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 @cindex filtering killed text
903 The commands described below can filter the killed text before they
904 save it in the kill ring. They call @code{filter-buffer-substring}
905 (@pxref{Buffer Contents}) to perform the filtering. By default,
906 there's no filtering, but major and minor modes and hook functions can
907 set up filtering, so that text saved in the kill ring is different
908 from what was in the buffer.
910 @deffn Command kill-region start end &optional region
911 This function kills the stretch of text between @var{start} and
912 @var{end}; but if the optional argument @var{region} is
913 non-@code{nil}, it ignores @var{start} and @var{end}, and kills the
914 text in the current region instead. The text is deleted but saved in
915 the kill ring, along with its text properties. The value is always
918 In an interactive call, @var{start} and @var{end} are point and
919 the mark, and @var{region} is always non-@code{nil}, so the command
920 always kills the text in the current region.
922 If the buffer or text is read-only, @code{kill-region} modifies the kill
923 ring just the same, then signals an error without modifying the buffer.
924 This is convenient because it lets the user use a series of kill
925 commands to copy text from a read-only buffer into the kill ring.
928 @defopt kill-read-only-ok
929 If this option is non-@code{nil}, @code{kill-region} does not signal an
930 error if the buffer or text is read-only. Instead, it simply returns,
931 updating the kill ring but not changing the buffer.
934 @deffn Command copy-region-as-kill start end &optional region
935 This function saves the stretch of text between @var{start} and
936 @var{end} on the kill ring (including text properties), but does not
937 delete the text from the buffer. However, if the optional argument
938 @var{region} is non-@code{nil}, the function ignores @var{start} and
939 @var{end}, and saves the current region instead. It always returns
942 In an interactive call, @var{start} and @var{end} are point and
943 the mark, and @var{region} is always non-@code{nil}, so the command
944 always saves the text in the current region.
946 The command does not set @code{this-command} to @code{kill-region}, so a
947 subsequent kill command does not append to the same kill ring entry.
953 Yanking means inserting text from the kill ring, but it does not
954 insert the text blindly. The @code{yank} command, and related
955 commands, use @code{insert-for-yank} to perform special processing on
956 the text before it is inserted.
958 @defun insert-for-yank string
959 This function works like @code{insert}, except that it processes the
960 text in @var{string} according to the @code{yank-handler} text
961 property, as well as the variables @code{yank-handled-properties} and
962 @code{yank-excluded-properties} (see below), before inserting the
963 result into the current buffer.
966 @defun insert-buffer-substring-as-yank buf &optional start end
967 This function resembles @code{insert-buffer-substring}, except that it
968 processes the text according to @code{yank-handled-properties} and
969 @code{yank-excluded-properties}. (It does not handle the
970 @code{yank-handler} property, which does not normally occur in buffer
974 @c FIXME: Add an index for yank-handler.
975 If you put a @code{yank-handler} text property on all or part of a
976 string, that alters how @code{insert-for-yank} inserts the string. If
977 different parts of the string have different @code{yank-handler}
978 values (comparison being done with @code{eq}), each substring is
979 handled separately. The property value must be a list of one to four
980 elements, with the following format (where elements after the first
984 (@var{function} @var{param} @var{noexclude} @var{undo})
987 Here is what the elements do:
991 When @var{function} is non-@code{nil}, it is called instead of
992 @code{insert} to insert the string, with one argument---the string to
996 If @var{param} is present and non-@code{nil}, it replaces @var{string}
997 (or the substring of @var{string} being processed) as the object
998 passed to @var{function} (or @code{insert}). For example, if
999 @var{function} is @code{yank-rectangle}, @var{param} should be a list
1000 of strings to insert as a rectangle.
1003 If @var{noexclude} is present and non-@code{nil}, that disables the
1004 normal action of @code{yank-handled-properties} and
1005 @code{yank-excluded-properties} on the inserted string.
1008 If @var{undo} is present and non-@code{nil}, it is a function that will be
1009 called by @code{yank-pop} to undo the insertion of the current object.
1010 It is called with two arguments, the start and end of the current
1011 region. @var{function} can set @code{yank-undo-function} to override
1012 the @var{undo} value.
1015 @cindex yanking and text properties
1016 @defopt yank-handled-properties
1017 This variable specifies special text property handling conditions for
1018 yanked text. It takes effect after the text has been inserted (either
1019 normally, or via the @code{yank-handler} property), and prior to
1020 @code{yank-excluded-properties} taking effect.
1022 The value should be an alist of elements @code{(@var{prop}
1023 . @var{fun})}. Each alist element is handled in order. The inserted
1024 text is scanned for stretches of text having text properties @code{eq}
1025 to @var{prop}; for each such stretch, @var{fun} is called with three
1026 arguments: the value of the property, and the start and end positions
1030 @defopt yank-excluded-properties
1031 The value of this variable is the list of properties to remove from
1032 inserted text. Its default value contains properties that might lead
1033 to annoying results, such as causing the text to respond to the mouse
1034 or specifying key bindings. It takes effect after
1035 @code{yank-handled-properties}.
1040 @subsection Functions for Yanking
1042 This section describes higher-level commands for yanking, which are
1043 intended primarily for the user but useful also in Lisp programs.
1044 Both @code{yank} and @code{yank-pop} honor the
1045 @code{yank-excluded-properties} variable and @code{yank-handler} text
1046 property (@pxref{Yanking}).
1048 @deffn Command yank &optional arg
1049 @cindex inserting killed text
1050 This command inserts before point the text at the front of the kill
1051 ring. It sets the mark at the beginning of that text, using
1052 @code{push-mark} (@pxref{The Mark}), and puts point at the end.
1054 If @var{arg} is a non-@code{nil} list (which occurs interactively when
1055 the user types @kbd{C-u} with no digits), then @code{yank} inserts the
1056 text as described above, but puts point before the yanked text and
1057 sets the mark after it.
1059 If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
1060 most recently killed text---the @var{arg}th element of the kill ring
1061 list, counted cyclically from the front, which is considered the
1062 first element for this purpose.
1064 @code{yank} does not alter the contents of the kill ring, unless it
1065 used text provided by another program, in which case it pushes that text
1066 onto the kill ring. However if @var{arg} is an integer different from
1067 one, it rotates the kill ring to place the yanked string at the front.
1069 @code{yank} returns @code{nil}.
1072 @deffn Command yank-pop &optional arg
1073 This command replaces the just-yanked entry from the kill ring with a
1074 different entry from the kill ring.
1076 This is allowed only immediately after a @code{yank} or another
1077 @code{yank-pop}. At such a time, the region contains text that was just
1078 inserted by yanking. @code{yank-pop} deletes that text and inserts in
1079 its place a different piece of killed text. It does not add the deleted
1080 text to the kill ring, since it is already in the kill ring somewhere.
1081 It does however rotate the kill ring to place the newly yanked string at
1084 If @var{arg} is @code{nil}, then the replacement text is the previous
1085 element of the kill ring. If @var{arg} is numeric, the replacement is
1086 the @var{arg}th previous kill. If @var{arg} is negative, a more recent
1087 kill is the replacement.
1089 The sequence of kills in the kill ring wraps around, so that after the
1090 oldest one comes the newest one, and before the newest one goes the
1093 The return value is always @code{nil}.
1096 @defvar yank-undo-function
1097 If this variable is non-@code{nil}, the function @code{yank-pop} uses
1098 its value instead of @code{delete-region} to delete the text
1099 inserted by the previous @code{yank} or
1100 @code{yank-pop} command. The value must be a function of two
1101 arguments, the start and end of the current region.
1103 The function @code{insert-for-yank} automatically sets this variable
1104 according to the @var{undo} element of the @code{yank-handler}
1105 text property, if there is one.
1108 @node Low-Level Kill Ring
1109 @subsection Low-Level Kill Ring
1111 These functions and variables provide access to the kill ring at a
1112 lower level, but are still convenient for use in Lisp programs,
1113 because they take care of interaction with window system selections
1114 (@pxref{Window System Selections}).
1116 @defun current-kill n &optional do-not-move
1117 The function @code{current-kill} rotates the yanking pointer, which
1118 designates the front of the kill ring, by @var{n} places (from newer
1119 kills to older ones), and returns the text at that place in the ring.
1121 If the optional second argument @var{do-not-move} is non-@code{nil},
1122 then @code{current-kill} doesn't alter the yanking pointer; it just
1123 returns the @var{n}th kill, counting from the current yanking pointer.
1125 If @var{n} is zero, indicating a request for the latest kill,
1126 @code{current-kill} calls the value of
1127 @code{interprogram-paste-function} (documented below) before
1128 consulting the kill ring. If that value is a function and calling it
1129 returns a string or a list of several string, @code{current-kill}
1130 pushes the strings onto the kill ring and returns the first string.
1131 It also sets the yanking pointer to point to the kill-ring entry of
1132 the first string returned by @code{interprogram-paste-function},
1133 regardless of the value of @var{do-not-move}. Otherwise,
1134 @code{current-kill} does not treat a zero value for @var{n} specially:
1135 it returns the entry pointed at by the yanking pointer and does not
1136 move the yanking pointer.
1139 @defun kill-new string &optional replace
1140 This function pushes the text @var{string} onto the kill ring and
1141 makes the yanking pointer point to it. It discards the oldest entry
1142 if appropriate. It also invokes the value of
1143 @code{interprogram-cut-function} (see below).
1145 If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
1146 first element of the kill ring with @var{string}, rather than pushing
1147 @var{string} onto the kill ring.
1150 @defun kill-append string before-p
1151 This function appends the text @var{string} to the first entry in the
1152 kill ring and makes the yanking pointer point to the combined entry.
1153 Normally @var{string} goes at the end of the entry, but if
1154 @var{before-p} is non-@code{nil}, it goes at the beginning. This
1155 function also invokes the value of @code{interprogram-cut-function}
1159 @defvar interprogram-paste-function
1160 This variable provides a way of transferring killed text from other
1161 programs, when you are using a window system. Its value should be
1162 @code{nil} or a function of no arguments.
1164 If the value is a function, @code{current-kill} calls it to get the
1165 most recent kill. If the function returns a non-@code{nil} value,
1166 then that value is used as the most recent kill. If it returns
1167 @code{nil}, then the front of the kill ring is used.
1169 To facilitate support for window systems that support multiple
1170 selections, this function may also return a list of strings. In that
1171 case, the first string is used as the most recent kill, and all
1172 the other strings are pushed onto the kill ring, for easy access by
1175 The normal use of this function is to get the window system's
1176 clipboard as the most recent kill, even if the selection belongs to
1177 another application. @xref{Window System Selections}. However, if
1178 the clipboard contents come from the current Emacs session, this
1179 function should return @code{nil}.
1182 @defvar interprogram-cut-function
1183 This variable provides a way of communicating killed text to other
1184 programs, when you are using a window system. Its value should be
1185 @code{nil} or a function of one required argument.
1187 If the value is a function, @code{kill-new} and @code{kill-append} call
1188 it with the new first element of the kill ring as the argument.
1190 The normal use of this function is to put newly killed text in the
1191 window system's clipboard. @xref{Window System Selections}.
1194 @node Internals of Kill Ring
1195 @subsection Internals of the Kill Ring
1197 The variable @code{kill-ring} holds the kill ring contents, in the
1198 form of a list of strings. The most recent kill is always at the front
1201 The @code{kill-ring-yank-pointer} variable points to a link in the
1202 kill ring list, whose @sc{car} is the text to yank next. We say it
1203 identifies the front of the ring. Moving
1204 @code{kill-ring-yank-pointer} to a different link is called
1205 @dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
1206 the functions that move the yank pointer wrap around from the end of the
1207 list to the beginning, or vice-versa. Rotation of the kill ring is
1208 virtual; it does not change the value of @code{kill-ring}.
1210 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
1211 variables whose values are normally lists. The word ``pointer'' in the
1212 name of the @code{kill-ring-yank-pointer} indicates that the variable's
1213 purpose is to identify one element of the list for use by the next yank
1216 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
1217 of the links in the kill ring list. The element it identifies is the
1218 @sc{car} of that link. Kill commands, which change the kill ring, also
1219 set this variable to the value of @code{kill-ring}. The effect is to
1220 rotate the ring so that the newly killed text is at the front.
1222 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
1223 pointing to the second entry in the kill ring @code{("some text" "a
1224 different piece of text" "yet older text")}.
1228 kill-ring ---- kill-ring-yank-pointer
1231 | --- --- --- --- --- ---
1232 --> | | |------> | | |--> | | |--> nil
1233 --- --- --- --- --- ---
1236 | | -->"yet older text"
1238 | --> "a different piece of text"
1245 This state of affairs might occur after @kbd{C-y} (@code{yank})
1246 immediately followed by @kbd{M-y} (@code{yank-pop}).
1249 This variable holds the list of killed text sequences, most recently
1253 @defvar kill-ring-yank-pointer
1254 This variable's value indicates which element of the kill ring is at the
1255 front of the ring for yanking. More precisely, the value is a tail
1256 of the value of @code{kill-ring}, and its @sc{car} is the kill string
1257 that @kbd{C-y} should yank.
1260 @defopt kill-ring-max
1261 The value of this variable is the maximum length to which the kill
1262 ring can grow, before elements are thrown away at the end. The default
1263 value for @code{kill-ring-max} is 60.
1270 Most buffers have an @dfn{undo list}, which records all changes made
1271 to the buffer's text so that they can be undone. (The buffers that
1272 don't have one are usually special-purpose buffers for which Emacs
1273 assumes that undoing is not useful. In particular, any buffer whose
1274 name begins with a space has its undo recording off by default;
1275 see @ref{Buffer Names}.) All the primitives that modify the
1276 text in the buffer automatically add elements to the front of the undo
1277 list, which is in the variable @code{buffer-undo-list}.
1279 @defvar buffer-undo-list
1280 This buffer-local variable's value is the undo list of the current
1281 buffer. A value of @code{t} disables the recording of undo information.
1284 Here are the kinds of elements an undo list can have:
1287 @item @var{position}
1288 This kind of element records a previous value of point; undoing this
1289 element moves point to @var{position}. Ordinary cursor motion does not
1290 make any sort of undo record, but deletion operations use these entries
1291 to record where point was before the command.
1293 @item (@var{beg} . @var{end})
1294 This kind of element indicates how to delete text that was inserted.
1295 Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1298 @item (@var{text} . @var{position})
1299 This kind of element indicates how to reinsert text that was deleted.
1300 The deleted text itself is the string @var{text}. The place to
1301 reinsert it is @code{(abs @var{position})}. If @var{position} is
1302 positive, point was at the beginning of the deleted text, otherwise it
1303 was at the end. Zero or more (@var{marker} . @var{adjustment})
1304 elements follow immediately after this element.
1306 @item (t . @var{time-flag})
1307 This kind of element indicates that an unmodified buffer became
1308 modified. A @var{time-flag} of the form
1309 @code{(@var{sec-high} @var{sec-low} @var{microsec}
1310 @var{picosec})} represents the visited file's modification time as of
1311 when it was previously visited or saved, using the same format as
1312 @code{current-time}; see @ref{Time of Day}.
1313 A @var{time-flag} of 0 means the buffer does not correspond to any file;
1314 @minus{}1 means the visited file previously did not exist.
1315 @code{primitive-undo} uses these
1316 values to determine whether to mark the buffer as unmodified once again;
1317 it does so only if the file's status matches that of @var{time-flag}.
1319 @item (nil @var{property} @var{value} @var{beg} . @var{end})
1320 This kind of element records a change in a text property.
1321 Here's how you might undo the change:
1324 (put-text-property @var{beg} @var{end} @var{property} @var{value})
1327 @item (@var{marker} . @var{adjustment})
1328 This kind of element records the fact that the marker @var{marker} was
1329 relocated due to deletion of surrounding text, and that it moved
1330 @var{adjustment} character positions. If the marker's location is
1331 consistent with the (@var{text} . @var{position}) element preceding it
1332 in the undo list, then undoing this element moves @var{marker}
1333 @minus{} @var{adjustment} characters.
1335 @item (apply @var{funname} . @var{args})
1336 This is an extensible undo item, which is undone by calling
1337 @var{funname} with arguments @var{args}.
1339 @item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1340 This is an extensible undo item, which records a change limited to the
1341 range @var{beg} to @var{end}, which increased the size of the buffer
1342 by @var{delta} characters. It is undone by calling @var{funname} with
1343 arguments @var{args}.
1345 This kind of element enables undo limited to a region to determine
1346 whether the element pertains to that region.
1349 This element is a boundary. The elements between two boundaries are
1350 called a @dfn{change group}; normally, each change group corresponds to
1351 one keyboard command, and undo commands normally undo an entire group as
1355 @defun undo-boundary
1356 This function places a boundary element in the undo list. The undo
1357 command stops at such a boundary, and successive undo commands undo
1358 to earlier and earlier boundaries. This function returns @code{nil}.
1360 Calling this function explicitly is useful for splitting the effects of
1361 a command into more than one unit. For example, @code{query-replace}
1362 calls @code{undo-boundary} after each replacement, so that the user can
1363 undo individual replacements one by one.
1365 Mostly, however, this function is called automatically at an
1369 @defun undo-auto-amalgamate
1370 @cindex amalgamating commands, and undo
1371 The editor command loop automatically calls @code{undo-boundary} just
1372 before executing each key sequence, so that each undo normally undoes
1373 the effects of one command. A few exceptional commands are
1374 @dfn{amalgamating}: these commands generally cause small changes to
1375 buffers, so with these a boundary is inserted only every 20th command,
1376 allowing to undo them as a group. By default, commands
1377 @code{self-insert-command}, which produces self-inserting input
1378 characters (@pxref{Commands for Insertion}), and @code{delete-char}
1379 which deletes characters (@pxref{Deletion}) are amalgamating.
