1 This is Info file ../../info/lispref.info, produced by Makeinfo version
2 1.68 from the input file lispref.texi.
4 INFO-DIR-SECTION XEmacs Editor
6 * Lispref: (lispref). XEmacs Lisp Reference Manual.
11 GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU
12 Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid
13 Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994
14 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995
15 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp
16 Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp
17 Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp
18 Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May,
19 November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998
21 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software
22 Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc.
23 Copyright (C) 1995, 1996 Ben Wing.
25 Permission is granted to make and distribute verbatim copies of this
26 manual provided the copyright notice and this permission notice are
27 preserved on all copies.
29 Permission is granted to copy and distribute modified versions of
30 this manual under the conditions for verbatim copying, provided that the
31 entire resulting derived work is distributed under the terms of a
32 permission notice identical to this one.
34 Permission is granted to copy and distribute translations of this
35 manual into another language, under the above conditions for modified
36 versions, except that this permission notice may be stated in a
37 translation approved by the Foundation.
39 Permission is granted to copy and distribute modified versions of
40 this manual under the conditions for verbatim copying, provided also
41 that the section entitled "GNU General Public License" is included
42 exactly as in the original, and provided that the entire resulting
43 derived work is distributed under the terms of a permission notice
44 identical to this one.
46 Permission is granted to copy and distribute translations of this
47 manual into another language, under the above conditions for modified
48 versions, except that the section entitled "GNU General Public License"
49 may be included in a translation approved by the Free Software
50 Foundation instead of in the original English.
53 File: lispref.info, Node: Commands for Insertion, Next: Deletion, Prev: Insertion, Up: Text
55 User-Level Insertion Commands
56 =============================
58 This section describes higher-level commands for inserting text,
59 commands intended primarily for the user but useful also in Lisp
62 - Command: insert-buffer FROM-BUFFER-OR-NAME
63 This command inserts the entire contents of FROM-BUFFER-OR-NAME
64 (which must exist) into the current buffer after point. It leaves
65 the mark after the inserted text. The value is `nil'.
67 - Command: self-insert-command COUNT
68 This command inserts the last character typed; it does so COUNT
69 times, before point, and returns `nil'. Most printing characters
70 are bound to this command. In routine use, `self-insert-command'
71 is the most frequently called function in XEmacs, but programs
72 rarely use it except to install it on a keymap.
74 In an interactive call, COUNT is the numeric prefix argument.
76 This command calls `auto-fill-function' whenever that is non-`nil'
77 and the character inserted is a space or a newline (*note Auto
80 This command performs abbrev expansion if Abbrev mode is enabled
81 and the inserted character does not have word-constituent syntax.
82 (*Note Abbrevs::, and *Note Syntax Class Table::.)
84 This is also responsible for calling `blink-paren-function' when
85 the inserted character has close parenthesis syntax (*note
88 - Command: newline &optional NUMBER-OF-NEWLINES
89 This command inserts newlines into the current buffer before point.
90 If NUMBER-OF-NEWLINES is supplied, that many newline characters
93 This function calls `auto-fill-function' if the current column
94 number is greater than the value of `fill-column' and
95 NUMBER-OF-NEWLINES is `nil'. Typically what `auto-fill-function'
96 does is insert a newline; thus, the overall result in this case is
97 to insert two newlines at different places: one at point, and
98 another earlier in the line. `newline' does not auto-fill if
99 NUMBER-OF-NEWLINES is non-`nil'.
101 This command indents to the left margin if that is not zero.
104 The value returned is `nil'. In an interactive call, COUNT is the
105 numeric prefix argument.
107 - Command: split-line
108 This command splits the current line, moving the portion of the
109 line after point down vertically so that it is on the next line
110 directly below where it was before. Whitespace is inserted as
111 needed at the beginning of the lower line, using the `indent-to'
112 function. `split-line' returns the position of point.
114 Programs hardly ever use this function.
116 - Variable: overwrite-mode
117 This variable controls whether overwrite mode is in effect: a
118 non-`nil' value enables the mode. It is automatically made
119 buffer-local when set in any fashion.
122 File: lispref.info, Node: Deletion, Next: User-Level Deletion, Prev: Commands for Insertion, Up: Text
127 Deletion means removing part of the text in a buffer, without saving
128 it in the kill ring (*note The Kill Ring::.). Deleted text can't be
129 yanked, but can be reinserted using the undo mechanism (*note Undo::.).
130 Some deletion functions do save text in the kill ring in some special
133 All of the deletion functions operate on the current buffer, and all
134 return a value of `nil'.
136 - Function: erase-buffer &optional BUFFER
137 This function deletes the entire text of BUFFER, leaving it empty.
138 If the buffer is read-only, it signals a `buffer-read-only'
139 error. Otherwise, it deletes the text without asking for any
140 confirmation. It returns `nil'. BUFFER defaults to the current
143 Normally, deleting a large amount of text from a buffer inhibits
144 further auto-saving of that buffer "because it has shrunk".
