Another doc fix for `buffer-undo-list'.
[bpt/emacs.git] / doc / lispref / text.texi
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1@c -*-texinfo-*-
2@c This is part of the GNU Emacs Lisp Reference Manual.
ab422c4d 3@c Copyright (C) 1990-1995, 1998-2013 Free Software Foundation, Inc.
b8d4c8d0 4@c See the file elisp.texi for copying conditions.
ecc6530d 5@node Text
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6@chapter Text
7@cindex text
8
9 This chapter describes the functions that deal with the text in a
10buffer. Most examine, insert, or delete text in the current buffer,
11often operating at point or on text adjacent to point. Many are
12interactive. All the functions that change the text provide for undoing
13the changes (@pxref{Undo}).
14
15 Many text-related functions operate on a region of text defined by two
16buffer positions passed in arguments named @var{start} and @var{end}.
17These arguments should be either markers (@pxref{Markers}) or numeric
18character positions (@pxref{Positions}). The order of these arguments
19does not matter; it is all right for @var{start} to be the end of the
20region and @var{end} the beginning. For example, @code{(delete-region 1
2110)} 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
24interactive call, point and the mark are used for these arguments.
25
26@cindex buffer contents
27 Throughout this chapter, ``text'' refers to the characters in the
28buffer, together with their properties (when relevant). Keep in mind
29that point is always between two characters, and the cursor appears on
30the character after point.
31
32@menu
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.
d24880de 43 How to control how much information is kept.
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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.
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54* Registers:: How registers are implemented. Accessing the text or
55 position stored in a register.
d4913798 56* Transposition:: Swapping two portions of a buffer.
b8d4c8d0 57* Base 64:: Conversion to or from base 64 encoding.
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58* Checksum/Hash:: Computing cryptographic hashes.
59* Parsing HTML/XML:: Parsing HTML and XML.
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60* Atomic Changes:: Installing several buffer changes "atomically".
61* Change Hooks:: Supplying functions to be run when text is changed.
62@end menu
63
64@node Near Point
65@section Examining Text Near Point
66@cindex text near point
67
68 Many functions are provided to look at the characters around point.
69Several simple functions are described here. See also @code{looking-at}
70in @ref{Regexp Search}.
71
72In the following four functions, ``beginning'' or ``end'' of buffer
73refers to the beginning or end of the accessible portion.
74
75@defun char-after &optional position
76This function returns the character in the current buffer at (i.e.,
77immediately after) position @var{position}. If @var{position} is out of
78range for this purpose, either before the beginning of the buffer, or at
79or beyond the end, then the value is @code{nil}. The default for
80@var{position} is point.
81
82In the following example, assume that the first character in the
83buffer is @samp{@@}:
84
85@example
86@group
3e99b825 87(string (char-after 1))
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88 @result{} "@@"
89@end group
90@end example
91@end defun
92
93@defun char-before &optional position
94This function returns the character in the current buffer immediately
95before position @var{position}. If @var{position} is out of range for
96this purpose, either at or before the beginning of the buffer, or beyond
97the end, then the value is @code{nil}. The default for
98@var{position} is point.
99@end defun
100
101@defun following-char
102This function returns the character following point in the current
103buffer. This is similar to @code{(char-after (point))}. However, if
104point is at the end of the buffer, then @code{following-char} returns 0.
105
106Remember that point is always between characters, and the cursor
107normally appears over the character following point. Therefore, the
108character returned by @code{following-char} is the character the
109cursor is over.
110
111In this example, point is between the @samp{a} and the @samp{c}.
112
113@example
114@group
115---------- Buffer: foo ----------
116Gentlemen may cry ``Pea@point{}ce! Peace!,''
117but there is no peace.
118---------- Buffer: foo ----------
119@end group
120
121@group
3e99b825 122(string (preceding-char))
b8d4c8d0 123 @result{} "a"
3e99b825 124(string (following-char))
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125 @result{} "c"
126@end group
127@end example
128@end defun
129
130@defun preceding-char
131This function returns the character preceding point in the current
132buffer. See above, under @code{following-char}, for an example. If
133point is at the beginning of the buffer, @code{preceding-char} returns
1340.
135@end defun
136
137@defun bobp
138This function returns @code{t} if point is at the beginning of the
139buffer. If narrowing is in effect, this means the beginning of the
140accessible portion of the text. See also @code{point-min} in
141@ref{Point}.
142@end defun
143
144@defun eobp
145This function returns @code{t} if point is at the end of the buffer.
146If narrowing is in effect, this means the end of accessible portion of
147the text. See also @code{point-max} in @xref{Point}.
148@end defun
149
150@defun bolp
151This function returns @code{t} if point is at the beginning of a line.
152@xref{Text Lines}. The beginning of the buffer (or of its accessible
153portion) always counts as the beginning of a line.
154@end defun
155
156@defun eolp
157This function returns @code{t} if point is at the end of a line. The
158end of the buffer (or of its accessible portion) is always considered
159the end of a line.
160@end defun
161
162@node Buffer Contents
163@section Examining Buffer Contents
164
165 This section describes functions that allow a Lisp program to
166convert any portion of the text in the buffer into a string.
167
168@defun buffer-substring start end
169This function returns a string containing a copy of the text of the
170region defined by positions @var{start} and @var{end} in the current
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171buffer. If the arguments are not positions in the accessible portion
172of the buffer, @code{buffer-substring} signals an
173@code{args-out-of-range} error.
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174
175Here's an example which assumes Font-Lock mode is not enabled:
176
177@example
178@group
179---------- Buffer: foo ----------
180This is the contents of buffer foo
181
182---------- Buffer: foo ----------
183@end group
184
185@group
186(buffer-substring 1 10)
187 @result{} "This is t"
188@end group
189@group
190(buffer-substring (point-max) 10)
191 @result{} "he contents of buffer foo\n"
192@end group
193@end example
194
195If the text being copied has any text properties, these are copied into
196the string along with the characters they belong to. @xref{Text
197Properties}. However, overlays (@pxref{Overlays}) in the buffer and
198their properties are ignored, not copied.
199
200For example, if Font-Lock mode is enabled, you might get results like
201these:
202
203@example
204@group
205(buffer-substring 1 10)
206 @result{} #("This is t" 0 1 (fontified t) 1 9 (fontified t))
207@end group
208@end example
209@end defun
210
211@defun buffer-substring-no-properties start end
212This is like @code{buffer-substring}, except that it does not copy text
213properties, just the characters themselves. @xref{Text Properties}.
214@end defun
215
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216@defun buffer-string
217This function returns the contents of the entire accessible portion of
84f4a531 218the current buffer, as a string.
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219@end defun
220
34c99998 221@defun filter-buffer-substring start end &optional delete
b8d4c8d0 222This function passes the buffer text between @var{start} and @var{end}
34c99998 223through the filter functions specified by the wrapper hook
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224@code{filter-buffer-substring-functions}, and returns the result. The
225obsolete variable @code{buffer-substring-filters} is also consulted.
226If both of these variables are @code{nil}, the value is the unaltered
1df7defd 227text from the buffer, i.e., what @code{buffer-substring} would
67cd45a2 228return.
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229
230If @var{delete} is non-@code{nil}, this function deletes the text
231between @var{start} and @var{end} after copying it, like
232@code{delete-and-extract-region}.
233
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234Lisp code should use this function instead of @code{buffer-substring},
235@code{buffer-substring-no-properties},
236or @code{delete-and-extract-region} when copying into user-accessible
237data structures such as the kill-ring, X clipboard, and registers.
238Major and minor modes can add functions to
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239@code{filter-buffer-substring-functions} to alter such text as it is
240copied out of the buffer.
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241@end defun
242
2bede2ed 243@c FIXME: `filter-buffer-substring-function' should be documented.
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244@defvar filter-buffer-substring-functions
245This variable is a wrapper hook (@pxref{Running Hooks}), whose members
246should be functions that accept four arguments: @var{fun},
247@var{start}, @var{end}, and @var{delete}. @var{fun} is a function
248that takes three arguments (@var{start}, @var{end}, and @var{delete}),
249and returns a string. In both cases, the @var{start}, @var{end}, and
250@var{delete} arguments are the same as those of
251@code{filter-buffer-substring}.
252
253The first hook function is passed a @var{fun} that is equivalent to
1df7defd 254the default operation of @code{filter-buffer-substring}, i.e., it
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255returns the buffer-substring between @var{start} and @var{end}
256(processed by any @code{buffer-substring-filters}) and optionally
257deletes the original text from the buffer. In most cases, the hook
258function will call @var{fun} once, and then do its own processing of
259the result. The next hook function receives a @var{fun} equivalent to
260this, and so on. The actual return value is the result of all the
261hook functions acting in sequence.
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262@end defvar
263
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264@defvar buffer-substring-filters
265This variable is obsoleted by
266@code{filter-buffer-substring-functions}, but is still supported for
267backward compatibility. Its value should should be a list of
268functions which accept a single string argument and return another
269string. @code{filter-buffer-substring} passes the buffer substring to
270the first function in this list, and the return value of each function
271is passed to the next function. The return value of the last function
272is passed to @code{filter-buffer-substring-functions}.
273@end defvar
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274
275@defun current-word &optional strict really-word
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276This function returns the symbol (or word) at or near point, as a
277string. The return value includes no text properties.
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278
279If the optional argument @var{really-word} is non-@code{nil}, it finds a
280word; otherwise, it finds a symbol (which includes both word
281characters and symbol constituent characters).
282
283If the optional argument @var{strict} is non-@code{nil}, then point
284must be in or next to the symbol or word---if no symbol or word is
285there, the function returns @code{nil}. Otherwise, a nearby symbol or
286word on the same line is acceptable.
287@end defun
288
289@defun thing-at-point thing
290Return the @var{thing} around or next to point, as a string.
291
292The argument @var{thing} is a symbol which specifies a kind of syntactic
293entity. Possibilities include @code{symbol}, @code{list}, @code{sexp},
294@code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
295@code{whitespace}, @code{line}, @code{page}, and others.
296
297@example
298---------- Buffer: foo ----------
299Gentlemen may cry ``Pea@point{}ce! Peace!,''
300but there is no peace.
301---------- Buffer: foo ----------
302
303(thing-at-point 'word)
304 @result{} "Peace"
305(thing-at-point 'line)
306 @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
307(thing-at-point 'whitespace)
308 @result{} nil
309@end example
310@end defun
311
312@node Comparing Text
313@section Comparing Text
314@cindex comparing buffer text
315
316 This function lets you compare portions of the text in a buffer, without
317copying them into strings first.
318
319@defun compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2
320This function lets you compare two substrings of the same buffer or two
321different buffers. The first three arguments specify one substring,
322giving a buffer (or a buffer name) and two positions within the
323buffer. The last three arguments specify the other substring in the
324same way. You can use @code{nil} for @var{buffer1}, @var{buffer2}, or
325both to stand for the current buffer.
326
327The value is negative if the first substring is less, positive if the
328first is greater, and zero if they are equal. The absolute value of
329the result is one plus the index of the first differing characters
330within the substrings.
331
332This function ignores case when comparing characters
333if @code{case-fold-search} is non-@code{nil}. It always ignores
334text properties.
335
336Suppose the current buffer contains the text @samp{foobarbar
337haha!rara!}; then in this example the two substrings are @samp{rbar }
338and @samp{rara!}. The value is 2 because the first substring is greater
339at the second character.
340
341@example
342(compare-buffer-substrings nil 6 11 nil 16 21)
343 @result{} 2
344@end example
345@end defun
346
347@node Insertion
348@section Inserting Text
349@cindex insertion of text
350@cindex text insertion
351
352@cindex insertion before point
353@cindex before point, insertion
354 @dfn{Insertion} means adding new text to a buffer. The inserted text
355goes at point---between the character before point and the character
356after point. Some insertion functions leave point before the inserted
357text, while other functions leave it after. We call the former
358insertion @dfn{after point} and the latter insertion @dfn{before point}.
359
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360 Insertion moves markers located at positions after the insertion
361point, so that they stay with the surrounding text (@pxref{Markers}).
362When a marker points at the place of insertion, insertion may or may
363not relocate the marker, depending on the marker's insertion type
364(@pxref{Marker Insertion Types}). Certain special functions such as
365@code{insert-before-markers} relocate all such markers to point after
366the inserted text, regardless of the markers' insertion type.
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367
368 Insertion functions signal an error if the current buffer is
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369read-only (@pxref{Read Only Buffers}) or if they insert within
370read-only text (@pxref{Special Properties}).
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371
372 These functions copy text characters from strings and buffers along
373with their properties. The inserted characters have exactly the same
374properties as the characters they were copied from. By contrast,
375characters specified as separate arguments, not part of a string or
376buffer, inherit their text properties from the neighboring text.
377
378 The insertion functions convert text from unibyte to multibyte in
379order to insert in a multibyte buffer, and vice versa---if the text
380comes from a string or from a buffer. However, they do not convert
381unibyte character codes 128 through 255 to multibyte characters, not
382even if the current buffer is a multibyte buffer. @xref{Converting
383Representations}.
384
385@defun insert &rest args
386This function inserts the strings and/or characters @var{args} into the
387current buffer, at point, moving point forward. In other words, it
388inserts the text before point. An error is signaled unless all
389@var{args} are either strings or characters. The value is @code{nil}.
390@end defun
391
392@defun insert-before-markers &rest args
393This function inserts the strings and/or characters @var{args} into the
394current buffer, at point, moving point forward. An error is signaled
395unless all @var{args} are either strings or characters. The value is
396@code{nil}.
397
398This function is unlike the other insertion functions in that it
399relocates markers initially pointing at the insertion point, to point
400after the inserted text. If an overlay begins at the insertion point,
401the inserted text falls outside the overlay; if a nonempty overlay
402ends at the insertion point, the inserted text falls inside that
403overlay.
404@end defun
405
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406@deffn Command insert-char character &optional count inherit
407This command inserts @var{count} instances of @var{character} into the
408current buffer before point. The argument @var{count} must be an
409integer, and @var{character} must be a character.
410
411If called interactively, this command prompts for @var{character}
412using its Unicode name or its code point. @xref{Inserting Text,,,
413emacs, The GNU Emacs Manual}.
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414
415This function does not convert unibyte character codes 128 through 255
416to multibyte characters, not even if the current buffer is a multibyte
417buffer. @xref{Converting Representations}.
418
9ea10cc3 419If @var{inherit} is non-@code{nil}, the inserted characters inherit
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420sticky text properties from the two characters before and after the
421insertion point. @xref{Sticky Properties}.
9ea10cc3 422@end deffn
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423
424@defun insert-buffer-substring from-buffer-or-name &optional start end
425This function inserts a portion of buffer @var{from-buffer-or-name}
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426into the current buffer before point. The text inserted is the region
427between @var{start} (inclusive) and @var{end} (exclusive). (These
428arguments default to the beginning and end of the accessible portion
429of that buffer.) This function returns @code{nil}.
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430
431In this example, the form is executed with buffer @samp{bar} as the
432current buffer. We assume that buffer @samp{bar} is initially empty.
433
434@example
435@group
436---------- Buffer: foo ----------
437We hold these truths to be self-evident, that all
438---------- Buffer: foo ----------
439@end group
440
441@group
442(insert-buffer-substring "foo" 1 20)
443 @result{} nil
444
445---------- Buffer: bar ----------
446We hold these truth@point{}
447---------- Buffer: bar ----------
448@end group
449@end example
450@end defun
451
452@defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
453This is like @code{insert-buffer-substring} except that it does not
454copy any text properties.
455@end defun
456
457 @xref{Sticky Properties}, for other insertion functions that inherit
458text properties from the nearby text in addition to inserting it.
459Whitespace inserted by indentation functions also inherits text
460properties.
461
462@node Commands for Insertion
463@section User-Level Insertion Commands
464
465 This section describes higher-level commands for inserting text,
466commands intended primarily for the user but useful also in Lisp
467programs.
468
469@deffn Command insert-buffer from-buffer-or-name
470This command inserts the entire accessible contents of
471@var{from-buffer-or-name} (which must exist) into the current buffer
472after point. It leaves the mark after the inserted text. The value
473is @code{nil}.
474@end deffn
475
476@deffn Command self-insert-command count
477@cindex character insertion
478@cindex self-insertion
479This command inserts the last character typed; it does so @var{count}
480times, before point, and returns @code{nil}. Most printing characters
481are bound to this command. In routine use, @code{self-insert-command}
482is the most frequently called function in Emacs, but programs rarely use
483it except to install it on a keymap.
484
485In an interactive call, @var{count} is the numeric prefix argument.
486
bd805d5b 487@c FIXME: This variable is obsolete since 23.1.
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488Self-insertion translates the input character through
489@code{translation-table-for-input}. @xref{Translation of Characters}.
490
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491This command calls @code{auto-fill-function} whenever that is
492non-@code{nil} and the character inserted is in the table
493@code{auto-fill-chars} (@pxref{Auto Filling}).
494
495@c Cross refs reworded to prevent overfull hbox. --rjc 15mar92
496This command performs abbrev expansion if Abbrev mode is enabled and
497the inserted character does not have word-constituent
498syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.) It is also
499responsible for calling @code{blink-paren-function} when the inserted
500character has close parenthesis syntax (@pxref{Blinking}).
501
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502@vindex post-self-insert-hook
503The final thing this command does is to run the hook
504@code{post-self-insert-hook}. You could use this to automatically
505reindent text as it is typed, for example.
506
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507Do not try substituting your own definition of
508@code{self-insert-command} for the standard one. The editor command
509loop handles this function specially.
510@end deffn
511
512@deffn Command newline &optional number-of-newlines
513This command inserts newlines into the current buffer before point.
514If @var{number-of-newlines} is supplied, that many newline characters
515are inserted.
516
517@cindex newline and Auto Fill mode
518This function calls @code{auto-fill-function} if the current column
519number is greater than the value of @code{fill-column} and
520@var{number-of-newlines} is @code{nil}. Typically what
521@code{auto-fill-function} does is insert a newline; thus, the overall
522result in this case is to insert two newlines at different places: one
523at point, and another earlier in the line. @code{newline} does not
524auto-fill if @var{number-of-newlines} is non-@code{nil}.
525
526This command indents to the left margin if that is not zero.
527@xref{Margins}.
528
529The value returned is @code{nil}. In an interactive call, @var{count}
530is the numeric prefix argument.
531@end deffn
532
533@defvar overwrite-mode
534This variable controls whether overwrite mode is in effect. The value
535should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
536or @code{nil}. @code{overwrite-mode-textual} specifies textual
537overwrite mode (treats newlines and tabs specially), and
538@code{overwrite-mode-binary} specifies binary overwrite mode (treats
539newlines and tabs like any other characters).
540@end defvar
541
542@node Deletion
543@section Deleting Text
544@cindex text deletion
545
546@cindex deleting text vs killing
547 Deletion means removing part of the text in a buffer, without saving
548it in the kill ring (@pxref{The Kill Ring}). Deleted text can't be
549yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
550Some deletion functions do save text in the kill ring in some special
551cases.
552
553 All of the deletion functions operate on the current buffer.
554
555@deffn Command erase-buffer
556This function deletes the entire text of the current buffer
557(@emph{not} just the accessible portion), leaving it
558empty. If the buffer is read-only, it signals a @code{buffer-read-only}
559error; if some of the text in it is read-only, it signals a
560@code{text-read-only} error. Otherwise, it deletes the text without
561asking for any confirmation. It returns @code{nil}.
562
563Normally, deleting a large amount of text from a buffer inhibits further
16152b76 564auto-saving of that buffer ``because it has shrunk''. However,
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565@code{erase-buffer} does not do this, the idea being that the future
566text is not really related to the former text, and its size should not
567be compared with that of the former text.
568@end deffn
569
570@deffn Command delete-region start end
571This command deletes the text between positions @var{start} and
572@var{end} in the current buffer, and returns @code{nil}. If point was
573inside the deleted region, its value afterward is @var{start}.
574Otherwise, point relocates with the surrounding text, as markers do.
575@end deffn
576
577@defun delete-and-extract-region start end
578This function deletes the text between positions @var{start} and
579@var{end} in the current buffer, and returns a string containing the
580text just deleted.
581
582If point was inside the deleted region, its value afterward is
583@var{start}. Otherwise, point relocates with the surrounding text, as
584markers do.
585@end defun
586
587@deffn Command delete-char count &optional killp
588This command deletes @var{count} characters directly after point, or
589before point if @var{count} is negative. If @var{killp} is
590non-@code{nil}, then it saves the deleted characters in the kill ring.
591
592In an interactive call, @var{count} is the numeric prefix argument, and
593@var{killp} is the unprocessed prefix argument. Therefore, if a prefix
594argument is supplied, the text is saved in the kill ring. If no prefix
595argument is supplied, then one character is deleted, but not saved in
596the kill ring.
597
598The value returned is always @code{nil}.
599@end deffn
600
601@deffn Command delete-backward-char count &optional killp
602@cindex deleting previous char
603This command deletes @var{count} characters directly before point, or
604after point if @var{count} is negative. If @var{killp} is
605non-@code{nil}, then it saves the deleted characters in the kill ring.
606
607In an interactive call, @var{count} is the numeric prefix argument, and
608@var{killp} is the unprocessed prefix argument. Therefore, if a prefix
609argument is supplied, the text is saved in the kill ring. If no prefix
610argument is supplied, then one character is deleted, but not saved in
611the kill ring.
612
613The value returned is always @code{nil}.
614@end deffn
615
616@deffn Command backward-delete-char-untabify count &optional killp
617@cindex tab deletion
618This command deletes @var{count} characters backward, changing tabs
619into spaces. When the next character to be deleted is a tab, it is
620first replaced with the proper number of spaces to preserve alignment
621and then one of those spaces is deleted instead of the tab. If
622@var{killp} is non-@code{nil}, then the command saves the deleted
623characters in the kill ring.
