. If it returns
903 @code{nil}, then the first element of @code{kill-ring} is used.
905 The normal use of this hook is to get the window system's primary
906 selection as the most recent kill, even if the selection belongs to
907 another application. @xref{Window System Selections}.
910 @defvar interprogram-cut-function
911 This variable provides a way of communicating killed text to other
912 programs, when you are using a window system. Its value should be
913 @code{nil} or a function of one argument.
915 If the value is a function, @code{kill-new} and @code{kill-append} call
916 it with the new first element of the kill ring as an argument.
918 The normal use of this hook is to set the window system's primary
919 selection from the newly killed text. @xref{Window System Selections}.
922 @node Internals of Kill Ring
923 @comment node-name, next, previous, up
924 @subsection Internals of the Kill Ring
926 The variable @code{kill-ring} holds the kill ring contents, in the
927 form of a list of strings. The most recent kill is always at the front
930 The @code{kill-ring-yank-pointer} variable points to a link in the
931 kill ring list, whose @sc{car} is the text to yank next. We say it
932 identifies the ``front'' of the ring. Moving
933 @code{kill-ring-yank-pointer} to a different link is called
934 @dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
935 the functions that move the yank pointer wrap around from the end of the
936 list to the beginning, or vice-versa. Rotation of the kill ring is
937 virtual; it does not change the value of @code{kill-ring}.
939 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
940 variables whose values are normally lists. The word ``pointer'' in the
941 name of the @code{kill-ring-yank-pointer} indicates that the variable's
942 purpose is to identify one element of the list for use by the next yank
945 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
946 of the links in the kill ring list. The element it identifies is the
947 @sc{car} of that link. Kill commands, which change the kill ring, also
948 set this variable to the value of @code{kill-ring}. The effect is to
949 rotate the ring so that the newly killed text is at the front.
951 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
952 pointing to the second entry in the kill ring @code{("some text" "a
953 different piece of text" "yet older text")}.
957 kill-ring ---- kill-ring-yank-pointer
960 | --- --- --- --- --- ---
961 --> | | |------> | | |--> | | |--> nil
962 --- --- --- --- --- ---
965 | | -->"yet older text"
967 | --> "a different piece of text"
974 This state of affairs might occur after @kbd{C-y} (@code{yank})
975 immediately followed by @kbd{M-y} (@code{yank-pop}).
978 This variable holds the list of killed text sequences, most recently
982 @defvar kill-ring-yank-pointer
983 This variable's value indicates which element of the kill ring is at the
984 ``front'' of the ring for yanking. More precisely, the value is a tail
985 of the value of @code{kill-ring}, and its @sc{car} is the kill string
986 that @kbd{C-y} should yank.
989 @defopt kill-ring-max
990 The value of this variable is the maximum length to which the kill
991 ring can grow, before elements are thrown away at the end. The default
992 value for @code{kill-ring-max} is 30.
996 @comment node-name, next, previous, up
1000 Most buffers have an @dfn{undo list}, which records all changes made
1001 to the buffer's text so that they can be undone. (The buffers that
1002 don't have one are usually special-purpose buffers for which Emacs
1003 assumes that undoing is not useful.) All the primitives that modify the
1004 text in the buffer automatically add elements to the front of the undo
1005 list, which is in the variable @code{buffer-undo-list}.
1007 @defvar buffer-undo-list
1008 This variable's value is the undo list of the current buffer.
1009 A value of @code{t} disables the recording of undo information.
1012 Here are the kinds of elements an undo list can have:
1015 @item @var{position}
1016 This kind of element records a previous value of point; undoing this
1017 element moves point to @var{position}. Ordinary cursor motion does not
1018 make any sort of undo record, but deletion operations use these entries
1019 to record where point was before the command.
1021 @item (@var{beg} . @var{end})
1022 This kind of element indicates how to delete text that was inserted.
1023 Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1026 @item (@var{text} . @var{position})
1027 This kind of element indicates how to reinsert text that was deleted.
1028 The deleted text itself is the string @var{text}. The place to
1029 reinsert it is @code{(abs @var{position})}.
1031 @item (t @var{high} . @var{low})
1032 This kind of element indicates that an unmodified buffer became
1033 modified. The elements @var{high} and @var{low} are two integers, each
1034 recording 16 bits of the visited file's modification time as of when it
1035 was previously visited or saved. @code{primitive-undo} uses those
1036 values to determine whether to mark the buffer as unmodified once again;
1037 it does so only if the file's modification time matches those numbers.
1039 @item (nil @var{property} @var{value} @var{beg} . @var{end})
1040 This kind of element records a change in a text property.
1041 Here's how you might undo the change:
1044 (put-text-property @var{beg} @var{end} @var{property} @var{value})
1047 @item (@var{marker} . @var{adjustment})
1048 This kind of element records the fact that the marker @var{marker} was
1049 relocated due to deletion of surrounding text, and that it moved
1050 @var{adjustment} character positions. Undoing this element moves
1051 @var{marker} @minus{} @var{adjustment} characters.
1054 This element is a boundary. The elements between two boundaries are
1055 called a @dfn{change group}; normally, each change group corresponds to
1056 one keyboard command, and undo commands normally undo an entire group as
1060 @defun undo-boundary
1061 This function places a boundary element in the undo list. The undo
1062 command stops at such a boundary, and successive undo commands undo
1063 to earlier and earlier boundaries. This function returns @code{nil}.
1065 The editor command loop automatically creates an undo boundary before
1066 each key sequence is executed. Thus, each undo normally undoes the
1067 effects of one command. Self-inserting input characters are an
1068 exception. The command loop makes a boundary for the first such
1069 character; the next 19 consecutive self-inserting input characters do
1070 not make boundaries, and then the 20th does, and so on as long as
1071 self-inserting characters continue.
1073 All buffer modifications add a boundary whenever the previous undoable
1074 change was made in some other buffer. This is to ensure that
1075 each command makes a boundary in each buffer where it makes changes.
1077 Calling this function explicitly is useful for splitting the effects of
1078 a command into more than one unit. For example, @code{query-replace}
1079 calls @code{undo-boundary} after each replacement, so that the user can
1080 undo individual replacements one by one.
1083 @defun primitive-undo count list
1084 This is the basic function for undoing elements of an undo list.
1085 It undoes the first @var{count} elements of @var{list}, returning
1086 the rest of @var{list}. You could write this function in Lisp,
1087 but it is convenient to have it in C.
1089 @code{primitive-undo} adds elements to the buffer's undo list when it
1090 changes the buffer. Undo commands avoid confusion by saving the undo
1091 list value at the beginning of a sequence of undo operations. Then the
1092 undo operations use and update the saved value. The new elements added
1093 by undoing are not part of this saved value, so they don't interfere with
1097 @node Maintaining Undo
1098 @section Maintaining Undo Lists
1100 This section describes how to enable and disable undo information for
1101 a given buffer. It also explains how the undo list is truncated
1102 automatically so it doesn't get too big.
1104 Recording of undo information in a newly created buffer is normally
1105 enabled to start with; but if the buffer name starts with a space, the
1106 undo recording is initially disabled. You can explicitly enable or
1107 disable undo recording with the following two functions, or by setting
1108 @code{buffer-undo-list} yourself.
1110 @deffn Command buffer-enable-undo &optional buffer-or-name
1111 This command enables recording undo information for buffer
1112 @var{buffer-or-name}, so that subsequent changes can be undone. If no
1113 argument is supplied, then the current buffer is used. This function
1114 does nothing if undo recording is already enabled in the buffer. It
1117 In an interactive call, @var{buffer-or-name} is the current buffer.
1118 You cannot specify any other buffer.
1121 @deffn Command buffer-disable-undo &optional buffer
1122 @deffnx Command buffer-flush-undo &optional buffer
1123 @cindex disable undo
1124 This function discards the undo list of @var{buffer}, and disables
1125 further recording of undo information. As a result, it is no longer
1126 possible to undo either previous changes or any subsequent changes. If
1127 the undo list of @var{buffer} is already disabled, this function
1130 This function returns @code{nil}.
1132 The name @code{buffer-flush-undo} is not considered obsolete, but the
1133 preferred name is @code{buffer-disable-undo}.
1136 As editing continues, undo lists get longer and longer. To prevent
1137 them from using up all available memory space, garbage collection trims
1138 them back to size limits you can set. (For this purpose, the ``size''
1139 of an undo list measures the cons cells that make up the list, plus the
1140 strings of deleted text.) Two variables control the range of acceptable
1141 sizes: @code{undo-limit} and @code{undo-strong-limit}.
1144 This is the soft limit for the acceptable size of an undo list. The
1145 change group at which this size is exceeded is the last one kept.
1148 @defvar undo-strong-limit
1149 This is the upper limit for the acceptable size of an undo list. The
1150 change group at which this size is exceeded is discarded itself (along
1151 with all older change groups). There is one exception: the very latest
1152 change group is never discarded no matter how big it is.
1156 @comment node-name, next, previous, up
1158 @cindex filling, explicit
1160 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1161 breaks) so that they are nearly (but no greater than) a specified
1162 maximum width. Additionally, lines can be @dfn{justified}, which means
1163 inserting spaces to make the left and/or right margins line up
1164 precisely. The width is controlled by the variable @code{fill-column}.
1165 For ease of reading, lines should be no longer than 70 or so columns.
1167 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1168 automatically as you insert it, but changes to existing text may leave
1169 it improperly filled. Then you must fill the text explicitly.
1171 Most of the commands in this section return values that are not
1172 meaningful. All the functions that do filling take note of the current
1173 left margin, current right margin, and current justification style
1174 (@pxref{Margins}). If the current justification style is
1175 @code{none}, the filling functions don't actually do anything.
1177 Several of the filling functions have an argument @var{justify}.
1178 If it is non-@code{nil}, that requests some kind of justification. It
1179 can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1180 request a specific style of justification. If it is @code{t}, that
1181 means to use the current justification style for this part of the text
1182 (see @code{current-justification}, below). Any other value is treated
1185 When you call the filling functions interactively, using a prefix
1186 argument implies the value @code{full} for @var{justify}.
1188 @deffn Command fill-paragraph justify
1189 @cindex filling a paragraph
1190 This command fills the paragraph at or after point. If
1191 @var{justify} is non-@code{nil}, each line is justified as well.
1192 It uses the ordinary paragraph motion commands to find paragraph
1193 boundaries. @xref{Paragraphs,,, emacs, The Emacs Manual}.
