2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000, 2001,
4 @c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/text
7 @node Text, Non-ASCII Characters, Markers, Top
11 This chapter describes the functions that deal with the text in a
12 buffer. Most examine, insert, or delete text in the current buffer,
13 often operating at point or on text adjacent to point. Many are
14 interactive. All the functions that change the text provide for undoing
15 the changes (@pxref{Undo}).
17 Many text-related functions operate on a region of text defined by two
18 buffer positions passed in arguments named @var{start} and @var{end}.
19 These arguments should be either markers (@pxref{Markers}) or numeric
20 character positions (@pxref{Positions}). The order of these arguments
21 does not matter; it is all right for @var{start} to be the end of the
22 region and @var{end} the beginning. For example, @code{(delete-region 1
23 10)} and @code{(delete-region 10 1)} are equivalent. An
24 @code{args-out-of-range} error is signaled if either @var{start} or
25 @var{end} is outside the accessible portion of the buffer. In an
26 interactive call, point and the mark are used for these arguments.
28 @cindex buffer contents
29 Throughout this chapter, ``text'' refers to the characters in the
30 buffer, together with their properties (when relevant). Keep in mind
31 that point is always between two characters, and the cursor appears on
32 the character after point.
35 * Near Point:: Examining text in the vicinity of point.
36 * Buffer Contents:: Examining text in a general fashion.
37 * Comparing Text:: Comparing substrings of buffers.
38 * Insertion:: Adding new text to a buffer.
39 * Commands for Insertion:: User-level commands to insert text.
40 * Deletion:: Removing text from a buffer.
41 * User-Level Deletion:: User-level commands to delete text.
42 * The Kill Ring:: Where removed text sometimes is saved for later use.
43 * Undo:: Undoing changes to the text of a buffer.
44 * Maintaining Undo:: How to enable and disable undo information.
45 How to control how much information is kept.
46 * Filling:: Functions for explicit filling.
47 * Margins:: How to specify margins for filling commands.
48 * Adaptive Fill:: Adaptive Fill mode chooses a fill prefix from context.
49 * Auto Filling:: How auto-fill mode is implemented to break lines.
50 * Sorting:: Functions for sorting parts of the buffer.
51 * Columns:: Computing horizontal positions, and using them.
52 * Indentation:: Functions to insert or adjust indentation.
53 * Case Changes:: Case conversion of parts of the buffer.
54 * Text Properties:: Assigning Lisp property lists to text characters.
55 * Substitution:: Replacing a given character wherever it appears.
56 * Transposition:: Swapping two portions of a buffer.
57 * Registers:: How registers are implemented. Accessing the text or
58 position stored in a register.
59 * Base 64:: Conversion to or from base 64 encoding.
60 * MD5 Checksum:: Compute the MD5 "message digest"/"checksum".
61 * Atomic Changes:: Installing several buffer changes "atomically".
62 * Change Hooks:: Supplying functions to be run when text is changed.
66 @section Examining Text Near Point
67 @cindex text near point
69 Many functions are provided to look at the characters around point.
70 Several simple functions are described here. See also @code{looking-at}
71 in @ref{Regexp Search}.
73 In the following four functions, ``beginning'' or ``end'' of buffer
74 refers to the beginning or end of the accessible portion.
76 @defun char-after &optional position
77 This function returns the character in the current buffer at (i.e.,
78 immediately after) position @var{position}. If @var{position} is out of
79 range for this purpose, either before the beginning of the buffer, or at
80 or beyond the end, then the value is @code{nil}. The default for
81 @var{position} is point.
83 In the following example, assume that the first character in the
88 (char-to-string (char-after 1))
94 @defun char-before &optional position
95 This function returns the character in the current buffer immediately
96 before position @var{position}. If @var{position} is out of range for
97 this purpose, either at or before the beginning of the buffer, or beyond
98 the end, then the value is @code{nil}. The default for
99 @var{position} is point.
102 @defun following-char
103 This function returns the character following point in the current
104 buffer. This is similar to @code{(char-after (point))}. However, if
105 point is at the end of the buffer, then @code{following-char} returns 0.
107 Remember that point is always between characters, and the cursor
108 normally appears over the character following point. Therefore, the
109 character returned by @code{following-char} is the character the
112 In this example, point is between the @samp{a} and the @samp{c}.
116 ---------- Buffer: foo ----------
117 Gentlemen may cry ``Pea@point{}ce! Peace!,''
118 but there is no peace.
119 ---------- Buffer: foo ----------
123 (char-to-string (preceding-char))
125 (char-to-string (following-char))
131 @defun preceding-char
132 This function returns the character preceding point in the current
133 buffer. See above, under @code{following-char}, for an example. If
134 point is at the beginning of the buffer, @code{preceding-char} returns
139 This function returns @code{t} if point is at the beginning of the
140 buffer. If narrowing is in effect, this means the beginning of the
141 accessible portion of the text. See also @code{point-min} in
146 This function returns @code{t} if point is at the end of the buffer.
147 If narrowing is in effect, this means the end of accessible portion of
148 the text. See also @code{point-max} in @xref{Point}.
152 This function returns @code{t} if point is at the beginning of a line.
153 @xref{Text Lines}. The beginning of the buffer (or of its accessible
154 portion) always counts as the beginning of a line.
158 This function returns @code{t} if point is at the end of a line. The
159 end of the buffer (or of its accessible portion) is always considered
163 @node Buffer Contents
164 @section Examining Buffer Contents
166 This section describes functions that allow a Lisp program to
167 convert any portion of the text in the buffer into a string.
169 @defun buffer-substring start end
170 This function returns a string containing a copy of the text of the
171 region defined by positions @var{start} and @var{end} in the current
172 buffer. If the arguments are not positions in the accessible portion of
173 the buffer, @code{buffer-substring} signals an @code{args-out-of-range}
176 It is not necessary for @var{start} to be less than @var{end}; the
177 arguments can be given in either order. But most often the smaller
178 argument is written first.
180 Here's an example which assumes Font-Lock mode is not enabled:
184 ---------- Buffer: foo ----------
185 This is the contents of buffer foo
187 ---------- Buffer: foo ----------
191 (buffer-substring 1 10)
192 @result{} "This is t"
195 (buffer-substring (point-max) 10)
196 @result{} "he contents of buffer foo\n"
200 If the text being copied has any text properties, these are copied into
201 the string along with the characters they belong to. @xref{Text
202 Properties}. However, overlays (@pxref{Overlays}) in the buffer and
203 their properties are ignored, not copied.
205 For example, if Font-Lock mode is enabled, you might get results like
210 (buffer-substring 1 10)
211 @result{} #("This is t" 0 1 (fontified t) 1 9 (fontified t))
216 @defun buffer-substring-no-properties start end
217 This is like @code{buffer-substring}, except that it does not copy text
218 properties, just the characters themselves. @xref{Text Properties}.
221 @defun filter-buffer-substring start end &optional delete noprops
222 This function passes the buffer text between @var{start} and @var{end}
223 through the filter functions specified by the variable
224 @code{buffer-substring-filters}, and returns the value from the last
225 filter function. If @code{buffer-substring-filters} is @code{nil},
226 the value is the unaltered text from the buffer, what
227 @code{buffer-substring} would return.
229 If @var{delete} is non-@code{nil}, this function deletes the text
230 between @var{start} and @var{end} after copying it, like
231 @code{delete-and-extract-region}.
233 If @var{noprops} is non-@code{nil}, the final string returned does not
234 include text properties, while the string passed through the filters
235 still includes text properties from the buffer text.
237 Lisp code should use this function instead of @code{buffer-substring},
238 @code{buffer-substring-no-properties},
239 or @code{delete-and-extract-region} when copying into user-accessible
240 data structures such as the kill-ring, X clipboard, and registers.
241 Major and minor modes can add functions to
242 @code{buffer-substring-filters} to alter such text as it is copied out
246 @defvar buffer-substring-filters
247 This variable should be a list of functions that accept a single
248 argument, a string, and return a string.
249 @code{filter-buffer-substring} passes the buffer substring to the
250 first function in this list, and the return value of each function is
251 passed to the next function. The return value of the last function is
252 used as the return value of @code{filter-buffer-substring}.
254 As a special convention, point is set to the start of the buffer text
255 being operated on (i.e., the @var{start} argument for
256 @code{filter-buffer-substring}) before these functions are called.
258 If this variable is @code{nil}, no filtering is performed.
262 This function returns the contents of the entire accessible portion of
263 the current buffer as a string. It is equivalent to
266 (buffer-substring (point-min) (point-max))
271 ---------- Buffer: foo ----------
272 This is the contents of buffer foo
274 ---------- Buffer: foo ----------
277 @result{} "This is the contents of buffer foo\n"
282 @defun current-word &optional strict really-word
283 This function returns the symbol (or word) at or near point, as a string.
284 The return value includes no text properties.
286 If the optional argument @var{really-word} is non-@code{nil}, it finds a
287 word; otherwise, it finds a symbol (which includes both word
288 characters and symbol constituent characters).
290 If the optional argument @var{strict} is non-@code{nil}, then point
291 must be in or next to the symbol or word---if no symbol or word is
292 there, the function returns @code{nil}. Otherwise, a nearby symbol or
293 word on the same line is acceptable.
296 @defun thing-at-point thing
297 Return the @var{thing} around or next to point, as a string.
299 The argument @var{thing} is a symbol which specifies a kind of syntactic
300 entity. Possibilities include @code{symbol}, @code{list}, @code{sexp},
301 @code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
302 @code{whitespace}, @code{line}, @code{page}, and others.
305 ---------- Buffer: foo ----------
306 Gentlemen may cry ``Pea@point{}ce! Peace!,''
307 but there is no peace.
308 ---------- Buffer: foo ----------
310 (thing-at-point 'word)
312 (thing-at-point 'line)
313 @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
314 (thing-at-point 'whitespace)
320 @section Comparing Text
321 @cindex comparing buffer text
323 This function lets you compare portions of the text in a buffer, without
324 copying them into strings first.
326 @defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
327 This function lets you compare two substrings of the same buffer or two
328 different buffers. The first three arguments specify one substring,
329 giving a buffer (or a buffer name) and two positions within the
330 buffer. The last three arguments specify the other substring in the
331 same way. You can use @code{nil} for @var{buffer1}, @var{buffer2}, or
332 both to stand for the current buffer.
334 The value is negative if the first substring is less, positive if the
335 first is greater, and zero if they are equal. The absolute value of
336 the result is one plus the index of the first differing characters
337 within the substrings.
339 This function ignores case when comparing characters
340 if @code{case-fold-search} is non-@code{nil}. It always ignores
343 Suppose the current buffer contains the text @samp{foobarbar
344 haha!rara!}; then in this example the two substrings are @samp{rbar }
345 and @samp{rara!}. The value is 2 because the first substring is greater
346 at the second character.
349 (compare-buffer-substrings nil 6 11 nil 16 21)
355 @section Inserting Text
356 @cindex insertion of text
357 @cindex text insertion
359 @cindex insertion before point
360 @cindex before point, insertion
361 @dfn{Insertion} means adding new text to a buffer. The inserted text
362 goes at point---between the character before point and the character
363 after point. Some insertion functions leave point before the inserted
364 text, while other functions leave it after. We call the former
365 insertion @dfn{after point} and the latter insertion @dfn{before point}.
367 Insertion relocates markers that point at positions after the
368 insertion point, so that they stay with the surrounding text
369 (@pxref{Markers}). When a marker points at the place of insertion,
370 insertion may or may not relocate the marker, depending on the marker's
371 insertion type (@pxref{Marker Insertion Types}). Certain special
372 functions such as @code{insert-before-markers} relocate all such markers
373 to point after the inserted text, regardless of the markers' insertion
376 Insertion functions signal an error if the current buffer is
377 read-only or if they insert within read-only text.
379 These functions copy text characters from strings and buffers along
380 with their properties. The inserted characters have exactly the same
381 properties as the characters they were copied from. By contrast,
382 characters specified as separate arguments, not part of a string or
383 buffer, inherit their text properties from the neighboring text.
385 The insertion functions convert text from unibyte to multibyte in
386 order to insert in a multibyte buffer, and vice versa---if the text
387 comes from a string or from a buffer. However, they do not convert
388 unibyte character codes 128 through 255 to multibyte characters, not
389 even if the current buffer is a multibyte buffer. @xref{Converting
392 @defun insert &rest args
393 This function inserts the strings and/or characters @var{args} into the
394 current buffer, at point, moving point forward. In other words, it
395 inserts the text before point. An error is signaled unless all
396 @var{args} are either strings or characters. The value is @code{nil}.
399 @defun insert-before-markers &rest args
400 This function inserts the strings and/or characters @var{args} into the
401 current buffer, at point, moving point forward. An error is signaled
402 unless all @var{args} are either strings or characters. The value is
405 This function is unlike the other insertion functions in that it
406 relocates markers initially pointing at the insertion point, to point
407 after the inserted text. If an overlay begins at the insertion point,
408 the inserted text falls outside the overlay; if a nonempty overlay
409 ends at the insertion point, the inserted text falls inside that
413 @defun insert-char character count &optional inherit
414 This function inserts @var{count} instances of @var{character} into the
415 current buffer before point. The argument @var{count} should be an
416 integer, and @var{character} must be a character. The value is @code{nil}.
418 This function does not convert unibyte character codes 128 through 255
419 to multibyte characters, not even if the current buffer is a multibyte
420 buffer. @xref{Converting Representations}.
422 If @var{inherit} is non-@code{nil}, then the inserted characters inherit
423 sticky text properties from the two characters before and after the
424 insertion point. @xref{Sticky Properties}.
427 @defun insert-buffer-substring from-buffer-or-name &optional start end
428 This function inserts a portion of buffer @var{from-buffer-or-name}
429 (which must already exist) into the current buffer before point. The
430 text inserted is the region between @var{start} and @var{end}. (These
431 arguments default to the beginning and end of the accessible portion of
432 that buffer.) This function returns @code{nil}.
434 In this example, the form is executed with buffer @samp{bar} as the
435 current buffer. We assume that buffer @samp{bar} is initially empty.
439 ---------- Buffer: foo ----------
440 We hold these truths to be self-evident, that all
441 ---------- Buffer: foo ----------
445 (insert-buffer-substring "foo" 1 20)
448 ---------- Buffer: bar ----------
449 We hold these truth@point{}
450 ---------- Buffer: bar ----------
455 @defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
456 This is like @code{insert-buffer-substring} except that it does not
457 copy any text properties.
460 @xref{Sticky Properties}, for other insertion functions that inherit
461 text properties from the nearby text in addition to inserting it.
462 Whitespace inserted by indentation functions also inherits text
465 @node Commands for Insertion
466 @section User-Level Insertion Commands
468 This section describes higher-level commands for inserting text,
469 commands intended primarily for the user but useful also in Lisp
472 @deffn Command insert-buffer from-buffer-or-name
473 This command inserts the entire accessible contents of
474 @var{from-buffer-or-name} (which must exist) into the current buffer
475 after point. It leaves the mark after the inserted text. The value
479 @deffn Command self-insert-command count
480 @cindex character insertion
481 @cindex self-insertion
482 This command inserts the last character typed; it does so @var{count}
483 times, before point, and returns @code{nil}. Most printing characters
484 are bound to this command. In routine use, @code{self-insert-command}
485 is the most frequently called function in Emacs, but programs rarely use
486 it except to install it on a keymap.
488 In an interactive call, @var{count} is the numeric prefix argument.
490 Self-insertion translates the input character through
491 @code{translation-table-for-input}. @xref{Translation of Characters}.
493 This command calls @code{auto-fill-function} whenever that is
494 non-@code{nil} and the character inserted is in the table
495 @code{auto-fill-chars} (@pxref{Auto Filling}).
497 @c Cross refs reworded to prevent overfull hbox. --rjc 15mar92
498 This command performs abbrev expansion if Abbrev mode is enabled and
499 the inserted character does not have word-constituent
500 syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.) It is also
501 responsible for calling @code{blink-paren-function} when the inserted
502 character has close parenthesis syntax (@pxref{Blinking}).
504 Do not try substituting your own definition of
505 @code{self-insert-command} for the standard one. The editor command
506 loop handles this function specially.
509 @deffn Command newline &optional number-of-newlines
510 This command inserts newlines into the current buffer before point.
511 If @var{number-of-newlines} is supplied, that many newline characters
514 @cindex newline and Auto Fill mode
515 This function calls @code{auto-fill-function} if the current column
516 number is greater than the value of @code{fill-column} and
517 @var{number-of-newlines} is @code{nil}. Typically what
518 @code{auto-fill-function} does is insert a newline; thus, the overall
519 result in this case is to insert two newlines at different places: one
520 at point, and another earlier in the line. @code{newline} does not
521 auto-fill if @var{number-of-newlines} is non-@code{nil}.
523 This command indents to the left margin if that is not zero.
526 The value returned is @code{nil}. In an interactive call, @var{count}
527 is the numeric prefix argument.
530 @defvar overwrite-mode
531 This variable controls whether overwrite mode is in effect. The value
532 should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
533 or @code{nil}. @code{overwrite-mode-textual} specifies textual
534 overwrite mode (treats newlines and tabs specially), and
535 @code{overwrite-mode-binary} specifies binary overwrite mode (treats
536 newlines and tabs like any other characters).
540 @section Deleting Text
541 @cindex text deletion
543 @cindex deleting text vs killing
544 Deletion means removing part of the text in a buffer, without saving
545 it in the kill ring (@pxref{The Kill Ring}). Deleted text can't be
546 yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
547 Some deletion functions do save text in the kill ring in some special
550 All of the deletion functions operate on the current buffer.
552 @deffn Command erase-buffer
553 This function deletes the entire text of the current buffer
554 (@emph{not} just the accessible portion), leaving it
555 empty. If the buffer is read-only, it signals a @code{buffer-read-only}
556 error; if some of the text in it is read-only, it signals a
557 @code{text-read-only} error. Otherwise, it deletes the text without
558 asking for any confirmation. It returns @code{nil}.
560 Normally, deleting a large amount of text from a buffer inhibits further
561 auto-saving of that buffer ``because it has shrunk.'' However,
562 @code{erase-buffer} does not do this, the idea being that the future
563 text is not really related to the former text, and its size should not
564 be compared with that of the former text.
567 @deffn Command delete-region start end
568 This command deletes the text between positions @var{start} and
569 @var{end} in the current buffer, and returns @code{nil}. If point was
570 inside the deleted region, its value afterward is @var{start}.
571 Otherwise, point relocates with the surrounding text, as markers do.
574 @defun delete-and-extract-region start end
575 This function deletes the text between positions @var{start} and
576 @var{end} in the current buffer, and returns a string containing the
579 If point was inside the deleted region, its value afterward is
580 @var{start}. Otherwise, point relocates with the surrounding text, as
584 @deffn Command delete-char count &optional killp
585 This command deletes @var{count} characters directly after point, or
586 before point if @var{count} is negative. If @var{killp} is
587 non-@code{nil}, then it saves the deleted characters in the kill ring.