1380 Where a command affects the contents of several buffers, as may happen,
1381 for example, when a function on the @code{post-command-hook} affects a
1382 buffer other than the @code{current-buffer}, then @code{undo-boundary}
1383 will be called in each of the affected buffers.
1386 @defvar undo-auto-current-boundary-timer
1387 Some buffers, such as process buffers, can change even when no
1388 commands are executing. In these cases, @code{undo-boundary} is
1389 normally called periodically by the timer in this variable. Setting
1390 this variable to non-@code{nil} prevents this behavior.
1393 @defvar undo-in-progress
1394 This variable is normally @code{nil}, but the undo commands bind it to
1395 @code{t}. This is so that various kinds of change hooks can tell when
1396 they're being called for the sake of undoing.
1399 @defun primitive-undo count list
1400 This is the basic function for undoing elements of an undo list.
1401 It undoes the first @var{count} elements of @var{list}, returning
1402 the rest of @var{list}.
1404 @code{primitive-undo} adds elements to the buffer's undo list when it
1405 changes the buffer. Undo commands avoid confusion by saving the undo
1406 list value at the beginning of a sequence of undo operations. Then the
1407 undo operations use and update the saved value. The new elements added
1408 by undoing are not part of this saved value, so they don't interfere with
1411 This function does not bind @code{undo-in-progress}.
1414 @node Maintaining Undo
1415 @section Maintaining Undo Lists
1417 This section describes how to enable and disable undo information for
1418 a given buffer. It also explains how the undo list is truncated
1419 automatically so it doesn't get too big.
1421 Recording of undo information in a newly created buffer is normally
1422 enabled to start with; but if the buffer name starts with a space, the
1423 undo recording is initially disabled. You can explicitly enable or
1424 disable undo recording with the following two functions, or by setting
1425 @code{buffer-undo-list} yourself.
1427 @deffn Command buffer-enable-undo &optional buffer-or-name
1428 This command enables recording undo information for buffer
1429 @var{buffer-or-name}, so that subsequent changes can be undone. If no
1430 argument is supplied, then the current buffer is used. This function
1431 does nothing if undo recording is already enabled in the buffer. It
1434 In an interactive call, @var{buffer-or-name} is the current buffer.
1435 You cannot specify any other buffer.
1438 @deffn Command buffer-disable-undo &optional buffer-or-name
1439 @cindex disabling undo
1440 This function discards the undo list of @var{buffer-or-name}, and disables
1441 further recording of undo information. As a result, it is no longer
1442 possible to undo either previous changes or any subsequent changes. If
1443 the undo list of @var{buffer-or-name} is already disabled, this function
1446 In an interactive call, BUFFER-OR-NAME is the current buffer. You
1447 cannot specify any other buffer. This function returns @code{nil}.
1450 As editing continues, undo lists get longer and longer. To prevent
1451 them from using up all available memory space, garbage collection trims
1452 them back to size limits you can set. (For this purpose, the size
1453 of an undo list measures the cons cells that make up the list, plus the
1454 strings of deleted text.) Three variables control the range of acceptable
1455 sizes: @code{undo-limit}, @code{undo-strong-limit} and
1456 @code{undo-outer-limit}. In these variables, size is counted as the
1457 number of bytes occupied, which includes both saved text and other
1461 This is the soft limit for the acceptable size of an undo list. The
1462 change group at which this size is exceeded is the last one kept.
1465 @defopt undo-strong-limit
1466 This is the upper limit for the acceptable size of an undo list. The
1467 change group at which this size is exceeded is discarded itself (along
1468 with all older change groups). There is one exception: the very latest
1469 change group is only discarded if it exceeds @code{undo-outer-limit}.
1472 @defopt undo-outer-limit
1473 If at garbage collection time the undo info for the current command
1474 exceeds this limit, Emacs discards the info and displays a warning.
1475 This is a last ditch limit to prevent memory overflow.
1478 @defopt undo-ask-before-discard
1479 If this variable is non-@code{nil}, when the undo info exceeds
1480 @code{undo-outer-limit}, Emacs asks in the echo area whether to
1481 discard the info. The default value is @code{nil}, which means to
1482 discard it automatically.
1484 This option is mainly intended for debugging. Garbage collection is
1485 inhibited while the question is asked, which means that Emacs might
1486 leak memory if the user waits too long before answering the question.
1491 @cindex filling text
1493 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1494 breaks) so that they are nearly (but no greater than) a specified
1495 maximum width. Additionally, lines can be @dfn{justified}, which means
1496 inserting spaces to make the left and/or right margins line up
1497 precisely. The width is controlled by the variable @code{fill-column}.
1498 For ease of reading, lines should be no longer than 70 or so columns.
1500 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1501 automatically as you insert it, but changes to existing text may leave
1502 it improperly filled. Then you must fill the text explicitly.
1504 Most of the commands in this section return values that are not
1505 meaningful. All the functions that do filling take note of the current
1506 left margin, current right margin, and current justification style
1507 (@pxref{Margins}). If the current justification style is
1508 @code{none}, the filling functions don't actually do anything.
1510 Several of the filling functions have an argument @var{justify}.
1511 If it is non-@code{nil}, that requests some kind of justification. It
1512 can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1513 request a specific style of justification. If it is @code{t}, that
1514 means to use the current justification style for this part of the text
1515 (see @code{current-justification}, below). Any other value is treated
1518 When you call the filling functions interactively, using a prefix
1519 argument implies the value @code{full} for @var{justify}.
1521 @deffn Command fill-paragraph &optional justify region
1522 This command fills the paragraph at or after point. If
1523 @var{justify} is non-@code{nil}, each line is justified as well.
1524 It uses the ordinary paragraph motion commands to find paragraph
1525 boundaries. @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
1527 When @var{region} is non-@code{nil}, then if Transient Mark mode is
1528 enabled and the mark is active, this command calls @code{fill-region}
1529 to fill all the paragraphs in the region, instead of filling only the
1530 current paragraph. When this command is called interactively,
1531 @var{region} is @code{t}.
1534 @deffn Command fill-region start end &optional justify nosqueeze to-eop
1535 This command fills each of the paragraphs in the region from @var{start}
1536 to @var{end}. It justifies as well if @var{justify} is
1539 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1540 other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1541 that means to keep filling to the end of the paragraph---or the next hard
1542 newline, if @code{use-hard-newlines} is enabled (see below).
1544 The variable @code{paragraph-separate} controls how to distinguish
1545 paragraphs. @xref{Standard Regexps}.
1548 @deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
1549 This command fills each paragraph in the region according to its
1550 individual fill prefix. Thus, if the lines of a paragraph were indented
1551 with spaces, the filled paragraph will remain indented in the same
1554 The first two arguments, @var{start} and @var{end}, are the beginning
1555 and end of the region to be filled. The third and fourth arguments,
1556 @var{justify} and @var{citation-regexp}, are optional. If
1557 @var{justify} is non-@code{nil}, the paragraphs are justified as
1558 well as filled. If @var{citation-regexp} is non-@code{nil}, it means the
1559 function is operating on a mail message and therefore should not fill
1560 the header lines. If @var{citation-regexp} is a string, it is used as
1561 a regular expression; if it matches the beginning of a line, that line
1562 is treated as a citation marker.
1564 @c FIXME: "That mode" is confusing. It isn't a major/minor mode.
1565 Ordinarily, @code{fill-individual-paragraphs} regards each change in
1566 indentation as starting a new paragraph. If
1567 @code{fill-individual-varying-indent} is non-@code{nil}, then only
1568 separator lines separate paragraphs. That mode can handle indented
1569 paragraphs with additional indentation on the first line.
1572 @defopt fill-individual-varying-indent
1573 This variable alters the action of @code{fill-individual-paragraphs} as
1577 @deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1578 This command considers a region of text as a single paragraph and fills
1579 it. If the region was made up of many paragraphs, the blank lines
1580 between paragraphs are removed. This function justifies as well as
1581 filling when @var{justify} is non-@code{nil}.
1583 If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1584 other than line breaks untouched. If @var{squeeze-after} is
1585 non-@code{nil}, it specifies a position in the region, and means don't
1586 canonicalize spaces before that position.
1588 In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1589 choose a fill prefix by default. @xref{Adaptive Fill}.
1592 @deffn Command justify-current-line &optional how eop nosqueeze
1593 This command inserts spaces between the words of the current line so
1594 that the line ends exactly at @code{fill-column}. It returns
1597 The argument @var{how}, if non-@code{nil} specifies explicitly the style
1598 of justification. It can be @code{left}, @code{right}, @code{full},
1599 @code{center}, or @code{none}. If it is @code{t}, that means to do
1600 follow specified justification style (see @code{current-justification},
1601 below). @code{nil} means to do full justification.
1603 If @var{eop} is non-@code{nil}, that means do only left-justification
1604 if @code{current-justification} specifies full justification. This is
1605 used for the last line of a paragraph; even if the paragraph as a
1606 whole is fully justified, the last line should not be.
1608 If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1612 @defopt default-justification
1613 This variable's value specifies the style of justification to use for
1614 text that doesn't specify a style with a text property. The possible
1615 values are @code{left}, @code{right}, @code{full}, @code{center}, or
1616 @code{none}. The default value is @code{left}.
1619 @defun current-justification
1620 This function returns the proper justification style to use for filling
1621 the text around point.
1623 This returns the value of the @code{justification} text property at
1624 point, or the variable @var{default-justification} if there is no such
1625 text property. However, it returns @code{nil} rather than @code{none}
1626 to mean ``don't justify''.
1629 @defopt sentence-end-double-space
1630 @anchor{Definition of sentence-end-double-space}
1631 If this variable is non-@code{nil}, a period followed by just one space
1632 does not count as the end of a sentence, and the filling functions
1633 avoid breaking the line at such a place.
1636 @defopt sentence-end-without-period
1637 If this variable is non-@code{nil}, a sentence can end without a
1638 period. This is used for languages like Thai, where sentences end
1639 with a double space but without a period.
1642 @defopt sentence-end-without-space
1643 If this variable is non-@code{nil}, it should be a string of
1644 characters that can end a sentence without following spaces.
1647 @defvar fill-paragraph-function
1648 This variable provides a way to override the filling of paragraphs.
1649 If its value is non-@code{nil}, @code{fill-paragraph} calls this
1650 function to do the work. If the function returns a non-@code{nil}
1651 value, @code{fill-paragraph} assumes the job is done, and immediately
1654 The usual use of this feature is to fill comments in programming
1655 language modes. If the function needs to fill a paragraph in the usual
1656 way, it can do so as follows:
1659 (let ((fill-paragraph-function nil))
1660 (fill-paragraph arg))
1664 @defvar fill-forward-paragraph-function
1665 This variable provides a way to override how the filling functions,
1666 such as @code{fill-region} and @code{fill-paragraph}, move forward to
1667 the next paragraph. Its value should be a function, which is called
1668 with a single argument @var{n}, the number of paragraphs to move, and
1669 should return the difference between @var{n} and the number of
1670 paragraphs actually moved. The default value of this variable is
1671 @code{forward-paragraph}. @xref{Paragraphs,,, emacs, The GNU Emacs
1675 @defvar use-hard-newlines
1676 If this variable is non-@code{nil}, the filling functions do not delete
1677 newlines that have the @code{hard} text property. These hard
1678 newlines act as paragraph separators. @xref{Hard and Soft
1679 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
1683 @section Margins for Filling
1684 @cindex margins, filling
1687 This buffer-local variable, if non-@code{nil}, specifies a string of
1688 text that appears at the beginning of normal text lines and should be
1689 disregarded when filling them. Any line that fails to start with the
1690 fill prefix is considered the start of a paragraph; so is any line
1691 that starts with the fill prefix followed by additional whitespace.
1692 Lines that start with the fill prefix but no additional whitespace are
1693 ordinary text lines that can be filled together. The resulting filled
1694 lines also start with the fill prefix.
1696 The fill prefix follows the left margin whitespace, if any.
1700 This buffer-local variable specifies the maximum width of filled lines.
1701 Its value should be an integer, which is a number of columns. All the
1702 filling, justification, and centering commands are affected by this
1703 variable, including Auto Fill mode (@pxref{Auto Filling}).
1705 As a practical matter, if you are writing text for other people to
1706 read, you should set @code{fill-column} to no more than 70. Otherwise
1707 the line will be too long for people to read comfortably, and this can
1708 make the text seem clumsy.
1710 The default value for @code{fill-column} is 70.
1713 @deffn Command set-left-margin from to margin
1714 This sets the @code{left-margin} property on the text from @var{from} to
1715 @var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1716 command also refills the region to fit the new margin.
1719 @deffn Command set-right-margin from to margin
1720 This sets the @code{right-margin} property on the text from @var{from}
1721 to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1722 this command also refills the region to fit the new margin.
1725 @defun current-left-margin
1726 This function returns the proper left margin value to use for filling
1727 the text around point. The value is the sum of the @code{left-margin}
1728 property of the character at the start of the current line (or zero if
1729 none), and the value of the variable @code{left-margin}.
1732 @defun current-fill-column
1733 This function returns the proper fill column value to use for filling
1734 the text around point. The value is the value of the @code{fill-column}
1735 variable, minus the value of the @code{right-margin} property of the
1736 character after point.
1739 @deffn Command move-to-left-margin &optional n force
1740 This function moves point to the left margin of the current line. The
1741 column moved to is determined by calling the function
1742 @code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1743 @code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1745 If @var{force} is non-@code{nil}, that says to fix the line's
1746 indentation if that doesn't match the left margin value.
1749 @defun delete-to-left-margin &optional from to
1750 This function removes left margin indentation from the text between
1751 @var{from} and @var{to}. The amount of indentation to delete is
1752 determined by calling @code{current-left-margin}. In no case does this
1753 function delete non-whitespace. If @var{from} and @var{to} are omitted,
1754 they default to the whole buffer.
1757 @defun indent-to-left-margin
1758 This function adjusts the indentation at the beginning of the current
1759 line to the value specified by the variable @code{left-margin}. (That
1760 may involve either inserting or deleting whitespace.) This function
1761 is value of @code{indent-line-function} in Paragraph-Indent Text mode.
1765 This variable specifies the base left margin column. In Fundamental
1766 mode, @kbd{RET} indents to this column. This variable automatically
1767 becomes buffer-local when set in any fashion.
1770 @defopt fill-nobreak-predicate
1771 This variable gives major modes a way to specify not to break a line
1772 at certain places. Its value should be a list of functions. Whenever
1773 filling considers breaking the line at a certain place in the buffer,
1774 it calls each of these functions with no arguments and with point
1775 located at that place. If any of the functions returns
1776 non-@code{nil}, then the line won't be broken there.
1780 @section Adaptive Fill Mode
1781 @c @cindex Adaptive Fill mode "adaptive-fill-mode" is adjacent.
1783 When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
1784 prefix automatically from the text in each paragraph being filled
1785 rather than using a predetermined value. During filling, this fill
1786 prefix gets inserted at the start of the second and subsequent lines
1787 of the paragraph as described in @ref{Filling}, and in @ref{Auto
1790 @defopt adaptive-fill-mode
1791 Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1792 It is @code{t} by default.
1795 @defun fill-context-prefix from to
1796 This function implements the heart of Adaptive Fill mode; it chooses a
1797 fill prefix based on the text between @var{from} and @var{to},
1798 typically the start and end of a paragraph. It does this by looking
1799 at the first two lines of the paragraph, based on the variables
1801 @c The optional argument first-line-regexp is not documented
1802 @c because it exists for internal purposes and might be eliminated
1805 Usually, this function returns the fill prefix, a string. However,
1806 before doing this, the function makes a final check (not specially
1807 mentioned in the following) that a line starting with this prefix
1808 wouldn't look like the start of a paragraph. Should this happen, the
1809 function signals the anomaly by returning @code{nil} instead.
1811 In detail, @code{fill-context-prefix} does this:
1815 It takes a candidate for the fill prefix from the first line---it
1816 tries first the function in @code{adaptive-fill-function} (if any),
1817 then the regular expression @code{adaptive-fill-regexp} (see below).
1818 The first non-@code{nil} result of these, or the empty string if
1819 they're both @code{nil}, becomes the first line's candidate.
1821 If the paragraph has as yet only one line, the function tests the
1822 validity of the prefix candidate just found. The function then
1823 returns the candidate if it's valid, or a string of spaces otherwise.
1824 (see the description of @code{adaptive-fill-first-line-regexp} below).
1826 When the paragraph already has two lines, the function next looks for
1827 a prefix candidate on the second line, in just the same way it did for
1828 the first line. If it doesn't find one, it returns @code{nil}.
1830 The function now compares the two candidate prefixes heuristically: if
1831 the non-whitespace characters in the line 2 candidate occur in the
1832 same order in the line 1 candidate, the function returns the line 2
1833 candidate. Otherwise, it returns the largest initial substring which
1834 is common to both candidates (which might be the empty string).
1838 @defopt adaptive-fill-regexp
1839 Adaptive Fill mode matches this regular expression against the text
1840 starting after the left margin whitespace (if any) on a line; the
1841 characters it matches are that line's candidate for the fill prefix.