1196 @deffn Command fill-region start end &optional justify nosqueeze
1197 This command fills each of the paragraphs in the region from @var{start}
1198 to @var{end}. It justifies as well if @var{justify} is
1201 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1202 other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1203 that means to keep filling to the end of the paragraph---or the next hard
1204 newline, if @code{use-hard-newlines} is enabled (see below).
1206 The variable @code{paragraph-separate} controls how to distinguish
1207 paragraphs. @xref{Standard Regexps}.
1210 @deffn Command fill-individual-paragraphs start end &optional justify mail-flag
1211 This command fills each paragraph in the region according to its
1212 individual fill prefix. Thus, if the lines of a paragraph were indented
1213 with spaces, the filled paragraph will remain indented in the same
1216 The first two arguments, @var{start} and @var{end}, are the beginning
1217 and end of the region to be filled. The third and fourth arguments,
1218 @var{justify} and @var{mail-flag}, are optional. If
1219 @var{justify} is non-@code{nil}, the paragraphs are justified as
1220 well as filled. If @var{mail-flag} is non-@code{nil}, it means the
1221 function is operating on a mail message and therefore should not fill
1224 Ordinarily, @code{fill-individual-paragraphs} regards each change in
1225 indentation as starting a new paragraph. If
1226 @code{fill-individual-varying-indent} is non-@code{nil}, then only
1227 separator lines separate paragraphs. That mode can handle indented
1228 paragraphs with additional indentation on the first line.
1231 @defopt fill-individual-varying-indent
1232 This variable alters the action of @code{fill-individual-paragraphs} as
1236 @deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1237 This command considers a region of text as a single paragraph and fills
1238 it. If the region was made up of many paragraphs, the blank lines
1239 between paragraphs are removed. This function justifies as well as
1240 filling when @var{justify} is non-@code{nil}.
1242 In an interactive call, any prefix argument requests justification.
1244 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1245 other than line breaks untouched. If @var{squeeze-after} is
1246 non-@code{nil}, it specifies a position in the region, and means don't
1247 canonicalize spaces before that position.
1249 In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1250 choose a fill prefix by default. @xref{Adaptive Fill}.
1253 @deffn Command justify-current-line how eop nosqueeze
1254 This command inserts spaces between the words of the current line so
1255 that the line ends exactly at @code{fill-column}. It returns
1258 The argument @var{how}, if non-@code{nil} specifies explicitly the style
1259 of justification. It can be @code{left}, @code{right}, @code{full},
1260 @code{center}, or @code{none}. If it is @code{t}, that means to do
1261 follow specified justification style (see @code{current-justification},
1262 below). @code{nil} means to do full justification.
1264 If @var{eop} is non-@code{nil}, that means do left-justification if
1265 @code{current-justification} specifies full justification. This is used
1266 for the last line of a paragraph; even if the paragraph as a whole is
1267 fully justified, the last line should not be.
1269 If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1273 @defopt default-justification
1274 This variable's value specifies the style of justification to use for
1275 text that doesn't specify a style with a text property. The possible
1276 values are @code{left}, @code{right}, @code{full}, @code{center}, or
1277 @code{none}. The default value is @code{left}.
1280 @defun current-justification
1281 This function returns the proper justification style to use for filling
1282 the text around point.
1285 @defopt sentence-end-double-space
1286 If this variable is non-@code{nil}, a period followed by just one space
1287 does not count as the end of a sentence, and the filling functions
1288 avoid breaking the line at such a place.
1291 @defvar fill-paragraph-function
1292 This variable provides a way for major modes to override the filling of
1293 paragraphs. If the value is non-@code{nil}, @code{fill-paragraph} calls
1294 this function to do the work. If the function returns a non-@code{nil}
1295 value, @code{fill-paragraph} assumes the job is done, and immediately
1298 The usual use of this feature is to fill comments in programming
1299 language modes. If the function needs to fill a paragraph in the usual
1300 way, it can do so as follows:
1303 (let ((fill-paragraph-function nil))
1304 (fill-paragraph arg))
1308 @defvar use-hard-newlines
1309 If this variable is non-@code{nil}, the filling functions do not delete
1310 newlines that have the @code{hard} text property. These ``hard
1311 newlines'' act as paragraph separators.
1315 @section Margins for Filling
1318 This buffer-local variable specifies a string of text that appears at
1320 of normal text lines and should be disregarded when filling them. Any
1321 line that fails to start with the fill prefix is considered the start of
1322 a paragraph; so is any line that starts with the fill prefix followed by
1323 additional whitespace. Lines that start with the fill prefix but no
1324 additional whitespace are ordinary text lines that can be filled
1325 together. The resulting filled lines also start with the fill prefix.
1327 The fill prefix follows the left margin whitespace, if any.
1331 This buffer-local variable specifies the maximum width of filled lines.
1332 Its value should be an integer, which is a number of columns. All the
1333 filling, justification, and centering commands are affected by this
1334 variable, including Auto Fill mode (@pxref{Auto Filling}).
1336 As a practical matter, if you are writing text for other people to
1337 read, you should set @code{fill-column} to no more than 70. Otherwise
1338 the line will be too long for people to read comfortably, and this can
1339 make the text seem clumsy.
1342 @defvar default-fill-column
1343 The value of this variable is the default value for @code{fill-column} in
1344 buffers that do not override it. This is the same as
1345 @code{(default-value 'fill-column)}.
1347 The default value for @code{default-fill-column} is 70.
1350 @deffn Command set-left-margin from to margin
1351 This sets the @code{left-margin} property on the text from @var{from} to
1352 @var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1353 command also refills the region to fit the new margin.
1356 @deffn Command set-right-margin from to margin
1357 This sets the @code{right-margin} property on the text from @var{from}
1358 to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1359 this command also refills the region to fit the new margin.
1362 @defun current-left-margin
1363 This function returns the proper left margin value to use for filling
1364 the text around point. The value is the sum of the @code{left-margin}
1365 property of the character at the start of the current line (or zero if
1366 none), and the value of the variable @code{left-margin}.
1369 @defun current-fill-column
1370 This function returns the proper fill column value to use for filling
1371 the text around point. The value is the value of the @code{fill-column}
1372 variable, minus the value of the @code{right-margin} property of the
1373 character after point.
1376 @deffn Command move-to-left-margin &optional n force
1377 This function moves point to the left margin of the current line. The
1378 column moved to is determined by calling the function
1379 @code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1380 @code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1382 If @var{force} is non-@code{nil}, that says to fix the line's
1383 indentation if that doesn't match the left margin value.
1386 @defun delete-to-left-margin from to
1387 This function removes left margin indentation from the text
1388 between @var{from} and @var{to}. The amount of indentation
1389 to delete is determined by calling @code{current-left-margin}.
1390 In no case does this function delete non-whitespace.
1393 @defun indent-to-left-margin
1394 This is the default @code{indent-line-function}, used in Fundamental
1395 mode, Text mode, etc. Its effect is to adjust the indentation at the
1396 beginning of the current line to the value specified by the variable
1397 @code{left-margin}. This may involve either inserting or deleting
1402 This variable specifies the base left margin column. In Fundamental
1403 mode, @kbd{C-j} indents to this column. This variable automatically
1404 becomes buffer-local when set in any fashion.
1407 @defvar fill-nobreak-predicate
1408 @tindex fill-nobreak-predicate
1409 This variable gives major modes a way to specify not to break a line at
1410 certain places. Its value should be a function. This function is
1411 called during filling, with no arguments and with point located at the
1412 place where a break is being considered. If the function returns
1413 non-@code{nil}, then the line won't be broken there.
1417 @section Adaptive Fill Mode
1418 @cindex Adaptive Fill mode
1420 Adaptive Fill mode chooses a fill prefix automatically from the text
1421 in each paragraph being filled.
1423 @defopt adaptive-fill-mode
1424 Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1425 It is @code{t} by default.
1428 @defun fill-context-prefix from to
1429 This function implements the heart of Adaptive Fill mode; it chooses a
1430 fill prefix based on the text between @var{from} and @var{to}. It does
1431 this by looking at the first two lines of the paragraph, based on the
1432 variables described below.
1435 @defopt adaptive-fill-regexp
1436 This variable holds a regular expression to control Adaptive Fill mode.
1437 Adaptive Fill mode matches this regular expression against the text
1438 starting after the left margin whitespace (if any) on a line; the
1439 characters it matches are that line's candidate for the fill prefix.
1442 @defopt adaptive-fill-first-line-regexp
1443 In a one-line paragraph, if the candidate fill prefix matches this
1444 regular expression, or if it matches @code{comment-start-skip}, then it
1445 is used---otherwise, spaces amounting to the same width are used
1448 However, the fill prefix is never taken from a one-line paragraph
1449 if it would act as a paragraph starter on subsequent lines.
1452 @defopt adaptive-fill-function
1453 You can specify more complex ways of choosing a fill prefix
1454 automatically by setting this variable to a function. The function is
1455 called when @code{adaptive-fill-regexp} does not match, with point after
1456 the left margin of a line, and it should return the appropriate fill
1457 prefix based on that line. If it returns @code{nil}, that means it sees
1458 no fill prefix in that line.
1462 @comment node-name, next, previous, up
1463 @section Auto Filling
1464 @cindex filling, automatic
1465 @cindex Auto Fill mode
1467 Auto Fill mode is a minor mode that fills lines automatically as text
1468 is inserted. This section describes the hook used by Auto Fill mode.
1469 For a description of functions that you can call explicitly to fill and
1470 justify existing text, see @ref{Filling}.
1472 Auto Fill mode also enables the functions that change the margins and
1473 justification style to refill portions of the text. @xref{Margins}.
1475 @defvar auto-fill-function
1476 The value of this variable should be a function (of no arguments) to be
1477 called after self-inserting a space or a newline. It may be @code{nil},
1478 in which case nothing special is done in that case.
1480 The value of @code{auto-fill-function} is @code{do-auto-fill} when
1481 Auto-Fill mode is enabled. That is a function whose sole purpose is to
1482 implement the usual strategy for breaking a line.
1485 In older Emacs versions, this variable was named @code{auto-fill-hook},
1486 but since it is not called with the standard convention for hooks, it
1487 was renamed to @code{auto-fill-function} in version 19.