589 In an interactive call, @var{count} is the numeric prefix argument, and
590 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
591 argument is supplied, the text is saved in the kill ring. If no prefix
592 argument is supplied, then one character is deleted, but not saved in
595 The value returned is always @code{nil}.
598 @deffn Command delete-backward-char count &optional killp
599 @cindex deleting previous char
600 This command deletes @var{count} characters directly before point, or
601 after point if @var{count} is negative. If @var{killp} is
602 non-@code{nil}, then it saves the deleted characters in the kill ring.
604 In an interactive call, @var{count} is the numeric prefix argument, and
605 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
606 argument is supplied, the text is saved in the kill ring. If no prefix
607 argument is supplied, then one character is deleted, but not saved in
610 The value returned is always @code{nil}.
613 @deffn Command backward-delete-char-untabify count &optional killp
615 This command deletes @var{count} characters backward, changing tabs
616 into spaces. When the next character to be deleted is a tab, it is
617 first replaced with the proper number of spaces to preserve alignment
618 and then one of those spaces is deleted instead of the tab. If
619 @var{killp} is non-@code{nil}, then the command saves the deleted
620 characters in the kill ring.
622 Conversion of tabs to spaces happens only if @var{count} is positive.
623 If it is negative, exactly @minus{}@var{count} characters after point
626 In an interactive call, @var{count} is the numeric prefix argument, and
627 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
628 argument is supplied, the text is saved in the kill ring. If no prefix
629 argument is supplied, then one character is deleted, but not saved in
632 The value returned is always @code{nil}.
635 @defopt backward-delete-char-untabify-method
636 This option specifies how @code{backward-delete-char-untabify} should
637 deal with whitespace. Possible values include @code{untabify}, the
638 default, meaning convert a tab to many spaces and delete one;
639 @code{hungry}, meaning delete all tabs and spaces before point with
640 one command; @code{all} meaning delete all tabs, spaces and newlines
641 before point, and @code{nil}, meaning do nothing special for
642 whitespace characters.
645 @node User-Level Deletion
646 @section User-Level Deletion Commands
648 This section describes higher-level commands for deleting text,
649 commands intended primarily for the user but useful also in Lisp
652 @deffn Command delete-horizontal-space &optional backward-only
653 @cindex deleting whitespace
654 This function deletes all spaces and tabs around point. It returns
657 If @var{backward-only} is non-@code{nil}, the function deletes
658 spaces and tabs before point, but not after point.
660 In the following examples, we call @code{delete-horizontal-space} four
661 times, once on each line, with point between the second and third
662 characters on the line each time.
666 ---------- Buffer: foo ----------
671 ---------- Buffer: foo ----------
675 (delete-horizontal-space) ; @r{Four times.}
678 ---------- Buffer: foo ----------
683 ---------- Buffer: foo ----------
688 @deffn Command delete-indentation &optional join-following-p
689 This function joins the line point is on to the previous line, deleting
690 any whitespace at the join and in some cases replacing it with one
691 space. If @var{join-following-p} is non-@code{nil},
692 @code{delete-indentation} joins this line to the following line
693 instead. The function returns @code{nil}.
695 If there is a fill prefix, and the second of the lines being joined
696 starts with the prefix, then @code{delete-indentation} deletes the
697 fill prefix before joining the lines. @xref{Margins}.
699 In the example below, point is located on the line starting
700 @samp{events}, and it makes no difference if there are trailing spaces
701 in the preceding line.
705 ---------- Buffer: foo ----------
706 When in the course of human
707 @point{} events, it becomes necessary
708 ---------- Buffer: foo ----------
715 ---------- Buffer: foo ----------
716 When in the course of human@point{} events, it becomes necessary
717 ---------- Buffer: foo ----------
721 After the lines are joined, the function @code{fixup-whitespace} is
722 responsible for deciding whether to leave a space at the junction.
725 @deffn Command fixup-whitespace
726 This function replaces all the horizontal whitespace surrounding point
727 with either one space or no space, according to the context. It
730 At the beginning or end of a line, the appropriate amount of space is
731 none. Before a character with close parenthesis syntax, or after a
732 character with open parenthesis or expression-prefix syntax, no space is
733 also appropriate. Otherwise, one space is appropriate. @xref{Syntax
736 In the example below, @code{fixup-whitespace} is called the first time
737 with point before the word @samp{spaces} in the first line. For the
738 second invocation, point is directly after the @samp{(}.
742 ---------- Buffer: foo ----------
743 This has too many @point{}spaces
744 This has too many spaces at the start of (@point{} this list)
745 ---------- Buffer: foo ----------
756 ---------- Buffer: foo ----------
757 This has too many spaces
758 This has too many spaces at the start of (this list)
759 ---------- Buffer: foo ----------
764 @deffn Command just-one-space &optional n
765 @comment !!SourceFile simple.el
766 This command replaces any spaces and tabs around point with a single
767 space, or @var{n} spaces if @var{n} is specified. It returns
771 @deffn Command delete-blank-lines
772 This function deletes blank lines surrounding point. If point is on a
773 blank line with one or more blank lines before or after it, then all but
774 one of them are deleted. If point is on an isolated blank line, then it
775 is deleted. If point is on a nonblank line, the command deletes all
776 blank lines immediately following it.
778 A blank line is defined as a line containing only tabs and spaces.
780 @code{delete-blank-lines} returns @code{nil}.
784 @section The Kill Ring
787 @dfn{Kill functions} delete text like the deletion functions, but save
788 it so that the user can reinsert it by @dfn{yanking}. Most of these
789 functions have @samp{kill-} in their name. By contrast, the functions
790 whose names start with @samp{delete-} normally do not save text for
791 yanking (though they can still be undone); these are ``deletion''
794 Most of the kill commands are primarily for interactive use, and are
795 not described here. What we do describe are the functions provided for
796 use in writing such commands. You can use these functions to write
797 commands for killing text. When you need to delete text for internal
798 purposes within a Lisp function, you should normally use deletion
799 functions, so as not to disturb the kill ring contents.
802 Killed text is saved for later yanking in the @dfn{kill ring}. This
803 is a list that holds a number of recent kills, not just the last text
804 kill. We call this a ``ring'' because yanking treats it as having
805 elements in a cyclic order. The list is kept in the variable
806 @code{kill-ring}, and can be operated on with the usual functions for
807 lists; there are also specialized functions, described in this section,
808 that treat it as a ring.
810 Some people think this use of the word ``kill'' is unfortunate, since
811 it refers to operations that specifically @emph{do not} destroy the
812 entities ``killed.'' This is in sharp contrast to ordinary life, in
813 which death is permanent and ``killed'' entities do not come back to
814 life. Therefore, other metaphors have been proposed. For example, the
815 term ``cut ring'' makes sense to people who, in pre-computer days, used
816 scissors and paste to cut up and rearrange manuscripts. However, it
817 would be difficult to change the terminology now.
820 * Kill Ring Concepts:: What text looks like in the kill ring.
821 * Kill Functions:: Functions that kill text.
822 * Yanking:: How yanking is done.
823 * Yank Commands:: Commands that access the kill ring.
824 * Low-Level Kill Ring:: Functions and variables for kill ring access.
825 * Internals of Kill Ring:: Variables that hold kill ring data.
828 @node Kill Ring Concepts
829 @comment node-name, next, previous, up
830 @subsection Kill Ring Concepts
832 The kill ring records killed text as strings in a list, most recent
833 first. A short kill ring, for example, might look like this:
836 ("some text" "a different piece of text" "even older text")
840 When the list reaches @code{kill-ring-max} entries in length, adding a
841 new entry automatically deletes the last entry.
843 When kill commands are interwoven with other commands, each kill
844 command makes a new entry in the kill ring. Multiple kill commands in
845 succession build up a single kill ring entry, which would be yanked as a
846 unit; the second and subsequent consecutive kill commands add text to
847 the entry made by the first one.
849 For yanking, one entry in the kill ring is designated the ``front'' of
850 the ring. Some yank commands ``rotate'' the ring by designating a
851 different element as the ``front.'' But this virtual rotation doesn't
852 change the list itself---the most recent entry always comes first in the
856 @comment node-name, next, previous, up
857 @subsection Functions for Killing
859 @code{kill-region} is the usual subroutine for killing text. Any
860 command that calls this function is a ``kill command'' (and should
861 probably have @samp{kill} in its name). @code{kill-region} puts the
862 newly killed text in a new element at the beginning of the kill ring or
863 adds it to the most recent element. It determines automatically (using
864 @code{last-command}) whether the previous command was a kill command,
865 and if so appends the killed text to the most recent entry.
867 @deffn Command kill-region start end &optional yank-handler
868 This function kills the text in the region defined by @var{start} and
869 @var{end}. The text is deleted but saved in the kill ring, along with
870 its text properties. The value is always @code{nil}.
872 In an interactive call, @var{start} and @var{end} are point and
876 If the buffer or text is read-only, @code{kill-region} modifies the kill
877 ring just the same, then signals an error without modifying the buffer.
878 This is convenient because it lets the user use a series of kill
879 commands to copy text from a read-only buffer into the kill ring.
881 If @var{yank-handler} is non-@code{nil}, this puts that value onto
882 the string of killed text, as a @code{yank-handler} text property.
883 @xref{Yanking}. Note that if @var{yank-handler} is @code{nil}, any
884 @code{yank-handler} properties present on the killed text are copied
885 onto the kill ring, like other text properties.
888 @defopt kill-read-only-ok
889 If this option is non-@code{nil}, @code{kill-region} does not signal an
890 error if the buffer or text is read-only. Instead, it simply returns,
891 updating the kill ring but not changing the buffer.
894 @deffn Command copy-region-as-kill start end
895 This command saves the region defined by @var{start} and @var{end} on
896 the kill ring (including text properties), but does not delete the text
897 from the buffer. It returns @code{nil}.
899 The command does not set @code{this-command} to @code{kill-region}, so a
900 subsequent kill command does not append to the same kill ring entry.
902 Don't call @code{copy-region-as-kill} in Lisp programs unless you aim to
903 support Emacs 18. For newer Emacs versions, it is better to use
904 @code{kill-new} or @code{kill-append} instead. @xref{Low-Level Kill
911 Yanking means inserting text from the kill ring, but it does
912 not insert the text blindly. Yank commands and some other commands
913 use @code{insert-for-yank} to perform special processing on the
914 text that they copy into the buffer.
916 @defun insert-for-yank string
917 This function normally works like @code{insert} except that it doesn't
918 insert the text properties in the @code{yank-excluded-properties}
919 list. However, if any part of @var{string} has a non-@code{nil}
920 @code{yank-handler} text property, that property can do various
921 special processing on that part of the text being inserted.
924 @defun insert-buffer-substring-as-yank buf &optional start end
925 This function resembles @code{insert-buffer-substring} except that it
926 doesn't insert the text properties in the
927 @code{yank-excluded-properties} list.
930 You can put a @code{yank-handler} text property on all or part of
931 the text to control how it will be inserted if it is yanked. The
932 @code{insert-for-yank} function looks for that property. The property
933 value must be a list of one to four elements, with the following
934 format (where elements after the first may be omitted):
937 (@var{function} @var{param} @var{noexclude} @var{undo})
940 Here is what the elements do:
944 When @var{function} is present and non-@code{nil}, it is called instead of
945 @code{insert} to insert the string. @var{function} takes one
946 argument---the string to insert.
949 If @var{param} is present and non-@code{nil}, it replaces @var{string}
950 (or the part of @var{string} being processed) as the object passed to
951 @var{function} (or @code{insert}); for example, if @var{function} is
952 @code{yank-rectangle}, @var{param} should be a list of strings to
953 insert as a rectangle.
956 If @var{noexclude} is present and non-@code{nil}, the normal removal of the
957 yank-excluded-properties is not performed; instead @var{function} is
958 responsible for removing those properties. This may be necessary
959 if @var{function} adjusts point before or after inserting the object.
962 If @var{undo} is present and non-@code{nil}, it is a function that will be
963 called by @code{yank-pop} to undo the insertion of the current object.
964 It is called with two arguments, the start and end of the current
965 region. @var{function} can set @code{yank-undo-function} to override
966 the @var{undo} value.
970 @comment node-name, next, previous, up
971 @subsection Functions for Yanking
973 This section describes higher-level commands for yanking, which are
974 intended primarily for the user but useful also in Lisp programs.
975 Both @code{yank} and @code{yank-pop} honor the
976 @code{yank-excluded-properties} variable and @code{yank-handler} text
977 property (@pxref{Yanking}).
979 @deffn Command yank &optional arg
980 @cindex inserting killed text
981 This command inserts before point the text at the front of the
982 kill ring. It positions the mark at the beginning of that text, and
985 If @var{arg} is a non-@code{nil} list (which occurs interactively when
986 the user types @kbd{C-u} with no digits), then @code{yank} inserts the
987 text as described above, but puts point before the yanked text and
988 puts the mark after it.
990 If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
991 most recently killed text---the @var{arg}th element of the kill ring
992 list, counted cyclically from the front, which is considered the
993 first element for this purpose.
995 @code{yank} does not alter the contents of the kill ring, unless it
996 used text provided by another program, in which case it pushes that text
997 onto the kill ring. However if @var{arg} is an integer different from
998 one, it rotates the kill ring to place the yanked string at the front.
1000 @code{yank} returns @code{nil}.
1003 @deffn Command yank-pop &optional arg
1004 This command replaces the just-yanked entry from the kill ring with a
1005 different entry from the kill ring.
1007 This is allowed only immediately after a @code{yank} or another
1008 @code{yank-pop}. At such a time, the region contains text that was just
1009 inserted by yanking. @code{yank-pop} deletes that text and inserts in
1010 its place a different piece of killed text. It does not add the deleted
1011 text to the kill ring, since it is already in the kill ring somewhere.
1012 It does however rotate the kill ring to place the newly yanked string at
1015 If @var{arg} is @code{nil}, then the replacement text is the previous
1016 element of the kill ring. If @var{arg} is numeric, the replacement is
1017 the @var{arg}th previous kill. If @var{arg} is negative, a more recent
1018 kill is the replacement.
1020 The sequence of kills in the kill ring wraps around, so that after the
1021 oldest one comes the newest one, and before the newest one goes the
1024 The return value is always @code{nil}.
1027 @defvar yank-undo-function
1028 If this variable is non-@code{nil}, the function @code{yank-pop} uses
1029 its value instead of @code{delete-region} to delete the text
1030 inserted by the previous @code{yank} or
1031 @code{yank-pop} command. The value must be a function of two
1032 arguments, the start and end of the current region.
1034 The function @code{insert-for-yank} automatically sets this variable
1035 according to the @var{undo} element of the @code{yank-handler}
1036 text property, if there is one.
1039 @node Low-Level Kill Ring
1040 @subsection Low-Level Kill Ring
1042 These functions and variables provide access to the kill ring at a
1043 lower level, but still convenient for use in Lisp programs, because they
1044 take care of interaction with window system selections
1045 (@pxref{Window System Selections}).
1047 @defun current-kill n &optional do-not-move
1048 The function @code{current-kill} rotates the yanking pointer, which
1049 designates the ``front'' of the kill ring, by @var{n} places (from newer
1050 kills to older ones), and returns the text at that place in the ring.
1052 If the optional second argument @var{do-not-move} is non-@code{nil},
1053 then @code{current-kill} doesn't alter the yanking pointer; it just
1054 returns the @var{n}th kill, counting from the current yanking pointer.
1056 If @var{n} is zero, indicating a request for the latest kill,
1057 @code{current-kill} calls the value of
1058 @code{interprogram-paste-function} (documented below) before
1059 consulting the kill ring. If that value is a function and calling it
1060 returns a string, @code{current-kill} pushes that string onto the kill
1061 ring and returns it. It also sets the yanking pointer to point to
1062 that new entry, regardless of the value of @var{do-not-move}.
1063 Otherwise, @code{current-kill} does not treat a zero value for @var{n}
1064 specially: it returns the entry pointed at by the yanking pointer and
1065 does not move the yanking pointer.
1068 @defun kill-new string &optional replace yank-handler
1069 This function pushes the text @var{string} onto the kill ring and
1070 makes the yanking pointer point to it. It discards the oldest entry
1071 if appropriate. It also invokes the value of
1072 @code{interprogram-cut-function} (see below).
1074 If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
1075 first element of the kill ring with @var{string}, rather than pushing
1076 @var{string} onto the kill ring.
1078 If @var{yank-handler} is non-@code{nil}, this puts that value onto
1079 the string of killed text, as a @code{yank-handler} property.
1080 @xref{Yanking}. Note that if @var{yank-handler} is @code{nil}, then
1081 @code{kill-new} copies any @code{yank-handler} properties present on
1082 @var{string} onto the kill ring, as it does with other text properties.
1085 @defun kill-append string before-p &optional yank-handler
1086 This function appends the text @var{string} to the first entry in the
1087 kill ring and makes the yanking pointer point to the combined entry.
1088 Normally @var{string} goes at the end of the entry, but if
1089 @var{before-p} is non-@code{nil}, it goes at the beginning. This
1090 function also invokes the value of @code{interprogram-cut-function}
1091 (see below). This handles @var{yank-handler} just like
1092 @code{kill-new}, except that if @var{yank-handler} is different from
1093 the @code{yank-handler} property of the first entry of the kill ring,
1094 @code{kill-append} pushes the concatenated string onto the kill ring,
1095 instead of replacing the original first entry with it.
1098 @defvar interprogram-paste-function
1099 This variable provides a way of transferring killed text from other
1100 programs, when you are using a window system. Its value should be
1101 @code{nil} or a function of no arguments.
1103 If the value is a function, @code{current-kill} calls it to get the
1104 ``most recent kill.'' If the function returns a non-@code{nil} value,
1105 then that value is used as the ``most recent kill.'' If it returns
1106 @code{nil}, then the front of the kill ring is used.
1108 The normal use of this hook is to get the window system's primary
1109 selection as the most recent kill, even if the selection belongs to
1110 another application. @xref{Window System Selections}.
1113 @defvar interprogram-cut-function
1114 This variable provides a way of communicating killed text to other
1115 programs, when you are using a window system. Its value should be
1116 @code{nil} or a function of one required and one optional argument.
1118 If the value is a function, @code{kill-new} and @code{kill-append} call
1119 it with the new first element of the kill ring as the first argument.
1120 The second, optional, argument has the same meaning as the @var{push}
1121 argument to @code{x-set-cut-buffer} (@pxref{Definition of
1122 x-set-cut-buffer}) and only affects the second and later cut buffers.
1124 The normal use of this hook is to set the window system's primary
1125 selection (and first cut buffer) from the newly killed text.
1126 @xref{Window System Selections}.
