2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2015 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
9 This chapter describes the functions that deal with the text in a
10 buffer. Most examine, insert, or delete text in the current buffer,
11 often operating at point or on text adjacent to point. Many are
12 interactive. All the functions that change the text provide for undoing
13 the changes (@pxref{Undo}).
15 Many text-related functions operate on a region of text defined by two
16 buffer positions passed in arguments named @var{start} and @var{end}.
17 These arguments should be either markers (@pxref{Markers}) or numeric
18 character positions (@pxref{Positions}). The order of these arguments
19 does not matter; it is all right for @var{start} to be the end of the
20 region and @var{end} the beginning. For example, @code{(delete-region 1
21 10)} and @code{(delete-region 10 1)} are equivalent. An
22 @code{args-out-of-range} error is signaled if either @var{start} or
23 @var{end} is outside the accessible portion of the buffer. In an
24 interactive call, point and the mark are used for these arguments.
26 @cindex buffer contents
27 Throughout this chapter, ``text'' refers to the characters in the
28 buffer, together with their properties (when relevant). Keep in mind
29 that point is always between two characters, and the cursor appears on
30 the character after point.
33 * Near Point:: Examining text in the vicinity of point.
34 * Buffer Contents:: Examining text in a general fashion.
35 * Comparing Text:: Comparing substrings of buffers.
36 * Insertion:: Adding new text to a buffer.
37 * Commands for Insertion:: User-level commands to insert text.
38 * Deletion:: Removing text from a buffer.
39 * User-Level Deletion:: User-level commands to delete text.
40 * The Kill Ring:: Where removed text sometimes is saved for later use.
41 * Undo:: Undoing changes to the text of a buffer.
42 * Maintaining Undo:: How to enable and disable undo information.
43 How to control how much information is kept.
44 * Filling:: Functions for explicit filling.
45 * Margins:: How to specify margins for filling commands.
46 * Adaptive Fill:: Adaptive Fill mode chooses a fill prefix from context.
47 * Auto Filling:: How auto-fill mode is implemented to break lines.
48 * Sorting:: Functions for sorting parts of the buffer.
49 * Columns:: Computing horizontal positions, and using them.
50 * Indentation:: Functions to insert or adjust indentation.
51 * Case Changes:: Case conversion of parts of the buffer.
52 * Text Properties:: Assigning Lisp property lists to text characters.
53 * Substitution:: Replacing a given character wherever it appears.
54 * Registers:: How registers are implemented. Accessing the text or
55 position stored in a register.
56 * Transposition:: Swapping two portions of a buffer.
57 * Decompression:: Dealing with compressed data.
58 * Base 64:: Conversion to or from base 64 encoding.
59 * Checksum/Hash:: Computing cryptographic hashes.
60 * Parsing HTML/XML:: Parsing HTML and XML.
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 (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 (string (preceding-char))
125 (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
165 @cindex buffer portion as string
167 This section describes functions that allow a Lisp program to
168 convert any portion of the text in the buffer into a string.
170 @defun buffer-substring start end
171 This function returns a string containing a copy of the text of the
172 region defined by positions @var{start} and @var{end} in the current
173 buffer. If the arguments are not positions in the accessible portion
174 of the buffer, @code{buffer-substring} signals an
175 @code{args-out-of-range} error.
177 Here's an example which assumes Font-Lock mode is not enabled:
181 ---------- Buffer: foo ----------
182 This is the contents of buffer foo
184 ---------- Buffer: foo ----------
188 (buffer-substring 1 10)
189 @result{} "This is t"
192 (buffer-substring (point-max) 10)
193 @result{} "he contents of buffer foo\n"
197 If the text being copied has any text properties, these are copied into
198 the string along with the characters they belong to. @xref{Text
199 Properties}. However, overlays (@pxref{Overlays}) in the buffer and
200 their properties are ignored, not copied.
202 For example, if Font-Lock mode is enabled, you might get results like
207 (buffer-substring 1 10)
208 @result{} #("This is t" 0 1 (fontified t) 1 9 (fontified t))
213 @defun buffer-substring-no-properties start end
214 This is like @code{buffer-substring}, except that it does not copy text
215 properties, just the characters themselves. @xref{Text Properties}.
219 This function returns the contents of the entire accessible portion of
220 the current buffer, as a string.
223 If you need to make sure the resulting string, when copied to a
224 different location, will not change its visual appearance due to
225 reordering of bidirectional text, use the
226 @code{buffer-substring-with-bidi-context} function
227 (@pxref{Bidirectional Display, buffer-substring-with-bidi-context}).
229 @defun filter-buffer-substring start end &optional delete
230 This function filters the buffer text between @var{start} and @var{end}
231 using a function specified by the variable
232 @code{filter-buffer-substring-function}, and returns the result.
234 The default filter function consults the obsolete wrapper hook
235 @code{filter-buffer-substring-functions}, and the obsolete variable
236 @code{buffer-substring-filters}. If both of these are @code{nil}, it
237 returns the unaltered text from the buffer, i.e., what
238 @code{buffer-substring} would return.
240 If @var{delete} is non-@code{nil}, the function deletes the text
241 between @var{start} and @var{end} after copying it, like
242 @code{delete-and-extract-region}.
244 Lisp code should use this function instead of @code{buffer-substring},
245 @code{buffer-substring-no-properties},
246 or @code{delete-and-extract-region} when copying into user-accessible
247 data structures such as the kill-ring, X clipboard, and registers.
248 Major and minor modes can modify @code{filter-buffer-substring-function}
249 to alter such text as it is copied out of the buffer.
252 @defvar filter-buffer-substring-function
253 The value of this variable is a function that @code{filter-buffer-substring}
254 will call to do the actual work. The function receives three
255 arguments, the same as those of @code{filter-buffer-substring},
256 which it should treat as per the documentation of that function. It
257 should return the filtered text (and optionally delete the source text).
260 @noindent The following two variables are obsoleted by
261 @code{filter-buffer-substring-function}, but are still supported for
262 backward compatibility.
264 @defvar filter-buffer-substring-functions
265 This obsolete variable is a wrapper hook, whose members should be functions
266 that accept four arguments: @var{fun}, @var{start}, @var{end}, and
267 @var{delete}. @var{fun} is a function that takes three arguments
268 (@var{start}, @var{end}, and @var{delete}), and returns a string. In
269 both cases, the @var{start}, @var{end}, and @var{delete} arguments are
270 the same as those of @code{filter-buffer-substring}.
272 The first hook function is passed a @var{fun} that is equivalent to
273 the default operation of @code{filter-buffer-substring}, i.e., it
274 returns the buffer-substring between @var{start} and @var{end}
275 (processed by any @code{buffer-substring-filters}) and optionally
276 deletes the original text from the buffer. In most cases, the hook
277 function will call @var{fun} once, and then do its own processing of
278 the result. The next hook function receives a @var{fun} equivalent to
279 this, and so on. The actual return value is the result of all the
280 hook functions acting in sequence.
283 @defvar buffer-substring-filters
284 The value of this obsolete variable should be a list of functions
285 that accept a single string argument and return another string.
286 The default @code{filter-buffer-substring} function passes the buffer
287 substring to the first function in this list, and the return value of
288 each function is passed to the next function. The return value of the
289 last function is passed to @code{filter-buffer-substring-functions}.
292 @defun current-word &optional strict really-word
293 This function returns the symbol (or word) at or near point, as a
294 string. The return value includes no text properties.
296 If the optional argument @var{really-word} is non-@code{nil}, it finds a
297 word; otherwise, it finds a symbol (which includes both word
298 characters and symbol constituent characters).
300 If the optional argument @var{strict} is non-@code{nil}, then point
301 must be in or next to the symbol or word---if no symbol or word is
302 there, the function returns @code{nil}. Otherwise, a nearby symbol or
303 word on the same line is acceptable.
306 @defun thing-at-point thing
307 Return the @var{thing} around or next to point, as a string.
309 The argument @var{thing} is a symbol which specifies a kind of syntactic
310 entity. Possibilities include @code{symbol}, @code{list}, @code{sexp},
311 @code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
312 @code{whitespace}, @code{line}, @code{page}, and others.
315 ---------- Buffer: foo ----------
316 Gentlemen may cry ``Pea@point{}ce! Peace!,''
317 but there is no peace.
318 ---------- Buffer: foo ----------
320 (thing-at-point 'word)
322 (thing-at-point 'line)
323 @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
324 (thing-at-point 'whitespace)
330 @section Comparing Text
331 @cindex comparing buffer text
333 This function lets you compare portions of the text in a buffer, without
334 copying them into strings first.
336 @defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
337 This function lets you compare two substrings of the same buffer or two
338 different buffers. The first three arguments specify one substring,
339 giving a buffer (or a buffer name) and two positions within the
340 buffer. The last three arguments specify the other substring in the
341 same way. You can use @code{nil} for @var{buffer1}, @var{buffer2}, or
342 both to stand for the current buffer.
344 The value is negative if the first substring is less, positive if the
345 first is greater, and zero if they are equal. The absolute value of
346 the result is one plus the index of the first differing characters
347 within the substrings.
349 This function ignores case when comparing characters
350 if @code{case-fold-search} is non-@code{nil}. It always ignores
353 Suppose you have the text @w{@samp{foobarbar haha!rara!}} in the
354 current buffer; then in this example the two substrings are @samp{rbar
355 } and @samp{rara!}. The value is 2 because the first substring is
356 greater at the second character.
359 (compare-buffer-substrings nil 6 11 nil 16 21)
365 @section Inserting Text
366 @cindex insertion of text
367 @cindex text insertion
369 @cindex insertion before point
370 @cindex before point, insertion
371 @dfn{Insertion} means adding new text to a buffer. The inserted text
372 goes at point---between the character before point and the character
373 after point. Some insertion functions leave point before the inserted
374 text, while other functions leave it after. We call the former
375 insertion @dfn{after point} and the latter insertion @dfn{before point}.
377 Insertion moves markers located at positions after the insertion
378 point, so that they stay with the surrounding text (@pxref{Markers}).
379 When a marker points at the place of insertion, insertion may or may
380 not relocate the marker, depending on the marker's insertion type
381 (@pxref{Marker Insertion Types}). Certain special functions such as
382 @code{insert-before-markers} relocate all such markers to point after
383 the inserted text, regardless of the markers' insertion type.
385 Insertion functions signal an error if the current buffer is
386 read-only (@pxref{Read Only Buffers}) or if they insert within
387 read-only text (@pxref{Special Properties}).
389 These functions copy text characters from strings and buffers along
390 with their properties. The inserted characters have exactly the same
391 properties as the characters they were copied from. By contrast,
392 characters specified as separate arguments, not part of a string or
393 buffer, inherit their text properties from the neighboring text.
395 The insertion functions convert text from unibyte to multibyte in
396 order to insert in a multibyte buffer, and vice versa---if the text
397 comes from a string or from a buffer. However, they do not convert
398 unibyte character codes 128 through 255 to multibyte characters, not
399 even if the current buffer is a multibyte buffer. @xref{Converting
402 @defun insert &rest args
403 This function inserts the strings and/or characters @var{args} into the
404 current buffer, at point, moving point forward. In other words, it
405 inserts the text before point. An error is signaled unless all
406 @var{args} are either strings or characters. The value is @code{nil}.
409 @defun insert-before-markers &rest args
410 This function inserts the strings and/or characters @var{args} into the
411 current buffer, at point, moving point forward. An error is signaled
412 unless all @var{args} are either strings or characters. The value is
415 This function is unlike the other insertion functions in that it
416 relocates markers initially pointing at the insertion point, to point
417 after the inserted text. If an overlay begins at the insertion point,
418 the inserted text falls outside the overlay; if a nonempty overlay
419 ends at the insertion point, the inserted text falls inside that
423 @deffn Command insert-char character &optional count inherit
424 This command inserts @var{count} instances of @var{character} into the
425 current buffer before point. The argument @var{count} must be an
426 integer, and @var{character} must be a character.
428 If called interactively, this command prompts for @var{character}
429 using its Unicode name or its code point. @xref{Inserting Text,,,
430 emacs, The GNU Emacs Manual}.
432 This function does not convert unibyte character codes 128 through 255
433 to multibyte characters, not even if the current buffer is a multibyte
434 buffer. @xref{Converting Representations}.
436 If @var{inherit} is non-@code{nil}, the inserted characters inherit
437 sticky text properties from the two characters before and after the
438 insertion point. @xref{Sticky Properties}.
441 @defun insert-buffer-substring from-buffer-or-name &optional start end
442 This function inserts a portion of buffer @var{from-buffer-or-name}
443 into the current buffer before point. The text inserted is the region
444 between @var{start} (inclusive) and @var{end} (exclusive). (These
445 arguments default to the beginning and end of the accessible portion
446 of that buffer.) This function returns @code{nil}.
448 In this example, the form is executed with buffer @samp{bar} as the
449 current buffer. We assume that buffer @samp{bar} is initially empty.
453 ---------- Buffer: foo ----------
454 We hold these truths to be self-evident, that all
455 ---------- Buffer: foo ----------
459 (insert-buffer-substring "foo" 1 20)
462 ---------- Buffer: bar ----------
463 We hold these truth@point{}
464 ---------- Buffer: bar ----------
469 @defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
470 This is like @code{insert-buffer-substring} except that it does not
471 copy any text properties.
474 @xref{Sticky Properties}, for other insertion functions that inherit
475 text properties from the nearby text in addition to inserting it.
476 Whitespace inserted by indentation functions also inherits text
479 @node Commands for Insertion
480 @section User-Level Insertion Commands
482 This section describes higher-level commands for inserting text,
483 commands intended primarily for the user but useful also in Lisp
486 @deffn Command insert-buffer from-buffer-or-name
487 This command inserts the entire accessible contents of
488 @var{from-buffer-or-name} (which must exist) into the current buffer
489 after point. It leaves the mark after the inserted text. The value
493 @deffn Command self-insert-command count
494 @cindex character insertion
495 @cindex self-insertion
496 This command inserts the last character typed; it does so @var{count}
497 times, before point, and returns @code{nil}. Most printing characters
498 are bound to this command. In routine use, @code{self-insert-command}
499 is the most frequently called function in Emacs, but programs rarely use
500 it except to install it on a keymap.
502 In an interactive call, @var{count} is the numeric prefix argument.
504 @c FIXME: This variable is obsolete since 23.1.
505 Self-insertion translates the input character through
506 @code{translation-table-for-input}. @xref{Translation of Characters}.
508 This command calls @code{auto-fill-function} whenever that is
509 non-@code{nil} and the character inserted is in the table
510 @code{auto-fill-chars} (@pxref{Auto Filling}).
512 @c Cross refs reworded to prevent overfull hbox. --rjc 15mar92
513 This command performs abbrev expansion if Abbrev mode is enabled and
514 the inserted character does not have word-constituent
515 syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.) It is also
516 responsible for calling @code{blink-paren-function} when the inserted
517 character has close parenthesis syntax (@pxref{Blinking}).
519 @vindex post-self-insert-hook
520 The final thing this command does is to run the hook
521 @code{post-self-insert-hook}. You could use this to automatically
522 reindent text as it is typed, for example.
524 Do not try substituting your own definition of
525 @code{self-insert-command} for the standard one. The editor command
526 loop handles this function specially.
529 @deffn Command newline &optional number-of-newlines
530 This command inserts newlines into the current buffer before point.
531 If @var{number-of-newlines} is supplied, that many newline characters
534 @cindex newline and Auto Fill mode
535 This function calls @code{auto-fill-function} if the current column
536 number is greater than the value of @code{fill-column} and
537 @var{number-of-newlines} is @code{nil}. Typically what
538 @code{auto-fill-function} does is insert a newline; thus, the overall
539 result in this case is to insert two newlines at different places: one
540 at point, and another earlier in the line. @code{newline} does not
541 auto-fill if @var{number-of-newlines} is non-@code{nil}.
543 This command indents to the left margin if that is not zero.
546 The value returned is @code{nil}. In an interactive call, @var{count}
547 is the numeric prefix argument.
550 @defvar overwrite-mode
551 This variable controls whether overwrite mode is in effect. The value
552 should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
553 or @code{nil}. @code{overwrite-mode-textual} specifies textual
554 overwrite mode (treats newlines and tabs specially), and
555 @code{overwrite-mode-binary} specifies binary overwrite mode (treats
556 newlines and tabs like any other characters).
560 @section Deleting Text
561 @cindex text deletion
563 @cindex deleting text vs killing
564 Deletion means removing part of the text in a buffer, without saving
565 it in the kill ring (@pxref{The Kill Ring}). Deleted text can't be
566 yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
567 Some deletion functions do save text in the kill ring in some special
570 All of the deletion functions operate on the current buffer.
572 @deffn Command erase-buffer
573 This function deletes the entire text of the current buffer
574 (@emph{not} just the accessible portion), leaving it
575 empty. If the buffer is read-only, it signals a @code{buffer-read-only}
576 error; if some of the text in it is read-only, it signals a
577 @code{text-read-only} error. Otherwise, it deletes the text without
578 asking for any confirmation. It returns @code{nil}.
580 Normally, deleting a large amount of text from a buffer inhibits further
581 auto-saving of that buffer because it has shrunk. However,
582 @code{erase-buffer} does not do this, the idea being that the future
583 text is not really related to the former text, and its size should not
584 be compared with that of the former text.
587 @deffn Command delete-region start end
588 This command deletes the text between positions @var{start} and
589 @var{end} in the current buffer, and returns @code{nil}. If point was
590 inside the deleted region, its value afterward is @var{start}.
591 Otherwise, point relocates with the surrounding text, as markers do.
594 @defun delete-and-extract-region start end
595 This function deletes the text between positions @var{start} and
596 @var{end} in the current buffer, and returns a string containing the
599 If point was inside the deleted region, its value afterward is
600 @var{start}. Otherwise, point relocates with the surrounding text, as
604 @deffn Command delete-char count &optional killp
605 This command deletes @var{count} characters directly after point, or
606 before point if @var{count} is negative. If @var{killp} is
607 non-@code{nil}, then it saves the deleted characters in the kill ring.
609 In an interactive call, @var{count} is the numeric prefix argument, and
610 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
611 argument is supplied, the text is saved in the kill ring. If no prefix
612 argument is supplied, then one character is deleted, but not saved in
615 The value returned is always @code{nil}.
618 @deffn Command delete-backward-char count &optional killp
619 @cindex deleting previous char
620 This command deletes @var{count} characters directly before point, or
621 after point if @var{count} is negative. If @var{killp} is
622 non-@code{nil}, then it saves the deleted characters in the kill ring.
624 In an interactive call, @var{count} is the numeric prefix argument, and
625 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
626 argument is supplied, the text is saved in the kill ring. If no prefix
627 argument is supplied, then one character is deleted, but not saved in
630 The value returned is always @code{nil}.
633 @deffn Command backward-delete-char-untabify count &optional killp
635 This command deletes @var{count} characters backward, changing tabs
636 into spaces. When the next character to be deleted is a tab, it is
637 first replaced with the proper number of spaces to preserve alignment
638 and then one of those spaces is deleted instead of the tab. If
639 @var{killp} is non-@code{nil}, then the command saves the deleted
640 characters in the kill ring.
642 Conversion of tabs to spaces happens only if @var{count} is positive.
643 If it is negative, exactly @minus{}@var{count} characters after point
646 In an interactive call, @var{count} is the numeric prefix argument, and
647 @var{killp} is the unprocessed prefix argument. Therefore, if a prefix
648 argument is supplied, the text is saved in the kill ring. If no prefix
649 argument is supplied, then one character is deleted, but not saved in
652 The value returned is always @code{nil}.
655 @defopt backward-delete-char-untabify-method
656 This option specifies how @code{backward-delete-char-untabify} should
657 deal with whitespace. Possible values include @code{untabify}, the
658 default, meaning convert a tab to many spaces and delete one;
659 @code{hungry}, meaning delete all tabs and spaces before point with
660 one command; @code{all} meaning delete all tabs, spaces and newlines
661 before point, and @code{nil}, meaning do nothing special for
662 whitespace characters.
665 @node User-Level Deletion
666 @section User-Level Deletion Commands
668 This section describes higher-level commands for deleting text,
669 commands intended primarily for the user but useful also in Lisp
672 @deffn Command delete-horizontal-space &optional backward-only
673 @cindex deleting whitespace
674 This function deletes all spaces and tabs around point. It returns
677 If @var{backward-only} is non-@code{nil}, the function deletes
678 spaces and tabs before point, but not after point.