1843 The default value matches whitespace with certain punctuation
1844 characters intermingled.
1847 @defopt adaptive-fill-first-line-regexp
1848 Used only in one-line paragraphs, this regular expression acts as an
1849 additional check of the validity of the one available candidate fill
1850 prefix: the candidate must match this regular expression, or match
1851 @code{comment-start-skip}. If it doesn't, @code{fill-context-prefix}
1852 replaces the candidate with a string of spaces of the same width
1855 The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
1856 matches only a string of whitespace. The effect of this default is to
1857 force the fill prefixes found in one-line paragraphs always to be pure
1861 @defopt adaptive-fill-function
1862 You can specify more complex ways of choosing a fill prefix
1863 automatically by setting this variable to a function. The function is
1864 called with point after the left margin (if any) of a line, and it
1865 must preserve point. It should return either that line's fill
1866 prefix or @code{nil}, meaning it has failed to determine a prefix.
1870 @section Auto Filling
1871 @cindex filling, automatic
1872 @cindex Auto Fill mode
1874 @c FIXME: I don't think any of the variables below is a/an normal/abnormal hook.
1875 Auto Fill mode is a minor mode that fills lines automatically as text
1876 is inserted. This section describes the hook used by Auto Fill mode.
1877 For a description of functions that you can call explicitly to fill and
1878 justify existing text, see @ref{Filling}.
1880 Auto Fill mode also enables the functions that change the margins and
1881 justification style to refill portions of the text. @xref{Margins}.
1883 @defvar auto-fill-function
1884 The value of this buffer-local variable should be a function (of no
1885 arguments) to be called after self-inserting a character from the table
1886 @code{auto-fill-chars}. It may be @code{nil}, in which case nothing
1887 special is done in that case.
1889 The value of @code{auto-fill-function} is @code{do-auto-fill} when
1890 Auto-Fill mode is enabled. That is a function whose sole purpose is to
1891 implement the usual strategy for breaking a line.
1894 @defvar normal-auto-fill-function
1895 This variable specifies the function to use for
1896 @code{auto-fill-function}, if and when Auto Fill is turned on. Major
1897 modes can set buffer-local values for this variable to alter how Auto
1901 @defvar auto-fill-chars
1902 A char table of characters which invoke @code{auto-fill-function} when
1903 self-inserted---space and newline in most language environments. They
1904 have an entry @code{t} in the table.
1908 @section Sorting Text
1909 @cindex sorting text
1911 The sorting functions described in this section all rearrange text in
1912 a buffer. This is in contrast to the function @code{sort}, which
1913 rearranges the order of the elements of a list (@pxref{Rearrangement}).
1914 The values returned by these functions are not meaningful.
1916 @defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
1917 This function is the general text-sorting routine that subdivides a
1918 buffer into records and then sorts them. Most of the commands in this
1919 section use this function.
1921 To understand how @code{sort-subr} works, consider the whole accessible
1922 portion of the buffer as being divided into disjoint pieces called
1923 @dfn{sort records}. The records may or may not be contiguous, but they
1924 must not overlap. A portion of each sort record (perhaps all of it) is
1925 designated as the sort key. Sorting rearranges the records in order by
1928 Usually, the records are rearranged in order of ascending sort key.
1929 If the first argument to the @code{sort-subr} function, @var{reverse},
1930 is non-@code{nil}, the sort records are rearranged in order of
1931 descending sort key.
1933 The next four arguments to @code{sort-subr} are functions that are
1934 called to move point across a sort record. They are called many times
1935 from within @code{sort-subr}.
1939 @var{nextrecfun} is called with point at the end of a record. This
1940 function moves point to the start of the next record. The first record
1941 is assumed to start at the position of point when @code{sort-subr} is
1942 called. Therefore, you should usually move point to the beginning of
1943 the buffer before calling @code{sort-subr}.
1945 This function can indicate there are no more sort records by leaving
1946 point at the end of the buffer.
1949 @var{endrecfun} is called with point within a record. It moves point to
1950 the end of the record.
1953 @var{startkeyfun} is called to move point from the start of a record to
1954 the start of the sort key. This argument is optional; if it is omitted,
1955 the whole record is the sort key. If supplied, the function should
1956 either return a non-@code{nil} value to be used as the sort key, or
1957 return @code{nil} to indicate that the sort key is in the buffer
1958 starting at point. In the latter case, @var{endkeyfun} is called to
1959 find the end of the sort key.
1962 @var{endkeyfun} is called to move point from the start of the sort key
1963 to the end of the sort key. This argument is optional. If
1964 @var{startkeyfun} returns @code{nil} and this argument is omitted (or
1965 @code{nil}), then the sort key extends to the end of the record. There
1966 is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1967 non-@code{nil} value.
1970 The argument @var{predicate} is the function to use to compare keys.
1971 If keys are numbers, it defaults to @code{<}; otherwise it defaults to
1974 As an example of @code{sort-subr}, here is the complete function
1975 definition for @code{sort-lines}:
1979 ;; @r{Note that the first two lines of doc string}
1980 ;; @r{are effectively one line when viewed by a user.}
1981 (defun sort-lines (reverse beg end)
1982 "Sort lines in region alphabetically;\
1983 argument means descending order.
1984 Called from a program, there are three arguments:
1987 REVERSE (non-nil means reverse order),\
1988 BEG and END (region to sort).
1989 The variable `sort-fold-case' determines\
1990 whether alphabetic case affects
1994 (interactive "P\nr")
1997 (narrow-to-region beg end)
1998 (goto-char (point-min))
1999 (let ((inhibit-field-text-motion t))
2000 (sort-subr reverse 'forward-line 'end-of-line)))))
2004 Here @code{forward-line} moves point to the start of the next record,
2005 and @code{end-of-line} moves point to the end of record. We do not pass
2006 the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
2007 record is used as the sort key.
2009 The @code{sort-paragraphs} function is very much the same, except that
2010 its @code{sort-subr} call looks like this:
2017 (while (and (not (eobp))
2018 (looking-at paragraph-separate))
2024 Markers pointing into any sort records are left with no useful
2025 position after @code{sort-subr} returns.
2028 @defopt sort-fold-case
2029 If this variable is non-@code{nil}, @code{sort-subr} and the other
2030 buffer sorting functions ignore case when comparing strings.
2033 @deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
2034 This command sorts the region between @var{start} and @var{end}
2035 alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
2036 If @var{reverse} is a negative integer, then sorting is in reverse
2039 Alphabetical sorting means that two sort keys are compared by
2040 comparing the first characters of each, the second characters of each,
2041 and so on. If a mismatch is found, it means that the sort keys are
2042 unequal; the sort key whose character is less at the point of first
2043 mismatch is the lesser sort key. The individual characters are compared
2044 according to their numerical character codes in the Emacs character set.
2046 The value of the @var{record-regexp} argument specifies how to divide
2047 the buffer into sort records. At the end of each record, a search is
2048 done for this regular expression, and the text that matches it is taken
2049 as the next record. For example, the regular expression @samp{^.+$},
2050 which matches lines with at least one character besides a newline, would
2051 make each such line into a sort record. @xref{Regular Expressions}, for
2052 a description of the syntax and meaning of regular expressions.
2054 The value of the @var{key-regexp} argument specifies what part of each
2055 record is the sort key. The @var{key-regexp} could match the whole
2056 record, or only a part. In the latter case, the rest of the record has
2057 no effect on the sorted order of records, but it is carried along when
2058 the record moves to its new position.
2060 The @var{key-regexp} argument can refer to the text matched by a
2061 subexpression of @var{record-regexp}, or it can be a regular expression
2064 If @var{key-regexp} is:
2067 @item @samp{\@var{digit}}
2068 then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
2069 grouping in @var{record-regexp} is the sort key.
2072 then the whole record is the sort key.
2074 @item a regular expression
2075 then @code{sort-regexp-fields} searches for a match for the regular
2076 expression within the record. If such a match is found, it is the sort
2077 key. If there is no match for @var{key-regexp} within a record then
2078 that record is ignored, which means its position in the buffer is not
2079 changed. (The other records may move around it.)
2082 For example, if you plan to sort all the lines in the region by the
2083 first word on each line starting with the letter @samp{f}, you should
2084 set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
2085 @samp{\<f\w*\>}. The resulting expression looks like this:
2089 (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
2095 If you call @code{sort-regexp-fields} interactively, it prompts for
2096 @var{record-regexp} and @var{key-regexp} in the minibuffer.
2099 @deffn Command sort-lines reverse start end
2100 This command alphabetically sorts lines in the region between
2101 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2102 is in reverse order.
2105 @deffn Command sort-paragraphs reverse start end
2106 This command alphabetically sorts paragraphs in the region between
2107 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2108 is in reverse order.
2111 @deffn Command sort-pages reverse start end
2112 This command alphabetically sorts pages in the region between
2113 @var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2114 is in reverse order.
2117 @deffn Command sort-fields field start end
2118 This command sorts lines in the region between @var{start} and
2119 @var{end}, comparing them alphabetically by the @var{field}th field
2120 of each line. Fields are separated by whitespace and numbered starting
2121 from 1. If @var{field} is negative, sorting is by the
2122 @w{@minus{}@var{field}th} field from the end of the line. This command
2123 is useful for sorting tables.
2126 @deffn Command sort-numeric-fields field start end
2127 This command sorts lines in the region between @var{start} and
2128 @var{end}, comparing them numerically by the @var{field}th field of
2129 each line. Fields are separated by whitespace and numbered starting
2130 from 1. The specified field must contain a number in each line of the
2131 region. Numbers starting with 0 are treated as octal, and numbers
2132 starting with @samp{0x} are treated as hexadecimal.
2134 If @var{field} is negative, sorting is by the
2135 @w{@minus{}@var{field}th} field from the end of the line. This
2136 command is useful for sorting tables.
2139 @defopt sort-numeric-base
2140 This variable specifies the default radix for
2141 @code{sort-numeric-fields} to parse numbers.
2144 @deffn Command sort-columns reverse &optional beg end
2145 This command sorts the lines in the region between @var{beg} and
2146 @var{end}, comparing them alphabetically by a certain range of
2147 columns. The column positions of @var{beg} and @var{end} bound the
2148 range of columns to sort on.
2150 If @var{reverse} is non-@code{nil}, the sort is in reverse order.
2152 One unusual thing about this command is that the entire line
2153 containing position @var{beg}, and the entire line containing position
2154 @var{end}, are included in the region sorted.
2156 Note that @code{sort-columns} rejects text that contains tabs, because
2157 tabs could be split across the specified columns. Use @kbd{M-x
2158 untabify} to convert tabs to spaces before sorting.
2160 When possible, this command actually works by calling the @code{sort}
2165 @section Counting Columns
2167 @cindex counting columns
2168 @cindex horizontal position
2170 The column functions convert between a character position (counting
2171 characters from the beginning of the buffer) and a column position
2172 (counting screen characters from the beginning of a line).
2174 These functions count each character according to the number of
2175 columns it occupies on the screen. This means control characters count
2176 as occupying 2 or 4 columns, depending upon the value of
2177 @code{ctl-arrow}, and tabs count as occupying a number of columns that
2178 depends on the value of @code{tab-width} and on the column where the tab
2179 begins. @xref{Usual Display}.
2181 Column number computations ignore the width of the window and the
2182 amount of horizontal scrolling. Consequently, a column value can be
2183 arbitrarily high. The first (or leftmost) column is numbered 0. They
2184 also ignore overlays and text properties, aside from invisibility.
2186 @defun current-column
2187 This function returns the horizontal position of point, measured in
2188 columns, counting from 0 at the left margin. The column position is the
2189 sum of the widths of all the displayed representations of the characters
2190 between the start of the current line and point.
2192 For an example of using @code{current-column}, see the description of
2193 @code{count-lines} in @ref{Text Lines}.
2196 @deffn Command move-to-column column &optional force
2197 This function moves point to @var{column} in the current line. The
2198 calculation of @var{column} takes into account the widths of the
2199 displayed representations of the characters between the start of the
2202 When called interactively, @var{column} is the value of prefix numeric
2203 argument. If @var{column} is not an integer, an error is signaled.
2205 @c This behavior used to be documented until 2013/08.
2207 If column @var{column} is beyond the end of the line, point moves to
2208 the end of the line. If @var{column} is negative, point moves to the
2209 beginning of the line.
2212 If it is impossible to move to column @var{column} because that is in
2213 the middle of a multicolumn character such as a tab, point moves to the
2214 end of that character. However, if @var{force} is non-@code{nil}, and
2215 @var{column} is in the middle of a tab, then @code{move-to-column}
2216 converts the tab into spaces so that it can move precisely to column
2217 @var{column}. Other multicolumn characters can cause anomalies despite
2218 @var{force}, since there is no way to split them.
2220 The argument @var{force} also has an effect if the line isn't long
2221 enough to reach column @var{column}; if it is @code{t}, that means to
2222 add whitespace at the end of the line to reach that column.
2224 The return value is the column number actually moved to.
2228 @section Indentation
2231 The indentation functions are used to examine, move to, and change
2232 whitespace that is at the beginning of a line. Some of the functions
2233 can also change whitespace elsewhere on a line. Columns and indentation
2234 count from zero at the left margin.
2237 * Primitive Indent:: Functions used to count and insert indentation.
2238 * Mode-Specific Indent:: Customize indentation for different modes.
2239 * Region Indent:: Indent all the lines in a region.
2240 * Relative Indent:: Indent the current line based on previous lines.
2241 * Indent Tabs:: Adjustable, typewriter-like tab stops.
2242 * Motion by Indent:: Move to first non-blank character.
2245 @node Primitive Indent
2246 @subsection Indentation Primitives
2248 This section describes the primitive functions used to count and
2249 insert indentation. The functions in the following sections use these
2250 primitives. @xref{Size of Displayed Text}, for related functions.
2252 @defun current-indentation
2253 @comment !!Type Primitive Function
2254 @comment !!SourceFile indent.c
2255 This function returns the indentation of the current line, which is
2256 the horizontal position of the first nonblank character. If the
2257 contents are entirely blank, then this is the horizontal position of the
2261 @deffn Command indent-to column &optional minimum
2262 @comment !!Type Primitive Function
2263 @comment !!SourceFile indent.c
2264 This function indents from point with tabs and spaces until @var{column}
2265 is reached. If @var{minimum} is specified and non-@code{nil}, then at
2266 least that many spaces are inserted even if this requires going beyond
2267 @var{column}. Otherwise the function does nothing if point is already
2268 beyond @var{column}. The value is the column at which the inserted
2271 The inserted whitespace characters inherit text properties from the
2272 surrounding text (usually, from the preceding text only). @xref{Sticky
2276 @defopt indent-tabs-mode
2277 @comment !!SourceFile indent.c
2278 If this variable is non-@code{nil}, indentation functions can insert
2279 tabs as well as spaces. Otherwise, they insert only spaces. Setting
2280 this variable automatically makes it buffer-local in the current buffer.
2283 @node Mode-Specific Indent
2284 @subsection Indentation Controlled by Major Mode
2286 An important function of each major mode is to customize the @key{TAB}
2287 key to indent properly for the language being edited. This section
2288 describes the mechanism of the @key{TAB} key and how to control it.
2289 The functions in this section return unpredictable values.
2291 @deffn Command indent-for-tab-command &optional rigid
2292 This is the command bound to @key{TAB} in most editing modes. Its
2293 usual action is to indent the current line, but it can alternatively
2294 insert a tab character or indent a region.
2296 Here is what it does:
2300 First, it checks whether Transient Mark mode is enabled and the region
2301 is active. If so, it called @code{indent-region} to indent all the
2302 text in the region (@pxref{Region Indent}).
2305 Otherwise, if the indentation function in @code{indent-line-function}
2306 is @code{indent-to-left-margin} (a trivial command that inserts a tab
2307 character), or if the variable @code{tab-always-indent} specifies that
2308 a tab character ought to be inserted (see below), then it inserts a
2312 Otherwise, it indents the current line; this is done by calling the
2313 function in @code{indent-line-function}. If the line is already
2314 indented, and the value of @code{tab-always-indent} is @code{complete}
2315 (see below), it tries completing the text at point.
2318 If @var{rigid} is non-@code{nil} (interactively, with a prefix
2319 argument), then after this command indents a line or inserts a tab, it
2320 also rigidly indents the entire balanced expression which starts at
2321 the beginning of the current line, in order to reflect the new
2322 indentation. This argument is ignored if the command indents the
2326 @defvar indent-line-function
2327 This variable's value is the function to be used by
2328 @code{indent-for-tab-command}, and various other indentation commands,
2329 to indent the current line. It is usually assigned by the major mode;
2330 for instance, Lisp mode sets it to @code{lisp-indent-line}, C mode
2331 sets it to @code{c-indent-line}, and so on. The default value is
2332 @code{indent-relative}. @xref{Auto-Indentation}.
2335 @deffn Command indent-according-to-mode
2336 This command calls the function in @code{indent-line-function} to
2337 indent the current line in a way appropriate for the current major mode.
2340 @deffn Command newline-and-indent
2341 This function inserts a newline, then indents the new line (the one
2342 following the newline just inserted) according to the major mode. It
2343 does indentation by calling @code{indent-according-to-mode}.
2346 @deffn Command reindent-then-newline-and-indent
2347 This command reindents the current line, inserts a newline at point,
2348 and then indents the new line (the one following the newline just
2349 inserted). It does indentation on both lines by calling
2350 @code{indent-according-to-mode}.