1129 @node Internals of Kill Ring
1130 @comment node-name, next, previous, up
1131 @subsection Internals of the Kill Ring
1133 The variable @code{kill-ring} holds the kill ring contents, in the
1134 form of a list of strings. The most recent kill is always at the front
1137 The @code{kill-ring-yank-pointer} variable points to a link in the
1138 kill ring list, whose @sc{car} is the text to yank next. We say it
1139 identifies the ``front'' of the ring. Moving
1140 @code{kill-ring-yank-pointer} to a different link is called
1141 @dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
1142 the functions that move the yank pointer wrap around from the end of the
1143 list to the beginning, or vice-versa. Rotation of the kill ring is
1144 virtual; it does not change the value of @code{kill-ring}.
1146 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
1147 variables whose values are normally lists. The word ``pointer'' in the
1148 name of the @code{kill-ring-yank-pointer} indicates that the variable's
1149 purpose is to identify one element of the list for use by the next yank
1152 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
1153 of the links in the kill ring list. The element it identifies is the
1154 @sc{car} of that link. Kill commands, which change the kill ring, also
1155 set this variable to the value of @code{kill-ring}. The effect is to
1156 rotate the ring so that the newly killed text is at the front.
1158 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
1159 pointing to the second entry in the kill ring @code{("some text" "a
1160 different piece of text" "yet older text")}.
1164 kill-ring ---- kill-ring-yank-pointer
1167 | --- --- --- --- --- ---
1168 --> | | |------> | | |--> | | |--> nil
1169 --- --- --- --- --- ---
1172 | | -->"yet older text"
1174 | --> "a different piece of text"
1181 This state of affairs might occur after @kbd{C-y} (@code{yank})
1182 immediately followed by @kbd{M-y} (@code{yank-pop}).
1185 This variable holds the list of killed text sequences, most recently
1189 @defvar kill-ring-yank-pointer
1190 This variable's value indicates which element of the kill ring is at the
1191 ``front'' of the ring for yanking. More precisely, the value is a tail
1192 of the value of @code{kill-ring}, and its @sc{car} is the kill string
1193 that @kbd{C-y} should yank.
1196 @defopt kill-ring-max
1197 The value of this variable is the maximum length to which the kill
1198 ring can grow, before elements are thrown away at the end. The default
1199 value for @code{kill-ring-max} is 60.
1203 @comment node-name, next, previous, up
1207 Most buffers have an @dfn{undo list}, which records all changes made
1208 to the buffer's text so that they can be undone. (The buffers that
1209 don't have one are usually special-purpose buffers for which Emacs
1210 assumes that undoing is not useful. In particular, any buffer whose
1211 name begins with a space has its undo recording off by default;
1212 see @ref{Buffer Names}.) All the primitives that modify the
1213 text in the buffer automatically add elements to the front of the undo
1214 list, which is in the variable @code{buffer-undo-list}.
1216 @defvar buffer-undo-list
1217 This buffer-local variable's value is the undo list of the current
1218 buffer. A value of @code{t} disables the recording of undo information.
1221 Here are the kinds of elements an undo list can have:
1224 @item @var{position}
1225 This kind of element records a previous value of point; undoing this
1226 element moves point to @var{position}. Ordinary cursor motion does not
1227 make any sort of undo record, but deletion operations use these entries
1228 to record where point was before the command.
1230 @item (@var{beg} . @var{end})
1231 This kind of element indicates how to delete text that was inserted.
1232 Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1235 @item (@var{text} . @var{position})
1236 This kind of element indicates how to reinsert text that was deleted.
1237 The deleted text itself is the string @var{text}. The place to
1238 reinsert it is @code{(abs @var{position})}. If @var{position} is
1239 positive, point was at the beginning of the deleted text, otherwise it
1242 @item (t @var{high} . @var{low})
1243 This kind of element indicates that an unmodified buffer became
1244 modified. The elements @var{high} and @var{low} are two integers, each
1245 recording 16 bits of the visited file's modification time as of when it
1246 was previously visited or saved. @code{primitive-undo} uses those
1247 values to determine whether to mark the buffer as unmodified once again;
1248 it does so only if the file's modification time matches those numbers.
1250 @item (nil @var{property} @var{value} @var{beg} . @var{end})
1251 This kind of element records a change in a text property.
1252 Here's how you might undo the change:
1255 (put-text-property @var{beg} @var{end} @var{property} @var{value})
1258 @item (@var{marker} . @var{adjustment})
1259 This kind of element records the fact that the marker @var{marker} was
1260 relocated due to deletion of surrounding text, and that it moved
1261 @var{adjustment} character positions. Undoing this element moves
1262 @var{marker} @minus{} @var{adjustment} characters.
1264 @item (apply @var{funname} . @var{args})
1265 This is an extensible undo item, which is undone by calling
1266 @var{funname} with arguments @var{args}.
1268 @item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1269 This is an extensible undo item, which records a change limited to the
1270 range @var{beg} to @var{end}, which increased the size of the buffer
1271 by @var{delta}. It is undone by calling @var{funname} with arguments
1274 This kind of element enables undo limited to a region to determine
1275 whether the element pertains to that region.
1278 This element is a boundary. The elements between two boundaries are
1279 called a @dfn{change group}; normally, each change group corresponds to
1280 one keyboard command, and undo commands normally undo an entire group as
1284 @defun undo-boundary
1285 This function places a boundary element in the undo list. The undo
1286 command stops at such a boundary, and successive undo commands undo
1287 to earlier and earlier boundaries. This function returns @code{nil}.
1289 The editor command loop automatically creates an undo boundary before
1290 each key sequence is executed. Thus, each undo normally undoes the
1291 effects of one command. Self-inserting input characters are an
1292 exception. The command loop makes a boundary for the first such
1293 character; the next 19 consecutive self-inserting input characters do
1294 not make boundaries, and then the 20th does, and so on as long as
1295 self-inserting characters continue.
1297 All buffer modifications add a boundary whenever the previous undoable
1298 change was made in some other buffer. This is to ensure that
1299 each command makes a boundary in each buffer where it makes changes.
1301 Calling this function explicitly is useful for splitting the effects of
1302 a command into more than one unit. For example, @code{query-replace}
1303 calls @code{undo-boundary} after each replacement, so that the user can
1304 undo individual replacements one by one.
1307 @defvar undo-in-progress
1308 This variable is normally @code{nil}, but the undo commands bind it to
1309 @code{t}. This is so that various kinds of change hooks can tell when
1310 they're being called for the sake of undoing.
1313 @defun primitive-undo count list
1314 This is the basic function for undoing elements of an undo list.
1315 It undoes the first @var{count} elements of @var{list}, returning
1316 the rest of @var{list}.
1318 @code{primitive-undo} adds elements to the buffer's undo list when it
1319 changes the buffer. Undo commands avoid confusion by saving the undo
1320 list value at the beginning of a sequence of undo operations. Then the
1321 undo operations use and update the saved value. The new elements added
1322 by undoing are not part of this saved value, so they don't interfere with
1325 This function does not bind @code{undo-in-progress}.
1328 @node Maintaining Undo
1329 @section Maintaining Undo Lists
1331 This section describes how to enable and disable undo information for
1332 a given buffer. It also explains how the undo list is truncated
1333 automatically so it doesn't get too big.
1335 Recording of undo information in a newly created buffer is normally
1336 enabled to start with; but if the buffer name starts with a space, the
1337 undo recording is initially disabled. You can explicitly enable or
1338 disable undo recording with the following two functions, or by setting
1339 @code{buffer-undo-list} yourself.
1341 @deffn Command buffer-enable-undo &optional buffer-or-name
1342 This command enables recording undo information for buffer
1343 @var{buffer-or-name}, so that subsequent changes can be undone. If no
1344 argument is supplied, then the current buffer is used. This function
1345 does nothing if undo recording is already enabled in the buffer. It
1348 In an interactive call, @var{buffer-or-name} is the current buffer.
1349 You cannot specify any other buffer.
1352 @deffn Command buffer-disable-undo &optional buffer-or-name
1353 @cindex disabling undo
1354 This function discards the undo list of @var{buffer-or-name}, and disables
1355 further recording of undo information. As a result, it is no longer
1356 possible to undo either previous changes or any subsequent changes. If
1357 the undo list of @var{buffer-or-name} is already disabled, this function
1360 This function returns @code{nil}.
1363 As editing continues, undo lists get longer and longer. To prevent
1364 them from using up all available memory space, garbage collection trims
1365 them back to size limits you can set. (For this purpose, the ``size''
1366 of an undo list measures the cons cells that make up the list, plus the
1367 strings of deleted text.) Three variables control the range of acceptable
1368 sizes: @code{undo-limit}, @code{undo-strong-limit} and
1369 @code{undo-outer-limit}. In these variables, size is counted as the
1370 number of bytes occupied, which includes both saved text and other
1374 This is the soft limit for the acceptable size of an undo list. The
1375 change group at which this size is exceeded is the last one kept.
1378 @defopt undo-strong-limit
1379 This is the upper limit for the acceptable size of an undo list. The
1380 change group at which this size is exceeded is discarded itself (along
1381 with all older change groups). There is one exception: the very latest
1382 change group is only discarded if it exceeds @code{undo-outer-limit}.
1385 @defopt undo-outer-limit
1386 If at garbage collection time the undo info for the current command
1387 exceeds this limit, Emacs discards the info and displays a warning.
1388 This is a last ditch limit to prevent memory overflow.
1391 @defopt undo-ask-before-discard
1392 If this variable is non-@code{nil}, when the undo info exceeds
1393 @code{undo-outer-limit}, Emacs asks in the echo area whether to
1394 discard the info. The default value is @code{nil}, which means to
1395 discard it automatically.
1397 This option is mainly intended for debugging. Garbage collection is
1398 inhibited while the question is asked, which means that Emacs might
1399 leak memory if the user waits too long before answering the question.
1403 @comment node-name, next, previous, up
1405 @cindex filling text
1407 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1408 breaks) so that they are nearly (but no greater than) a specified
1409 maximum width. Additionally, lines can be @dfn{justified}, which means
1410 inserting spaces to make the left and/or right margins line up
1411 precisely. The width is controlled by the variable @code{fill-column}.
1412 For ease of reading, lines should be no longer than 70 or so columns.
1414 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1415 automatically as you insert it, but changes to existing text may leave
1416 it improperly filled. Then you must fill the text explicitly.
1418 Most of the commands in this section return values that are not
1419 meaningful. All the functions that do filling take note of the current
1420 left margin, current right margin, and current justification style
1421 (@pxref{Margins}). If the current justification style is
1422 @code{none}, the filling functions don't actually do anything.
1424 Several of the filling functions have an argument @var{justify}.
1425 If it is non-@code{nil}, that requests some kind of justification. It
1426 can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1427 request a specific style of justification. If it is @code{t}, that
1428 means to use the current justification style for this part of the text
1429 (see @code{current-justification}, below). Any other value is treated
1432 When you call the filling functions interactively, using a prefix
1433 argument implies the value @code{full} for @var{justify}.
1435 @deffn Command fill-paragraph justify
1436 This command fills the paragraph at or after point. If
1437 @var{justify} is non-@code{nil}, each line is justified as well.
1438 It uses the ordinary paragraph motion commands to find paragraph
1439 boundaries. @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
1442 @deffn Command fill-region start end &optional justify nosqueeze to-eop
1443 This command fills each of the paragraphs in the region from @var{start}
1444 to @var{end}. It justifies as well if @var{justify} is
1447 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1448 other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1449 that means to keep filling to the end of the paragraph---or the next hard
1450 newline, if @code{use-hard-newlines} is enabled (see below).
1452 The variable @code{paragraph-separate} controls how to distinguish
1453 paragraphs. @xref{Standard Regexps}.
1456 @deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
1457 This command fills each paragraph in the region according to its
1458 individual fill prefix. Thus, if the lines of a paragraph were indented
1459 with spaces, the filled paragraph will remain indented in the same
1462 The first two arguments, @var{start} and @var{end}, are the beginning
1463 and end of the region to be filled. The third and fourth arguments,
1464 @var{justify} and @var{citation-regexp}, are optional. If
1465 @var{justify} is non-@code{nil}, the paragraphs are justified as
1466 well as filled. If @var{citation-regexp} is non-@code{nil}, it means the
1467 function is operating on a mail message and therefore should not fill
1468 the header lines. If @var{citation-regexp} is a string, it is used as
1469 a regular expression; if it matches the beginning of a line, that line
1470 is treated as a citation marker.
1472 Ordinarily, @code{fill-individual-paragraphs} regards each change in
1473 indentation as starting a new paragraph. If
1474 @code{fill-individual-varying-indent} is non-@code{nil}, then only
1475 separator lines separate paragraphs. That mode can handle indented
1476 paragraphs with additional indentation on the first line.
1479 @defopt fill-individual-varying-indent
1480 This variable alters the action of @code{fill-individual-paragraphs} as
1484 @deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1485 This command considers a region of text as a single paragraph and fills
1486 it. If the region was made up of many paragraphs, the blank lines
1487 between paragraphs are removed. This function justifies as well as
1488 filling when @var{justify} is non-@code{nil}.
1490 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1491 other than line breaks untouched. If @var{squeeze-after} is
1492 non-@code{nil}, it specifies a position in the region, and means don't
1493 canonicalize spaces before that position.
1495 In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1496 choose a fill prefix by default. @xref{Adaptive Fill}.
1499 @deffn Command justify-current-line &optional how eop nosqueeze
1500 This command inserts spaces between the words of the current line so
1501 that the line ends exactly at @code{fill-column}. It returns
1504 The argument @var{how}, if non-@code{nil} specifies explicitly the style
1505 of justification. It can be @code{left}, @code{right}, @code{full},
1506 @code{center}, or @code{none}. If it is @code{t}, that means to do
1507 follow specified justification style (see @code{current-justification},
1508 below). @code{nil} means to do full justification.
1510 If @var{eop} is non-@code{nil}, that means do only left-justification
1511 if @code{current-justification} specifies full justification. This is
1512 used for the last line of a paragraph; even if the paragraph as a
1513 whole is fully justified, the last line should not be.
1515 If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1519 @defopt default-justification
1520 This variable's value specifies the style of justification to use for
1521 text that doesn't specify a style with a text property. The possible
1522 values are @code{left}, @code{right}, @code{full}, @code{center}, or
1523 @code{none}. The default value is @code{left}.
1526 @defun current-justification
1527 This function returns the proper justification style to use for filling
1528 the text around point.
1530 This returns the value of the @code{justification} text property at
1531 point, or the variable @var{default-justification} if there is no such
1532 text property. However, it returns @code{nil} rather than @code{none}
1533 to mean ``don't justify''.
1536 @defopt sentence-end-double-space
1537 @anchor{Definition of sentence-end-double-space}
1538 If this variable is non-@code{nil}, a period followed by just one space
1539 does not count as the end of a sentence, and the filling functions
1540 avoid breaking the line at such a place.
1543 @defopt sentence-end-without-period
1544 If this variable is non-@code{nil}, a sentence can end without a
1545 period. This is used for languages like Thai, where sentences end
1546 with a double space but without a period.
1549 @defopt sentence-end-without-space
1550 If this variable is non-@code{nil}, it should be a string of
1551 characters that can end a sentence without following spaces.
1554 @defvar fill-paragraph-function
1555 This variable provides a way for major modes to override the filling of
1556 paragraphs. If the value is non-@code{nil}, @code{fill-paragraph} calls
1557 this function to do the work. If the function returns a non-@code{nil}
1558 value, @code{fill-paragraph} assumes the job is done, and immediately
1561 The usual use of this feature is to fill comments in programming
1562 language modes. If the function needs to fill a paragraph in the usual
1563 way, it can do so as follows:
1566 (let ((fill-paragraph-function nil))
1567 (fill-paragraph arg))
1571 @defvar use-hard-newlines
1572 If this variable is non-@code{nil}, the filling functions do not delete
1573 newlines that have the @code{hard} text property. These ``hard
1574 newlines'' act as paragraph separators.
1578 @section Margins for Filling
1581 This buffer-local variable, if non-@code{nil}, specifies a string of
1582 text that appears at the beginning of normal text lines and should be
1583 disregarded when filling them. Any line that fails to start with the
1584 fill prefix is considered the start of a paragraph; so is any line
1585 that starts with the fill prefix followed by additional whitespace.
1586 Lines that start with the fill prefix but no additional whitespace are
1587 ordinary text lines that can be filled together. The resulting filled
1588 lines also start with the fill prefix.
1590 The fill prefix follows the left margin whitespace, if any.
1594 This buffer-local variable specifies the maximum width of filled lines.
1595 Its value should be an integer, which is a number of columns. All the
1596 filling, justification, and centering commands are affected by this
1597 variable, including Auto Fill mode (@pxref{Auto Filling}).
1599 As a practical matter, if you are writing text for other people to
1600 read, you should set @code{fill-column} to no more than 70. Otherwise
1601 the line will be too long for people to read comfortably, and this can
1602 make the text seem clumsy.
1605 @defvar default-fill-column
1606 The value of this variable is the default value for @code{fill-column} in
1607 buffers that do not override it. This is the same as
1608 @code{(default-value 'fill-column)}.
1610 The default value for @code{default-fill-column} is 70.
1613 @deffn Command set-left-margin from to margin
1614 This sets the @code{left-margin} property on the text from @var{from} to
1615 @var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1616 command also refills the region to fit the new margin.
1619 @deffn Command set-right-margin from to margin
1620 This sets the @code{right-margin} property on the text from @var{from}
1621 to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1622 this command also refills the region to fit the new margin.
1625 @defun current-left-margin
1626 This function returns the proper left margin value to use for filling
1627 the text around point. The value is the sum of the @code{left-margin}
1628 property of the character at the start of the current line (or zero if
1629 none), and the value of the variable @code{left-margin}.
1632 @defun current-fill-column
1633 This function returns the proper fill column value to use for filling
1634 the text around point. The value is the value of the @code{fill-column}
1635 variable, minus the value of the @code{right-margin} property of the
1636 character after point.
1639 @deffn Command move-to-left-margin &optional n force
1640 This function moves point to the left margin of the current line. The
1641 column moved to is determined by calling the function
1642 @code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1643 @code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1645 If @var{force} is non-@code{nil}, that says to fix the line's
1646 indentation if that doesn't match the left margin value.
1649 @defun delete-to-left-margin &optional from to
1650 This function removes left margin indentation from the text between
1651 @var{from} and @var{to}. The amount of indentation to delete is
1652 determined by calling @code{current-left-margin}. In no case does this
1653 function delete non-whitespace. If @var{from} and @var{to} are omitted,
1654 they default to the whole buffer.
1657 @defun indent-to-left-margin
1658 This is the default @code{indent-line-function}, used in Fundamental
1659 mode, Text mode, etc. Its effect is to adjust the indentation at the
1660 beginning of the current line to the value specified by the variable
1661 @code{left-margin}. This may involve either inserting or deleting
1666 This variable specifies the base left margin column. In Fundamental
1667 mode, @kbd{C-j} indents to this column. This variable automatically
1668 becomes buffer-local when set in any fashion.