1491 @defvar normal-auto-fill-function
1492 This variable specifies the function to use for
1493 @code{auto-fill-function}, if and when Auto Fill is turned on. Major
1494 modes can set buffer-local values for this variable to alter how Auto
1499 @section Sorting Text
1500 @cindex sorting text
1502 The sorting functions described in this section all rearrange text in
1503 a buffer. This is in contrast to the function @code{sort}, which
1504 rearranges the order of the elements of a list (@pxref{Rearrangement}).
1505 The values returned by these functions are not meaningful.
1507 @defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun
1508 This function is the general text-sorting routine that subdivides a
1509 buffer into records and then sorts them. Most of the commands in this
1510 section use this function.
1512 To understand how @code{sort-subr} works, consider the whole accessible
1513 portion of the buffer as being divided into disjoint pieces called
1514 @dfn{sort records}. The records may or may not be contiguous, but they
1515 must not overlap. A portion of each sort record (perhaps all of it) is
1516 designated as the sort key. Sorting rearranges the records in order by
1519 Usually, the records are rearranged in order of ascending sort key.
1520 If the first argument to the @code{sort-subr} function, @var{reverse},
1521 is non-@code{nil}, the sort records are rearranged in order of
1522 descending sort key.
1524 The next four arguments to @code{sort-subr} are functions that are
1525 called to move point across a sort record. They are called many times
1526 from within @code{sort-subr}.
1530 @var{nextrecfun} is called with point at the end of a record. This
1531 function moves point to the start of the next record. The first record
1532 is assumed to start at the position of point when @code{sort-subr} is
1533 called. Therefore, you should usually move point to the beginning of
1534 the buffer before calling @code{sort-subr}.
1536 This function can indicate there are no more sort records by leaving
1537 point at the end of the buffer.
1540 @var{endrecfun} is called with point within a record. It moves point to
1541 the end of the record.
1544 @var{startkeyfun} is called to move point from the start of a record to
1545 the start of the sort key. This argument is optional; if it is omitted,
1546 the whole record is the sort key. If supplied, the function should
1547 either return a non-@code{nil} value to be used as the sort key, or
1548 return @code{nil} to indicate that the sort key is in the buffer
1549 starting at point. In the latter case, @var{endkeyfun} is called to
1550 find the end of the sort key.
1553 @var{endkeyfun} is called to move point from the start of the sort key
1554 to the end of the sort key. This argument is optional. If
1555 @var{startkeyfun} returns @code{nil} and this argument is omitted (or
1556 @code{nil}), then the sort key extends to the end of the record. There
1557 is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1558 non-@code{nil} value.
1561 As an example of @code{sort-subr}, here is the complete function
1562 definition for @code{sort-lines}:
1566 ;; @r{Note that the first two lines of doc string}
1567 ;; @r{are effectively one line when viewed by a user.}
1568 (defun sort-lines (reverse beg end)
1569 "Sort lines in region alphabetically;\
1570 argument means descending order.
1571 Called from a program, there are three arguments:
1574 REVERSE (non-nil means reverse order),\
1575 BEG and END (region to sort).
1576 The variable `sort-fold-case' determines\
1577 whether alphabetic case affects
1581 (interactive "P\nr")
1584 (narrow-to-region beg end)
1585 (goto-char (point-min))
1586 (sort-subr reverse 'forward-line 'end-of-line))))
1590 Here @code{forward-line} moves point to the start of the next record,
1591 and @code{end-of-line} moves point to the end of record. We do not pass
1592 the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
1593 record is used as the sort key.
1595 The @code{sort-paragraphs} function is very much the same, except that
1596 its @code{sort-subr} call looks like this:
1603 (while (and (not (eobp))
1604 (looking-at paragraph-separate))
1610 Markers pointing into any sort records are left with no useful
1611 position after @code{sort-subr} returns.
1614 @defopt sort-fold-case
1615 If this variable is non-@code{nil}, @code{sort-subr} and the other
1616 buffer sorting functions ignore case when comparing strings.
1619 @deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
1620 This command sorts the region between @var{start} and @var{end}
1621 alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
1622 If @var{reverse} is a negative integer, then sorting is in reverse
1625 Alphabetical sorting means that two sort keys are compared by
1626 comparing the first characters of each, the second characters of each,
1627 and so on. If a mismatch is found, it means that the sort keys are
1628 unequal; the sort key whose character is less at the point of first
1629 mismatch is the lesser sort key. The individual characters are compared
1630 according to their numerical character codes in the Emacs character set.
1632 The value of the @var{record-regexp} argument specifies how to divide
1633 the buffer into sort records. At the end of each record, a search is
1634 done for this regular expression, and the text that matches it is taken
1635 as the next record. For example, the regular expression @samp{^.+$},
1636 which matches lines with at least one character besides a newline, would
1637 make each such line into a sort record. @xref{Regular Expressions}, for
1638 a description of the syntax and meaning of regular expressions.
1640 The value of the @var{key-regexp} argument specifies what part of each
1641 record is the sort key. The @var{key-regexp} could match the whole
1642 record, or only a part. In the latter case, the rest of the record has
1643 no effect on the sorted order of records, but it is carried along when
1644 the record moves to its new position.
1646 The @var{key-regexp} argument can refer to the text matched by a
1647 subexpression of @var{record-regexp}, or it can be a regular expression
1650 If @var{key-regexp} is:
1653 @item @samp{\@var{digit}}
1654 then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
1655 grouping in @var{record-regexp} is the sort key.
1658 then the whole record is the sort key.
1660 @item a regular expression
1661 then @code{sort-regexp-fields} searches for a match for the regular
1662 expression within the record. If such a match is found, it is the sort
1663 key. If there is no match for @var{key-regexp} within a record then
1664 that record is ignored, which means its position in the buffer is not
1665 changed. (The other records may move around it.)
1668 For example, if you plan to sort all the lines in the region by the
1669 first word on each line starting with the letter @samp{f}, you should
1670 set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
1671 @samp{\<f\w*\>}. The resulting expression looks like this:
1675 (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
1681 If you call @code{sort-regexp-fields} interactively, it prompts for
1682 @var{record-regexp} and @var{key-regexp} in the minibuffer.
1685 @deffn Command sort-lines reverse start end
1686 This command alphabetically sorts lines in the region between
1687 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
1688 is in reverse order.
1691 @deffn Command sort-paragraphs reverse start end
1692 This command alphabetically sorts paragraphs in the region between
1693 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
1694 is in reverse order.
1697 @deffn Command sort-pages reverse start end
1698 This command alphabetically sorts pages in the region between
1699 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
1700 is in reverse order.
1703 @deffn Command sort-fields field start end
1704 This command sorts lines in the region between @var{start} and
1705 @var{end}, comparing them alphabetically by the @var{field}th field
1706 of each line. Fields are separated by whitespace and numbered starting
1707 from 1. If @var{field} is negative, sorting is by the
1708 @w{@minus{}@var{field}th} field from the end of the line. This command
1709 is useful for sorting tables.
1712 @deffn Command sort-numeric-fields field start end
1713 This command sorts lines in the region between @var{start} and
1714 @var{end}, comparing them numerically by the @var{field}th field of each
1715 line. The specified field must contain a number in each line of the
1716 region. Fields are separated by whitespace and numbered starting from
1717 1. If @var{field} is negative, sorting is by the
1718 @w{@minus{}@var{field}th} field from the end of the line. This command
1719 is useful for sorting tables.
1722 @deffn Command sort-columns reverse &optional beg end
1723 This command sorts the lines in the region between @var{beg} and
1724 @var{end}, comparing them alphabetically by a certain range of columns.
1725 The column positions of @var{beg} and @var{end} bound the range of
1728 If @var{reverse} is non-@code{nil}, the sort is in reverse order.
1730 One unusual thing about this command is that the entire line
1731 containing position @var{beg}, and the entire line containing position
1732 @var{end}, are included in the region sorted.
1734 Note that @code{sort-columns} uses the @code{sort} utility program,
1735 and so cannot work properly on text containing tab characters. Use
1736 @kbd{M-x untabify} to convert tabs to spaces before sorting.
1740 @comment node-name, next, previous, up
1741 @section Counting Columns
1743 @cindex counting columns
1744 @cindex horizontal position
1746 The column functions convert between a character position (counting
1747 characters from the beginning of the buffer) and a column position
1748 (counting screen characters from the beginning of a line).
1750 These functions count each character according to the number of
1751 columns it occupies on the screen. This means control characters count
1752 as occupying 2 or 4 columns, depending upon the value of
1753 @code{ctl-arrow}, and tabs count as occupying a number of columns that
1754 depends on the value of @code{tab-width} and on the column where the tab
1755 begins. @xref{Usual Display}.
1757 Column number computations ignore the width of the window and the
1758 amount of horizontal scrolling. Consequently, a column value can be
1759 arbitrarily high. The first (or leftmost) column is numbered 0.
1761 @defun current-column
1762 This function returns the horizontal position of point, measured in
1763 columns, counting from 0 at the left margin. The column position is the
1764 sum of the widths of all the displayed representations of the characters
1765 between the start of the current line and point.
1767 For an example of using @code{current-column}, see the description of
1768 @code{count-lines} in @ref{Text Lines}.
1771 @defun move-to-column column &optional force
1772 This function moves point to @var{column} in the current line. The
1773 calculation of @var{column} takes into account the widths of the
1774 displayed representations of the characters between the start of the
1777 If column @var{column} is beyond the end of the line, point moves to the
1778 end of the line. If @var{column} is negative, point moves to the
1779 beginning of the line.
1781 If it is impossible to move to column @var{column} because that is in
1782 the middle of a multicolumn character such as a tab, point moves to the
1783 end of that character. However, if @var{force} is non-@code{nil}, and
1784 @var{column} is in the middle of a tab, then @code{move-to-column}
1785 converts the tab into spaces so that it can move precisely to column
1786 @var{column}. Other multicolumn characters can cause anomalies despite
1787 @var{force}, since there is no way to split them.
1789 The argument @var{force} also has an effect if the line isn't long
1790 enough to reach column @var{column}; in that case, it says to add
1791 whitespace at the end of the line to reach that column.
1793 If @var{column} is not an integer, an error is signaled.
1795 The return value is the column number actually moved to.
1799 @section Indentation
1802 The indentation functions are used to examine, move to, and change
1803 whitespace that is at the beginning of a line. Some of the functions
1804 can also change whitespace elsewhere on a line. Columns and indentation
1805 count from zero at the left margin.
1808 * Primitive Indent:: Functions used to count and insert indentation.