2353 @defopt tab-always-indent
2354 This variable can be used to customize the behavior of the @key{TAB}
2355 (@code{indent-for-tab-command}) command. If the value is @code{t}
2356 (the default), the command normally just indents the current line. If
2357 the value is @code{nil}, the command indents the current line only if
2358 point is at the left margin or in the line's indentation; otherwise,
2359 it inserts a tab character. If the value is @code{complete}, the
2360 command first tries to indent the current line, and if the line was
2361 already indented, it calls @code{completion-at-point} to complete the
2362 text at point (@pxref{Completion in Buffers}).
2365 @cindex literate programming
2366 @cindex multi-mode indentation
2367 Some major modes need to support embedded regions of text whose
2368 syntax belongs to a different major mode. Examples include
2369 @dfn{literate programming} source files that combine documentation and
2370 snippets of source code, Yacc/Bison programs that include snippets of
2371 plain C code, etc. To correctly indent the embedded chunks, the major
2372 mode needs to delegate the indentation to another mode's indentation
2373 engine (e.g., call @code{c-indent-defun} for C code or
2374 @code{python-indent-line} for Python), while providing it with some
2375 context to guide the indentation. The following facilities support
2376 such multi-mode indentation.
2378 @defvar prog-indentation-context
2379 This variable, when non-@code{nil}, holds the indentation context for
2380 the sub-mode's indentation engine provided by the superior major mode.
2381 The value should be a list of the form @code{(@var{first-column}
2382 @w{(@var{start} . @var{end})} @code{prev-chunk})}. The members of the
2383 list have the following meaning:
2387 The column to be used for top-level constructs. This replaces the
2388 default value of the top-level column used by the sub-mode, usually
2392 The region of the code chunk to be indented by the sub-mode. The
2393 value of @var{end} can be @code{nil}, which stands for the value of
2396 If this is non-@code{nil}, it should provide the sub-mode's
2397 indentation engine with a virtual context of the code chunk. Valid
2402 A string whose contents is the text the sub-mode's indentation engine
2403 should consider to precede the code chunk. The sub-mode's indentation
2404 engine can add text properties to that string, to be reused in
2405 repeated calls with the same string, thus using it as a cache. An
2406 example where this is useful is code chunks that need to be indented
2407 as function bodies, but lack the function's preamble---the string
2408 could then include that missing preamble.
2410 A function. It is expected to be called with the start position of
2411 the current chunk, and should return a cons cell
2412 @w{@code{(@var{prev-start} . @var{prev-end})}} that specifies the
2413 region of the previous code chunk, or @code{nil} if there is no previous
2414 chunk. This is useful in literate-programming sources, where code is
2415 split into chunks, and correct indentation needs to access previous
2421 The following convenience functions should be used by major mode's
2422 indentation engine in support of invocations as sub-modes of another
2425 @defun prog-first-column
2426 Call this function instead of using a literal value (usually, zero) of
2427 the column number for indenting top-level program constructs. The
2428 function's value is the column number to use for top-level constructs.
2429 When no superior mode is in effect, this function returns zero.
2433 Call this function instead of @code{widen} to remove any restrictions
2434 imposed by the mode's indentation engine and restore the restrictions
2435 recorded in @code{prog-indentation-context}. This prevents the
2436 indentation engine of a sub-mode from inadvertently operating on text
2437 outside of the chunk it was supposed to indent, and preserves the
2438 restriction imposed by the superior mode. When no superior mode is in
2439 effect, this function just calls @code{widen}.
2444 @subsection Indenting an Entire Region
2446 This section describes commands that indent all the lines in the
2447 region. They return unpredictable values.
2449 @deffn Command indent-region start end &optional to-column
2450 This command indents each nonblank line starting between @var{start}
2451 (inclusive) and @var{end} (exclusive). If @var{to-column} is
2452 @code{nil}, @code{indent-region} indents each nonblank line by calling
2453 the current mode's indentation function, the value of
2454 @code{indent-line-function}.
2456 If @var{to-column} is non-@code{nil}, it should be an integer
2457 specifying the number of columns of indentation; then this function
2458 gives each line exactly that much indentation, by either adding or
2459 deleting whitespace.
2461 If there is a fill prefix, @code{indent-region} indents each line
2462 by making it start with the fill prefix.
2465 @defvar indent-region-function
2466 The value of this variable is a function that can be used by
2467 @code{indent-region} as a short cut. It should take two arguments, the
2468 start and end of the region. You should design the function so
2469 that it will produce the same results as indenting the lines of the
2470 region one by one, but presumably faster.
2472 If the value is @code{nil}, there is no short cut, and
2473 @code{indent-region} actually works line by line.
2475 A short-cut function is useful in modes such as C mode and Lisp mode,
2476 where the @code{indent-line-function} must scan from the beginning of
2477 the function definition: applying it to each line would be quadratic in
2478 time. The short cut can update the scan information as it moves through
2479 the lines indenting them; this takes linear time. In a mode where
2480 indenting a line individually is fast, there is no need for a short cut.
2482 @code{indent-region} with a non-@code{nil} argument @var{to-column} has
2483 a different meaning and does not use this variable.
2486 @deffn Command indent-rigidly start end count
2487 This function indents all lines starting between @var{start}
2488 (inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
2489 This preserves the shape of the affected region, moving it as a
2492 This is useful not only for indenting regions of unindented text, but
2493 also for indenting regions of formatted code. For example, if
2494 @var{count} is 3, this command adds 3 columns of indentation to every
2495 line that begins in the specified region.
2497 If called interactively with no prefix argument, this command invokes
2498 a transient mode for adjusting indentation rigidly. @xref{Indentation
2499 Commands,,, emacs, The GNU Emacs Manual}.
2502 @deffn Command indent-code-rigidly start end columns &optional nochange-regexp
2503 This is like @code{indent-rigidly}, except that it doesn't alter lines
2504 that start within strings or comments.
2506 In addition, it doesn't alter a line if @var{nochange-regexp} matches at
2507 the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
2510 @node Relative Indent
2511 @subsection Indentation Relative to Previous Lines
2513 This section describes two commands that indent the current line
2514 based on the contents of previous lines.
2516 @deffn Command indent-relative &optional unindented-ok
2517 This command inserts whitespace at point, extending to the same
2518 column as the next @dfn{indent point} of the previous nonblank line. An
2519 indent point is a non-whitespace character following whitespace. The
2520 next indent point is the first one at a column greater than the current
2521 column of point. For example, if point is underneath and to the left of
2522 the first non-blank character of a line of text, it moves to that column
2523 by inserting whitespace.
2525 If the previous nonblank line has no next indent point (i.e., none at a
2526 great enough column position), @code{indent-relative} either does
2527 nothing (if @var{unindented-ok} is non-@code{nil}) or calls
2528 @code{tab-to-tab-stop}. Thus, if point is underneath and to the right
2529 of the last column of a short line of text, this command ordinarily
2530 moves point to the next tab stop by inserting whitespace.
2532 The return value of @code{indent-relative} is unpredictable.
2534 In the following example, point is at the beginning of the second
2539 This line is indented twelve spaces.
2540 @point{}The quick brown fox jumped.
2545 Evaluation of the expression @code{(indent-relative nil)} produces the
2550 This line is indented twelve spaces.
2551 @point{}The quick brown fox jumped.
2555 In this next example, point is between the @samp{m} and @samp{p} of
2560 This line is indented twelve spaces.
2561 The quick brown fox jum@point{}ped.
2566 Evaluation of the expression @code{(indent-relative nil)} produces the
2571 This line is indented twelve spaces.
2572 The quick brown fox jum @point{}ped.
2577 @deffn Command indent-relative-maybe
2578 @comment !!SourceFile indent.el
2579 This command indents the current line like the previous nonblank line,
2580 by calling @code{indent-relative} with @code{t} as the
2581 @var{unindented-ok} argument. The return value is unpredictable.
2583 If the previous nonblank line has no indent points beyond the current
2584 column, this command does nothing.
2588 @subsection Adjustable Tab Stops
2589 @cindex tabs stops for indentation
2591 This section explains the mechanism for user-specified tab stops
2592 and the mechanisms that use and set them. The name ``tab stops'' is
2593 used because the feature is similar to that of the tab stops on a
2594 typewriter. The feature works by inserting an appropriate number of
2595 spaces and tab characters to reach the next tab stop column; it does not
2596 affect the display of tab characters in the buffer (@pxref{Usual
2597 Display}). Note that the @key{TAB} character as input uses this tab
2598 stop feature only in a few major modes, such as Text mode.
2599 @xref{Tab Stops,,, emacs, The GNU Emacs Manual}.
2601 @deffn Command tab-to-tab-stop
2602 This command inserts spaces or tabs before point, up to the next tab
2603 stop column defined by @code{tab-stop-list}.
2606 @defopt tab-stop-list
2607 This variable defines the tab stop columns used by @code{tab-to-tab-stop}.
2608 It should be either @code{nil}, or a list of increasing integers,
2609 which need not be evenly spaced. The list is implicitly
2610 extended to infinity through repetition of the interval between the
2611 last and penultimate elements (or @code{tab-width} if the list has
2612 fewer than two elements). A value of @code{nil} means a tab stop
2613 every @code{tab-width} columns.
2615 Use @kbd{M-x edit-tab-stops} to edit the location of tab stops interactively.
2618 @node Motion by Indent
2619 @subsection Indentation-Based Motion Commands
2621 These commands, primarily for interactive use, act based on the
2622 indentation in the text.
2624 @deffn Command back-to-indentation
2625 @comment !!SourceFile simple.el
2626 This command moves point to the first non-whitespace character in the
2627 current line (which is the line in which point is located). It returns
2631 @deffn Command backward-to-indentation &optional arg
2632 @comment !!SourceFile simple.el
2633 This command moves point backward @var{arg} lines and then to the
2634 first nonblank character on that line. It returns @code{nil}.
2635 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2638 @deffn Command forward-to-indentation &optional arg
2639 @comment !!SourceFile simple.el
2640 This command moves point forward @var{arg} lines and then to the first
2641 nonblank character on that line. It returns @code{nil}.
2642 If @var{arg} is omitted or @code{nil}, it defaults to 1.
2646 @section Case Changes
2647 @cindex case conversion in buffers
2649 The case change commands described here work on text in the current
2650 buffer. @xref{Case Conversion}, for case conversion functions that work
2651 on strings and characters. @xref{Case Tables}, for how to customize
2652 which characters are upper or lower case and how to convert them.
2654 @deffn Command capitalize-region start end
2655 This function capitalizes all words in the region defined by
2656 @var{start} and @var{end}. To capitalize means to convert each word's
2657 first character to upper case and convert the rest of each word to lower
2658 case. The function returns @code{nil}.
2660 If one end of the region is in the middle of a word, the part of the
2661 word within the region is treated as an entire word.
2663 When @code{capitalize-region} is called interactively, @var{start} and
2664 @var{end} are point and the mark, with the smallest first.
2668 ---------- Buffer: foo ----------
2669 This is the contents of the 5th foo.
2670 ---------- Buffer: foo ----------
2674 (capitalize-region 1 37)
2677 ---------- Buffer: foo ----------
2678 This Is The Contents Of The 5th Foo.
2679 ---------- Buffer: foo ----------
2684 @deffn Command downcase-region start end
2685 This function converts all of the letters in the region defined by
2686 @var{start} and @var{end} to lower case. The function returns
2689 When @code{downcase-region} is called interactively, @var{start} and
2690 @var{end} are point and the mark, with the smallest first.
2693 @deffn Command upcase-region start end
2694 This function converts all of the letters in the region defined by
2695 @var{start} and @var{end} to upper case. The function returns
2698 When @code{upcase-region} is called interactively, @var{start} and
2699 @var{end} are point and the mark, with the smallest first.
2702 @deffn Command capitalize-word count
2703 This function capitalizes @var{count} words after point, moving point
2704 over as it does. To capitalize means to convert each word's first
2705 character to upper case and convert the rest of each word to lower case.
2706 If @var{count} is negative, the function capitalizes the
2707 @minus{}@var{count} previous words but does not move point. The value
2710 If point is in the middle of a word, the part of the word before point
2711 is ignored when moving forward. The rest is treated as an entire word.
2713 When @code{capitalize-word} is called interactively, @var{count} is
2714 set to the numeric prefix argument.
2717 @deffn Command downcase-word count
2718 This function converts the @var{count} words after point to all lower
2719 case, moving point over as it does. If @var{count} is negative, it
2720 converts the @minus{}@var{count} previous words but does not move point.
2721 The value is @code{nil}.
2723 When @code{downcase-word} is called interactively, @var{count} is set
2724 to the numeric prefix argument.
2727 @deffn Command upcase-word count
2728 This function converts the @var{count} words after point to all upper
2729 case, moving point over as it does. If @var{count} is negative, it
2730 converts the @minus{}@var{count} previous words but does not move point.
2731 The value is @code{nil}.
2733 When @code{upcase-word} is called interactively, @var{count} is set to
2734 the numeric prefix argument.
2737 @node Text Properties
2738 @section Text Properties
2739 @cindex text properties
2740 @cindex attributes of text
2741 @cindex properties of text
2743 Each character position in a buffer or a string can have a @dfn{text
2744 property list}, much like the property list of a symbol (@pxref{Property
2745 Lists}). The properties belong to a particular character at a
2746 particular place, such as, the letter @samp{T} at the beginning of this
2747 sentence or the first @samp{o} in @samp{foo}---if the same character
2748 occurs in two different places, the two occurrences in general have
2749 different properties.
2751 Each property has a name and a value. Both of these can be any Lisp
2752 object, but the name is normally a symbol. Typically each property
2753 name symbol is used for a particular purpose; for instance, the text
2754 property @code{face} specifies the faces for displaying the character
2755 (@pxref{Special Properties}). The usual way to access the property
2756 list is to specify a name and ask what value corresponds to it.
2758 If a character has a @code{category} property, we call it the
2759 @dfn{property category} of the character. It should be a symbol. The
2760 properties of the symbol serve as defaults for the properties of the
2763 Copying text between strings and buffers preserves the properties
2764 along with the characters; this includes such diverse functions as
2765 @code{substring}, @code{insert}, and @code{buffer-substring}.
2768 * Examining Properties:: Looking at the properties of one character.
2769 * Changing Properties:: Setting the properties of a range of text.
2770 * Property Search:: Searching for where a property changes value.
2771 * Special Properties:: Particular properties with special meanings.
2772 * Format Properties:: Properties for representing formatting of text.
2773 * Sticky Properties:: How inserted text gets properties from
2775 * Lazy Properties:: Computing text properties in a lazy fashion
2776 only when text is examined.
2777 * Clickable Text:: Using text properties to make regions of text
2778 do something when you click on them.
2779 * Fields:: The @code{field} property defines
2780 fields within the buffer.
2781 * Not Intervals:: Why text properties do not use
2782 Lisp-visible text intervals.
2785 @node Examining Properties
2786 @subsection Examining Text Properties
2787 @cindex examining text properties
2788 @cindex text properties, examining
2790 The simplest way to examine text properties is to ask for the value of
2791 a particular property of a particular character. For that, use
2792 @code{get-text-property}. Use @code{text-properties-at} to get the
2793 entire property list of a character. @xref{Property Search}, for
2794 functions to examine the properties of a number of characters at once.
2796 These functions handle both strings and buffers. Keep in mind that
2797 positions in a string start from 0, whereas positions in a buffer start
2800 @defun get-text-property pos prop &optional object
2801 This function returns the value of the @var{prop} property of the
2802 character after position @var{pos} in @var{object} (a buffer or
2803 string). The argument @var{object} is optional and defaults to the
2806 If there is no @var{prop} property strictly speaking, but the character
2807 has a property category that is a symbol, then @code{get-text-property} returns
2808 the @var{prop} property of that symbol.
2811 @defun get-char-property position prop &optional object
2812 This function is like @code{get-text-property}, except that it checks
2813 overlays first and then text properties. @xref{Overlays}.
2815 The argument @var{object} may be a string, a buffer, or a window. If
2816 it is a window, then the buffer displayed in that window is used for
2817 text properties and overlays, but only the overlays active for that
2818 window are considered. If @var{object} is a buffer, then overlays in
2819 that buffer are considered first, in order of decreasing priority,
2820 followed by the text properties. If @var{object} is a string, only
2821 text properties are considered, since strings never have overlays.
2824 @defun get-pos-property position prop &optional object
2825 This function is like @code{get-char-property}, except that it pays
2826 attention to properties' stickiness and overlays' advancement settings
2827 instead of the property of the character at (i.e., right after)
2831 @defun get-char-property-and-overlay position prop &optional object
2832 This is like @code{get-char-property}, but gives extra information
2833 about the overlay that the property value comes from.
2835 Its value is a cons cell whose @sc{car} is the property value, the
2836 same value @code{get-char-property} would return with the same
2837 arguments. Its @sc{cdr} is the overlay in which the property was
2838 found, or @code{nil}, if it was found as a text property or not found
2841 If @var{position} is at the end of @var{object}, both the @sc{car} and
2842 the @sc{cdr} of the value are @code{nil}.
2845 @defvar char-property-alias-alist
2846 This variable holds an alist which maps property names to a list of
2847 alternative property names. If a character does not specify a direct
2848 value for a property, the alternative property names are consulted in
2849 order; the first non-@code{nil} value is used. This variable takes
2850 precedence over @code{default-text-properties}, and @code{category}
2851 properties take precedence over this variable.