680 In the following examples, we call @code{delete-horizontal-space} four
681 times, once on each line, with point between the second and third
682 characters on the line each time.
686 ---------- Buffer: foo ----------
691 ---------- Buffer: foo ----------
695 (delete-horizontal-space) ; @r{Four times.}
698 ---------- Buffer: foo ----------
703 ---------- Buffer: foo ----------
708 @deffn Command delete-indentation &optional join-following-p
709 This function joins the line point is on to the previous line, deleting
710 any whitespace at the join and in some cases replacing it with one
711 space. If @var{join-following-p} is non-@code{nil},
712 @code{delete-indentation} joins this line to the following line
713 instead. The function returns @code{nil}.
715 If there is a fill prefix, and the second of the lines being joined
716 starts with the prefix, then @code{delete-indentation} deletes the
717 fill prefix before joining the lines. @xref{Margins}.
719 In the example below, point is located on the line starting
720 @samp{events}, and it makes no difference if there are trailing spaces
721 in the preceding line.
725 ---------- Buffer: foo ----------
726 When in the course of human
727 @point{} events, it becomes necessary
728 ---------- Buffer: foo ----------
735 ---------- Buffer: foo ----------
736 When in the course of human@point{} events, it becomes necessary
737 ---------- Buffer: foo ----------
741 After the lines are joined, the function @code{fixup-whitespace} is
742 responsible for deciding whether to leave a space at the junction.
745 @deffn Command fixup-whitespace
746 This function replaces all the horizontal whitespace surrounding point
747 with either one space or no space, according to the context. It
750 At the beginning or end of a line, the appropriate amount of space is
751 none. Before a character with close parenthesis syntax, or after a
752 character with open parenthesis or expression-prefix syntax, no space is
753 also appropriate. Otherwise, one space is appropriate. @xref{Syntax
756 In the example below, @code{fixup-whitespace} is called the first time
757 with point before the word @samp{spaces} in the first line. For the
758 second invocation, point is directly after the @samp{(}.
762 ---------- Buffer: foo ----------
763 This has too many @point{}spaces
764 This has too many spaces at the start of (@point{} this list)
765 ---------- Buffer: foo ----------
776 ---------- Buffer: foo ----------
777 This has too many spaces
778 This has too many spaces at the start of (this list)
779 ---------- Buffer: foo ----------
784 @deffn Command just-one-space &optional n
785 @comment !!SourceFile simple.el
786 This command replaces any spaces and tabs around point with a single
787 space, or @var{n} spaces if @var{n} is specified. It returns
791 @c There is also cycle-spacing, but I cannot see it being useful in
792 @c Lisp programs, so it is not mentioned here.
794 @deffn Command delete-blank-lines
795 This function deletes blank lines surrounding point. If point is on a
796 blank line with one or more blank lines before or after it, then all but
797 one of them are deleted. If point is on an isolated blank line, then it
798 is deleted. If point is on a nonblank line, the command deletes all
799 blank lines immediately following it.
801 A blank line is defined as a line containing only tabs and spaces.
802 @c and the Newline character?
804 @code{delete-blank-lines} returns @code{nil}.
807 @deffn Command delete-trailing-whitespace start end
808 Delete trailing whitespace in the region defined by @var{start} and
811 This command deletes whitespace characters after the last
812 non-whitespace character in each line in the region.
814 If this command acts on the entire buffer (i.e., if called
815 interactively with the mark inactive, or called from Lisp with
816 @var{end} @code{nil}), it also deletes all trailing lines at the end of the
817 buffer if the variable @code{delete-trailing-lines} is non-@code{nil}.
821 @section The Kill Ring
824 @dfn{Kill functions} delete text like the deletion functions, but save
825 it so that the user can reinsert it by @dfn{yanking}. Most of these
826 functions have @samp{kill-} in their name. By contrast, the functions
827 whose names start with @samp{delete-} normally do not save text for
828 yanking (though they can still be undone); these are deletion
831 Most of the kill commands are primarily for interactive use, and are
832 not described here. What we do describe are the functions provided for
833 use in writing such commands. You can use these functions to write
834 commands for killing text. When you need to delete text for internal
835 purposes within a Lisp function, you should normally use deletion
836 functions, so as not to disturb the kill ring contents.
839 Killed text is saved for later yanking in the @dfn{kill ring}. This
840 is a list that holds a number of recent kills, not just the last text
841 kill. We call this a ``ring'' because yanking treats it as having
842 elements in a cyclic order. The list is kept in the variable
843 @code{kill-ring}, and can be operated on with the usual functions for
844 lists; there are also specialized functions, described in this section,
845 that treat it as a ring.
847 Some people think this use of the word ``kill'' is unfortunate, since
848 it refers to operations that specifically @emph{do not} destroy the
849 entities killed. This is in sharp contrast to ordinary life, in
850 which death is permanent and killed entities do not come back to
851 life. Therefore, other metaphors have been proposed. For example, the
852 term ``cut ring'' makes sense to people who, in pre-computer days, used
853 scissors and paste to cut up and rearrange manuscripts. However, it
854 would be difficult to change the terminology now.
857 * Kill Ring Concepts:: What text looks like in the kill ring.
858 * Kill Functions:: Functions that kill text.
859 * Yanking:: How yanking is done.
860 * Yank Commands:: Commands that access the kill ring.
861 * Low-Level Kill Ring:: Functions and variables for kill ring access.
862 * Internals of Kill Ring:: Variables that hold kill ring data.
865 @node Kill Ring Concepts
866 @subsection Kill Ring Concepts
868 The kill ring records killed text as strings in a list, most recent
869 first. A short kill ring, for example, might look like this:
872 ("some text" "a different piece of text" "even older text")
876 When the list reaches @code{kill-ring-max} entries in length, adding a
877 new entry automatically deletes the last entry.
879 When kill commands are interwoven with other commands, each kill
880 command makes a new entry in the kill ring. Multiple kill commands in
881 succession build up a single kill ring entry, which would be yanked as a
882 unit; the second and subsequent consecutive kill commands add text to
883 the entry made by the first one.
885 For yanking, one entry in the kill ring is designated the front of
886 the ring. Some yank commands rotate the ring by designating a
887 different element as the front. But this virtual rotation doesn't
888 change the list itself---the most recent entry always comes first in the
892 @subsection Functions for Killing
894 @code{kill-region} is the usual subroutine for killing text. Any
895 command that calls this function is a kill command (and should
896 probably have @samp{kill} in its name). @code{kill-region} puts the
897 newly killed text in a new element at the beginning of the kill ring or
898 adds it to the most recent element. It determines automatically (using
899 @code{last-command}) whether the previous command was a kill command,
900 and if so appends the killed text to the most recent entry.
902 @deffn Command kill-region start end
903 This function kills the text in the region defined by @var{start} and
904 @var{end}. The text is deleted but saved in the kill ring, along with
905 its text properties. The value is always @code{nil}.
907 In an interactive call, @var{start} and @var{end} are point and
910 If the buffer or text is read-only, @code{kill-region} modifies the kill
911 ring just the same, then signals an error without modifying the buffer.
912 This is convenient because it lets the user use a series of kill
913 commands to copy text from a read-only buffer into the kill ring.
916 @defopt kill-read-only-ok
917 If this option is non-@code{nil}, @code{kill-region} does not signal an
918 error if the buffer or text is read-only. Instead, it simply returns,
919 updating the kill ring but not changing the buffer.
922 @deffn Command copy-region-as-kill start end
923 This command saves the region defined by @var{start} and @var{end} on
924 the kill ring (including text properties), but does not delete the text
925 from the buffer. It returns @code{nil}.
927 The command does not set @code{this-command} to @code{kill-region}, so a
928 subsequent kill command does not append to the same kill ring entry.
930 @c FIXME Why is it better? Why isn't copy-region-as-kill obsolete then?
931 @c Why is it used in many places in Emacs?
932 In Lisp programs, it is better to use @code{kill-new} or
933 @code{kill-append} instead of this command. @xref{Low-Level Kill Ring}.
939 Yanking means inserting text from the kill ring, but it does not
940 insert the text blindly. The @code{yank} command, and related
941 commands, use @code{insert-for-yank} to perform special processing on
942 the text before it is inserted.
944 @defun insert-for-yank string
945 This function works like @code{insert}, except that it processes the
946 text in @var{string} according to the @code{yank-handler} text
947 property, as well as the variables @code{yank-handled-properties} and
948 @code{yank-excluded-properties} (see below), before inserting the
949 result into the current buffer.
952 @defun insert-buffer-substring-as-yank buf &optional start end
953 This function resembles @code{insert-buffer-substring}, except that it
954 processes the text according to @code{yank-handled-properties} and
955 @code{yank-excluded-properties}. (It does not handle the
956 @code{yank-handler} property, which does not normally occur in buffer
960 @c FIXME: Add an index for yank-handler.
961 If you put a @code{yank-handler} text property on all or part of a
962 string, that alters how @code{insert-for-yank} inserts the string. If
963 different parts of the string have different @code{yank-handler}
964 values (comparison being done with @code{eq}), each substring is
965 handled separately. The property value must be a list of one to four
966 elements, with the following format (where elements after the first
970 (@var{function} @var{param} @var{noexclude} @var{undo})
973 Here is what the elements do:
977 When @var{function} is non-@code{nil}, it is called instead of
978 @code{insert} to insert the string, with one argument---the string to
982 If @var{param} is present and non-@code{nil}, it replaces @var{string}
983 (or the substring of @var{string} being processed) as the object
984 passed to @var{function} (or @code{insert}). For example, if
985 @var{function} is @code{yank-rectangle}, @var{param} should be a list
986 of strings to insert as a rectangle.
989 If @var{noexclude} is present and non-@code{nil}, that disables the
990 normal action of @code{yank-handled-properties} and
991 @code{yank-excluded-properties} on the inserted string.
994 If @var{undo} is present and non-@code{nil}, it is a function that will be
995 called by @code{yank-pop} to undo the insertion of the current object.
996 It is called with two arguments, the start and end of the current
997 region. @var{function} can set @code{yank-undo-function} to override
998 the @var{undo} value.
1001 @cindex yanking and text properties
1002 @defopt yank-handled-properties
1003 This variable specifies special text property handling conditions for
1004 yanked text. It takes effect after the text has been inserted (either
1005 normally, or via the @code{yank-handler} property), and prior to
1006 @code{yank-excluded-properties} taking effect.
1008 The value should be an alist of elements @code{(@var{prop}
1009 . @var{fun})}. Each alist element is handled in order. The inserted
1010 text is scanned for stretches of text having text properties @code{eq}
1011 to @var{prop}; for each such stretch, @var{fun} is called with three
1012 arguments: the value of the property, and the start and end positions
1016 @defopt yank-excluded-properties
1017 The value of this variable is the list of properties to remove from
1018 inserted text. Its default value contains properties that might lead
1019 to annoying results, such as causing the text to respond to the mouse
1020 or specifying key bindings. It takes effect after
1021 @code{yank-handled-properties}.
1026 @subsection Functions for Yanking
1028 This section describes higher-level commands for yanking, which are
1029 intended primarily for the user but useful also in Lisp programs.
1030 Both @code{yank} and @code{yank-pop} honor the
1031 @code{yank-excluded-properties} variable and @code{yank-handler} text
1032 property (@pxref{Yanking}).
1034 @deffn Command yank &optional arg
1035 @cindex inserting killed text
1036 This command inserts before point the text at the front of the kill
1037 ring. It sets the mark at the beginning of that text, using
1038 @code{push-mark} (@pxref{The Mark}), and puts point at the end.
1040 If @var{arg} is a non-@code{nil} list (which occurs interactively when
1041 the user types @kbd{C-u} with no digits), then @code{yank} inserts the
1042 text as described above, but puts point before the yanked text and
1043 sets the mark after it.
1045 If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
1046 most recently killed text---the @var{arg}th element of the kill ring
1047 list, counted cyclically from the front, which is considered the
1048 first element for this purpose.
1050 @code{yank} does not alter the contents of the kill ring, unless it
1051 used text provided by another program, in which case it pushes that text
1052 onto the kill ring. However if @var{arg} is an integer different from
1053 one, it rotates the kill ring to place the yanked string at the front.
1055 @code{yank} returns @code{nil}.
1058 @deffn Command yank-pop &optional arg
1059 This command replaces the just-yanked entry from the kill ring with a
1060 different entry from the kill ring.
1062 This is allowed only immediately after a @code{yank} or another
1063 @code{yank-pop}. At such a time, the region contains text that was just
1064 inserted by yanking. @code{yank-pop} deletes that text and inserts in
1065 its place a different piece of killed text. It does not add the deleted
1066 text to the kill ring, since it is already in the kill ring somewhere.
1067 It does however rotate the kill ring to place the newly yanked string at
1070 If @var{arg} is @code{nil}, then the replacement text is the previous
1071 element of the kill ring. If @var{arg} is numeric, the replacement is
1072 the @var{arg}th previous kill. If @var{arg} is negative, a more recent
1073 kill is the replacement.
1075 The sequence of kills in the kill ring wraps around, so that after the
1076 oldest one comes the newest one, and before the newest one goes the
1079 The return value is always @code{nil}.
1082 @defvar yank-undo-function
1083 If this variable is non-@code{nil}, the function @code{yank-pop} uses
1084 its value instead of @code{delete-region} to delete the text
1085 inserted by the previous @code{yank} or
1086 @code{yank-pop} command. The value must be a function of two
1087 arguments, the start and end of the current region.
1089 The function @code{insert-for-yank} automatically sets this variable
1090 according to the @var{undo} element of the @code{yank-handler}
1091 text property, if there is one.
1094 @node Low-Level Kill Ring
1095 @subsection Low-Level Kill Ring
1097 These functions and variables provide access to the kill ring at a
1098 lower level, but are still convenient for use in Lisp programs,
1099 because they take care of interaction with window system selections
1100 (@pxref{Window System Selections}).
1102 @defun current-kill n &optional do-not-move
1103 The function @code{current-kill} rotates the yanking pointer, which
1104 designates the front of the kill ring, by @var{n} places (from newer
1105 kills to older ones), and returns the text at that place in the ring.
1107 If the optional second argument @var{do-not-move} is non-@code{nil},
1108 then @code{current-kill} doesn't alter the yanking pointer; it just
1109 returns the @var{n}th kill, counting from the current yanking pointer.
1111 If @var{n} is zero, indicating a request for the latest kill,
1112 @code{current-kill} calls the value of
1113 @code{interprogram-paste-function} (documented below) before
1114 consulting the kill ring. If that value is a function and calling it
1115 returns a string or a list of several string, @code{current-kill}
1116 pushes the strings onto the kill ring and returns the first string.
1117 It also sets the yanking pointer to point to the kill-ring entry of
1118 the first string returned by @code{interprogram-paste-function},
1119 regardless of the value of @var{do-not-move}. Otherwise,
1120 @code{current-kill} does not treat a zero value for @var{n} specially:
1121 it returns the entry pointed at by the yanking pointer and does not
1122 move the yanking pointer.
1125 @defun kill-new string &optional replace
1126 This function pushes the text @var{string} onto the kill ring and
1127 makes the yanking pointer point to it. It discards the oldest entry
1128 if appropriate. It also invokes the value of
1129 @code{interprogram-cut-function} (see below).
1131 If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
1132 first element of the kill ring with @var{string}, rather than pushing
1133 @var{string} onto the kill ring.
1136 @defun kill-append string before-p
1137 This function appends the text @var{string} to the first entry in the
1138 kill ring and makes the yanking pointer point to the combined entry.
1139 Normally @var{string} goes at the end of the entry, but if
1140 @var{before-p} is non-@code{nil}, it goes at the beginning. This
1141 function also invokes the value of @code{interprogram-cut-function}
1145 @defvar interprogram-paste-function
1146 This variable provides a way of transferring killed text from other
1147 programs, when you are using a window system. Its value should be
1148 @code{nil} or a function of no arguments.
1150 If the value is a function, @code{current-kill} calls it to get the
1151 most recent kill. If the function returns a non-@code{nil} value,
1152 then that value is used as the most recent kill. If it returns
1153 @code{nil}, then the front of the kill ring is used.
1155 To facilitate support for window systems that support multiple
1156 selections, this function may also return a list of strings. In that
1157 case, the first string is used as the most recent kill, and all
1158 the other strings are pushed onto the kill ring, for easy access by
1161 The normal use of this function is to get the window system's
1162 clipboard as the most recent kill, even if the selection belongs to
1163 another application. @xref{Window System Selections}. However, if
1164 the clipboard contents come from the current Emacs session, this
1165 function should return @code{nil}.
1168 @defvar interprogram-cut-function
1169 This variable provides a way of communicating killed text to other
1170 programs, when you are using a window system. Its value should be
1171 @code{nil} or a function of one required argument.
1173 If the value is a function, @code{kill-new} and @code{kill-append} call
1174 it with the new first element of the kill ring as the argument.
1176 The normal use of this function is to put newly killed text in the
1177 window system's clipboard. @xref{Window System Selections}.
1180 @node Internals of Kill Ring
1181 @subsection Internals of the Kill Ring
1183 The variable @code{kill-ring} holds the kill ring contents, in the
1184 form of a list of strings. The most recent kill is always at the front
1187 The @code{kill-ring-yank-pointer} variable points to a link in the
1188 kill ring list, whose @sc{car} is the text to yank next. We say it
1189 identifies the front of the ring. Moving
1190 @code{kill-ring-yank-pointer} to a different link is called
1191 @dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
1192 the functions that move the yank pointer wrap around from the end of the
1193 list to the beginning, or vice-versa. Rotation of the kill ring is
1194 virtual; it does not change the value of @code{kill-ring}.
1196 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
1197 variables whose values are normally lists. The word ``pointer'' in the
1198 name of the @code{kill-ring-yank-pointer} indicates that the variable's
1199 purpose is to identify one element of the list for use by the next yank
1202 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
1203 of the links in the kill ring list. The element it identifies is the
1204 @sc{car} of that link. Kill commands, which change the kill ring, also
1205 set this variable to the value of @code{kill-ring}. The effect is to
1206 rotate the ring so that the newly killed text is at the front.
1208 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
1209 pointing to the second entry in the kill ring @code{("some text" "a
1210 different piece of text" "yet older text")}.
1214 kill-ring ---- kill-ring-yank-pointer
1217 | --- --- --- --- --- ---
1218 --> | | |------> | | |--> | | |--> nil
1219 --- --- --- --- --- ---
1222 | | -->"yet older text"
1224 | --> "a different piece of text"
1231 This state of affairs might occur after @kbd{C-y} (@code{yank})
1232 immediately followed by @kbd{M-y} (@code{yank-pop}).
1235 This variable holds the list of killed text sequences, most recently
1239 @defvar kill-ring-yank-pointer
1240 This variable's value indicates which element of the kill ring is at the
1241 front of the ring for yanking. More precisely, the value is a tail
1242 of the value of @code{kill-ring}, and its @sc{car} is the kill string
1243 that @kbd{C-y} should yank.
1246 @defopt kill-ring-max
1247 The value of this variable is the maximum length to which the kill
1248 ring can grow, before elements are thrown away at the end. The default
1249 value for @code{kill-ring-max} is 60.
1256 Most buffers have an @dfn{undo list}, which records all changes made
1257 to the buffer's text so that they can be undone. (The buffers that
1258 don't have one are usually special-purpose buffers for which Emacs
1259 assumes that undoing is not useful. In particular, any buffer whose
1260 name begins with a space has its undo recording off by default;
1261 see @ref{Buffer Names}.) All the primitives that modify the
1262 text in the buffer automatically add elements to the front of the undo
1263 list, which is in the variable @code{buffer-undo-list}.
1265 @defvar buffer-undo-list
1266 This buffer-local variable's value is the undo list of the current
1267 buffer. A value of @code{t} disables the recording of undo information.
1270 Here are the kinds of elements an undo list can have:
1273 @item @var{position}
1274 This kind of element records a previous value of point; undoing this
1275 element moves point to @var{position}. Ordinary cursor motion does not
1276 make any sort of undo record, but deletion operations use these entries
1277 to record where point was before the command.