624
625Conversion of tabs to spaces happens only if @var{count} is positive.
626If it is negative, exactly @minus{}@var{count} characters after point
627are deleted.
628
629In an interactive call, @var{count} is the numeric prefix argument, and
630@var{killp} is the unprocessed prefix argument. Therefore, if a prefix
631argument is supplied, the text is saved in the kill ring. If no prefix
632argument is supplied, then one character is deleted, but not saved in
633the kill ring.
634
635The value returned is always @code{nil}.
636@end deffn
637
638@defopt backward-delete-char-untabify-method
639This option specifies how @code{backward-delete-char-untabify} should
640deal with whitespace. Possible values include @code{untabify}, the
641default, meaning convert a tab to many spaces and delete one;
642@code{hungry}, meaning delete all tabs and spaces before point with
643one command; @code{all} meaning delete all tabs, spaces and newlines
644before point, and @code{nil}, meaning do nothing special for
645whitespace characters.
646@end defopt
647
648@node User-Level Deletion
649@section User-Level Deletion Commands
650
651 This section describes higher-level commands for deleting text,
652commands intended primarily for the user but useful also in Lisp
653programs.
654
655@deffn Command delete-horizontal-space &optional backward-only
656@cindex deleting whitespace
657This function deletes all spaces and tabs around point. It returns
658@code{nil}.
659
660If @var{backward-only} is non-@code{nil}, the function deletes
661spaces and tabs before point, but not after point.
662
663In the following examples, we call @code{delete-horizontal-space} four
664times, once on each line, with point between the second and third
665characters on the line each time.
666
667@example
668@group
669---------- Buffer: foo ----------
670I @point{}thought
671I @point{} thought
672We@point{} thought
673Yo@point{}u thought
674---------- Buffer: foo ----------
675@end group
676
677@group
678(delete-horizontal-space) ; @r{Four times.}
679 @result{} nil
680
681---------- Buffer: foo ----------
682Ithought
683Ithought
684Wethought
685You thought
686---------- Buffer: foo ----------
687@end group
688@end example
689@end deffn
690
691@deffn Command delete-indentation &optional join-following-p
692This function joins the line point is on to the previous line, deleting
693any whitespace at the join and in some cases replacing it with one
694space. If @var{join-following-p} is non-@code{nil},
695@code{delete-indentation} joins this line to the following line
696instead. The function returns @code{nil}.
697
698If there is a fill prefix, and the second of the lines being joined
699starts with the prefix, then @code{delete-indentation} deletes the
700fill prefix before joining the lines. @xref{Margins}.
701
702In the example below, point is located on the line starting
703@samp{events}, and it makes no difference if there are trailing spaces
704in the preceding line.
705
706@smallexample
707@group
708---------- Buffer: foo ----------
709When in the course of human
710@point{} events, it becomes necessary
711---------- Buffer: foo ----------
712@end group
713
714(delete-indentation)
715 @result{} nil
716
717@group
718---------- Buffer: foo ----------
719When in the course of human@point{} events, it becomes necessary
720---------- Buffer: foo ----------
721@end group
722@end smallexample
723
724After the lines are joined, the function @code{fixup-whitespace} is
725responsible for deciding whether to leave a space at the junction.
726@end deffn
727
728@deffn Command fixup-whitespace
729This function replaces all the horizontal whitespace surrounding point
730with either one space or no space, according to the context. It
731returns @code{nil}.
732
733At the beginning or end of a line, the appropriate amount of space is
734none. Before a character with close parenthesis syntax, or after a
735character with open parenthesis or expression-prefix syntax, no space is
736also appropriate. Otherwise, one space is appropriate. @xref{Syntax
737Class Table}.
738
739In the example below, @code{fixup-whitespace} is called the first time
740with point before the word @samp{spaces} in the first line. For the
741second invocation, point is directly after the @samp{(}.
742
743@smallexample
744@group
745---------- Buffer: foo ----------
746This has too many @point{}spaces
747This has too many spaces at the start of (@point{} this list)
748---------- Buffer: foo ----------
749@end group
750
751@group
752(fixup-whitespace)
753 @result{} nil
754(fixup-whitespace)
755 @result{} nil
756@end group
757
758@group
759---------- Buffer: foo ----------
760This has too many spaces
761This has too many spaces at the start of (this list)
762---------- Buffer: foo ----------
763@end group
764@end smallexample
765@end deffn
766
767@deffn Command just-one-space &optional n
768@comment !!SourceFile simple.el
769This command replaces any spaces and tabs around point with a single
770space, or @var{n} spaces if @var{n} is specified. It returns
771@code{nil}.
772@end deffn
773
774@deffn Command delete-blank-lines
775This function deletes blank lines surrounding point. If point is on a
776blank line with one or more blank lines before or after it, then all but
777one of them are deleted. If point is on an isolated blank line, then it
778is deleted. If point is on a nonblank line, the command deletes all
779blank lines immediately following it.
780
781A blank line is defined as a line containing only tabs and spaces.
7bef426b 782@c and the Newline character?
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783
784@code{delete-blank-lines} returns @code{nil}.
785@end deffn
786
787@node The Kill Ring
788@section The Kill Ring
789@cindex kill ring
790
791 @dfn{Kill functions} delete text like the deletion functions, but save
792it so that the user can reinsert it by @dfn{yanking}. Most of these
793functions have @samp{kill-} in their name. By contrast, the functions
794whose names start with @samp{delete-} normally do not save text for
795yanking (though they can still be undone); these are ``deletion''
796functions.
797
798 Most of the kill commands are primarily for interactive use, and are
799not described here. What we do describe are the functions provided for
800use in writing such commands. You can use these functions to write
801commands for killing text. When you need to delete text for internal
802purposes within a Lisp function, you should normally use deletion
803functions, so as not to disturb the kill ring contents.
804@xref{Deletion}.
805
806 Killed text is saved for later yanking in the @dfn{kill ring}. This
807is a list that holds a number of recent kills, not just the last text
808kill. We call this a ``ring'' because yanking treats it as having
809elements in a cyclic order. The list is kept in the variable
810@code{kill-ring}, and can be operated on with the usual functions for
811lists; there are also specialized functions, described in this section,
812that treat it as a ring.
813
814 Some people think this use of the word ``kill'' is unfortunate, since
815it refers to operations that specifically @emph{do not} destroy the
16152b76 816entities ``killed''. This is in sharp contrast to ordinary life, in
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817which death is permanent and ``killed'' entities do not come back to
818life. Therefore, other metaphors have been proposed. For example, the
819term ``cut ring'' makes sense to people who, in pre-computer days, used
820scissors and paste to cut up and rearrange manuscripts. However, it
821would be difficult to change the terminology now.
822
823@menu
824* Kill Ring Concepts:: What text looks like in the kill ring.
825* Kill Functions:: Functions that kill text.
826* Yanking:: How yanking is done.
827* Yank Commands:: Commands that access the kill ring.
d24880de 828* Low-Level Kill Ring:: Functions and variables for kill ring access.
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829* Internals of Kill Ring:: Variables that hold kill ring data.
830@end menu
831
832@node Kill Ring Concepts
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833@subsection Kill Ring Concepts
834
835 The kill ring records killed text as strings in a list, most recent
836first. A short kill ring, for example, might look like this:
837
838@example
839("some text" "a different piece of text" "even older text")
840@end example
841
842@noindent
843When the list reaches @code{kill-ring-max} entries in length, adding a
844new entry automatically deletes the last entry.
845
846 When kill commands are interwoven with other commands, each kill
847command makes a new entry in the kill ring. Multiple kill commands in
848succession build up a single kill ring entry, which would be yanked as a
849unit; the second and subsequent consecutive kill commands add text to
850the entry made by the first one.
851
852 For yanking, one entry in the kill ring is designated the ``front'' of
853the ring. Some yank commands ``rotate'' the ring by designating a
16152b76 854different element as the ``front''. But this virtual rotation doesn't
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855change the list itself---the most recent entry always comes first in the
856list.
857
858@node Kill Functions
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859@subsection Functions for Killing
860
861 @code{kill-region} is the usual subroutine for killing text. Any
862command that calls this function is a ``kill command'' (and should
863probably have @samp{kill} in its name). @code{kill-region} puts the
864newly killed text in a new element at the beginning of the kill ring or
865adds it to the most recent element. It determines automatically (using
866@code{last-command}) whether the previous command was a kill command,
867and if so appends the killed text to the most recent entry.
868
ec8a6295 869@deffn Command kill-region start end
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870This function kills the text in the region defined by @var{start} and
871@var{end}. The text is deleted but saved in the kill ring, along with
872its text properties. The value is always @code{nil}.
873
874In an interactive call, @var{start} and @var{end} are point and
875the mark.
876
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877If the buffer or text is read-only, @code{kill-region} modifies the kill
878ring just the same, then signals an error without modifying the buffer.
879This is convenient because it lets the user use a series of kill
880commands to copy text from a read-only buffer into the kill ring.
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881@end deffn
882
883@defopt kill-read-only-ok
884If this option is non-@code{nil}, @code{kill-region} does not signal an
885error if the buffer or text is read-only. Instead, it simply returns,
886updating the kill ring but not changing the buffer.
887@end defopt
888
889@deffn Command copy-region-as-kill start end
890This command saves the region defined by @var{start} and @var{end} on
891the kill ring (including text properties), but does not delete the text
892from the buffer. It returns @code{nil}.
893
894The command does not set @code{this-command} to @code{kill-region}, so a
895subsequent kill command does not append to the same kill ring entry.
896
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897@c FIXME Why is it better? Why isn't copy-region-as-kill obsolete then?
898@c Why is it used in many places in Emacs?
899In Lisp programs, it is better to use @code{kill-new} or
900@code{kill-append} instead of this command. @xref{Low-Level Kill Ring}.
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901@end deffn
902
903@node Yanking
904@subsection Yanking
905
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906 Yanking means inserting text from the kill ring, but it does not
907insert the text blindly. The @code{yank} command, and related
908commands, use @code{insert-for-yank} to perform special processing on
909the text before it is inserted.
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910
911@defun insert-for-yank string
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912This function works like @code{insert}, except that it processes the
913text in @var{string} according to the @code{yank-handler} text
914property, as well as the variables @code{yank-handled-properties} and
915@code{yank-excluded-properties} (see below), before inserting the
916result into the current buffer.
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917@end defun
918
919@defun insert-buffer-substring-as-yank buf &optional start end
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920This function resembles @code{insert-buffer-substring}, except that it
921processes the text according to @code{yank-handled-properties} and
922@code{yank-excluded-properties}. (It does not handle the
923@code{yank-handler} property, which does not normally occur in buffer
924text anyway.)
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925@end defun
926
90769946 927@c FIXME: Add an index for yank-handler.
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928 If you put a @code{yank-handler} text property on all or part of a
929string, that alters how @code{insert-for-yank} inserts the string. If
930different parts of the string have different @code{yank-handler}
931values (comparison being done with @code{eq}), each substring is
932handled separately. The property value must be a list of one to four
933elements, with the following format (where elements after the first
934may be omitted):
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935
936@example
937(@var{function} @var{param} @var{noexclude} @var{undo})
938@end example
939
940 Here is what the elements do:
941
942@table @var
943@item function
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944When @var{function} is non-@code{nil}, it is called instead of
945@code{insert} to insert the string, with one argument---the string to
946insert.
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947
948@item param
949If @var{param} is present and non-@code{nil}, it replaces @var{string}
05b621a6
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950(or the substring of @var{string} being processed) as the object
951passed to @var{function} (or @code{insert}). For example, if
952@var{function} is @code{yank-rectangle}, @var{param} should be a list
953of strings to insert as a rectangle.
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954
955@item noexclude
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956If @var{noexclude} is present and non-@code{nil}, that disables the
957normal action of @code{yank-handled-properties} and
958@code{yank-excluded-properties} on the inserted string.
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959
960@item undo
961If @var{undo} is present and non-@code{nil}, it is a function that will be
962called by @code{yank-pop} to undo the insertion of the current object.
963It is called with two arguments, the start and end of the current
964region. @var{function} can set @code{yank-undo-function} to override
965the @var{undo} value.
966@end table
967
50b063c3 968@cindex yanking and text properties
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969@defopt yank-handled-properties
970This variable specifies special text property handling conditions for
971yanked text. It takes effect after the text has been inserted (either
972normally, or via the @code{yank-handler} property), and prior to
973@code{yank-excluded-properties} taking effect.
974
975The value should be an alist of elements @code{(@var{prop}
976. @var{fun})}. Each alist element is handled in order. The inserted
977text is scanned for stretches of text having text properties @code{eq}
978to @var{prop}; for each such stretch, @var{fun} is called with three
979arguments: the value of the property, and the start and end positions
980of the text.
981@end defopt
982
50b063c3 983@defopt yank-excluded-properties
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984The value of this variable is the list of properties to remove from
985inserted text. Its default value contains properties that might lead
986to annoying results, such as causing the text to respond to the mouse
987or specifying key bindings. It takes effect after
988@code{yank-handled-properties}.
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989@end defopt
990
05b621a6 991
b8d4c8d0 992@node Yank Commands
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993@subsection Functions for Yanking
994
995 This section describes higher-level commands for yanking, which are
996intended primarily for the user but useful also in Lisp programs.
997Both @code{yank} and @code{yank-pop} honor the
998@code{yank-excluded-properties} variable and @code{yank-handler} text
999property (@pxref{Yanking}).
1000
1001@deffn Command yank &optional arg
1002@cindex inserting killed text
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1003This command inserts before point the text at the front of the kill
1004ring. It sets the mark at the beginning of that text, using
1005@code{push-mark} (@pxref{The Mark}), and puts point at the end.
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1006
1007If @var{arg} is a non-@code{nil} list (which occurs interactively when
1008the user types @kbd{C-u} with no digits), then @code{yank} inserts the
1009text as described above, but puts point before the yanked text and
2bad3299 1010sets the mark after it.
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1011
1012If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
1013most recently killed text---the @var{arg}th element of the kill ring
1014list, counted cyclically from the front, which is considered the
1015first element for this purpose.
1016
1017@code{yank} does not alter the contents of the kill ring, unless it
1018used text provided by another program, in which case it pushes that text
1019onto the kill ring. However if @var{arg} is an integer different from
1020one, it rotates the kill ring to place the yanked string at the front.
1021
1022@code{yank} returns @code{nil}.
1023@end deffn
1024
1025@deffn Command yank-pop &optional arg
1026This command replaces the just-yanked entry from the kill ring with a
1027different entry from the kill ring.
1028
1029This is allowed only immediately after a @code{yank} or another
1030@code{yank-pop}. At such a time, the region contains text that was just
1031inserted by yanking. @code{yank-pop} deletes that text and inserts in
1032its place a different piece of killed text. It does not add the deleted
1033text to the kill ring, since it is already in the kill ring somewhere.
1034It does however rotate the kill ring to place the newly yanked string at
1035the front.
1036
1037If @var{arg} is @code{nil}, then the replacement text is the previous
1038element of the kill ring. If @var{arg} is numeric, the replacement is
1039the @var{arg}th previous kill. If @var{arg} is negative, a more recent
1040kill is the replacement.
1041
1042The sequence of kills in the kill ring wraps around, so that after the
1043oldest one comes the newest one, and before the newest one goes the
1044oldest.
1045
1046The return value is always @code{nil}.
1047@end deffn
1048
1049@defvar yank-undo-function
1050If this variable is non-@code{nil}, the function @code{yank-pop} uses
1051its value instead of @code{delete-region} to delete the text
1052inserted by the previous @code{yank} or
1053@code{yank-pop} command. The value must be a function of two
1054arguments, the start and end of the current region.
1055
1056The function @code{insert-for-yank} automatically sets this variable
1057according to the @var{undo} element of the @code{yank-handler}
1058text property, if there is one.
1059@end defvar
1060
1061@node Low-Level Kill Ring
1062@subsection Low-Level Kill Ring
1063
1064 These functions and variables provide access to the kill ring at a
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1065lower level, but are still convenient for use in Lisp programs,
1066because they take care of interaction with window system selections
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1067(@pxref{Window System Selections}).
1068
1069@defun current-kill n &optional do-not-move
1070The function @code{current-kill} rotates the yanking pointer, which
1071designates the ``front'' of the kill ring, by @var{n} places (from newer
1072kills to older ones), and returns the text at that place in the ring.
1073
1074If the optional second argument @var{do-not-move} is non-@code{nil},
1075then @code{current-kill} doesn't alter the yanking pointer; it just
1076returns the @var{n}th kill, counting from the current yanking pointer.
1077
1078If @var{n} is zero, indicating a request for the latest kill,
1079@code{current-kill} calls the value of
1080@code{interprogram-paste-function} (documented below) before
1081consulting the kill ring. If that value is a function and calling it
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1082returns a string or a list of several string, @code{current-kill}
1083pushes the strings onto the kill ring and returns the first string.
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1084It also sets the yanking pointer to point to the kill-ring entry of
1085the first string returned by @code{interprogram-paste-function},
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1086regardless of the value of @var{do-not-move}. Otherwise,
1087@code{current-kill} does not treat a zero value for @var{n} specially:
1088it returns the entry pointed at by the yanking pointer and does not
1089move the yanking pointer.
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1090@end defun
1091
ec8a6295 1092@defun kill-new string &optional replace
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1093This function pushes the text @var{string} onto the kill ring and
1094makes the yanking pointer point to it. It discards the oldest entry
1095if appropriate. It also invokes the value of
1096@code{interprogram-cut-function} (see below).
1097
1098If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
1099first element of the kill ring with @var{string}, rather than pushing
1100@var{string} onto the kill ring.
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1101@end defun
1102
ec8a6295 1103@defun kill-append string before-p
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1104This function appends the text @var{string} to the first entry in the
1105kill ring and makes the yanking pointer point to the combined entry.
1106Normally @var{string} goes at the end of the entry, but if
1107@var{before-p} is non-@code{nil}, it goes at the beginning. This
1108function also invokes the value of @code{interprogram-cut-function}
ec8a6295 1109(see below).
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1110@end defun
1111
1112@defvar interprogram-paste-function
1113This variable provides a way of transferring killed text from other
1114programs, when you are using a window system. Its value should be
1115@code{nil} or a function of no arguments.
1116
1117If the value is a function, @code{current-kill} calls it to get the
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1118``most recent kill''. If the function returns a non-@code{nil} value,
1119then that value is used as the ``most recent kill''. If it returns
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1120@code{nil}, then the front of the kill ring is used.
1121
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1122To facilitate support for window systems that support multiple
1123selections, this function may also return a list of strings. In that
1124case, the first string is used as the ``most recent kill'', and all
1125the other strings are pushed onto the kill ring, for easy access by
1126@code{yank-pop}.
1127
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1128The normal use of this function is to get the window system's
1129clipboard as the most recent kill, even if the selection belongs to
8e8c1a72 1130another application. @xref{Window System Selections}. However, if
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1131the clipboard contents come from the current Emacs session, this
1132function should return @code{nil}.
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1133@end defvar
1134
1135@defvar interprogram-cut-function
1136This variable provides a way of communicating killed text to other
1137programs, when you are using a window system. Its value should be
45240125 1138@code{nil} or a function of one required argument.
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1139
1140If the value is a function, @code{kill-new} and @code{kill-append} call
45240125 1141it with the new first element of the kill ring as the argument.
b8d4c8d0 1142
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1143The normal use of this function is to put newly killed text in the
1144window system's clipboard. @xref{Window System Selections}.
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1145@end defvar
1146
1147@node Internals of Kill Ring
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1148@subsection Internals of the Kill Ring
1149
1150 The variable @code{kill-ring} holds the kill ring contents, in the
1151form of a list of strings. The most recent kill is always at the front
1152of the list.
1153
1154 The @code{kill-ring-yank-pointer} variable points to a link in the
1155kill ring list, whose @sc{car} is the text to yank next. We say it
1156identifies the ``front'' of the ring. Moving
1157@code{kill-ring-yank-pointer} to a different link is called
1158@dfn{rotating the kill ring}. We call the kill ring a ``ring'' because
1159the functions that move the yank pointer wrap around from the end of the
1160list to the beginning, or vice-versa. Rotation of the kill ring is
1161virtual; it does not change the value of @code{kill-ring}.
1162
1163 Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
1164variables whose values are normally lists. The word ``pointer'' in the
1165name of the @code{kill-ring-yank-pointer} indicates that the variable's
1166purpose is to identify one element of the list for use by the next yank
1167command.
1168
1169 The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
1170of the links in the kill ring list. The element it identifies is the
1171@sc{car} of that link. Kill commands, which change the kill ring, also
1172set this variable to the value of @code{kill-ring}. The effect is to
1173rotate the ring so that the newly killed text is at the front.
1174
1175 Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
1176pointing to the second entry in the kill ring @code{("some text" "a
1177different piece of text" "yet older text")}.
1178
1179@example
1180@group
1181kill-ring ---- kill-ring-yank-pointer
1182 | |
1183 | v
1184 | --- --- --- --- --- ---
1185 --> | | |------> | | |--> | | |--> nil
1186 --- --- --- --- --- ---
1187 | | |
1188 | | |
1189 | | -->"yet older text"
1190 | |
1191 | --> "a different piece of text"
1192 |
1193 --> "some text"
1194@end group
1195@end example
1196
1197@noindent
1198This state of affairs might occur after @kbd{C-y} (@code{yank})
1199immediately followed by @kbd{M-y} (@code{yank-pop}).
1200
1201@defvar kill-ring
1202This variable holds the list of killed text sequences, most recently
1203killed first.
1204@end defvar
1205
1206@defvar kill-ring-yank-pointer
1207This variable's value indicates which element of the kill ring is at the
1208``front'' of the ring for yanking. More precisely, the value is a tail
1209of the value of @code{kill-ring}, and its @sc{car} is the kill string
1210that @kbd{C-y} should yank.