1671 @defvar fill-nobreak-predicate
1672 This variable gives major modes a way to specify not to break a line
1673 at certain places. Its value should be a list of functions. Whenever
1674 filling considers breaking the line at a certain place in the buffer,
1675 it calls each of these functions with no arguments and with point
1676 located at that place. If any of the functions returns
1677 non-@code{nil}, then the line won't be broken there.
1681 @section Adaptive Fill Mode
1682 @c @cindex Adaptive Fill mode "adaptive-fill-mode" is adjacent.
1684 When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
1685 prefix automatically from the text in each paragraph being filled
1686 rather than using a predetermined value. During filling, this fill
1687 prefix gets inserted at the start of the second and subsequent lines
1688 of the paragraph as described in @ref{Filling}, and in @ref{Auto
1691 @defopt adaptive-fill-mode
1692 Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1693 It is @code{t} by default.
1696 @defun fill-context-prefix from to
1697 This function implements the heart of Adaptive Fill mode; it chooses a
1698 fill prefix based on the text between @var{from} and @var{to},
1699 typically the start and end of a paragraph. It does this by looking
1700 at the first two lines of the paragraph, based on the variables
1702 @c The optional argument first-line-regexp is not documented
1703 @c because it exists for internal purposes and might be eliminated
1706 Usually, this function returns the fill prefix, a string. However,
1707 before doing this, the function makes a final check (not specially
1708 mentioned in the following) that a line starting with this prefix
1709 wouldn't look like the start of a paragraph. Should this happen, the
1710 function signals the anomaly by returning @code{nil} instead.
1712 In detail, @code{fill-context-prefix} does this:
1716 It takes a candidate for the fill prefix from the first line---it
1717 tries first the function in @code{adaptive-fill-function} (if any),
1718 then the regular expression @code{adaptive-fill-regexp} (see below).
1719 The first non-@code{nil} result of these, or the empty string if
1720 they're both @code{nil}, becomes the first line's candidate.
1722 If the paragraph has as yet only one line, the function tests the
1723 validity of the prefix candidate just found. The function then
1724 returns the candidate if it's valid, or a string of spaces otherwise.
1725 (see the description of @code{adaptive-fill-first-line-regexp} below).
1727 When the paragraph already has two lines, the function next looks for
1728 a prefix candidate on the second line, in just the same way it did for
1729 the first line. If it doesn't find one, it returns @code{nil}.
1731 The function now compares the two candidate prefixes heuristically: if
1732 the non-whitespace characters in the line 2 candidate occur in the
1733 same order in the line 1 candidate, the function returns the line 2
1734 candidate. Otherwise, it returns the largest initial substring which
1735 is common to both candidates (which might be the empty string).
1739 @defopt adaptive-fill-regexp
1740 Adaptive Fill mode matches this regular expression against the text
1741 starting after the left margin whitespace (if any) on a line; the
1742 characters it matches are that line's candidate for the fill prefix.
1744 @w{@code{"[ \t]*\\([-!|#%;>*·•‣⁃◦]+[ \t]*\\|(?[0-9]+[.)][ \t]*\\)*"}} is the
1745 default value. This matches a number enclosed in parentheses or
1746 followed by a period, or certain punctuation characters, or any
1747 sequence of these intermingled with whitespace. In particular, it
1748 matches a sequence of whitespace, possibly empty.
1751 @defopt adaptive-fill-first-line-regexp
1752 Used only in one-line paragraphs, this regular expression acts as an
1753 additional check of the validity of the one available candidate fill
1754 prefix: the candidate must match this regular expression, or match
1755 @code{comment-start-skip}. If it doesn't, @code{fill-context-prefix}
1756 replaces the candidate with a string of spaces ``of the same width''
1759 The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
1760 matches only a string of whitespace. The effect of this default is to
1761 force the fill prefixes found in one-line paragraphs always to be pure
1765 @defopt adaptive-fill-function
1766 You can specify more complex ways of choosing a fill prefix
1767 automatically by setting this variable to a function. The function is
1768 called with point after the left margin (if any) of a line, and it
1769 must preserve point. It should return either ``that line's'' fill
1770 prefix or @code{nil}, meaning it has failed to determine a prefix.
1774 @comment node-name, next, previous, up
1775 @section Auto Filling
1776 @cindex filling, automatic
1777 @cindex Auto Fill mode
1779 Auto Fill mode is a minor mode that fills lines automatically as text
1780 is inserted. This section describes the hook used by Auto Fill mode.
1781 For a description of functions that you can call explicitly to fill and
1782 justify existing text, see @ref{Filling}.
1784 Auto Fill mode also enables the functions that change the margins and
1785 justification style to refill portions of the text. @xref{Margins}.
1787 @defvar auto-fill-function
1788 The value of this buffer-local variable should be a function (of no
1789 arguments) to be called after self-inserting a character from the table
1790 @code{auto-fill-chars}. It may be @code{nil}, in which case nothing
1791 special is done in that case.
1793 The value of @code{auto-fill-function} is @code{do-auto-fill} when
1794 Auto-Fill mode is enabled. That is a function whose sole purpose is to
1795 implement the usual strategy for breaking a line.
1798 In older Emacs versions, this variable was named @code{auto-fill-hook},
1799 but since it is not called with the standard convention for hooks, it
1800 was renamed to @code{auto-fill-function} in version 19.
1804 @defvar normal-auto-fill-function
1805 This variable specifies the function to use for
1806 @code{auto-fill-function}, if and when Auto Fill is turned on. Major
1807 modes can set buffer-local values for this variable to alter how Auto
1811 @defvar auto-fill-chars
1812 A char table of characters which invoke @code{auto-fill-function} when
1813 self-inserted---space and newline in most language environments. They
1814 have an entry @code{t} in the table.
1818 @section Sorting Text
1819 @cindex sorting text
1821 The sorting functions described in this section all rearrange text in
1822 a buffer. This is in contrast to the function @code{sort}, which
1823 rearranges the order of the elements of a list (@pxref{Rearrangement}).
1824 The values returned by these functions are not meaningful.
1826 @defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
1827 This function is the general text-sorting routine that subdivides a
1828 buffer into records and then sorts them. Most of the commands in this
1829 section use this function.
1831 To understand how @code{sort-subr} works, consider the whole accessible
1832 portion of the buffer as being divided into disjoint pieces called
1833 @dfn{sort records}. The records may or may not be contiguous, but they
1834 must not overlap. A portion of each sort record (perhaps all of it) is
1835 designated as the sort key. Sorting rearranges the records in order by
1838 Usually, the records are rearranged in order of ascending sort key.
1839 If the first argument to the @code{sort-subr} function, @var{reverse},
1840 is non-@code{nil}, the sort records are rearranged in order of
1841 descending sort key.
1843 The next four arguments to @code{sort-subr} are functions that are
1844 called to move point across a sort record. They are called many times
1845 from within @code{sort-subr}.
1849 @var{nextrecfun} is called with point at the end of a record. This
1850 function moves point to the start of the next record. The first record
1851 is assumed to start at the position of point when @code{sort-subr} is
1852 called. Therefore, you should usually move point to the beginning of
1853 the buffer before calling @code{sort-subr}.
1855 This function can indicate there are no more sort records by leaving
1856 point at the end of the buffer.
1859 @var{endrecfun} is called with point within a record. It moves point to
1860 the end of the record.
1863 @var{startkeyfun} is called to move point from the start of a record to
1864 the start of the sort key. This argument is optional; if it is omitted,
1865 the whole record is the sort key. If supplied, the function should
1866 either return a non-@code{nil} value to be used as the sort key, or
1867 return @code{nil} to indicate that the sort key is in the buffer
1868 starting at point. In the latter case, @var{endkeyfun} is called to
1869 find the end of the sort key.
1872 @var{endkeyfun} is called to move point from the start of the sort key
1873 to the end of the sort key. This argument is optional. If
1874 @var{startkeyfun} returns @code{nil} and this argument is omitted (or
1875 @code{nil}), then the sort key extends to the end of the record. There
1876 is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1877 non-@code{nil} value.
1880 The argument @var{predicate} is the function to use to compare keys.
1881 If keys are numbers, it defaults to @code{<}; otherwise it defaults to
1884 As an example of @code{sort-subr}, here is the complete function
1885 definition for @code{sort-lines}:
1889 ;; @r{Note that the first two lines of doc string}
1890 ;; @r{are effectively one line when viewed by a user.}
1891 (defun sort-lines (reverse beg end)
1892 "Sort lines in region alphabetically;\
1893 argument means descending order.
1894 Called from a program, there are three arguments:
1897 REVERSE (non-nil means reverse order),\
1898 BEG and END (region to sort).
1899 The variable `sort-fold-case' determines\
1900 whether alphabetic case affects
1904 (interactive "P\nr")
1907 (narrow-to-region beg end)
1908 (goto-char (point-min))
1909 (let ((inhibit-field-text-motion t))
1910 (sort-subr reverse 'forward-line 'end-of-line)))))
1914 Here @code{forward-line} moves point to the start of the next record,
1915 and @code{end-of-line} moves point to the end of record. We do not pass
1916 the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
1917 record is used as the sort key.
1919 The @code{sort-paragraphs} function is very much the same, except that
1920 its @code{sort-subr} call looks like this:
1927 (while (and (not (eobp))
1928 (looking-at paragraph-separate))
1934 Markers pointing into any sort records are left with no useful
1935 position after @code{sort-subr} returns.
1938 @defopt sort-fold-case
1939 If this variable is non-@code{nil}, @code{sort-subr} and the other
1940 buffer sorting functions ignore case when comparing strings.
1943 @deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
1944 This command sorts the region between @var{start} and @var{end}
1945 alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
1946 If @var{reverse} is a negative integer, then sorting is in reverse
1949 Alphabetical sorting means that two sort keys are compared by
1950 comparing the first characters of each, the second characters of each,
1951 and so on. If a mismatch is found, it means that the sort keys are
1952 unequal; the sort key whose character is less at the point of first
1953 mismatch is the lesser sort key. The individual characters are compared
1954 according to their numerical character codes in the Emacs character set.
1956 The value of the @var{record-regexp} argument specifies how to divide
1957 the buffer into sort records. At the end of each record, a search is
1958 done for this regular expression, and the text that matches it is taken
1959 as the next record. For example, the regular expression @samp{^.+$},
1960 which matches lines with at least one character besides a newline, would
1961 make each such line into a sort record. @xref{Regular Expressions}, for
1962 a description of the syntax and meaning of regular expressions.
1964 The value of the @var{key-regexp} argument specifies what part of each
1965 record is the sort key. The @var{key-regexp} could match the whole
1966 record, or only a part. In the latter case, the rest of the record has
1967 no effect on the sorted order of records, but it is carried along when
1968 the record moves to its new position.
1970 The @var{key-regexp} argument can refer to the text matched by a
1971 subexpression of @var{record-regexp}, or it can be a regular expression
1974 If @var{key-regexp} is:
1977 @item @samp{\@var{digit}}
1978 then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
1979 grouping in @var{record-regexp} is the sort key.
1982 then the whole record is the sort key.
1984 @item a regular expression
1985 then @code{sort-regexp-fields} searches for a match for the regular
1986 expression within the record. If such a match is found, it is the sort
1987 key. If there is no match for @var{key-regexp} within a record then
1988 that record is ignored, which means its position in the buffer is not
1989 changed. (The other records may move around it.)
1992 For example, if you plan to sort all the lines in the region by the
1993 first word on each line starting with the letter @samp{f}, you should
1994 set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
1995 @samp{\<f\w*\>}. The resulting expression looks like this:
1999 (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
2005 If you call @code{sort-regexp-fields} interactively, it prompts for
2006 @var{record-regexp} and @var{key-regexp} in the minibuffer.
2009 @deffn Command sort-lines reverse start end
2010 This command alphabetically sorts lines in the region between
2011 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2012 is in reverse order.
2015 @deffn Command sort-paragraphs reverse start end
2016 This command alphabetically sorts paragraphs in the region between
2017 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2018 is in reverse order.
2021 @deffn Command sort-pages reverse start end
2022 This command alphabetically sorts pages in the region between
2023 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2024 is in reverse order.
2027 @deffn Command sort-fields field start end
2028 This command sorts lines in the region between @var{start} and
2029 @var{end}, comparing them alphabetically by the @var{field}th field
2030 of each line. Fields are separated by whitespace and numbered starting
2031 from 1. If @var{field} is negative, sorting is by the
2032 @w{@minus{}@var{field}th} field from the end of the line. This command
2033 is useful for sorting tables.
2036 @deffn Command sort-numeric-fields field start end
2037 This command sorts lines in the region between @var{start} and
2038 @var{end}, comparing them numerically by the @var{field}th field of
2039 each line. Fields are separated by whitespace and numbered starting
2040 from 1. The specified field must contain a number in each line of the
2041 region. Numbers starting with 0 are treated as octal, and numbers
2042 starting with @samp{0x} are treated as hexadecimal.
2044 If @var{field} is negative, sorting is by the
2045 @w{@minus{}@var{field}th} field from the end of the line. This
2046 command is useful for sorting tables.
2049 @defopt sort-numeric-base
2050 This variable specifies the default radix for
2051 @code{sort-numeric-fields} to parse numbers.
2054 @deffn Command sort-columns reverse &optional beg end
2055 This command sorts the lines in the region between @var{beg} and
2056 @var{end}, comparing them alphabetically by a certain range of
2057 columns. The column positions of @var{beg} and @var{end} bound the
2058 range of columns to sort on.
2060 If @var{reverse} is non-@code{nil}, the sort is in reverse order.
2062 One unusual thing about this command is that the entire line
2063 containing position @var{beg}, and the entire line containing position
2064 @var{end}, are included in the region sorted.
2066 Note that @code{sort-columns} rejects text that contains tabs, because
2067 tabs could be split across the specified columns. Use @kbd{M-x
2068 untabify} to convert tabs to spaces before sorting.
2070 When possible, this command actually works by calling the @code{sort}
2075 @comment node-name, next, previous, up
2076 @section Counting Columns
2078 @cindex counting columns
2079 @cindex horizontal position
2081 The column functions convert between a character position (counting
2082 characters from the beginning of the buffer) and a column position
2083 (counting screen characters from the beginning of a line).
2085 These functions count each character according to the number of
2086 columns it occupies on the screen. This means control characters count
2087 as occupying 2 or 4 columns, depending upon the value of
2088 @code{ctl-arrow}, and tabs count as occupying a number of columns that
2089 depends on the value of @code{tab-width} and on the column where the tab
2090 begins. @xref{Usual Display}.
2092 Column number computations ignore the width of the window and the
2093 amount of horizontal scrolling. Consequently, a column value can be
2094 arbitrarily high. The first (or leftmost) column is numbered 0. They
2095 also ignore overlays and text properties, aside from invisibility.
2097 @defun current-column
2098 This function returns the horizontal position of point, measured in
2099 columns, counting from 0 at the left margin. The column position is the
2100 sum of the widths of all the displayed representations of the characters
2101 between the start of the current line and point.
2103 For an example of using @code{current-column}, see the description of
2104 @code{count-lines} in @ref{Text Lines}.
2107 @defun move-to-column column &optional force
2108 This function moves point to @var{column} in the current line. The
2109 calculation of @var{column} takes into account the widths of the
2110 displayed representations of the characters between the start of the
2113 If column @var{column} is beyond the end of the line, point moves to the
2114 end of the line. If @var{column} is negative, point moves to the
2115 beginning of the line.
2117 If it is impossible to move to column @var{column} because that is in
2118 the middle of a multicolumn character such as a tab, point moves to the
2119 end of that character. However, if @var{force} is non-@code{nil}, and
2120 @var{column} is in the middle of a tab, then @code{move-to-column}
2121 converts the tab into spaces so that it can move precisely to column
2122 @var{column}. Other multicolumn characters can cause anomalies despite
2123 @var{force}, since there is no way to split them.
2125 The argument @var{force} also has an effect if the line isn't long
2126 enough to reach column @var{column}; if it is @code{t}, that means to
2127 add whitespace at the end of the line to reach that column.
2129 If @var{column} is not an integer, an error is signaled.
2131 The return value is the column number actually moved to.
2135 @section Indentation
2138 The indentation functions are used to examine, move to, and change
2139 whitespace that is at the beginning of a line. Some of the functions
2140 can also change whitespace elsewhere on a line. Columns and indentation
2141 count from zero at the left margin.
2144 * Primitive Indent:: Functions used to count and insert indentation.
2145 * Mode-Specific Indent:: Customize indentation for different modes.
2146 * Region Indent:: Indent all the lines in a region.
2147 * Relative Indent:: Indent the current line based on previous lines.
2148 * Indent Tabs:: Adjustable, typewriter-like tab stops.
2149 * Motion by Indent:: Move to first non-blank character.
2152 @node Primitive Indent
2153 @subsection Indentation Primitives
2155 This section describes the primitive functions used to count and
2156 insert indentation. The functions in the following sections use these
2157 primitives. @xref{Width}, for related functions.
2159 @defun current-indentation
2160 @comment !!Type Primitive Function
2161 @comment !!SourceFile indent.c
2162 This function returns the indentation of the current line, which is
2163 the horizontal position of the first nonblank character. If the
2164 contents are entirely blank, then this is the horizontal position of the
2168 @deffn Command indent-to column &optional minimum
2169 @comment !!Type Primitive Function
2170 @comment !!SourceFile indent.c
2171 This function indents from point with tabs and spaces until @var{column}
2172 is reached. If @var{minimum} is specified and non-@code{nil}, then at
2173 least that many spaces are inserted even if this requires going beyond
2174 @var{column}. Otherwise the function does nothing if point is already
2175 beyond @var{column}. The value is the column at which the inserted
2178 The inserted whitespace characters inherit text properties from the
2179 surrounding text (usually, from the preceding text only). @xref{Sticky
2183 @defopt indent-tabs-mode
2184 @comment !!SourceFile indent.c
2185 If this variable is non-@code{nil}, indentation functions can insert
2186 tabs as well as spaces. Otherwise, they insert only spaces. Setting
2187 this variable automatically makes it buffer-local in the current buffer.
2190 @node Mode-Specific Indent
2191 @subsection Indentation Controlled by Major Mode
2193 An important function of each major mode is to customize the @key{TAB}
2194 key to indent properly for the language being edited. This section
2195 describes the mechanism of the @key{TAB} key and how to control it.
2196 The functions in this section return unpredictable values.
2198 @defvar indent-line-function
2199 This variable's value is the function to be used by @key{TAB} (and
2200 various commands) to indent the current line. The command
2201 @code{indent-according-to-mode} does no more than call this function.
2203 In Lisp mode, the value is the symbol @code{lisp-indent-line}; in C
2204 mode, @code{c-indent-line}; in Fortran mode, @code{fortran-indent-line}.