1279 @item (@var{beg} . @var{end})
1280 This kind of element indicates how to delete text that was inserted.
1281 Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1284 @item (@var{text} . @var{position})
1285 This kind of element indicates how to reinsert text that was deleted.
1286 The deleted text itself is the string @var{text}. The place to
1287 reinsert it is @code{(abs @var{position})}. If @var{position} is
1288 positive, point was at the beginning of the deleted text, otherwise it
1289 was at the end. Zero or more (@var{marker} . @var{adjustment})
1290 elements follow immediately after this element.
1292 @item (t . @var{time-flag})
1293 This kind of element indicates that an unmodified buffer became
1294 modified. A @var{time-flag} of the form
1295 @code{(@var{sec-high} @var{sec-low} @var{microsec}
1296 @var{picosec})} represents the visited file's modification time as of
1297 when it was previously visited or saved, using the same format as
1298 @code{current-time}; see @ref{Time of Day}.
1299 A @var{time-flag} of 0 means the buffer does not correspond to any file;
1300 @minus{}1 means the visited file previously did not exist.
1301 @code{primitive-undo} uses these
1302 values to determine whether to mark the buffer as unmodified once again;
1303 it does so only if the file's status matches that of @var{time-flag}.
1305 @item (nil @var{property} @var{value} @var{beg} . @var{end})
1306 This kind of element records a change in a text property.
1307 Here's how you might undo the change:
1310 (put-text-property @var{beg} @var{end} @var{property} @var{value})
1313 @item (@var{marker} . @var{adjustment})
1314 This kind of element records the fact that the marker @var{marker} was
1315 relocated due to deletion of surrounding text, and that it moved
1316 @var{adjustment} character positions. If the marker's location is
1317 consistent with the (@var{text} . @var{position}) element preceding it
1318 in the undo list, then undoing this element moves @var{marker}
1319 @minus{} @var{adjustment} characters.
1321 @item (apply @var{funname} . @var{args})
1322 This is an extensible undo item, which is undone by calling
1323 @var{funname} with arguments @var{args}.
1325 @item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1326 This is an extensible undo item, which records a change limited to the
1327 range @var{beg} to @var{end}, which increased the size of the buffer
1328 by @var{delta} characters. It is undone by calling @var{funname} with
1329 arguments @var{args}.
1331 This kind of element enables undo limited to a region to determine
1332 whether the element pertains to that region.
1335 This element is a boundary. The elements between two boundaries are
1336 called a @dfn{change group}; normally, each change group corresponds to
1337 one keyboard command, and undo commands normally undo an entire group as
1341 @defun undo-boundary
1342 This function places a boundary element in the undo list. The undo
1343 command stops at such a boundary, and successive undo commands undo
1344 to earlier and earlier boundaries. This function returns @code{nil}.
1346 Calling this function explicitly is useful for splitting the effects of
1347 a command into more than one unit. For example, @code{query-replace}
1348 calls @code{undo-boundary} after each replacement, so that the user can
1349 undo individual replacements one by one.
1351 Mostly, however, this function is called automatically at an
1355 @defun undo-auto--amalgamate
1356 The editor command loop automatically calls @code{undo-boundary} just
1357 before executing each key sequence, so that each undo normally undoes
1358 the effects of one command. A few exceptional commands are
1359 @emph{amalgamating}: these commands generally cause small changes to
1360 buffers. So with these a boundary is inserted only every 20th command,
1361 so that these can be undone as a group. By default commands
1362 @code{self-insert-command}, which produces self-inserting input
1363 characters (@pxref{Commands for Insertion}), and @code{delete-char}
1364 which deletes characters (@pxref{Deletion}) are amalgamating.
1365 Where a command affects the contents of several buffers as may happen,
1366 for example, if a function on the @code{post-command-hook} affects a
1367 buffer other than the @code{current-buffer}, then @code{undo-boundary}
1368 will be called in each of them.
1371 @defvar undo-auto--boundary-timer
1372 Some buffers, such as process buffers, can change even when no
1373 commands are executing. In these cases, @code{undo-boundary} is
1374 normally called periodically by the timer in this variable. Setting
1375 this variable to non-@code{nil} prevents this behaviour.
1378 @defvar undo-in-progress
1379 This variable is normally @code{nil}, but the undo commands bind it to
1380 @code{t}. This is so that various kinds of change hooks can tell when
1381 they're being called for the sake of undoing.
1384 @defun primitive-undo count list
1385 This is the basic function for undoing elements of an undo list.
1386 It undoes the first @var{count} elements of @var{list}, returning
1387 the rest of @var{list}.
1389 @code{primitive-undo} adds elements to the buffer's undo list when it
1390 changes the buffer. Undo commands avoid confusion by saving the undo
1391 list value at the beginning of a sequence of undo operations. Then the
1392 undo operations use and update the saved value. The new elements added
1393 by undoing are not part of this saved value, so they don't interfere with
1396 This function does not bind @code{undo-in-progress}.
1399 @node Maintaining Undo
1400 @section Maintaining Undo Lists
1402 This section describes how to enable and disable undo information for
1403 a given buffer. It also explains how the undo list is truncated
1404 automatically so it doesn't get too big.
1406 Recording of undo information in a newly created buffer is normally
1407 enabled to start with; but if the buffer name starts with a space, the
1408 undo recording is initially disabled. You can explicitly enable or
1409 disable undo recording with the following two functions, or by setting
1410 @code{buffer-undo-list} yourself.
1412 @deffn Command buffer-enable-undo &optional buffer-or-name
1413 This command enables recording undo information for buffer
1414 @var{buffer-or-name}, so that subsequent changes can be undone. If no
1415 argument is supplied, then the current buffer is used. This function
1416 does nothing if undo recording is already enabled in the buffer. It
1419 In an interactive call, @var{buffer-or-name} is the current buffer.
1420 You cannot specify any other buffer.
1423 @deffn Command buffer-disable-undo &optional buffer-or-name
1424 @cindex disabling undo
1425 This function discards the undo list of @var{buffer-or-name}, and disables
1426 further recording of undo information. As a result, it is no longer
1427 possible to undo either previous changes or any subsequent changes. If
1428 the undo list of @var{buffer-or-name} is already disabled, this function
1431 In an interactive call, BUFFER-OR-NAME is the current buffer. You
1432 cannot specify any other buffer. This function returns @code{nil}.
1435 As editing continues, undo lists get longer and longer. To prevent
1436 them from using up all available memory space, garbage collection trims
1437 them back to size limits you can set. (For this purpose, the size
1438 of an undo list measures the cons cells that make up the list, plus the
1439 strings of deleted text.) Three variables control the range of acceptable
1440 sizes: @code{undo-limit}, @code{undo-strong-limit} and
1441 @code{undo-outer-limit}. In these variables, size is counted as the
1442 number of bytes occupied, which includes both saved text and other
1446 This is the soft limit for the acceptable size of an undo list. The
1447 change group at which this size is exceeded is the last one kept.
1450 @defopt undo-strong-limit
1451 This is the upper limit for the acceptable size of an undo list. The
1452 change group at which this size is exceeded is discarded itself (along
1453 with all older change groups). There is one exception: the very latest
1454 change group is only discarded if it exceeds @code{undo-outer-limit}.
1457 @defopt undo-outer-limit
1458 If at garbage collection time the undo info for the current command
1459 exceeds this limit, Emacs discards the info and displays a warning.
1460 This is a last ditch limit to prevent memory overflow.
1463 @defopt undo-ask-before-discard
1464 If this variable is non-@code{nil}, when the undo info exceeds
1465 @code{undo-outer-limit}, Emacs asks in the echo area whether to
1466 discard the info. The default value is @code{nil}, which means to
1467 discard it automatically.
1469 This option is mainly intended for debugging. Garbage collection is
1470 inhibited while the question is asked, which means that Emacs might
1471 leak memory if the user waits too long before answering the question.
1476 @cindex filling text
1478 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1479 breaks) so that they are nearly (but no greater than) a specified
1480 maximum width. Additionally, lines can be @dfn{justified}, which means
1481 inserting spaces to make the left and/or right margins line up
1482 precisely. The width is controlled by the variable @code{fill-column}.
1483 For ease of reading, lines should be no longer than 70 or so columns.
1485 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1486 automatically as you insert it, but changes to existing text may leave
1487 it improperly filled. Then you must fill the text explicitly.
1489 Most of the commands in this section return values that are not
1490 meaningful. All the functions that do filling take note of the current
1491 left margin, current right margin, and current justification style
1492 (@pxref{Margins}). If the current justification style is
1493 @code{none}, the filling functions don't actually do anything.
1495 Several of the filling functions have an argument @var{justify}.
1496 If it is non-@code{nil}, that requests some kind of justification. It
1497 can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1498 request a specific style of justification. If it is @code{t}, that
1499 means to use the current justification style for this part of the text
1500 (see @code{current-justification}, below). Any other value is treated
1503 When you call the filling functions interactively, using a prefix
1504 argument implies the value @code{full} for @var{justify}.
1506 @deffn Command fill-paragraph &optional justify region
1507 This command fills the paragraph at or after point. If
1508 @var{justify} is non-@code{nil}, each line is justified as well.
1509 It uses the ordinary paragraph motion commands to find paragraph
1510 boundaries. @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
1512 When @var{region} is non-@code{nil}, then if Transient Mark mode is
1513 enabled and the mark is active, this command calls @code{fill-region}
1514 to fill all the paragraphs in the region, instead of filling only the
1515 current paragraph. When this command is called interactively,
1516 @var{region} is @code{t}.
1519 @deffn Command fill-region start end &optional justify nosqueeze to-eop
1520 This command fills each of the paragraphs in the region from @var{start}
1521 to @var{end}. It justifies as well if @var{justify} is
1524 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1525 other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1526 that means to keep filling to the end of the paragraph---or the next hard
1527 newline, if @code{use-hard-newlines} is enabled (see below).
1529 The variable @code{paragraph-separate} controls how to distinguish
1530 paragraphs. @xref{Standard Regexps}.
1533 @deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
1534 This command fills each paragraph in the region according to its
1535 individual fill prefix. Thus, if the lines of a paragraph were indented
1536 with spaces, the filled paragraph will remain indented in the same
1539 The first two arguments, @var{start} and @var{end}, are the beginning
1540 and end of the region to be filled. The third and fourth arguments,
1541 @var{justify} and @var{citation-regexp}, are optional. If
1542 @var{justify} is non-@code{nil}, the paragraphs are justified as
1543 well as filled. If @var{citation-regexp} is non-@code{nil}, it means the
1544 function is operating on a mail message and therefore should not fill
1545 the header lines. If @var{citation-regexp} is a string, it is used as
1546 a regular expression; if it matches the beginning of a line, that line
1547 is treated as a citation marker.
1549 @c FIXME: "That mode" is confusing. It isn't a major/minor mode.
1550 Ordinarily, @code{fill-individual-paragraphs} regards each change in
1551 indentation as starting a new paragraph. If
1552 @code{fill-individual-varying-indent} is non-@code{nil}, then only
1553 separator lines separate paragraphs. That mode can handle indented
1554 paragraphs with additional indentation on the first line.
1557 @defopt fill-individual-varying-indent
1558 This variable alters the action of @code{fill-individual-paragraphs} as
1562 @deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1563 This command considers a region of text as a single paragraph and fills
1564 it. If the region was made up of many paragraphs, the blank lines
1565 between paragraphs are removed. This function justifies as well as
1566 filling when @var{justify} is non-@code{nil}.
1568 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1569 other than line breaks untouched. If @var{squeeze-after} is
1570 non-@code{nil}, it specifies a position in the region, and means don't
1571 canonicalize spaces before that position.
1573 In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1574 choose a fill prefix by default. @xref{Adaptive Fill}.
1577 @deffn Command justify-current-line &optional how eop nosqueeze
1578 This command inserts spaces between the words of the current line so
1579 that the line ends exactly at @code{fill-column}. It returns
1582 The argument @var{how}, if non-@code{nil} specifies explicitly the style
1583 of justification. It can be @code{left}, @code{right}, @code{full},
1584 @code{center}, or @code{none}. If it is @code{t}, that means to do
1585 follow specified justification style (see @code{current-justification},
1586 below). @code{nil} means to do full justification.
1588 If @var{eop} is non-@code{nil}, that means do only left-justification
1589 if @code{current-justification} specifies full justification. This is
1590 used for the last line of a paragraph; even if the paragraph as a
1591 whole is fully justified, the last line should not be.
1593 If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1597 @defopt default-justification
1598 This variable's value specifies the style of justification to use for
1599 text that doesn't specify a style with a text property. The possible
1600 values are @code{left}, @code{right}, @code{full}, @code{center}, or
1601 @code{none}. The default value is @code{left}.
1604 @defun current-justification
1605 This function returns the proper justification style to use for filling
1606 the text around point.
1608 This returns the value of the @code{justification} text property at
1609 point, or the variable @var{default-justification} if there is no such
1610 text property. However, it returns @code{nil} rather than @code{none}
1611 to mean ``don't justify''.
1614 @defopt sentence-end-double-space
1615 @anchor{Definition of sentence-end-double-space}
1616 If this variable is non-@code{nil}, a period followed by just one space
1617 does not count as the end of a sentence, and the filling functions
1618 avoid breaking the line at such a place.
1621 @defopt sentence-end-without-period
1622 If this variable is non-@code{nil}, a sentence can end without a
1623 period. This is used for languages like Thai, where sentences end
1624 with a double space but without a period.
1627 @defopt sentence-end-without-space
1628 If this variable is non-@code{nil}, it should be a string of
1629 characters that can end a sentence without following spaces.
1632 @defvar fill-paragraph-function
1633 This variable provides a way to override the filling of paragraphs.
1634 If its value is non-@code{nil}, @code{fill-paragraph} calls this
1635 function to do the work. If the function returns a non-@code{nil}
1636 value, @code{fill-paragraph} assumes the job is done, and immediately
1639 The usual use of this feature is to fill comments in programming
1640 language modes. If the function needs to fill a paragraph in the usual
1641 way, it can do so as follows:
1644 (let ((fill-paragraph-function nil))
1645 (fill-paragraph arg))
1649 @defvar fill-forward-paragraph-function
1650 This variable provides a way to override how the filling functions,
1651 such as @code{fill-region} and @code{fill-paragraph}, move forward to
1652 the next paragraph. Its value should be a function, which is called
1653 with a single argument @var{n}, the number of paragraphs to move, and
1654 should return the difference between @var{n} and the number of
1655 paragraphs actually moved. The default value of this variable is
1656 @code{forward-paragraph}. @xref{Paragraphs,,, emacs, The GNU Emacs
1660 @defvar use-hard-newlines
1661 If this variable is non-@code{nil}, the filling functions do not delete
1662 newlines that have the @code{hard} text property. These hard
1663 newlines act as paragraph separators. @xref{Hard and Soft
1664 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
1668 @section Margins for Filling
1669 @cindex margins, filling
1672 This buffer-local variable, if non-@code{nil}, specifies a string of
1673 text that appears at the beginning of normal text lines and should be
1674 disregarded when filling them. Any line that fails to start with the
1675 fill prefix is considered the start of a paragraph; so is any line
1676 that starts with the fill prefix followed by additional whitespace.
1677 Lines that start with the fill prefix but no additional whitespace are
1678 ordinary text lines that can be filled together. The resulting filled
1679 lines also start with the fill prefix.
1681 The fill prefix follows the left margin whitespace, if any.
1685 This buffer-local variable specifies the maximum width of filled lines.
1686 Its value should be an integer, which is a number of columns. All the
1687 filling, justification, and centering commands are affected by this
1688 variable, including Auto Fill mode (@pxref{Auto Filling}).
1690 As a practical matter, if you are writing text for other people to
1691 read, you should set @code{fill-column} to no more than 70. Otherwise
1692 the line will be too long for people to read comfortably, and this can
1693 make the text seem clumsy.
1695 The default value for @code{fill-column} is 70.
1698 @deffn Command set-left-margin from to margin
1699 This sets the @code{left-margin} property on the text from @var{from} to
1700 @var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1701 command also refills the region to fit the new margin.
1704 @deffn Command set-right-margin from to margin
1705 This sets the @code{right-margin} property on the text from @var{from}
1706 to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1707 this command also refills the region to fit the new margin.
1710 @defun current-left-margin
1711 This function returns the proper left margin value to use for filling
1712 the text around point. The value is the sum of the @code{left-margin}
1713 property of the character at the start of the current line (or zero if
1714 none), and the value of the variable @code{left-margin}.
1717 @defun current-fill-column
1718 This function returns the proper fill column value to use for filling
1719 the text around point. The value is the value of the @code{fill-column}
1720 variable, minus the value of the @code{right-margin} property of the
1721 character after point.
1724 @deffn Command move-to-left-margin &optional n force
1725 This function moves point to the left margin of the current line. The
1726 column moved to is determined by calling the function
1727 @code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1728 @code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1730 If @var{force} is non-@code{nil}, that says to fix the line's
1731 indentation if that doesn't match the left margin value.
1734 @defun delete-to-left-margin &optional from to
1735 This function removes left margin indentation from the text between
1736 @var{from} and @var{to}. The amount of indentation to delete is
1737 determined by calling @code{current-left-margin}. In no case does this
1738 function delete non-whitespace. If @var{from} and @var{to} are omitted,
1739 they default to the whole buffer.
1742 @defun indent-to-left-margin
1743 This function adjusts the indentation at the beginning of the current
1744 line to the value specified by the variable @code{left-margin}. (That
1745 may involve either inserting or deleting whitespace.) This function
1746 is value of @code{indent-line-function} in Paragraph-Indent Text mode.
1750 This variable specifies the base left margin column. In Fundamental
1751 mode, @kbd{RET} indents to this column. This variable automatically
1752 becomes buffer-local when set in any fashion.
1755 @defopt fill-nobreak-predicate
1756 This variable gives major modes a way to specify not to break a line
1757 at certain places. Its value should be a list of functions. Whenever
1758 filling considers breaking the line at a certain place in the buffer,
1759 it calls each of these functions with no arguments and with point
1760 located at that place. If any of the functions returns
1761 non-@code{nil}, then the line won't be broken there.
1765 @section Adaptive Fill Mode
1766 @c @cindex Adaptive Fill mode "adaptive-fill-mode" is adjacent.
1768 When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
1769 prefix automatically from the text in each paragraph being filled
1770 rather than using a predetermined value. During filling, this fill
1771 prefix gets inserted at the start of the second and subsequent lines
1772 of the paragraph as described in @ref{Filling}, and in @ref{Auto
1775 @defopt adaptive-fill-mode
1776 Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1777 It is @code{t} by default.
1780 @defun fill-context-prefix from to
1781 This function implements the heart of Adaptive Fill mode; it chooses a
1782 fill prefix based on the text between @var{from} and @var{to},
1783 typically the start and end of a paragraph. It does this by looking
1784 at the first two lines of the paragraph, based on the variables
1786 @c The optional argument first-line-regexp is not documented
1787 @c because it exists for internal purposes and might be eliminated
1790 Usually, this function returns the fill prefix, a string. However,
1791 before doing this, the function makes a final check (not specially
1792 mentioned in the following) that a line starting with this prefix
1793 wouldn't look like the start of a paragraph. Should this happen, the
1794 function signals the anomaly by returning @code{nil} instead.
1796 In detail, @code{fill-context-prefix} does this:
1800 It takes a candidate for the fill prefix from the first line---it
1801 tries first the function in @code{adaptive-fill-function} (if any),
1802 then the regular expression @code{adaptive-fill-regexp} (see below).
1803 The first non-@code{nil} result of these, or the empty string if
1804 they're both @code{nil}, becomes the first line's candidate.
1806 If the paragraph has as yet only one line, the function tests the
1807 validity of the prefix candidate just found. The function then
1808 returns the candidate if it's valid, or a string of spaces otherwise.
1809 (see the description of @code{adaptive-fill-first-line-regexp} below).
1811 When the paragraph already has two lines, the function next looks for
1812 a prefix candidate on the second line, in just the same way it did for
1813 the first line. If it doesn't find one, it returns @code{nil}.
1815 The function now compares the two candidate prefixes heuristically: if
1816 the non-whitespace characters in the line 2 candidate occur in the
1817 same order in the line 1 candidate, the function returns the line 2
1818 candidate. Otherwise, it returns the largest initial substring which
1819 is common to both candidates (which might be the empty string).