2854 @defun text-properties-at position &optional object
2855 This function returns the entire property list of the character at
2856 @var{position} in the string or buffer @var{object}. If @var{object} is
2857 @code{nil}, it defaults to the current buffer.
2860 @defvar default-text-properties
2861 This variable holds a property list giving default values for text
2862 properties. Whenever a character does not specify a value for a
2863 property, neither directly, through a category symbol, or through
2864 @code{char-property-alias-alist}, the value stored in this list is
2865 used instead. Here is an example:
2868 (setq default-text-properties '(foo 69)
2869 char-property-alias-alist nil)
2870 ;; @r{Make sure character 1 has no properties of its own.}
2871 (set-text-properties 1 2 nil)
2872 ;; @r{What we get, when we ask, is the default value.}
2873 (get-text-property 1 'foo)
2878 @node Changing Properties
2879 @subsection Changing Text Properties
2880 @cindex changing text properties
2881 @cindex text properties, changing
2883 The primitives for changing properties apply to a specified range of
2884 text in a buffer or string. The function @code{set-text-properties}
2885 (see end of section) sets the entire property list of the text in that
2886 range; more often, it is useful to add, change, or delete just certain
2887 properties specified by name.
2889 Since text properties are considered part of the contents of the
2890 buffer (or string), and can affect how a buffer looks on the screen,
2891 any change in buffer text properties marks the buffer as modified.
2892 Buffer text property changes are undoable also (@pxref{Undo}).
2893 Positions in a string start from 0, whereas positions in a buffer
2896 @defun put-text-property start end prop value &optional object
2897 This function sets the @var{prop} property to @var{value} for the text
2898 between @var{start} and @var{end} in the string or buffer @var{object}.
2899 If @var{object} is @code{nil}, it defaults to the current buffer.
2902 @defun add-text-properties start end props &optional object
2903 This function adds or overrides text properties for the text between
2904 @var{start} and @var{end} in the string or buffer @var{object}. If
2905 @var{object} is @code{nil}, it defaults to the current buffer.
2907 The argument @var{props} specifies which properties to add. It should
2908 have the form of a property list (@pxref{Property Lists}): a list whose
2909 elements include the property names followed alternately by the
2910 corresponding values.
2912 The return value is @code{t} if the function actually changed some
2913 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2914 its values agree with those in the text).
2916 For example, here is how to set the @code{comment} and @code{face}
2917 properties of a range of text:
2920 (add-text-properties @var{start} @var{end}
2921 '(comment t face highlight))
2925 @defun remove-text-properties start end props &optional object
2926 This function deletes specified text properties from the text between
2927 @var{start} and @var{end} in the string or buffer @var{object}. If
2928 @var{object} is @code{nil}, it defaults to the current buffer.
2930 The argument @var{props} specifies which properties to delete. It
2931 should have the form of a property list (@pxref{Property Lists}): a list
2932 whose elements are property names alternating with corresponding values.
2933 But only the names matter---the values that accompany them are ignored.
2934 For example, here's how to remove the @code{face} property.
2937 (remove-text-properties @var{start} @var{end} '(face nil))
2940 The return value is @code{t} if the function actually changed some
2941 property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2942 if no character in the specified text had any of those properties).
2944 To remove all text properties from certain text, use
2945 @code{set-text-properties} and specify @code{nil} for the new property
2949 @defun remove-list-of-text-properties start end list-of-properties &optional object
2950 Like @code{remove-text-properties} except that
2951 @var{list-of-properties} is a list of property names only, not an
2952 alternating list of property names and values.
2955 @defun set-text-properties start end props &optional object
2956 This function completely replaces the text property list for the text
2957 between @var{start} and @var{end} in the string or buffer @var{object}.
2958 If @var{object} is @code{nil}, it defaults to the current buffer.
2960 The argument @var{props} is the new property list. It should be a list
2961 whose elements are property names alternating with corresponding values.
2963 After @code{set-text-properties} returns, all the characters in the
2964 specified range have identical properties.
2966 If @var{props} is @code{nil}, the effect is to get rid of all properties
2967 from the specified range of text. Here's an example:
2970 (set-text-properties @var{start} @var{end} nil)
2973 Do not rely on the return value of this function.
2976 @defun add-face-text-property start end face &optional appendp object
2977 This function acts on the text between @var{start} and @var{end},
2978 adding the face @var{face} to the @code{face} text property.
2979 @var{face} should be a valid value for the @code{face} property
2980 (@pxref{Special Properties}), such as a face name or an anonymous face
2983 If any text in the region already has a non-@code{nil} @code{face} property,
2984 those face(s) are retained. This function sets the @code{face}
2985 property to a list of faces, with @var{face} as the first element (by
2986 default) and the pre-existing faces as the remaining elements. If the
2987 optional argument @var{append} is non-@code{nil}, @var{face} is
2988 appended to the end of the list instead. Note that in a face list,
2989 the first occurring value for each attribute takes precedence.
2991 For example, the following code would assign a italicized green face
2992 to the text between @var{start} and @var{end}:
2995 (add-face-text-property @var{start} @var{end} 'italic)
2996 (add-face-text-property @var{start} @var{end} '(:foreground "red"))
2997 (add-face-text-property @var{start} @var{end} '(:foreground "green"))
3000 The optional argument @var{object}, if non-@code{nil}, specifies a
3001 buffer or string to act on, rather than the current buffer. If
3002 @var{object} is a string, then @var{start} and @var{end} are
3003 zero-based indices into the string.
3006 The easiest way to make a string with text properties is with
3009 @defun propertize string &rest properties
3010 This function returns a copy of @var{string} with the text properties
3011 @var{properties} added. These properties apply to all the characters
3012 in the string that is returned. Here is an example that constructs a
3013 string with a @code{face} property and a @code{mouse-face} property:
3016 (propertize "foo" 'face 'italic
3017 'mouse-face 'bold-italic)
3018 @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
3021 To put different properties on various parts of a string, you can
3022 construct each part with @code{propertize} and then combine them with
3027 (propertize "foo" 'face 'italic
3028 'mouse-face 'bold-italic)
3030 (propertize "bar" 'face 'italic
3031 'mouse-face 'bold-italic))
3032 @result{} #("foo and bar"
3033 0 3 (face italic mouse-face bold-italic)
3035 8 11 (face italic mouse-face bold-italic))
3039 @xref{Buffer Contents}, for the function
3040 @code{buffer-substring-no-properties}, which copies text from the
3041 buffer but does not copy its properties.
3043 @node Property Search
3044 @subsection Text Property Search Functions
3045 @cindex searching text properties
3046 @cindex text properties, searching
3048 In typical use of text properties, most of the time several or many
3049 consecutive characters have the same value for a property. Rather than
3050 writing your programs to examine characters one by one, it is much
3051 faster to process chunks of text that have the same property value.
3053 Here are functions you can use to do this. They use @code{eq} for
3054 comparing property values. In all cases, @var{object} defaults to the
3057 For good performance, it's very important to use the @var{limit}
3058 argument to these functions, especially the ones that search for a
3059 single property---otherwise, they may spend a long time scanning to the
3060 end of the buffer, if the property you are interested in does not change.
3062 These functions do not move point; instead, they return a position (or
3063 @code{nil}). Remember that a position is always between two characters;
3064 the position returned by these functions is between two characters with
3065 different properties.
3067 @defun next-property-change pos &optional object limit
3068 The function scans the text forward from position @var{pos} in the
3069 string or buffer @var{object} until it finds a change in some text
3070 property, then returns the position of the change. In other words, it
3071 returns the position of the first character beyond @var{pos} whose
3072 properties are not identical to those of the character just after
3075 If @var{limit} is non-@code{nil}, then the scan ends at position
3076 @var{limit}. If there is no property change before that point, this
3077 function returns @var{limit}.
3079 The value is @code{nil} if the properties remain unchanged all the way
3080 to the end of @var{object} and @var{limit} is @code{nil}. If the value
3081 is non-@code{nil}, it is a position greater than or equal to @var{pos}.
3082 The value equals @var{pos} only when @var{limit} equals @var{pos}.
3084 Here is an example of how to scan the buffer by chunks of text within
3085 which all properties are constant:
3089 (let ((plist (text-properties-at (point)))
3091 (or (next-property-change (point) (current-buffer))
3093 @r{Process text from point to @var{next-change}@dots{}}
3094 (goto-char next-change)))
3098 @defun previous-property-change pos &optional object limit
3099 This is like @code{next-property-change}, but scans back from @var{pos}
3100 instead of forward. If the value is non-@code{nil}, it is a position
3101 less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
3105 @defun next-single-property-change pos prop &optional object limit
3106 The function scans text for a change in the @var{prop} property, then
3107 returns the position of the change. The scan goes forward from
3108 position @var{pos} in the string or buffer @var{object}. In other
3109 words, this function returns the position of the first character
3110 beyond @var{pos} whose @var{prop} property differs from that of the
3111 character just after @var{pos}.
3113 If @var{limit} is non-@code{nil}, then the scan ends at position
3114 @var{limit}. If there is no property change before that point,
3115 @code{next-single-property-change} returns @var{limit}.
3117 The value is @code{nil} if the property remains unchanged all the way to
3118 the end of @var{object} and @var{limit} is @code{nil}. If the value is
3119 non-@code{nil}, it is a position greater than or equal to @var{pos}; it
3120 equals @var{pos} only if @var{limit} equals @var{pos}.
3123 @defun previous-single-property-change pos prop &optional object limit
3124 This is like @code{next-single-property-change}, but scans back from
3125 @var{pos} instead of forward. If the value is non-@code{nil}, it is a
3126 position less than or equal to @var{pos}; it equals @var{pos} only if
3127 @var{limit} equals @var{pos}.
3130 @defun next-char-property-change pos &optional limit
3131 This is like @code{next-property-change} except that it considers
3132 overlay properties as well as text properties, and if no change is
3133 found before the end of the buffer, it returns the maximum buffer
3134 position rather than @code{nil} (in this sense, it resembles the
3135 corresponding overlay function @code{next-overlay-change}, rather than
3136 @code{next-property-change}). There is no @var{object} operand
3137 because this function operates only on the current buffer. It returns
3138 the next address at which either kind of property changes.
3141 @defun previous-char-property-change pos &optional limit
3142 This is like @code{next-char-property-change}, but scans back from
3143 @var{pos} instead of forward, and returns the minimum buffer
3144 position if no change is found.
3147 @defun next-single-char-property-change pos prop &optional object limit
3148 This is like @code{next-single-property-change} except that it
3149 considers overlay properties as well as text properties, and if no
3150 change is found before the end of the @var{object}, it returns the
3151 maximum valid position in @var{object} rather than @code{nil}. Unlike
3152 @code{next-char-property-change}, this function @emph{does} have an
3153 @var{object} operand; if @var{object} is not a buffer, only
3154 text-properties are considered.
3157 @defun previous-single-char-property-change pos prop &optional object limit
3158 This is like @code{next-single-char-property-change}, but scans back
3159 from @var{pos} instead of forward, and returns the minimum valid
3160 position in @var{object} if no change is found.
3163 @defun text-property-any start end prop value &optional object
3164 This function returns non-@code{nil} if at least one character between
3165 @var{start} and @var{end} has a property @var{prop} whose value is
3166 @var{value}. More precisely, it returns the position of the first such
3167 character. Otherwise, it returns @code{nil}.
3169 The optional fifth argument, @var{object}, specifies the string or
3170 buffer to scan. Positions are relative to @var{object}. The default
3171 for @var{object} is the current buffer.
3174 @defun text-property-not-all start end prop value &optional object
3175 This function returns non-@code{nil} if at least one character between
3176 @var{start} and @var{end} does not have a property @var{prop} with value
3177 @var{value}. More precisely, it returns the position of the first such
3178 character. Otherwise, it returns @code{nil}.
3180 The optional fifth argument, @var{object}, specifies the string or
3181 buffer to scan. Positions are relative to @var{object}. The default
3182 for @var{object} is the current buffer.
3185 @node Special Properties
3186 @subsection Properties with Special Meanings
3188 Here is a table of text property names that have special built-in
3189 meanings. The following sections list a few additional special property
3190 names that control filling and property inheritance. All other names
3191 have no standard meaning, and you can use them as you like.
3193 Note: the properties @code{composition}, @code{display},
3194 @code{invisible} and @code{intangible} can also cause point to move to
3195 an acceptable place, after each Emacs command. @xref{Adjusting
3199 @cindex property category of text character
3200 @c FIXME: Isn't @kindex for keyboard commands?
3201 @kindex category @r{(text property)}
3203 If a character has a @code{category} property, we call it the
3204 @dfn{property category} of the character. It should be a symbol. The
3205 properties of this symbol serve as defaults for the properties of the
3209 @cindex face codes of text
3210 @kindex face @r{(text property)}
3211 The @code{face} property controls the appearance of the character
3212 (@pxref{Faces}). The value of the property can be the following:
3216 A face name (a symbol or string).
3219 An anonymous face: a property list of the form @code{(@var{keyword}
3220 @var{value} @dots{})}, where each @var{keyword} is a face attribute
3221 name and @var{value} is a value for that attribute.
3224 A list of faces. Each list element should be either a face name or an
3225 anonymous face. This specifies a face which is an aggregate of the
3226 attributes of each of the listed faces. Faces occurring earlier in
3227 the list have higher priority.
3230 A cons cell of the form @code{(foreground-color . @var{color-name})}
3231 or @code{(background-color . @var{color-name})}. This specifies the
3232 foreground or background color, similar to @code{(:foreground
3233 @var{color-name})} or @code{(:background @var{color-name})}. This
3234 form is supported for backward compatibility only, and should be
3238 Font Lock mode (@pxref{Font Lock Mode}) works in most buffers by
3239 dynamically updating the @code{face} property of characters based on
3242 The @code{add-face-text-property} function provides a convenient way
3243 to set this text property. @xref{Changing Properties}.
3245 @item font-lock-face
3246 @kindex font-lock-face @r{(text property)}
3247 This property specifies a value for the @code{face} property that Font
3248 Lock mode should apply to the underlying text. It is one of the
3249 fontification methods used by Font Lock mode, and is useful for
3250 special modes that implement their own highlighting.
3251 @xref{Precalculated Fontification}. When Font Lock mode is disabled,
3252 @code{font-lock-face} has no effect.
3255 @kindex mouse-face @r{(text property)}
3256 This property is used instead of @code{face} when the mouse is on or
3257 near the character. For this purpose, ``near'' means that all text
3258 between the character and where the mouse is have the same
3259 @code{mouse-face} property value.
3261 Emacs ignores all face attributes from the @code{mouse-face} property
3262 that alter the text size (e.g., @code{:height}, @code{:weight}, and
3263 @code{:slant}). Those attributes are always the same as for the
3267 @kindex fontified @r{(text property)}
3268 This property says whether the text is ready for display. If
3269 @code{nil}, Emacs's redisplay routine calls the functions in
3270 @code{fontification-functions} (@pxref{Auto Faces}) to prepare this
3271 part of the buffer before it is displayed. It is used internally by
3272 the just-in-time font locking code.
3275 This property activates various features that change the
3276 way text is displayed. For example, it can make text appear taller
3277 or shorter, higher or lower, wider or narrow, or replaced with an image.
3278 @xref{Display Property}.
3281 @kindex help-echo @r{(text property)}
3283 @anchor{Text help-echo}
3284 If text has a string as its @code{help-echo} property, then when you
3285 move the mouse onto that text, Emacs displays that string in the echo
3286 area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
3289 If the value of the @code{help-echo} property is a function, that
3290 function is called with three arguments, @var{window}, @var{object} and
3291 @var{pos} and should return a help string or @code{nil} for
3292 none. The first argument, @var{window} is the window in which
3293 the help was found. The second, @var{object}, is the buffer, overlay or
3294 string which had the @code{help-echo} property. The @var{pos}
3295 argument is as follows:
3299 If @var{object} is a buffer, @var{pos} is the position in the buffer.
3301 If @var{object} is an overlay, that overlay has a @code{help-echo}
3302 property, and @var{pos} is the position in the overlay's buffer.
3304 If @var{object} is a string (an overlay string or a string displayed
3305 with the @code{display} property), @var{pos} is the position in that
3309 If the value of the @code{help-echo} property is neither a function nor
3310 a string, it is evaluated to obtain a help string.
3312 You can alter the way help text is displayed by setting the variable
3313 @code{show-help-function} (@pxref{Help display}).
3315 This feature is used in the mode line and for other active text.
3318 @cindex keymap of character
3319 @kindex keymap @r{(text property)}
3320 The @code{keymap} property specifies an additional keymap for
3321 commands. When this keymap applies, it is used for key lookup before
3322 the minor mode keymaps and before the buffer's local map.
3323 @xref{Active Keymaps}. If the property value is a symbol, the
3324 symbol's function definition is used as the keymap.
3326 The property's value for the character before point applies if it is
3327 non-@code{nil} and rear-sticky, and the property's value for the
3328 character after point applies if it is non-@code{nil} and
3329 front-sticky. (For mouse clicks, the position of the click is used
3330 instead of the position of point.)
3333 @kindex local-map @r{(text property)}
3334 This property works like @code{keymap} except that it specifies a
3335 keymap to use @emph{instead of} the buffer's local map. For most
3336 purposes (perhaps all purposes), it is better to use the @code{keymap}
3340 The @code{syntax-table} property overrides what the syntax table says
3341 about this particular character. @xref{Syntax Properties}.