1809 * Mode-Specific Indent:: Customize indentation for different modes.
1810 * Region Indent:: Indent all the lines in a region.
1811 * Relative Indent:: Indent the current line based on previous lines.
1812 * Indent Tabs:: Adjustable, typewriter-like tab stops.
1813 * Motion by Indent:: Move to first non-blank character.
1816 @node Primitive Indent
1817 @subsection Indentation Primitives
1819 This section describes the primitive functions used to count and
1820 insert indentation. The functions in the following sections use these
1821 primitives. @xref{Width}, for related functions.
1823 @defun current-indentation
1824 @comment !!Type Primitive Function
1825 @comment !!SourceFile indent.c
1826 This function returns the indentation of the current line, which is
1827 the horizontal position of the first nonblank character. If the
1828 contents are entirely blank, then this is the horizontal position of the
1832 @deffn Command indent-to column &optional minimum
1833 @comment !!Type Primitive Function
1834 @comment !!SourceFile indent.c
1835 This function indents from point with tabs and spaces until @var{column}
1836 is reached. If @var{minimum} is specified and non-@code{nil}, then at
1837 least that many spaces are inserted even if this requires going beyond
1838 @var{column}. Otherwise the function does nothing if point is already
1839 beyond @var{column}. The value is the column at which the inserted
1842 The inserted whitespace characters inherit text properties from the
1843 surrounding text (usually, from the preceding text only). @xref{Sticky
1847 @defopt indent-tabs-mode
1848 @comment !!SourceFile indent.c
1849 If this variable is non-@code{nil}, indentation functions can insert
1850 tabs as well as spaces. Otherwise, they insert only spaces. Setting
1851 this variable automatically makes it buffer-local in the current buffer.
1854 @node Mode-Specific Indent
1855 @subsection Indentation Controlled by Major Mode
1857 An important function of each major mode is to customize the @key{TAB}
1858 key to indent properly for the language being edited. This section
1859 describes the mechanism of the @key{TAB} key and how to control it.
1860 The functions in this section return unpredictable values.
1862 @defvar indent-line-function
1863 This variable's value is the function to be used by @key{TAB} (and
1864 various commands) to indent the current line. The command
1865 @code{indent-according-to-mode} does no more than call this function.
1867 In Lisp mode, the value is the symbol @code{lisp-indent-line}; in C
1868 mode, @code{c-indent-line}; in Fortran mode, @code{fortran-indent-line}.
1869 In Fundamental mode, Text mode, and many other modes with no standard
1870 for indentation, the value is @code{indent-to-left-margin} (which is the
1874 @deffn Command indent-according-to-mode
1875 This command calls the function in @code{indent-line-function} to
1876 indent the current line in a way appropriate for the current major mode.
1879 @deffn Command indent-for-tab-command
1880 This command calls the function in @code{indent-line-function} to indent
1881 the current line; however, if that function is
1882 @code{indent-to-left-margin}, @code{insert-tab} is called instead. (That
1883 is a trivial command that inserts a tab character.)
1886 @deffn Command newline-and-indent
1887 @comment !!SourceFile simple.el
1888 This function inserts a newline, then indents the new line (the one
1889 following the newline just inserted) according to the major mode.
1891 It does indentation by calling the current @code{indent-line-function}.
1892 In programming language modes, this is the same thing @key{TAB} does,
1893 but in some text modes, where @key{TAB} inserts a tab,
1894 @code{newline-and-indent} indents to the column specified by
1898 @deffn Command reindent-then-newline-and-indent
1899 @comment !!SourceFile simple.el
1900 This command reindents the current line, inserts a newline at point,
1901 and then indents the new line (the one following the newline just
1904 This command does indentation on both lines according to the current
1905 major mode, by calling the current value of @code{indent-line-function}.
1906 In programming language modes, this is the same thing @key{TAB} does,
1907 but in some text modes, where @key{TAB} inserts a tab,
1908 @code{reindent-then-newline-and-indent} indents to the column specified
1909 by @code{left-margin}.
1913 @subsection Indenting an Entire Region
1915 This section describes commands that indent all the lines in the
1916 region. They return unpredictable values.
1918 @deffn Command indent-region start end to-column
1919 This command indents each nonblank line starting between @var{start}
1920 (inclusive) and @var{end} (exclusive). If @var{to-column} is
1921 @code{nil}, @code{indent-region} indents each nonblank line by calling
1922 the current mode's indentation function, the value of
1923 @code{indent-line-function}.
1925 If @var{to-column} is non-@code{nil}, it should be an integer
1926 specifying the number of columns of indentation; then this function
1927 gives each line exactly that much indentation, by either adding or
1928 deleting whitespace.
1930 If there is a fill prefix, @code{indent-region} indents each line
1931 by making it start with the fill prefix.
1934 @defvar indent-region-function
1935 The value of this variable is a function that can be used by
1936 @code{indent-region} as a short cut. It should take two arguments, the
1937 start and end of the region. You should design the function so
1938 that it will produce the same results as indenting the lines of the
1939 region one by one, but presumably faster.
1941 If the value is @code{nil}, there is no short cut, and
1942 @code{indent-region} actually works line by line.
1944 A short-cut function is useful in modes such as C mode and Lisp mode,
1945 where the @code{indent-line-function} must scan from the beginning of
1946 the function definition: applying it to each line would be quadratic in
1947 time. The short cut can update the scan information as it moves through
1948 the lines indenting them; this takes linear time. In a mode where
1949 indenting a line individually is fast, there is no need for a short cut.
1951 @code{indent-region} with a non-@code{nil} argument @var{to-column} has
1952 a different meaning and does not use this variable.
1955 @deffn Command indent-rigidly start end count
1956 @comment !!SourceFile indent.el
1957 This command indents all lines starting between @var{start}
1958 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
1959 This ``preserves the shape'' of the affected region, moving it as a
1960 rigid unit. Consequently, this command is useful not only for indenting
1961 regions of unindented text, but also for indenting regions of formatted
1964 For example, if @var{count} is 3, this command adds 3 columns of
1965 indentation to each of the lines beginning in the region specified.
1967 In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses
1968 @code{indent-rigidly} to indent the text copied from the message being
1972 @defun indent-code-rigidly start end columns &optional nochange-regexp
1973 This is like @code{indent-rigidly}, except that it doesn't alter lines
1974 that start within strings or comments.
1976 In addition, it doesn't alter a line if @var{nochange-regexp} matches at
1977 the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
1980 @node Relative Indent
1981 @subsection Indentation Relative to Previous Lines
1983 This section describes two commands that indent the current line
1984 based on the contents of previous lines.
1986 @deffn Command indent-relative &optional unindented-ok
1987 This command inserts whitespace at point, extending to the same
1988 column as the next @dfn{indent point} of the previous nonblank line. An
1989 indent point is a non-whitespace character following whitespace. The
1990 next indent point is the first one at a column greater than the current
1991 column of point. For example, if point is underneath and to the left of
1992 the first non-blank character of a line of text, it moves to that column
1993 by inserting whitespace.
1995 If the previous nonblank line has no next indent point (i.e., none at a
1996 great enough column position), @code{indent-relative} either does
1997 nothing (if @var{unindented-ok} is non-@code{nil}) or calls
1998 @code{tab-to-tab-stop}. Thus, if point is underneath and to the right
1999 of the last column of a short line of text, this command ordinarily
2000 moves point to the next tab stop by inserting whitespace.
2002 The return value of @code{indent-relative} is unpredictable.
2004 In the following example, point is at the beginning of the second
2009 This line is indented twelve spaces.
2010 @point{}The quick brown fox jumped.
2015 Evaluation of the expression @code{(indent-relative nil)} produces the
2020 This line is indented twelve spaces.
2021 @point{}The quick brown fox jumped.
2025 In this next example, point is between the @samp{m} and @samp{p} of
2030 This line is indented twelve spaces.
2031 The quick brown fox jum@point{}ped.
2036 Evaluation of the expression @code{(indent-relative nil)} produces the
2041 This line is indented twelve spaces.
2042 The quick brown fox jum @point{}ped.
2047 @deffn Command indent-relative-maybe
2048 @comment !!SourceFile indent.el
2049 This command indents the current line like the previous nonblank line,
2050 by calling @code{indent-relative} with @code{t} as the
2051 @var{unindented-ok} argument. The return value is unpredictable.
2053 If the previous nonblank line has no indent points beyond the current
2054 column, this command does nothing.
2058 @comment node-name, next, previous, up
2059 @subsection Adjustable ``Tab Stops''
2060 @cindex tabs stops for indentation
2062 This section explains the mechanism for user-specified ``tab stops''
2063 and the mechanisms that use and set them. The name ``tab stops'' is
2064 used because the feature is similar to that of the tab stops on a
2065 typewriter. The feature works by inserting an appropriate number of
2066 spaces and tab characters to reach the next tab stop column; it does not
2067 affect the display of tab characters in the buffer (@pxref{Usual
2068 Display}). Note that the @key{TAB} character as input uses this tab
2069 stop feature only in a few major modes, such as Text mode.
2071 @deffn Command tab-to-tab-stop
2072 This command inserts spaces or tabs before point, up to the next tab
2073 stop column defined by @code{tab-stop-list}. It searches the list for
2074 an element greater than the current column number, and uses that element
2075 as the column to indent to. It does nothing if no such element is
2079 @defopt tab-stop-list
2080 This variable is the list of tab stop columns used by
2081 @code{tab-to-tab-stops}. The elements should be integers in increasing
2082 order. The tab stop columns need not be evenly spaced.
2084 Use @kbd{M-x edit-tab-stops} to edit the location of tab stops
2088 @node Motion by Indent
2089 @subsection Indentation-Based Motion Commands
2091 These commands, primarily for interactive use, act based on the
2092 indentation in the text.
2094 @deffn Command back-to-indentation
2095 @comment !!SourceFile simple.el
2096 This command moves point to the first non-whitespace character in the
2097 current line (which is the line in which point is located). It returns
2101 @deffn Command backward-to-indentation arg
2102 @comment !!SourceFile simple.el
2103 This command moves point backward @var{arg} lines and then to the
2104 first nonblank character on that line. It returns @code{nil}.
2107 @deffn Command forward-to-indentation arg
2108 @comment !!SourceFile simple.el
2109 This command moves point forward @var{arg} lines and then to the first
2110 nonblank character on that line. It returns @code{nil}.