1823 @defopt adaptive-fill-regexp
1824 Adaptive Fill mode matches this regular expression against the text
1825 starting after the left margin whitespace (if any) on a line; the
1826 characters it matches are that line's candidate for the fill prefix.
1828 The default value matches whitespace with certain punctuation
1829 characters intermingled.
1832 @defopt adaptive-fill-first-line-regexp
1833 Used only in one-line paragraphs, this regular expression acts as an
1834 additional check of the validity of the one available candidate fill
1835 prefix: the candidate must match this regular expression, or match
1836 @code{comment-start-skip}. If it doesn't, @code{fill-context-prefix}
1837 replaces the candidate with a string of spaces of the same width
1840 The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
1841 matches only a string of whitespace. The effect of this default is to
1842 force the fill prefixes found in one-line paragraphs always to be pure
1846 @defopt adaptive-fill-function
1847 You can specify more complex ways of choosing a fill prefix
1848 automatically by setting this variable to a function. The function is
1849 called with point after the left margin (if any) of a line, and it
1850 must preserve point. It should return either that line's fill
1851 prefix or @code{nil}, meaning it has failed to determine a prefix.
1855 @section Auto Filling
1856 @cindex filling, automatic
1857 @cindex Auto Fill mode
1859 @c FIXME: I don't think any of the variables below is a/an normal/abnormal hook.
1860 Auto Fill mode is a minor mode that fills lines automatically as text
1861 is inserted. This section describes the hook used by Auto Fill mode.
1862 For a description of functions that you can call explicitly to fill and
1863 justify existing text, see @ref{Filling}.
1865 Auto Fill mode also enables the functions that change the margins and
1866 justification style to refill portions of the text. @xref{Margins}.
1868 @defvar auto-fill-function
1869 The value of this buffer-local variable should be a function (of no
1870 arguments) to be called after self-inserting a character from the table
1871 @code{auto-fill-chars}. It may be @code{nil}, in which case nothing
1872 special is done in that case.
1874 The value of @code{auto-fill-function} is @code{do-auto-fill} when
1875 Auto-Fill mode is enabled. That is a function whose sole purpose is to
1876 implement the usual strategy for breaking a line.
1879 @defvar normal-auto-fill-function
1880 This variable specifies the function to use for
1881 @code{auto-fill-function}, if and when Auto Fill is turned on. Major
1882 modes can set buffer-local values for this variable to alter how Auto
1886 @defvar auto-fill-chars
1887 A char table of characters which invoke @code{auto-fill-function} when
1888 self-inserted---space and newline in most language environments. They
1889 have an entry @code{t} in the table.
1893 @section Sorting Text
1894 @cindex sorting text
1896 The sorting functions described in this section all rearrange text in
1897 a buffer. This is in contrast to the function @code{sort}, which
1898 rearranges the order of the elements of a list (@pxref{Rearrangement}).
1899 The values returned by these functions are not meaningful.
1901 @defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
1902 This function is the general text-sorting routine that subdivides a
1903 buffer into records and then sorts them. Most of the commands in this
1904 section use this function.
1906 To understand how @code{sort-subr} works, consider the whole accessible
1907 portion of the buffer as being divided into disjoint pieces called
1908 @dfn{sort records}. The records may or may not be contiguous, but they
1909 must not overlap. A portion of each sort record (perhaps all of it) is
1910 designated as the sort key. Sorting rearranges the records in order by
1913 Usually, the records are rearranged in order of ascending sort key.
1914 If the first argument to the @code{sort-subr} function, @var{reverse},
1915 is non-@code{nil}, the sort records are rearranged in order of
1916 descending sort key.
1918 The next four arguments to @code{sort-subr} are functions that are
1919 called to move point across a sort record. They are called many times
1920 from within @code{sort-subr}.
1924 @var{nextrecfun} is called with point at the end of a record. This
1925 function moves point to the start of the next record. The first record
1926 is assumed to start at the position of point when @code{sort-subr} is
1927 called. Therefore, you should usually move point to the beginning of
1928 the buffer before calling @code{sort-subr}.
1930 This function can indicate there are no more sort records by leaving
1931 point at the end of the buffer.
1934 @var{endrecfun} is called with point within a record. It moves point to
1935 the end of the record.
1938 @var{startkeyfun} is called to move point from the start of a record to
1939 the start of the sort key. This argument is optional; if it is omitted,
1940 the whole record is the sort key. If supplied, the function should
1941 either return a non-@code{nil} value to be used as the sort key, or
1942 return @code{nil} to indicate that the sort key is in the buffer
1943 starting at point. In the latter case, @var{endkeyfun} is called to
1944 find the end of the sort key.
1947 @var{endkeyfun} is called to move point from the start of the sort key
1948 to the end of the sort key. This argument is optional. If
1949 @var{startkeyfun} returns @code{nil} and this argument is omitted (or
1950 @code{nil}), then the sort key extends to the end of the record. There
1951 is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1952 non-@code{nil} value.
1955 The argument @var{predicate} is the function to use to compare keys.
1956 If keys are numbers, it defaults to @code{<}; otherwise it defaults to
1959 As an example of @code{sort-subr}, here is the complete function
1960 definition for @code{sort-lines}:
1964 ;; @r{Note that the first two lines of doc string}
1965 ;; @r{are effectively one line when viewed by a user.}
1966 (defun sort-lines (reverse beg end)
1967 "Sort lines in region alphabetically;\
1968 argument means descending order.
1969 Called from a program, there are three arguments:
1972 REVERSE (non-nil means reverse order),\
1973 BEG and END (region to sort).
1974 The variable `sort-fold-case' determines\
1975 whether alphabetic case affects
1979 (interactive "P\nr")
1982 (narrow-to-region beg end)
1983 (goto-char (point-min))
1984 (let ((inhibit-field-text-motion t))
1985 (sort-subr reverse 'forward-line 'end-of-line)))))
1989 Here @code{forward-line} moves point to the start of the next record,
1990 and @code{end-of-line} moves point to the end of record. We do not pass
1991 the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
1992 record is used as the sort key.
1994 The @code{sort-paragraphs} function is very much the same, except that
1995 its @code{sort-subr} call looks like this:
2002 (while (and (not (eobp))
2003 (looking-at paragraph-separate))
2009 Markers pointing into any sort records are left with no useful
2010 position after @code{sort-subr} returns.
2013 @defopt sort-fold-case
2014 If this variable is non-@code{nil}, @code{sort-subr} and the other
2015 buffer sorting functions ignore case when comparing strings.
2018 @deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
2019 This command sorts the region between @var{start} and @var{end}
2020 alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
2021 If @var{reverse} is a negative integer, then sorting is in reverse
2024 Alphabetical sorting means that two sort keys are compared by
2025 comparing the first characters of each, the second characters of each,
2026 and so on. If a mismatch is found, it means that the sort keys are
2027 unequal; the sort key whose character is less at the point of first
2028 mismatch is the lesser sort key. The individual characters are compared
2029 according to their numerical character codes in the Emacs character set.
2031 The value of the @var{record-regexp} argument specifies how to divide
2032 the buffer into sort records. At the end of each record, a search is
2033 done for this regular expression, and the text that matches it is taken
2034 as the next record. For example, the regular expression @samp{^.+$},
2035 which matches lines with at least one character besides a newline, would
2036 make each such line into a sort record. @xref{Regular Expressions}, for
2037 a description of the syntax and meaning of regular expressions.
2039 The value of the @var{key-regexp} argument specifies what part of each
2040 record is the sort key. The @var{key-regexp} could match the whole
2041 record, or only a part. In the latter case, the rest of the record has
2042 no effect on the sorted order of records, but it is carried along when
2043 the record moves to its new position.
2045 The @var{key-regexp} argument can refer to the text matched by a
2046 subexpression of @var{record-regexp}, or it can be a regular expression
2049 If @var{key-regexp} is:
2052 @item @samp{\@var{digit}}
2053 then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
2054 grouping in @var{record-regexp} is the sort key.
2057 then the whole record is the sort key.
2059 @item a regular expression
2060 then @code{sort-regexp-fields} searches for a match for the regular
2061 expression within the record. If such a match is found, it is the sort
2062 key. If there is no match for @var{key-regexp} within a record then
2063 that record is ignored, which means its position in the buffer is not
2064 changed. (The other records may move around it.)
2067 For example, if you plan to sort all the lines in the region by the
2068 first word on each line starting with the letter @samp{f}, you should
2069 set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
2070 @samp{\<f\w*\>}. The resulting expression looks like this:
2074 (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
2080 If you call @code{sort-regexp-fields} interactively, it prompts for
2081 @var{record-regexp} and @var{key-regexp} in the minibuffer.
2084 @deffn Command sort-lines reverse start end
2085 This command alphabetically sorts lines in the region between
2086 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2087 is in reverse order.
2090 @deffn Command sort-paragraphs reverse start end
2091 This command alphabetically sorts paragraphs in the region between
2092 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2093 is in reverse order.
2096 @deffn Command sort-pages reverse start end
2097 This command alphabetically sorts pages in the region between
2098 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2099 is in reverse order.
2102 @deffn Command sort-fields field start end
2103 This command sorts lines in the region between @var{start} and
2104 @var{end}, comparing them alphabetically by the @var{field}th field
2105 of each line. Fields are separated by whitespace and numbered starting
2106 from 1. If @var{field} is negative, sorting is by the
2107 @w{@minus{}@var{field}th} field from the end of the line. This command
2108 is useful for sorting tables.
2111 @deffn Command sort-numeric-fields field start end
2112 This command sorts lines in the region between @var{start} and
2113 @var{end}, comparing them numerically by the @var{field}th field of
2114 each line. Fields are separated by whitespace and numbered starting
2115 from 1. The specified field must contain a number in each line of the
2116 region. Numbers starting with 0 are treated as octal, and numbers
2117 starting with @samp{0x} are treated as hexadecimal.
2119 If @var{field} is negative, sorting is by the
2120 @w{@minus{}@var{field}th} field from the end of the line. This
2121 command is useful for sorting tables.
2124 @defopt sort-numeric-base
2125 This variable specifies the default radix for
2126 @code{sort-numeric-fields} to parse numbers.
2129 @deffn Command sort-columns reverse &optional beg end
2130 This command sorts the lines in the region between @var{beg} and
2131 @var{end}, comparing them alphabetically by a certain range of
2132 columns. The column positions of @var{beg} and @var{end} bound the
2133 range of columns to sort on.
2135 If @var{reverse} is non-@code{nil}, the sort is in reverse order.
2137 One unusual thing about this command is that the entire line
2138 containing position @var{beg}, and the entire line containing position
2139 @var{end}, are included in the region sorted.
2141 Note that @code{sort-columns} rejects text that contains tabs, because
2142 tabs could be split across the specified columns. Use @kbd{M-x
2143 untabify} to convert tabs to spaces before sorting.
2145 When possible, this command actually works by calling the @code{sort}
2150 @section Counting Columns
2152 @cindex counting columns
2153 @cindex horizontal position
2155 The column functions convert between a character position (counting
2156 characters from the beginning of the buffer) and a column position
2157 (counting screen characters from the beginning of a line).
2159 These functions count each character according to the number of
2160 columns it occupies on the screen. This means control characters count
2161 as occupying 2 or 4 columns, depending upon the value of
2162 @code{ctl-arrow}, and tabs count as occupying a number of columns that
2163 depends on the value of @code{tab-width} and on the column where the tab
2164 begins. @xref{Usual Display}.
2166 Column number computations ignore the width of the window and the
2167 amount of horizontal scrolling. Consequently, a column value can be
2168 arbitrarily high. The first (or leftmost) column is numbered 0. They
2169 also ignore overlays and text properties, aside from invisibility.
2171 @defun current-column
2172 This function returns the horizontal position of point, measured in
2173 columns, counting from 0 at the left margin. The column position is the
2174 sum of the widths of all the displayed representations of the characters
2175 between the start of the current line and point.
2177 For an example of using @code{current-column}, see the description of
2178 @code{count-lines} in @ref{Text Lines}.
2181 @deffn Command move-to-column column &optional force
2182 This function moves point to @var{column} in the current line. The
2183 calculation of @var{column} takes into account the widths of the
2184 displayed representations of the characters between the start of the
2187 When called interactively, @var{column} is the value of prefix numeric
2188 argument. If @var{column} is not an integer, an error is signaled.
2190 @c This behavior used to be documented until 2013/08.
2192 If column @var{column} is beyond the end of the line, point moves to
2193 the end of the line. If @var{column} is negative, point moves to the
2194 beginning of the line.
2197 If it is impossible to move to column @var{column} because that is in
2198 the middle of a multicolumn character such as a tab, point moves to the
2199 end of that character. However, if @var{force} is non-@code{nil}, and
2200 @var{column} is in the middle of a tab, then @code{move-to-column}
2201 converts the tab into spaces so that it can move precisely to column
2202 @var{column}. Other multicolumn characters can cause anomalies despite
2203 @var{force}, since there is no way to split them.
2205 The argument @var{force} also has an effect if the line isn't long
2206 enough to reach column @var{column}; if it is @code{t}, that means to
2207 add whitespace at the end of the line to reach that column.
2209 The return value is the column number actually moved to.
2213 @section Indentation
2216 The indentation functions are used to examine, move to, and change
2217 whitespace that is at the beginning of a line. Some of the functions
2218 can also change whitespace elsewhere on a line. Columns and indentation
2219 count from zero at the left margin.
2222 * Primitive Indent:: Functions used to count and insert indentation.
2223 * Mode-Specific Indent:: Customize indentation for different modes.
2224 * Region Indent:: Indent all the lines in a region.
2225 * Relative Indent:: Indent the current line based on previous lines.
2226 * Indent Tabs:: Adjustable, typewriter-like tab stops.
2227 * Motion by Indent:: Move to first non-blank character.
2230 @node Primitive Indent
2231 @subsection Indentation Primitives
2233 This section describes the primitive functions used to count and
2234 insert indentation. The functions in the following sections use these
2235 primitives. @xref{Size of Displayed Text}, for related functions.
2237 @defun current-indentation
2238 @comment !!Type Primitive Function
2239 @comment !!SourceFile indent.c
2240 This function returns the indentation of the current line, which is
2241 the horizontal position of the first nonblank character. If the
2242 contents are entirely blank, then this is the horizontal position of the
2246 @deffn Command indent-to column &optional minimum
2247 @comment !!Type Primitive Function
2248 @comment !!SourceFile indent.c
2249 This function indents from point with tabs and spaces until @var{column}
2250 is reached. If @var{minimum} is specified and non-@code{nil}, then at
2251 least that many spaces are inserted even if this requires going beyond
2252 @var{column}. Otherwise the function does nothing if point is already
2253 beyond @var{column}. The value is the column at which the inserted
2256 The inserted whitespace characters inherit text properties from the
2257 surrounding text (usually, from the preceding text only). @xref{Sticky
2261 @defopt indent-tabs-mode
2262 @comment !!SourceFile indent.c
2263 If this variable is non-@code{nil}, indentation functions can insert
2264 tabs as well as spaces. Otherwise, they insert only spaces. Setting
2265 this variable automatically makes it buffer-local in the current buffer.
2268 @node Mode-Specific Indent
2269 @subsection Indentation Controlled by Major Mode
2271 An important function of each major mode is to customize the @key{TAB}
2272 key to indent properly for the language being edited. This section
2273 describes the mechanism of the @key{TAB} key and how to control it.
2274 The functions in this section return unpredictable values.
2276 @deffn Command indent-for-tab-command &optional rigid
2277 This is the command bound to @key{TAB} in most editing modes. Its
2278 usual action is to indent the current line, but it can alternatively
2279 insert a tab character or indent a region.
2281 Here is what it does:
2285 First, it checks whether Transient Mark mode is enabled and the region
2286 is active. If so, it called @code{indent-region} to indent all the
2287 text in the region (@pxref{Region Indent}).
2290 Otherwise, if the indentation function in @code{indent-line-function}
2291 is @code{indent-to-left-margin} (a trivial command that inserts a tab
2292 character), or if the variable @code{tab-always-indent} specifies that
2293 a tab character ought to be inserted (see below), then it inserts a
2297 Otherwise, it indents the current line; this is done by calling the
2298 function in @code{indent-line-function}. If the line is already
2299 indented, and the value of @code{tab-always-indent} is @code{complete}
2300 (see below), it tries completing the text at point.
2303 If @var{rigid} is non-@code{nil} (interactively, with a prefix
2304 argument), then after this command indents a line or inserts a tab, it
2305 also rigidly indents the entire balanced expression which starts at
2306 the beginning of the current line, in order to reflect the new
2307 indentation. This argument is ignored if the command indents the
2311 @defvar indent-line-function
2312 This variable's value is the function to be used by
2313 @code{indent-for-tab-command}, and various other indentation commands,
2314 to indent the current line. It is usually assigned by the major mode;
2315 for instance, Lisp mode sets it to @code{lisp-indent-line}, C mode
2316 sets it to @code{c-indent-line}, and so on. The default value is
2317 @code{indent-relative}. @xref{Auto-Indentation}.
2320 @deffn Command indent-according-to-mode
2321 This command calls the function in @code{indent-line-function} to
2322 indent the current line in a way appropriate for the current major mode.
2325 @deffn Command newline-and-indent
2326 This function inserts a newline, then indents the new line (the one
2327 following the newline just inserted) according to the major mode. It
2328 does indentation by calling @code{indent-according-to-mode}.
2331 @deffn Command reindent-then-newline-and-indent
2332 This command reindents the current line, inserts a newline at point,
2333 and then indents the new line (the one following the newline just
2334 inserted). It does indentation on both lines by calling
2335 @code{indent-according-to-mode}.
2338 @defopt tab-always-indent
2339 This variable can be used to customize the behavior of the @key{TAB}
2340 (@code{indent-for-tab-command}) command. If the value is @code{t}
2341 (the default), the command normally just indents the current line. If
2342 the value is @code{nil}, the command indents the current line only if
2343 point is at the left margin or in the line's indentation; otherwise,
2344 it inserts a tab character. If the value is @code{complete}, the
2345 command first tries to indent the current line, and if the line was
2346 already indented, it calls @code{completion-at-point} to complete the
2347 text at point (@pxref{Completion in Buffers}).
2351 @subsection Indenting an Entire Region
2353 This section describes commands that indent all the lines in the
2354 region. They return unpredictable values.
2356 @deffn Command indent-region start end &optional to-column
2357 This command indents each nonblank line starting between @var{start}
2358 (inclusive) and @var{end} (exclusive). If @var{to-column} is
2359 @code{nil}, @code{indent-region} indents each nonblank line by calling
2360 the current mode's indentation function, the value of
2361 @code{indent-line-function}.
2363 If @var{to-column} is non-@code{nil}, it should be an integer
2364 specifying the number of columns of indentation; then this function
2365 gives each line exactly that much indentation, by either adding or
2366 deleting whitespace.
2368 If there is a fill prefix, @code{indent-region} indents each line
2369 by making it start with the fill prefix.
2372 @defvar indent-region-function
2373 The value of this variable is a function that can be used by
2374 @code{indent-region} as a short cut. It should take two arguments, the
2375 start and end of the region. You should design the function so
2376 that it will produce the same results as indenting the lines of the
2377 region one by one, but presumably faster.
2379 If the value is @code{nil}, there is no short cut, and
2380 @code{indent-region} actually works line by line.
2382 A short-cut function is useful in modes such as C mode and Lisp mode,
2383 where the @code{indent-line-function} must scan from the beginning of
2384 the function definition: applying it to each line would be quadratic in
2385 time. The short cut can update the scan information as it moves through
2386 the lines indenting them; this takes linear time. In a mode where
2387 indenting a line individually is fast, there is no need for a short cut.
2389 @code{indent-region} with a non-@code{nil} argument @var{to-column} has
2390 a different meaning and does not use this variable.
2393 @deffn Command indent-rigidly start end count
2394 This function indents all lines starting between @var{start}
2395 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
2396 This preserves the shape of the affected region, moving it as a
2399 This is useful not only for indenting regions of unindented text, but
2400 also for indenting regions of formatted code. For example, if
2401 @var{count} is 3, this command adds 3 columns of indentation to every
2402 line that begins in the specified region.