3344 @cindex read-only character
3345 @kindex read-only @r{(text property)}
3346 If a character has the property @code{read-only}, then modifying that
3347 character is not allowed. Any command that would do so gets an error,
3348 @code{text-read-only}. If the property value is a string, that string
3349 is used as the error message.
3351 Insertion next to a read-only character is an error if inserting
3352 ordinary text there would inherit the @code{read-only} property due to
3353 stickiness. Thus, you can control permission to insert next to
3354 read-only text by controlling the stickiness. @xref{Sticky Properties}.
3356 Since changing properties counts as modifying the buffer, it is not
3357 possible to remove a @code{read-only} property unless you know the
3358 special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
3359 and then remove the property. @xref{Read Only Buffers}.
3361 @item inhibit-read-only
3362 @kindex inhibit-read-only @r{(text property)}
3363 Characters that have the property @code{inhibit-read-only} can be
3364 edited even in read-only buffers. @xref{Read Only Buffers}.
3367 @kindex invisible @r{(text property)}
3368 A non-@code{nil} @code{invisible} property can make a character invisible
3369 on the screen. @xref{Invisible Text}, for details.
3372 @kindex intangible @r{(text property)}
3373 If a group of consecutive characters have equal and non-@code{nil}
3374 @code{intangible} properties, then you cannot place point between them.
3375 If you try to move point forward into the group, point actually moves to
3376 the end of the group. If you try to move point backward into the group,
3377 point actually moves to the start of the group.
3379 If consecutive characters have unequal non-@code{nil}
3380 @code{intangible} properties, they belong to separate groups; each
3381 group is separately treated as described above.
3383 When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
3384 the @code{intangible} property is ignored.
3386 Beware: this property operates at a very low level, and affects a lot of code
3387 in unexpected ways. So use it with extreme caution. A common misuse is to put
3388 an intangible property on invisible text, which is actually unnecessary since
3389 the command loop will move point outside of the invisible text at the end of
3390 each command anyway. @xref{Adjusting Point}.
3393 @kindex field @r{(text property)}
3394 Consecutive characters with the same @code{field} property constitute a
3395 @dfn{field}. Some motion functions including @code{forward-word} and
3396 @code{beginning-of-line} stop moving at a field boundary.
3400 @kindex cursor @r{(text property)}
3401 Normally, the cursor is displayed at the beginning or the end of any
3402 overlay and text property strings present at the current buffer
3403 position. You can place the cursor on any desired character of these
3404 strings by giving that character a non-@code{nil} @code{cursor} text
3405 property. In addition, if the value of the @code{cursor} property is
3406 an integer, it specifies the number of buffer's character
3407 positions, starting with the position where the overlay or the
3408 @code{display} property begins, for which the cursor should be
3409 displayed on that character. Specifically, if the value of the
3410 @code{cursor} property of a character is the number @var{n}, the
3411 cursor will be displayed on this character for any buffer position in
3412 the range @code{[@var{ovpos}..@var{ovpos}+@var{n})}, where @var{ovpos}
3413 is the overlay's starting position given by @code{overlay-start}
3414 (@pxref{Managing Overlays}), or the position where the @code{display}
3415 text property begins in the buffer.
3417 In other words, the string character with the @code{cursor} property
3418 of any non-@code{nil} value is the character where to display the
3419 cursor. The value of the property says for which buffer positions to
3420 display the cursor there. If the value is an integer @var{n},
3421 the cursor is displayed there when point is anywhere between the
3422 beginning of the overlay or @code{display} property and @var{n}
3423 positions after that. If the value is anything else and
3424 non-@code{nil}, the cursor is displayed there only when point is at
3425 the beginning of the @code{display} property or at
3426 @code{overlay-start}.
3428 @cindex cursor position for @code{display} properties and overlays
3429 When the buffer has many overlay strings (e.g., @pxref{Overlay
3430 Properties, before-string}) or @code{display} properties that are
3431 strings, it is a good idea to use the @code{cursor} property on these
3432 strings to cue the Emacs display about the places where to put the
3433 cursor while traversing these strings. This directly communicates to
3434 the display engine where the Lisp program wants to put the cursor, or
3435 where the user would expect the cursor.
3438 @kindex pointer @r{(text property)}
3439 This specifies a specific pointer shape when the mouse pointer is over
3440 this text or image. @xref{Pointer Shape}, for possible pointer
3444 @kindex line-spacing @r{(text property)}
3445 A newline can have a @code{line-spacing} text or overlay property that
3446 controls the height of the display line ending with that newline. The
3447 property value overrides the default frame line spacing and the buffer
3448 local @code{line-spacing} variable. @xref{Line Height}.
3451 @kindex line-height @r{(text property)}
3452 A newline can have a @code{line-height} text or overlay property that
3453 controls the total height of the display line ending in that newline.
3457 If text has a @code{wrap-prefix} property, the prefix it defines will
3458 be added at display time to the beginning of every continuation line
3459 due to text wrapping (so if lines are truncated, the wrap-prefix is
3460 never used). It may be a string or an image (@pxref{Other Display
3461 Specs}), or a stretch of whitespace such as specified by the
3462 @code{:width} or @code{:align-to} display properties (@pxref{Specified
3465 A wrap-prefix may also be specified for an entire buffer using the
3466 @code{wrap-prefix} buffer-local variable (however, a
3467 @code{wrap-prefix} text-property takes precedence over the value of
3468 the @code{wrap-prefix} variable). @xref{Truncation}.
3471 If text has a @code{line-prefix} property, the prefix it defines will
3472 be added at display time to the beginning of every non-continuation
3473 line. It may be a string or an image (@pxref{Other Display
3474 Specs}), or a stretch of whitespace such as specified by the
3475 @code{:width} or @code{:align-to} display properties (@pxref{Specified
3478 A line-prefix may also be specified for an entire buffer using the
3479 @code{line-prefix} buffer-local variable (however, a
3480 @code{line-prefix} text-property takes precedence over the value of
3481 the @code{line-prefix} variable). @xref{Truncation}.
3483 @item modification-hooks
3484 @cindex change hooks for a character
3485 @cindex hooks for changing a character
3486 @kindex modification-hooks @r{(text property)}
3487 If a character has the property @code{modification-hooks}, then its
3488 value should be a list of functions; modifying that character calls
3489 all of those functions before the actual modification. Each function
3490 receives two arguments: the beginning and end of the part of the
3491 buffer being modified. Note that if a particular modification hook
3492 function appears on several characters being modified by a single
3493 primitive, you can't predict how many times the function will
3495 Furthermore, insertion will not modify any existing character, so this
3496 hook will only be run when removing some characters, replacing them
3497 with others, or changing their text-properties.
3499 If these functions modify the buffer, they should bind
3500 @code{inhibit-modification-hooks} to @code{t} around doing so, to
3501 avoid confusing the internal mechanism that calls these hooks.
3503 Overlays also support the @code{modification-hooks} property, but the
3504 details are somewhat different (@pxref{Overlay Properties}).
3506 @item insert-in-front-hooks
3507 @itemx insert-behind-hooks
3508 @kindex insert-in-front-hooks @r{(text property)}
3509 @kindex insert-behind-hooks @r{(text property)}
3510 The operation of inserting text in a buffer also calls the functions
3511 listed in the @code{insert-in-front-hooks} property of the following
3512 character and in the @code{insert-behind-hooks} property of the
3513 preceding character. These functions receive two arguments, the
3514 beginning and end of the inserted text. The functions are called
3515 @emph{after} the actual insertion takes place.
3517 See also @ref{Change Hooks}, for other hooks that are called
3518 when you change text in a buffer.
3522 @cindex hooks for motion of point
3523 @kindex point-entered @r{(text property)}
3524 @kindex point-left @r{(text property)}
3525 The special properties @code{point-entered} and @code{point-left}
3526 record hook functions that report motion of point. Each time point
3527 moves, Emacs compares these two property values:
3531 the @code{point-left} property of the character after the old location,
3534 the @code{point-entered} property of the character after the new
3539 If these two values differ, each of them is called (if not @code{nil})
3540 with two arguments: the old value of point, and the new one.
3542 The same comparison is made for the characters before the old and new
3543 locations. The result may be to execute two @code{point-left} functions
3544 (which may be the same function) and/or two @code{point-entered}
3545 functions (which may be the same function). In any case, all the
3546 @code{point-left} functions are called first, followed by all the
3547 @code{point-entered} functions.
3549 It is possible to use @code{char-after} to examine characters at various
3550 buffer positions without moving point to those positions. Only an
3551 actual change in the value of point runs these hook functions.
3553 The variable @code{inhibit-point-motion-hooks} can inhibit running the
3554 @code{point-left} and @code{point-entered} hooks, see @ref{Inhibit
3555 point motion hooks}.
3558 @kindex composition @r{(text property)}
3559 This text property is used to display a sequence of characters as a
3560 single glyph composed from components. But the value of the property
3561 itself is completely internal to Emacs and should not be manipulated
3562 directly by, for instance, @code{put-text-property}.
3566 @defvar inhibit-point-motion-hooks
3567 @anchor{Inhibit point motion hooks} When this variable is
3568 non-@code{nil}, @code{point-left} and @code{point-entered} hooks are
3569 not run, and the @code{intangible} property has no effect. Do not set
3570 this variable globally; bind it with @code{let}.
3573 @defvar show-help-function
3574 @anchor{Help display} If this variable is non-@code{nil}, it specifies a
3575 function called to display help strings. These may be @code{help-echo}
3576 properties, menu help strings (@pxref{Simple Menu Items},
3577 @pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
3578 Bar}). The specified function is called with one argument, the help
3579 string to display, which is passed through
3580 @code{substitute-command-keys} before being given to the function; see
3581 @ref{Keys in Documentation}. Tooltip mode (@pxref{Tooltips,,, emacs,
3582 The GNU Emacs Manual}) provides an example.
3585 @node Format Properties
3586 @subsection Formatted Text Properties
3588 These text properties affect the behavior of the fill commands. They
3589 are used for representing formatted text. @xref{Filling}, and
3594 If a newline character has this property, it is a ``hard'' newline.
3595 The fill commands do not alter hard newlines and do not move words
3596 across them. However, this property takes effect only if the
3597 @code{use-hard-newlines} minor mode is enabled. @xref{Hard and Soft
3598 Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
3601 This property specifies an extra right margin for filling this part of the
3605 This property specifies an extra left margin for filling this part of the
3609 This property specifies the style of justification for filling this part
3613 @node Sticky Properties
3614 @subsection Stickiness of Text Properties
3615 @cindex sticky text properties
3616 @cindex inheritance, text property
3618 Self-inserting characters, the ones that get inserted into a buffer
3619 when the user types them (@pxref{Commands for Insertion}), normally
3620 take on the same properties as the preceding character. This is
3621 called @dfn{inheritance} of properties.
3623 By contrast, a Lisp program can do insertion with inheritance or without,
3624 depending on the choice of insertion primitive. The ordinary text
3625 insertion functions, such as @code{insert}, do not inherit any
3626 properties. They insert text with precisely the properties of the
3627 string being inserted, and no others. This is correct for programs
3628 that copy text from one context to another---for example, into or out
3629 of the kill ring. To insert with inheritance, use the special
3630 primitives described in this section. Self-inserting characters
3631 inherit properties because they work using these primitives.
3633 When you do insertion with inheritance, @emph{which} properties are
3634 inherited, and from where, depends on which properties are @dfn{sticky}.
3635 Insertion after a character inherits those of its properties that are
3636 @dfn{rear-sticky}. Insertion before a character inherits those of its
3637 properties that are @dfn{front-sticky}. When both sides offer different
3638 sticky values for the same property, the previous character's value
3641 By default, a text property is rear-sticky but not front-sticky; thus,
3642 the default is to inherit all the properties of the preceding character,
3643 and nothing from the following character.
3645 You can control the stickiness of various text properties with two
3646 specific text properties, @code{front-sticky} and @code{rear-nonsticky},
3647 and with the variable @code{text-property-default-nonsticky}. You can
3648 use the variable to specify a different default for a given property.
3649 You can use those two text properties to make any specific properties
3650 sticky or nonsticky in any particular part of the text.
3652 If a character's @code{front-sticky} property is @code{t}, then all
3653 its properties are front-sticky. If the @code{front-sticky} property is
3654 a list, then the sticky properties of the character are those whose
3655 names are in the list. For example, if a character has a
3656 @code{front-sticky} property whose value is @code{(face read-only)},
3657 then insertion before the character can inherit its @code{face} property
3658 and its @code{read-only} property, but no others.
3660 The @code{rear-nonsticky} property works the opposite way. Most
3661 properties are rear-sticky by default, so the @code{rear-nonsticky}
3662 property says which properties are @emph{not} rear-sticky. If a
3663 character's @code{rear-nonsticky} property is @code{t}, then none of its
3664 properties are rear-sticky. If the @code{rear-nonsticky} property is a
3665 list, properties are rear-sticky @emph{unless} their names are in the
3668 @defvar text-property-default-nonsticky
3669 This variable holds an alist which defines the default rear-stickiness
3670 of various text properties. Each element has the form
3671 @code{(@var{property} . @var{nonstickiness})}, and it defines the
3672 stickiness of a particular text property, @var{property}.
3674 If @var{nonstickiness} is non-@code{nil}, this means that the property
3675 @var{property} is rear-nonsticky by default. Since all properties are
3676 front-nonsticky by default, this makes @var{property} nonsticky in both
3677 directions by default.
3679 The text properties @code{front-sticky} and @code{rear-nonsticky}, when
3680 used, take precedence over the default @var{nonstickiness} specified in
3681 @code{text-property-default-nonsticky}.
3684 Here are the functions that insert text with inheritance of properties:
3686 @defun insert-and-inherit &rest strings
3687 Insert the strings @var{strings}, just like the function @code{insert},
3688 but inherit any sticky properties from the adjoining text.
3691 @defun insert-before-markers-and-inherit &rest strings
3692 Insert the strings @var{strings}, just like the function
3693 @code{insert-before-markers}, but inherit any sticky properties from the
3697 @xref{Insertion}, for the ordinary insertion functions which do not
3700 @node Lazy Properties
3701 @subsection Lazy Computation of Text Properties
3703 Instead of computing text properties for all the text in the buffer,
3704 you can arrange to compute the text properties for parts of the text
3705 when and if something depends on them.
3707 The primitive that extracts text from the buffer along with its
3708 properties is @code{buffer-substring}. Before examining the properties,
3709 this function runs the abnormal hook @code{buffer-access-fontify-functions}.
3711 @defvar buffer-access-fontify-functions
3712 This variable holds a list of functions for computing text properties.
3713 Before @code{buffer-substring} copies the text and text properties for a
3714 portion of the buffer, it calls all the functions in this list. Each of
3715 the functions receives two arguments that specify the range of the
3716 buffer being accessed. (The buffer itself is always the current
3720 The function @code{buffer-substring-no-properties} does not call these
3721 functions, since it ignores text properties anyway.
3723 In order to prevent the hook functions from being called more than
3724 once for the same part of the buffer, you can use the variable
3725 @code{buffer-access-fontified-property}.
3727 @defvar buffer-access-fontified-property
3728 If this variable's value is non-@code{nil}, it is a symbol which is used
3729 as a text property name. A non-@code{nil} value for that text property
3730 means the other text properties for this character have already been
3733 If all the characters in the range specified for @code{buffer-substring}
3734 have a non-@code{nil} value for this property, @code{buffer-substring}
3735 does not call the @code{buffer-access-fontify-functions} functions. It
3736 assumes these characters already have the right text properties, and
3737 just copies the properties they already have.
3739 The normal way to use this feature is that the
3740 @code{buffer-access-fontify-functions} functions add this property, as
3741 well as others, to the characters they operate on. That way, they avoid
3742 being called over and over for the same text.
3745 @node Clickable Text
3746 @subsection Defining Clickable Text
3747 @cindex clickable text
3748 @cindex follow links
3751 @dfn{Clickable text} is text that can be clicked, with either the
3752 mouse or via a keyboard command, to produce some result. Many major
3753 modes use clickable text to implement textual hyper-links, or
3754 @dfn{links} for short.
3756 The easiest way to insert and manipulate links is to use the
3757 @code{button} package. @xref{Buttons}. In this section, we will
3758 explain how to manually set up clickable text in a buffer, using text
3759 properties. For simplicity, we will refer to the clickable text as a
3762 Implementing a link involves three separate steps: (1) indicating
3763 clickability when the mouse moves over the link; (2) making @key{RET}
3764 or @kbd{Mouse-2} on that link do something; and (3) setting up a
3765 @code{follow-link} condition so that the link obeys
3766 @code{mouse-1-click-follows-link}.
3768 To indicate clickability, add the @code{mouse-face} text property to
3769 the text of the link; then Emacs will highlight the link when the
3770 mouse moves over it. In addition, you should define a tooltip or echo
3771 area message, using the @code{help-echo} text property. @xref{Special
3772 Properties}. For instance, here is how Dired indicates that file
3773 names are clickable:
3776 (if (dired-move-to-filename)
3777 (add-text-properties
3780 (dired-move-to-end-of-filename)
3782 '(mouse-face highlight
3783 help-echo "mouse-2: visit this file in other window")))
3786 To make the link clickable, bind @key{RET} and @kbd{Mouse-2} to
3787 commands that perform the desired action. Each command should check
3788 to see whether it was called on a link, and act accordingly. For
3789 instance, Dired's major mode keymap binds @kbd{Mouse-2} to the
3793 (defun dired-mouse-find-file-other-window (event)
3794 "In Dired, visit the file or directory name you click on."