1211@end defvar
1212
1213@defopt kill-ring-max
1214The value of this variable is the maximum length to which the kill
1215ring can grow, before elements are thrown away at the end. The default
1216value for @code{kill-ring-max} is 60.
1217@end defopt
1218
1219@node Undo
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1220@section Undo
1221@cindex redo
1222
1223 Most buffers have an @dfn{undo list}, which records all changes made
1224to the buffer's text so that they can be undone. (The buffers that
1225don't have one are usually special-purpose buffers for which Emacs
1226assumes that undoing is not useful. In particular, any buffer whose
1227name begins with a space has its undo recording off by default;
1228see @ref{Buffer Names}.) All the primitives that modify the
1229text in the buffer automatically add elements to the front of the undo
1230list, which is in the variable @code{buffer-undo-list}.
1231
1232@defvar buffer-undo-list
1233This buffer-local variable's value is the undo list of the current
254408ca 1234buffer. A value of @code{t} disables the recording of undo information.
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1235@end defvar
1236
1237Here are the kinds of elements an undo list can have:
1238
1239@table @code
1240@item @var{position}
1241This kind of element records a previous value of point; undoing this
1242element moves point to @var{position}. Ordinary cursor motion does not
1243make any sort of undo record, but deletion operations use these entries
1244to record where point was before the command.
1245
1246@item (@var{beg} . @var{end})
1247This kind of element indicates how to delete text that was inserted.
1248Upon insertion, the text occupied the range @var{beg}--@var{end} in the
1249buffer.
1250
1251@item (@var{text} . @var{position})
1252This kind of element indicates how to reinsert text that was deleted.
1253The deleted text itself is the string @var{text}. The place to
1254reinsert it is @code{(abs @var{position})}. If @var{position} is
1255positive, point was at the beginning of the deleted text, otherwise it
1256was at the end.
1257
954b166e 1258@item (t . @var{time-flag})
b8d4c8d0 1259This kind of element indicates that an unmodified buffer became
954b166e
PE
1260modified. A @var{time-flag} of the form
1261@code{(@var{sec-high} @var{sec-low} @var{microsec}
c4132fd4
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1262@var{picosec})} represents the visited file's modification time as of
1263when it was previously visited or saved, using the same format as
954b166e
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1264@code{current-time}; see @ref{Time of Day}.
1265A @var{time-flag} of 0 means the buffer does not correspond to any file;
1266@minus{}1 means the visited file previously did not exist.
1267@code{primitive-undo} uses these
b8d4c8d0 1268values to determine whether to mark the buffer as unmodified once again;
954b166e 1269it does so only if the file's status matches that of @var{time-flag}.
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1270
1271@item (nil @var{property} @var{value} @var{beg} . @var{end})
1272This kind of element records a change in a text property.
1273Here's how you might undo the change:
1274
1275@example
1276(put-text-property @var{beg} @var{end} @var{property} @var{value})
1277@end example
1278
1279@item (@var{marker} . @var{adjustment})
1280This kind of element records the fact that the marker @var{marker} was
1281relocated due to deletion of surrounding text, and that it moved
1282@var{adjustment} character positions. Undoing this element moves
1283@var{marker} @minus{} @var{adjustment} characters.
1284
1285@item (apply @var{funname} . @var{args})
1286This is an extensible undo item, which is undone by calling
1287@var{funname} with arguments @var{args}.
1288
1289@item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
1290This is an extensible undo item, which records a change limited to the
1291range @var{beg} to @var{end}, which increased the size of the buffer
70ff8240 1292by @var{delta} characters. It is undone by calling @var{funname} with
e4043ba0 1293arguments @var{args}.
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1294
1295This kind of element enables undo limited to a region to determine
1296whether the element pertains to that region.
1297
1298@item nil
1299This element is a boundary. The elements between two boundaries are
1300called a @dfn{change group}; normally, each change group corresponds to
1301one keyboard command, and undo commands normally undo an entire group as
1302a unit.
1303@end table
1304
1305@defun undo-boundary
1306This function places a boundary element in the undo list. The undo
1307command stops at such a boundary, and successive undo commands undo
1308to earlier and earlier boundaries. This function returns @code{nil}.
1309
51422d6d
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1310The editor command loop automatically calls @code{undo-boundary} just
1311before executing each key sequence, so that each undo normally undoes
1312the effects of one command. As an exception, the command
1313@code{self-insert-command}, which produces self-inserting input
1314characters (@pxref{Commands for Insertion}), may remove the boundary
1315inserted by the command loop: a boundary is accepted for the first
1316such character, the next 19 consecutive self-inserting input
1317characters do not have boundaries, and then the 20th does; and so on
1318as long as the self-inserting characters continue. Hence, sequences
1319of consecutive character insertions can be undone as a group.
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1320
1321All buffer modifications add a boundary whenever the previous undoable
1322change was made in some other buffer. This is to ensure that
1323each command makes a boundary in each buffer where it makes changes.
1324
1325Calling this function explicitly is useful for splitting the effects of
1326a command into more than one unit. For example, @code{query-replace}
1327calls @code{undo-boundary} after each replacement, so that the user can
1328undo individual replacements one by one.
1329@end defun
1330
1331@defvar undo-in-progress
1332This variable is normally @code{nil}, but the undo commands bind it to
1333@code{t}. This is so that various kinds of change hooks can tell when
1334they're being called for the sake of undoing.
1335@end defvar
1336
1337@defun primitive-undo count list
1338This is the basic function for undoing elements of an undo list.
1339It undoes the first @var{count} elements of @var{list}, returning
1340the rest of @var{list}.
1341
1342@code{primitive-undo} adds elements to the buffer's undo list when it
1343changes the buffer. Undo commands avoid confusion by saving the undo
1344list value at the beginning of a sequence of undo operations. Then the
1345undo operations use and update the saved value. The new elements added
1346by undoing are not part of this saved value, so they don't interfere with
1347continuing to undo.
1348
1349This function does not bind @code{undo-in-progress}.
1350@end defun
1351
1352@node Maintaining Undo
1353@section Maintaining Undo Lists
1354
1355 This section describes how to enable and disable undo information for
1356a given buffer. It also explains how the undo list is truncated
1357automatically so it doesn't get too big.
1358
1359 Recording of undo information in a newly created buffer is normally
1360enabled to start with; but if the buffer name starts with a space, the
1361undo recording is initially disabled. You can explicitly enable or
1362disable undo recording with the following two functions, or by setting
1363@code{buffer-undo-list} yourself.
1364
1365@deffn Command buffer-enable-undo &optional buffer-or-name
1366This command enables recording undo information for buffer
1367@var{buffer-or-name}, so that subsequent changes can be undone. If no
1368argument is supplied, then the current buffer is used. This function
1369does nothing if undo recording is already enabled in the buffer. It
1370returns @code{nil}.
1371
1372In an interactive call, @var{buffer-or-name} is the current buffer.
1373You cannot specify any other buffer.
1374@end deffn
1375
1376@deffn Command buffer-disable-undo &optional buffer-or-name
1377@cindex disabling undo
1378This function discards the undo list of @var{buffer-or-name}, and disables
1379further recording of undo information. As a result, it is no longer
1380possible to undo either previous changes or any subsequent changes. If
1381the undo list of @var{buffer-or-name} is already disabled, this function
1382has no effect.
1383
1384This function returns @code{nil}.
1385@end deffn
1386
1387 As editing continues, undo lists get longer and longer. To prevent
1388them from using up all available memory space, garbage collection trims
1389them back to size limits you can set. (For this purpose, the ``size''
1390of an undo list measures the cons cells that make up the list, plus the
1391strings of deleted text.) Three variables control the range of acceptable
1392sizes: @code{undo-limit}, @code{undo-strong-limit} and
1393@code{undo-outer-limit}. In these variables, size is counted as the
1394number of bytes occupied, which includes both saved text and other
1395data.
1396
1397@defopt undo-limit
1398This is the soft limit for the acceptable size of an undo list. The
1399change group at which this size is exceeded is the last one kept.
1400@end defopt
1401
1402@defopt undo-strong-limit
1403This is the upper limit for the acceptable size of an undo list. The
1404change group at which this size is exceeded is discarded itself (along
1405with all older change groups). There is one exception: the very latest
1406change group is only discarded if it exceeds @code{undo-outer-limit}.
1407@end defopt
1408
1409@defopt undo-outer-limit
1410If at garbage collection time the undo info for the current command
1411exceeds this limit, Emacs discards the info and displays a warning.
1412This is a last ditch limit to prevent memory overflow.
1413@end defopt
1414
1415@defopt undo-ask-before-discard
1416If this variable is non-@code{nil}, when the undo info exceeds
1417@code{undo-outer-limit}, Emacs asks in the echo area whether to
1418discard the info. The default value is @code{nil}, which means to
1419discard it automatically.
1420
1421This option is mainly intended for debugging. Garbage collection is
1422inhibited while the question is asked, which means that Emacs might
1423leak memory if the user waits too long before answering the question.
1424@end defopt
1425
1426@node Filling
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GM
1427@section Filling
1428@cindex filling text
1429
1430 @dfn{Filling} means adjusting the lengths of lines (by moving the line
1431breaks) so that they are nearly (but no greater than) a specified
1432maximum width. Additionally, lines can be @dfn{justified}, which means
1433inserting spaces to make the left and/or right margins line up
1434precisely. The width is controlled by the variable @code{fill-column}.
1435For ease of reading, lines should be no longer than 70 or so columns.
1436
1437 You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
1438automatically as you insert it, but changes to existing text may leave
1439it improperly filled. Then you must fill the text explicitly.
1440
1441 Most of the commands in this section return values that are not
1442meaningful. All the functions that do filling take note of the current
1443left margin, current right margin, and current justification style
1444(@pxref{Margins}). If the current justification style is
1445@code{none}, the filling functions don't actually do anything.
1446
1447 Several of the filling functions have an argument @var{justify}.
1448If it is non-@code{nil}, that requests some kind of justification. It
1449can be @code{left}, @code{right}, @code{full}, or @code{center}, to
1450request a specific style of justification. If it is @code{t}, that
1451means to use the current justification style for this part of the text
1452(see @code{current-justification}, below). Any other value is treated
1453as @code{full}.
1454
1455 When you call the filling functions interactively, using a prefix
1456argument implies the value @code{full} for @var{justify}.
1457
65ced25f 1458@deffn Command fill-paragraph &optional justify region
b8d4c8d0
GM
1459This command fills the paragraph at or after point. If
1460@var{justify} is non-@code{nil}, each line is justified as well.
1461It uses the ordinary paragraph motion commands to find paragraph
1462boundaries. @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
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1463
1464When @var{region} is non-@code{nil}, then if Transient Mark mode is
1465enabled and the mark is active, this command calls @code{fill-region}
1466to fill all the paragraphs in the region, instead of filling only the
1467current paragraph. When this command is called interactively,
1468@var{region} is @code{t}.
b8d4c8d0
GM
1469@end deffn
1470
1471@deffn Command fill-region start end &optional justify nosqueeze to-eop
1472This command fills each of the paragraphs in the region from @var{start}
1473to @var{end}. It justifies as well if @var{justify} is
1474non-@code{nil}.
1475
1476If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1477other than line breaks untouched. If @var{to-eop} is non-@code{nil},
1478that means to keep filling to the end of the paragraph---or the next hard
1479newline, if @code{use-hard-newlines} is enabled (see below).
1480
1481The variable @code{paragraph-separate} controls how to distinguish
1482paragraphs. @xref{Standard Regexps}.
1483@end deffn
1484
1485@deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
1486This command fills each paragraph in the region according to its
1487individual fill prefix. Thus, if the lines of a paragraph were indented
1488with spaces, the filled paragraph will remain indented in the same
1489fashion.
1490
1491The first two arguments, @var{start} and @var{end}, are the beginning
1492and end of the region to be filled. The third and fourth arguments,
1493@var{justify} and @var{citation-regexp}, are optional. If
1494@var{justify} is non-@code{nil}, the paragraphs are justified as
1495well as filled. If @var{citation-regexp} is non-@code{nil}, it means the
1496function is operating on a mail message and therefore should not fill
1497the header lines. If @var{citation-regexp} is a string, it is used as
1498a regular expression; if it matches the beginning of a line, that line
1499is treated as a citation marker.
1500
1501Ordinarily, @code{fill-individual-paragraphs} regards each change in
1502indentation as starting a new paragraph. If
1503@code{fill-individual-varying-indent} is non-@code{nil}, then only
1504separator lines separate paragraphs. That mode can handle indented
1505paragraphs with additional indentation on the first line.
1506@end deffn
1507
1508@defopt fill-individual-varying-indent
1509This variable alters the action of @code{fill-individual-paragraphs} as
1510described above.
1511@end defopt
1512
1513@deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
1514This command considers a region of text as a single paragraph and fills
1515it. If the region was made up of many paragraphs, the blank lines
1516between paragraphs are removed. This function justifies as well as
1517filling when @var{justify} is non-@code{nil}.
1518
1519If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
1520other than line breaks untouched. If @var{squeeze-after} is
1521non-@code{nil}, it specifies a position in the region, and means don't
1522canonicalize spaces before that position.
1523
1524In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
1525choose a fill prefix by default. @xref{Adaptive Fill}.
1526@end deffn
1527
1528@deffn Command justify-current-line &optional how eop nosqueeze
1529This command inserts spaces between the words of the current line so
1530that the line ends exactly at @code{fill-column}. It returns
1531@code{nil}.
1532
1533The argument @var{how}, if non-@code{nil} specifies explicitly the style
1534of justification. It can be @code{left}, @code{right}, @code{full},
1535@code{center}, or @code{none}. If it is @code{t}, that means to do
1536follow specified justification style (see @code{current-justification},
1537below). @code{nil} means to do full justification.
1538
1539If @var{eop} is non-@code{nil}, that means do only left-justification
1540if @code{current-justification} specifies full justification. This is
1541used for the last line of a paragraph; even if the paragraph as a
1542whole is fully justified, the last line should not be.
1543
1544If @var{nosqueeze} is non-@code{nil}, that means do not change interior
1545whitespace.
1546@end deffn
1547
1548@defopt default-justification
1549This variable's value specifies the style of justification to use for
1550text that doesn't specify a style with a text property. The possible
1551values are @code{left}, @code{right}, @code{full}, @code{center}, or
1552@code{none}. The default value is @code{left}.
1553@end defopt
1554
1555@defun current-justification
1556This function returns the proper justification style to use for filling
1557the text around point.
1558
1559This returns the value of the @code{justification} text property at
1560point, or the variable @var{default-justification} if there is no such
1561text property. However, it returns @code{nil} rather than @code{none}
1562to mean ``don't justify''.
1563@end defun
1564
1565@defopt sentence-end-double-space
1566@anchor{Definition of sentence-end-double-space}
1567If this variable is non-@code{nil}, a period followed by just one space
1568does not count as the end of a sentence, and the filling functions
1569avoid breaking the line at such a place.
1570@end defopt
1571
1572@defopt sentence-end-without-period
1573If this variable is non-@code{nil}, a sentence can end without a
1574period. This is used for languages like Thai, where sentences end
1575with a double space but without a period.
1576@end defopt
1577
1578@defopt sentence-end-without-space
1579If this variable is non-@code{nil}, it should be a string of
1580characters that can end a sentence without following spaces.
1581@end defopt
1582
1583@defvar fill-paragraph-function
2bad3299
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1584This variable provides a way to override the filling of paragraphs.
1585If its value is non-@code{nil}, @code{fill-paragraph} calls this
1586function to do the work. If the function returns a non-@code{nil}
b8d4c8d0
GM
1587value, @code{fill-paragraph} assumes the job is done, and immediately
1588returns that value.
1589
1590The usual use of this feature is to fill comments in programming
1591language modes. If the function needs to fill a paragraph in the usual
1592way, it can do so as follows:
1593
1594@example
1595(let ((fill-paragraph-function nil))
1596 (fill-paragraph arg))
1597@end example
1598@end defvar
1599
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1600@defvar fill-forward-paragraph-function
1601This variable provides a way to override how the filling functions,
1602such as @code{fill-region} and @code{fill-paragraph}, move forward to
1603the next paragraph. Its value should be a function, which is called
1604with a single argument @var{n}, the number of paragraphs to move, and
1605should return the difference between @var{n} and the number of
1606paragraphs actually moved. The default value of this variable is
1607@code{forward-paragraph}. @xref{Paragraphs,,, emacs, The GNU Emacs
1608Manual}.
1609@end defvar
1610
b8d4c8d0
GM
1611@defvar use-hard-newlines
1612If this variable is non-@code{nil}, the filling functions do not delete
1613newlines that have the @code{hard} text property. These ``hard
1614newlines'' act as paragraph separators.
1615@end defvar
1616
1617@node Margins
1618@section Margins for Filling
bd805d5b 1619@cindex margins, filling
b8d4c8d0
GM
1620
1621@defopt fill-prefix
1622This buffer-local variable, if non-@code{nil}, specifies a string of
1623text that appears at the beginning of normal text lines and should be
1624disregarded when filling them. Any line that fails to start with the
1625fill prefix is considered the start of a paragraph; so is any line
1626that starts with the fill prefix followed by additional whitespace.
1627Lines that start with the fill prefix but no additional whitespace are
1628ordinary text lines that can be filled together. The resulting filled
1629lines also start with the fill prefix.
1630
1631The fill prefix follows the left margin whitespace, if any.
1632@end defopt
1633
1634@defopt fill-column
1635This buffer-local variable specifies the maximum width of filled lines.
1636Its value should be an integer, which is a number of columns. All the
1637filling, justification, and centering commands are affected by this
1638variable, including Auto Fill mode (@pxref{Auto Filling}).
1639
1640As a practical matter, if you are writing text for other people to
1641read, you should set @code{fill-column} to no more than 70. Otherwise
1642the line will be too long for people to read comfortably, and this can
1643make the text seem clumsy.
b8d4c8d0 1644
4e3b4528
SM
1645The default value for @code{fill-column} is 70.
1646@end defopt
b8d4c8d0
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1647
1648@deffn Command set-left-margin from to margin
1649This sets the @code{left-margin} property on the text from @var{from} to
1650@var{to} to the value @var{margin}. If Auto Fill mode is enabled, this
1651command also refills the region to fit the new margin.
1652@end deffn
1653
1654@deffn Command set-right-margin from to margin
1655This sets the @code{right-margin} property on the text from @var{from}
1656to @var{to} to the value @var{margin}. If Auto Fill mode is enabled,
1657this command also refills the region to fit the new margin.
1658@end deffn
1659
1660@defun current-left-margin
1661This function returns the proper left margin value to use for filling
1662the text around point. The value is the sum of the @code{left-margin}
1663property of the character at the start of the current line (or zero if
1664none), and the value of the variable @code{left-margin}.
1665@end defun
1666
1667@defun current-fill-column
1668This function returns the proper fill column value to use for filling
1669the text around point. The value is the value of the @code{fill-column}
1670variable, minus the value of the @code{right-margin} property of the
1671character after point.
1672@end defun
1673
1674@deffn Command move-to-left-margin &optional n force
1675This function moves point to the left margin of the current line. The
1676column moved to is determined by calling the function
1677@code{current-left-margin}. If the argument @var{n} is non-@code{nil},
1678@code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.
1679
1680If @var{force} is non-@code{nil}, that says to fix the line's
1681indentation if that doesn't match the left margin value.
1682@end deffn
1683
1684@defun delete-to-left-margin &optional from to
1685This function removes left margin indentation from the text between
1686@var{from} and @var{to}. The amount of indentation to delete is
1687determined by calling @code{current-left-margin}. In no case does this
1688function delete non-whitespace. If @var{from} and @var{to} are omitted,
1689they default to the whole buffer.
1690@end defun
1691
1692@defun indent-to-left-margin
1693This function adjusts the indentation at the beginning of the current
1694line to the value specified by the variable @code{left-margin}. (That
1695may involve either inserting or deleting whitespace.) This function
1696is value of @code{indent-line-function} in Paragraph-Indent Text mode.
1697@end defun
1698
01f17ae2 1699@defopt left-margin
b8d4c8d0
GM
1700This variable specifies the base left margin column. In Fundamental
1701mode, @kbd{C-j} indents to this column. This variable automatically
1702becomes buffer-local when set in any fashion.
01f17ae2 1703@end defopt
b8d4c8d0 1704
01f17ae2 1705@defopt fill-nobreak-predicate
b8d4c8d0
GM
1706This variable gives major modes a way to specify not to break a line
1707at certain places. Its value should be a list of functions. Whenever
1708filling considers breaking the line at a certain place in the buffer,
1709it calls each of these functions with no arguments and with point
1710located at that place. If any of the functions returns
1711non-@code{nil}, then the line won't be broken there.
01f17ae2 1712@end defopt
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1713
1714@node Adaptive Fill
1715@section Adaptive Fill Mode
1716@c @cindex Adaptive Fill mode "adaptive-fill-mode" is adjacent.
1717
1718 When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
1719prefix automatically from the text in each paragraph being filled
1720rather than using a predetermined value. During filling, this fill
1721prefix gets inserted at the start of the second and subsequent lines
1722of the paragraph as described in @ref{Filling}, and in @ref{Auto
1723Filling}.
1724
1725@defopt adaptive-fill-mode
1726Adaptive Fill mode is enabled when this variable is non-@code{nil}.
1727It is @code{t} by default.
1728@end defopt
1729
1730@defun fill-context-prefix from to
1731This function implements the heart of Adaptive Fill mode; it chooses a
1732fill prefix based on the text between @var{from} and @var{to},
1733typically the start and end of a paragraph. It does this by looking
1734at the first two lines of the paragraph, based on the variables
1735described below.