145 However, `erase-buffer' does not do this, the idea being that the
146 future text is not really related to the former text, and its size
147 should not be compared with that of the former text.
149 - Command: delete-region START END &optional BUFFER
150 This command deletes the text in BUFFER in the region defined by
151 START and END. The value is `nil'. If optional argument BUFFER
152 is `nil', the current buffer is assumed.
154 - Command: delete-char COUNT &optional KILLP
155 This command deletes COUNT characters directly after point, or
156 before point if COUNT is negative. If KILLP is non-`nil', then it
157 saves the deleted characters in the kill ring.
159 In an interactive call, COUNT is the numeric prefix argument, and
160 KILLP is the unprocessed prefix argument. Therefore, if a prefix
161 argument is supplied, the text is saved in the kill ring. If no
162 prefix argument is supplied, then one character is deleted, but
163 not saved in the kill ring.
165 The value returned is always `nil'.
167 - Command: delete-backward-char COUNT &optional KILLP
168 This command deletes COUNT characters directly before point, or
169 after point if COUNT is negative. If KILLP is non-`nil', then it
170 saves the deleted characters in the kill ring.
172 In an interactive call, COUNT is the numeric prefix argument, and
173 KILLP is the unprocessed prefix argument. Therefore, if a prefix
174 argument is supplied, the text is saved in the kill ring. If no
175 prefix argument is supplied, then one character is deleted, but
176 not saved in the kill ring.
178 The value returned is always `nil'.
180 - Command: backward-delete-char-untabify COUNT &optional KILLP
181 This command deletes COUNT characters backward, changing tabs into
182 spaces. When the next character to be deleted is a tab, it is
183 first replaced with the proper number of spaces to preserve
184 alignment and then one of those spaces is deleted instead of the
185 tab. If KILLP is non-`nil', then the command saves the deleted
186 characters in the kill ring.
188 Conversion of tabs to spaces happens only if COUNT is positive.
189 If it is negative, exactly -COUNT characters after point are
192 In an interactive call, COUNT is the numeric prefix argument, and
193 KILLP is the unprocessed prefix argument. Therefore, if a prefix
194 argument is supplied, the text is saved in the kill ring. If no
195 prefix argument is supplied, then one character is deleted, but
196 not saved in the kill ring.
198 The value returned is always `nil'.
201 File: lispref.info, Node: User-Level Deletion, Next: The Kill Ring, Prev: Deletion, Up: Text
203 User-Level Deletion Commands
204 ============================
206 This section describes higher-level commands for deleting text,
207 commands intended primarily for the user but useful also in Lisp
210 - Command: delete-horizontal-space
211 This function deletes all spaces and tabs around point. It returns
214 In the following examples, we call `delete-horizontal-space' four
215 times, once on each line, with point between the second and third
216 characters on the line each time.
218 ---------- Buffer: foo ----------
223 ---------- Buffer: foo ----------
225 (delete-horizontal-space) ; Four times.
228 ---------- Buffer: foo ----------
233 ---------- Buffer: foo ----------
235 - Command: delete-indentation &optional JOIN-FOLLOWING-P
236 This function joins the line point is on to the previous line,
237 deleting any whitespace at the join and in some cases replacing it
238 with one space. If JOIN-FOLLOWING-P is non-`nil',
239 `delete-indentation' joins this line to the following line
240 instead. The value is `nil'.
242 If there is a fill prefix, and the second of the lines being joined
243 starts with the prefix, then `delete-indentation' deletes the fill
244 prefix before joining the lines. *Note Margins::.
246 In the example below, point is located on the line starting
247 `events', and it makes no difference if there are trailing spaces
248 in the preceding line.
250 ---------- Buffer: foo ----------
251 When in the course of human
252 -!- events, it becomes necessary
253 ---------- Buffer: foo ----------
257 ---------- Buffer: foo ----------
258 When in the course of human-!- events, it becomes necessary
259 ---------- Buffer: foo ----------
261 After the lines are joined, the function `fixup-whitespace' is
262 responsible for deciding whether to leave a space at the junction.
264 - Function: fixup-whitespace
265 This function replaces all the white space surrounding point with
266 either one space or no space, according to the context. It
269 At the beginning or end of a line, the appropriate amount of space
270 is none. Before a character with close parenthesis syntax, or
271 after a character with open parenthesis or expression-prefix
272 syntax, no space is also appropriate. Otherwise, one space is
273 appropriate. *Note Syntax Class Table::.
275 In the example below, `fixup-whitespace' is called the first time
276 with point before the word `spaces' in the first line. For the
277 second invocation, point is directly after the `('.