2205 In Fundamental mode, Text mode, and many other modes with no standard
2206 for indentation, the value is @code{indent-to-left-margin} (which is the
2210 @deffn Command indent-according-to-mode
2211 This command calls the function in @code{indent-line-function} to
2212 indent the current line in a way appropriate for the current major mode.
2215 @deffn Command indent-for-tab-command
2216 This command calls the function in @code{indent-line-function} to indent
2217 the current line; however, if that function is
2218 @code{indent-to-left-margin}, @code{insert-tab} is called instead. (That
2219 is a trivial command that inserts a tab character.)
2222 @deffn Command newline-and-indent
2223 @comment !!SourceFile simple.el
2224 This function inserts a newline, then indents the new line (the one
2225 following the newline just inserted) according to the major mode.
2227 It does indentation by calling the current @code{indent-line-function}.
2228 In programming language modes, this is the same thing @key{TAB} does,
2229 but in some text modes, where @key{TAB} inserts a tab,
2230 @code{newline-and-indent} indents to the column specified by
2234 @deffn Command reindent-then-newline-and-indent
2235 @comment !!SourceFile simple.el
2236 This command reindents the current line, inserts a newline at point,
2237 and then indents the new line (the one following the newline just
2240 This command does indentation on both lines according to the current
2241 major mode, by calling the current value of @code{indent-line-function}.
2242 In programming language modes, this is the same thing @key{TAB} does,
2243 but in some text modes, where @key{TAB} inserts a tab,
2244 @code{reindent-then-newline-and-indent} indents to the column specified
2245 by @code{left-margin}.
2249 @subsection Indenting an Entire Region
2251 This section describes commands that indent all the lines in the
2252 region. They return unpredictable values.
2254 @deffn Command indent-region start end to-column
2255 This command indents each nonblank line starting between @var{start}
2256 (inclusive) and @var{end} (exclusive). If @var{to-column} is
2257 @code{nil}, @code{indent-region} indents each nonblank line by calling
2258 the current mode's indentation function, the value of
2259 @code{indent-line-function}.
2261 If @var{to-column} is non-@code{nil}, it should be an integer
2262 specifying the number of columns of indentation; then this function
2263 gives each line exactly that much indentation, by either adding or
2264 deleting whitespace.
2266 If there is a fill prefix, @code{indent-region} indents each line
2267 by making it start with the fill prefix.
2270 @defvar indent-region-function
2271 The value of this variable is a function that can be used by
2272 @code{indent-region} as a short cut. It should take two arguments, the
2273 start and end of the region. You should design the function so
2274 that it will produce the same results as indenting the lines of the
2275 region one by one, but presumably faster.
2277 If the value is @code{nil}, there is no short cut, and
2278 @code{indent-region} actually works line by line.
2280 A short-cut function is useful in modes such as C mode and Lisp mode,
2281 where the @code{indent-line-function} must scan from the beginning of
2282 the function definition: applying it to each line would be quadratic in
2283 time. The short cut can update the scan information as it moves through
2284 the lines indenting them; this takes linear time. In a mode where
2285 indenting a line individually is fast, there is no need for a short cut.
2287 @code{indent-region} with a non-@code{nil} argument @var{to-column} has
2288 a different meaning and does not use this variable.
2291 @deffn Command indent-rigidly start end count
2292 @comment !!SourceFile indent.el
2293 This command indents all lines starting between @var{start}
2294 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
2295 This ``preserves the shape'' of the affected region, moving it as a
2296 rigid unit. Consequently, this command is useful not only for indenting
2297 regions of unindented text, but also for indenting regions of formatted
2300 For example, if @var{count} is 3, this command adds 3 columns of
2301 indentation to each of the lines beginning in the region specified.
2303 In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses
2304 @code{indent-rigidly} to indent the text copied from the message being
2308 @defun indent-code-rigidly start end columns &optional nochange-regexp
2309 This is like @code{indent-rigidly}, except that it doesn't alter lines
2310 that start within strings or comments.
2312 In addition, it doesn't alter a line if @var{nochange-regexp} matches at
2313 the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
2316 @node Relative Indent
2317 @subsection Indentation Relative to Previous Lines
2319 This section describes two commands that indent the current line
2320 based on the contents of previous lines.
2322 @deffn Command indent-relative &optional unindented-ok
2323 This command inserts whitespace at point, extending to the same
2324 column as the next @dfn{indent point} of the previous nonblank line. An
2325 indent point is a non-whitespace character following whitespace. The
2326 next indent point is the first one at a column greater than the current
2327 column of point. For example, if point is underneath and to the left of
2328 the first non-blank character of a line of text, it moves to that column
2329 by inserting whitespace.
2331 If the previous nonblank line has no next indent point (i.e., none at a
2332 great enough column position), @code{indent-relative} either does
2333 nothing (if @var{unindented-ok} is non-@code{nil}) or calls
2334 @code{tab-to-tab-stop}. Thus, if point is underneath and to the right
2335 of the last column of a short line of text, this command ordinarily
2336 moves point to the next tab stop by inserting whitespace.
2338 The return value of @code{indent-relative} is unpredictable.
2340 In the following example, point is at the beginning of the second
2345 This line is indented twelve spaces.
2346 @point{}The quick brown fox jumped.
2351 Evaluation of the expression @code{(indent-relative nil)} produces the
2356 This line is indented twelve spaces.
2357 @point{}The quick brown fox jumped.
2361 In this next example, point is between the @samp{m} and @samp{p} of
2366 This line is indented twelve spaces.
2367 The quick brown fox jum@point{}ped.
2372 Evaluation of the expression @code{(indent-relative nil)} produces the
2377 This line is indented twelve spaces.
2378 The quick brown fox jum @point{}ped.
2383 @deffn Command indent-relative-maybe
2384 @comment !!SourceFile indent.el
2385 This command indents the current line like the previous nonblank line,
2386 by calling @code{indent-relative} with @code{t} as the
2387 @var{unindented-ok} argument. The return value is unpredictable.
2389 If the previous nonblank line has no indent points beyond the current
2390 column, this command does nothing.
2394 @comment node-name, next, previous, up
2395 @subsection Adjustable ``Tab Stops''
2396 @cindex tabs stops for indentation
2398 This section explains the mechanism for user-specified ``tab stops''
2399 and the mechanisms that use and set them. The name ``tab stops'' is
2400 used because the feature is similar to that of the tab stops on a
2401 typewriter. The feature works by inserting an appropriate number of
2402 spaces and tab characters to reach the next tab stop column; it does not
2403 affect the display of tab characters in the buffer (@pxref{Usual
2404 Display}). Note that the @key{TAB} character as input uses this tab
2405 stop feature only in a few major modes, such as Text mode.
2406 @xref{Tab Stops,,, emacs, The GNU Emacs Manual}.
2408 @deffn Command tab-to-tab-stop
2409 This command inserts spaces or tabs before point, up to the next tab
2410 stop column defined by @code{tab-stop-list}. It searches the list for
2411 an element greater than the current column number, and uses that element
2412 as the column to indent to. It does nothing if no such element is
2416 @defopt tab-stop-list
2417 This variable is the list of tab stop columns used by
2418 @code{tab-to-tab-stops}. The elements should be integers in increasing
2419 order. The tab stop columns need not be evenly spaced.
2421 Use @kbd{M-x edit-tab-stops} to edit the location of tab stops
2425 @node Motion by Indent
2426 @subsection Indentation-Based Motion Commands
2428 These commands, primarily for interactive use, act based on the
2429 indentation in the text.
2431 @deffn Command back-to-indentation
2432 @comment !!SourceFile simple.el
2433 This command moves point to the first non-whitespace character in the
2434 current line (which is the line in which point is located). It returns
2438 @deffn Command backward-to-indentation &optional arg
2439 @comment !!SourceFile simple.el
2440 This command moves point backward @var{arg} lines and then to the
2441 first nonblank character on that line. It returns @code{nil}.
2442 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2445 @deffn Command forward-to-indentation &optional arg
2446 @comment !!SourceFile simple.el
2447 This command moves point forward @var{arg} lines and then to the first
2448 nonblank character on that line. It returns @code{nil}.
2449 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2453 @comment node-name, next, previous, up
2454 @section Case Changes
2455 @cindex case conversion in buffers
2457 The case change commands described here work on text in the current
2458 buffer. @xref{Case Conversion}, for case conversion functions that work
2459 on strings and characters. @xref{Case Tables}, for how to customize
2460 which characters are upper or lower case and how to convert them.
2462 @deffn Command capitalize-region start end
2463 This function capitalizes all words in the region defined by
2464 @var{start} and @var{end}. To capitalize means to convert each word's
2465 first character to upper case and convert the rest of each word to lower
2466 case. The function returns @code{nil}.
2468 If one end of the region is in the middle of a word, the part of the
2469 word within the region is treated as an entire word.
2471 When @code{capitalize-region} is called interactively, @var{start} and
2472 @var{end} are point and the mark, with the smallest first.
2476 ---------- Buffer: foo ----------
2477 This is the contents of the 5th foo.
2478 ---------- Buffer: foo ----------
2482 (capitalize-region 1 44)
2485 ---------- Buffer: foo ----------
2486 This Is The Contents Of The 5th Foo.
2487 ---------- Buffer: foo ----------
2492 @deffn Command downcase-region start end
2493 This function converts all of the letters in the region defined by
2494 @var{start} and @var{end} to lower case. The function returns
2497 When @code{downcase-region} is called interactively, @var{start} and
2498 @var{end} are point and the mark, with the smallest first.
2501 @deffn Command upcase-region start end
2502 This function converts all of the letters in the region defined by
2503 @var{start} and @var{end} to upper case. The function returns
2506 When @code{upcase-region} is called interactively, @var{start} and
2507 @var{end} are point and the mark, with the smallest first.
2510 @deffn Command capitalize-word count
2511 This function capitalizes @var{count} words after point, moving point
2512 over as it does. To capitalize means to convert each word's first
2513 character to upper case and convert the rest of each word to lower case.
2514 If @var{count} is negative, the function capitalizes the
2515 @minus{}@var{count} previous words but does not move point. The value
2518 If point is in the middle of a word, the part of the word before point
2519 is ignored when moving forward. The rest is treated as an entire word.
2521 When @code{capitalize-word} is called interactively, @var{count} is
2522 set to the numeric prefix argument.
2525 @deffn Command downcase-word count
2526 This function converts the @var{count} words after point to all lower
2527 case, moving point over as it does. If @var{count} is negative, it
2528 converts the @minus{}@var{count} previous words but does not move point.
2529 The value is @code{nil}.
2531 When @code{downcase-word} is called interactively, @var{count} is set
2532 to the numeric prefix argument.
2535 @deffn Command upcase-word count
2536 This function converts the @var{count} words after point to all upper
2537 case, moving point over as it does. If @var{count} is negative, it
2538 converts the @minus{}@var{count} previous words but does not move point.
2539 The value is @code{nil}.
2541 When @code{upcase-word} is called interactively, @var{count} is set to
2542 the numeric prefix argument.
2545 @node Text Properties
2546 @section Text Properties
2547 @cindex text properties
2548 @cindex attributes of text
2549 @cindex properties of text
2551 Each character position in a buffer or a string can have a @dfn{text
2552 property list}, much like the property list of a symbol (@pxref{Property
2553 Lists}). The properties belong to a particular character at a
2554 particular place, such as, the letter @samp{T} at the beginning of this
2555 sentence or the first @samp{o} in @samp{foo}---if the same character
2556 occurs in two different places, the two occurrences in general have
2557 different properties.
2559 Each property has a name and a value. Both of these can be any Lisp
2560 object, but the name is normally a symbol. Typically each property
2561 name symbol is used for a particular purpose; for instance, the text
2562 property @code{face} specifies the faces for displaying the character
2563 (@pxref{Special Properties}). The usual way to access the property
2564 list is to specify a name and ask what value corresponds to it.
2566 If a character has a @code{category} property, we call it the
2567 @dfn{property category} of the character. It should be a symbol. The
2568 properties of the symbol serve as defaults for the properties of the
2571 Copying text between strings and buffers preserves the properties
2572 along with the characters; this includes such diverse functions as
2573 @code{substring}, @code{insert}, and @code{buffer-substring}.
2576 * Examining Properties:: Looking at the properties of one character.
2577 * Changing Properties:: Setting the properties of a range of text.
2578 * Property Search:: Searching for where a property changes value.
2579 * Special Properties:: Particular properties with special meanings.
2580 * Format Properties:: Properties for representing formatting of text.
2581 * Sticky Properties:: How inserted text gets properties from
2583 * Saving Properties:: Saving text properties in files, and reading
2585 * Lazy Properties:: Computing text properties in a lazy fashion
2586 only when text is examined.
2587 * Clickable Text:: Using text properties to make regions of text
2588 do something when you click on them.
2589 * Links and Mouse-1:: How to make @key{Mouse-1} follow a link.
2590 * Fields:: The @code{field} property defines
2591 fields within the buffer.
2592 * Not Intervals:: Why text properties do not use
2593 Lisp-visible text intervals.
2596 @node Examining Properties
2597 @subsection Examining Text Properties
2599 The simplest way to examine text properties is to ask for the value of
2600 a particular property of a particular character. For that, use
2601 @code{get-text-property}. Use @code{text-properties-at} to get the
2602 entire property list of a character. @xref{Property Search}, for
2603 functions to examine the properties of a number of characters at once.
2605 These functions handle both strings and buffers. Keep in mind that
2606 positions in a string start from 0, whereas positions in a buffer start
2609 @defun get-text-property pos prop &optional object
2610 This function returns the value of the @var{prop} property of the
2611 character after position @var{pos} in @var{object} (a buffer or
2612 string). The argument @var{object} is optional and defaults to the
2615 If there is no @var{prop} property strictly speaking, but the character
2616 has a property category that is a symbol, then @code{get-text-property} returns
2617 the @var{prop} property of that symbol.
2620 @defun get-char-property position prop &optional object
2621 This function is like @code{get-text-property}, except that it checks
2622 overlays first and then text properties. @xref{Overlays}.
2624 The argument @var{object} may be a string, a buffer, or a window. If it
2625 is a window, then the buffer displayed in that window is used for text
2626 properties and overlays, but only the overlays active for that window
2627 are considered. If @var{object} is a buffer, then all overlays in that
2628 buffer are considered, as well as text properties. If @var{object} is a
2629 string, only text properties are considered, since strings never have
2633 @defun get-char-property-and-overlay position prop &optional object
2634 This is like @code{get-char-property}, but gives extra information
2635 about the overlay that the property value comes from.
2637 Its value is a cons cell whose @sc{car} is the property value, the
2638 same value @code{get-char-property} would return with the same
2639 arguments. Its @sc{cdr} is the overlay in which the property was
2640 found, or @code{nil}, if it was found as a text property or not found
2643 If @var{position} is at the end of @var{object}, both the @sc{car} and
2644 the @sc{cdr} of the value are @code{nil}.
2647 @defvar char-property-alias-alist
2648 This variable holds an alist which maps property names to a list of
2649 alternative property names. If a character does not specify a direct
2650 value for a property, the alternative property names are consulted in
2651 order; the first non-@code{nil} value is used. This variable takes
2652 precedence over @code{default-text-properties}, and @code{category}
2653 properties take precedence over this variable.
2656 @defun text-properties-at position &optional object
2657 This function returns the entire property list of the character at
2658 @var{position} in the string or buffer @var{object}. If @var{object} is
2659 @code{nil}, it defaults to the current buffer.
2662 @defvar default-text-properties
2663 This variable holds a property list giving default values for text
2664 properties. Whenever a character does not specify a value for a
2665 property, neither directly, through a category symbol, or through
2666 @code{char-property-alias-alist}, the value stored in this list is
2667 used instead. Here is an example:
2670 (setq default-text-properties '(foo 69)
2671 char-property-alias-alist nil)
2672 ;; @r{Make sure character 1 has no properties of its own.}
2673 (set-text-properties 1 2 nil)
2674 ;; @r{What we get, when we ask, is the default value.}
2675 (get-text-property 1 'foo)
2680 @node Changing Properties
2681 @subsection Changing Text Properties
2683 The primitives for changing properties apply to a specified range of
2684 text in a buffer or string. The function @code{set-text-properties}
2685 (see end of section) sets the entire property list of the text in that
2686 range; more often, it is useful to add, change, or delete just certain
2687 properties specified by name.
2689 Since text properties are considered part of the contents of the
2690 buffer (or string), and can affect how a buffer looks on the screen,
2691 any change in buffer text properties marks the buffer as modified.
2692 Buffer text property changes are undoable also (@pxref{Undo}).
2693 Positions in a string start from 0, whereas positions in a buffer
2696 @defun put-text-property start end prop value &optional object
2697 This function sets the @var{prop} property to @var{value} for the text
2698 between @var{start} and @var{end} in the string or buffer @var{object}.
2699 If @var{object} is @code{nil}, it defaults to the current buffer.
2702 @defun add-text-properties start end props &optional object
2703 This function adds or overrides text properties for the text between
2704 @var{start} and @var{end} in the string or buffer @var{object}. If
2705 @var{object} is @code{nil}, it defaults to the current buffer.
2707 The argument @var{props} specifies which properties to add. It should
2708 have the form of a property list (@pxref{Property Lists}): a list whose
2709 elements include the property names followed alternately by the
2710 corresponding values.
2712 The return value is @code{t} if the function actually changed some
2713 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2714 its values agree with those in the text).
2716 For example, here is how to set the @code{comment} and @code{face}
2717 properties of a range of text:
2720 (add-text-properties @var{start} @var{end}
2721 '(comment t face highlight))
2725 @defun remove-text-properties start end props &optional object
2726 This function deletes specified text properties from the text between
2727 @var{start} and @var{end} in the string or buffer @var{object}. If
2728 @var{object} is @code{nil}, it defaults to the current buffer.
2730 The argument @var{props} specifies which properties to delete. It
2731 should have the form of a property list (@pxref{Property Lists}): a list
2732 whose elements are property names alternating with corresponding values.
2733 But only the names matter---the values that accompany them are ignored.
2734 For example, here's how to remove the @code{face} property.
2737 (remove-text-properties @var{start} @var{end} '(face nil))
2740 The return value is @code{t} if the function actually changed some
2741 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2742 if no character in the specified text had any of those properties).
2744 To remove all text properties from certain text, use
2745 @code{set-text-properties} and specify @code{nil} for the new property
2749 @defun remove-list-of-text-properties start end list-of-properties &optional object
2750 Like @code{remove-text-properties} except that
2751 @var{list-of-properties} is a list of property names only, not an
2752 alternating list of property names and values.
2755 @defun set-text-properties start end props &optional object
2756 This function completely replaces the text property list for the text
2757 between @var{start} and @var{end} in the string or buffer @var{object}.
2758 If @var{object} is @code{nil}, it defaults to the current buffer.
2760 The argument @var{props} is the new property list. It should be a list
2761 whose elements are property names alternating with corresponding values.