3796 (let ((window (posn-window (event-end event)))
3797 (pos (posn-point (event-end event)))
3799 (if (not (windowp window))
3800 (error "No file chosen"))
3801 (with-current-buffer (window-buffer window)
3803 (setq file (dired-get-file-for-visit)))
3804 (if (file-directory-p file)
3805 (or (and (cdr dired-subdir-alist)
3806 (dired-goto-subdir file))
3808 (select-window window)
3809 (dired-other-window file)))
3810 (select-window window)
3811 (find-file-other-window (file-name-sans-versions file t)))))
3815 This command uses the functions @code{posn-window} and
3816 @code{posn-point} to determine where the click occurred, and
3817 @code{dired-get-file-for-visit} to determine which file to visit.
3819 Instead of binding the mouse command in a major mode keymap, you can
3820 bind it within the link text, using the @code{keymap} text property
3821 (@pxref{Special Properties}). For instance:
3824 (let ((map (make-sparse-keymap)))
3825 (define-key map [mouse-2] 'operate-this-button)
3826 (put-text-property link-start link-end 'keymap map))
3830 With this method, you can easily define different commands for
3831 different links. Furthermore, the global definition of @key{RET} and
3832 @kbd{Mouse-2} remain available for the rest of the text in the buffer.
3834 @vindex mouse-1-click-follows-link
3835 The basic Emacs command for clicking on links is @kbd{Mouse-2}.
3836 However, for compatibility with other graphical applications, Emacs
3837 also recognizes @kbd{Mouse-1} clicks on links, provided the user
3838 clicks on the link quickly without moving the mouse. This behavior is
3839 controlled by the user option @code{mouse-1-click-follows-link}.
3840 @xref{Mouse References,,, emacs, The GNU Emacs Manual}.
3842 @cindex follow-link (text or overlay property)
3843 To set up the link so that it obeys
3844 @code{mouse-1-click-follows-link}, you must either (1) apply a
3845 @code{follow-link} text or overlay property to the link text, or (2)
3846 bind the @code{follow-link} event to a keymap (which can be a major
3847 mode keymap or a local keymap specified via the @code{keymap} text
3848 property). The value of the @code{follow-link} property, or the
3849 binding for the @code{follow-link} event, acts as a condition for
3850 the link action. This condition tells Emacs two things: the
3851 circumstances under which a @kbd{Mouse-1} click should be regarded as
3852 occurring inside the link, and how to compute an action code
3853 that says what to translate the @kbd{Mouse-1} click into. The link
3854 action condition can be one of the following:
3857 @item @code{mouse-face}
3858 If the condition is the symbol @code{mouse-face}, a position is inside
3859 a link if there is a non-@code{nil} @code{mouse-face} property at that
3860 position. The action code is always @code{t}.
3862 For example, here is how Info mode handles @key{Mouse-1}:
3865 (define-key Info-mode-map [follow-link] 'mouse-face)
3869 If the condition is a function, @var{func}, then a position @var{pos}
3870 is inside a link if @code{(@var{func} @var{pos})} evaluates to
3871 non-@code{nil}. The value returned by @var{func} serves as the action
3874 For example, here is how pcvs enables @kbd{Mouse-1} to follow links on
3878 (define-key map [follow-link]
3880 (eq (get-char-property pos 'face) 'cvs-filename-face)))
3884 If the condition value is anything else, then the position is inside a
3885 link and the condition itself is the action code. Clearly, you should
3886 specify this kind of condition only when applying the condition via a
3887 text or property overlay on the link text (so that it does not apply
3888 to the entire buffer).
3892 The action code tells @kbd{Mouse-1} how to follow the link:
3895 @item a string or vector
3896 If the action code is a string or vector, the @kbd{Mouse-1} event is
3897 translated into the first element of the string or vector; i.e., the
3898 action of the @kbd{Mouse-1} click is the local or global binding of
3899 that character or symbol. Thus, if the action code is @code{"foo"},
3900 @kbd{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
3901 @kbd{Mouse-1} translates into @key{foo}.
3904 For any other non-@code{nil} action code, the @kbd{Mouse-1} event is
3905 translated into a @kbd{Mouse-2} event at the same position.
3908 To define @kbd{Mouse-1} to activate a button defined with
3909 @code{define-button-type}, give the button a @code{follow-link}
3910 property. The property value should be a link action condition, as
3911 described above. @xref{Buttons}. For example, here is how Help mode
3912 handles @kbd{Mouse-1}:
3915 (define-button-type 'help-xref
3917 'action #'help-button-action)
3920 To define @kbd{Mouse-1} on a widget defined with
3921 @code{define-widget}, give the widget a @code{:follow-link} property.
3922 The property value should be a link action condition, as described
3923 above. For example, here is how the @code{link} widget specifies that
3924 a @key{Mouse-1} click shall be translated to @key{RET}:
3927 (define-widget 'link 'item
3929 :button-prefix 'widget-link-prefix
3930 :button-suffix 'widget-link-suffix
3932 :help-echo "Follow the link."
3936 @defun mouse-on-link-p pos
3937 This function returns non-@code{nil} if position @var{pos} in the
3938 current buffer is on a link. @var{pos} can also be a mouse event
3939 location, as returned by @code{event-start} (@pxref{Accessing Mouse}).
3943 @subsection Defining and Using Fields
3946 A field is a range of consecutive characters in the buffer that are
3947 identified by having the same value (comparing with @code{eq}) of the
3948 @code{field} property (either a text-property or an overlay property).
3949 This section describes special functions that are available for
3950 operating on fields.
3952 You specify a field with a buffer position, @var{pos}. We think of
3953 each field as containing a range of buffer positions, so the position
3954 you specify stands for the field containing that position.
3956 When the characters before and after @var{pos} are part of the same
3957 field, there is no doubt which field contains @var{pos}: the one those
3958 characters both belong to. When @var{pos} is at a boundary between
3959 fields, which field it belongs to depends on the stickiness of the
3960 @code{field} properties of the two surrounding characters (@pxref{Sticky
3961 Properties}). The field whose property would be inherited by text
3962 inserted at @var{pos} is the field that contains @var{pos}.
3964 There is an anomalous case where newly inserted text at @var{pos}
3965 would not inherit the @code{field} property from either side. This
3966 happens if the previous character's @code{field} property is not
3967 rear-sticky, and the following character's @code{field} property is not
3968 front-sticky. In this case, @var{pos} belongs to neither the preceding
3969 field nor the following field; the field functions treat it as belonging
3970 to an empty field whose beginning and end are both at @var{pos}.
3972 In all of these functions, if @var{pos} is omitted or @code{nil}, the
3973 value of point is used by default. If narrowing is in effect, then
3974 @var{pos} should fall within the accessible portion. @xref{Narrowing}.
3976 @defun field-beginning &optional pos escape-from-edge limit
3977 This function returns the beginning of the field specified by @var{pos}.
3979 If @var{pos} is at the beginning of its field, and
3980 @var{escape-from-edge} is non-@code{nil}, then the return value is
3981 always the beginning of the preceding field that @emph{ends} at @var{pos},
3982 regardless of the stickiness of the @code{field} properties around
3985 If @var{limit} is non-@code{nil}, it is a buffer position; if the
3986 beginning of the field is before @var{limit}, then @var{limit} will be
3990 @defun field-end &optional pos escape-from-edge limit
3991 This function returns the end of the field specified by @var{pos}.
3993 If @var{pos} is at the end of its field, and @var{escape-from-edge} is
3994 non-@code{nil}, then the return value is always the end of the following
3995 field that @emph{begins} at @var{pos}, regardless of the stickiness of
3996 the @code{field} properties around @var{pos}.
3998 If @var{limit} is non-@code{nil}, it is a buffer position; if the end
3999 of the field is after @var{limit}, then @var{limit} will be returned
4003 @defun field-string &optional pos
4004 This function returns the contents of the field specified by @var{pos},
4008 @defun field-string-no-properties &optional pos
4009 This function returns the contents of the field specified by @var{pos},
4010 as a string, discarding text properties.
4013 @defun delete-field &optional pos
4014 This function deletes the text of the field specified by @var{pos}.
4017 @defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
4018 This function constrains @var{new-pos} to the field that
4019 @var{old-pos} belongs to---in other words, it returns the position
4020 closest to @var{new-pos} that is in the same field as @var{old-pos}.
4022 If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
4023 the value of point instead, and moves point to the resulting position
4024 in addition to returning that position.
4026 If @var{old-pos} is at the boundary of two fields, then the acceptable
4027 final positions depend on the argument @var{escape-from-edge}. If
4028 @var{escape-from-edge} is @code{nil}, then @var{new-pos} must be in
4029 the field whose @code{field} property equals what new characters
4030 inserted at @var{old-pos} would inherit. (This depends on the
4031 stickiness of the @code{field} property for the characters before and
4032 after @var{old-pos}.) If @var{escape-from-edge} is non-@code{nil},
4033 @var{new-pos} can be anywhere in the two adjacent fields.
4034 Additionally, if two fields are separated by another field with the
4035 special value @code{boundary}, then any point within this special
4036 field is also considered to be on the boundary.
4038 Commands like @kbd{C-a} with no argument, that normally move backward
4039 to a specific kind of location and stay there once there, probably
4040 should specify @code{nil} for @var{escape-from-edge}. Other motion
4041 commands that check fields should probably pass @code{t}.
4043 If the optional argument @var{only-in-line} is non-@code{nil}, and
4044 constraining @var{new-pos} in the usual way would move it to a different
4045 line, @var{new-pos} is returned unconstrained. This used in commands
4046 that move by line, such as @code{next-line} and
4047 @code{beginning-of-line}, so that they respect field boundaries only in
4048 the case where they can still move to the right line.
4050 If the optional argument @var{inhibit-capture-property} is
4051 non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
4052 name, then any field boundaries are ignored.
4054 You can cause @code{constrain-to-field} to ignore all field boundaries
4055 (and so never constrain anything) by binding the variable
4056 @code{inhibit-field-text-motion} to a non-@code{nil} value.
4060 @subsection Why Text Properties are not Intervals
4063 Some editors that support adding attributes to text in the buffer do
4064 so by letting the user specify intervals within the text, and adding
4065 the properties to the intervals. Those editors permit the user or the
4066 programmer to determine where individual intervals start and end. We
4067 deliberately provided a different sort of interface in Emacs Lisp to
4068 avoid certain paradoxical behavior associated with text modification.
4070 If the actual subdivision into intervals is meaningful, that means you
4071 can distinguish between a buffer that is just one interval with a
4072 certain property, and a buffer containing the same text subdivided into
4073 two intervals, both of which have that property.
4075 Suppose you take the buffer with just one interval and kill part of
4076 the text. The text remaining in the buffer is one interval, and the
4077 copy in the kill ring (and the undo list) becomes a separate interval.
4078 Then if you yank back the killed text, you get two intervals with the
4079 same properties. Thus, editing does not preserve the distinction
4080 between one interval and two.
4082 Suppose we attempt to fix this problem by coalescing the two intervals when
4083 the text is inserted. That works fine if the buffer originally was a
4084 single interval. But suppose instead that we have two adjacent
4085 intervals with the same properties, and we kill the text of one interval
4086 and yank it back. The same interval-coalescence feature that rescues
4087 the other case causes trouble in this one: after yanking, we have just
4088 one interval. Once again, editing does not preserve the distinction
4089 between one interval and two.
4091 Insertion of text at the border between intervals also raises
4092 questions that have no satisfactory answer.
4094 However, it is easy to arrange for editing to behave consistently
4095 for questions of the form, ``What are the properties of text at this
4096 buffer or string position?'' So we have decided these are the only
4097 questions that make sense; we have not implemented asking questions
4098 about where intervals start or end.
4100 In practice, you can usually use the text property search functions in
4101 place of explicit interval boundaries. You can think of them as finding
4102 the boundaries of intervals, assuming that intervals are always
4103 coalesced whenever possible. @xref{Property Search}.
4105 Emacs also provides explicit intervals as a presentation feature; see
4109 @section Substituting for a Character Code
4110 @cindex replace characters in region
4111 @cindex substitute characters
4113 The following functions replace characters within a specified region
4114 based on their character codes.
4116 @defun subst-char-in-region start end old-char new-char &optional noundo
4117 @cindex replace characters
4118 This function replaces all occurrences of the character @var{old-char}
4119 with the character @var{new-char} in the region of the current buffer
4120 defined by @var{start} and @var{end}.
4122 @cindex undo avoidance
4123 If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
4124 not record the change for undo and does not mark the buffer as modified.
4125 This was useful for controlling the old selective display feature
4126 (@pxref{Selective Display}).
4128 @code{subst-char-in-region} does not move point and returns
4133 ---------- Buffer: foo ----------
4134 This is the contents of the buffer before.
4135 ---------- Buffer: foo ----------
4139 (subst-char-in-region 1 20 ?i ?X)
4142 ---------- Buffer: foo ----------
4143 ThXs Xs the contents of the buffer before.
4144 ---------- Buffer: foo ----------
4149 @deffn Command translate-region start end table
4150 This function applies a translation table to the characters in the
4151 buffer between positions @var{start} and @var{end}.
4153 The translation table @var{table} is a string or a char-table;
4154 @code{(aref @var{table} @var{ochar})} gives the translated character
4155 corresponding to @var{ochar}. If @var{table} is a string, any
4156 characters with codes larger than the length of @var{table} are not
4157 altered by the translation.
4159 The return value of @code{translate-region} is the number of
4160 characters that were actually changed by the translation. This does
4161 not count characters that were mapped into themselves in the
4169 A register is a sort of variable used in Emacs editing that can hold a
4170 variety of different kinds of values. Each register is named by a
4171 single character. All @acronym{ASCII} characters and their meta variants
4172 (but with the exception of @kbd{C-g}) can be used to name registers.
4173 Thus, there are 255 possible registers. A register is designated in
4174 Emacs Lisp by the character that is its name.
4176 @defvar register-alist
4177 This variable is an alist of elements of the form @code{(@var{name} .
4178 @var{contents})}. Normally, there is one element for each Emacs
4179 register that has been used.
4181 The object @var{name} is a character (an integer) identifying the
4185 The @var{contents} of a register can have several possible types:
4189 A number stands for itself. If @code{insert-register} finds a number
4190 in the register, it converts the number to decimal.
4193 A marker represents a buffer position to jump to.
4196 A string is text saved in the register.
4199 A rectangle is represented by a list of strings.
4201 @item @code{(@var{window-configuration} @var{position})}
4202 This represents a window configuration to restore in one frame, and a
4203 position to jump to in the current buffer.
4205 @c FIXME: Mention frameset here.
4206 @item @code{(@var{frame-configuration} @var{position})}
4207 This represents a frame configuration to restore, and a position
4208 to jump to in the current buffer.
4210 @item (file @var{filename})
4211 This represents a file to visit; jumping to this value visits file
4214 @item (file-query @var{filename} @var{position})
4215 This represents a file to visit and a position in it; jumping to this
4216 value visits file @var{filename} and goes to buffer position
4217 @var{position}. Restoring this type of position asks the user for
4221 The functions in this section return unpredictable values unless
4224 @defun get-register reg
4225 This function returns the contents of the register
4226 @var{reg}, or @code{nil} if it has no contents.
4229 @defun set-register reg value
4230 This function sets the contents of register @var{reg} to @var{value}.
4231 A register can be set to any value, but the other register functions
4232 expect only certain data types. The return value is @var{value}.
4235 @deffn Command view-register reg
4236 This command displays what is contained in register @var{reg}.
4239 @deffn Command insert-register reg &optional beforep
4240 This command inserts contents of register @var{reg} into the current
4243 Normally, this command puts point before the inserted text, and the
4244 mark after it. However, if the optional second argument @var{beforep}
4245 is non-@code{nil}, it puts the mark before and point after.
4247 When called interactively, the command defaults to putting point after
4248 text, and a prefix argument inverts this behavior.
4250 If the register contains a rectangle, then the rectangle is inserted
4251 with its upper left corner at point. This means that text is inserted
4252 in the current line and underneath it on successive lines.
4254 If the register contains something other than saved text (a string) or
4255 a rectangle (a list), currently useless things happen. This may be
4256 changed in the future.
4259 @defun register-read-with-preview prompt
4260 @cindex register preview
4261 This function reads and returns a register name, prompting with
4262 @var{prompt} and possibly showing a preview of the existing registers
4263 and their contents. The preview is shown in a temporary window, after
4264 the delay specified by the user option @code{register-preview-delay},
4265 if its value and @code{register-alist} are both non-@code{nil}. The
4266 preview is also shown if the user requests help (e.g., by typing the
4267 help character). We recommend that all interactive commands which
4268 read register names use this function.
4272 @section Transposition of Text
4274 This function can be used to transpose stretches of text:
4276 @defun transpose-regions start1 end1 start2 end2 &optional leave-markers
4277 This function exchanges two nonoverlapping portions of the buffer.
4278 Arguments @var{start1} and @var{end1} specify the bounds of one portion
4279 and arguments @var{start2} and @var{end2} specify the bounds of the
4282 Normally, @code{transpose-regions} relocates markers with the transposed
4283 text; a marker previously positioned within one of the two transposed
4284 portions moves along with that portion, thus remaining between the same
4285 two characters in their new position. However, if @var{leave-markers}
4286 is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
4287 all markers unrelocated.