2114 @comment node-name, next, previous, up
2115 @section Case Changes
2116 @cindex case conversion in buffers
2118 The case change commands described here work on text in the current
2119 buffer. @xref{Case Conversion}, for case conversion functions that work
2120 on strings and characters. @xref{Case Tables}, for how to customize
2121 which characters are upper or lower case and how to convert them.
2123 @deffn Command capitalize-region start end
2124 This function capitalizes all words in the region defined by
2125 @var{start} and @var{end}. To capitalize means to convert each word's
2126 first character to upper case and convert the rest of each word to lower
2127 case. The function returns @code{nil}.
2129 If one end of the region is in the middle of a word, the part of the
2130 word within the region is treated as an entire word.
2132 When @code{capitalize-region} is called interactively, @var{start} and
2133 @var{end} are point and the mark, with the smallest first.
2137 ---------- Buffer: foo ----------
2138 This is the contents of the 5th foo.
2139 ---------- Buffer: foo ----------
2143 (capitalize-region 1 44)
2146 ---------- Buffer: foo ----------
2147 This Is The Contents Of The 5th Foo.
2148 ---------- Buffer: foo ----------
2153 @deffn Command downcase-region start end
2154 This function converts all of the letters in the region defined by
2155 @var{start} and @var{end} to lower case. The function returns
2158 When @code{downcase-region} is called interactively, @var{start} and
2159 @var{end} are point and the mark, with the smallest first.
2162 @deffn Command upcase-region start end
2163 This function converts all of the letters in the region defined by
2164 @var{start} and @var{end} to upper case. The function returns
2167 When @code{upcase-region} is called interactively, @var{start} and
2168 @var{end} are point and the mark, with the smallest first.
2171 @deffn Command capitalize-word count
2172 This function capitalizes @var{count} words after point, moving point
2173 over as it does. To capitalize means to convert each word's first
2174 character to upper case and convert the rest of each word to lower case.
2175 If @var{count} is negative, the function capitalizes the
2176 @minus{}@var{count} previous words but does not move point. The value
2179 If point is in the middle of a word, the part of the word before point
2180 is ignored when moving forward. The rest is treated as an entire word.
2182 When @code{capitalize-word} is called interactively, @var{count} is
2183 set to the numeric prefix argument.
2186 @deffn Command downcase-word count
2187 This function converts the @var{count} words after point to all lower
2188 case, moving point over as it does. If @var{count} is negative, it
2189 converts the @minus{}@var{count} previous words but does not move point.
2190 The value is @code{nil}.
2192 When @code{downcase-word} is called interactively, @var{count} is set
2193 to the numeric prefix argument.
2196 @deffn Command upcase-word count
2197 This function converts the @var{count} words after point to all upper
2198 case, moving point over as it does. If @var{count} is negative, it
2199 converts the @minus{}@var{count} previous words but does not move point.
2200 The value is @code{nil}.
2202 When @code{upcase-word} is called interactively, @var{count} is set to
2203 the numeric prefix argument.
2206 @node Text Properties
2207 @section Text Properties
2208 @cindex text properties
2209 @cindex attributes of text
2210 @cindex properties of text
2212 Each character position in a buffer or a string can have a @dfn{text
2213 property list}, much like the property list of a symbol (@pxref{Property
2214 Lists}). The properties belong to a particular character at a
2215 particular place, such as, the letter @samp{T} at the beginning of this
2216 sentence or the first @samp{o} in @samp{foo}---if the same character
2217 occurs in two different places, the two occurrences generally have
2218 different properties.
2220 Each property has a name and a value. Both of these can be any Lisp
2221 object, but the name is normally a symbol. The usual way to access the
2222 property list is to specify a name and ask what value corresponds to it.
2224 If a character has a @code{category} property, we call it the
2225 @dfn{category} of the character. It should be a symbol. The properties
2226 of the symbol serve as defaults for the properties of the character.
2228 Copying text between strings and buffers preserves the properties
2229 along with the characters; this includes such diverse functions as
2230 @code{substring}, @code{insert}, and @code{buffer-substring}.
2233 * Examining Properties:: Looking at the properties of one character.
2234 * Changing Properties:: Setting the properties of a range of text.
2235 * Property Search:: Searching for where a property changes value.
2236 * Special Properties:: Particular properties with special meanings.
2237 * Format Properties:: Properties for representing formatting of text.
2238 * Sticky Properties:: How inserted text gets properties from
2240 * Saving Properties:: Saving text properties in files, and reading
2242 * Lazy Properties:: Computing text properties in a lazy fashion
2243 only when text is examined.
2244 * Clickable Text:: Using text properties to make regions of text
2245 do something when you click on them.
2246 * Not Intervals:: Why text properties do not use
2247 Lisp-visible text intervals.
2250 @node Examining Properties
2251 @subsection Examining Text Properties
2253 The simplest way to examine text properties is to ask for the value of
2254 a particular property of a particular character. For that, use
2255 @code{get-text-property}. Use @code{text-properties-at} to get the
2256 entire property list of a character. @xref{Property Search}, for
2257 functions to examine the properties of a number of characters at once.
2259 These functions handle both strings and buffers. Keep in mind that
2260 positions in a string start from 0, whereas positions in a buffer start
2263 @defun get-text-property pos prop &optional object
2264 This function returns the value of the @var{prop} property of the
2265 character after position @var{pos} in @var{object} (a buffer or
2266 string). The argument @var{object} is optional and defaults to the
2269 If there is no @var{prop} property strictly speaking, but the character
2270 has a category that is a symbol, then @code{get-text-property} returns
2271 the @var{prop} property of that symbol.
2274 @defun get-char-property pos prop &optional object
2275 This function is like @code{get-text-property}, except that it checks
2276 overlays first and then text properties. @xref{Overlays}.
2278 The argument @var{object} may be a string, a buffer, or a window. If it
2279 is a window, then the buffer displayed in that window is used for text
2280 properties and overlays, but only the overlays active for that window
2281 are considered. If @var{object} is a buffer, then all overlays in that
2282 buffer are considered, as well as text properties. If @var{object} is a
2283 string, only text properties are considered, since strings never have
2287 @defun text-properties-at position &optional object
2288 This function returns the entire property list of the character at
2289 @var{position} in the string or buffer @var{object}. If @var{object} is
2290 @code{nil}, it defaults to the current buffer.
2293 @defvar default-text-properties
2294 This variable holds a property list giving default values for text
2295 properties. Whenever a character does not specify a value for a
2296 property, neither directly nor through a category symbol, the value
2297 stored in this list is used instead. Here is an example:
2300 (setq default-text-properties '(foo 69))
2301 ;; @r{Make sure character 1 has no properties of its own.}
2302 (set-text-properties 1 2 nil)
2303 ;; @r{What we get, when we ask, is the default value.}
2304 (get-text-property 1 'foo)
2309 @node Changing Properties
2310 @subsection Changing Text Properties
2312 The primitives for changing properties apply to a specified range of
2313 text in a buffer or string. The function @code{set-text-properties}
2314 (see end of section) sets the entire property list of the text in that
2315 range; more often, it is useful to add, change, or delete just certain
2316 properties specified by name.
2318 Since text properties are considered part of the contents of the
2319 buffer (or string), and can affect how a buffer looks on the screen, any
2320 change in buffer text properties mark the buffer as modified. Buffer
2321 text property changes are undoable also (@pxref{Undo}).
2323 @defun put-text-property start end prop value &optional object
2324 This function sets the @var{prop} property to @var{value} for the text
2325 between @var{start} and @var{end} in the string or buffer @var{object}.
2326 If @var{object} is @code{nil}, it defaults to the current buffer.
2329 @defun add-text-properties start end props &optional object
2330 This function adds or overrides text properties for the text between
2331 @var{start} and @var{end} in the string or buffer @var{object}. If
2332 @var{object} is @code{nil}, it defaults to the current buffer.
2334 The argument @var{props} specifies which properties to add. It should
2335 have the form of a property list (@pxref{Property Lists}): a list whose
2336 elements include the property names followed alternately by the
2337 corresponding values.
2339 The return value is @code{t} if the function actually changed some
2340 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2341 its values agree with those in the text).
2343 For example, here is how to set the @code{comment} and @code{face}
2344 properties of a range of text:
2347 (add-text-properties @var{start} @var{end}
2348 '(comment t face highlight))
2352 @defun remove-text-properties start end props &optional object
2353 This function deletes specified text properties from the text between
2354 @var{start} and @var{end} in the string or buffer @var{object}. If
2355 @var{object} is @code{nil}, it defaults to the current buffer.
2357 The argument @var{props} specifies which properties to delete. It
2358 should have the form of a property list (@pxref{Property Lists}): a list
2359 whose elements are property names alternating with corresponding values.
2360 But only the names matter---the values that accompany them are ignored.
2361 For example, here's how to remove the @code{face} property.
2364 (remove-text-properties @var{start} @var{end} '(face nil))
2367 The return value is @code{t} if the function actually changed some
2368 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2369 if no character in the specified text had any of those properties).
2371 To remove all text properties from certain text, use
2372 @code{set-text-properties} and specify @code{nil} for the new property
2376 @defun set-text-properties start end props &optional object
2377 This function completely replaces the text property list for the text
2378 between @var{start} and @var{end} in the string or buffer @var{object}.
2379 If @var{object} is @code{nil}, it defaults to the current buffer.
2381 The argument @var{props} is the new property list. It should be a list
2382 whose elements are property names alternating with corresponding values.
2384 After @code{set-text-properties} returns, all the characters in the
2385 specified range have identical properties.
2387 If @var{props} is @code{nil}, the effect is to get rid of all properties
2388 from the specified range of text. Here's an example:
2391 (set-text-properties @var{start} @var{end} nil)
2395 See also the function @code{buffer-substring-no-properties}
2396 (@pxref{Buffer Contents}) which copies text from the buffer
2397 but does not copy its properties.
2399 @node Property Search
2400 @subsection Text Property Search Functions
2402 In typical use of text properties, most of the time several or many
2403 consecutive characters have the same value for a property. Rather than
2404 writing your programs to examine characters one by one, it is much
2405 faster to process chunks of text that have the same property value.
2407 Here are functions you can use to do this. They use @code{eq} for
2408 comparing property values. In all cases, @var{object} defaults to the
2411 For high performance, it's very important to use the @var{limit}
2412 argument to these functions, especially the ones that search for a
2413 single property---otherwise, they may spend a long time scanning to the
2414 end of the buffer, if the property you are interested in does not change.