2404 If called interactively with no prefix argument, this command invokes
2405 a transient mode for adjusting indentation rigidly. @xref{Indentation
2406 Commands,,, emacs, The GNU Emacs Manual}.
2409 @deffn Command indent-code-rigidly start end columns &optional nochange-regexp
2410 This is like @code{indent-rigidly}, except that it doesn't alter lines
2411 that start within strings or comments.
2413 In addition, it doesn't alter a line if @var{nochange-regexp} matches at
2414 the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
2417 @node Relative Indent
2418 @subsection Indentation Relative to Previous Lines
2420 This section describes two commands that indent the current line
2421 based on the contents of previous lines.
2423 @deffn Command indent-relative &optional unindented-ok
2424 This command inserts whitespace at point, extending to the same
2425 column as the next @dfn{indent point} of the previous nonblank line. An
2426 indent point is a non-whitespace character following whitespace. The
2427 next indent point is the first one at a column greater than the current
2428 column of point. For example, if point is underneath and to the left of
2429 the first non-blank character of a line of text, it moves to that column
2430 by inserting whitespace.
2432 If the previous nonblank line has no next indent point (i.e., none at a
2433 great enough column position), @code{indent-relative} either does
2434 nothing (if @var{unindented-ok} is non-@code{nil}) or calls
2435 @code{tab-to-tab-stop}. Thus, if point is underneath and to the right
2436 of the last column of a short line of text, this command ordinarily
2437 moves point to the next tab stop by inserting whitespace.
2439 The return value of @code{indent-relative} is unpredictable.
2441 In the following example, point is at the beginning of the second
2446 This line is indented twelve spaces.
2447 @point{}The quick brown fox jumped.
2452 Evaluation of the expression @code{(indent-relative nil)} produces the
2457 This line is indented twelve spaces.
2458 @point{}The quick brown fox jumped.
2462 In this next example, point is between the @samp{m} and @samp{p} of
2467 This line is indented twelve spaces.
2468 The quick brown fox jum@point{}ped.
2473 Evaluation of the expression @code{(indent-relative nil)} produces the
2478 This line is indented twelve spaces.
2479 The quick brown fox jum @point{}ped.
2484 @deffn Command indent-relative-maybe
2485 @comment !!SourceFile indent.el
2486 This command indents the current line like the previous nonblank line,
2487 by calling @code{indent-relative} with @code{t} as the
2488 @var{unindented-ok} argument. The return value is unpredictable.
2490 If the previous nonblank line has no indent points beyond the current
2491 column, this command does nothing.
2495 @subsection Adjustable Tab Stops
2496 @cindex tabs stops for indentation
2498 This section explains the mechanism for user-specified tab stops
2499 and the mechanisms that use and set them. The name ``tab stops'' is
2500 used because the feature is similar to that of the tab stops on a
2501 typewriter. The feature works by inserting an appropriate number of
2502 spaces and tab characters to reach the next tab stop column; it does not
2503 affect the display of tab characters in the buffer (@pxref{Usual
2504 Display}). Note that the @key{TAB} character as input uses this tab
2505 stop feature only in a few major modes, such as Text mode.
2506 @xref{Tab Stops,,, emacs, The GNU Emacs Manual}.
2508 @deffn Command tab-to-tab-stop
2509 This command inserts spaces or tabs before point, up to the next tab
2510 stop column defined by @code{tab-stop-list}.
2513 @defopt tab-stop-list
2514 This variable defines the tab stop columns used by @code{tab-to-tab-stop}.
2515 It should be either @code{nil}, or a list of increasing integers,
2516 which need not be evenly spaced. The list is implicitly
2517 extended to infinity through repetition of the interval between the
2518 last and penultimate elements (or @code{tab-width} if the list has
2519 fewer than two elements). A value of @code{nil} means a tab stop
2520 every @code{tab-width} columns.
2522 Use @kbd{M-x edit-tab-stops} to edit the location of tab stops interactively.
2525 @node Motion by Indent
2526 @subsection Indentation-Based Motion Commands
2528 These commands, primarily for interactive use, act based on the
2529 indentation in the text.
2531 @deffn Command back-to-indentation
2532 @comment !!SourceFile simple.el
2533 This command moves point to the first non-whitespace character in the
2534 current line (which is the line in which point is located). It returns
2538 @deffn Command backward-to-indentation &optional arg
2539 @comment !!SourceFile simple.el
2540 This command moves point backward @var{arg} lines and then to the
2541 first nonblank character on that line. It returns @code{nil}.
2542 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2545 @deffn Command forward-to-indentation &optional arg
2546 @comment !!SourceFile simple.el
2547 This command moves point forward @var{arg} lines and then to the first
2548 nonblank character on that line. It returns @code{nil}.
2549 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2553 @section Case Changes
2554 @cindex case conversion in buffers
2556 The case change commands described here work on text in the current
2557 buffer. @xref{Case Conversion}, for case conversion functions that work
2558 on strings and characters. @xref{Case Tables}, for how to customize
2559 which characters are upper or lower case and how to convert them.
2561 @deffn Command capitalize-region start end
2562 This function capitalizes all words in the region defined by
2563 @var{start} and @var{end}. To capitalize means to convert each word's
2564 first character to upper case and convert the rest of each word to lower
2565 case. The function returns @code{nil}.
2567 If one end of the region is in the middle of a word, the part of the
2568 word within the region is treated as an entire word.
2570 When @code{capitalize-region} is called interactively, @var{start} and
2571 @var{end} are point and the mark, with the smallest first.
2575 ---------- Buffer: foo ----------
2576 This is the contents of the 5th foo.
2577 ---------- Buffer: foo ----------
2581 (capitalize-region 1 37)
2584 ---------- Buffer: foo ----------
2585 This Is The Contents Of The 5th Foo.
2586 ---------- Buffer: foo ----------
2591 @deffn Command downcase-region start end
2592 This function converts all of the letters in the region defined by
2593 @var{start} and @var{end} to lower case. The function returns
2596 When @code{downcase-region} is called interactively, @var{start} and
2597 @var{end} are point and the mark, with the smallest first.
2600 @deffn Command upcase-region start end
2601 This function converts all of the letters in the region defined by
2602 @var{start} and @var{end} to upper case. The function returns
2605 When @code{upcase-region} is called interactively, @var{start} and
2606 @var{end} are point and the mark, with the smallest first.
2609 @deffn Command capitalize-word count
2610 This function capitalizes @var{count} words after point, moving point
2611 over as it does. To capitalize means to convert each word's first
2612 character to upper case and convert the rest of each word to lower case.
2613 If @var{count} is negative, the function capitalizes the
2614 @minus{}@var{count} previous words but does not move point. The value
2617 If point is in the middle of a word, the part of the word before point
2618 is ignored when moving forward. The rest is treated as an entire word.
2620 When @code{capitalize-word} is called interactively, @var{count} is
2621 set to the numeric prefix argument.
2624 @deffn Command downcase-word count
2625 This function converts the @var{count} words after point to all lower
2626 case, moving point over as it does. If @var{count} is negative, it
2627 converts the @minus{}@var{count} previous words but does not move point.
2628 The value is @code{nil}.
2630 When @code{downcase-word} is called interactively, @var{count} is set
2631 to the numeric prefix argument.
2634 @deffn Command upcase-word count
2635 This function converts the @var{count} words after point to all upper
2636 case, moving point over as it does. If @var{count} is negative, it
2637 converts the @minus{}@var{count} previous words but does not move point.
2638 The value is @code{nil}.
2640 When @code{upcase-word} is called interactively, @var{count} is set to
2641 the numeric prefix argument.
2644 @node Text Properties
2645 @section Text Properties
2646 @cindex text properties
2647 @cindex attributes of text
2648 @cindex properties of text
2650 Each character position in a buffer or a string can have a @dfn{text
2651 property list}, much like the property list of a symbol (@pxref{Property
2652 Lists}). The properties belong to a particular character at a
2653 particular place, such as, the letter @samp{T} at the beginning of this
2654 sentence or the first @samp{o} in @samp{foo}---if the same character
2655 occurs in two different places, the two occurrences in general have
2656 different properties.
2658 Each property has a name and a value. Both of these can be any Lisp
2659 object, but the name is normally a symbol. Typically each property
2660 name symbol is used for a particular purpose; for instance, the text
2661 property @code{face} specifies the faces for displaying the character
2662 (@pxref{Special Properties}). The usual way to access the property
2663 list is to specify a name and ask what value corresponds to it.
2665 If a character has a @code{category} property, we call it the
2666 @dfn{property category} of the character. It should be a symbol. The
2667 properties of the symbol serve as defaults for the properties of the
2670 Copying text between strings and buffers preserves the properties
2671 along with the characters; this includes such diverse functions as
2672 @code{substring}, @code{insert}, and @code{buffer-substring}.
2675 * Examining Properties:: Looking at the properties of one character.
2676 * Changing Properties:: Setting the properties of a range of text.
2677 * Property Search:: Searching for where a property changes value.
2678 * Special Properties:: Particular properties with special meanings.
2679 * Format Properties:: Properties for representing formatting of text.
2680 * Sticky Properties:: How inserted text gets properties from
2682 * Lazy Properties:: Computing text properties in a lazy fashion
2683 only when text is examined.
2684 * Clickable Text:: Using text properties to make regions of text
2685 do something when you click on them.
2686 * Fields:: The @code{field} property defines
2687 fields within the buffer.
2688 * Not Intervals:: Why text properties do not use
2689 Lisp-visible text intervals.
2692 @node Examining Properties
2693 @subsection Examining Text Properties
2694 @cindex examining text properties
2695 @cindex text properties, examining
2697 The simplest way to examine text properties is to ask for the value of
2698 a particular property of a particular character. For that, use
2699 @code{get-text-property}. Use @code{text-properties-at} to get the
2700 entire property list of a character. @xref{Property Search}, for
2701 functions to examine the properties of a number of characters at once.
2703 These functions handle both strings and buffers. Keep in mind that
2704 positions in a string start from 0, whereas positions in a buffer start
2707 @defun get-text-property pos prop &optional object
2708 This function returns the value of the @var{prop} property of the
2709 character after position @var{pos} in @var{object} (a buffer or
2710 string). The argument @var{object} is optional and defaults to the
2713 If there is no @var{prop} property strictly speaking, but the character
2714 has a property category that is a symbol, then @code{get-text-property} returns
2715 the @var{prop} property of that symbol.
2718 @defun get-char-property position prop &optional object
2719 This function is like @code{get-text-property}, except that it checks
2720 overlays first and then text properties. @xref{Overlays}.
2722 The argument @var{object} may be a string, a buffer, or a window. If
2723 it is a window, then the buffer displayed in that window is used for
2724 text properties and overlays, but only the overlays active for that
2725 window are considered. If @var{object} is a buffer, then overlays in
2726 that buffer are considered first, in order of decreasing priority,
2727 followed by the text properties. If @var{object} is a string, only
2728 text properties are considered, since strings never have overlays.
2731 @defun get-pos-property position prop &optional object
2732 This function is like @code{get-char-property}, except that it pays
2733 attention to properties' stickiness and overlays' advancement settings
2734 instead of the property of the character at (i.e., right after)
2738 @defun get-char-property-and-overlay position prop &optional object
2739 This is like @code{get-char-property}, but gives extra information
2740 about the overlay that the property value comes from.
2742 Its value is a cons cell whose @sc{car} is the property value, the
2743 same value @code{get-char-property} would return with the same
2744 arguments. Its @sc{cdr} is the overlay in which the property was
2745 found, or @code{nil}, if it was found as a text property or not found
2748 If @var{position} is at the end of @var{object}, both the @sc{car} and
2749 the @sc{cdr} of the value are @code{nil}.
2752 @defvar char-property-alias-alist
2753 This variable holds an alist which maps property names to a list of
2754 alternative property names. If a character does not specify a direct
2755 value for a property, the alternative property names are consulted in
2756 order; the first non-@code{nil} value is used. This variable takes
2757 precedence over @code{default-text-properties}, and @code{category}
2758 properties take precedence over this variable.
2761 @defun text-properties-at position &optional object
2762 This function returns the entire property list of the character at
2763 @var{position} in the string or buffer @var{object}. If @var{object} is
2764 @code{nil}, it defaults to the current buffer.
2767 @defvar default-text-properties
2768 This variable holds a property list giving default values for text
2769 properties. Whenever a character does not specify a value for a
2770 property, neither directly, through a category symbol, or through
2771 @code{char-property-alias-alist}, the value stored in this list is
2772 used instead. Here is an example:
2775 (setq default-text-properties '(foo 69)
2776 char-property-alias-alist nil)
2777 ;; @r{Make sure character 1 has no properties of its own.}
2778 (set-text-properties 1 2 nil)
2779 ;; @r{What we get, when we ask, is the default value.}
2780 (get-text-property 1 'foo)
2785 @node Changing Properties
2786 @subsection Changing Text Properties
2787 @cindex changing text properties
2788 @cindex text properties, changing
2790 The primitives for changing properties apply to a specified range of
2791 text in a buffer or string. The function @code{set-text-properties}
2792 (see end of section) sets the entire property list of the text in that
2793 range; more often, it is useful to add, change, or delete just certain
2794 properties specified by name.
2796 Since text properties are considered part of the contents of the
2797 buffer (or string), and can affect how a buffer looks on the screen,
2798 any change in buffer text properties marks the buffer as modified.
2799 Buffer text property changes are undoable also (@pxref{Undo}).
2800 Positions in a string start from 0, whereas positions in a buffer
2803 @defun put-text-property start end prop value &optional object
2804 This function sets the @var{prop} property to @var{value} for the text
2805 between @var{start} and @var{end} in the string or buffer @var{object}.
2806 If @var{object} is @code{nil}, it defaults to the current buffer.
2809 @defun add-text-properties start end props &optional object
2810 This function adds or overrides text properties for the text between
2811 @var{start} and @var{end} in the string or buffer @var{object}. If
2812 @var{object} is @code{nil}, it defaults to the current buffer.
2814 The argument @var{props} specifies which properties to add. It should
2815 have the form of a property list (@pxref{Property Lists}): a list whose
2816 elements include the property names followed alternately by the
2817 corresponding values.
2819 The return value is @code{t} if the function actually changed some
2820 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2821 its values agree with those in the text).
2823 For example, here is how to set the @code{comment} and @code{face}
2824 properties of a range of text:
2827 (add-text-properties @var{start} @var{end}
2828 '(comment t face highlight))
2832 @defun remove-text-properties start end props &optional object
2833 This function deletes specified text properties from the text between
2834 @var{start} and @var{end} in the string or buffer @var{object}. If
2835 @var{object} is @code{nil}, it defaults to the current buffer.
2837 The argument @var{props} specifies which properties to delete. It
2838 should have the form of a property list (@pxref{Property Lists}): a list
2839 whose elements are property names alternating with corresponding values.
2840 But only the names matter---the values that accompany them are ignored.
2841 For example, here's how to remove the @code{face} property.
2844 (remove-text-properties @var{start} @var{end} '(face nil))
2847 The return value is @code{t} if the function actually changed some
2848 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2849 if no character in the specified text had any of those properties).
2851 To remove all text properties from certain text, use
2852 @code{set-text-properties} and specify @code{nil} for the new property
2856 @defun remove-list-of-text-properties start end list-of-properties &optional object
2857 Like @code{remove-text-properties} except that
2858 @var{list-of-properties} is a list of property names only, not an
2859 alternating list of property names and values.
2862 @defun set-text-properties start end props &optional object
2863 This function completely replaces the text property list for the text
2864 between @var{start} and @var{end} in the string or buffer @var{object}.
2865 If @var{object} is @code{nil}, it defaults to the current buffer.
2867 The argument @var{props} is the new property list. It should be a list
2868 whose elements are property names alternating with corresponding values.
2870 After @code{set-text-properties} returns, all the characters in the
2871 specified range have identical properties.
2873 If @var{props} is @code{nil}, the effect is to get rid of all properties
2874 from the specified range of text. Here's an example:
2877 (set-text-properties @var{start} @var{end} nil)
2880 Do not rely on the return value of this function.
2883 @defun add-face-text-property start end face &optional appendp object
2884 This function acts on the text between @var{start} and @var{end},
2885 adding the face @var{face} to the @code{face} text property.
2886 @var{face} should be a valid value for the @code{face} property
2887 (@pxref{Special Properties}), such as a face name or an anonymous face
2890 If any text in the region already has a non-@code{nil} @code{face} property,
2891 those face(s) are retained. This function sets the @code{face}
2892 property to a list of faces, with @var{face} as the first element (by
2893 default) and the pre-existing faces as the remaining elements. If the
2894 optional argument @var{append} is non-@code{nil}, @var{face} is
2895 appended to the end of the list instead. Note that in a face list,
2896 the first occurring value for each attribute takes precedence.
2898 For example, the following code would assign a italicized green face
2899 to the text between @var{start} and @var{end}:
2902 (add-face-text-property @var{start} @var{end} 'italic)
2903 (add-face-text-property @var{start} @var{end} '(:foreground "red"))
2904 (add-face-text-property @var{start} @var{end} '(:foreground "green"))
2907 The optional argument @var{object}, if non-@code{nil}, specifies a
2908 buffer or string to act on, rather than the current buffer. If
2909 @var{object} is a string, then @var{start} and @var{end} are
2910 zero-based indices into the string.
2913 The easiest way to make a string with text properties is with
2916 @defun propertize string &rest properties
2917 This function returns a copy of @var{string} with the text properties
2918 @var{properties} added. These properties apply to all the characters
2919 in the string that is returned. Here is an example that constructs a
2920 string with a @code{face} property and a @code{mouse-face} property:
2923 (propertize "foo" 'face 'italic
2924 'mouse-face 'bold-italic)
2925 @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
2928 To put different properties on various parts of a string, you can
2929 construct each part with @code{propertize} and then combine them with
2934 (propertize "foo" 'face 'italic
2935 'mouse-face 'bold-italic)
2937 (propertize "bar" 'face 'italic
2938 'mouse-face 'bold-italic))
2939 @result{} #("foo and bar"
2940 0 3 (face italic mouse-face bold-italic)
2942 8 11 (face italic mouse-face bold-italic))
2946 @xref{Buffer Contents}, for the function
2947 @code{buffer-substring-no-properties}, which copies text from the
2948 buffer but does not copy its properties.
2950 @node Property Search
2951 @subsection Text Property Search Functions
2952 @cindex searching text properties
2953 @cindex text properties, searching
2955 In typical use of text properties, most of the time several or many
2956 consecutive characters have the same value for a property. Rather than
2957 writing your programs to examine characters one by one, it is much
2958 faster to process chunks of text that have the same property value.
2960 Here are functions you can use to do this. They use @code{eq} for
2961 comparing property values. In all cases, @var{object} defaults to the
2964 For good performance, it's very important to use the @var{limit}
2965 argument to these functions, especially the ones that search for a
2966 single property---otherwise, they may spend a long time scanning to the
2967 end of the buffer, if the property you are interested in does not change.
2969 These functions do not move point; instead, they return a position (or
2970 @code{nil}). Remember that a position is always between two characters;
2971 the position returned by these functions is between two characters with
2972 different properties.
2974 @defun next-property-change pos &optional object limit
2975 The function scans the text forward from position @var{pos} in the
2976 string or buffer @var{object} until it finds a change in some text
2977 property, then returns the position of the change. In other words, it
2978 returns the position of the first character beyond @var{pos} whose
2979 properties are not identical to those of the character just after
2982 If @var{limit} is non-@code{nil}, then the scan ends at position
2983 @var{limit}. If there is no property change before that point, this
2984 function returns @var{limit}.
2986 The value is @code{nil} if the properties remain unchanged all the way
2987 to the end of @var{object} and @var{limit} is @code{nil}. If the value
2988 is non-@code{nil}, it is a position greater than or equal to @var{pos}.
2989 The value equals @var{pos} only when @var{limit} equals @var{pos}.
2991 Here is an example of how to scan the buffer by chunks of text within
2992 which all properties are constant:
2996 (let ((plist (text-properties-at (point)))
2998 (or (next-property-change (point) (current-buffer))
3000 @r{Process text from point to @var{next-change}@dots{}}
3001 (goto-char next-change)))
3005 @defun previous-property-change pos &optional object limit
3006 This is like @code{next-property-change}, but scans back from @var{pos}
3007 instead of forward. If the value is non-@code{nil}, it is a position
3008 less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
3012 @defun next-single-property-change pos prop &optional object limit
3013 The function scans text for a change in the @var{prop} property, then
3014 returns the position of the change. The scan goes forward from
3015 position @var{pos} in the string or buffer @var{object}. In other
3016 words, this function returns the position of the first character
3017 beyond @var{pos} whose @var{prop} property differs from that of the
3018 character just after @var{pos}.