4291 @section Dealing With Compressed Data
4293 When @code{auto-compression-mode} is enabled, Emacs automatically
4294 uncompresses compressed files when you visit them, and automatically
4295 recompresses them if you alter and save them. @xref{Compressed
4296 Files,,, emacs, The GNU Emacs Manual}.
4298 The above feature works by calling an external executable (e.g.,
4299 @command{gzip}). Emacs can also be compiled with support for built-in
4300 decompression using the zlib library, which is faster than calling an
4303 @defun zlib-available-p
4304 This function returns non-@code{nil} if built-in zlib decompression is
4308 @defun zlib-decompress-region start end
4309 This function decompresses the region between @var{start} and
4310 @var{end}, using built-in zlib decompression. The region should
4311 contain data that were compressed with gzip or zlib. On success, the
4312 function replaces the contents of the region with the decompressed
4313 data. On failure, the function leaves the region unchanged and
4314 returns @code{nil}. This function can be called only in unibyte
4320 @section Base 64 Encoding
4321 @cindex base 64 encoding
4323 Base 64 code is used in email to encode a sequence of 8-bit bytes as
4324 a longer sequence of @acronym{ASCII} graphic characters. It is defined in
4325 Internet RFC@footnote{
4326 An RFC, an acronym for @dfn{Request for Comments}, is a numbered
4327 Internet informational document describing a standard. RFCs are
4328 usually written by technical experts acting on their own initiative,
4329 and are traditionally written in a pragmatic, experience-driven
4331 }2045. This section describes the functions for
4332 converting to and from this code.
4334 @deffn Command base64-encode-region beg end &optional no-line-break
4335 This function converts the region from @var{beg} to @var{end} into base
4336 64 code. It returns the length of the encoded text. An error is
4337 signaled if a character in the region is multibyte, i.e., in a
4338 multibyte buffer the region must contain only characters from the
4339 charsets @code{ascii}, @code{eight-bit-control} and
4340 @code{eight-bit-graphic}.
4342 Normally, this function inserts newline characters into the encoded
4343 text, to avoid overlong lines. However, if the optional argument
4344 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4345 the output is just one long line.
4348 @defun base64-encode-string string &optional no-line-break
4349 This function converts the string @var{string} into base 64 code. It
4350 returns a string containing the encoded text. As for
4351 @code{base64-encode-region}, an error is signaled if a character in the
4352 string is multibyte.
4354 Normally, this function inserts newline characters into the encoded
4355 text, to avoid overlong lines. However, if the optional argument
4356 @var{no-line-break} is non-@code{nil}, these newlines are not added, so
4357 the result string is just one long line.
4360 @deffn Command base64-decode-region beg end
4361 This function converts the region from @var{beg} to @var{end} from base
4362 64 code into the corresponding decoded text. It returns the length of
4365 The decoding functions ignore newline characters in the encoded text.
4368 @defun base64-decode-string string
4369 This function converts the string @var{string} from base 64 code into
4370 the corresponding decoded text. It returns a unibyte string containing the
4373 The decoding functions ignore newline characters in the encoded text.
4377 @section Checksum/Hash
4378 @cindex MD5 checksum
4380 @cindex hash, cryptographic
4381 @cindex cryptographic hash
4383 Emacs has built-in support for computing @dfn{cryptographic hashes}.
4384 A cryptographic hash, or @dfn{checksum}, is a digital fingerprint
4385 of a piece of data (e.g., a block of text) which can be used to check
4386 that you have an unaltered copy of that data.
4388 @cindex message digest
4389 Emacs supports several common cryptographic hash algorithms: MD5,
4390 SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512. MD5 is the
4391 oldest of these algorithms, and is commonly used in @dfn{message
4392 digests} to check the integrity of messages transmitted over a
4393 network. MD5 is not collision resistant (i.e., it is possible to
4394 deliberately design different pieces of data which have the same MD5
4395 hash), so you should not used it for anything security-related. A
4396 similar theoretical weakness also exists in SHA-1. Therefore, for
4397 security-related applications you should use the other hash types,
4400 @defun secure-hash algorithm object &optional start end binary
4401 This function returns a hash for @var{object}. The argument
4402 @var{algorithm} is a symbol stating which hash to compute: one of
4403 @code{md5}, @code{sha1}, @code{sha224}, @code{sha256}, @code{sha384}
4404 or @code{sha512}. The argument @var{object} should be a buffer or a
4407 The optional arguments @var{start} and @var{end} are character
4408 positions specifying the portion of @var{object} to compute the
4409 message digest for. If they are @code{nil} or omitted, the hash is
4410 computed for the whole of @var{object}.
4412 If the argument @var{binary} is omitted or @code{nil}, the function
4413 returns the @dfn{text form} of the hash, as an ordinary Lisp string.
4414 If @var{binary} is non-@code{nil}, it returns the hash in @dfn{binary
4415 form}, as a sequence of bytes stored in a unibyte string.
4417 This function does not compute the hash directly from the internal
4418 representation of @var{object}'s text (@pxref{Text Representations}).
4419 Instead, it encodes the text using a coding system (@pxref{Coding
4420 Systems}), and computes the hash from that encoded text. If
4421 @var{object} is a buffer, the coding system used is the one which
4422 would be chosen by default for writing the text into a file. If
4423 @var{object} is a string, the user's preferred coding system is used
4424 (@pxref{Recognize Coding,,, emacs, GNU Emacs Manual}).
4427 @defun md5 object &optional start end coding-system noerror
4428 This function returns an MD5 hash. It is semi-obsolete, since for
4429 most purposes it is equivalent to calling @code{secure-hash} with
4430 @code{md5} as the @var{algorithm} argument. The @var{object},
4431 @var{start} and @var{end} arguments have the same meanings as in
4434 If @var{coding-system} is non-@code{nil}, it specifies a coding system
4435 to use to encode the text; if omitted or @code{nil}, the default
4436 coding system is used, like in @code{secure-hash}.
4438 Normally, @code{md5} signals an error if the text can't be encoded
4439 using the specified or chosen coding system. However, if
4440 @var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
4444 @node Parsing HTML/XML
4445 @section Parsing HTML and XML
4446 @cindex parsing html
4448 When Emacs is compiled with libxml2 support, the following functions
4449 are available to parse HTML or XML text into Lisp object trees.
4451 @defun libxml-parse-html-region start end &optional base-url discard-comments
4452 This function parses the text between @var{start} and @var{end} as
4453 HTML, and returns a list representing the HTML @dfn{parse tree}. It
4454 attempts to handle real-world HTML by robustly coping with syntax
4457 The optional argument @var{base-url}, if non-@code{nil}, should be a
4458 string specifying the base URL for relative URLs occurring in links.
4460 If the optional argument @var{discard-comments} is non-@code{nil},
4461 then the parse tree is created without any comments.
4463 In the parse tree, each HTML node is represented by a list in which
4464 the first element is a symbol representing the node name, the second
4465 element is an alist of node attributes, and the remaining elements are
4468 The following example demonstrates this. Given this (malformed) HTML
4472 <html><head></head><body width=101><div class=thing>Foo<div>Yes
4476 A call to @code{libxml-parse-html-region} returns this @acronym{DOM}
4477 (document object model):
4482 (body ((width . "101"))
4483 (div ((class . "thing"))
4490 @cindex rendering html
4491 @defun shr-insert-document dom
4492 This function renders the parsed HTML in @var{dom} into the current
4493 buffer. The argument @var{dom} should be a list as generated by
4494 @code{libxml-parse-html-region}. This function is, e.g., used by
4495 @ref{Top, EWW,, eww, The Emacs Web Wowser Manual}.
4499 @defun libxml-parse-xml-region start end &optional base-url discard-comments
4500 This function is the same as @code{libxml-parse-html-region}, except
4501 that it parses the text as XML rather than HTML (so it is stricter
4506 * Document Object Model:: Access, manipulate and search the @acronym{DOM}.
4509 @node Document Object Model
4510 @subsection Document Object Model
4514 @cindex Document Object Model
4516 The @acronym{DOM} returned by @code{libxml-parse-html-region} (and the
4517 other @acronym{XML} parsing functions) is a tree structure where each
4518 node has a node name (called a @dfn{tag}), and optional key/value
4519 @dfn{attribute} list, and then a list of @dfn{child nodes}. The child
4520 nodes are either strings or @acronym{DOM} objects.
4523 (body ((width . "101"))
4524 (div ((class . "thing"))
4530 @defun dom-node tag &optional attributes &rest children
4531 This function creates a @acronym{DOM} node of type @var{tag}. If
4532 given, @var{attributes} should be a key/value pair list.
4533 If given, @var{children} should be @acronym{DOM} nodes.
4536 The following functions can be used to work with this structure. Each
4537 function takes a @acronym{DOM} node, or a list of nodes. In the
4538 latter case, only the first node in the list is used.
4543 @item dom-tag @var{node}
4544 Return the @dfn{tag} (also called ``node name'') of the node.
4546 @item dom-attr @var{node} @var{attribute}
4547 Return the value of @var{attribute} in the node. A common usage
4551 (dom-attr img 'href)
4552 => "http://fsf.org/logo.png"
4555 @item dom-children @var{node}
4556 Return all the children of the node.
4558 @item dom-non-text-children @var{node}
4559 Return all the non-string children of the node.
4561 @item dom-attributes @var{node}
4562 Return the key/value pair list of attributes of the node.
4564 @item dom-text @var{node}
4565 Return all the textual elements of the node as a concatenated string.
4567 @item dom-texts @var{node}
4568 Return all the textual elements of the node, as well as the textual
4569 elements of all the children of the node, recursively, as a
4570 concatenated string. This function also takes an optional separator
4571 to be inserted between the textual elements.
4573 @item dom-parent @var{dom} @var{node}
4574 Return the parent of @var{node} in @var{dom}.
4577 The following are functions for altering the @acronym{DOM}.
4580 @item dom-set-attribute @var{node} @var{attribute} @var{value}
4581 Set the @var{attribute} of the node to @var{value}.
4583 @item dom-append-child @var{node} @var{child}
4584 Append @var{child} as the last child of @var{node}.
4586 @item dom-add-child-before @var{node} @var{child} @var{before}
4587 Add @var{child} to @var{node}'s child list before the @var{before}
4588 node. If @var{before} is @code{nil}, make @var{child} the first child.
4590 @item dom-set-attributes @var{node} @var{attributes}
4591 Replace all the attributes of the node with a new key/value list.
4594 The following are functions for searching for elements in the
4595 @acronym{DOM}. They all return lists of matching nodes.
4598 @item dom-by-tag @var{dom} @var{tag}
4599 Return all nodes in @var{dom} that are of type @var{tag}. A typical
4603 (dom-by-tag dom 'td)
4604 => '((td ...) (td ...) (td ...))
4607 @item dom-by-class @var{dom} @var{match}
4608 Return all nodes in @var{dom} that have class names that match
4609 @var{match}, which is a regular expression.
4611 @item dom-by-style @var{dom} @var{style}
4612 Return all nodes in @var{dom} that have styles that match @var{match},
4613 which is a regular expression.
4615 @item dom-by-id @var{dom} @var{style}
4616 Return all nodes in @var{dom} that have IDs that match @var{match},
4617 which is a regular expression.
4619 @item dom-strings @var{dom}
4620 Return all strings in @var{DOM}.
4627 @item dom-pp @var{dom} &optional @var{remove-empty}
4628 Pretty-print @var{dom} at point. If @var{remove-empty}, don't print
4629 textual nodes that just contain white-space.
4633 @node Atomic Changes
4634 @section Atomic Change Groups
4635 @cindex atomic changes
4637 In database terminology, an @dfn{atomic} change is an indivisible
4638 change---it can succeed entirely or it can fail entirely, but it
4639 cannot partly succeed. A Lisp program can make a series of changes to
4640 one or several buffers as an @dfn{atomic change group}, meaning that
4641 either the entire series of changes will be installed in their buffers
4642 or, in case of an error, none of them will be.
4644 To do this for one buffer, the one already current, simply write a
4645 call to @code{atomic-change-group} around the code that makes the
4649 (atomic-change-group
4651 (delete-region x y))
4655 If an error (or other nonlocal exit) occurs inside the body of
4656 @code{atomic-change-group}, it unmakes all the changes in that buffer
4657 that were during the execution of the body. This kind of change group
4658 has no effect on any other buffers---any such changes remain.
4660 If you need something more sophisticated, such as to make changes in
4661 various buffers constitute one atomic group, you must directly call
4662 lower-level functions that @code{atomic-change-group} uses.
4664 @defun prepare-change-group &optional buffer
4665 This function sets up a change group for buffer @var{buffer}, which
4666 defaults to the current buffer. It returns a handle that
4667 represents the change group. You must use this handle to activate the
4668 change group and subsequently to finish it.
4671 To use the change group, you must @dfn{activate} it. You must do
4672 this before making any changes in the text of @var{buffer}.
4674 @defun activate-change-group handle
4675 This function activates the change group that @var{handle} designates.
4678 After you activate the change group, any changes you make in that
4679 buffer become part of it. Once you have made all the desired changes
4680 in the buffer, you must @dfn{finish} the change group. There are two
4681 ways to do this: you can either accept (and finalize) all the changes,
4684 @defun accept-change-group handle
4685 This function accepts all the changes in the change group specified by
4686 @var{handle}, making them final.
4689 @defun cancel-change-group handle
4690 This function cancels and undoes all the changes in the change group
4691 specified by @var{handle}.
4694 Your code should use @code{unwind-protect} to make sure the group is
4695 always finished. The call to @code{activate-change-group} should be
4696 inside the @code{unwind-protect}, in case the user types @kbd{C-g}
4697 just after it runs. (This is one reason why
4698 @code{prepare-change-group} and @code{activate-change-group} are
4699 separate functions, because normally you would call
4700 @code{prepare-change-group} before the start of that
4701 @code{unwind-protect}.) Once you finish the group, don't use the
4702 handle again---in particular, don't try to finish the same group
4705 To make a multibuffer change group, call @code{prepare-change-group}
4706 once for each buffer you want to cover, then use @code{nconc} to
4707 combine the returned values, like this:
4710 (nconc (prepare-change-group buffer-1)
4711 (prepare-change-group buffer-2))
4714 You can then activate the multibuffer change group with a single call
4715 to @code{activate-change-group}, and finish it with a single call to
4716 @code{accept-change-group} or @code{cancel-change-group}.
4718 Nested use of several change groups for the same buffer works as you
4719 would expect. Non-nested use of change groups for the same buffer
4720 will get Emacs confused, so don't let it happen; the first change
4721 group you start for any given buffer should be the last one finished.
4724 @section Change Hooks
4725 @cindex change hooks
4726 @cindex hooks for text changes
4728 These hook variables let you arrange to take notice of all changes in
4729 all buffers (or in a particular buffer, if you make them buffer-local).
4730 See also @ref{Special Properties}, for how to detect changes to specific
4733 The functions you use in these hooks should save and restore the match
4734 data if they do anything that uses regular expressions; otherwise, they
4735 will interfere in bizarre ways with the editing operations that call
4738 @defvar before-change-functions
4739 This variable holds a list of functions to call before any buffer
4740 modification. Each function gets two arguments, the beginning and end
4741 of the region that is about to change, represented as integers. The
4742 buffer that is about to change is always the current buffer.
4745 @defvar after-change-functions
4746 This variable holds a list of functions to call after any buffer
4747 modification. Each function receives three arguments: the beginning
4748 and end of the region just changed, and the length of the text that
4749 existed before the change. All three arguments are integers. The
4750 buffer that has been changed is always the current buffer.
4752 The length of the old text is the difference between the buffer
4753 positions before and after that text as it was before the change. As
4754 for the changed text, its length is simply the difference between the
4755 first two arguments.
4758 Output of messages into the @file{*Messages*} buffer does not
4759 call these functions.
4761 @defmac combine-after-change-calls body@dots{}
4762 The macro executes @var{body} normally, but arranges to call the
4763 after-change functions just once for a series of several changes---if
4766 If a program makes several text changes in the same area of the buffer,
4767 using the macro @code{combine-after-change-calls} around that part of
4768 the program can make it run considerably faster when after-change hooks
4769 are in use. When the after-change hooks are ultimately called, the
4770 arguments specify a portion of the buffer including all of the changes
4771 made within the @code{combine-after-change-calls} body.
4773 @strong{Warning:} You must not alter the values of
4774 @code{after-change-functions} within
4775 the body of a @code{combine-after-change-calls} form.
4777 @strong{Warning:} if the changes you combine occur in widely scattered
4778 parts of the buffer, this will still work, but it is not advisable,
4779 because it may lead to inefficient behavior for some change hook
4783 @defvar first-change-hook
4784 This variable is a normal hook that is run whenever a buffer is changed
4785 that was previously in the unmodified state.
4788 @defvar inhibit-modification-hooks
4789 If this variable is non-@code{nil}, all of the change hooks are
4790 disabled; none of them run. This affects all the hook variables
4791 described above in this section, as well as the hooks attached to
4792 certain special text properties (@pxref{Special Properties}) and overlay
4793 properties (@pxref{Overlay Properties}).
4795 Also, this variable is bound to non-@code{nil} while running those
4796 same hook variables, so that by default modifying the buffer from
4797 a modification hook does not cause other modification hooks to be run.
4798 If you do want modification hooks to be run in a particular piece of
4799 code that is itself run from a modification hook, then rebind locally
4800 @code{inhibit-modification-hooks} to @code{nil}.