2763 After @code{set-text-properties} returns, all the characters in the
2764 specified range have identical properties.
2766 If @var{props} is @code{nil}, the effect is to get rid of all properties
2767 from the specified range of text. Here's an example:
2770 (set-text-properties @var{start} @var{end} nil)
2773 Do not rely on the return value of this function.
2776 The easiest way to make a string with text properties
2777 is with @code{propertize}:
2779 @defun propertize string &rest properties
2780 This function returns a copy of @var{string} which has the text
2781 properties @var{properties}. These properties apply to all the
2782 characters in the string that is returned. Here is an example that
2783 constructs a string with a @code{face} property and a @code{mouse-face}
2787 (propertize "foo" 'face 'italic
2788 'mouse-face 'bold-italic)
2789 @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
2792 To put different properties on various parts of a string, you can
2793 construct each part with @code{propertize} and then combine them with
2798 (propertize "foo" 'face 'italic
2799 'mouse-face 'bold-italic)
2801 (propertize "bar" 'face 'italic
2802 'mouse-face 'bold-italic))
2803 @result{} #("foo and bar"
2804 0 3 (face italic mouse-face bold-italic)
2806 8 11 (face italic mouse-face bold-italic))
2810 See also the function @code{buffer-substring-no-properties}
2811 (@pxref{Buffer Contents}) which copies text from the buffer
2812 but does not copy its properties.
2814 @node Property Search
2815 @subsection Text Property Search Functions
2817 In typical use of text properties, most of the time several or many
2818 consecutive characters have the same value for a property. Rather than
2819 writing your programs to examine characters one by one, it is much
2820 faster to process chunks of text that have the same property value.
2822 Here are functions you can use to do this. They use @code{eq} for
2823 comparing property values. In all cases, @var{object} defaults to the
2826 For high performance, it's very important to use the @var{limit}
2827 argument to these functions, especially the ones that search for a
2828 single property---otherwise, they may spend a long time scanning to the
2829 end of the buffer, if the property you are interested in does not change.
2831 These functions do not move point; instead, they return a position (or
2832 @code{nil}). Remember that a position is always between two characters;
2833 the position returned by these functions is between two characters with
2834 different properties.
2836 @defun next-property-change pos &optional object limit
2837 The function scans the text forward from position @var{pos} in the
2838 string or buffer @var{object} till it finds a change in some text
2839 property, then returns the position of the change. In other words, it
2840 returns the position of the first character beyond @var{pos} whose
2841 properties are not identical to those of the character just after
2844 If @var{limit} is non-@code{nil}, then the scan ends at position
2845 @var{limit}. If there is no property change before that point,
2846 @code{next-property-change} returns @var{limit}.
2848 The value is @code{nil} if the properties remain unchanged all the way
2849 to the end of @var{object} and @var{limit} is @code{nil}. If the value
2850 is non-@code{nil}, it is a position greater than or equal to @var{pos}.
2851 The value equals @var{pos} only when @var{limit} equals @var{pos}.
2853 Here is an example of how to scan the buffer by chunks of text within
2854 which all properties are constant:
2858 (let ((plist (text-properties-at (point)))
2860 (or (next-property-change (point) (current-buffer))
2862 @r{Process text from point to @var{next-change}@dots{}}
2863 (goto-char next-change)))
2867 @defun previous-property-change pos &optional object limit
2868 This is like @code{next-property-change}, but scans back from @var{pos}
2869 instead of forward. If the value is non-@code{nil}, it is a position
2870 less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
2874 @defun next-single-property-change pos prop &optional object limit
2875 The function scans text for a change in the @var{prop} property, then
2876 returns the position of the change. The scan goes forward from
2877 position @var{pos} in the string or buffer @var{object}. In other
2878 words, this function returns the position of the first character
2879 beyond @var{pos} whose @var{prop} property differs from that of the
2880 character just after @var{pos}.
2882 If @var{limit} is non-@code{nil}, then the scan ends at position
2883 @var{limit}. If there is no property change before that point,
2884 @code{next-single-property-change} returns @var{limit}.
2886 The value is @code{nil} if the property remains unchanged all the way to
2887 the end of @var{object} and @var{limit} is @code{nil}. If the value is
2888 non-@code{nil}, it is a position greater than or equal to @var{pos}; it
2889 equals @var{pos} only if @var{limit} equals @var{pos}.
2892 @defun previous-single-property-change pos prop &optional object limit
2893 This is like @code{next-single-property-change}, but scans back from
2894 @var{pos} instead of forward. If the value is non-@code{nil}, it is a
2895 position less than or equal to @var{pos}; it equals @var{pos} only if
2896 @var{limit} equals @var{pos}.
2899 @defun next-char-property-change pos &optional limit
2900 This is like @code{next-property-change} except that it considers
2901 overlay properties as well as text properties, and if no change is
2902 found before the end of the buffer, it returns the maximum buffer
2903 position rather than @code{nil} (in this sense, it resembles the
2904 corresponding overlay function @code{next-overlay-change}, rather than
2905 @code{next-property-change}). There is no @var{object} operand
2906 because this function operates only on the current buffer. It returns
2907 the next address at which either kind of property changes.
2910 @defun previous-char-property-change pos &optional limit
2911 This is like @code{next-char-property-change}, but scans back from
2912 @var{pos} instead of forward, and returns the minimum buffer
2913 position if no change is found.
2916 @defun next-single-char-property-change pos prop &optional object limit
2917 This is like @code{next-single-property-change} except that it
2918 considers overlay properties as well as text properties, and if no
2919 change is found before the end of the @var{object}, it returns the
2920 maximum valid position in @var{object} rather than @code{nil}. Unlike
2921 @code{next-char-property-change}, this function @emph{does} have an
2922 @var{object} operand; if @var{object} is not a buffer, only
2923 text-properties are considered.
2926 @defun previous-single-char-property-change pos prop &optional object limit
2927 This is like @code{next-single-char-property-change}, but scans back
2928 from @var{pos} instead of forward, and returns the minimum valid
2929 position in @var{object} if no change is found.
2932 @defun text-property-any start end prop value &optional object
2933 This function returns non-@code{nil} if at least one character between
2934 @var{start} and @var{end} has a property @var{prop} whose value is
2935 @var{value}. More precisely, it returns the position of the first such
2936 character. Otherwise, it returns @code{nil}.
2938 The optional fifth argument, @var{object}, specifies the string or
2939 buffer to scan. Positions are relative to @var{object}. The default
2940 for @var{object} is the current buffer.
2943 @defun text-property-not-all start end prop value &optional object
2944 This function returns non-@code{nil} if at least one character between
2945 @var{start} and @var{end} does not have a property @var{prop} with value
2946 @var{value}. More precisely, it returns the position of the first such
2947 character. Otherwise, it returns @code{nil}.
2949 The optional fifth argument, @var{object}, specifies the string or
2950 buffer to scan. Positions are relative to @var{object}. The default
2951 for @var{object} is the current buffer.
2954 @node Special Properties
2955 @subsection Properties with Special Meanings
2957 Here is a table of text property names that have special built-in
2958 meanings. The following sections list a few additional special property
2959 names that control filling and property inheritance. All other names
2960 have no standard meaning, and you can use them as you like.
2963 @cindex property category of text character
2964 @kindex category @r{(text property)}
2966 If a character has a @code{category} property, we call it the
2967 @dfn{property category} of the character. It should be a symbol. The
2968 properties of this symbol serve as defaults for the properties of the
2972 @cindex face codes of text
2973 @kindex face @r{(text property)}
2974 You can use the property @code{face} to control the font and color of
2975 text. @xref{Faces}, for more information.
2977 In the simplest case, the value is a face name. It can also be a list;
2978 then each element can be any of these possibilities;
2982 A face name (a symbol or string).
2985 A property list of face attributes. This has the
2986 form (@var{keyword} @var{value} @dots{}), where each @var{keyword} is a
2987 face attribute name and @var{value} is a meaningful value for that
2988 attribute. With this feature, you do not need to create a face each
2989 time you want to specify a particular attribute for certain text.
2990 @xref{Face Attributes}.
2993 A cons cell of the form @code{(foreground-color . @var{color-name})} or
2994 @code{(background-color . @var{color-name})}. These elements specify
2995 just the foreground color or just the background color. @xref{Color
2996 Names}, for the supported forms of @var{color-name}.
2998 @code{(foreground-color . @var{color-name})} is equivalent to
2999 specifying @code{(:foreground @var{color-name})}, and likewise for the
3003 You can use Font Lock Mode (@pxref{Font Lock Mode}), to dynamically
3004 update @code{face} properties based on the contents of the text.
3006 @item font-lock-face
3007 @kindex font-lock-face @r{(text property)}
3008 The @code{font-lock-face} property is the same in all respects as the
3009 @code{face} property, but its state of activation is controlled by
3010 @code{font-lock-mode}. This can be advantageous for special buffers
3011 which are not intended to be user-editable, or for static areas of
3012 text which are always fontified in the same way.
3013 @xref{Precalculated Fontification}.
3015 Strictly speaking, @code{font-lock-face} is not a built-in text
3016 property; rather, it is implemented in Font Lock mode using
3017 @code{char-property-alias-alist}. @xref{Examining Properties}.
3019 This property is new in Emacs 22.1.
3022 @kindex mouse-face @r{(text property)}
3023 The property @code{mouse-face} is used instead of @code{face} when the
3024 mouse is on or near the character. For this purpose, ``near'' means
3025 that all text between the character and where the mouse is have the same
3026 @code{mouse-face} property value.
3029 @kindex fontified @r{(text property)}
3030 This property says whether the character has a face assigned to it by font
3031 locking. The display engine tests it to decide whether a buffer
3032 portion needs refontifying before display. @xref{Auto Faces}. It
3033 takes one of three values:
3037 Font locking is disabled, or the character's @code{face} property, if
3041 This value is only used when ``just in time'' font locking is enabled
3042 and it means that the character's @code{face} property is invalid and
3043 needs deferred fontification.
3046 The character's @code{face} property, or absence of one, is valid.
3050 This property activates various features that change the
3051 way text is displayed. For example, it can make text appear taller
3052 or shorter, higher or lower, wider or narrow, or replaced with an image.
3053 @xref{Display Property}.
3056 @kindex help-echo @r{(text property)}
3058 @anchor{Text help-echo}
3059 If text has a string as its @code{help-echo} property, then when you
3060 move the mouse onto that text, Emacs displays that string in the echo
3061 area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
3064 If the value of the @code{help-echo} property is a function, that
3065 function is called with three arguments, @var{window}, @var{object} and
3066 @var{pos} and should return a help string or @code{nil} for
3067 none. The first argument, @var{window} is the window in which
3068 the help was found. The second, @var{object}, is the buffer, overlay or
3069 string which had the @code{help-echo} property. The @var{pos}
3070 argument is as follows:
3074 If @var{object} is a buffer, @var{pos} is the position in the buffer.
3076 If @var{object} is an overlay, that overlay has a @code{help-echo}
3077 property, and @var{pos} is the position in the overlay's buffer.
3079 If @var{object} is a string (an overlay string or a string displayed
3080 with the @code{display} property), @var{pos} is the position in that
3084 If the value of the @code{help-echo} property is neither a function nor
3085 a string, it is evaluated to obtain a help string.
3087 You can alter the way help text is displayed by setting the variable
3088 @code{show-help-function} (@pxref{Help display}).
3090 This feature is used in the mode line and for other active text.
3093 @cindex keymap of character
3094 @kindex keymap @r{(text property)}
3095 The @code{keymap} property specifies an additional keymap for
3096 commands. When this keymap applies, it is used for key lookup before
3097 the minor mode keymaps and before the buffer's local map.
3098 @xref{Active Keymaps}. If the property value is a symbol, the
3099 symbol's function definition is used as the keymap.
3101 The property's value for the character before point applies if it is
3102 non-@code{nil} and rear-sticky, and the property's value for the
3103 character after point applies if it is non-@code{nil} and
3104 front-sticky. (For mouse clicks, the position of the click is used
3105 instead of the position of point.)
3108 @kindex local-map @r{(text property)}
3109 This property works like @code{keymap} except that it specifies a
3110 keymap to use @emph{instead of} the buffer's local map. For most
3111 purposes (perhaps all purposes), it is better to use the @code{keymap}
3115 The @code{syntax-table} property overrides what the syntax table says
3116 about this particular character. @xref{Syntax Properties}.
3119 @cindex read-only character
3120 @kindex read-only @r{(text property)}
3121 If a character has the property @code{read-only}, then modifying that
3122 character is not allowed. Any command that would do so gets an error,
3123 @code{text-read-only}. If the property value is a string, that string
3124 is used as the error message.
3126 Insertion next to a read-only character is an error if inserting
3127 ordinary text there would inherit the @code{read-only} property due to
3128 stickiness. Thus, you can control permission to insert next to
3129 read-only text by controlling the stickiness. @xref{Sticky Properties}.
3131 Since changing properties counts as modifying the buffer, it is not
3132 possible to remove a @code{read-only} property unless you know the
3133 special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
3134 and then remove the property. @xref{Read Only Buffers}.
3137 @kindex invisible @r{(text property)}
3138 A non-@code{nil} @code{invisible} property can make a character invisible
3139 on the screen. @xref{Invisible Text}, for details.
3142 @kindex intangible @r{(text property)}
3143 If a group of consecutive characters have equal and non-@code{nil}
3144 @code{intangible} properties, then you cannot place point between them.
3145 If you try to move point forward into the group, point actually moves to
3146 the end of the group. If you try to move point backward into the group,
3147 point actually moves to the start of the group.
3149 When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
3150 the @code{intangible} property is ignored.
3153 @kindex field @r{(text property)}
3154 Consecutive characters with the same @code{field} property constitute a
3155 @dfn{field}. Some motion functions including @code{forward-word} and
3156 @code{beginning-of-line} stop moving at a field boundary.
3160 @kindex cursor @r{(text property)}
3161 Normally, the cursor is displayed at the end of any overlay and text
3162 property strings present at the current window position. You can
3163 place the cursor on any desired character of these strings by giving
3164 that character a non-@code{nil} @var{cursor} text property.
3167 @kindex pointer @r{(text property)}
3168 This specifies a specific pointer shape when the mouse pointer is over
3169 this text or image. @xref{Pointer Shape}, for possible pointer
3173 @kindex line-spacing @r{(text property)}
3174 A newline can have a @code{line-spacing} text or overlay property that
3175 controls the height of the display line ending with that newline. The
3176 property value overrides the default frame line spacing and the buffer
3177 local @code{line-spacing} variable. @xref{Line Height}.
3180 @kindex line-height @r{(text property)}
3181 A newline can have a @code{line-height} text or overlay property that
3182 controls the total height of the display line ending in that newline.
3185 @item modification-hooks
3186 @cindex change hooks for a character
3187 @cindex hooks for changing a character
3188 @kindex modification-hooks @r{(text property)}
3189 If a character has the property @code{modification-hooks}, then its
3190 value should be a list of functions; modifying that character calls all
3191 of those functions. Each function receives two arguments: the beginning
3192 and end of the part of the buffer being modified. Note that if a
3193 particular modification hook function appears on several characters
3194 being modified by a single primitive, you can't predict how many times
3195 the function will be called.
3197 If these functions modify the buffer, they should bind
3198 @code{inhibit-modification-hooks} to @code{t} around doing so, to
3199 avoid confusing the internal mechanism that calls these hooks.
3201 @item insert-in-front-hooks
3202 @itemx insert-behind-hooks
3203 @kindex insert-in-front-hooks @r{(text property)}
3204 @kindex insert-behind-hooks @r{(text property)}
3205 The operation of inserting text in a buffer also calls the functions
3206 listed in the @code{insert-in-front-hooks} property of the following
3207 character and in the @code{insert-behind-hooks} property of the
3208 preceding character. These functions receive two arguments, the
3209 beginning and end of the inserted text. The functions are called
3210 @emph{after} the actual insertion takes place.
3212 See also @ref{Change Hooks}, for other hooks that are called
3213 when you change text in a buffer.
3217 @cindex hooks for motion of point
3218 @kindex point-entered @r{(text property)}
3219 @kindex point-left @r{(text property)}
3220 The special properties @code{point-entered} and @code{point-left}
3221 record hook functions that report motion of point. Each time point
3222 moves, Emacs compares these two property values:
3226 the @code{point-left} property of the character after the old location,
3229 the @code{point-entered} property of the character after the new
3234 If these two values differ, each of them is called (if not @code{nil})
3235 with two arguments: the old value of point, and the new one.
3237 The same comparison is made for the characters before the old and new
3238 locations. The result may be to execute two @code{point-left} functions
3239 (which may be the same function) and/or two @code{point-entered}
3240 functions (which may be the same function). In any case, all the
3241 @code{point-left} functions are called first, followed by all the
3242 @code{point-entered} functions.
3244 It is possible with @code{char-after} to examine characters at various
3245 buffer positions without moving point to those positions. Only an
3246 actual change in the value of point runs these hook functions.
3249 @defvar inhibit-point-motion-hooks
3250 When this variable is non-@code{nil}, @code{point-left} and
3251 @code{point-entered} hooks are not run, and the @code{intangible}
3252 property has no effect. Do not set this variable globally; bind it with
3256 @defvar show-help-function
3257 @anchor{Help display} If this variable is non-@code{nil}, it specifies a
3258 function called to display help strings. These may be @code{help-echo}
3259 properties, menu help strings (@pxref{Simple Menu Items},
3260 @pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
3261 Bar}). The specified function is called with one argument, the help
3262 string to display. Tooltip mode (@pxref{Tooltips,,, emacs, The GNU Emacs
3263 Manual}) provides an example.
3266 @node Format Properties
3267 @subsection Formatted Text Properties
3269 These text properties affect the behavior of the fill commands. They
3270 are used for representing formatted text. @xref{Filling}, and
3275 If a newline character has this property, it is a ``hard'' newline.
3276 The fill commands do not alter hard newlines and do not move words
3277 across them. However, this property takes effect only if the
3278 @code{use-hard-newlines} minor mode is enabled. @xref{Hard and Soft
3279 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
3282 This property specifies an extra right margin for filling this part of the
3286 This property specifies an extra left margin for filling this part of the
3290 This property specifies the style of justification for filling this part
3294 @node Sticky Properties
3295 @subsection Stickiness of Text Properties
3296 @cindex sticky text properties
3297 @cindex inheritance of text properties
3299 Self-inserting characters normally take on the same properties as the
3300 preceding character. This is called @dfn{inheritance} of properties.
3302 In a Lisp program, you can do insertion with inheritance or without,
3303 depending on your choice of insertion primitive. The ordinary text
3304 insertion functions such as @code{insert} do not inherit any properties.
3305 They insert text with precisely the properties of the string being
3306 inserted, and no others. This is correct for programs that copy text
3307 from one context to another---for example, into or out of the kill ring.