3020 If @var{limit} is non-@code{nil}, then the scan ends at position
3021 @var{limit}. If there is no property change before that point,
3022 @code{next-single-property-change} returns @var{limit}.
3024 The value is @code{nil} if the property remains unchanged all the way to
3025 the end of @var{object} and @var{limit} is @code{nil}. If the value is
3026 non-@code{nil}, it is a position greater than or equal to @var{pos}; it
3027 equals @var{pos} only if @var{limit} equals @var{pos}.
3030 @defun previous-single-property-change pos prop &optional object limit
3031 This is like @code{next-single-property-change}, but scans back from
3032 @var{pos} instead of forward. If the value is non-@code{nil}, it is a
3033 position less than or equal to @var{pos}; it equals @var{pos} only if
3034 @var{limit} equals @var{pos}.
3037 @defun next-char-property-change pos &optional limit
3038 This is like @code{next-property-change} except that it considers
3039 overlay properties as well as text properties, and if no change is
3040 found before the end of the buffer, it returns the maximum buffer
3041 position rather than @code{nil} (in this sense, it resembles the
3042 corresponding overlay function @code{next-overlay-change}, rather than
3043 @code{next-property-change}). There is no @var{object} operand
3044 because this function operates only on the current buffer. It returns
3045 the next address at which either kind of property changes.
3048 @defun previous-char-property-change pos &optional limit
3049 This is like @code{next-char-property-change}, but scans back from
3050 @var{pos} instead of forward, and returns the minimum buffer
3051 position if no change is found.
3054 @defun next-single-char-property-change pos prop &optional object limit
3055 This is like @code{next-single-property-change} except that it
3056 considers overlay properties as well as text properties, and if no
3057 change is found before the end of the @var{object}, it returns the
3058 maximum valid position in @var{object} rather than @code{nil}. Unlike
3059 @code{next-char-property-change}, this function @emph{does} have an
3060 @var{object} operand; if @var{object} is not a buffer, only
3061 text-properties are considered.
3064 @defun previous-single-char-property-change pos prop &optional object limit
3065 This is like @code{next-single-char-property-change}, but scans back
3066 from @var{pos} instead of forward, and returns the minimum valid
3067 position in @var{object} if no change is found.
3070 @defun text-property-any start end prop value &optional object
3071 This function returns non-@code{nil} if at least one character between
3072 @var{start} and @var{end} has a property @var{prop} whose value is
3073 @var{value}. More precisely, it returns the position of the first such
3074 character. Otherwise, it returns @code{nil}.
3076 The optional fifth argument, @var{object}, specifies the string or
3077 buffer to scan. Positions are relative to @var{object}. The default
3078 for @var{object} is the current buffer.
3081 @defun text-property-not-all start end prop value &optional object
3082 This function returns non-@code{nil} if at least one character between
3083 @var{start} and @var{end} does not have a property @var{prop} with value
3084 @var{value}. More precisely, it returns the position of the first such
3085 character. Otherwise, it returns @code{nil}.
3087 The optional fifth argument, @var{object}, specifies the string or
3088 buffer to scan. Positions are relative to @var{object}. The default
3089 for @var{object} is the current buffer.
3092 @node Special Properties
3093 @subsection Properties with Special Meanings
3095 Here is a table of text property names that have special built-in
3096 meanings. The following sections list a few additional special property
3097 names that control filling and property inheritance. All other names
3098 have no standard meaning, and you can use them as you like.
3100 Note: the properties @code{composition}, @code{display},
3101 @code{invisible} and @code{intangible} can also cause point to move to
3102 an acceptable place, after each Emacs command. @xref{Adjusting
3106 @cindex property category of text character
3107 @c FIXME: Isn't @kindex for keyboard commands?
3108 @kindex category @r{(text property)}
3110 If a character has a @code{category} property, we call it the
3111 @dfn{property category} of the character. It should be a symbol. The
3112 properties of this symbol serve as defaults for the properties of the
3116 @cindex face codes of text
3117 @kindex face @r{(text property)}
3118 The @code{face} property controls the appearance of the character
3119 (@pxref{Faces}). The value of the property can be the following:
3123 A face name (a symbol or string).
3126 An anonymous face: a property list of the form @code{(@var{keyword}
3127 @var{value} @dots{})}, where each @var{keyword} is a face attribute
3128 name and @var{value} is a value for that attribute.
3131 A list of faces. Each list element should be either a face name or an
3132 anonymous face. This specifies a face which is an aggregate of the
3133 attributes of each of the listed faces. Faces occurring earlier in
3134 the list have higher priority.
3137 A cons cell of the form @code{(foreground-color . @var{color-name})}
3138 or @code{(background-color . @var{color-name})}. This specifies the
3139 foreground or background color, similar to @code{(:foreground
3140 @var{color-name})} or @code{(:background @var{color-name})}. This
3141 form is supported for backward compatibility only, and should be
3145 Font Lock mode (@pxref{Font Lock Mode}) works in most buffers by
3146 dynamically updating the @code{face} property of characters based on
3149 The @code{add-face-text-property} function provides a convenient way
3150 to set this text property. @xref{Changing Properties}.
3152 @item font-lock-face
3153 @kindex font-lock-face @r{(text property)}
3154 This property specifies a value for the @code{face} property that Font
3155 Lock mode should apply to the underlying text. It is one of the
3156 fontification methods used by Font Lock mode, and is useful for
3157 special modes that implement their own highlighting.
3158 @xref{Precalculated Fontification}. When Font Lock mode is disabled,
3159 @code{font-lock-face} has no effect.
3162 @kindex mouse-face @r{(text property)}
3163 This property is used instead of @code{face} when the mouse is on or
3164 near the character. For this purpose, ``near'' means that all text
3165 between the character and where the mouse is have the same
3166 @code{mouse-face} property value.
3168 Emacs ignores all face attributes from the @code{mouse-face} property
3169 that alter the text size (e.g., @code{:height}, @code{:weight}, and
3170 @code{:slant}). Those attributes are always the same as for the
3174 @kindex fontified @r{(text property)}
3175 This property says whether the text is ready for display. If
3176 @code{nil}, Emacs's redisplay routine calls the functions in
3177 @code{fontification-functions} (@pxref{Auto Faces}) to prepare this
3178 part of the buffer before it is displayed. It is used internally by
3179 the just-in-time font locking code.
3182 This property activates various features that change the
3183 way text is displayed. For example, it can make text appear taller
3184 or shorter, higher or lower, wider or narrow, or replaced with an image.
3185 @xref{Display Property}.
3188 @kindex help-echo @r{(text property)}
3190 @anchor{Text help-echo}
3191 If text has a string as its @code{help-echo} property, then when you
3192 move the mouse onto that text, Emacs displays that string in the echo
3193 area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
3196 If the value of the @code{help-echo} property is a function, that
3197 function is called with three arguments, @var{window}, @var{object} and
3198 @var{pos} and should return a help string or @code{nil} for
3199 none. The first argument, @var{window} is the window in which
3200 the help was found. The second, @var{object}, is the buffer, overlay or
3201 string which had the @code{help-echo} property. The @var{pos}
3202 argument is as follows:
3206 If @var{object} is a buffer, @var{pos} is the position in the buffer.
3208 If @var{object} is an overlay, that overlay has a @code{help-echo}
3209 property, and @var{pos} is the position in the overlay's buffer.
3211 If @var{object} is a string (an overlay string or a string displayed
3212 with the @code{display} property), @var{pos} is the position in that
3216 If the value of the @code{help-echo} property is neither a function nor
3217 a string, it is evaluated to obtain a help string.
3219 You can alter the way help text is displayed by setting the variable
3220 @code{show-help-function} (@pxref{Help display}).
3222 This feature is used in the mode line and for other active text.
3225 @cindex keymap of character
3226 @kindex keymap @r{(text property)}
3227 The @code{keymap} property specifies an additional keymap for
3228 commands. When this keymap applies, it is used for key lookup before
3229 the minor mode keymaps and before the buffer's local map.
3230 @xref{Active Keymaps}. If the property value is a symbol, the
3231 symbol's function definition is used as the keymap.
3233 The property's value for the character before point applies if it is
3234 non-@code{nil} and rear-sticky, and the property's value for the
3235 character after point applies if it is non-@code{nil} and
3236 front-sticky. (For mouse clicks, the position of the click is used
3237 instead of the position of point.)
3240 @kindex local-map @r{(text property)}
3241 This property works like @code{keymap} except that it specifies a
3242 keymap to use @emph{instead of} the buffer's local map. For most
3243 purposes (perhaps all purposes), it is better to use the @code{keymap}
3247 The @code{syntax-table} property overrides what the syntax table says
3248 about this particular character. @xref{Syntax Properties}.
3251 @cindex read-only character
3252 @kindex read-only @r{(text property)}
3253 If a character has the property @code{read-only}, then modifying that
3254 character is not allowed. Any command that would do so gets an error,
3255 @code{text-read-only}. If the property value is a string, that string
3256 is used as the error message.
3258 Insertion next to a read-only character is an error if inserting
3259 ordinary text there would inherit the @code{read-only} property due to
3260 stickiness. Thus, you can control permission to insert next to
3261 read-only text by controlling the stickiness. @xref{Sticky Properties}.
3263 Since changing properties counts as modifying the buffer, it is not
3264 possible to remove a @code{read-only} property unless you know the
3265 special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
3266 and then remove the property. @xref{Read Only Buffers}.
3268 @item inhibit-read-only
3269 @kindex inhibit-read-only @r{(text property)}
3270 If a character has the property @code{inhibit-read-only}, and the
3271 buffer is read-only, editing the character in question is allowed.
3274 @kindex invisible @r{(text property)}
3275 A non-@code{nil} @code{invisible} property can make a character invisible
3276 on the screen. @xref{Invisible Text}, for details.
3279 @kindex intangible @r{(text property)}
3280 If a group of consecutive characters have equal and non-@code{nil}
3281 @code{intangible} properties, then you cannot place point between them.
3282 If you try to move point forward into the group, point actually moves to
3283 the end of the group. If you try to move point backward into the group,
3284 point actually moves to the start of the group.
3286 If consecutive characters have unequal non-@code{nil}
3287 @code{intangible} properties, they belong to separate groups; each
3288 group is separately treated as described above.
3290 When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
3291 the @code{intangible} property is ignored.
3293 Beware: this property operates at a very low level, and affects a lot of code
3294 in unexpected ways. So use it with extreme caution. A common misuse is to put
3295 an intangible property on invisible text, which is actually unnecessary since
3296 the command loop will move point outside of the invisible text at the end of
3297 each command anyway. @xref{Adjusting Point}.
3300 @kindex field @r{(text property)}
3301 Consecutive characters with the same @code{field} property constitute a
3302 @dfn{field}. Some motion functions including @code{forward-word} and
3303 @code{beginning-of-line} stop moving at a field boundary.
3307 @kindex cursor @r{(text property)}
3308 Normally, the cursor is displayed at the beginning or the end of any
3309 overlay and text property strings present at the current buffer
3310 position. You can place the cursor on any desired character of these
3311 strings by giving that character a non-@code{nil} @code{cursor} text
3312 property. In addition, if the value of the @code{cursor} property is
3313 an integer, it specifies the number of buffer's character
3314 positions, starting with the position where the overlay or the
3315 @code{display} property begins, for which the cursor should be
3316 displayed on that character. Specifically, if the value of the
3317 @code{cursor} property of a character is the number @var{n}, the
3318 cursor will be displayed on this character for any buffer position in
3319 the range @code{[@var{ovpos}..@var{ovpos}+@var{n})}, where @var{ovpos}
3320 is the overlay's starting position given by @code{overlay-start}
3321 (@pxref{Managing Overlays}), or the position where the @code{display}
3322 text property begins in the buffer.
3324 In other words, the string character with the @code{cursor} property
3325 of any non-@code{nil} value is the character where to display the
3326 cursor. The value of the property says for which buffer positions to
3327 display the cursor there. If the value is an integer @var{n},
3328 the cursor is displayed there when point is anywhere between the
3329 beginning of the overlay or @code{display} property and @var{n}
3330 positions after that. If the value is anything else and
3331 non-@code{nil}, the cursor is displayed there only when point is at
3332 the beginning of the @code{display} property or at
3333 @code{overlay-start}.
3335 @cindex cursor position for @code{display} properties and overlays
3336 When the buffer has many overlay strings (e.g., @pxref{Overlay
3337 Properties, before-string}) or @code{display} properties that are
3338 strings, it is a good idea to use the @code{cursor} property on these
3339 strings to cue the Emacs display about the places where to put the
3340 cursor while traversing these strings. This directly communicates to
3341 the display engine where the Lisp program wants to put the cursor, or
3342 where the user would expect the cursor.
3345 @kindex pointer @r{(text property)}
3346 This specifies a specific pointer shape when the mouse pointer is over
3347 this text or image. @xref{Pointer Shape}, for possible pointer
3351 @kindex line-spacing @r{(text property)}
3352 A newline can have a @code{line-spacing} text or overlay property that
3353 controls the height of the display line ending with that newline. The
3354 property value overrides the default frame line spacing and the buffer
3355 local @code{line-spacing} variable. @xref{Line Height}.
3358 @kindex line-height @r{(text property)}
3359 A newline can have a @code{line-height} text or overlay property that
3360 controls the total height of the display line ending in that newline.
3364 If text has a @code{wrap-prefix} property, the prefix it defines will
3365 be added at display time to the beginning of every continuation line
3366 due to text wrapping (so if lines are truncated, the wrap-prefix is
3367 never used). It may be a string or an image (@pxref{Other Display
3368 Specs}), or a stretch of whitespace such as specified by the
3369 @code{:width} or @code{:align-to} display properties (@pxref{Specified
3372 A wrap-prefix may also be specified for an entire buffer using the
3373 @code{wrap-prefix} buffer-local variable (however, a
3374 @code{wrap-prefix} text-property takes precedence over the value of
3375 the @code{wrap-prefix} variable). @xref{Truncation}.
3378 If text has a @code{line-prefix} property, the prefix it defines will
3379 be added at display time to the beginning of every non-continuation
3380 line. It may be a string or an image (@pxref{Other Display
3381 Specs}), or a stretch of whitespace such as specified by the
3382 @code{:width} or @code{:align-to} display properties (@pxref{Specified
3385 A line-prefix may also be specified for an entire buffer using the
3386 @code{line-prefix} buffer-local variable (however, a
3387 @code{line-prefix} text-property takes precedence over the value of
3388 the @code{line-prefix} variable). @xref{Truncation}.
3390 @item modification-hooks
3391 @cindex change hooks for a character
3392 @cindex hooks for changing a character
3393 @kindex modification-hooks @r{(text property)}
3394 If a character has the property @code{modification-hooks}, then its
3395 value should be a list of functions; modifying that character calls
3396 all of those functions before the actual modification. Each function
3397 receives two arguments: the beginning and end of the part of the
3398 buffer being modified. Note that if a particular modification hook
3399 function appears on several characters being modified by a single
3400 primitive, you can't predict how many times the function will
3402 Furthermore, insertion will not modify any existing character, so this
3403 hook will only be run when removing some characters, replacing them
3404 with others, or changing their text-properties.
3406 If these functions modify the buffer, they should bind
3407 @code{inhibit-modification-hooks} to @code{t} around doing so, to
3408 avoid confusing the internal mechanism that calls these hooks.
3410 Overlays also support the @code{modification-hooks} property, but the
3411 details are somewhat different (@pxref{Overlay Properties}).
3413 @item insert-in-front-hooks
3414 @itemx insert-behind-hooks
3415 @kindex insert-in-front-hooks @r{(text property)}
3416 @kindex insert-behind-hooks @r{(text property)}
3417 The operation of inserting text in a buffer also calls the functions
3418 listed in the @code{insert-in-front-hooks} property of the following
3419 character and in the @code{insert-behind-hooks} property of the
3420 preceding character. These functions receive two arguments, the
3421 beginning and end of the inserted text. The functions are called
3422 @emph{after} the actual insertion takes place.
3424 See also @ref{Change Hooks}, for other hooks that are called
3425 when you change text in a buffer.
3429 @cindex hooks for motion of point
3430 @kindex point-entered @r{(text property)}
3431 @kindex point-left @r{(text property)}
3432 The special properties @code{point-entered} and @code{point-left}
3433 record hook functions that report motion of point. Each time point
3434 moves, Emacs compares these two property values:
3438 the @code{point-left} property of the character after the old location,
3441 the @code{point-entered} property of the character after the new
3446 If these two values differ, each of them is called (if not @code{nil})
3447 with two arguments: the old value of point, and the new one.
3449 The same comparison is made for the characters before the old and new
3450 locations. The result may be to execute two @code{point-left} functions
3451 (which may be the same function) and/or two @code{point-entered}
3452 functions (which may be the same function). In any case, all the
3453 @code{point-left} functions are called first, followed by all the
3454 @code{point-entered} functions.
3456 It is possible to use @code{char-after} to examine characters at various
3457 buffer positions without moving point to those positions. Only an
3458 actual change in the value of point runs these hook functions.
3460 The variable @code{inhibit-point-motion-hooks} can inhibit running the
3461 @code{point-left} and @code{point-entered} hooks, see @ref{Inhibit
3462 point motion hooks}.
3465 @kindex composition @r{(text property)}
3466 This text property is used to display a sequence of characters as a
3467 single glyph composed from components. But the value of the property
3468 itself is completely internal to Emacs and should not be manipulated
3469 directly by, for instance, @code{put-text-property}.
3473 @defvar inhibit-point-motion-hooks
3474 @anchor{Inhibit point motion hooks} When this variable is
3475 non-@code{nil}, @code{point-left} and @code{point-entered} hooks are
3476 not run, and the @code{intangible} property has no effect. Do not set
3477 this variable globally; bind it with @code{let}.
3480 @defvar show-help-function
3481 @anchor{Help display} If this variable is non-@code{nil}, it specifies a
3482 function called to display help strings. These may be @code{help-echo}
3483 properties, menu help strings (@pxref{Simple Menu Items},
3484 @pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
3485 Bar}). The specified function is called with one argument, the help
3486 string to display, which is passed through
3487 @code{substitute-command-keys} before being given to the function; see
3488 @ref{Keys in Documentation}. Tooltip mode (@pxref{Tooltips,,, emacs,
3489 The GNU Emacs Manual}) provides an example.
3492 @node Format Properties
3493 @subsection Formatted Text Properties
3495 These text properties affect the behavior of the fill commands. They
3496 are used for representing formatted text. @xref{Filling}, and
3501 If a newline character has this property, it is a ``hard'' newline.
3502 The fill commands do not alter hard newlines and do not move words
3503 across them. However, this property takes effect only if the
3504 @code{use-hard-newlines} minor mode is enabled. @xref{Hard and Soft
3505 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
3508 This property specifies an extra right margin for filling this part of the
3512 This property specifies an extra left margin for filling this part of the
3516 This property specifies the style of justification for filling this part
3520 @node Sticky Properties
3521 @subsection Stickiness of Text Properties
3522 @cindex sticky text properties
3523 @cindex inheritance, text property
3525 Self-inserting characters, the ones that get inserted into a buffer
3526 when the user types them (@pxref{Commands for Insertion}), normally
3527 take on the same properties as the preceding character. This is
3528 called @dfn{inheritance} of properties.
3530 By contrast, a Lisp program can do insertion with inheritance or without,
3531 depending on the choice of insertion primitive. The ordinary text
3532 insertion functions, such as @code{insert}, do not inherit any
3533 properties. They insert text with precisely the properties of the
3534 string being inserted, and no others. This is correct for programs
3535 that copy text from one context to another---for example, into or out
3536 of the kill ring. To insert with inheritance, use the special
3537 primitives described in this section. Self-inserting characters
3538 inherit properties because they work using these primitives.
3540 When you do insertion with inheritance, @emph{which} properties are
3541 inherited, and from where, depends on which properties are @dfn{sticky}.