1736@c The optional argument first-line-regexp is not documented
1737@c because it exists for internal purposes and might be eliminated
1738@c in the future.
1739
1740Usually, this function returns the fill prefix, a string. However,
1741before doing this, the function makes a final check (not specially
1742mentioned in the following) that a line starting with this prefix
1743wouldn't look like the start of a paragraph. Should this happen, the
1744function signals the anomaly by returning @code{nil} instead.
1745
1746In detail, @code{fill-context-prefix} does this:
1747
1748@enumerate
1749@item
1750It takes a candidate for the fill prefix from the first line---it
1751tries first the function in @code{adaptive-fill-function} (if any),
1752then the regular expression @code{adaptive-fill-regexp} (see below).
1753The first non-@code{nil} result of these, or the empty string if
1754they're both @code{nil}, becomes the first line's candidate.
1755@item
1756If the paragraph has as yet only one line, the function tests the
1757validity of the prefix candidate just found. The function then
1758returns the candidate if it's valid, or a string of spaces otherwise.
1759(see the description of @code{adaptive-fill-first-line-regexp} below).
1760@item
1761When the paragraph already has two lines, the function next looks for
1762a prefix candidate on the second line, in just the same way it did for
1763the first line. If it doesn't find one, it returns @code{nil}.
1764@item
1765The function now compares the two candidate prefixes heuristically: if
1766the non-whitespace characters in the line 2 candidate occur in the
1767same order in the line 1 candidate, the function returns the line 2
1768candidate. Otherwise, it returns the largest initial substring which
1769is common to both candidates (which might be the empty string).
1770@end enumerate
1771@end defun
1772
1773@defopt adaptive-fill-regexp
1774Adaptive Fill mode matches this regular expression against the text
1775starting after the left margin whitespace (if any) on a line; the
1776characters it matches are that line's candidate for the fill prefix.
1777
1778The default value matches whitespace with certain punctuation
1779characters intermingled.
1780@end defopt
1781
1782@defopt adaptive-fill-first-line-regexp
1783Used only in one-line paragraphs, this regular expression acts as an
1784additional check of the validity of the one available candidate fill
1785prefix: the candidate must match this regular expression, or match
1786@code{comment-start-skip}. If it doesn't, @code{fill-context-prefix}
1787replaces the candidate with a string of spaces ``of the same width''
1788as it.
1789
1790The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
1791matches only a string of whitespace. The effect of this default is to
1792force the fill prefixes found in one-line paragraphs always to be pure
1793whitespace.
1794@end defopt
1795
1796@defopt adaptive-fill-function
1797You can specify more complex ways of choosing a fill prefix
1798automatically by setting this variable to a function. The function is
1799called with point after the left margin (if any) of a line, and it
1800must preserve point. It should return either ``that line's'' fill
1801prefix or @code{nil}, meaning it has failed to determine a prefix.
1802@end defopt
1803
1804@node Auto Filling
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1805@section Auto Filling
1806@cindex filling, automatic
1807@cindex Auto Fill mode
1808
1809 Auto Fill mode is a minor mode that fills lines automatically as text
1810is inserted. This section describes the hook used by Auto Fill mode.
1811For a description of functions that you can call explicitly to fill and
1812justify existing text, see @ref{Filling}.
1813
1814 Auto Fill mode also enables the functions that change the margins and
1815justification style to refill portions of the text. @xref{Margins}.
1816
1817@defvar auto-fill-function
1818The value of this buffer-local variable should be a function (of no
1819arguments) to be called after self-inserting a character from the table
1820@code{auto-fill-chars}. It may be @code{nil}, in which case nothing
1821special is done in that case.
1822
1823The value of @code{auto-fill-function} is @code{do-auto-fill} when
1824Auto-Fill mode is enabled. That is a function whose sole purpose is to
1825implement the usual strategy for breaking a line.
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1826@end defvar
1827
1828@defvar normal-auto-fill-function
1829This variable specifies the function to use for
1830@code{auto-fill-function}, if and when Auto Fill is turned on. Major
1831modes can set buffer-local values for this variable to alter how Auto
1832Fill works.
1833@end defvar
1834
1835@defvar auto-fill-chars
1836A char table of characters which invoke @code{auto-fill-function} when
1837self-inserted---space and newline in most language environments. They
1838have an entry @code{t} in the table.
1839@end defvar
1840
1841@node Sorting
1842@section Sorting Text
1843@cindex sorting text
1844
1845 The sorting functions described in this section all rearrange text in
1846a buffer. This is in contrast to the function @code{sort}, which
1847rearranges the order of the elements of a list (@pxref{Rearrangement}).
1848The values returned by these functions are not meaningful.
1849
1850@defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
1851This function is the general text-sorting routine that subdivides a
1852buffer into records and then sorts them. Most of the commands in this
1853section use this function.
1854
1855To understand how @code{sort-subr} works, consider the whole accessible
1856portion of the buffer as being divided into disjoint pieces called
1857@dfn{sort records}. The records may or may not be contiguous, but they
1858must not overlap. A portion of each sort record (perhaps all of it) is
1859designated as the sort key. Sorting rearranges the records in order by
1860their sort keys.
1861
1862Usually, the records are rearranged in order of ascending sort key.
1863If the first argument to the @code{sort-subr} function, @var{reverse},
1864is non-@code{nil}, the sort records are rearranged in order of
1865descending sort key.
1866
1867The next four arguments to @code{sort-subr} are functions that are
1868called to move point across a sort record. They are called many times
1869from within @code{sort-subr}.
1870
1871@enumerate
1872@item
1873@var{nextrecfun} is called with point at the end of a record. This
1874function moves point to the start of the next record. The first record
1875is assumed to start at the position of point when @code{sort-subr} is
1876called. Therefore, you should usually move point to the beginning of
1877the buffer before calling @code{sort-subr}.
1878
1879This function can indicate there are no more sort records by leaving
1880point at the end of the buffer.
1881
1882@item
1883@var{endrecfun} is called with point within a record. It moves point to
1884the end of the record.
1885
1886@item
1887@var{startkeyfun} is called to move point from the start of a record to
1888the start of the sort key. This argument is optional; if it is omitted,
1889the whole record is the sort key. If supplied, the function should
1890either return a non-@code{nil} value to be used as the sort key, or
1891return @code{nil} to indicate that the sort key is in the buffer
1892starting at point. In the latter case, @var{endkeyfun} is called to
1893find the end of the sort key.
1894
1895@item
1896@var{endkeyfun} is called to move point from the start of the sort key
1897to the end of the sort key. This argument is optional. If
1898@var{startkeyfun} returns @code{nil} and this argument is omitted (or
1899@code{nil}), then the sort key extends to the end of the record. There
1900is no need for @var{endkeyfun} if @var{startkeyfun} returns a
1901non-@code{nil} value.
1902@end enumerate
1903
1904The argument @var{predicate} is the function to use to compare keys.
1905If keys are numbers, it defaults to @code{<}; otherwise it defaults to
1906@code{string<}.
1907
1908As an example of @code{sort-subr}, here is the complete function
1909definition for @code{sort-lines}:
1910
1911@example
1912@group
1913;; @r{Note that the first two lines of doc string}
1914;; @r{are effectively one line when viewed by a user.}
1915(defun sort-lines (reverse beg end)
1916 "Sort lines in region alphabetically;\
1917 argument means descending order.
1918Called from a program, there are three arguments:
1919@end group
1920@group
1921REVERSE (non-nil means reverse order),\
1922 BEG and END (region to sort).
1923The variable `sort-fold-case' determines\
1924 whether alphabetic case affects
1925the sort order."
1926@end group
1927@group
1928 (interactive "P\nr")
1929 (save-excursion
1930 (save-restriction
1931 (narrow-to-region beg end)
1932 (goto-char (point-min))
1933 (let ((inhibit-field-text-motion t))
1934 (sort-subr reverse 'forward-line 'end-of-line)))))
1935@end group
1936@end example
1937
1938Here @code{forward-line} moves point to the start of the next record,
1939and @code{end-of-line} moves point to the end of record. We do not pass
1940the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
1941record is used as the sort key.
1942
1943The @code{sort-paragraphs} function is very much the same, except that
1944its @code{sort-subr} call looks like this:
1945
1946@example
1947@group
1948(sort-subr reverse
1949 (function
1950 (lambda ()
1951 (while (and (not (eobp))
1952 (looking-at paragraph-separate))
1953 (forward-line 1))))
1954 'forward-paragraph)
1955@end group
1956@end example
1957
1958Markers pointing into any sort records are left with no useful
1959position after @code{sort-subr} returns.
1960@end defun
1961
1962@defopt sort-fold-case
1963If this variable is non-@code{nil}, @code{sort-subr} and the other
1964buffer sorting functions ignore case when comparing strings.
1965@end defopt
1966
1967@deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
1968This command sorts the region between @var{start} and @var{end}
1969alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
1970If @var{reverse} is a negative integer, then sorting is in reverse
1971order.
1972
1973Alphabetical sorting means that two sort keys are compared by
1974comparing the first characters of each, the second characters of each,
1975and so on. If a mismatch is found, it means that the sort keys are
1976unequal; the sort key whose character is less at the point of first
1977mismatch is the lesser sort key. The individual characters are compared
1978according to their numerical character codes in the Emacs character set.
1979
1980The value of the @var{record-regexp} argument specifies how to divide
1981the buffer into sort records. At the end of each record, a search is
1982done for this regular expression, and the text that matches it is taken
1983as the next record. For example, the regular expression @samp{^.+$},
1984which matches lines with at least one character besides a newline, would
1985make each such line into a sort record. @xref{Regular Expressions}, for
1986a description of the syntax and meaning of regular expressions.
1987
1988The value of the @var{key-regexp} argument specifies what part of each
1989record is the sort key. The @var{key-regexp} could match the whole
1990record, or only a part. In the latter case, the rest of the record has
1991no effect on the sorted order of records, but it is carried along when
1992the record moves to its new position.
1993
1994The @var{key-regexp} argument can refer to the text matched by a
1995subexpression of @var{record-regexp}, or it can be a regular expression
1996on its own.
1997
1998If @var{key-regexp} is:
1999
2000@table @asis
2001@item @samp{\@var{digit}}
2002then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
2003grouping in @var{record-regexp} is the sort key.
2004
2005@item @samp{\&}
2006then the whole record is the sort key.
2007
2008@item a regular expression
2009then @code{sort-regexp-fields} searches for a match for the regular
2010expression within the record. If such a match is found, it is the sort
2011key. If there is no match for @var{key-regexp} within a record then
2012that record is ignored, which means its position in the buffer is not
2013changed. (The other records may move around it.)
2014@end table
2015
2016For example, if you plan to sort all the lines in the region by the
2017first word on each line starting with the letter @samp{f}, you should
2018set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
2019@samp{\<f\w*\>}. The resulting expression looks like this:
2020
2021@example
2022@group
2023(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
2024 (region-beginning)
2025 (region-end))
2026@end group
2027@end example
2028
2029If you call @code{sort-regexp-fields} interactively, it prompts for
2030@var{record-regexp} and @var{key-regexp} in the minibuffer.
2031@end deffn
2032
2033@deffn Command sort-lines reverse start end
2034This command alphabetically sorts lines in the region between
2035@var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2036is in reverse order.
2037@end deffn
2038
2039@deffn Command sort-paragraphs reverse start end
2040This command alphabetically sorts paragraphs in the region between
2041@var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2042is in reverse order.
2043@end deffn
2044
2045@deffn Command sort-pages reverse start end
2046This command alphabetically sorts pages in the region between
2047@var{start} and @var{end}. If @var{reverse} is non-@code{nil}, the sort
2048is in reverse order.
2049@end deffn
2050
2051@deffn Command sort-fields field start end
2052This command sorts lines in the region between @var{start} and
2053@var{end}, comparing them alphabetically by the @var{field}th field
2054of each line. Fields are separated by whitespace and numbered starting
2055from 1. If @var{field} is negative, sorting is by the
2056@w{@minus{}@var{field}th} field from the end of the line. This command
2057is useful for sorting tables.
2058@end deffn
2059
2060@deffn Command sort-numeric-fields field start end
2061This command sorts lines in the region between @var{start} and
2062@var{end}, comparing them numerically by the @var{field}th field of
2063each line. Fields are separated by whitespace and numbered starting
2064from 1. The specified field must contain a number in each line of the
2065region. Numbers starting with 0 are treated as octal, and numbers
2066starting with @samp{0x} are treated as hexadecimal.
2067
2068If @var{field} is negative, sorting is by the
2069@w{@minus{}@var{field}th} field from the end of the line. This
2070command is useful for sorting tables.
2071@end deffn
2072
2073@defopt sort-numeric-base
2074This variable specifies the default radix for
2075@code{sort-numeric-fields} to parse numbers.
2076@end defopt
2077
2078@deffn Command sort-columns reverse &optional beg end
2079This command sorts the lines in the region between @var{beg} and
2080@var{end}, comparing them alphabetically by a certain range of
2081columns. The column positions of @var{beg} and @var{end} bound the
2082range of columns to sort on.
2083
2084If @var{reverse} is non-@code{nil}, the sort is in reverse order.
2085
2086One unusual thing about this command is that the entire line
2087containing position @var{beg}, and the entire line containing position
2088@var{end}, are included in the region sorted.
2089
2090Note that @code{sort-columns} rejects text that contains tabs, because
2091tabs could be split across the specified columns. Use @kbd{M-x
2092untabify} to convert tabs to spaces before sorting.
2093
2094When possible, this command actually works by calling the @code{sort}
2095utility program.
2096@end deffn
2097
2098@node Columns
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2099@section Counting Columns
2100@cindex columns
2101@cindex counting columns
2102@cindex horizontal position
2103
2104 The column functions convert between a character position (counting
2105characters from the beginning of the buffer) and a column position
2106(counting screen characters from the beginning of a line).
2107
2108 These functions count each character according to the number of
2109columns it occupies on the screen. This means control characters count
2110as occupying 2 or 4 columns, depending upon the value of
2111@code{ctl-arrow}, and tabs count as occupying a number of columns that
2112depends on the value of @code{tab-width} and on the column where the tab
2113begins. @xref{Usual Display}.
2114
2115 Column number computations ignore the width of the window and the
2116amount of horizontal scrolling. Consequently, a column value can be
2117arbitrarily high. The first (or leftmost) column is numbered 0. They
2118also ignore overlays and text properties, aside from invisibility.
2119
2120@defun current-column
2121This function returns the horizontal position of point, measured in
2122columns, counting from 0 at the left margin. The column position is the
2123sum of the widths of all the displayed representations of the characters
2124between the start of the current line and point.
2125
2126For an example of using @code{current-column}, see the description of
2127@code{count-lines} in @ref{Text Lines}.
2128@end defun
2129
106e6894 2130@deffn Command move-to-column column &optional force
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2131This function moves point to @var{column} in the current line. The
2132calculation of @var{column} takes into account the widths of the
2133displayed representations of the characters between the start of the
2134line and point.
2135
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2136When called interactively, @var{column} is the value of prefix numeric
2137argument. If @var{column} is not an integer, an error is signaled.
2138
2139If column @var{column} is beyond the end of the line, point moves to
2140the end of the line. If @var{column} is negative, point moves to the
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2141beginning of the line.
2142
2143If it is impossible to move to column @var{column} because that is in
2144the middle of a multicolumn character such as a tab, point moves to the
2145end of that character. However, if @var{force} is non-@code{nil}, and
2146@var{column} is in the middle of a tab, then @code{move-to-column}
2147converts the tab into spaces so that it can move precisely to column
2148@var{column}. Other multicolumn characters can cause anomalies despite
2149@var{force}, since there is no way to split them.
2150
2151The argument @var{force} also has an effect if the line isn't long
2152enough to reach column @var{column}; if it is @code{t}, that means to
2153add whitespace at the end of the line to reach that column.
2154
b8d4c8d0 2155The return value is the column number actually moved to.
106e6894 2156@end deffn
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2157
2158@node Indentation
2159@section Indentation
2160@cindex indentation
2161
2162 The indentation functions are used to examine, move to, and change
2163whitespace that is at the beginning of a line. Some of the functions
2164can also change whitespace elsewhere on a line. Columns and indentation
2165count from zero at the left margin.
2166
2167@menu
2168* Primitive Indent:: Functions used to count and insert indentation.
2169* Mode-Specific Indent:: Customize indentation for different modes.
2170* Region Indent:: Indent all the lines in a region.
2171* Relative Indent:: Indent the current line based on previous lines.
2172* Indent Tabs:: Adjustable, typewriter-like tab stops.
2173* Motion by Indent:: Move to first non-blank character.
2174@end menu
2175
2176@node Primitive Indent
2177@subsection Indentation Primitives
2178
2179 This section describes the primitive functions used to count and
2180insert indentation. The functions in the following sections use these
2181primitives. @xref{Width}, for related functions.
2182
2183@defun current-indentation
2184@comment !!Type Primitive Function
2185@comment !!SourceFile indent.c
2186This function returns the indentation of the current line, which is
2187the horizontal position of the first nonblank character. If the
2188contents are entirely blank, then this is the horizontal position of the
2189end of the line.
2190@end defun
2191
2192@deffn Command indent-to column &optional minimum
2193@comment !!Type Primitive Function
2194@comment !!SourceFile indent.c
2195This function indents from point with tabs and spaces until @var{column}
2196is reached. If @var{minimum} is specified and non-@code{nil}, then at
2197least that many spaces are inserted even if this requires going beyond
2198@var{column}. Otherwise the function does nothing if point is already
2199beyond @var{column}. The value is the column at which the inserted
2200indentation ends.
2201
2202The inserted whitespace characters inherit text properties from the
2203surrounding text (usually, from the preceding text only). @xref{Sticky
2204Properties}.
2205@end deffn
2206
2207@defopt indent-tabs-mode
2208@comment !!SourceFile indent.c
2209If this variable is non-@code{nil}, indentation functions can insert
2210tabs as well as spaces. Otherwise, they insert only spaces. Setting
2211this variable automatically makes it buffer-local in the current buffer.
2212@end defopt
2213
2214@node Mode-Specific Indent
2215@subsection Indentation Controlled by Major Mode
2216
2217 An important function of each major mode is to customize the @key{TAB}
2218key to indent properly for the language being edited. This section
2219describes the mechanism of the @key{TAB} key and how to control it.
2220The functions in this section return unpredictable values.
2221
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2222@deffn Command indent-for-tab-command &optional rigid
2223This is the command bound to @key{TAB} in most editing modes. Its
2224usual action is to indent the current line, but it can alternatively
2225insert a tab character or indent a region.
2226
2227Here is what it does:
b8d4c8d0 2228
483ab230
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2229@itemize
2230@item
2231First, it checks whether Transient Mark mode is enabled and the region
2232is active. If so, it called @code{indent-region} to indent all the
2233text in the region (@pxref{Region Indent}).
2234
2235@item
2236Otherwise, if the indentation function in @code{indent-line-function}
2237is @code{indent-to-left-margin} (a trivial command that inserts a tab
2238character), or if the variable @code{tab-always-indent} specifies that
2239a tab character ought to be inserted (see below), then it inserts a
2240tab character.
2241
2242@item
2243Otherwise, it indents the current line; this is done by calling the
2244function in @code{indent-line-function}. If the line is already
2245indented, and the value of @code{tab-always-indent} is @code{complete}
2246(see below), it tries completing the text at point.
2247@end itemize
2248
2249If @var{rigid} is non-@code{nil} (interactively, with a prefix
2250argument), then after this command indents a line or inserts a tab, it
2251also rigidly indents the entire balanced expression which starts at
2252the beginning of the current line, in order to reflect the new
2253indentation. This argument is ignored if the command indents the
2254region.
2255@end deffn
2256
2257@defvar indent-line-function
2258This variable's value is the function to be used by
2259@code{indent-for-tab-command}, and various other indentation commands,
2260to indent the current line. It is usually assigned by the major mode;
2261for instance, Lisp mode sets it to @code{lisp-indent-line}, C mode
2262sets it to @code{c-indent-line}, and so on. The default value is
2263@code{indent-relative}. @xref{Auto-Indentation}.
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2264@end defvar
2265
2266@deffn Command indent-according-to-mode
2267This command calls the function in @code{indent-line-function} to
2268indent the current line in a way appropriate for the current major mode.
2269@end deffn
2270
b8d4c8d0 2271@deffn Command newline-and-indent
b8d4c8d0 2272This function inserts a newline, then indents the new line (the one
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2273following the newline just inserted) according to the major mode. It
2274does indentation by calling @code{indent-according-to-mode}.
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2275@end deffn
2276
2277@deffn Command reindent-then-newline-and-indent
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2278This command reindents the current line, inserts a newline at point,
2279and then indents the new line (the one following the newline just
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2280inserted). It does indentation on both lines by calling
2281@code{indent-according-to-mode}.
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2282@end deffn
2283
483ab230
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2284@defopt tab-always-indent
2285This variable can be used to customize the behavior of the @key{TAB}
2286(@code{indent-for-tab-command}) command. If the value is @code{t}
2287(the default), the command normally just indents the current line. If
2288the value is @code{nil}, the command indents the current line only if
2289point is at the left margin or in the line's indentation; otherwise,
2290it inserts a tab character. If the value is @code{complete}, the
2291command first tries to indent the current line, and if the line was
2292already indented, it calls @code{completion-at-point} to complete the
2293text at point (@pxref{Completion in Buffers}).
2294@end defopt
2295
b8d4c8d0
GM
2296@node Region Indent
2297@subsection Indenting an Entire Region
2298
2299 This section describes commands that indent all the lines in the
2300region. They return unpredictable values.
2301
106e6894 2302@deffn Command indent-region start end &optional to-column
b8d4c8d0
GM
2303This command indents each nonblank line starting between @var{start}
2304(inclusive) and @var{end} (exclusive). If @var{to-column} is
2305@code{nil}, @code{indent-region} indents each nonblank line by calling
2306the current mode's indentation function, the value of
2307@code{indent-line-function}.