2416 These functions do not move point; instead, they return a position (or
2417 @code{nil}). Remember that a position is always between two characters;
2418 the position returned by these functions is between two characters with
2419 different properties.
2421 @defun next-property-change pos &optional object limit
2422 The function scans the text forward from position @var{pos} in the
2423 string or buffer @var{object} till it finds a change in some text
2424 property, then returns the position of the change. In other words, it
2425 returns the position of the first character beyond @var{pos} whose
2426 properties are not identical to those of the character just after
2429 If @var{limit} is non-@code{nil}, then the scan ends at position
2430 @var{limit}. If there is no property change before that point,
2431 @code{next-property-change} returns @var{limit}.
2433 The value is @code{nil} if the properties remain unchanged all the way
2434 to the end of @var{object} and @var{limit} is @code{nil}. If the value
2435 is non-@code{nil}, it is a position greater than or equal to @var{pos}.
2436 The value equals @var{pos} only when @var{limit} equals @var{pos}.
2438 Here is an example of how to scan the buffer by chunks of text within
2439 which all properties are constant:
2443 (let ((plist (text-properties-at (point)))
2445 (or (next-property-change (point) (current-buffer))
2447 @r{Process text from point to @var{next-change}@dots{}}
2448 (goto-char next-change)))
2452 @defun next-single-property-change pos prop &optional object limit
2453 The function scans the text forward from position @var{pos} in the
2454 string or buffer @var{object} till it finds a change in the @var{prop}
2455 property, then returns the position of the change. In other words, it
2456 returns the position of the first character beyond @var{pos} whose
2457 @var{prop} property differs from that of the character just after
2460 If @var{limit} is non-@code{nil}, then the scan ends at position
2461 @var{limit}. If there is no property change before that point,
2462 @code{next-single-property-change} returns @var{limit}.
2464 The value is @code{nil} if the property remains unchanged all the way to
2465 the end of @var{object} and @var{limit} is @code{nil}. If the value is
2466 non-@code{nil}, it is a position greater than or equal to @var{pos}; it
2467 equals @var{pos} only if @var{limit} equals @var{pos}.
2470 @defun previous-property-change pos &optional object limit
2471 This is like @code{next-property-change}, but scans back from @var{pos}
2472 instead of forward. If the value is non-@code{nil}, it is a position
2473 less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
2477 @defun previous-single-property-change pos prop &optional object limit
2478 This is like @code{next-single-property-change}, but scans back from
2479 @var{pos} instead of forward. If the value is non-@code{nil}, it is a
2480 position less than or equal to @var{pos}; it equals @var{pos} only if
2481 @var{limit} equals @var{pos}.
2484 @defun next-char-property-change position &optional limit
2485 @tindex next-char-property-change
2486 This is like @code{next-property-change} except that it considers
2487 overlay properties as well as text properties. There is no @var{object}
2488 operand because this function operates only on the current buffer. It
2489 returns the next address at which either kind of property changes.
2492 @defun previous-char-property-change position &optional limit
2493 @tindex previous-char-property-change
2494 This is like @code{next-char-property-change}, but scans back from
2495 @var{position} instead of forward.
2498 @defun text-property-any start end prop value &optional object
2499 This function returns non-@code{nil} if at least one character between
2500 @var{start} and @var{end} has a property @var{prop} whose value is
2501 @var{value}. More precisely, it returns the position of the first such
2502 character. Otherwise, it returns @code{nil}.
2504 The optional fifth argument, @var{object}, specifies the string or
2505 buffer to scan. Positions are relative to @var{object}. The default
2506 for @var{object} is the current buffer.
2509 @defun text-property-not-all start end prop value &optional object
2510 This function returns non-@code{nil} if at least one character between
2511 @var{start} and @var{end} does not have a property @var{prop} with value
2512 @var{value}. More precisely, it returns the position of the first such
2513 character. Otherwise, it returns @code{nil}.
2515 The optional fifth argument, @var{object}, specifies the string or
2516 buffer to scan. Positions are relative to @var{object}. The default
2517 for @var{object} is the current buffer.
2520 @node Special Properties
2521 @subsection Properties with Special Meanings
2523 Here is a table of text property names that have special built-in
2524 meanings. The following sections list a few additional special property
2525 names that control filling and property inheritance. All other names
2526 have no standard meaning, and you can use them as you like.
2529 @cindex category of text character
2530 @kindex category @r{(text property)}
2532 If a character has a @code{category} property, we call it the
2533 @dfn{category} of the character. It should be a symbol. The properties
2534 of the symbol serve as defaults for the properties of the character.
2537 @cindex face codes of text
2538 @kindex face @r{(text property)}
2539 You can use the property @code{face} to control the font and color of
2540 text. Its value is a face name or a list of face names. @xref{Faces},
2541 for more information.
2543 If the property value is a list, elements may also have the form
2544 @code{(foreground-color . @var{color-name})} or @code{(background-color
2545 . @var{color-name})}. These elements specify just the foreground color
2546 or just the background color; therefore, there is no need to create a
2547 face for each color that you want to use.
2549 @xref{Font Lock Mode}, for information on how to update @code{face}
2550 properties automatically based on the contents of the text.
2553 @kindex mouse-face @r{(text property)}
2554 The property @code{mouse-face} is used instead of @code{face} when the
2555 mouse is on or near the character. For this purpose, ``near'' means
2556 that all text between the character and where the mouse is have the same
2557 @code{mouse-face} property value.
2560 @cindex keymap of character
2561 @kindex local-map @r{(text property)}
2562 You can specify a different keymap for some of the text in a buffer by
2563 means of the @code{local-map} property. The property's value for the
2564 character after point, if non-@code{nil}, is used for key lookup instead
2565 of the buffer's local map. If the property value is a symbol, the
2566 symbol's function definition is used as the keymap. @xref{Active
2570 The @code{syntax-table} property overrides what the syntax table says
2571 about this particular character. @xref{Syntax Properties}.
2574 @cindex read-only character
2575 @kindex read-only @r{(text property)}
2576 If a character has the property @code{read-only}, then modifying that
2577 character is not allowed. Any command that would do so gets an error.
2579 Insertion next to a read-only character is an error if inserting
2580 ordinary text there would inherit the @code{read-only} property due to
2581 stickiness. Thus, you can control permission to insert next to
2582 read-only text by controlling the stickiness. @xref{Sticky Properties}.
2584 Since changing properties counts as modifying the buffer, it is not
2585 possible to remove a @code{read-only} property unless you know the
2586 special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
2587 and then remove the property. @xref{Read Only Buffers}.
2590 @kindex invisible @r{(text property)}
2591 A non-@code{nil} @code{invisible} property can make a character invisible
2592 on the screen. @xref{Invisible Text}, for details.
2595 @kindex intangible @r{(text property)}
2596 If a group of consecutive characters have equal and non-@code{nil}
2597 @code{intangible} properties, then you cannot place point between them.
2598 If you try to move point forward into the group, point actually moves to
2599 the end of the group. If you try to move point backward into the group,
2600 point actually moves to the start of the group.
2602 When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
2603 the @code{intangible} property is ignored.
2605 @item modification-hooks
2606 @cindex change hooks for a character
2607 @cindex hooks for changing a character
2608 @kindex modification-hooks @r{(text property)}
2609 If a character has the property @code{modification-hooks}, then its
2610 value should be a list of functions; modifying that character calls all
2611 of those functions. Each function receives two arguments: the beginning
2612 and end of the part of the buffer being modified. Note that if a
2613 particular modification hook function appears on several characters
2614 being modified by a single primitive, you can't predict how many times
2615 the function will be called.
2617 @item insert-in-front-hooks
2618 @itemx insert-behind-hooks
2619 @kindex insert-in-front-hooks @r{(text property)}
2620 @kindex insert-behind-hooks @r{(text property)}
2621 The operation of inserting text in a buffer also calls the functions
2622 listed in the @code{insert-in-front-hooks} property of the following
2623 character and in the @code{insert-behind-hooks} property of the
2624 preceding character. These functions receive two arguments, the
2625 beginning and end of the inserted text. The functions are called
2626 @emph{after} the actual insertion takes place.
2628 See also @ref{Change Hooks}, for other hooks that are called
2629 when you change text in a buffer.
2633 @cindex hooks for motion of point
2634 @kindex point-entered @r{(text property)}
2635 @kindex point-left @r{(text property)}
2636 The special properties @code{point-entered} and @code{point-left}
2637 record hook functions that report motion of point. Each time point
2638 moves, Emacs compares these two property values:
2642 the @code{point-left} property of the character after the old location,
2645 the @code{point-entered} property of the character after the new
2650 If these two values differ, each of them is called (if not @code{nil})
2651 with two arguments: the old value of point, and the new one.
2653 The same comparison is made for the characters before the old and new
2654 locations. The result may be to execute two @code{point-left} functions
2655 (which may be the same function) and/or two @code{point-entered}
2656 functions (which may be the same function). In any case, all the
2657 @code{point-left} functions are called first, followed by all the
2658 @code{point-entered} functions.
2660 It is possible using @code{char-after} to examine characters at various
2661 positions without moving point to those positions. Only an actual
2662 change in the value of point runs these hook functions.
2665 @defvar inhibit-point-motion-hooks
2666 When this variable is non-@code{nil}, @code{point-left} and
2667 @code{point-entered} hooks are not run, and the @code{intangible}
2668 property has no effect. Do not set this variable globally; bind it with
2672 @node Format Properties
2673 @subsection Formatted Text Properties
2675 These text properties affect the behavior of the fill commands. They
2676 are used for representing formatted text. @xref{Filling}, and
2681 If a newline character has this property, it is a ``hard'' newline.
2682 The fill commands do not alter hard newlines and do not move words
2683 across them. However, this property takes effect only if the variable
2684 @code{use-hard-newlines} is non-@code{nil}.
2687 This property specifies an extra right margin for filling this part of the
2691 This property specifies an extra left margin for filling this part of the
2695 This property specifies the style of justification for filling this part
2699 @node Sticky Properties
2700 @subsection Stickiness of Text Properties
2701 @cindex sticky text properties
2702 @cindex inheritance of text properties
2704 Self-inserting characters normally take on the same properties as the
2705 preceding character. This is called @dfn{inheritance} of properties.
2707 In a Lisp program, you can do insertion with inheritance or without,
2708 depending on your choice of insertion primitive. The ordinary text
2709 insertion functions such as @code{insert} do not inherit any properties.