3542 Insertion after a character inherits those of its properties that are
3543 @dfn{rear-sticky}. Insertion before a character inherits those of its
3544 properties that are @dfn{front-sticky}. When both sides offer different
3545 sticky values for the same property, the previous character's value
3548 By default, a text property is rear-sticky but not front-sticky; thus,
3549 the default is to inherit all the properties of the preceding character,
3550 and nothing from the following character.
3552 You can control the stickiness of various text properties with two
3553 specific text properties, @code{front-sticky} and @code{rear-nonsticky},
3554 and with the variable @code{text-property-default-nonsticky}. You can
3555 use the variable to specify a different default for a given property.
3556 You can use those two text properties to make any specific properties
3557 sticky or nonsticky in any particular part of the text.
3559 If a character's @code{front-sticky} property is @code{t}, then all
3560 its properties are front-sticky. If the @code{front-sticky} property is
3561 a list, then the sticky properties of the character are those whose
3562 names are in the list. For example, if a character has a
3563 @code{front-sticky} property whose value is @code{(face read-only)},
3564 then insertion before the character can inherit its @code{face} property
3565 and its @code{read-only} property, but no others.
3567 The @code{rear-nonsticky} property works the opposite way. Most
3568 properties are rear-sticky by default, so the @code{rear-nonsticky}
3569 property says which properties are @emph{not} rear-sticky. If a
3570 character's @code{rear-nonsticky} property is @code{t}, then none of its
3571 properties are rear-sticky. If the @code{rear-nonsticky} property is a
3572 list, properties are rear-sticky @emph{unless} their names are in the
3575 @defvar text-property-default-nonsticky
3576 This variable holds an alist which defines the default rear-stickiness
3577 of various text properties. Each element has the form
3578 @code{(@var{property} . @var{nonstickiness})}, and it defines the
3579 stickiness of a particular text property, @var{property}.
3581 If @var{nonstickiness} is non-@code{nil}, this means that the property
3582 @var{property} is rear-nonsticky by default. Since all properties are
3583 front-nonsticky by default, this makes @var{property} nonsticky in both
3584 directions by default.
3586 The text properties @code{front-sticky} and @code{rear-nonsticky}, when
3587 used, take precedence over the default @var{nonstickiness} specified in
3588 @code{text-property-default-nonsticky}.
3591 Here are the functions that insert text with inheritance of properties:
3593 @defun insert-and-inherit &rest strings
3594 Insert the strings @var{strings}, just like the function @code{insert},
3595 but inherit any sticky properties from the adjoining text.
3598 @defun insert-before-markers-and-inherit &rest strings
3599 Insert the strings @var{strings}, just like the function
3600 @code{insert-before-markers}, but inherit any sticky properties from the
3604 @xref{Insertion}, for the ordinary insertion functions which do not
3607 @node Lazy Properties
3608 @subsection Lazy Computation of Text Properties
3610 Instead of computing text properties for all the text in the buffer,
3611 you can arrange to compute the text properties for parts of the text
3612 when and if something depends on them.
3614 The primitive that extracts text from the buffer along with its
3615 properties is @code{buffer-substring}. Before examining the properties,
3616 this function runs the abnormal hook @code{buffer-access-fontify-functions}.
3618 @defvar buffer-access-fontify-functions
3619 This variable holds a list of functions for computing text properties.
3620 Before @code{buffer-substring} copies the text and text properties for a
3621 portion of the buffer, it calls all the functions in this list. Each of
3622 the functions receives two arguments that specify the range of the
3623 buffer being accessed. (The buffer itself is always the current
3627 The function @code{buffer-substring-no-properties} does not call these
3628 functions, since it ignores text properties anyway.
3630 In order to prevent the hook functions from being called more than
3631 once for the same part of the buffer, you can use the variable
3632 @code{buffer-access-fontified-property}.
3634 @defvar buffer-access-fontified-property
3635 If this variable's value is non-@code{nil}, it is a symbol which is used
3636 as a text property name. A non-@code{nil} value for that text property
3637 means the other text properties for this character have already been
3640 If all the characters in the range specified for @code{buffer-substring}
3641 have a non-@code{nil} value for this property, @code{buffer-substring}
3642 does not call the @code{buffer-access-fontify-functions} functions. It
3643 assumes these characters already have the right text properties, and
3644 just copies the properties they already have.
3646 The normal way to use this feature is that the
3647 @code{buffer-access-fontify-functions} functions add this property, as
3648 well as others, to the characters they operate on. That way, they avoid
3649 being called over and over for the same text.
3652 @node Clickable Text
3653 @subsection Defining Clickable Text
3654 @cindex clickable text
3655 @cindex follow links
3658 @dfn{Clickable text} is text that can be clicked, with either the
3659 mouse or via a keyboard command, to produce some result. Many major
3660 modes use clickable text to implement textual hyper-links, or
3661 @dfn{links} for short.
3663 The easiest way to insert and manipulate links is to use the
3664 @code{button} package. @xref{Buttons}. In this section, we will
3665 explain how to manually set up clickable text in a buffer, using text
3666 properties. For simplicity, we will refer to the clickable text as a
3669 Implementing a link involves three separate steps: (1) indicating
3670 clickability when the mouse moves over the link; (2) making @key{RET}
3671 or @kbd{Mouse-2} on that link do something; and (3) setting up a
3672 @code{follow-link} condition so that the link obeys
3673 @code{mouse-1-click-follows-link}.
3675 To indicate clickability, add the @code{mouse-face} text property to
3676 the text of the link; then Emacs will highlight the link when the
3677 mouse moves over it. In addition, you should define a tooltip or echo
3678 area message, using the @code{help-echo} text property. @xref{Special
3679 Properties}. For instance, here is how Dired indicates that file
3680 names are clickable:
3683 (if (dired-move-to-filename)
3684 (add-text-properties
3687 (dired-move-to-end-of-filename)
3689 '(mouse-face highlight
3690 help-echo "mouse-2: visit this file in other window")))
3693 To make the link clickable, bind @key{RET} and @kbd{Mouse-2} to
3694 commands that perform the desired action. Each command should check
3695 to see whether it was called on a link, and act accordingly. For
3696 instance, Dired's major mode keymap binds @kbd{Mouse-2} to the
3700 (defun dired-mouse-find-file-other-window (event)
3701 "In Dired, visit the file or directory name you click on."
3703 (let ((window (posn-window (event-end event)))
3704 (pos (posn-point (event-end event)))
3706 (if (not (windowp window))
3707 (error "No file chosen"))
3708 (with-current-buffer (window-buffer window)
3710 (setq file (dired-get-file-for-visit)))
3711 (if (file-directory-p file)
3712 (or (and (cdr dired-subdir-alist)
3713 (dired-goto-subdir file))
3715 (select-window window)
3716 (dired-other-window file)))
3717 (select-window window)
3718 (find-file-other-window (file-name-sans-versions file t)))))
3722 This command uses the functions @code{posn-window} and
3723 @code{posn-point} to determine where the click occurred, and
3724 @code{dired-get-file-for-visit} to determine which file to visit.
3726 Instead of binding the mouse command in a major mode keymap, you can
3727 bind it within the link text, using the @code{keymap} text property
3728 (@pxref{Special Properties}). For instance:
3731 (let ((map (make-sparse-keymap)))
3732 (define-key map [mouse-2] 'operate-this-button)
3733 (put-text-property link-start link-end 'keymap map))
3737 With this method, you can easily define different commands for
3738 different links. Furthermore, the global definition of @key{RET} and
3739 @kbd{Mouse-2} remain available for the rest of the text in the buffer.
3741 @vindex mouse-1-click-follows-link
3742 The basic Emacs command for clicking on links is @kbd{Mouse-2}.
3743 However, for compatibility with other graphical applications, Emacs
3744 also recognizes @kbd{Mouse-1} clicks on links, provided the user
3745 clicks on the link quickly without moving the mouse. This behavior is
3746 controlled by the user option @code{mouse-1-click-follows-link}.
3747 @xref{Mouse References,,, emacs, The GNU Emacs Manual}.
3749 @cindex follow-link (text or overlay property)
3750 To set up the link so that it obeys
3751 @code{mouse-1-click-follows-link}, you must either (1) apply a
3752 @code{follow-link} text or overlay property to the link text, or (2)
3753 bind the @code{follow-link} event to a keymap (which can be a major
3754 mode keymap or a local keymap specified via the @code{keymap} text
3755 property). The value of the @code{follow-link} property, or the
3756 binding for the @code{follow-link} event, acts as a condition for
3757 the link action. This condition tells Emacs two things: the
3758 circumstances under which a @kbd{Mouse-1} click should be regarded as
3759 occurring inside the link, and how to compute an action code
3760 that says what to translate the @kbd{Mouse-1} click into. The link
3761 action condition can be one of the following:
3764 @item @code{mouse-face}
3765 If the condition is the symbol @code{mouse-face}, a position is inside
3766 a link if there is a non-@code{nil} @code{mouse-face} property at that
3767 position. The action code is always @code{t}.
3769 For example, here is how Info mode handles @key{Mouse-1}:
3772 (define-key Info-mode-map [follow-link] 'mouse-face)
3776 If the condition is a function, @var{func}, then a position @var{pos}
3777 is inside a link if @code{(@var{func} @var{pos})} evaluates to
3778 non-@code{nil}. The value returned by @var{func} serves as the action
3781 For example, here is how pcvs enables @kbd{Mouse-1} to follow links on
3785 (define-key map [follow-link]
3787 (eq (get-char-property pos 'face) 'cvs-filename-face)))
3791 If the condition value is anything else, then the position is inside a
3792 link and the condition itself is the action code. Clearly, you should
3793 specify this kind of condition only when applying the condition via a
3794 text or property overlay on the link text (so that it does not apply
3795 to the entire buffer).
3799 The action code tells @kbd{Mouse-1} how to follow the link:
3802 @item a string or vector
3803 If the action code is a string or vector, the @kbd{Mouse-1} event is
3804 translated into the first element of the string or vector; i.e., the
3805 action of the @kbd{Mouse-1} click is the local or global binding of
3806 that character or symbol. Thus, if the action code is @code{"foo"},
3807 @kbd{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
3808 @kbd{Mouse-1} translates into @key{foo}.
3811 For any other non-@code{nil} action code, the @kbd{Mouse-1} event is
3812 translated into a @kbd{Mouse-2} event at the same position.
3815 To define @kbd{Mouse-1} to activate a button defined with
3816 @code{define-button-type}, give the button a @code{follow-link}
3817 property. The property value should be a link action condition, as
3818 described above. @xref{Buttons}. For example, here is how Help mode
3819 handles @kbd{Mouse-1}:
3822 (define-button-type 'help-xref
3824 'action #'help-button-action)
3827 To define @kbd{Mouse-1} on a widget defined with
3828 @code{define-widget}, give the widget a @code{:follow-link} property.
3829 The property value should be a link action condition, as described
3830 above. For example, here is how the @code{link} widget specifies that
3831 a @key{Mouse-1} click shall be translated to @key{RET}:
3834 (define-widget 'link 'item
3836 :button-prefix 'widget-link-prefix
3837 :button-suffix 'widget-link-suffix
3839 :help-echo "Follow the link."
3843 @defun mouse-on-link-p pos
3844 This function returns non-@code{nil} if position @var{pos} in the
3845 current buffer is on a link. @var{pos} can also be a mouse event
3846 location, as returned by @code{event-start} (@pxref{Accessing Mouse}).
3850 @subsection Defining and Using Fields
3853 A field is a range of consecutive characters in the buffer that are
3854 identified by having the same value (comparing with @code{eq}) of the
3855 @code{field} property (either a text-property or an overlay property).
3856 This section describes special functions that are available for
3857 operating on fields.
3859 You specify a field with a buffer position, @var{pos}. We think of
3860 each field as containing a range of buffer positions, so the position
3861 you specify stands for the field containing that position.
3863 When the characters before and after @var{pos} are part of the same
3864 field, there is no doubt which field contains @var{pos}: the one those
3865 characters both belong to. When @var{pos} is at a boundary between
3866 fields, which field it belongs to depends on the stickiness of the
3867 @code{field} properties of the two surrounding characters (@pxref{Sticky
3868 Properties}). The field whose property would be inherited by text
3869 inserted at @var{pos} is the field that contains @var{pos}.
3871 There is an anomalous case where newly inserted text at @var{pos}
3872 would not inherit the @code{field} property from either side. This
3873 happens if the previous character's @code{field} property is not
3874 rear-sticky, and the following character's @code{field} property is not
3875 front-sticky. In this case, @var{pos} belongs to neither the preceding
3876 field nor the following field; the field functions treat it as belonging
3877 to an empty field whose beginning and end are both at @var{pos}.
3879 In all of these functions, if @var{pos} is omitted or @code{nil}, the
3880 value of point is used by default. If narrowing is in effect, then
3881 @var{pos} should fall within the accessible portion. @xref{Narrowing}.
3883 @defun field-beginning &optional pos escape-from-edge limit
3884 This function returns the beginning of the field specified by @var{pos}.
3886 If @var{pos} is at the beginning of its field, and
3887 @var{escape-from-edge} is non-@code{nil}, then the return value is
3888 always the beginning of the preceding field that @emph{ends} at @var{pos},
3889 regardless of the stickiness of the @code{field} properties around
3892 If @var{limit} is non-@code{nil}, it is a buffer position; if the
3893 beginning of the field is before @var{limit}, then @var{limit} will be
3897 @defun field-end &optional pos escape-from-edge limit
3898 This function returns the end of the field specified by @var{pos}.
3900 If @var{pos} is at the end of its field, and @var{escape-from-edge} is
3901 non-@code{nil}, then the return value is always the end of the following
3902 field that @emph{begins} at @var{pos}, regardless of the stickiness of
3903 the @code{field} properties around @var{pos}.
3905 If @var{limit} is non-@code{nil}, it is a buffer position; if the end
3906 of the field is after @var{limit}, then @var{limit} will be returned
3910 @defun field-string &optional pos
3911 This function returns the contents of the field specified by @var{pos},
3915 @defun field-string-no-properties &optional pos
3916 This function returns the contents of the field specified by @var{pos},
3917 as a string, discarding text properties.
3920 @defun delete-field &optional pos
3921 This function deletes the text of the field specified by @var{pos}.
3924 @defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
3925 This function constrains @var{new-pos} to the field that
3926 @var{old-pos} belongs to---in other words, it returns the position
3927 closest to @var{new-pos} that is in the same field as @var{old-pos}.
3929 If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
3930 the value of point instead, and moves point to the resulting position
3931 in addition to returning that position.
3933 If @var{old-pos} is at the boundary of two fields, then the acceptable
3934 final positions depend on the argument @var{escape-from-edge}. If
3935 @var{escape-from-edge} is @code{nil}, then @var{new-pos} must be in
3936 the field whose @code{field} property equals what new characters
3937 inserted at @var{old-pos} would inherit. (This depends on the
3938 stickiness of the @code{field} property for the characters before and
3939 after @var{old-pos}.) If @var{escape-from-edge} is non-@code{nil},
3940 @var{new-pos} can be anywhere in the two adjacent fields.
3941 Additionally, if two fields are separated by another field with the
3942 special value @code{boundary}, then any point within this special
3943 field is also considered to be on the boundary.
3945 Commands like @kbd{C-a} with no argument, that normally move backward
3946 to a specific kind of location and stay there once there, probably
3947 should specify @code{nil} for @var{escape-from-edge}. Other motion
3948 commands that check fields should probably pass @code{t}.
3950 If the optional argument @var{only-in-line} is non-@code{nil}, and
3951 constraining @var{new-pos} in the usual way would move it to a different
3952 line, @var{new-pos} is returned unconstrained. This used in commands
3953 that move by line, such as @code{next-line} and
3954 @code{beginning-of-line}, so that they respect field boundaries only in
3955 the case where they can still move to the right line.
3957 If the optional argument @var{inhibit-capture-property} is
3958 non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
3959 name, then any field boundaries are ignored.
3961 You can cause @code{constrain-to-field} to ignore all field boundaries
3962 (and so never constrain anything) by binding the variable
3963 @code{inhibit-field-text-motion} to a non-@code{nil} value.
3967 @subsection Why Text Properties are not Intervals
3970 Some editors that support adding attributes to text in the buffer do
3971 so by letting the user specify intervals within the text, and adding
3972 the properties to the intervals. Those editors permit the user or the
3973 programmer to determine where individual intervals start and end. We
3974 deliberately provided a different sort of interface in Emacs Lisp to
3975 avoid certain paradoxical behavior associated with text modification.
3977 If the actual subdivision into intervals is meaningful, that means you
3978 can distinguish between a buffer that is just one interval with a
3979 certain property, and a buffer containing the same text subdivided into
3980 two intervals, both of which have that property.
3982 Suppose you take the buffer with just one interval and kill part of
3983 the text. The text remaining in the buffer is one interval, and the
3984 copy in the kill ring (and the undo list) becomes a separate interval.
3985 Then if you yank back the killed text, you get two intervals with the
3986 same properties. Thus, editing does not preserve the distinction
3987 between one interval and two.
3989 Suppose we attempt to fix this problem by coalescing the two intervals when
3990 the text is inserted. That works fine if the buffer originally was a
3991 single interval. But suppose instead that we have two adjacent
3992 intervals with the same properties, and we kill the text of one interval
3993 and yank it back. The same interval-coalescence feature that rescues
3994 the other case causes trouble in this one: after yanking, we have just
3995 one interval. Once again, editing does not preserve the distinction
3996 between one interval and two.
3998 Insertion of text at the border between intervals also raises
3999 questions that have no satisfactory answer.
4001 However, it is easy to arrange for editing to behave consistently
4002 for questions of the form, ``What are the properties of text at this
4003 buffer or string position?'' So we have decided these are the only
4004 questions that make sense; we have not implemented asking questions
4005 about where intervals start or end.
4007 In practice, you can usually use the text property search functions in
4008 place of explicit interval boundaries. You can think of them as finding
4009 the boundaries of intervals, assuming that intervals are always
4010 coalesced whenever possible. @xref{Property Search}.
4012 Emacs also provides explicit intervals as a presentation feature; see
4016 @section Substituting for a Character Code
4017 @cindex replace characters in region
4018 @cindex substitute characters
4020 The following functions replace characters within a specified region
4021 based on their character codes.
4023 @defun subst-char-in-region start end old-char new-char &optional noundo
4024 @cindex replace characters
4025 This function replaces all occurrences of the character @var{old-char}
4026 with the character @var{new-char} in the region of the current buffer
4027 defined by @var{start} and @var{end}.
4029 @cindex undo avoidance
4030 If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
4031 not record the change for undo and does not mark the buffer as modified.
4032 This was useful for controlling the old selective display feature
4033 (@pxref{Selective Display}).
4035 @code{subst-char-in-region} does not move point and returns
4040 ---------- Buffer: foo ----------
4041 This is the contents of the buffer before.
4042 ---------- Buffer: foo ----------
4046 (subst-char-in-region 1 20 ?i ?X)
4049 ---------- Buffer: foo ----------
4050 ThXs Xs the contents of the buffer before.
4051 ---------- Buffer: foo ----------
4056 @deffn Command translate-region start end table
4057 This function applies a translation table to the characters in the
4058 buffer between positions @var{start} and @var{end}.
4060 The translation table @var{table} is a string or a char-table;
4061 @code{(aref @var{table} @var{ochar})} gives the translated character
4062 corresponding to @var{ochar}. If @var{table} is a string, any
4063 characters with codes larger than the length of @var{table} are not
4064 altered by the translation.
4066 The return value of @code{translate-region} is the number of
4067 characters that were actually changed by the translation. This does
4068 not count characters that were mapped into themselves in the
4076 A register is a sort of variable used in Emacs editing that can hold a
4077 variety of different kinds of values. Each register is named by a
4078 single character. All @acronym{ASCII} characters and their meta variants
4079 (but with the exception of @kbd{C-g}) can be used to name registers.
4080 Thus, there are 255 possible registers. A register is designated in
4081 Emacs Lisp by the character that is its name.
4083 @defvar register-alist
4084 This variable is an alist of elements of the form @code{(@var{name} .
4085 @var{contents})}. Normally, there is one element for each Emacs
4086 register that has been used.
4088 The object @var{name} is a character (an integer) identifying the
4092 The @var{contents} of a register can have several possible types:
4096 A number stands for itself. If @code{insert-register} finds a number
4097 in the register, it converts the number to decimal.