2308
2309If @var{to-column} is non-@code{nil}, it should be an integer
2310specifying the number of columns of indentation; then this function
2311gives each line exactly that much indentation, by either adding or
2312deleting whitespace.
2313
2314If there is a fill prefix, @code{indent-region} indents each line
2315by making it start with the fill prefix.
2316@end deffn
2317
2318@defvar indent-region-function
2319The value of this variable is a function that can be used by
2320@code{indent-region} as a short cut. It should take two arguments, the
2321start and end of the region. You should design the function so
2322that it will produce the same results as indenting the lines of the
2323region one by one, but presumably faster.
2324
2325If the value is @code{nil}, there is no short cut, and
2326@code{indent-region} actually works line by line.
2327
2328A short-cut function is useful in modes such as C mode and Lisp mode,
2329where the @code{indent-line-function} must scan from the beginning of
2330the function definition: applying it to each line would be quadratic in
2331time. The short cut can update the scan information as it moves through
2332the lines indenting them; this takes linear time. In a mode where
2333indenting a line individually is fast, there is no need for a short cut.
2334
2335@code{indent-region} with a non-@code{nil} argument @var{to-column} has
2336a different meaning and does not use this variable.
2337@end defvar
2338
2339@deffn Command indent-rigidly start end count
b8d4c8d0
GM
2340This command indents all lines starting between @var{start}
2341(inclusive) and @var{end} (exclusive) sideways by @var{count} columns.
2342This ``preserves the shape'' of the affected region, moving it as a
2343rigid unit. Consequently, this command is useful not only for indenting
2344regions of unindented text, but also for indenting regions of formatted
2345code.
2346
2347For example, if @var{count} is 3, this command adds 3 columns of
2348indentation to each of the lines beginning in the region specified.
2349
2350In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses
2351@code{indent-rigidly} to indent the text copied from the message being
2352replied to.
2353@end deffn
2354
106e6894 2355@deffn Command indent-code-rigidly start end columns &optional nochange-regexp
b8d4c8d0
GM
2356This is like @code{indent-rigidly}, except that it doesn't alter lines
2357that start within strings or comments.
2358
2359In addition, it doesn't alter a line if @var{nochange-regexp} matches at
2360the beginning of the line (if @var{nochange-regexp} is non-@code{nil}).
106e6894 2361@end deffn
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GM
2362
2363@node Relative Indent
2364@subsection Indentation Relative to Previous Lines
2365
2366 This section describes two commands that indent the current line
2367based on the contents of previous lines.
2368
2369@deffn Command indent-relative &optional unindented-ok
2370This command inserts whitespace at point, extending to the same
2371column as the next @dfn{indent point} of the previous nonblank line. An
2372indent point is a non-whitespace character following whitespace. The
2373next indent point is the first one at a column greater than the current
2374column of point. For example, if point is underneath and to the left of
2375the first non-blank character of a line of text, it moves to that column
2376by inserting whitespace.
2377
2378If the previous nonblank line has no next indent point (i.e., none at a
2379great enough column position), @code{indent-relative} either does
2380nothing (if @var{unindented-ok} is non-@code{nil}) or calls
2381@code{tab-to-tab-stop}. Thus, if point is underneath and to the right
2382of the last column of a short line of text, this command ordinarily
2383moves point to the next tab stop by inserting whitespace.
2384
2385The return value of @code{indent-relative} is unpredictable.
2386
2387In the following example, point is at the beginning of the second
2388line:
2389
2390@example
2391@group
2392 This line is indented twelve spaces.
2393@point{}The quick brown fox jumped.
2394@end group
2395@end example
2396
2397@noindent
2398Evaluation of the expression @code{(indent-relative nil)} produces the
2399following:
2400
2401@example
2402@group
2403 This line is indented twelve spaces.
2404 @point{}The quick brown fox jumped.
2405@end group
2406@end example
2407
2408 In this next example, point is between the @samp{m} and @samp{p} of
2409@samp{jumped}:
2410
2411@example
2412@group
2413 This line is indented twelve spaces.
2414The quick brown fox jum@point{}ped.
2415@end group
2416@end example
2417
2418@noindent
2419Evaluation of the expression @code{(indent-relative nil)} produces the
2420following:
2421
2422@example
2423@group
2424 This line is indented twelve spaces.
2425The quick brown fox jum @point{}ped.
2426@end group
2427@end example
2428@end deffn
2429
2430@deffn Command indent-relative-maybe
2431@comment !!SourceFile indent.el
2432This command indents the current line like the previous nonblank line,
2433by calling @code{indent-relative} with @code{t} as the
2434@var{unindented-ok} argument. The return value is unpredictable.
2435
2436If the previous nonblank line has no indent points beyond the current
2437column, this command does nothing.
2438@end deffn
2439
2440@node Indent Tabs
b8d4c8d0
GM
2441@subsection Adjustable ``Tab Stops''
2442@cindex tabs stops for indentation
2443
2444 This section explains the mechanism for user-specified ``tab stops''
2445and the mechanisms that use and set them. The name ``tab stops'' is
2446used because the feature is similar to that of the tab stops on a
2447typewriter. The feature works by inserting an appropriate number of
2448spaces and tab characters to reach the next tab stop column; it does not
2449affect the display of tab characters in the buffer (@pxref{Usual
2450Display}). Note that the @key{TAB} character as input uses this tab
2451stop feature only in a few major modes, such as Text mode.
2452@xref{Tab Stops,,, emacs, The GNU Emacs Manual}.
2453
2454@deffn Command tab-to-tab-stop
2455This command inserts spaces or tabs before point, up to the next tab
2456stop column defined by @code{tab-stop-list}. It searches the list for
2457an element greater than the current column number, and uses that element
2458as the column to indent to. It does nothing if no such element is
2459found.
2460@end deffn
2461
2462@defopt tab-stop-list
2463This variable is the list of tab stop columns used by
2464@code{tab-to-tab-stops}. The elements should be integers in increasing
2465order. The tab stop columns need not be evenly spaced.
2466
2467Use @kbd{M-x edit-tab-stops} to edit the location of tab stops
2468interactively.
2469@end defopt
2470
2471@node Motion by Indent
2472@subsection Indentation-Based Motion Commands
2473
2474 These commands, primarily for interactive use, act based on the
2475indentation in the text.
2476
2477@deffn Command back-to-indentation
2478@comment !!SourceFile simple.el
2479This command moves point to the first non-whitespace character in the
2480current line (which is the line in which point is located). It returns
2481@code{nil}.
2482@end deffn
2483
2484@deffn Command backward-to-indentation &optional arg
2485@comment !!SourceFile simple.el
2486This command moves point backward @var{arg} lines and then to the
2487first nonblank character on that line. It returns @code{nil}.
2488If @var{arg} is omitted or @code{nil}, it defaults to 1.
2489@end deffn
2490
2491@deffn Command forward-to-indentation &optional arg
2492@comment !!SourceFile simple.el
2493This command moves point forward @var{arg} lines and then to the first
2494nonblank character on that line. It returns @code{nil}.
2495If @var{arg} is omitted or @code{nil}, it defaults to 1.
2496@end deffn
2497
2498@node Case Changes
b8d4c8d0
GM
2499@section Case Changes
2500@cindex case conversion in buffers
2501
2502 The case change commands described here work on text in the current
2503buffer. @xref{Case Conversion}, for case conversion functions that work
2504on strings and characters. @xref{Case Tables}, for how to customize
2505which characters are upper or lower case and how to convert them.
2506
2507@deffn Command capitalize-region start end
2508This function capitalizes all words in the region defined by
2509@var{start} and @var{end}. To capitalize means to convert each word's
2510first character to upper case and convert the rest of each word to lower
2511case. The function returns @code{nil}.
2512
2513If one end of the region is in the middle of a word, the part of the
2514word within the region is treated as an entire word.
2515
2516When @code{capitalize-region} is called interactively, @var{start} and
2517@var{end} are point and the mark, with the smallest first.
2518
2519@example
2520@group
2521---------- Buffer: foo ----------
2522This is the contents of the 5th foo.
2523---------- Buffer: foo ----------
2524@end group
2525
2526@group
2527(capitalize-region 1 44)
2528@result{} nil
2529
2530---------- Buffer: foo ----------
2531This Is The Contents Of The 5th Foo.
2532---------- Buffer: foo ----------
2533@end group
2534@end example
2535@end deffn
2536
2537@deffn Command downcase-region start end
2538This function converts all of the letters in the region defined by
2539@var{start} and @var{end} to lower case. The function returns
2540@code{nil}.
2541
2542When @code{downcase-region} is called interactively, @var{start} and
2543@var{end} are point and the mark, with the smallest first.
2544@end deffn
2545
2546@deffn Command upcase-region start end
2547This function converts all of the letters in the region defined by
2548@var{start} and @var{end} to upper case. The function returns
2549@code{nil}.
2550
2551When @code{upcase-region} is called interactively, @var{start} and
2552@var{end} are point and the mark, with the smallest first.
2553@end deffn
2554
2555@deffn Command capitalize-word count
2556This function capitalizes @var{count} words after point, moving point
2557over as it does. To capitalize means to convert each word's first
2558character to upper case and convert the rest of each word to lower case.
2559If @var{count} is negative, the function capitalizes the
2560@minus{}@var{count} previous words but does not move point. The value
2561is @code{nil}.
2562
2563If point is in the middle of a word, the part of the word before point
2564is ignored when moving forward. The rest is treated as an entire word.
2565
2566When @code{capitalize-word} is called interactively, @var{count} is
2567set to the numeric prefix argument.
2568@end deffn
2569
2570@deffn Command downcase-word count
2571This function converts the @var{count} words after point to all lower
2572case, moving point over as it does. If @var{count} is negative, it
2573converts the @minus{}@var{count} previous words but does not move point.
2574The value is @code{nil}.
2575
2576When @code{downcase-word} is called interactively, @var{count} is set
2577to the numeric prefix argument.
2578@end deffn
2579
2580@deffn Command upcase-word count
2581This function converts the @var{count} words after point to all upper
2582case, moving point over as it does. If @var{count} is negative, it
2583converts the @minus{}@var{count} previous words but does not move point.
2584The value is @code{nil}.
2585
2586When @code{upcase-word} is called interactively, @var{count} is set to
2587the numeric prefix argument.
2588@end deffn
2589
2590@node Text Properties
2591@section Text Properties
2592@cindex text properties
2593@cindex attributes of text
2594@cindex properties of text
2595
2596 Each character position in a buffer or a string can have a @dfn{text
2597property list}, much like the property list of a symbol (@pxref{Property
2598Lists}). The properties belong to a particular character at a
2599particular place, such as, the letter @samp{T} at the beginning of this
2600sentence or the first @samp{o} in @samp{foo}---if the same character
2601occurs in two different places, the two occurrences in general have
2602different properties.
2603
2604 Each property has a name and a value. Both of these can be any Lisp
2605object, but the name is normally a symbol. Typically each property
2606name symbol is used for a particular purpose; for instance, the text
2607property @code{face} specifies the faces for displaying the character
2608(@pxref{Special Properties}). The usual way to access the property
2609list is to specify a name and ask what value corresponds to it.
2610
2611 If a character has a @code{category} property, we call it the
2612@dfn{property category} of the character. It should be a symbol. The
2613properties of the symbol serve as defaults for the properties of the
2614character.
2615
2616 Copying text between strings and buffers preserves the properties
2617along with the characters; this includes such diverse functions as
2618@code{substring}, @code{insert}, and @code{buffer-substring}.
2619
2620@menu
2621* Examining Properties:: Looking at the properties of one character.
d24880de
GM
2622* Changing Properties:: Setting the properties of a range of text.
2623* Property Search:: Searching for where a property changes value.
2624* Special Properties:: Particular properties with special meanings.
b8d4c8d0
GM
2625* Format Properties:: Properties for representing formatting of text.
2626* Sticky Properties:: How inserted text gets properties from
2627 neighboring text.
2628* Lazy Properties:: Computing text properties in a lazy fashion
2629 only when text is examined.
2630* Clickable Text:: Using text properties to make regions of text
2631 do something when you click on them.
b8d4c8d0
GM
2632* Fields:: The @code{field} property defines
2633 fields within the buffer.
d24880de
GM
2634* Not Intervals:: Why text properties do not use
2635 Lisp-visible text intervals.
b8d4c8d0
GM
2636@end menu
2637
2638@node Examining Properties
2639@subsection Examining Text Properties
2640
2641 The simplest way to examine text properties is to ask for the value of
2642a particular property of a particular character. For that, use
2643@code{get-text-property}. Use @code{text-properties-at} to get the
2644entire property list of a character. @xref{Property Search}, for
2645functions to examine the properties of a number of characters at once.
2646
2647 These functions handle both strings and buffers. Keep in mind that
2648positions in a string start from 0, whereas positions in a buffer start
2649from 1.
2650
2651@defun get-text-property pos prop &optional object
2652This function returns the value of the @var{prop} property of the
2653character after position @var{pos} in @var{object} (a buffer or
2654string). The argument @var{object} is optional and defaults to the
2655current buffer.
2656
2657If there is no @var{prop} property strictly speaking, but the character
2658has a property category that is a symbol, then @code{get-text-property} returns
2659the @var{prop} property of that symbol.
2660@end defun
2661
2662@defun get-char-property position prop &optional object
2663This function is like @code{get-text-property}, except that it checks
2664overlays first and then text properties. @xref{Overlays}.
2665
af23e1e8
RS
2666The argument @var{object} may be a string, a buffer, or a window. If
2667it is a window, then the buffer displayed in that window is used for
2668text properties and overlays, but only the overlays active for that
2669window are considered. If @var{object} is a buffer, then overlays in
2670that buffer are considered first, in order of decreasing priority,
2671followed by the text properties. If @var{object} is a string, only
2672text properties are considered, since strings never have overlays.
b8d4c8d0
GM
2673@end defun
2674
2675@defun get-char-property-and-overlay position prop &optional object
2676This is like @code{get-char-property}, but gives extra information
2677about the overlay that the property value comes from.
2678
2679Its value is a cons cell whose @sc{car} is the property value, the
2680same value @code{get-char-property} would return with the same
2681arguments. Its @sc{cdr} is the overlay in which the property was
2682found, or @code{nil}, if it was found as a text property or not found
2683at all.
2684
2685If @var{position} is at the end of @var{object}, both the @sc{car} and
2686the @sc{cdr} of the value are @code{nil}.
2687@end defun
2688
2689@defvar char-property-alias-alist
2690This variable holds an alist which maps property names to a list of
2691alternative property names. If a character does not specify a direct
2692value for a property, the alternative property names are consulted in
2693order; the first non-@code{nil} value is used. This variable takes
2694precedence over @code{default-text-properties}, and @code{category}
2695properties take precedence over this variable.
2696@end defvar
2697
2698@defun text-properties-at position &optional object
2699This function returns the entire property list of the character at
2700@var{position} in the string or buffer @var{object}. If @var{object} is
2701@code{nil}, it defaults to the current buffer.
2702@end defun
2703
2704@defvar default-text-properties
2705This variable holds a property list giving default values for text
2706properties. Whenever a character does not specify a value for a
2707property, neither directly, through a category symbol, or through
2708@code{char-property-alias-alist}, the value stored in this list is
2709used instead. Here is an example:
2710
2711@example
2712(setq default-text-properties '(foo 69)
2713 char-property-alias-alist nil)
2714;; @r{Make sure character 1 has no properties of its own.}
2715(set-text-properties 1 2 nil)
2716;; @r{What we get, when we ask, is the default value.}
2717(get-text-property 1 'foo)
2718 @result{} 69
2719@end example
2720@end defvar
2721
2722@node Changing Properties
2723@subsection Changing Text Properties
2724
2725 The primitives for changing properties apply to a specified range of
2726text in a buffer or string. The function @code{set-text-properties}
2727(see end of section) sets the entire property list of the text in that
2728range; more often, it is useful to add, change, or delete just certain
2729properties specified by name.
2730
2731 Since text properties are considered part of the contents of the
2732buffer (or string), and can affect how a buffer looks on the screen,
2733any change in buffer text properties marks the buffer as modified.
2734Buffer text property changes are undoable also (@pxref{Undo}).
2735Positions in a string start from 0, whereas positions in a buffer
2736start from 1.
2737
2738@defun put-text-property start end prop value &optional object
2739This function sets the @var{prop} property to @var{value} for the text
2740between @var{start} and @var{end} in the string or buffer @var{object}.
2741If @var{object} is @code{nil}, it defaults to the current buffer.
2742@end defun
2743
2744@defun add-text-properties start end props &optional object
2745This function adds or overrides text properties for the text between
2746@var{start} and @var{end} in the string or buffer @var{object}. If
2747@var{object} is @code{nil}, it defaults to the current buffer.
2748
2749The argument @var{props} specifies which properties to add. It should
2750have the form of a property list (@pxref{Property Lists}): a list whose
2751elements include the property names followed alternately by the
2752corresponding values.
2753
2754The return value is @code{t} if the function actually changed some
2755property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2756its values agree with those in the text).
2757
2758For example, here is how to set the @code{comment} and @code{face}
2759properties of a range of text:
2760
2761@example
2762(add-text-properties @var{start} @var{end}
2763 '(comment t face highlight))
2764@end example
2765@end defun
2766
2767@defun remove-text-properties start end props &optional object
2768This function deletes specified text properties from the text between
2769@var{start} and @var{end} in the string or buffer @var{object}. If
2770@var{object} is @code{nil}, it defaults to the current buffer.
2771
2772The argument @var{props} specifies which properties to delete. It
2773should have the form of a property list (@pxref{Property Lists}): a list
2774whose elements are property names alternating with corresponding values.
2775But only the names matter---the values that accompany them are ignored.
2776For example, here's how to remove the @code{face} property.
2777
2778@example
2779(remove-text-properties @var{start} @var{end} '(face nil))
2780@end example
2781
2782The return value is @code{t} if the function actually changed some
2783property's value; @code{nil} otherwise (if @var{props} is @code{nil} or
2784if no character in the specified text had any of those properties).
2785
2786To remove all text properties from certain text, use
2787@code{set-text-properties} and specify @code{nil} for the new property
2788list.
2789@end defun
2790
2791@defun remove-list-of-text-properties start end list-of-properties &optional object
2792Like @code{remove-text-properties} except that
2793@var{list-of-properties} is a list of property names only, not an
2794alternating list of property names and values.
2795@end defun
2796
2797@defun set-text-properties start end props &optional object
2798This function completely replaces the text property list for the text
2799between @var{start} and @var{end} in the string or buffer @var{object}.
2800If @var{object} is @code{nil}, it defaults to the current buffer.
2801
2802The argument @var{props} is the new property list. It should be a list
2803whose elements are property names alternating with corresponding values.
2804
2805After @code{set-text-properties} returns, all the characters in the
2806specified range have identical properties.
2807
2808If @var{props} is @code{nil}, the effect is to get rid of all properties
2809from the specified range of text. Here's an example:
2810
2811@example
2812(set-text-properties @var{start} @var{end} nil)
2813@end example
2814
2815Do not rely on the return value of this function.
708e05f6
LMI
2816@end defun
2817
2818@defun add-face-text-property start end face &optional appendp object
2819@code{face} text attributes can be combined. If you want to make a
2820section both italic and green, you can either define a new face that
2821have those attributes, or you can add both these attributes separately
2822to text:
2823
2824@example
2825(add-face-text-property @var{start} @var{end} 'italic)
2826(add-face-text-property @var{start} @var{end} '(:foreground "#00ff00"))
2827@end example
2828
2829The attribute is (by default) prepended to the list of face
2830attributes, and the first attribute of the same type takes
254408ca 2831precedence. So if you have two @code{:foreground} specifications, the
708e05f6
LMI
2832first one will take effect.
2833
2834If you pass in @var{appendp}, the attribute will be appended instead
2835of prepended, which means that it will have no effect if there is
2836already an attribute of the same type.
2837
b8d4c8d0
GM
2838@end defun
2839
2840 The easiest way to make a string with text properties
2841is with @code{propertize}:
2842
2843@defun propertize string &rest properties
2844This function returns a copy of @var{string} which has the text
2845properties @var{properties}. These properties apply to all the
2846characters in the string that is returned. Here is an example that
2847constructs a string with a @code{face} property and a @code{mouse-face}
2848property:
2849
2850@smallexample
2851(propertize "foo" 'face 'italic
2852 'mouse-face 'bold-italic)
2853 @result{} #("foo" 0 3 (mouse-face bold-italic face italic))
2854@end smallexample
2855
2856To put different properties on various parts of a string, you can
2857construct each part with @code{propertize} and then combine them with
2858@code{concat}:
2859
2860@smallexample
2861(concat
2862 (propertize "foo" 'face 'italic
2863 'mouse-face 'bold-italic)
2864 " and "
2865 (propertize "bar" 'face 'italic
2866 'mouse-face 'bold-italic))
2867 @result{} #("foo and bar"
2868 0 3 (face italic mouse-face bold-italic)
2869 3 8 nil
2870 8 11 (face italic mouse-face bold-italic))
2871@end smallexample
2872@end defun
2873
049bcbcb
CY
2874 @xref{Buffer Contents}, for the function
2875@code{buffer-substring-no-properties}, which copies text from the
2876buffer but does not copy its properties.
b8d4c8d0
GM
2877
2878@node Property Search
2879@subsection Text Property Search Functions
2880
2881 In typical use of text properties, most of the time several or many
2882consecutive characters have the same value for a property. Rather than
2883writing your programs to examine characters one by one, it is much
2884faster to process chunks of text that have the same property value.
2885
2886 Here are functions you can use to do this. They use @code{eq} for
2887comparing property values. In all cases, @var{object} defaults to the
2888current buffer.