3308 To insert with inheritance, use the special primitives described in this
3309 section. Self-inserting characters inherit properties because they work
3310 using these primitives.
3312 When you do insertion with inheritance, @emph{which} properties are
3313 inherited, and from where, depends on which properties are @dfn{sticky}.
3314 Insertion after a character inherits those of its properties that are
3315 @dfn{rear-sticky}. Insertion before a character inherits those of its
3316 properties that are @dfn{front-sticky}. When both sides offer different
3317 sticky values for the same property, the previous character's value
3320 By default, a text property is rear-sticky but not front-sticky; thus,
3321 the default is to inherit all the properties of the preceding character,
3322 and nothing from the following character.
3324 You can control the stickiness of various text properties with two
3325 specific text properties, @code{front-sticky} and @code{rear-nonsticky},
3326 and with the variable @code{text-property-default-nonsticky}. You can
3327 use the variable to specify a different default for a given property.
3328 You can use those two text properties to make any specific properties
3329 sticky or nonsticky in any particular part of the text.
3331 If a character's @code{front-sticky} property is @code{t}, then all
3332 its properties are front-sticky. If the @code{front-sticky} property is
3333 a list, then the sticky properties of the character are those whose
3334 names are in the list. For example, if a character has a
3335 @code{front-sticky} property whose value is @code{(face read-only)},
3336 then insertion before the character can inherit its @code{face} property
3337 and its @code{read-only} property, but no others.
3339 The @code{rear-nonsticky} property works the opposite way. Most
3340 properties are rear-sticky by default, so the @code{rear-nonsticky}
3341 property says which properties are @emph{not} rear-sticky. If a
3342 character's @code{rear-nonsticky} property is @code{t}, then none of its
3343 properties are rear-sticky. If the @code{rear-nonsticky} property is a
3344 list, properties are rear-sticky @emph{unless} their names are in the
3347 @defvar text-property-default-nonsticky
3348 This variable holds an alist which defines the default rear-stickiness
3349 of various text properties. Each element has the form
3350 @code{(@var{property} . @var{nonstickiness})}, and it defines the
3351 stickiness of a particular text property, @var{property}.
3353 If @var{nonstickiness} is non-@code{nil}, this means that the property
3354 @var{property} is rear-nonsticky by default. Since all properties are
3355 front-nonsticky by default, this makes @var{property} nonsticky in both
3356 directions by default.
3358 The text properties @code{front-sticky} and @code{rear-nonsticky}, when
3359 used, take precedence over the default @var{nonstickiness} specified in
3360 @code{text-property-default-nonsticky}.
3363 Here are the functions that insert text with inheritance of properties:
3365 @defun insert-and-inherit &rest strings
3366 Insert the strings @var{strings}, just like the function @code{insert},
3367 but inherit any sticky properties from the adjoining text.
3370 @defun insert-before-markers-and-inherit &rest strings
3371 Insert the strings @var{strings}, just like the function
3372 @code{insert-before-markers}, but inherit any sticky properties from the
3376 @xref{Insertion}, for the ordinary insertion functions which do not
3379 @node Saving Properties
3380 @subsection Saving Text Properties in Files
3381 @cindex text properties in files
3382 @cindex saving text properties
3384 You can save text properties in files (along with the text itself),
3385 and restore the same text properties when visiting or inserting the
3386 files, using these two hooks:
3388 @defvar write-region-annotate-functions
3389 This variable's value is a list of functions for @code{write-region} to
3390 run to encode text properties in some fashion as annotations to the text
3391 being written in the file. @xref{Writing to Files}.
3393 Each function in the list is called with two arguments: the start and
3394 end of the region to be written. These functions should not alter the
3395 contents of the buffer. Instead, they should return lists indicating
3396 annotations to write in the file in addition to the text in the
3399 Each function should return a list of elements of the form
3400 @code{(@var{position} . @var{string})}, where @var{position} is an
3401 integer specifying the relative position within the text to be written,
3402 and @var{string} is the annotation to add there.
3404 Each list returned by one of these functions must be already sorted in
3405 increasing order by @var{position}. If there is more than one function,
3406 @code{write-region} merges the lists destructively into one sorted list.
3408 When @code{write-region} actually writes the text from the buffer to the
3409 file, it intermixes the specified annotations at the corresponding
3410 positions. All this takes place without modifying the buffer.
3413 @defvar after-insert-file-functions
3414 This variable holds a list of functions for @code{insert-file-contents}
3415 to call after inserting a file's contents. These functions should scan
3416 the inserted text for annotations, and convert them to the text
3417 properties they stand for.
3419 Each function receives one argument, the length of the inserted text;
3420 point indicates the start of that text. The function should scan that
3421 text for annotations, delete them, and create the text properties that
3422 the annotations specify. The function should return the updated length
3423 of the inserted text, as it stands after those changes. The value
3424 returned by one function becomes the argument to the next function.
3426 These functions should always return with point at the beginning of
3429 The intended use of @code{after-insert-file-functions} is for converting
3430 some sort of textual annotations into actual text properties. But other
3431 uses may be possible.
3434 We invite users to write Lisp programs to store and retrieve text
3435 properties in files, using these hooks, and thus to experiment with
3436 various data formats and find good ones. Eventually we hope users
3437 will produce good, general extensions we can install in Emacs.
3439 We suggest not trying to handle arbitrary Lisp objects as text property
3440 names or values---because a program that general is probably difficult
3441 to write, and slow. Instead, choose a set of possible data types that
3442 are reasonably flexible, and not too hard to encode.
3444 @xref{Format Conversion}, for a related feature.
3446 @c ??? In next edition, merge this info Format Conversion.
3448 @node Lazy Properties
3449 @subsection Lazy Computation of Text Properties
3451 Instead of computing text properties for all the text in the buffer,
3452 you can arrange to compute the text properties for parts of the text
3453 when and if something depends on them.
3455 The primitive that extracts text from the buffer along with its
3456 properties is @code{buffer-substring}. Before examining the properties,
3457 this function runs the abnormal hook @code{buffer-access-fontify-functions}.
3459 @defvar buffer-access-fontify-functions
3460 This variable holds a list of functions for computing text properties.
3461 Before @code{buffer-substring} copies the text and text properties for a
3462 portion of the buffer, it calls all the functions in this list. Each of
3463 the functions receives two arguments that specify the range of the
3464 buffer being accessed. (The buffer itself is always the current
3468 The function @code{buffer-substring-no-properties} does not call these
3469 functions, since it ignores text properties anyway.
3471 In order to prevent the hook functions from being called more than
3472 once for the same part of the buffer, you can use the variable
3473 @code{buffer-access-fontified-property}.
3475 @defvar buffer-access-fontified-property
3476 If this value's variable is non-@code{nil}, it is a symbol which is used
3477 as a text property name. A non-@code{nil} value for that text property
3478 means, ``the other text properties for this character have already been
3481 If all the characters in the range specified for @code{buffer-substring}
3482 have a non-@code{nil} value for this property, @code{buffer-substring}
3483 does not call the @code{buffer-access-fontify-functions} functions. It
3484 assumes these characters already have the right text properties, and
3485 just copies the properties they already have.
3487 The normal way to use this feature is that the
3488 @code{buffer-access-fontify-functions} functions add this property, as
3489 well as others, to the characters they operate on. That way, they avoid
3490 being called over and over for the same text.
3493 @node Clickable Text
3494 @subsection Defining Clickable Text
3495 @cindex clickable text
3497 @dfn{Clickable text} is text that can be clicked, with either the
3498 the mouse or via keyboard commands, to produce some result. Many
3499 major modes use clickable text to implement features such as
3500 hyper-links. The @code{button} package provides an easy way to insert
3501 and manipulate clickable text. @xref{Buttons}.
3503 In this section, we will explain how to manually set up clickable
3504 text in a buffer using text properties. This involves two things: (1)
3505 indicating clickability when the mouse moves over the text, and (2)
3506 making @kbd{RET} or a mouse click on that text do something.
3508 Indicating clickability usually involves highlighting the text, and
3509 often involves displaying helpful information about the action, such
3510 as which mouse button to press, or a short summary of the action.
3511 This can be done with the @code{mouse-face} and @code{help-echo}
3512 text properties. @xref{Special Properties}.
3513 Here is an example of how Dired does it:
3517 (if (dired-move-to-filename)
3518 (add-text-properties
3521 (dired-move-to-end-of-filename)
3523 '(mouse-face highlight
3524 help-echo "mouse-2: visit this file in other window")))
3529 The first two arguments to @code{add-text-properties} specify the
3530 beginning and end of the text.
3532 The usual way to make the mouse do something when you click it
3533 on this text is to define @code{mouse-2} in the major mode's
3534 keymap. The job of checking whether the click was on clickable text
3535 is done by the command definition. Here is how Dired does it:
3538 (defun dired-mouse-find-file-other-window (event)
3539 "In Dired, visit the file or directory name you click on."
3541 (let (window pos file)
3543 (setq window (posn-window (event-end event))
3544 pos (posn-point (event-end event)))
3545 (if (not (windowp window))
3546 (error "No file chosen"))
3547 (set-buffer (window-buffer window))
3549 (setq file (dired-get-file-for-visit)))
3550 (if (file-directory-p file)
3551 (or (and (cdr dired-subdir-alist)
3552 (dired-goto-subdir file))
3554 (select-window window)
3555 (dired-other-window file)))
3556 (select-window window)
3557 (find-file-other-window (file-name-sans-versions file t)))))
3561 The reason for the @code{save-excursion} construct is to avoid
3562 changing the current buffer. In this case,
3563 Dired uses the functions @code{posn-window} and @code{posn-point}
3564 to determine which buffer the click happened in and where, and
3565 in that buffer, @code{dired-get-file-for-visit} to determine which
3568 Instead of defining a mouse command for the major mode, you can define
3569 a key binding for the clickable text itself, using the @code{keymap}
3573 (let ((map (make-sparse-keymap)))
3574 (define-key map [mouse-2] 'operate-this-button)
3575 (put-text-property (point)
3577 (dired-move-to-end-of-filename)
3583 This method makes it possible to define different commands for various
3584 clickable pieces of text. Also, the major mode definition (or the
3585 global definition) remains available for the rest of the text in the
3588 @node Links and Mouse-1
3589 @subsection Links and Mouse-1
3590 @cindex follow links
3593 The normal Emacs command for activating text in read-only buffers is
3594 @key{Mouse-2}, which includes following textual links. However, most
3595 graphical applications use @key{Mouse-1} for following links. For
3596 compatibility, @key{Mouse-1} follows links in Emacs too, when you
3597 click on a link quickly without moving the mouse. The user can
3598 customize this behavior through the variable
3599 @code{mouse-1-click-follows-link}.
3601 To define text as a link at the Lisp level, you should bind the
3602 @code{mouse-2} event to a command to follow the link. Then, to indicate that
3603 @key{Mouse-1} should also follow the link, you should specify a
3604 @code{follow-link} condition either as a text property or as a key
3608 @item @code{follow-link} property
3609 If the clickable text has a non-@code{nil} @code{follow-link} text or overlay
3610 property, that specifies the condition.
3612 @item @code{follow-link} event
3613 If there is a binding for the @code{follow-link} event, either on the
3614 clickable text or in the local keymap, the binding is the condition.
3617 Regardless of how you set the @code{follow-link} condition, its
3618 value is used as follows to determine whether the given position is
3619 inside a link, and (if so) to compute an @dfn{action code} saying how
3620 @key{Mouse-1} should handle the link.
3623 @item @code{mouse-face}
3624 If the condition is @code{mouse-face}, a position is inside a link if
3625 there is a non-@code{nil} @code{mouse-face} property at that position.
3626 The action code is always @code{t}.
3628 For example, here is how Info mode handles @key{Mouse-1}:
3631 (define-key Info-mode-map [follow-link] 'mouse-face)
3635 If the condition is a valid function, @var{func}, then a position
3636 @var{pos} is inside a link if @code{(@var{func} @var{pos})} evaluates
3637 to non-@code{nil}. The value returned by @var{func} serves as the
3640 For example, here is how pcvs enables @key{Mouse-1} to follow links on
3644 (define-key map [follow-link]
3646 (eq (get-char-property pos 'face) 'cvs-filename-face)))
3650 If the condition value is anything else, then the position is inside a
3651 link and the condition itself is the action code. Clearly you should
3652 only specify this kind of condition on the text that constitutes a
3657 The action code tells @key{Mouse-1} how to follow the link:
3660 @item a string or vector
3661 If the action code is a string or vector, the @key{Mouse-1} event is
3662 translated into the first element of the string or vector; i.e., the
3663 action of the @key{Mouse-1} click is the local or global binding of
3664 that character or symbol. Thus, if the action code is @code{"foo"},
3665 @key{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
3666 @key{Mouse-1} translates into @key{foo}.
3669 For any other non-@code{nil} action code, the @code{mouse-1} event is
3670 translated into a @code{mouse-2} event at the same position.
3673 To define @key{Mouse-1} to activate a button defined with
3674 @code{define-button-type}, give the button a @code{follow-link}
3675 property with a value as specified above to determine how to follow
3676 the link. For example, here is how Help mode handles @key{Mouse-1}:
3679 (define-button-type 'help-xref
3681 'action #'help-button-action)
3684 To define @key{Mouse-1} on a widget defined with
3685 @code{define-widget}, give the widget a @code{:follow-link} property
3686 with a value as specified above to determine how to follow the link.
3688 For example, here is how the @code{link} widget specifies that
3689 a @key{Mouse-1} click shall be translated to @key{RET}:
3692 (define-widget 'link 'item
3694 :button-prefix 'widget-link-prefix
3695 :button-suffix 'widget-link-suffix
3697 :help-echo "Follow the link."
3701 @defun mouse-on-link-p pos
3702 This function returns non-@code{nil} if position @var{pos} in the
3703 current buffer is on a link. @var{pos} can also be a mouse event
3704 location, as returned by @code{event-start} (@pxref{Accessing Events}).
3708 @subsection Defining and Using Fields
3711 A field is a range of consecutive characters in the buffer that are
3712 identified by having the same value (comparing with @code{eq}) of the
3713 @code{field} property (either a text-property or an overlay property).
3714 This section describes special functions that are available for
3715 operating on fields.
3717 You specify a field with a buffer position, @var{pos}. We think of
3718 each field as containing a range of buffer positions, so the position
3719 you specify stands for the field containing that position.
3721 When the characters before and after @var{pos} are part of the same
3722 field, there is no doubt which field contains @var{pos}: the one those
3723 characters both belong to. When @var{pos} is at a boundary between
3724 fields, which field it belongs to depends on the stickiness of the
3725 @code{field} properties of the two surrounding characters (@pxref{Sticky
3726 Properties}). The field whose property would be inherited by text
3727 inserted at @var{pos} is the field that contains @var{pos}.
3729 There is an anomalous case where newly inserted text at @var{pos}
3730 would not inherit the @code{field} property from either side. This
3731 happens if the previous character's @code{field} property is not
3732 rear-sticky, and the following character's @code{field} property is not
3733 front-sticky. In this case, @var{pos} belongs to neither the preceding
3734 field nor the following field; the field functions treat it as belonging
3735 to an empty field whose beginning and end are both at @var{pos}.
3737 In all of these functions, if @var{pos} is omitted or @code{nil}, the
3738 value of point is used by default. If narrowing is in effect, then
3739 @var{pos} should fall within the accessible portion. @xref{Narrowing}.
3741 @defun field-beginning &optional pos escape-from-edge limit
3742 This function returns the beginning of the field specified by @var{pos}.
3744 If @var{pos} is at the beginning of its field, and
3745 @var{escape-from-edge} is non-@code{nil}, then the return value is
3746 always the beginning of the preceding field that @emph{ends} at @var{pos},
3747 regardless of the stickiness of the @code{field} properties around
3750 If @var{limit} is non-@code{nil}, it is a buffer position; if the
3751 beginning of the field is before @var{limit}, then @var{limit} will be
3755 @defun field-end &optional pos escape-from-edge limit
3756 This function returns the end of the field specified by @var{pos}.
3758 If @var{pos} is at the end of its field, and @var{escape-from-edge} is
3759 non-@code{nil}, then the return value is always the end of the following
3760 field that @emph{begins} at @var{pos}, regardless of the stickiness of
3761 the @code{field} properties around @var{pos}.
3763 If @var{limit} is non-@code{nil}, it is a buffer position; if the end
3764 of the field is after @var{limit}, then @var{limit} will be returned
3768 @defun field-string &optional pos
3769 This function returns the contents of the field specified by @var{pos},
3773 @defun field-string-no-properties &optional pos
3774 This function returns the contents of the field specified by @var{pos},
3775 as a string, discarding text properties.
3778 @defun delete-field &optional pos
3779 This function deletes the text of the field specified by @var{pos}.
3782 @defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
3783 This function ``constrains'' @var{new-pos} to the field that
3784 @var{old-pos} belongs to---in other words, it returns the position
3785 closest to @var{new-pos} that is in the same field as @var{old-pos}.
3787 If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
3788 the value of point instead, and moves point to the resulting position
3789 as well as returning it.
3791 If @var{old-pos} is at the boundary of two fields, then the acceptable
3792 final positions depend on the argument @var{escape-from-edge}. If
3793 @var{escape-from-edge} is @code{nil}, then @var{new-pos} must be in
3794 the field whose @code{field} property equals what new characters
3795 inserted at @var{old-pos} would inherit. (This depends on the
3796 stickiness of the @code{field} property for the characters before and
3797 after @var{old-pos}.) If @var{escape-from-edge} is non-@code{nil},
3798 @var{new-pos} can be anywhere in the two adjacent fields.
3799 Additionally, if two fields are separated by another field with the
3800 special value @code{boundary}, then any point within this special
3801 field is also considered to be ``on the boundary.''
3803 Commands like @kbd{C-a} with no argumemt, that normally move backward
3804 to a specific kind of location and stay there once there, probably
3805 should specify @code{nil} for @var{escape-from-edge}. Other motion
3806 commands that check fields should probably pass @code{t}.
3808 If the optional argument @var{only-in-line} is non-@code{nil}, and
3809 constraining @var{new-pos} in the usual way would move it to a different
3810 line, @var{new-pos} is returned unconstrained. This used in commands
3811 that move by line, such as @code{next-line} and
3812 @code{beginning-of-line}, so that they respect field boundaries only in
3813 the case where they can still move to the right line.
3815 If the optional argument @var{inhibit-capture-property} is
3816 non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
3817 name, then any field boundaries are ignored.
3819 You can cause @code{constrain-to-field} to ignore all field boundaries
3820 (and so never constrain anything) by binding the variable
3821 @code{inhibit-field-text-motion} to a non-@code{nil} value.