4100 A marker represents a buffer position to jump to.
4103 A string is text saved in the register.
4106 A rectangle is represented by a list of strings.
4108 @item @code{(@var{window-configuration} @var{position})}
4109 This represents a window configuration to restore in one frame, and a
4110 position to jump to in the current buffer.
4112 @c FIXME: Mention frameset here.
4113 @item @code{(@var{frame-configuration} @var{position})}
4114 This represents a frame configuration to restore, and a position
4115 to jump to in the current buffer.
4117 @item (file @var{filename})
4118 This represents a file to visit; jumping to this value visits file
4121 @item (file-query @var{filename} @var{position})
4122 This represents a file to visit and a position in it; jumping to this
4123 value visits file @var{filename} and goes to buffer position
4124 @var{position}. Restoring this type of position asks the user for
4128 The functions in this section return unpredictable values unless
4131 @defun get-register reg
4132 This function returns the contents of the register
4133 @var{reg}, or @code{nil} if it has no contents.
4136 @defun set-register reg value
4137 This function sets the contents of register @var{reg} to @var{value}.
4138 A register can be set to any value, but the other register functions
4139 expect only certain data types. The return value is @var{value}.
4142 @deffn Command view-register reg
4143 This command displays what is contained in register @var{reg}.
4146 @deffn Command insert-register reg &optional beforep
4147 This command inserts contents of register @var{reg} into the current
4150 Normally, this command puts point before the inserted text, and the
4151 mark after it. However, if the optional second argument @var{beforep}
4152 is non-@code{nil}, it puts the mark before and point after.
4154 When called interactively, the command defaults to putting point after
4155 text, and a prefix argument inverts this behavior.
4157 If the register contains a rectangle, then the rectangle is inserted
4158 with its upper left corner at point. This means that text is inserted
4159 in the current line and underneath it on successive lines.
4161 If the register contains something other than saved text (a string) or
4162 a rectangle (a list), currently useless things happen. This may be
4163 changed in the future.
4166 @defun register-read-with-preview prompt
4167 @cindex register preview
4168 This function reads and returns a register name, prompting with
4169 @var{prompt} and possibly showing a preview of the existing registers
4170 and their contents. The preview is shown in a temporary window, after
4171 the delay specified by the user option @code{register-preview-delay},
4172 if its value and @code{register-alist} are both non-@code{nil}. The
4173 preview is also shown if the user requests help (e.g., by typing the
4174 help character). We recommend that all interactive commands which
4175 read register names use this function.
4179 @section Transposition of Text
4181 This function can be used to transpose stretches of text:
4183 @defun transpose-regions start1 end1 start2 end2 &optional leave-markers
4184 This function exchanges two nonoverlapping portions of the buffer.
4185 Arguments @var{start1} and @var{end1} specify the bounds of one portion
4186 and arguments @var{start2} and @var{end2} specify the bounds of the
4189 Normally, @code{transpose-regions} relocates markers with the transposed
4190 text; a marker previously positioned within one of the two transposed
4191 portions moves along with that portion, thus remaining between the same
4192 two characters in their new position. However, if @var{leave-markers}
4193 is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
4194 all markers unrelocated.
4198 @section Dealing With Compressed Data
4200 When @code{auto-compression-mode} is enabled, Emacs automatically
4201 uncompresses compressed files when you visit them, and automatically
4202 recompresses them if you alter and save them. @xref{Compressed
4203 Files,,, emacs, The GNU Emacs Manual}.
4205 The above feature works by calling an external executable (e.g.,
4206 @command{gzip}). Emacs can also be compiled with support for built-in
4207 decompression using the zlib library, which is faster than calling an
4210 @defun zlib-available-p
4211 This function returns non-@code{nil} if built-in zlib decompression is
4215 @defun zlib-decompress-region start end
4216 This function decompresses the region between @var{start} and
4217 @var{end}, using built-in zlib decompression. The region should
4218 contain data that were compressed with gzip or zlib. On success, the
4219 function replaces the contents of the region with the decompressed
4220 data. On failure, the function leaves the region unchanged and
4221 returns @code{nil}. This function can be called only in unibyte
4227 @section Base 64 Encoding
4228 @cindex base 64 encoding
4230 Base 64 code is used in email to encode a sequence of 8-bit bytes as
4231 a longer sequence of @acronym{ASCII} graphic characters. It is defined in
4232 Internet RFC@footnote{
4233 An RFC, an acronym for @dfn{Request for Comments}, is a numbered
4234 Internet informational document describing a standard. RFCs are
4235 usually written by technical experts acting on their own initiative,
4236 and are traditionally written in a pragmatic, experience-driven
4238 }2045. This section describes the functions for
4239 converting to and from this code.
4241 @deffn Command base64-encode-region beg end &optional no-line-break
4242 This function converts the region from @var{beg} to @var{end} into base
4243 64 code. It returns the length of the encoded text. An error is
4244 signaled if a character in the region is multibyte, i.e., in a
4245 multibyte buffer the region must contain only characters from the
4246 charsets @code{ascii}, @code{eight-bit-control} and
4247 @code{eight-bit-graphic}.
4249 Normally, this function inserts newline characters into the encoded
4250 text, to avoid overlong lines. However, if the optional argument
4251 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4252 the output is just one long line.
4255 @defun base64-encode-string string &optional no-line-break
4256 This function converts the string @var{string} into base 64 code. It
4257 returns a string containing the encoded text. As for
4258 @code{base64-encode-region}, an error is signaled if a character in the
4259 string is multibyte.
4261 Normally, this function inserts newline characters into the encoded
4262 text, to avoid overlong lines. However, if the optional argument
4263 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4264 the result string is just one long line.
4267 @deffn Command base64-decode-region beg end
4268 This function converts the region from @var{beg} to @var{end} from base
4269 64 code into the corresponding decoded text. It returns the length of
4272 The decoding functions ignore newline characters in the encoded text.
4275 @defun base64-decode-string string
4276 This function converts the string @var{string} from base 64 code into
4277 the corresponding decoded text. It returns a unibyte string containing the
4280 The decoding functions ignore newline characters in the encoded text.
4284 @section Checksum/Hash
4285 @cindex MD5 checksum
4287 @cindex hash, cryptographic
4288 @cindex cryptographic hash
4290 Emacs has built-in support for computing @dfn{cryptographic hashes}.
4291 A cryptographic hash, or @dfn{checksum}, is a digital fingerprint
4292 of a piece of data (e.g., a block of text) which can be used to check
4293 that you have an unaltered copy of that data.
4295 @cindex message digest
4296 Emacs supports several common cryptographic hash algorithms: MD5,
4297 SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512. MD5 is the
4298 oldest of these algorithms, and is commonly used in @dfn{message
4299 digests} to check the integrity of messages transmitted over a
4300 network. MD5 is not collision resistant (i.e., it is possible to
4301 deliberately design different pieces of data which have the same MD5
4302 hash), so you should not used it for anything security-related. A
4303 similar theoretical weakness also exists in SHA-1. Therefore, for
4304 security-related applications you should use the other hash types,
4307 @defun secure-hash algorithm object &optional start end binary
4308 This function returns a hash for @var{object}. The argument
4309 @var{algorithm} is a symbol stating which hash to compute: one of
4310 @code{md5}, @code{sha1}, @code{sha224}, @code{sha256}, @code{sha384}
4311 or @code{sha512}. The argument @var{object} should be a buffer or a
4314 The optional arguments @var{start} and @var{end} are character
4315 positions specifying the portion of @var{object} to compute the
4316 message digest for. If they are @code{nil} or omitted, the hash is
4317 computed for the whole of @var{object}.
4319 If the argument @var{binary} is omitted or @code{nil}, the function
4320 returns the @dfn{text form} of the hash, as an ordinary Lisp string.
4321 If @var{binary} is non-@code{nil}, it returns the hash in @dfn{binary
4322 form}, as a sequence of bytes stored in a unibyte string.
4324 This function does not compute the hash directly from the internal
4325 representation of @var{object}'s text (@pxref{Text Representations}).
4326 Instead, it encodes the text using a coding system (@pxref{Coding
4327 Systems}), and computes the hash from that encoded text. If
4328 @var{object} is a buffer, the coding system used is the one which
4329 would be chosen by default for writing the text into a file. If
4330 @var{object} is a string, the user's preferred coding system is used
4331 (@pxref{Recognize Coding,,, emacs, GNU Emacs Manual}).
4334 @defun md5 object &optional start end coding-system noerror
4335 This function returns an MD5 hash. It is semi-obsolete, since for
4336 most purposes it is equivalent to calling @code{secure-hash} with
4337 @code{md5} as the @var{algorithm} argument. The @var{object},
4338 @var{start} and @var{end} arguments have the same meanings as in
4341 If @var{coding-system} is non-@code{nil}, it specifies a coding system
4342 to use to encode the text; if omitted or @code{nil}, the default
4343 coding system is used, like in @code{secure-hash}.
4345 Normally, @code{md5} signals an error if the text can't be encoded
4346 using the specified or chosen coding system. However, if
4347 @var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
4351 @node Parsing HTML/XML
4352 @section Parsing HTML and XML
4353 @cindex parsing html
4355 When Emacs is compiled with libxml2 support, the following functions
4356 are available to parse HTML or XML text into Lisp object trees.
4358 @defun libxml-parse-html-region start end &optional base-url discard-comments
4359 This function parses the text between @var{start} and @var{end} as
4360 HTML, and returns a list representing the HTML @dfn{parse tree}. It
4361 attempts to handle real-world HTML by robustly coping with syntax
4364 The optional argument @var{base-url}, if non-@code{nil}, should be a
4365 string specifying the base URL for relative URLs occurring in links.
4367 If the optional argument @var{discard-comments} is non-@code{nil},
4368 then the parse tree is created without any comments.
4370 In the parse tree, each HTML node is represented by a list in which
4371 the first element is a symbol representing the node name, the second
4372 element is an alist of node attributes, and the remaining elements are
4375 The following example demonstrates this. Given this (malformed) HTML
4379 <html><head></head><body width=101><div class=thing>Foo<div>Yes
4383 A call to @code{libxml-parse-html-region} returns this @acronym{DOM}
4384 (document object model):
4389 (body ((width . "101"))
4390 (div ((class . "thing"))
4397 @cindex rendering html
4398 @defun shr-insert-document dom
4399 This function renders the parsed HTML in @var{dom} into the current
4400 buffer. The argument @var{dom} should be a list as generated by
4401 @code{libxml-parse-html-region}. This function is, e.g., used by
4402 @ref{Top, EWW,, eww, The Emacs Web Wowser Manual}.
4406 @defun libxml-parse-xml-region start end &optional base-url discard-comments
4407 This function is the same as @code{libxml-parse-html-region}, except
4408 that it parses the text as XML rather than HTML (so it is stricter
4413 * Document Object Model:: Access, manipulate and search the @acronym{DOM}.
4416 @node Document Object Model
4417 @subsection Document Object Model
4421 @cindex Document Object Model
4423 The @acronym{DOM} returned by @code{libxml-parse-html-region} (and the
4424 other @acronym{XML} parsing functions) is a tree structure where each
4425 node has a node name (called a @dfn{tag}), and optional key/value
4426 @dfn{attribute} list, and then a list of @dfn{child nodes}. The child
4427 nodes are either strings or @acronym{DOM} objects.
4430 (body ((width . "101"))
4431 (div ((class . "thing"))
4437 @defun dom-node tag &optional attributes &rest children
4438 This function creates a @acronym{DOM} node of type @var{tag}. If
4439 given, @var{attributes} should be a key/value pair list.
4440 If given, @var{children} should be @acronym{DOM} nodes.
4443 The following functions can be used to work with this structure. Each
4444 function takes a @acronym{DOM} node, or a list of nodes. In the
4445 latter case, only the first node in the list is used.
4450 @item dom-tag @var{node}
4451 Return the @dfn{tag} (also called ``node name'') of the node.
4453 @item dom-attr @var{node} @var{attribute}
4454 Return the value of @var{attribute} in the node. A common usage
4458 (dom-attr img 'href)
4459 => "http://fsf.org/logo.png"
4462 @item dom-children @var{node}
4463 Return all the children of the node.
4465 @item dom-non-text-children @var{node}
4466 Return all the non-string children of the node.
4468 @item dom-attributes @var{node}
4469 Return the key/value pair list of attributes of the node.
4471 @item dom-text @var{node}
4472 Return all the textual elements of the node as a concatenated string.
4474 @item dom-texts @var{node}
4475 Return all the textual elements of the node, as well as the textual
4476 elements of all the children of the node, recursively, as a
4477 concatenated string. This function also takes an optional separator
4478 to be inserted between the textual elements.
4480 @item dom-parent @var{dom} @var{node}
4481 Return the parent of @var{node} in @var{dom}.
4484 The following are functions for altering the @acronym{DOM}.
4487 @item dom-set-attribute @var{node} @var{attribute} @var{value}
4488 Set the @var{attribute} of the node to @var{value}.
4490 @item dom-append-child @var{node} @var{child}
4491 Append @var{child} as the last child of @var{node}.
4493 @item dom-add-child-before @var{node} @var{child} @var{before}
4494 Add @var{child} to @var{node}'s child list before the @var{before}
4495 node. If @var{before} is @code{nil}, make @var{child} the first child.
4497 @item dom-set-attributes @var{node} @var{attributes}
4498 Replace all the attributes of the node with a new key/value list.
4501 The following are functions for searching for elements in the
4502 @acronym{DOM}. They all return lists of matching nodes.
4505 @item dom-by-tag @var{dom} @var{tag}
4506 Return all nodes in @var{dom} that are of type @var{tag}. A typical
4510 (dom-by-tag dom 'td)
4511 => '((td ...) (td ...) (td ...))
4514 @item dom-by-class @var{dom} @var{match}
4515 Return all nodes in @var{dom} that have class names that match
4516 @var{match}, which is a regular expression.
4518 @item dom-by-style @var{dom} @var{style}
4519 Return all nodes in @var{dom} that have styles that match @var{match},
4520 which is a regular expression.
4522 @item dom-by-id @var{dom} @var{style}
4523 Return all nodes in @var{dom} that have IDs that match @var{match},
4524 which is a regular expression.
4526 @item dom-strings @var{dom}
4527 Return all strings in @var{DOM}.
4534 @item dom-pp @var{dom} &optional @var{remove-empty}
4535 Pretty-print @var{dom} at point. If @var{remove-empty}, don't print
4536 textual nodes that just contain white-space.
4540 @node Atomic Changes
4541 @section Atomic Change Groups
4542 @cindex atomic changes
4544 In database terminology, an @dfn{atomic} change is an indivisible
4545 change---it can succeed entirely or it can fail entirely, but it
4546 cannot partly succeed. A Lisp program can make a series of changes to
4547 one or several buffers as an @dfn{atomic change group}, meaning that
4548 either the entire series of changes will be installed in their buffers
4549 or, in case of an error, none of them will be.
4551 To do this for one buffer, the one already current, simply write a
4552 call to @code{atomic-change-group} around the code that makes the
4556 (atomic-change-group
4558 (delete-region x y))
4562 If an error (or other nonlocal exit) occurs inside the body of
4563 @code{atomic-change-group}, it unmakes all the changes in that buffer
4564 that were during the execution of the body. This kind of change group
4565 has no effect on any other buffers---any such changes remain.
4567 If you need something more sophisticated, such as to make changes in
4568 various buffers constitute one atomic group, you must directly call
4569 lower-level functions that @code{atomic-change-group} uses.
4571 @defun prepare-change-group &optional buffer
4572 This function sets up a change group for buffer @var{buffer}, which
4573 defaults to the current buffer. It returns a handle that
4574 represents the change group. You must use this handle to activate the
4575 change group and subsequently to finish it.
4578 To use the change group, you must @dfn{activate} it. You must do
4579 this before making any changes in the text of @var{buffer}.
4581 @defun activate-change-group handle
4582 This function activates the change group that @var{handle} designates.
4585 After you activate the change group, any changes you make in that
4586 buffer become part of it. Once you have made all the desired changes
4587 in the buffer, you must @dfn{finish} the change group. There are two
4588 ways to do this: you can either accept (and finalize) all the changes,
4591 @defun accept-change-group handle
4592 This function accepts all the changes in the change group specified by
4593 @var{handle}, making them final.
4596 @defun cancel-change-group handle
4597 This function cancels and undoes all the changes in the change group
4598 specified by @var{handle}.
4601 Your code should use @code{unwind-protect} to make sure the group is
4602 always finished. The call to @code{activate-change-group} should be
4603 inside the @code{unwind-protect}, in case the user types @kbd{C-g}
4604 just after it runs. (This is one reason why
4605 @code{prepare-change-group} and @code{activate-change-group} are
4606 separate functions, because normally you would call
4607 @code{prepare-change-group} before the start of that
4608 @code{unwind-protect}.) Once you finish the group, don't use the
4609 handle again---in particular, don't try to finish the same group
4612 To make a multibuffer change group, call @code{prepare-change-group}
4613 once for each buffer you want to cover, then use @code{nconc} to
4614 combine the returned values, like this:
4617 (nconc (prepare-change-group buffer-1)
4618 (prepare-change-group buffer-2))
4621 You can then activate the multibuffer change group with a single call
4622 to @code{activate-change-group}, and finish it with a single call to
4623 @code{accept-change-group} or @code{cancel-change-group}.
4625 Nested use of several change groups for the same buffer works as you
4626 would expect. Non-nested use of change groups for the same buffer
4627 will get Emacs confused, so don't let it happen; the first change
4628 group you start for any given buffer should be the last one finished.
4631 @section Change Hooks
4632 @cindex change hooks
4633 @cindex hooks for text changes
4635 These hook variables let you arrange to take notice of all changes in
4636 all buffers (or in a particular buffer, if you make them buffer-local).
4637 See also @ref{Special Properties}, for how to detect changes to specific
4640 The functions you use in these hooks should save and restore the match
4641 data if they do anything that uses regular expressions; otherwise, they
4642 will interfere in bizarre ways with the editing operations that call
4645 @defvar before-change-functions
4646 This variable holds a list of functions to call before any buffer
4647 modification. Each function gets two arguments, the beginning and end
4648 of the region that is about to change, represented as integers. The
4649 buffer that is about to change is always the current buffer.
4652 @defvar after-change-functions
4653 This variable holds a list of functions to call after any buffer
4654 modification. Each function receives three arguments: the beginning
4655 and end of the region just changed, and the length of the text that
4656 existed before the change. All three arguments are integers. The
4657 buffer that has been changed is always the current buffer.
4659 The length of the old text is the difference between the buffer
4660 positions before and after that text as it was before the change. As
4661 for the changed text, its length is simply the difference between the
4662 first two arguments.
4665 Output of messages into the @file{*Messages*} buffer does not
4666 call these functions.
4668 @defmac combine-after-change-calls body@dots{}
4669 The macro executes @var{body} normally, but arranges to call the
4670 after-change functions just once for a series of several changes---if
4673 If a program makes several text changes in the same area of the buffer,
4674 using the macro @code{combine-after-change-calls} around that part of
4675 the program can make it run considerably faster when after-change hooks
4676 are in use. When the after-change hooks are ultimately called, the
4677 arguments specify a portion of the buffer including all of the changes
4678 made within the @code{combine-after-change-calls} body.
4680 @strong{Warning:} You must not alter the values of
4681 @code{after-change-functions} within
4682 the body of a @code{combine-after-change-calls} form.
4684 @strong{Warning:} if the changes you combine occur in widely scattered
4685 parts of the buffer, this will still work, but it is not advisable,
4686 because it may lead to inefficient behavior for some change hook
4690 @defvar first-change-hook
4691 This variable is a normal hook that is run whenever a buffer is changed
4692 that was previously in the unmodified state.
4695 @defvar inhibit-modification-hooks
4696 If this variable is non-@code{nil}, all of the change hooks are
4697 disabled; none of them run. This affects all the hook variables
4698 described above in this section, as well as the hooks attached to
4699 certain special text properties (@pxref{Special Properties}) and overlay
4700 properties (@pxref{Overlay Properties}).
4702 Also, this variable is bound to non-@code{nil} while running those
4703 same hook variables, so that by default modifying the buffer from
4704 a modification hook does not cause other modification hooks to be run.
4705 If you do want modification hooks to be run in a particular piece of
4706 code that is itself run from a modification hook, then rebind locally
4707 @code{inhibit-modification-hooks} to @code{nil}.