2889
483ab230 2890 For good performance, it's very important to use the @var{limit}
b8d4c8d0
GM
2891argument to these functions, especially the ones that search for a
2892single property---otherwise, they may spend a long time scanning to the
2893end of the buffer, if the property you are interested in does not change.
2894
2895 These functions do not move point; instead, they return a position (or
2896@code{nil}). Remember that a position is always between two characters;
2897the position returned by these functions is between two characters with
2898different properties.
2899
2900@defun next-property-change pos &optional object limit
2901The function scans the text forward from position @var{pos} in the
483ab230 2902string or buffer @var{object} until it finds a change in some text
b8d4c8d0
GM
2903property, then returns the position of the change. In other words, it
2904returns the position of the first character beyond @var{pos} whose
2905properties are not identical to those of the character just after
2906@var{pos}.
2907
2908If @var{limit} is non-@code{nil}, then the scan ends at position
483ab230
CY
2909@var{limit}. If there is no property change before that point, this
2910function returns @var{limit}.
b8d4c8d0
GM
2911
2912The value is @code{nil} if the properties remain unchanged all the way
2913to the end of @var{object} and @var{limit} is @code{nil}. If the value
2914is non-@code{nil}, it is a position greater than or equal to @var{pos}.
2915The value equals @var{pos} only when @var{limit} equals @var{pos}.
2916
2917Here is an example of how to scan the buffer by chunks of text within
2918which all properties are constant:
2919
2920@smallexample
2921(while (not (eobp))
2922 (let ((plist (text-properties-at (point)))
2923 (next-change
2924 (or (next-property-change (point) (current-buffer))
2925 (point-max))))
2926 @r{Process text from point to @var{next-change}@dots{}}
2927 (goto-char next-change)))
2928@end smallexample
2929@end defun
2930
2931@defun previous-property-change pos &optional object limit
2932This is like @code{next-property-change}, but scans back from @var{pos}
2933instead of forward. If the value is non-@code{nil}, it is a position
2934less than or equal to @var{pos}; it equals @var{pos} only if @var{limit}
2935equals @var{pos}.
2936@end defun
2937
2938@defun next-single-property-change pos prop &optional object limit
2939The function scans text for a change in the @var{prop} property, then
2940returns the position of the change. The scan goes forward from
2941position @var{pos} in the string or buffer @var{object}. In other
2942words, this function returns the position of the first character
2943beyond @var{pos} whose @var{prop} property differs from that of the
2944character just after @var{pos}.
2945
2946If @var{limit} is non-@code{nil}, then the scan ends at position
2947@var{limit}. If there is no property change before that point,
2948@code{next-single-property-change} returns @var{limit}.
2949
2950The value is @code{nil} if the property remains unchanged all the way to
2951the end of @var{object} and @var{limit} is @code{nil}. If the value is
2952non-@code{nil}, it is a position greater than or equal to @var{pos}; it
2953equals @var{pos} only if @var{limit} equals @var{pos}.
2954@end defun
2955
2956@defun previous-single-property-change pos prop &optional object limit
2957This is like @code{next-single-property-change}, but scans back from
2958@var{pos} instead of forward. If the value is non-@code{nil}, it is a
2959position less than or equal to @var{pos}; it equals @var{pos} only if
2960@var{limit} equals @var{pos}.
2961@end defun
2962
2963@defun next-char-property-change pos &optional limit
2964This is like @code{next-property-change} except that it considers
2965overlay properties as well as text properties, and if no change is
2966found before the end of the buffer, it returns the maximum buffer
2967position rather than @code{nil} (in this sense, it resembles the
2968corresponding overlay function @code{next-overlay-change}, rather than
2969@code{next-property-change}). There is no @var{object} operand
2970because this function operates only on the current buffer. It returns
2971the next address at which either kind of property changes.
2972@end defun
2973
2974@defun previous-char-property-change pos &optional limit
2975This is like @code{next-char-property-change}, but scans back from
2976@var{pos} instead of forward, and returns the minimum buffer
2977position if no change is found.
2978@end defun
2979
2980@defun next-single-char-property-change pos prop &optional object limit
2981This is like @code{next-single-property-change} except that it
2982considers overlay properties as well as text properties, and if no
2983change is found before the end of the @var{object}, it returns the
2984maximum valid position in @var{object} rather than @code{nil}. Unlike
2985@code{next-char-property-change}, this function @emph{does} have an
2986@var{object} operand; if @var{object} is not a buffer, only
2987text-properties are considered.
2988@end defun
2989
2990@defun previous-single-char-property-change pos prop &optional object limit
2991This is like @code{next-single-char-property-change}, but scans back
2992from @var{pos} instead of forward, and returns the minimum valid
2993position in @var{object} if no change is found.
2994@end defun
2995
2996@defun text-property-any start end prop value &optional object
2997This function returns non-@code{nil} if at least one character between
2998@var{start} and @var{end} has a property @var{prop} whose value is
2999@var{value}. More precisely, it returns the position of the first such
3000character. Otherwise, it returns @code{nil}.
3001
3002The optional fifth argument, @var{object}, specifies the string or
3003buffer to scan. Positions are relative to @var{object}. The default
3004for @var{object} is the current buffer.
3005@end defun
3006
3007@defun text-property-not-all start end prop value &optional object
3008This function returns non-@code{nil} if at least one character between
3009@var{start} and @var{end} does not have a property @var{prop} with value
3010@var{value}. More precisely, it returns the position of the first such
3011character. Otherwise, it returns @code{nil}.
3012
3013The optional fifth argument, @var{object}, specifies the string or
3014buffer to scan. Positions are relative to @var{object}. The default
3015for @var{object} is the current buffer.
3016@end defun
3017
3018@node Special Properties
3019@subsection Properties with Special Meanings
3020
3021 Here is a table of text property names that have special built-in
3022meanings. The following sections list a few additional special property
3023names that control filling and property inheritance. All other names
3024have no standard meaning, and you can use them as you like.
3025
3026 Note: the properties @code{composition}, @code{display},
3027@code{invisible} and @code{intangible} can also cause point to move to
3028an acceptable place, after each Emacs command. @xref{Adjusting
3029Point}.
3030
3031@table @code
3032@cindex property category of text character
e4043ba0 3033@c FIXME: Isn't @kindex for keyboard commands?
b8d4c8d0
GM
3034@kindex category @r{(text property)}
3035@item category
3036If a character has a @code{category} property, we call it the
3037@dfn{property category} of the character. It should be a symbol. The
3038properties of this symbol serve as defaults for the properties of the
3039character.
3040
3041@item face
3042@cindex face codes of text
3043@kindex face @r{(text property)}
cd542620
CY
3044The @code{face} property controls the appearance of the character
3045(@pxref{Faces}). The value of the property can be the following:
b8d4c8d0
GM
3046
3047@itemize @bullet
3048@item
3049A face name (a symbol or string).
3050
3051@item
cd542620
CY
3052An anonymous face: a property list of the form @code{(@var{keyword}
3053@var{value} @dots{})}, where each @var{keyword} is a face attribute
3054name and @var{value} is a value for that attribute.
b8d4c8d0 3055
483ab230 3056@item
cd542620
CY
3057A list of faces. Each list element should be either a face name or an
3058anonymous face. This specifies a face which is an aggregate of the
6175e34b 3059attributes of each of the listed faces. Faces occurring earlier in
cd542620
CY
3060the list have higher priority.
3061
3062@item
3063A cons cell of the form @code{(foreground-color . @var{color-name})}
3064or @code{(background-color . @var{color-name})}. This specifies the
3065foreground or background color, similar to @code{(:foreground
3066@var{color-name})} or @code{(:background @var{color-name})}. This
3067form is supported for backward compatibility only, and should be
3068avoided.
483ab230 3069@end itemize
db3625ba
RS
3070
3071Font Lock mode (@pxref{Font Lock Mode}) works in most buffers by
3072dynamically updating the @code{face} property of characters based on
3073the context.
b8d4c8d0
GM
3074
3075@item font-lock-face
3076@kindex font-lock-face @r{(text property)}
eeafcea7
CY
3077This property specifies a value for the @code{face} property that Font
3078Lock mode should apply to the underlying text. It is one of the
3079fontification methods used by Font Lock mode, and is useful for
3080special modes that implement their own highlighting.
3081@xref{Precalculated Fontification}. When Font Lock mode is disabled,
db3625ba 3082@code{font-lock-face} has no effect.
b8d4c8d0 3083
b8d4c8d0
GM
3084@item mouse-face
3085@kindex mouse-face @r{(text property)}
eeafcea7
CY
3086This property is used instead of @code{face} when the mouse is on or
3087near the character. For this purpose, ``near'' means that all text
3088between the character and where the mouse is have the same
b8d4c8d0
GM
3089@code{mouse-face} property value.
3090
ebb552ed 3091Emacs ignores all face attributes from the @code{mouse-face} property
1df7defd 3092that alter the text size (e.g., @code{:height}, @code{:weight}, and
ebb552ed
CY
3093@code{:slant}). Those attributes are always the same as for the
3094unhighlighted text.
3095
b8d4c8d0
GM
3096@item fontified
3097@kindex fontified @r{(text property)}
3098This property says whether the text is ready for display. If
3099@code{nil}, Emacs's redisplay routine calls the functions in
3100@code{fontification-functions} (@pxref{Auto Faces}) to prepare this
3101part of the buffer before it is displayed. It is used internally by
3102the ``just in time'' font locking code.
3103
3104@item display
3105This property activates various features that change the
3106way text is displayed. For example, it can make text appear taller
3107or shorter, higher or lower, wider or narrow, or replaced with an image.
3108@xref{Display Property}.
3109
3110@item help-echo
3111@kindex help-echo @r{(text property)}
3112@cindex tooltip
3113@anchor{Text help-echo}
3114If text has a string as its @code{help-echo} property, then when you
3115move the mouse onto that text, Emacs displays that string in the echo
3116area, or in the tooltip window (@pxref{Tooltips,,, emacs, The GNU Emacs
3117Manual}).
3118
3119If the value of the @code{help-echo} property is a function, that
3120function is called with three arguments, @var{window}, @var{object} and
3121@var{pos} and should return a help string or @code{nil} for
3122none. The first argument, @var{window} is the window in which
3123the help was found. The second, @var{object}, is the buffer, overlay or
3124string which had the @code{help-echo} property. The @var{pos}
3125argument is as follows:
3126
3127@itemize @bullet{}
3128@item
3129If @var{object} is a buffer, @var{pos} is the position in the buffer.
3130@item
3131If @var{object} is an overlay, that overlay has a @code{help-echo}
3132property, and @var{pos} is the position in the overlay's buffer.
3133@item
3134If @var{object} is a string (an overlay string or a string displayed
3135with the @code{display} property), @var{pos} is the position in that
3136string.
3137@end itemize
3138
3139If the value of the @code{help-echo} property is neither a function nor
3140a string, it is evaluated to obtain a help string.
3141
3142You can alter the way help text is displayed by setting the variable
3143@code{show-help-function} (@pxref{Help display}).
3144
3145This feature is used in the mode line and for other active text.
3146
3147@item keymap
3148@cindex keymap of character
3149@kindex keymap @r{(text property)}
3150The @code{keymap} property specifies an additional keymap for
3151commands. When this keymap applies, it is used for key lookup before
3152the minor mode keymaps and before the buffer's local map.
3153@xref{Active Keymaps}. If the property value is a symbol, the
3154symbol's function definition is used as the keymap.
3155
3156The property's value for the character before point applies if it is
3157non-@code{nil} and rear-sticky, and the property's value for the
3158character after point applies if it is non-@code{nil} and
3159front-sticky. (For mouse clicks, the position of the click is used
3160instead of the position of point.)
3161
3162@item local-map
3163@kindex local-map @r{(text property)}
3164This property works like @code{keymap} except that it specifies a
3165keymap to use @emph{instead of} the buffer's local map. For most
3166purposes (perhaps all purposes), it is better to use the @code{keymap}
3167property.
3168
3169@item syntax-table
3170The @code{syntax-table} property overrides what the syntax table says
3171about this particular character. @xref{Syntax Properties}.
3172
3173@item read-only
3174@cindex read-only character
3175@kindex read-only @r{(text property)}
3176If a character has the property @code{read-only}, then modifying that
3177character is not allowed. Any command that would do so gets an error,
3178@code{text-read-only}. If the property value is a string, that string
3179is used as the error message.
3180
3181Insertion next to a read-only character is an error if inserting
3182ordinary text there would inherit the @code{read-only} property due to
3183stickiness. Thus, you can control permission to insert next to
3184read-only text by controlling the stickiness. @xref{Sticky Properties}.
3185
3186Since changing properties counts as modifying the buffer, it is not
3187possible to remove a @code{read-only} property unless you know the
3188special trick: bind @code{inhibit-read-only} to a non-@code{nil} value
3189and then remove the property. @xref{Read Only Buffers}.
3190
3191@item invisible
3192@kindex invisible @r{(text property)}
3193A non-@code{nil} @code{invisible} property can make a character invisible
3194on the screen. @xref{Invisible Text}, for details.
3195
3196@item intangible
3197@kindex intangible @r{(text property)}
3198If a group of consecutive characters have equal and non-@code{nil}
3199@code{intangible} properties, then you cannot place point between them.
3200If you try to move point forward into the group, point actually moves to
3201the end of the group. If you try to move point backward into the group,
3202point actually moves to the start of the group.
3203
3204If consecutive characters have unequal non-@code{nil}
3205@code{intangible} properties, they belong to separate groups; each
3206group is separately treated as described above.
3207
3208When the variable @code{inhibit-point-motion-hooks} is non-@code{nil},
3209the @code{intangible} property is ignored.
3210
a7cdbfce
SM
3211Beware: this property operates at a very low level, and affects a lot of code
3212in unexpected ways. So use it with extreme caution. A common misuse is to put
3213an intangible property on invisible text, which is actually unnecessary since
3214the command loop will move point outside of the invisible text at the end of
3215each command anyway. @xref{Adjusting Point}.
3216
b8d4c8d0
GM
3217@item field
3218@kindex field @r{(text property)}
3219Consecutive characters with the same @code{field} property constitute a
3220@dfn{field}. Some motion functions including @code{forward-word} and
3221@code{beginning-of-line} stop moving at a field boundary.
3222@xref{Fields}.
3223
3224@item cursor
3225@kindex cursor @r{(text property)}
50fe197c
EZ
3226Normally, the cursor is displayed at the beginning or the end of any
3227overlay and text property strings present at the current buffer
3228position. You can place the cursor on any desired character of these
3229strings by giving that character a non-@code{nil} @code{cursor} text
3230property. In addition, if the value of the @code{cursor} property is
3231an integer number, it specifies the number of buffer's character
3232positions, starting with the position where the overlay or the
3233@code{display} property begins, for which the cursor should be
3234displayed on that character. Specifically, if the value of the
3235@code{cursor} property of a character is the number @var{n}, the
3236cursor will be displayed on this character for any buffer position in
3237the range @code{[@var{ovpos}..@var{ovpos}+@var{n})}, where @var{ovpos}
3238is the overlay's starting position given by @code{overlay-start}
3239(@pxref{Managing Overlays}), or the position where the @code{display}
3240text property begins in the buffer.
3241
3242In other words, the string character with the @code{cursor} property
3243of any non-@code{nil} value is the character where to display the
3244cursor. The value of the property says for which buffer positions to
3245display the cursor there. If the value is an integer number @var{n},
3246the cursor is displayed there when point is anywhere between the
3247beginning of the overlay or @code{display} property and @var{n}
3248positions after that. If the value is anything else and
3249non-@code{nil}, the cursor is displayed there only when point is at
3250the beginning of the @code{display} property or at
3251@code{overlay-start}.
3252
3253@cindex cursor position for @code{display} properties and overlays
3254When the buffer has many overlay strings (e.g., @pxref{Overlay
3255Properties, before-string}) or @code{display} properties that are
3256strings, it is a good idea to use the @code{cursor} property on these
3257strings to cue the Emacs display about the places where to put the
3258cursor while traversing these strings. This directly communicates to
3259the display engine where the Lisp program wants to put the cursor, or
3260where the user would expect the cursor.
b8d4c8d0
GM
3261
3262@item pointer
3263@kindex pointer @r{(text property)}
3264This specifies a specific pointer shape when the mouse pointer is over
3265this text or image. @xref{Pointer Shape}, for possible pointer
3266shapes.
3267
3268@item line-spacing
3269@kindex line-spacing @r{(text property)}
3270A newline can have a @code{line-spacing} text or overlay property that
3271controls the height of the display line ending with that newline. The
3272property value overrides the default frame line spacing and the buffer
3273local @code{line-spacing} variable. @xref{Line Height}.
3274
3275@item line-height
3276@kindex line-height @r{(text property)}
3277A newline can have a @code{line-height} text or overlay property that
3278controls the total height of the display line ending in that newline.
3279@xref{Line Height}.
3280
c4f4682b
MB
3281@item wrap-prefix
3282If text has a @code{wrap-prefix} property, the prefix it defines will
579ebf8f 3283be added at display time to the beginning of every continuation line
c4f4682b 3284due to text wrapping (so if lines are truncated, the wrap-prefix is
579ebf8f
EZ
3285never used). It may be a string or an image (@pxref{Other Display
3286Specs}), or a stretch of whitespace such as specified by the
3287@code{:width} or @code{:align-to} display properties (@pxref{Specified
3288Space}).
c4f4682b
MB
3289
3290A wrap-prefix may also be specified for an entire buffer using the
3291@code{wrap-prefix} buffer-local variable (however, a
3292@code{wrap-prefix} text-property takes precedence over the value of
3293the @code{wrap-prefix} variable). @xref{Truncation}.
3294
3295@item line-prefix
3296If text has a @code{line-prefix} property, the prefix it defines will
579ebf8f
EZ
3297be added at display time to the beginning of every non-continuation
3298line. It may be a string or an image (@pxref{Other Display
3299Specs}), or a stretch of whitespace such as specified by the
3300@code{:width} or @code{:align-to} display properties (@pxref{Specified
3301Space}).
c4f4682b
MB
3302
3303A line-prefix may also be specified for an entire buffer using the
3304@code{line-prefix} buffer-local variable (however, a
3305@code{line-prefix} text-property takes precedence over the value of
3306the @code{line-prefix} variable). @xref{Truncation}.
3307
b8d4c8d0
GM
3308@item modification-hooks
3309@cindex change hooks for a character
3310@cindex hooks for changing a character
3311@kindex modification-hooks @r{(text property)}
3312If a character has the property @code{modification-hooks}, then its
f816790b
SM
3313value should be a list of functions; modifying that character calls
3314all of those functions before the actual modification. Each function
3315receives two arguments: the beginning and end of the part of the
3316buffer being modified. Note that if a particular modification hook
3317function appears on several characters being modified by a single
3318primitive, you can't predict how many times the function will
3319be called.
3320Furthermore, insertion will not modify any existing character, so this
3321hook will only be run when removing some characters, replacing them
3322with others, or changing their text-properties.
b8d4c8d0
GM
3323
3324If these functions modify the buffer, they should bind
3325@code{inhibit-modification-hooks} to @code{t} around doing so, to
3326avoid confusing the internal mechanism that calls these hooks.
3327
3328Overlays also support the @code{modification-hooks} property, but the
3329details are somewhat different (@pxref{Overlay Properties}).
3330
3331@item insert-in-front-hooks
3332@itemx insert-behind-hooks
3333@kindex insert-in-front-hooks @r{(text property)}
3334@kindex insert-behind-hooks @r{(text property)}
3335The operation of inserting text in a buffer also calls the functions
3336listed in the @code{insert-in-front-hooks} property of the following
3337character and in the @code{insert-behind-hooks} property of the
3338preceding character. These functions receive two arguments, the
3339beginning and end of the inserted text. The functions are called
3340@emph{after} the actual insertion takes place.
3341
3342See also @ref{Change Hooks}, for other hooks that are called
3343when you change text in a buffer.
3344
3345@item point-entered
3346@itemx point-left
3347@cindex hooks for motion of point
3348@kindex point-entered @r{(text property)}
3349@kindex point-left @r{(text property)}
3350The special properties @code{point-entered} and @code{point-left}
3351record hook functions that report motion of point. Each time point
3352moves, Emacs compares these two property values:
3353
3354@itemize @bullet
3355@item
3356the @code{point-left} property of the character after the old location,
3357and
3358@item
3359the @code{point-entered} property of the character after the new
3360location.
3361@end itemize
3362
3363@noindent
3364If these two values differ, each of them is called (if not @code{nil})
3365with two arguments: the old value of point, and the new one.
3366
3367The same comparison is made for the characters before the old and new
3368locations. The result may be to execute two @code{point-left} functions
3369(which may be the same function) and/or two @code{point-entered}
3370functions (which may be the same function). In any case, all the
3371@code{point-left} functions are called first, followed by all the
3372@code{point-entered} functions.
3373
e3934a8a 3374It is possible to use @code{char-after} to examine characters at various
b8d4c8d0
GM
3375buffer positions without moving point to those positions. Only an
3376actual change in the value of point runs these hook functions.
3377
e3934a8a
EZ
3378The variable @code{inhibit-point-motion-hooks} can inhibit running the
3379@code{point-left} and @code{point-entered} hooks, see @ref{Inhibit
3380point motion hooks}.
3381
3382@item composition
3383@kindex composition @r{(text property)}
3384This text property is used to display a sequence of characters as a
3385single glyph composed from components. But the value of the property
3386itself is completely internal to Emacs and should not be manipulated
3387directly by, for instance, @code{put-text-property}.