2710 They insert text with precisely the properties of the string being
2711 inserted, and no others. This is correct for programs that copy text
2712 from one context to another---for example, into or out of the kill ring.
2713 To insert with inheritance, use the special primitives described in this
2714 section. Self-inserting characters inherit properties because they work
2715 using these primitives.
2717 When you do insertion with inheritance, @emph{which} properties are
2718 inherited depends on two specific properties: @code{front-sticky} and
2719 @code{rear-nonsticky}.
2721 Insertion after a character inherits those of its properties that are
2722 @dfn{rear-sticky}. Insertion before a character inherits those of its
2723 properties that are @dfn{front-sticky}. By default, a text property is
2724 rear-sticky but not front-sticky. Thus, the default is to inherit all
2725 the properties of the preceding character, and nothing from the
2726 following character. You can request different behavior by specifying
2727 the stickiness of certain properties.
2729 If a character's @code{front-sticky} property is @code{t}, then all
2730 its properties are front-sticky. If the @code{front-sticky} property is
2731 a list, then the sticky properties of the character are those whose
2732 names are in the list. For example, if a character has a
2733 @code{front-sticky} property whose value is @code{(face read-only)},
2734 then insertion before the character can inherit its @code{face} property
2735 and its @code{read-only} property, but no others.
2737 The @code{rear-nonsticky} works the opposite way. Every property is
2738 rear-sticky by default, so the @code{rear-nonsticky} property says which
2739 properties are @emph{not} rear-sticky. If a character's
2740 @code{rear-nonsticky} property is @code{t}, then none of its properties
2741 are rear-sticky. If the @code{rear-nonsticky} property is a list,
2742 properties are rear-sticky @emph{unless} their names are in the list.
2744 When you insert text with inheritance, it inherits all the rear-sticky
2745 properties of the preceding character, and all the front-sticky
2746 properties of the following character. The previous character's
2747 properties take precedence when both sides offer different sticky values
2748 for the same property.
2750 Here are the functions that insert text with inheritance of properties:
2752 @defun insert-and-inherit &rest strings
2753 Insert the strings @var{strings}, just like the function @code{insert},
2754 but inherit any sticky properties from the adjoining text.
2757 @defun insert-before-markers-and-inherit &rest strings
2758 Insert the strings @var{strings}, just like the function
2759 @code{insert-before-markers}, but inherit any sticky properties from the
2763 @xref{Insertion}, for the ordinary insertion functions which do not
2766 @node Saving Properties
2767 @subsection Saving Text Properties in Files
2768 @cindex text properties in files
2769 @cindex saving text properties
2771 You can save text properties in files (along with the text itself),
2772 and restore the same text properties when visiting or inserting the
2773 files, using these two hooks:
2775 @defvar write-region-annotate-functions
2776 This variable's value is a list of functions for @code{write-region} to
2777 run to encode text properties in some fashion as annotations to the text
2778 being written in the file. @xref{Writing to Files}.
2780 Each function in the list is called with two arguments: the start and
2781 end of the region to be written. These functions should not alter the
2782 contents of the buffer. Instead, they should return lists indicating
2783 annotations to write in the file in addition to the text in the
2786 Each function should return a list of elements of the form
2787 @code{(@var{position} . @var{string})}, where @var{position} is an
2788 integer specifying the relative position within the text to be written,
2789 and @var{string} is the annotation to add there.
2791 Each list returned by one of these functions must be already sorted in
2792 increasing order by @var{position}. If there is more than one function,
2793 @code{write-region} merges the lists destructively into one sorted list.
2795 When @code{write-region} actually writes the text from the buffer to the
2796 file, it intermixes the specified annotations at the corresponding
2797 positions. All this takes place without modifying the buffer.
2800 @defvar after-insert-file-functions
2801 This variable holds a list of functions for @code{insert-file-contents}
2802 to call after inserting a file's contents. These functions should scan
2803 the inserted text for annotations, and convert them to the text
2804 properties they stand for.
2806 Each function receives one argument, the length of the inserted text;
2807 point indicates the start of that text. The function should scan that
2808 text for annotations, delete them, and create the text properties that
2809 the annotations specify. The function should return the updated length
2810 of the inserted text, as it stands after those changes. The value
2811 returned by one function becomes the argument to the next function.
2813 These functions should always return with point at the beginning of
2816 The intended use of @code{after-insert-file-functions} is for converting
2817 some sort of textual annotations into actual text properties. But other
2818 uses may be possible.
2821 We invite users to write Lisp programs to store and retrieve text
2822 properties in files, using these hooks, and thus to experiment with
2823 various data formats and find good ones. Eventually we hope users
2824 will produce good, general extensions we can install in Emacs.
2826 We suggest not trying to handle arbitrary Lisp objects as text property
2827 names or values---because a program that general is probably difficult
2828 to write, and slow. Instead, choose a set of possible data types that
2829 are reasonably flexible, and not too hard to encode.
2831 @xref{Format Conversion}, for a related feature.
2833 @c ??? In next edition, merge this info Format Conversion.
2835 @node Lazy Properties
2836 @subsection Lazy Computation of Text Properties
2838 Instead of computing text properties for all the text in the buffer,
2839 you can arrange to compute the text properties for parts of the text
2840 when and if something depends on them.
2842 The primitive that extracts text from the buffer along with its
2843 properties is @code{buffer-substring}. Before examining the properties,
2844 this function runs the abnormal hook @code{buffer-access-fontify-functions}.
2846 @defvar buffer-access-fontify-functions
2847 This variable holds a list of functions for computing text properties.
2848 Before @code{buffer-substring} copies the text and text properties for a
2849 portion of the buffer, it calls all the functions in this list. Each of
2850 the functions receives two arguments that specify the range of the
2851 buffer being accessed. (The buffer itself is always the current
2855 The function @code{buffer-substring-no-properties} does not call these
2856 functions, since it ignores text properties anyway.
2858 In order to prevent the hook functions from being called more than
2859 once for the same part of the buffer, you can use the variable
2860 @code{buffer-access-fontified-property}.
2862 @defvar buffer-access-fontified-property
2863 If this value's variable is non-@code{nil}, it is a symbol which is used
2864 as a text property name. A non-@code{nil} value for that text property
2865 means, ``the other text properties for this character have already been
2868 If all the characters in the range specified for @code{buffer-substring}
2869 have a non-@code{nil} value for this property, @code{buffer-substring}
2870 does not call the @code{buffer-access-fontify-functions} functions. It
2871 assumes these characters already have the right text properties, and
2872 just copies the properties they already have.
2874 The normal way to use this feature is that the
2875 @code{buffer-access-fontify-functions} functions add this property, as
2876 well as others, to the characters they operate on. That way, they avoid
2877 being called over and over for the same text.
2880 @node Clickable Text
2881 @subsection Defining Clickable Text
2882 @cindex clickable text
2884 There are two ways to set up @dfn{clickable text} in a buffer.
2885 There are typically two parts of this: to make the text highlight
2886 when the mouse is over it, and to make a mouse button do something
2887 when you click it on that part of the text.
2889 Highlighting is done with the @code{mouse-face} text property.
2890 Here is an example of how Dired does it:
2894 (if (dired-move-to-filename)
2895 (put-text-property (point)
2897 (dired-move-to-end-of-filename)
2899 'mouse-face 'highlight))
2904 The first two arguments to @code{put-text-property} specify the
2905 beginning and end of the text.
2907 The usual way to make the mouse do something when you click it
2908 on this text is to define @code{mouse-2} in the major mode's
2909 keymap. The job of checking whether the click was on clickable text
2910 is done by the command definition. Here is how Dired does it:
2913 (defun dired-mouse-find-file-other-window (event)
2914 "In dired, visit the file or directory name you click on."
2918 (set-buffer (window-buffer (posn-window (event-end event))))
2920 (goto-char (posn-point (event-end event)))
2921 (setq file (dired-get-filename))))
2922 (select-window (posn-window (event-end event)))
2923 (find-file-other-window (file-name-sans-versions file t))))
2927 The reason for the outer @code{save-excursion} construct is to avoid
2928 changing the current buffer; the reason for the inner one is to avoid
2929 permanently altering point in the buffer you click on. In this case,
2930 Dired uses the function @code{dired-get-filename} to determine which
2931 file to visit, based on the position found in the event.
2933 Instead of defining a mouse command for the major mode, you can define
2934 a key binding for the clickable text itself, using the @code{local-map}
2938 (let ((map (make-sparse-keymap)))
2939 (define-key-binding map [mouse-2] 'operate-this-button)
2940 (put-text-property (point)
2942 (dired-move-to-end-of-filename)
2948 This method makes it possible to define different commands for various
2949 clickable pieces of text. Also, the major mode definition (or the
2950 global definition) remains available for the rest of the text in the
2954 @subsection Why Text Properties are not Intervals
2957 Some editors that support adding attributes to text in the buffer do
2958 so by letting the user specify ``intervals'' within the text, and adding
2959 the properties to the intervals. Those editors permit the user or the
2960 programmer to determine where individual intervals start and end. We
2961 deliberately provided a different sort of interface in Emacs Lisp to
2962 avoid certain paradoxical behavior associated with text modification.
2964 If the actual subdivision into intervals is meaningful, that means you
2965 can distinguish between a buffer that is just one interval with a
2966 certain property, and a buffer containing the same text subdivided into
2967 two intervals, both of which have that property.
2969 Suppose you take the buffer with just one interval and kill part of
2970 the text. The text remaining in the buffer is one interval, and the
2971 copy in the kill ring (and the undo list) becomes a separate interval.
2972 Then if you yank back the killed text, you get two intervals with the
2973 same properties. Thus, editing does not preserve the distinction
2974 between one interval and two.
2976 Suppose we ``fix'' this problem by coalescing the two intervals when
2977 the text is inserted. That works fine if the buffer originally was a
2978 single interval. But suppose instead that we have two adjacent
2979 intervals with the same properties, and we kill the text of one interval
2980 and yank it back. The same interval-coalescence feature that rescues
2981 the other case causes trouble in this one: after yanking, we have just
2982 one interval. One again, editing does not preserve the distinction
2983 between one interval and two.
2985 Insertion of text at the border between intervals also raises
2986 questions that have no satisfactory answer.
2988 However, it is easy to arrange for editing to behave consistently for
2989 questions of the form, ``What are the properties of this character?''
2990 So we have decided these are the only questions that make sense; we have
2991 not implemented asking questions about where intervals start or end.