3825 @subsection Why Text Properties are not Intervals
3828 Some editors that support adding attributes to text in the buffer do
3829 so by letting the user specify ``intervals'' within the text, and adding
3830 the properties to the intervals. Those editors permit the user or the
3831 programmer to determine where individual intervals start and end. We
3832 deliberately provided a different sort of interface in Emacs Lisp to
3833 avoid certain paradoxical behavior associated with text modification.
3835 If the actual subdivision into intervals is meaningful, that means you
3836 can distinguish between a buffer that is just one interval with a
3837 certain property, and a buffer containing the same text subdivided into
3838 two intervals, both of which have that property.
3840 Suppose you take the buffer with just one interval and kill part of
3841 the text. The text remaining in the buffer is one interval, and the
3842 copy in the kill ring (and the undo list) becomes a separate interval.
3843 Then if you yank back the killed text, you get two intervals with the
3844 same properties. Thus, editing does not preserve the distinction
3845 between one interval and two.
3847 Suppose we ``fix'' this problem by coalescing the two intervals when
3848 the text is inserted. That works fine if the buffer originally was a
3849 single interval. But suppose instead that we have two adjacent
3850 intervals with the same properties, and we kill the text of one interval
3851 and yank it back. The same interval-coalescence feature that rescues
3852 the other case causes trouble in this one: after yanking, we have just
3853 one interval. One again, editing does not preserve the distinction
3854 between one interval and two.
3856 Insertion of text at the border between intervals also raises
3857 questions that have no satisfactory answer.
3859 However, it is easy to arrange for editing to behave consistently for
3860 questions of the form, ``What are the properties of this character?''
3861 So we have decided these are the only questions that make sense; we have
3862 not implemented asking questions about where intervals start or end.
3864 In practice, you can usually use the text property search functions in
3865 place of explicit interval boundaries. You can think of them as finding
3866 the boundaries of intervals, assuming that intervals are always
3867 coalesced whenever possible. @xref{Property Search}.
3869 Emacs also provides explicit intervals as a presentation feature; see
3873 @section Substituting for a Character Code
3875 The following functions replace characters within a specified region
3876 based on their character codes.
3878 @defun subst-char-in-region start end old-char new-char &optional noundo
3879 @cindex replace characters
3880 This function replaces all occurrences of the character @var{old-char}
3881 with the character @var{new-char} in the region of the current buffer
3882 defined by @var{start} and @var{end}.
3884 @cindex undo avoidance
3885 If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
3886 not record the change for undo and does not mark the buffer as modified.
3887 This was useful for controlling the old selective display feature
3888 (@pxref{Selective Display}).
3890 @code{subst-char-in-region} does not move point and returns
3895 ---------- Buffer: foo ----------
3896 This is the contents of the buffer before.
3897 ---------- Buffer: foo ----------
3901 (subst-char-in-region 1 20 ?i ?X)
3904 ---------- Buffer: foo ----------
3905 ThXs Xs the contents of the buffer before.
3906 ---------- Buffer: foo ----------
3911 @defun translate-region start end table
3912 This function applies a translation table to the characters in the
3913 buffer between positions @var{start} and @var{end}.
3915 The translation table @var{table} is a string or a char-table;
3916 @code{(aref @var{table} @var{ochar})} gives the translated character
3917 corresponding to @var{ochar}. If @var{table} is a string, any
3918 characters with codes larger than the length of @var{table} are not
3919 altered by the translation.
3921 The return value of @code{translate-region} is the number of
3922 characters that were actually changed by the translation. This does
3923 not count characters that were mapped into themselves in the
3931 A register is a sort of variable used in Emacs editing that can hold a
3932 variety of different kinds of values. Each register is named by a
3933 single character. All @acronym{ASCII} characters and their meta variants
3934 (but with the exception of @kbd{C-g}) can be used to name registers.
3935 Thus, there are 255 possible registers. A register is designated in
3936 Emacs Lisp by the character that is its name.
3938 @defvar register-alist
3939 This variable is an alist of elements of the form @code{(@var{name} .
3940 @var{contents})}. Normally, there is one element for each Emacs
3941 register that has been used.
3943 The object @var{name} is a character (an integer) identifying the
3947 The @var{contents} of a register can have several possible types:
3951 A number stands for itself. If @code{insert-register} finds a number
3952 in the register, it converts the number to decimal.
3955 A marker represents a buffer position to jump to.
3958 A string is text saved in the register.
3961 A rectangle is represented by a list of strings.
3963 @item @code{(@var{window-configuration} @var{position})}
3964 This represents a window configuration to restore in one frame, and a
3965 position to jump to in the current buffer.
3967 @item @code{(@var{frame-configuration} @var{position})}
3968 This represents a frame configuration to restore, and a position
3969 to jump to in the current buffer.
3971 @item (file @var{filename})
3972 This represents a file to visit; jumping to this value visits file
3975 @item (file-query @var{filename} @var{position})
3976 This represents a file to visit and a position in it; jumping to this
3977 value visits file @var{filename} and goes to buffer position
3978 @var{position}. Restoring this type of position asks the user for
3982 The functions in this section return unpredictable values unless
3985 @defun get-register reg
3986 This function returns the contents of the register
3987 @var{reg}, or @code{nil} if it has no contents.
3990 @defun set-register reg value
3991 This function sets the contents of register @var{reg} to @var{value}.
3992 A register can be set to any value, but the other register functions
3993 expect only certain data types. The return value is @var{value}.
3996 @deffn Command view-register reg
3997 This command displays what is contained in register @var{reg}.
4001 @deffn Command point-to-register reg
4002 This command stores both the current location of point and the current
4003 buffer in register @var{reg} as a marker.
4006 @deffn Command jump-to-register reg
4007 @deffnx Command register-to-point reg
4008 @comment !!SourceFile register.el
4009 This command restores the status recorded in register @var{reg}.
4011 If @var{reg} contains a marker, it moves point to the position stored in
4012 the marker. Since both the buffer and the location within the buffer
4013 are stored by the @code{point-to-register} function, this command can
4014 switch you to another buffer.
4016 If @var{reg} contains a window configuration or a frame configuration.
4017 @code{jump-to-register} restores that configuration.
4021 @deffn Command insert-register reg &optional beforep
4022 This command inserts contents of register @var{reg} into the current
4025 Normally, this command puts point before the inserted text, and the
4026 mark after it. However, if the optional second argument @var{beforep}
4027 is non-@code{nil}, it puts the mark before and point after.
4028 You can pass a non-@code{nil} second argument @var{beforep} to this
4029 function interactively by supplying any prefix argument.
4031 If the register contains a rectangle, then the rectangle is inserted
4032 with its upper left corner at point. This means that text is inserted
4033 in the current line and underneath it on successive lines.
4035 If the register contains something other than saved text (a string) or
4036 a rectangle (a list), currently useless things happen. This may be
4037 changed in the future.
4041 @deffn Command copy-to-register reg start end &optional delete-flag
4042 This command copies the region from @var{start} to @var{end} into
4043 register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes
4044 the region from the buffer after copying it into the register.
4047 @deffn Command prepend-to-register reg start end &optional delete-flag
4048 This command prepends the region from @var{start} to @var{end} into
4049 register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes
4050 the region from the buffer after copying it to the register.
4053 @deffn Command append-to-register reg start end &optional delete-flag
4054 This command appends the region from @var{start} to @var{end} to the
4055 text already in register @var{reg}. If @var{delete-flag} is
4056 non-@code{nil}, it deletes the region from the buffer after copying it
4060 @deffn Command copy-rectangle-to-register reg start end &optional delete-flag
4061 This command copies a rectangular region from @var{start} to @var{end}
4062 into register @var{reg}. If @var{delete-flag} is non-@code{nil}, it
4063 deletes the region from the buffer after copying it to the register.
4066 @deffn Command window-configuration-to-register reg
4067 This function stores the window configuration of the selected frame in
4071 @deffn Command frame-configuration-to-register reg
4072 This function stores the current frame configuration in register
4078 @section Transposition of Text
4080 This subroutine is used by the transposition commands.
4082 @defun transpose-regions start1 end1 start2 end2 &optional leave-markers
4083 This function exchanges two nonoverlapping portions of the buffer.
4084 Arguments @var{start1} and @var{end1} specify the bounds of one portion
4085 and arguments @var{start2} and @var{end2} specify the bounds of the
4088 Normally, @code{transpose-regions} relocates markers with the transposed
4089 text; a marker previously positioned within one of the two transposed
4090 portions moves along with that portion, thus remaining between the same
4091 two characters in their new position. However, if @var{leave-markers}
4092 is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
4093 all markers unrelocated.
4097 @section Base 64 Encoding
4098 @cindex base 64 encoding
4100 Base 64 code is used in email to encode a sequence of 8-bit bytes as
4101 a longer sequence of @acronym{ASCII} graphic characters. It is defined in
4102 Internet RFC@footnote{
4103 An RFC, an acronym for @dfn{Request for Comments}, is a numbered
4104 Internet informational document describing a standard. RFCs are
4105 usually written by technical experts acting on their own initiative,
4106 and are traditionally written in a pragmatic, experience-driven
4108 }2045. This section describes the functions for
4109 converting to and from this code.
4111 @defun base64-encode-region beg end &optional no-line-break
4112 This function converts the region from @var{beg} to @var{end} into base
4113 64 code. It returns the length of the encoded text. An error is
4114 signaled if a character in the region is multibyte, i.e.@: in a
4115 multibyte buffer the region must contain only characters from the
4116 charsets @code{ascii}, @code{eight-bit-control} and
4117 @code{eight-bit-graphic}.
4119 Normally, this function inserts newline characters into the encoded
4120 text, to avoid overlong lines. However, if the optional argument
4121 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4122 the output is just one long line.
4125 @defun base64-encode-string string &optional no-line-break
4126 This function converts the string @var{string} into base 64 code. It
4127 returns a string containing the encoded text. As for
4128 @code{base64-encode-region}, an error is signaled if a character in the
4129 string is multibyte.
4131 Normally, this function inserts newline characters into the encoded
4132 text, to avoid overlong lines. However, if the optional argument
4133 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4134 the result string is just one long line.
4137 @defun base64-decode-region beg end
4138 This function converts the region from @var{beg} to @var{end} from base
4139 64 code into the corresponding decoded text. It returns the length of
4142 The decoding functions ignore newline characters in the encoded text.
4145 @defun base64-decode-string string
4146 This function converts the string @var{string} from base 64 code into
4147 the corresponding decoded text. It returns a unibyte string containing the
4150 The decoding functions ignore newline characters in the encoded text.
4154 @section MD5 Checksum
4155 @cindex MD5 checksum
4156 @cindex message digest computation
4158 MD5 cryptographic checksums, or @dfn{message digests}, are 128-bit
4159 ``fingerprints'' of a document or program. They are used to verify
4160 that you have an exact and unaltered copy of the data. The algorithm
4161 to calculate the MD5 message digest is defined in Internet
4163 For an explanation of what is an RFC, see the footnote in @ref{Base
4165 }1321. This section describes the Emacs facilities for computing
4168 @defun md5 object &optional start end coding-system noerror
4169 This function returns the MD5 message digest of @var{object}, which
4170 should be a buffer or a string.
4172 The two optional arguments @var{start} and @var{end} are character
4173 positions specifying the portion of @var{object} to compute the
4174 message digest for. If they are @code{nil} or omitted, the digest is
4175 computed for the whole of @var{object}.
4177 The function @code{md5} does not compute the message digest directly
4178 from the internal Emacs representation of the text (@pxref{Text
4179 Representations}). Instead, it encodes the text using a coding
4180 system, and computes the message digest from the encoded text. The
4181 optional fourth argument @var{coding-system} specifies which coding
4182 system to use for encoding the text. It should be the same coding
4183 system that you used to read the text, or that you used or will use
4184 when saving or sending the text. @xref{Coding Systems}, for more
4185 information about coding systems.
4187 If @var{coding-system} is @code{nil} or omitted, the default depends
4188 on @var{object}. If @var{object} is a buffer, the default for
4189 @var{coding-system} is whatever coding system would be chosen by
4190 default for writing this text into a file. If @var{object} is a
4191 string, the user's most preferred coding system (@pxref{Recognize
4192 Coding, prefer-coding-system, the description of
4193 @code{prefer-coding-system}, emacs, GNU Emacs Manual}) is used.
4195 Normally, @code{md5} signals an error if the text can't be encoded
4196 using the specified or chosen coding system. However, if
4197 @var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
4201 @node Atomic Changes
4202 @section Atomic Change Groups
4203 @cindex atomic changes
4205 In data base terminology, an @dfn{atomic} change is an indivisible
4206 change---it can succeed entirely or it can fail entirely, but it
4207 cannot partly succeed. A Lisp program can make a series of changes to
4208 one or several buffers as an @dfn{atomic change group}, meaning that
4209 either the entire series of changes will be installed in their buffers
4210 or, in case of an error, none of them will be.
4212 To do this for one buffer, the one already current, simply write a
4213 call to @code{atomic-change-group} around the code that makes the
4217 (atomic-change-group
4219 (delete-region x y))
4223 If an error (or other nonlocal exit) occurs inside the body of
4224 @code{atomic-change-group}, it unmakes all the changes in that buffer
4225 that were during the execution of the body. This kind of change group
4226 has no effect on any other buffers---any such changes remain.
4228 If you need something more sophisticated, such as to make changes in
4229 various buffers constitute one atomic group, you must directly call
4230 lower-level functions that @code{atomic-change-group} uses.
4232 @defun prepare-change-group &optional buffer
4233 This function sets up a change group for buffer @var{buffer}, which
4234 defaults to the current buffer. It returns a ``handle'' that
4235 represents the change group. You must use this handle to activate the
4236 change group and subsequently to finish it.
4239 To use the change group, you must @dfn{activate} it. You must do
4240 this before making any changes in the text of @var{buffer}.
4242 @defun activate-change-group handle
4243 This function activates the change group that @var{handle} designates.
4246 After you activate the change group, any changes you make in that
4247 buffer become part of it. Once you have made all the desired changes
4248 in the buffer, you must @dfn{finish} the change group. There are two
4249 ways to do this: you can either accept (and finalize) all the changes,
4252 @defun accept-change-group handle
4253 This function accepts all the changes in the change group specified by
4254 @var{handle}, making them final.
4257 @defun cancel-change-group handle
4258 This function cancels and undoes all the changes in the change group
4259 specified by @var{handle}.
4262 Your code should use @code{unwind-protect} to make sure the group is
4263 always finished. The call to @code{activate-change-group} should be
4264 inside the @code{unwind-protect}, in case the user types @kbd{C-g}
4265 just after it runs. (This is one reason why
4266 @code{prepare-change-group} and @code{activate-change-group} are
4267 separate functions, because normally you would call
4268 @code{prepare-change-group} before the start of that
4269 @code{unwind-protect}.) Once you finish the group, don't use the
4270 handle again---in particular, don't try to finish the same group
4273 To make a multibuffer change group, call @code{prepare-change-group}
4274 once for each buffer you want to cover, then use @code{nconc} to
4275 combine the returned values, like this:
4278 (nconc (prepare-change-group buffer-1)
4279 (prepare-change-group buffer-2))
4282 You can then activate the multibuffer change group with a single call
4283 to @code{activate-change-group}, and finish it with a single call to
4284 @code{accept-change-group} or @code{cancel-change-group}.
4286 Nested use of several change groups for the same buffer works as you
4287 would expect. Non-nested use of change groups for the same buffer
4288 will get Emacs confused, so don't let it happen; the first change
4289 group you start for any given buffer should be the last one finished.
4292 @section Change Hooks
4293 @cindex change hooks
4294 @cindex hooks for text changes
4296 These hook variables let you arrange to take notice of all changes in
4297 all buffers (or in a particular buffer, if you make them buffer-local).
4298 See also @ref{Special Properties}, for how to detect changes to specific
4301 The functions you use in these hooks should save and restore the match
4302 data if they do anything that uses regular expressions; otherwise, they
4303 will interfere in bizarre ways with the editing operations that call
4306 @defvar before-change-functions
4307 This variable holds a list of functions to call before any buffer
4308 modification. Each function gets two arguments, the beginning and end
4309 of the region that is about to change, represented as integers. The
4310 buffer that is about to change is always the current buffer.
4313 @defvar after-change-functions
4314 This variable holds a list of functions to call after any buffer
4315 modification. Each function receives three arguments: the beginning and
4316 end of the region just changed, and the length of the text that existed
4317 before the change. All three arguments are integers. The buffer that's
4318 about to change is always the current buffer.
4320 The length of the old text is the difference between the buffer positions
4321 before and after that text as it was before the change. As for the
4322 changed text, its length is simply the difference between the first two
4326 Output of messages into the @samp{*Messages*} buffer does not
4327 call these functions.
4329 @defmac combine-after-change-calls body@dots{}
4330 The macro executes @var{body} normally, but arranges to call the
4331 after-change functions just once for a series of several changes---if
4334 If a program makes several text changes in the same area of the buffer,
4335 using the macro @code{combine-after-change-calls} around that part of
4336 the program can make it run considerably faster when after-change hooks
4337 are in use. When the after-change hooks are ultimately called, the
4338 arguments specify a portion of the buffer including all of the changes
4339 made within the @code{combine-after-change-calls} body.
4341 @strong{Warning:} You must not alter the values of
4342 @code{after-change-functions} within
4343 the body of a @code{combine-after-change-calls} form.
4345 @strong{Warning:} if the changes you combine occur in widely scattered
4346 parts of the buffer, this will still work, but it is not advisable,
4347 because it may lead to inefficient behavior for some change hook
4351 The two variables above are temporarily bound to @code{nil} during the
4352 time that any of these functions is running. This means that if one of
4353 these functions changes the buffer, that change won't run these
4354 functions. If you do want a hook function to make changes that run
4355 these functions, make it bind these variables back to their usual
4358 One inconvenient result of this protective feature is that you cannot
4359 have a function in @code{after-change-functions} or
4360 @code{before-change-functions} which changes the value of that variable.
4361 But that's not a real limitation. If you want those functions to change
4362 the list of functions to run, simply add one fixed function to the hook,
4363 and code that function to look in another variable for other functions
4364 to call. Here is an example:
4367 (setq my-own-after-change-functions nil)
4368 (defun indirect-after-change-function (beg end len)
4369 (let ((list my-own-after-change-functions))
4371 (funcall (car list) beg end len)
4372 (setq list (cdr list)))))
4375 (add-hooks 'after-change-functions
4376 'indirect-after-change-function)
4380 @defvar first-change-hook
4381 This variable is a normal hook that is run whenever a buffer is changed
4382 that was previously in the unmodified state.
4385 @defvar inhibit-modification-hooks
4386 If this variable is non-@code{nil}, all of the change hooks are
4387 disabled; none of them run. This affects all the hook variables
4388 described above in this section, as well as the hooks attached to
4389 certain special text properties (@pxref{Special Properties}) and overlay
4390 properties (@pxref{Overlay Properties}).
4394 arch-tag: 3721e738-a1cb-4085-bc1a-6cb8d8e1d32b