3388
3389@end table
3390
b8d4c8d0 3391@defvar inhibit-point-motion-hooks
e3934a8a
EZ
3392@anchor{Inhibit point motion hooks} When this variable is
3393non-@code{nil}, @code{point-left} and @code{point-entered} hooks are
3394not run, and the @code{intangible} property has no effect. Do not set
3395this variable globally; bind it with @code{let}.
b8d4c8d0
GM
3396@end defvar
3397
3398@defvar show-help-function
3399@anchor{Help display} If this variable is non-@code{nil}, it specifies a
3400function called to display help strings. These may be @code{help-echo}
3401properties, menu help strings (@pxref{Simple Menu Items},
3402@pxref{Extended Menu Items}), or tool bar help strings (@pxref{Tool
3403Bar}). The specified function is called with one argument, the help
3404string to display. Tooltip mode (@pxref{Tooltips,,, emacs, The GNU Emacs
3405Manual}) provides an example.
3406@end defvar
3407
b8d4c8d0
GM
3408@node Format Properties
3409@subsection Formatted Text Properties
3410
3411 These text properties affect the behavior of the fill commands. They
3412are used for representing formatted text. @xref{Filling}, and
3413@ref{Margins}.
3414
3415@table @code
3416@item hard
3417If a newline character has this property, it is a ``hard'' newline.
3418The fill commands do not alter hard newlines and do not move words
3419across them. However, this property takes effect only if the
3420@code{use-hard-newlines} minor mode is enabled. @xref{Hard and Soft
3421Newlines,, Hard and Soft Newlines, emacs, The GNU Emacs Manual}.
3422
3423@item right-margin
3424This property specifies an extra right margin for filling this part of the
3425text.
3426
3427@item left-margin
3428This property specifies an extra left margin for filling this part of the
3429text.
3430
3431@item justification
3432This property specifies the style of justification for filling this part
3433of the text.
3434@end table
3435
3436@node Sticky Properties
3437@subsection Stickiness of Text Properties
3438@cindex sticky text properties
02676e5d 3439@cindex inheritance, text property
b8d4c8d0
GM
3440
3441 Self-inserting characters normally take on the same properties as the
3442preceding character. This is called @dfn{inheritance} of properties.
3443
483ab230
CY
3444 A Lisp program can do insertion with inheritance or without,
3445depending on the choice of insertion primitive. The ordinary text
3446insertion functions, such as @code{insert}, do not inherit any
3447properties. They insert text with precisely the properties of the
3448string being inserted, and no others. This is correct for programs
3449that copy text from one context to another---for example, into or out
3450of the kill ring. To insert with inheritance, use the special
3451primitives described in this section. Self-inserting characters
3452inherit properties because they work using these primitives.
b8d4c8d0
GM
3453
3454 When you do insertion with inheritance, @emph{which} properties are
3455inherited, and from where, depends on which properties are @dfn{sticky}.
3456Insertion after a character inherits those of its properties that are
3457@dfn{rear-sticky}. Insertion before a character inherits those of its
3458properties that are @dfn{front-sticky}. When both sides offer different
3459sticky values for the same property, the previous character's value
3460takes precedence.
3461
3462 By default, a text property is rear-sticky but not front-sticky; thus,
3463the default is to inherit all the properties of the preceding character,
3464and nothing from the following character.
3465
3466 You can control the stickiness of various text properties with two
3467specific text properties, @code{front-sticky} and @code{rear-nonsticky},
3468and with the variable @code{text-property-default-nonsticky}. You can
3469use the variable to specify a different default for a given property.
3470You can use those two text properties to make any specific properties
3471sticky or nonsticky in any particular part of the text.
3472
3473 If a character's @code{front-sticky} property is @code{t}, then all
3474its properties are front-sticky. If the @code{front-sticky} property is
3475a list, then the sticky properties of the character are those whose
3476names are in the list. For example, if a character has a
3477@code{front-sticky} property whose value is @code{(face read-only)},
3478then insertion before the character can inherit its @code{face} property
3479and its @code{read-only} property, but no others.
3480
3481 The @code{rear-nonsticky} property works the opposite way. Most
3482properties are rear-sticky by default, so the @code{rear-nonsticky}
3483property says which properties are @emph{not} rear-sticky. If a
3484character's @code{rear-nonsticky} property is @code{t}, then none of its
3485properties are rear-sticky. If the @code{rear-nonsticky} property is a
3486list, properties are rear-sticky @emph{unless} their names are in the
3487list.
3488
3489@defvar text-property-default-nonsticky
3490This variable holds an alist which defines the default rear-stickiness
3491of various text properties. Each element has the form
3492@code{(@var{property} . @var{nonstickiness})}, and it defines the
3493stickiness of a particular text property, @var{property}.
3494
3495If @var{nonstickiness} is non-@code{nil}, this means that the property
3496@var{property} is rear-nonsticky by default. Since all properties are
3497front-nonsticky by default, this makes @var{property} nonsticky in both
3498directions by default.
3499
3500The text properties @code{front-sticky} and @code{rear-nonsticky}, when
3501used, take precedence over the default @var{nonstickiness} specified in
3502@code{text-property-default-nonsticky}.
3503@end defvar
3504
3505 Here are the functions that insert text with inheritance of properties:
3506
3507@defun insert-and-inherit &rest strings
3508Insert the strings @var{strings}, just like the function @code{insert},
3509but inherit any sticky properties from the adjoining text.
3510@end defun
3511
3512@defun insert-before-markers-and-inherit &rest strings
3513Insert the strings @var{strings}, just like the function
3514@code{insert-before-markers}, but inherit any sticky properties from the
3515adjoining text.
3516@end defun
3517
3518 @xref{Insertion}, for the ordinary insertion functions which do not
3519inherit.
3520
3521@node Lazy Properties
3522@subsection Lazy Computation of Text Properties
3523
3524 Instead of computing text properties for all the text in the buffer,
3525you can arrange to compute the text properties for parts of the text
3526when and if something depends on them.
3527
3528 The primitive that extracts text from the buffer along with its
3529properties is @code{buffer-substring}. Before examining the properties,
3530this function runs the abnormal hook @code{buffer-access-fontify-functions}.
3531
3532@defvar buffer-access-fontify-functions
3533This variable holds a list of functions for computing text properties.
3534Before @code{buffer-substring} copies the text and text properties for a
3535portion of the buffer, it calls all the functions in this list. Each of
3536the functions receives two arguments that specify the range of the
3537buffer being accessed. (The buffer itself is always the current
3538buffer.)
3539@end defvar
3540
3541 The function @code{buffer-substring-no-properties} does not call these
3542functions, since it ignores text properties anyway.
3543
3544 In order to prevent the hook functions from being called more than
3545once for the same part of the buffer, you can use the variable
3546@code{buffer-access-fontified-property}.
3547
3548@defvar buffer-access-fontified-property
3549If this variable's value is non-@code{nil}, it is a symbol which is used
3550as a text property name. A non-@code{nil} value for that text property
3551means, ``the other text properties for this character have already been
16152b76 3552computed''.
b8d4c8d0
GM
3553
3554If all the characters in the range specified for @code{buffer-substring}
3555have a non-@code{nil} value for this property, @code{buffer-substring}
3556does not call the @code{buffer-access-fontify-functions} functions. It
3557assumes these characters already have the right text properties, and
3558just copies the properties they already have.
3559
3560The normal way to use this feature is that the
3561@code{buffer-access-fontify-functions} functions add this property, as
3562well as others, to the characters they operate on. That way, they avoid
3563being called over and over for the same text.
3564@end defvar
3565
3566@node Clickable Text
3567@subsection Defining Clickable Text
3568@cindex clickable text
2bad3299
CY
3569@cindex follow links
3570@cindex mouse-1
b8d4c8d0
GM
3571
3572 @dfn{Clickable text} is text that can be clicked, with either the
2bad3299
CY
3573mouse or via a keyboard command, to produce some result. Many major
3574modes use clickable text to implement textual hyper-links, or
3575@dfn{links} for short.
3576
3577 The easiest way to insert and manipulate links is to use the
3578@code{button} package. @xref{Buttons}. In this section, we will
3579explain how to manually set up clickable text in a buffer, using text
3580properties. For simplicity, we will refer to the clickable text as a
3581@dfn{link}.
3582
3583 Implementing a link involves three separate steps: (1) indicating
0b128ac4 3584clickability when the mouse moves over the link; (2) making @key{RET}
2bad3299
CY
3585or @kbd{Mouse-2} on that link do something; and (3) setting up a
3586@code{follow-link} condition so that the link obeys
3587@code{mouse-1-click-follows-link}.
3588
3589 To indicate clickability, add the @code{mouse-face} text property to
3590the text of the link; then Emacs will highlight the link when the
3591mouse moves over it. In addition, you should define a tooltip or echo
3592area message, using the @code{help-echo} text property. @xref{Special
3593Properties}. For instance, here is how Dired indicates that file
3594names are clickable:
b8d4c8d0
GM
3595
3596@smallexample
2bad3299
CY
3597 (if (dired-move-to-filename)
3598 (add-text-properties
3599 (point)
3600 (save-excursion
3601 (dired-move-to-end-of-filename)
3602 (point))
3603 '(mouse-face highlight
3604 help-echo "mouse-2: visit this file in other window")))
b8d4c8d0
GM
3605@end smallexample
3606
2bad3299
CY
3607 To make the link clickable, bind @key{RET} and @kbd{Mouse-2} to
3608commands that perform the desired action. Each command should check
3609to see whether it was called on a link, and act accordingly. For
3610instance, Dired's major mode keymap binds @kbd{Mouse-2} to the
3611following command:
b8d4c8d0
GM
3612
3613@smallexample
3614(defun dired-mouse-find-file-other-window (event)
3615 "In Dired, visit the file or directory name you click on."
3616 (interactive "e")
c57008f6
SM
3617 (let ((window (posn-window (event-end event)))
3618 (pos (posn-point (event-end event)))
3619 file)
3620 (if (not (windowp window))
3621 (error "No file chosen"))
3622 (with-current-buffer (window-buffer window)
b8d4c8d0
GM
3623 (goto-char pos)
3624 (setq file (dired-get-file-for-visit)))
3625 (if (file-directory-p file)
3626 (or (and (cdr dired-subdir-alist)
3627 (dired-goto-subdir file))
3628 (progn
3629 (select-window window)
3630 (dired-other-window file)))
3631 (select-window window)
3632 (find-file-other-window (file-name-sans-versions file t)))))
3633@end smallexample
3634
3635@noindent
2bad3299
CY
3636This command uses the functions @code{posn-window} and
3637@code{posn-point} to determine where the click occurred, and
3638@code{dired-get-file-for-visit} to determine which file to visit.
b8d4c8d0 3639
2bad3299
CY
3640 Instead of binding the mouse command in a major mode keymap, you can
3641bind it within the link text, using the @code{keymap} text property
3642(@pxref{Special Properties}). For instance:
b8d4c8d0
GM
3643
3644@example
3645(let ((map (make-sparse-keymap)))
3646 (define-key map [mouse-2] 'operate-this-button)
2bad3299 3647 (put-text-property link-start link-end 'keymap map))
b8d4c8d0
GM
3648@end example
3649
3650@noindent
2bad3299
CY
3651With this method, you can easily define different commands for
3652different links. Furthermore, the global definition of @key{RET} and
3653@kbd{Mouse-2} remain available for the rest of the text in the buffer.
3654
3655@vindex mouse-1-click-follows-link
3656 The basic Emacs command for clicking on links is @kbd{Mouse-2}.
3657However, for compatibility with other graphical applications, Emacs
3658also recognizes @kbd{Mouse-1} clicks on links, provided the user
3659clicks on the link quickly without moving the mouse. This behavior is
3660controlled by the user option @code{mouse-1-click-follows-link}.
3661@xref{Mouse References,,, emacs, The GNU Emacs Manual}.
3662
3663 To set up the link so that it obeys
3664@code{mouse-1-click-follows-link}, you must either (1) apply a
3665@code{follow-link} text or overlay property to the link text, or (2)
3666bind the @code{follow-link} event to a keymap (which can be a major
3667mode keymap or a local keymap specified via the @code{keymap} text
3668property). The value of the @code{follow-link} property, or the
3669binding for the @code{follow-link} event, acts as a ``condition'' for
3670the link action. This condition tells Emacs two things: the
3671circumstances under which a @kbd{Mouse-1} click should be regarded as
3672occurring ``inside'' the link, and how to compute an ``action code''
3673that says what to translate the @kbd{Mouse-1} click into. The link
3674action condition can be one of the following:
b8d4c8d0
GM
3675
3676@table @asis
3677@item @code{mouse-face}
2bad3299
CY
3678If the condition is the symbol @code{mouse-face}, a position is inside
3679a link if there is a non-@code{nil} @code{mouse-face} property at that
3680position. The action code is always @code{t}.
b8d4c8d0
GM
3681
3682For example, here is how Info mode handles @key{Mouse-1}:
3683
3684@smallexample
3685(define-key Info-mode-map [follow-link] 'mouse-face)
3686@end smallexample
3687
3688@item a function
2bad3299
CY
3689If the condition is a function, @var{func}, then a position @var{pos}
3690is inside a link if @code{(@var{func} @var{pos})} evaluates to
3691non-@code{nil}. The value returned by @var{func} serves as the action
3692code.
b8d4c8d0 3693
2bad3299 3694For example, here is how pcvs enables @kbd{Mouse-1} to follow links on
b8d4c8d0
GM
3695file names only:
3696
3697@smallexample
3698(define-key map [follow-link]
3699 (lambda (pos)
3700 (eq (get-char-property pos 'face) 'cvs-filename-face)))
3701@end smallexample
3702
3703@item anything else
3704If the condition value is anything else, then the position is inside a
2bad3299
CY
3705link and the condition itself is the action code. Clearly, you should
3706specify this kind of condition only when applying the condition via a
3707text or property overlay on the link text (so that it does not apply
3708to the entire buffer).
b8d4c8d0
GM
3709@end table
3710
3711@noindent
2bad3299 3712The action code tells @kbd{Mouse-1} how to follow the link:
b8d4c8d0
GM
3713
3714@table @asis
3715@item a string or vector
2bad3299 3716If the action code is a string or vector, the @kbd{Mouse-1} event is
b8d4c8d0 3717translated into the first element of the string or vector; i.e., the
2bad3299 3718action of the @kbd{Mouse-1} click is the local or global binding of
b8d4c8d0 3719that character or symbol. Thus, if the action code is @code{"foo"},
2bad3299
CY
3720@kbd{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
3721@kbd{Mouse-1} translates into @key{foo}.
b8d4c8d0
GM
3722
3723@item anything else
2bad3299
CY
3724For any other non-@code{nil} action code, the @kbd{Mouse-1} event is
3725translated into a @kbd{Mouse-2} event at the same position.
b8d4c8d0
GM
3726@end table
3727
2bad3299 3728 To define @kbd{Mouse-1} to activate a button defined with
b8d4c8d0 3729@code{define-button-type}, give the button a @code{follow-link}
2bad3299
CY
3730property. The property value should be a link action condition, as
3731described above. @xref{Buttons}. For example, here is how Help mode
3732handles @kbd{Mouse-1}:
b8d4c8d0
GM
3733
3734@smallexample
3735(define-button-type 'help-xref
3736 'follow-link t
3737 'action #'help-button-action)
3738@end smallexample
3739
2bad3299
CY
3740 To define @kbd{Mouse-1} on a widget defined with
3741@code{define-widget}, give the widget a @code{:follow-link} property.
3742The property value should be a link action condition, as described
3743above. For example, here is how the @code{link} widget specifies that
b8d4c8d0
GM
3744a @key{Mouse-1} click shall be translated to @key{RET}:
3745
3746@smallexample
3747(define-widget 'link 'item
3748 "An embedded link."
3749 :button-prefix 'widget-link-prefix
3750 :button-suffix 'widget-link-suffix
3751 :follow-link "\C-m"
3752 :help-echo "Follow the link."
3753 :format "%[%t%]")
3754@end smallexample
3755
3756@defun mouse-on-link-p pos
3757This function returns non-@code{nil} if position @var{pos} in the
3758current buffer is on a link. @var{pos} can also be a mouse event
db3625ba 3759location, as returned by @code{event-start} (@pxref{Accessing Mouse}).
b8d4c8d0
GM
3760@end defun
3761
3762@node Fields
3763@subsection Defining and Using Fields
3764@cindex fields
3765
3766 A field is a range of consecutive characters in the buffer that are
3767identified by having the same value (comparing with @code{eq}) of the
3768@code{field} property (either a text-property or an overlay property).
3769This section describes special functions that are available for
3770operating on fields.
3771
3772 You specify a field with a buffer position, @var{pos}. We think of
3773each field as containing a range of buffer positions, so the position
3774you specify stands for the field containing that position.
3775
3776 When the characters before and after @var{pos} are part of the same
3777field, there is no doubt which field contains @var{pos}: the one those
3778characters both belong to. When @var{pos} is at a boundary between
3779fields, which field it belongs to depends on the stickiness of the
3780@code{field} properties of the two surrounding characters (@pxref{Sticky
3781Properties}). The field whose property would be inherited by text
3782inserted at @var{pos} is the field that contains @var{pos}.
3783
3784 There is an anomalous case where newly inserted text at @var{pos}
3785would not inherit the @code{field} property from either side. This
3786happens if the previous character's @code{field} property is not
3787rear-sticky, and the following character's @code{field} property is not
3788front-sticky. In this case, @var{pos} belongs to neither the preceding
3789field nor the following field; the field functions treat it as belonging
3790to an empty field whose beginning and end are both at @var{pos}.
3791
3792 In all of these functions, if @var{pos} is omitted or @code{nil}, the
3793value of point is used by default. If narrowing is in effect, then
3794@var{pos} should fall within the accessible portion. @xref{Narrowing}.
3795
3796@defun field-beginning &optional pos escape-from-edge limit
3797This function returns the beginning of the field specified by @var{pos}.
3798
3799If @var{pos} is at the beginning of its field, and
3800@var{escape-from-edge} is non-@code{nil}, then the return value is
3801always the beginning of the preceding field that @emph{ends} at @var{pos},
3802regardless of the stickiness of the @code{field} properties around
3803@var{pos}.
3804
3805If @var{limit} is non-@code{nil}, it is a buffer position; if the
3806beginning of the field is before @var{limit}, then @var{limit} will be
3807returned instead.
3808@end defun
3809
3810@defun field-end &optional pos escape-from-edge limit
3811This function returns the end of the field specified by @var{pos}.
3812
3813If @var{pos} is at the end of its field, and @var{escape-from-edge} is
3814non-@code{nil}, then the return value is always the end of the following
3815field that @emph{begins} at @var{pos}, regardless of the stickiness of
3816the @code{field} properties around @var{pos}.
3817
3818If @var{limit} is non-@code{nil}, it is a buffer position; if the end
3819of the field is after @var{limit}, then @var{limit} will be returned
3820instead.
3821@end defun
3822
3823@defun field-string &optional pos
3824This function returns the contents of the field specified by @var{pos},
3825as a string.
3826@end defun
3827
3828@defun field-string-no-properties &optional pos
3829This function returns the contents of the field specified by @var{pos},
3830as a string, discarding text properties.
3831@end defun
3832
3833@defun delete-field &optional pos
3834This function deletes the text of the field specified by @var{pos}.
3835@end defun
3836
3837@defun constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property
3838This function ``constrains'' @var{new-pos} to the field that
3839@var{old-pos} belongs to---in other words, it returns the position
3840closest to @var{new-pos} that is in the same field as @var{old-pos}.
3841
3842If @var{new-pos} is @code{nil}, then @code{constrain-to-field} uses
3843the value of point instead, and moves point to the resulting position
66c5eebd 3844in addition to returning that position.
b8d4c8d0
GM
3845
3846If @var{old-pos} is at the boundary of two fields, then the acceptable
3847final positions depend on the argument @var{escape-from-edge}. If
3848@var{escape-from-edge} is @code{nil}, then @var{new-pos} must be in
3849the field whose @code{field} property equals what new characters
3850inserted at @var{old-pos} would inherit. (This depends on the
3851stickiness of the @code{field} property for the characters before and
3852after @var{old-pos}.) If @var{escape-from-edge} is non-@code{nil},
3853@var{new-pos} can be anywhere in the two adjacent fields.
3854Additionally, if two fields are separated by another field with the
3855special value @code{boundary}, then any point within this special
16152b76 3856field is also considered to be ``on the boundary''.
b8d4c8d0 3857
e4920bc9 3858Commands like @kbd{C-a} with no argument, that normally move backward
b8d4c8d0
GM
3859to a specific kind of location and stay there once there, probably
3860should specify @code{nil} for @var{escape-from-edge}. Other motion
3861commands that check fields should probably pass @code{t}.
3862
3863If the optional argument @var{only-in-line} is non-@code{nil}, and
3864constraining @var{new-pos} in the usual way would move it to a different
3865line, @var{new-pos} is returned unconstrained. This used in commands
3866that move by line, such as @code{next-line} and
3867@code{beginning-of-line}, so that they respect field boundaries only in
3868the case where they can still move to the right line.
3869
3870If the optional argument @var{inhibit-capture-property} is
3871non-@code{nil}, and @var{old-pos} has a non-@code{nil} property of that
3872name, then any field boundaries are ignored.
3873
3874You can cause @code{constrain-to-field} to ignore all field boundaries
3875(and so never constrain anything) by binding the variable
3876@code{inhibit-field-text-motion} to a non-@code{nil} value.
3877@end defun
3878
3879@node Not Intervals
3880@subsection Why Text Properties are not Intervals
3881@cindex intervals
3882
3883 Some editors that support adding attributes to text in the buffer do
3884so by letting the user specify ``intervals'' within the text, and adding
3885the properties to the intervals. Those editors permit the user or the
3886programmer to determine where individual intervals start and end. We
3887deliberately provided a different sort of interface in Emacs Lisp to
3888avoid certain paradoxical behavior associated with text modification.