2993 In practice, you can usually use the text property search functions in
2994 place of explicit interval boundaries. You can think of them as finding
2995 the boundaries of intervals, assuming that intervals are always
2996 coalesced whenever possible. @xref{Property Search}.
2998 Emacs also provides explicit intervals as a presentation feature; see
3002 @section Substituting for a Character Code
3004 The following functions replace characters within a specified region
3005 based on their character codes.
3007 @defun subst-char-in-region start end old-char new-char &optional noundo
3008 @cindex replace characters
3009 This function replaces all occurrences of the character @var{old-char}
3010 with the character @var{new-char} in the region of the current buffer
3011 defined by @var{start} and @var{end}.
3013 @cindex Outline mode
3014 @cindex undo avoidance
3015 If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
3016 not record the change for undo and does not mark the buffer as modified.
3017 This feature is used for controlling selective display (@pxref{Selective
3020 @code{subst-char-in-region} does not move point and returns
3025 ---------- Buffer: foo ----------
3026 This is the contents of the buffer before.
3027 ---------- Buffer: foo ----------
3031 (subst-char-in-region 1 20 ?i ?X)
3034 ---------- Buffer: foo ----------
3035 ThXs Xs the contents of the buffer before.
3036 ---------- Buffer: foo ----------
3041 @defun translate-region start end table
3042 This function applies a translation table to the characters in the
3043 buffer between positions @var{start} and @var{end}.
3045 The translation table @var{table} is a string; @code{(aref @var{table}
3046 @var{ochar})} gives the translated character corresponding to
3047 @var{ochar}. If the length of @var{table} is less than 256, any
3048 characters with codes larger than the length of @var{table} are not
3049 altered by the translation.
3051 The return value of @code{translate-region} is the number of
3052 characters that were actually changed by the translation. This does
3053 not count characters that were mapped into themselves in the
3061 A register is a sort of variable used in Emacs editing that can hold a
3062 variety of different kinds of values. Each register is named by a
3063 single character. All ASCII characters and their meta variants (but
3064 with the exception of @kbd{C-g}) can be used to name registers. Thus,
3065 there are 255 possible registers. A register is designated in Emacs
3066 Lisp by the character that is its name.
3068 @defvar register-alist
3069 This variable is an alist of elements of the form @code{(@var{name} .
3070 @var{contents})}. Normally, there is one element for each Emacs
3071 register that has been used.
3073 The object @var{name} is a character (an integer) identifying the
3077 The @var{contents} of a register can have several possible types:
3081 A number stands for itself. If @code{insert-register} finds a number
3082 in the register, it converts the number to decimal.
3085 A marker represents a buffer position to jump to.
3088 A string is text saved in the register.
3091 A rectangle is represented by a list of strings.
3093 @item @code{(@var{window-configuration} @var{position})}
3094 This represents a window configuration to restore in one frame, and a
3095 position to jump to in the current buffer.
3097 @item @code{(@var{frame-configuration} @var{position})}
3098 This represents a frame configuration to restore, and a position
3099 to jump to in the current buffer.
3101 @item (file @var{filename})
3102 This represents a file to visit; jumping to this value visits file
3105 @item (file-query @var{filename} @var{position})
3106 This represents a file to visit and a position in it; jumping to this
3107 value visits file @var{filename} and goes to buffer position
3108 @var{position}. Restoring this type of position asks the user for
3112 The functions in this section return unpredictable values unless
3115 @defun get-register reg
3116 This function returns the contents of the register
3117 @var{reg}, or @code{nil} if it has no contents.
3120 @defun set-register reg value
3121 This function sets the contents of register @var{reg} to @var{value}.
3122 A register can be set to any value, but the other register functions
3123 expect only certain data types. The return value is @var{value}.
3126 @deffn Command view-register reg
3127 This command displays what is contained in register @var{reg}.
3131 @deffn Command point-to-register reg
3132 This command stores both the current location of point and the current
3133 buffer in register @var{reg} as a marker.
3136 @deffn Command jump-to-register reg
3137 @deffnx Command register-to-point reg
3138 @comment !!SourceFile register.el
3139 This command restores the status recorded in register @var{reg}.
3141 If @var{reg} contains a marker, it moves point to the position stored in
3142 the marker. Since both the buffer and the location within the buffer
3143 are stored by the @code{point-to-register} function, this command can
3144 switch you to another buffer.
3146 If @var{reg} contains a window configuration or a frame configuration.
3147 @code{jump-to-register} restores that configuration.
3151 @deffn Command insert-register reg &optional beforep
3152 This command inserts contents of register @var{reg} into the current
3155 Normally, this command puts point before the inserted text, and the
3156 mark after it. However, if the optional second argument @var{beforep}
3157 is non-@code{nil}, it puts the mark before and point after.
3158 You can pass a non-@code{nil} second argument @var{beforep} to this
3159 function interactively by supplying any prefix argument.
3161 If the register contains a rectangle, then the rectangle is inserted
3162 with its upper left corner at point. This means that text is inserted
3163 in the current line and underneath it on successive lines.
3165 If the register contains something other than saved text (a string) or
3166 a rectangle (a list), currently useless things happen. This may be
3167 changed in the future.
3171 @deffn Command copy-to-register reg start end &optional delete-flag
3172 This command copies the region from @var{start} to @var{end} into
3173 register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes
3174 the region from the buffer after copying it into the register.
3177 @deffn Command prepend-to-register reg start end &optional delete-flag
3178 This command prepends the region from @var{start} to @var{end} into
3179 register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes
3180 the region from the buffer after copying it to the register.
3183 @deffn Command append-to-register reg start end &optional delete-flag
3184 This command appends the region from @var{start} to @var{end} to the
3185 text already in register @var{reg}. If @var{delete-flag} is
3186 non-@code{nil}, it deletes the region from the buffer after copying it
3190 @deffn Command copy-rectangle-to-register reg start end &optional delete-flag
3191 This command copies a rectangular region from @var{start} to @var{end}
3192 into register @var{reg}. If @var{delete-flag} is non-@code{nil}, it
3193 deletes the region from the buffer after copying it to the register.
3196 @deffn Command window-configuration-to-register reg
3197 This function stores the window configuration of the selected frame in
3201 @deffn Command frame-configuration-to-register reg
3202 This function stores the current frame configuration in register
3208 @section Transposition of Text
3210 This subroutine is used by the transposition commands.
3212 @defun transpose-regions start1 end1 start2 end2 &optional leave-markers
3213 This function exchanges two nonoverlapping portions of the buffer.
3214 Arguments @var{start1} and @var{end1} specify the bounds of one portion
3215 and arguments @var{start2} and @var{end2} specify the bounds of the
3218 Normally, @code{transpose-regions} relocates markers with the transposed
3219 text; a marker previously positioned within one of the two transposed
3220 portions moves along with that portion, thus remaining between the same
3221 two characters in their new position. However, if @var{leave-markers}
3222 is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
3223 all markers unrelocated.
3227 @section Change Hooks
3228 @cindex change hooks
3229 @cindex hooks for text changes
3231 These hook variables let you arrange to take notice of all changes in
3232 all buffers (or in a particular buffer, if you make them buffer-local).
3233 See also @ref{Special Properties}, for how to detect changes to specific
3236 The functions you use in these hooks should save and restore the match
3237 data if they do anything that uses regular expressions; otherwise, they
3238 will interfere in bizarre ways with the editing operations that call
3241 @defvar before-change-functions
3242 This variable holds a list of functions to call before any buffer
3243 modification. Each function gets two arguments, the beginning and end
3244 of the region that is about to change, represented as integers. The
3245 buffer that is about to change is always the current buffer.
3248 @defvar after-change-functions
3249 This variable holds a list of functions to call after any buffer
3250 modification. Each function receives three arguments: the beginning and
3251 end of the region just changed, and the length of the text that existed
3252 before the change. All three arguments are integers. The buffer that's
3253 about to change is always the current buffer.
3255 The length of the old text is the difference between the buffer positions
3256 before and after that text as it was before the change. As for the
3257 changed text, its length is simply the difference between the first two
3261 @defmac combine-after-change-calls body...
3262 @tindex combine-after-change-calls
3263 The macro executes @var{body} normally, but arranges to call the
3264 after-change functions just once for a series of several changes---if
3267 If a program makes several text changes in the same area of the buffer,
3268 using the macro @code{combine-after-change-calls} around that part of
3269 the program can make it run considerably faster when after-change hooks
3270 are in use. When the after-change hooks are ultimately called, the
3271 arguments specify a portion of the buffer including all of the changes
3272 made within the @code{combine-after-change-calls} body.
3274 @strong{Warning:} You must not alter the values of
3275 @code{after-change-functions} and @code{after-change-function} within
3276 the body of a @code{combine-after-change-calls} form.
3278 @strong{Note:} If the changes you combine occur in widely scattered
3279 parts of the buffer, this will still work, but it is not advisable,
3280 because it may lead to inefficient behavior for some change hook
3284 @defvar before-change-function
3285 This obsolete variable holds one function to call before any buffer
3286 modification (or @code{nil} for no function). It is called just like
3287 the functions in @code{before-change-functions}.
3290 @defvar after-change-function
3291 This obsolete variable holds one function to call after any buffer modification
3292 (or @code{nil} for no function). It is called just like the functions in
3293 @code{after-change-functions}.
3296 The four variables above are temporarily bound to @code{nil} during the
3297 time that any of these functions is running. This means that if one of
3298 these functions changes the buffer, that change won't run these
3299 functions. If you do want a hook function to make changes that run
3300 these functions, make it bind these variables back to their usual
3303 One inconvenient result of this protective feature is that you cannot
3304 have a function in @code{after-change-functions} or
3305 @code{before-change-functions} which changes the value of that variable.
3306 But that's not a real limitation. If you want those functions to change
3307 the list of functions to run, simply add one fixed function to the hook,
3308 and code that function to look in another variable for other functions
3309 to call. Here is an example:
3312 (setq my-own-after-change-functions nil)
3313 (defun indirect-after-change-function (beg end len)
3314 (let ((list my-own-after-change-functions))
3316 (funcall (car list) beg end len)
3317 (setq list (cdr list)))))
3320 (add-hooks 'after-change-functions
3321 'indirect-after-change-function)
3325 @defvar first-change-hook
3326 This variable is a normal hook that is run whenever a buffer is changed
3327 that was previously in the unmodified state.