3889
3890 If the actual subdivision into intervals is meaningful, that means you
3891can distinguish between a buffer that is just one interval with a
3892certain property, and a buffer containing the same text subdivided into
3893two intervals, both of which have that property.
3894
3895 Suppose you take the buffer with just one interval and kill part of
3896the text. The text remaining in the buffer is one interval, and the
3897copy in the kill ring (and the undo list) becomes a separate interval.
3898Then if you yank back the killed text, you get two intervals with the
3899same properties. Thus, editing does not preserve the distinction
3900between one interval and two.
3901
3902 Suppose we ``fix'' this problem by coalescing the two intervals when
3903the text is inserted. That works fine if the buffer originally was a
3904single interval. But suppose instead that we have two adjacent
3905intervals with the same properties, and we kill the text of one interval
3906and yank it back. The same interval-coalescence feature that rescues
3907the other case causes trouble in this one: after yanking, we have just
3908one interval. One again, editing does not preserve the distinction
3909between one interval and two.
3910
3911 Insertion of text at the border between intervals also raises
3912questions that have no satisfactory answer.
3913
3914 However, it is easy to arrange for editing to behave consistently for
3915questions of the form, ``What are the properties of this character?''
3916So we have decided these are the only questions that make sense; we have
3917not implemented asking questions about where intervals start or end.
3918
3919 In practice, you can usually use the text property search functions in
3920place of explicit interval boundaries. You can think of them as finding
3921the boundaries of intervals, assuming that intervals are always
3922coalesced whenever possible. @xref{Property Search}.
3923
3924 Emacs also provides explicit intervals as a presentation feature; see
3925@ref{Overlays}.
3926
3927@node Substitution
3928@section Substituting for a Character Code
3929
3930 The following functions replace characters within a specified region
3931based on their character codes.
3932
3933@defun subst-char-in-region start end old-char new-char &optional noundo
3934@cindex replace characters
3935This function replaces all occurrences of the character @var{old-char}
3936with the character @var{new-char} in the region of the current buffer
3937defined by @var{start} and @var{end}.
3938
3939@cindex undo avoidance
3940If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does
3941not record the change for undo and does not mark the buffer as modified.
3942This was useful for controlling the old selective display feature
3943(@pxref{Selective Display}).
3944
3945@code{subst-char-in-region} does not move point and returns
3946@code{nil}.
3947
3948@example
3949@group
3950---------- Buffer: foo ----------
3951This is the contents of the buffer before.
3952---------- Buffer: foo ----------
3953@end group
3954
3955@group
3956(subst-char-in-region 1 20 ?i ?X)
3957 @result{} nil
3958
3959---------- Buffer: foo ----------
3960ThXs Xs the contents of the buffer before.
3961---------- Buffer: foo ----------
3962@end group
3963@end example
3964@end defun
3965
106e6894 3966@deffn Command translate-region start end table
b8d4c8d0
GM
3967This function applies a translation table to the characters in the
3968buffer between positions @var{start} and @var{end}.
3969
3970The translation table @var{table} is a string or a char-table;
3971@code{(aref @var{table} @var{ochar})} gives the translated character
3972corresponding to @var{ochar}. If @var{table} is a string, any
3973characters with codes larger than the length of @var{table} are not
3974altered by the translation.
3975
3976The return value of @code{translate-region} is the number of
3977characters that were actually changed by the translation. This does
3978not count characters that were mapped into themselves in the
3979translation table.
106e6894 3980@end deffn
b8d4c8d0
GM
3981
3982@node Registers
3983@section Registers
3984@cindex registers
3985
3986 A register is a sort of variable used in Emacs editing that can hold a
3987variety of different kinds of values. Each register is named by a
3988single character. All @acronym{ASCII} characters and their meta variants
3989(but with the exception of @kbd{C-g}) can be used to name registers.
3990Thus, there are 255 possible registers. A register is designated in
3991Emacs Lisp by the character that is its name.
3992
3993@defvar register-alist
3994This variable is an alist of elements of the form @code{(@var{name} .
3995@var{contents})}. Normally, there is one element for each Emacs
3996register that has been used.
3997
3998The object @var{name} is a character (an integer) identifying the
3999register.
4000@end defvar
4001
4002 The @var{contents} of a register can have several possible types:
4003
4004@table @asis
4005@item a number
4006A number stands for itself. If @code{insert-register} finds a number
4007in the register, it converts the number to decimal.
4008
4009@item a marker
4010A marker represents a buffer position to jump to.
4011
4012@item a string
4013A string is text saved in the register.
4014
4015@item a rectangle
4016A rectangle is represented by a list of strings.
4017
4018@item @code{(@var{window-configuration} @var{position})}
4019This represents a window configuration to restore in one frame, and a
4020position to jump to in the current buffer.
4021
4022@item @code{(@var{frame-configuration} @var{position})}
4023This represents a frame configuration to restore, and a position
4024to jump to in the current buffer.
4025
4026@item (file @var{filename})
4027This represents a file to visit; jumping to this value visits file
4028@var{filename}.
4029
4030@item (file-query @var{filename} @var{position})
4031This represents a file to visit and a position in it; jumping to this
4032value visits file @var{filename} and goes to buffer position
4033@var{position}. Restoring this type of position asks the user for
4034confirmation first.
4035@end table
4036
4037 The functions in this section return unpredictable values unless
4038otherwise stated.
4039
4040@defun get-register reg
4041This function returns the contents of the register
4042@var{reg}, or @code{nil} if it has no contents.
4043@end defun
4044
4045@defun set-register reg value
4046This function sets the contents of register @var{reg} to @var{value}.
4047A register can be set to any value, but the other register functions
4048expect only certain data types. The return value is @var{value}.
4049@end defun
4050
4051@deffn Command view-register reg
4052This command displays what is contained in register @var{reg}.
4053@end deffn
4054
b8d4c8d0
GM
4055@deffn Command insert-register reg &optional beforep
4056This command inserts contents of register @var{reg} into the current
4057buffer.
4058
4059Normally, this command puts point before the inserted text, and the
4060mark after it. However, if the optional second argument @var{beforep}
4061is non-@code{nil}, it puts the mark before and point after.
4062You can pass a non-@code{nil} second argument @var{beforep} to this
4063function interactively by supplying any prefix argument.
4064
4065If the register contains a rectangle, then the rectangle is inserted
4066with its upper left corner at point. This means that text is inserted
4067in the current line and underneath it on successive lines.
4068
4069If the register contains something other than saved text (a string) or
4070a rectangle (a list), currently useless things happen. This may be
4071changed in the future.
4072@end deffn
4073
b8d4c8d0
GM
4074@node Transposition
4075@section Transposition of Text
4076
10256988 4077 This function can be used to transpose stretches of text:
b8d4c8d0
GM
4078
4079@defun transpose-regions start1 end1 start2 end2 &optional leave-markers
4080This function exchanges two nonoverlapping portions of the buffer.
4081Arguments @var{start1} and @var{end1} specify the bounds of one portion
4082and arguments @var{start2} and @var{end2} specify the bounds of the
4083other portion.
4084
4085Normally, @code{transpose-regions} relocates markers with the transposed
4086text; a marker previously positioned within one of the two transposed
4087portions moves along with that portion, thus remaining between the same
4088two characters in their new position. However, if @var{leave-markers}
4089is non-@code{nil}, @code{transpose-regions} does not do this---it leaves
4090all markers unrelocated.
4091@end defun
4092
4093@node Base 64
4094@section Base 64 Encoding
4095@cindex base 64 encoding
4096
4097 Base 64 code is used in email to encode a sequence of 8-bit bytes as
4098a longer sequence of @acronym{ASCII} graphic characters. It is defined in
4099Internet RFC@footnote{
4100An RFC, an acronym for @dfn{Request for Comments}, is a numbered
4101Internet informational document describing a standard. RFCs are
4102usually written by technical experts acting on their own initiative,
4103and are traditionally written in a pragmatic, experience-driven
4104manner.
4105}2045. This section describes the functions for
4106converting to and from this code.
4107
106e6894 4108@deffn Command base64-encode-region beg end &optional no-line-break
b8d4c8d0
GM
4109This function converts the region from @var{beg} to @var{end} into base
411064 code. It returns the length of the encoded text. An error is
1df7defd 4111signaled if a character in the region is multibyte, i.e., in a
b8d4c8d0
GM
4112multibyte buffer the region must contain only characters from the
4113charsets @code{ascii}, @code{eight-bit-control} and
4114@code{eight-bit-graphic}.
4115
4116Normally, this function inserts newline characters into the encoded
4117text, to avoid overlong lines. However, if the optional argument
4118@var{no-line-break} is non-@code{nil}, these newlines are not added, so
4119the output is just one long line.
106e6894 4120@end deffn
b8d4c8d0 4121
0b128ac4 4122@defun base64-encode-string string &optional no-line-break
b8d4c8d0
GM
4123This function converts the string @var{string} into base 64 code. It
4124returns a string containing the encoded text. As for
4125@code{base64-encode-region}, an error is signaled if a character in the
4126string is multibyte.
4127
4128Normally, this function inserts newline characters into the encoded
4129text, to avoid overlong lines. However, if the optional argument
4130@var{no-line-break} is non-@code{nil}, these newlines are not added, so
4131the result string is just one long line.
0b128ac4 4132@end defun
b8d4c8d0 4133
0b128ac4 4134@deffn Command base64-decode-region beg end
b8d4c8d0
GM
4135This function converts the region from @var{beg} to @var{end} from base
413664 code into the corresponding decoded text. It returns the length of
4137the decoded text.
4138
4139The decoding functions ignore newline characters in the encoded text.
0b128ac4 4140@end deffn
b8d4c8d0
GM
4141
4142@defun base64-decode-string string
4143This function converts the string @var{string} from base 64 code into
4144the corresponding decoded text. It returns a unibyte string containing the
4145decoded text.
4146
4147The decoding functions ignore newline characters in the encoded text.
4148@end defun
4149
5f5e4ea1
GM
4150@node Checksum/Hash
4151@section Checksum/Hash
b8d4c8d0 4152@cindex MD5 checksum
483ab230
CY
4153@cindex SHA hash
4154@cindex hash, cryptographic
4155@cindex cryptographic hash
4156
4157 Emacs has built-in support for computing @dfn{cryptographic hashes}.
4158A cryptographic hash, or @dfn{checksum}, is a digital ``fingerprint''
1df7defd 4159of a piece of data (e.g., a block of text) which can be used to check
483ab230
CY
4160that you have an unaltered copy of that data.
4161
4162@cindex message digest
4163 Emacs supports several common cryptographic hash algorithms: MD5,
4164SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512. MD5 is the
4165oldest of these algorithms, and is commonly used in @dfn{message
4166digests} to check the integrity of messages transmitted over a
1df7defd 4167network. MD5 is not ``collision resistant'' (i.e., it is possible to
483ab230
CY
4168deliberately design different pieces of data which have the same MD5
4169hash), so you should not used it for anything security-related. A
4170similar theoretical weakness also exists in SHA-1. Therefore, for
4171security-related applications you should use the other hash types,
4172such as SHA-2.
b8d4c8d0 4173
483ab230
CY
4174@defun secure-hash algorithm object &optional start end binary
4175This function returns a hash for @var{object}. The argument
4176@var{algorithm} is a symbol stating which hash to compute: one of
4177@code{md5}, @code{sha1}, @code{sha224}, @code{sha256}, @code{sha384}
4178or @code{sha512}. The argument @var{object} should be a buffer or a
4179string.
b8d4c8d0 4180
483ab230 4181The optional arguments @var{start} and @var{end} are character
b8d4c8d0 4182positions specifying the portion of @var{object} to compute the
483ab230 4183message digest for. If they are @code{nil} or omitted, the hash is
b8d4c8d0
GM
4184computed for the whole of @var{object}.
4185
483ab230
CY
4186If the argument @var{binary} is omitted or @code{nil}, the function
4187returns the @dfn{text form} of the hash, as an ordinary Lisp string.
4188If @var{binary} is non-@code{nil}, it returns the hash in @dfn{binary
4189form}, as a sequence of bytes stored in a unibyte string.
4190
4191This function does not compute the hash directly from the internal
4192representation of @var{object}'s text (@pxref{Text Representations}).
4193Instead, it encodes the text using a coding system (@pxref{Coding
4194Systems}), and computes the hash from that encoded text. If
4195@var{object} is a buffer, the coding system used is the one which
4196would be chosen by default for writing the text into a file. If
4197@var{object} is a string, the user's preferred coding system is used
4198(@pxref{Recognize Coding,,, emacs, GNU Emacs Manual}).
4199@end defun
4200
4201@defun md5 object &optional start end coding-system noerror
4202This function returns an MD5 hash. It is semi-obsolete, since for
4203most purposes it is equivalent to calling @code{secure-hash} with
4204@code{md5} as the @var{algorithm} argument. The @var{object},
4205@var{start} and @var{end} arguments have the same meanings as in
4206@code{secure-hash}.
4207
4208If @var{coding-system} is non-@code{nil}, it specifies a coding system
4209to use to encode the text; if omitted or @code{nil}, the default
4210coding system is used, like in @code{secure-hash}.
b8d4c8d0
GM
4211
4212Normally, @code{md5} signals an error if the text can't be encoded
4213using the specified or chosen coding system. However, if
4214@var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
4215coding instead.
4216@end defun
4217
483ab230
CY
4218@node Parsing HTML/XML
4219@section Parsing HTML and XML
381408e2 4220@cindex parsing html
381408e2 4221
483ab230
CY
4222When Emacs is compiled with libxml2 support, the following functions
4223are available to parse HTML or XML text into Lisp object trees.
4224
35a30759 4225@defun libxml-parse-html-region start end &optional base-url
483ab230
CY
4226This function parses the text between @var{start} and @var{end} as
4227HTML, and returns a list representing the HTML @dfn{parse tree}. It
4228attempts to handle ``real world'' HTML by robustly coping with syntax
4229mistakes.
381408e2 4230
483ab230
CY
4231The optional argument @var{base-url}, if non-@code{nil}, should be a
4232string specifying the base URL for relative URLs occurring in links.
381408e2 4233
483ab230
CY
4234In the parse tree, each HTML node is represented by a list in which
4235the first element is a symbol representing the node name, the second
4236element is an alist of node attributes, and the remaining elements are
4237the subnodes.
4238
4239The following example demonstrates this. Given this (malformed) HTML
4240document:
381408e2
LMI
4241
4242@example
483ab230 4243<html><head></head><body width=101><div class=thing>Foo<div>Yes
381408e2
LMI
4244@end example
4245
483ab230
CY
4246@noindent
4247A call to @code{libxml-parse-html-region} returns this:
381408e2
LMI
4248
4249@example
483ab230
CY
4250(html ()
4251 (head ())
4252 (body ((width . "101"))
4253 (div ((class . "thing"))
4254 "Foo"
4255 (div ()
4256 "Yes"))))
381408e2 4257@end example
35a30759
N
4258@end defun
4259
4260@cindex parsing xml
4261@defun libxml-parse-xml-region start end &optional base-url
483ab230
CY
4262This function is the same as @code{libxml-parse-html-region}, except
4263that it parses the text as XML rather than HTML (so it is stricter
4264about syntax).
35a30759 4265@end defun
381408e2 4266
b8d4c8d0
GM
4267@node Atomic Changes
4268@section Atomic Change Groups
4269@cindex atomic changes
4270
35a30759 4271 In database terminology, an @dfn{atomic} change is an indivisible
b8d4c8d0
GM
4272change---it can succeed entirely or it can fail entirely, but it
4273cannot partly succeed. A Lisp program can make a series of changes to
4274one or several buffers as an @dfn{atomic change group}, meaning that
4275either the entire series of changes will be installed in their buffers
4276or, in case of an error, none of them will be.
4277
4278 To do this for one buffer, the one already current, simply write a
4279call to @code{atomic-change-group} around the code that makes the
4280changes, like this:
4281
4282@example
4283(atomic-change-group
4284 (insert foo)
4285 (delete-region x y))
4286@end example
4287
4288@noindent
4289If an error (or other nonlocal exit) occurs inside the body of
4290@code{atomic-change-group}, it unmakes all the changes in that buffer
4291that were during the execution of the body. This kind of change group
4292has no effect on any other buffers---any such changes remain.
4293
4294 If you need something more sophisticated, such as to make changes in
4295various buffers constitute one atomic group, you must directly call
4296lower-level functions that @code{atomic-change-group} uses.
4297
4298@defun prepare-change-group &optional buffer
4299This function sets up a change group for buffer @var{buffer}, which
4300defaults to the current buffer. It returns a ``handle'' that
4301represents the change group. You must use this handle to activate the
4302change group and subsequently to finish it.
4303@end defun
4304
4305 To use the change group, you must @dfn{activate} it. You must do
4306this before making any changes in the text of @var{buffer}.
4307
4308@defun activate-change-group handle
4309This function activates the change group that @var{handle} designates.
4310@end defun
4311
4312 After you activate the change group, any changes you make in that
4313buffer become part of it. Once you have made all the desired changes
4314in the buffer, you must @dfn{finish} the change group. There are two
4315ways to do this: you can either accept (and finalize) all the changes,
4316or cancel them all.
4317
4318@defun accept-change-group handle
4319This function accepts all the changes in the change group specified by
4320@var{handle}, making them final.
4321@end defun
4322
4323@defun cancel-change-group handle
4324This function cancels and undoes all the changes in the change group
4325specified by @var{handle}.
4326@end defun
4327
4328 Your code should use @code{unwind-protect} to make sure the group is
4329always finished. The call to @code{activate-change-group} should be
4330inside the @code{unwind-protect}, in case the user types @kbd{C-g}
4331just after it runs. (This is one reason why
4332@code{prepare-change-group} and @code{activate-change-group} are
4333separate functions, because normally you would call
4334@code{prepare-change-group} before the start of that
4335@code{unwind-protect}.) Once you finish the group, don't use the
4336handle again---in particular, don't try to finish the same group
4337twice.
4338
4339 To make a multibuffer change group, call @code{prepare-change-group}
4340once for each buffer you want to cover, then use @code{nconc} to
4341combine the returned values, like this:
4342
4343@example
4344(nconc (prepare-change-group buffer-1)
4345 (prepare-change-group buffer-2))
4346@end example
4347
4348You can then activate the multibuffer change group with a single call
4349to @code{activate-change-group}, and finish it with a single call to
4350@code{accept-change-group} or @code{cancel-change-group}.
4351
4352 Nested use of several change groups for the same buffer works as you
4353would expect. Non-nested use of change groups for the same buffer
4354will get Emacs confused, so don't let it happen; the first change
4355group you start for any given buffer should be the last one finished.
4356
4357@node Change Hooks
4358@section Change Hooks
4359@cindex change hooks
4360@cindex hooks for text changes
4361
4362 These hook variables let you arrange to take notice of all changes in
4363all buffers (or in a particular buffer, if you make them buffer-local).
4364See also @ref{Special Properties}, for how to detect changes to specific
4365parts of the text.
4366
4367 The functions you use in these hooks should save and restore the match
4368data if they do anything that uses regular expressions; otherwise, they
4369will interfere in bizarre ways with the editing operations that call
4370them.
4371
4372@defvar before-change-functions
4373This variable holds a list of functions to call before any buffer
4374modification. Each function gets two arguments, the beginning and end
4375of the region that is about to change, represented as integers. The
4376buffer that is about to change is always the current buffer.
4377@end defvar
4378
4379@defvar after-change-functions
4380This variable holds a list of functions to call after any buffer
5a5fd9f3
CY
4381modification. Each function receives three arguments: the beginning
4382and end of the region just changed, and the length of the text that
4383existed before the change. All three arguments are integers. The
93c2fa46 4384buffer that has been changed is always the current buffer.
5a5fd9f3
CY
4385
4386The length of the old text is the difference between the buffer
4387positions before and after that text as it was before the change. As
4388for the changed text, its length is simply the difference between the
4389first two arguments.
b8d4c8d0
GM
4390@end defvar
4391
2bb0eca1 4392 Output of messages into the @file{*Messages*} buffer does not
b8d4c8d0
GM
4393call these functions.
4394
4395@defmac combine-after-change-calls body@dots{}
4396The macro executes @var{body} normally, but arranges to call the
4397after-change functions just once for a series of several changes---if
4398that seems safe.
4399
4400If a program makes several text changes in the same area of the buffer,
4401using the macro @code{combine-after-change-calls} around that part of
4402the program can make it run considerably faster when after-change hooks
4403are in use. When the after-change hooks are ultimately called, the
4404arguments specify a portion of the buffer including all of the changes
4405made within the @code{combine-after-change-calls} body.
4406
4407@strong{Warning:} You must not alter the values of
4408@code{after-change-functions} within
4409the body of a @code{combine-after-change-calls} form.
4410
4411@strong{Warning:} if the changes you combine occur in widely scattered
4412parts of the buffer, this will still work, but it is not advisable,
4413because it may lead to inefficient behavior for some change hook
4414functions.
4415@end defmac
4416
4417@defvar first-change-hook
4418This variable is a normal hook that is run whenever a buffer is changed
4419that was previously in the unmodified state.
4420@end defvar
4421
4422@defvar inhibit-modification-hooks
4423If this variable is non-@code{nil}, all of the change hooks are
4424disabled; none of them run. This affects all the hook variables
4425described above in this section, as well as the hooks attached to
4426certain special text properties (@pxref{Special Properties}) and overlay
4427properties (@pxref{Overlay Properties}).
4428
4429Also, this variable is bound to non-@code{nil} while running those
4430same hook variables, so that by default modifying the buffer from
4431a modification hook does not cause other modification hooks to be run.
4432If you do want modification hooks to be run in a particular piece of
4433code that is itself run from a modification hook, then rebind locally
4434@code{inhibit-modification-hooks} to @code{nil}.
4435@end defvar