279 ---------- Buffer: foo ----------
280 This has too many -!-spaces
281 This has too many spaces at the start of (-!- this list)
282 ---------- Buffer: foo ----------
289 ---------- Buffer: foo ----------
290 This has too many spaces
291 This has too many spaces at the start of (this list)
292 ---------- Buffer: foo ----------
294 - Command: just-one-space
295 This command replaces any spaces and tabs around point with a
296 single space. It returns `nil'.
298 - Command: delete-blank-lines
299 This function deletes blank lines surrounding point. If point is
300 on a blank line with one or more blank lines before or after it,
301 then all but one of them are deleted. If point is on an isolated
302 blank line, then it is deleted. If point is on a nonblank line,
303 the command deletes all blank lines following it.
305 A blank line is defined as a line containing only tabs and spaces.
307 `delete-blank-lines' returns `nil'.
310 File: lispref.info, Node: The Kill Ring, Next: Undo, Prev: User-Level Deletion, Up: Text
315 "Kill" functions delete text like the deletion functions, but save
316 it so that the user can reinsert it by "yanking". Most of these
317 functions have `kill-' in their name. By contrast, the functions whose
318 names start with `delete-' normally do not save text for yanking
319 (though they can still be undone); these are "deletion" functions.
321 Most of the kill commands are primarily for interactive use, and are
322 not described here. What we do describe are the functions provided for
323 use in writing such commands. You can use these functions to write
324 commands for killing text. When you need to delete text for internal
325 purposes within a Lisp function, you should normally use deletion
326 functions, so as not to disturb the kill ring contents. *Note
329 Killed text is saved for later yanking in the "kill ring". This is
330 a list that holds a number of recent kills, not just the last text
331 kill. We call this a "ring" because yanking treats it as having
332 elements in a cyclic order. The list is kept in the variable
333 `kill-ring', and can be operated on with the usual functions for lists;
334 there are also specialized functions, described in this section, that
337 Some people think this use of the word "kill" is unfortunate, since
338 it refers to operations that specifically *do not* destroy the entities
339 "killed". This is in sharp contrast to ordinary life, in which death
340 is permanent and "killed" entities do not come back to life.
341 Therefore, other metaphors have been proposed. For example, the term
342 "cut ring" makes sense to people who, in pre-computer days, used
343 scissors and paste to cut up and rearrange manuscripts. However, it
344 would be difficult to change the terminology now.
348 * Kill Ring Concepts:: What text looks like in the kill ring.
349 * Kill Functions:: Functions that kill text.
350 * Yank Commands:: Commands that access the kill ring.
351 * Low-Level Kill Ring:: Functions and variables for kill ring access.
352 * Internals of Kill Ring:: Variables that hold kill-ring data.
355 File: lispref.info, Node: Kill Ring Concepts, Next: Kill Functions, Up: The Kill Ring
360 The kill ring records killed text as strings in a list, most recent
361 first. A short kill ring, for example, might look like this:
363 ("some text" "a different piece of text" "even older text")
365 When the list reaches `kill-ring-max' entries in length, adding a new
366 entry automatically deletes the last entry.
368 When kill commands are interwoven with other commands, each kill
369 command makes a new entry in the kill ring. Multiple kill commands in
370 succession build up a single entry in the kill ring, which would be
371 yanked as a unit; the second and subsequent consecutive kill commands
372 add text to the entry made by the first one.
374 For yanking, one entry in the kill ring is designated the "front" of
375 the ring. Some yank commands "rotate" the ring by designating a
376 different element as the "front." But this virtual rotation doesn't
377 change the list itself--the most recent entry always comes first in the
381 File: lispref.info, Node: Kill Functions, Next: Yank Commands, Prev: Kill Ring Concepts, Up: The Kill Ring
383 Functions for Killing
384 ---------------------
386 `kill-region' is the usual subroutine for killing text. Any command
387 that calls this function is a "kill command" (and should probably have
388 `kill' in its name). `kill-region' puts the newly killed text in a new
389 element at the beginning of the kill ring or adds it to the most recent
390 element. It uses the `last-command' variable to determine whether the
391 previous command was a kill command, and if so appends the killed text
392 to the most recent entry.
394 - Command: kill-region START END
395 This function kills the text in the region defined by START and
396 END. The text is deleted but saved in the kill ring, along with
397 its text properties. The value is always `nil'.
399 In an interactive call, START and END are point and the mark.
401 If the buffer is read-only, `kill-region' modifies the kill ring
402 just the same, then signals an error without modifying the buffer.
403 This is convenient because it lets the user use all the kill
404 commands to copy text into the kill ring from a read-only buffer.
406 - Command: copy-region-as-kill START END
407 This command saves the region defined by START and END on the kill
408 ring (including text properties), but does not delete the text
409 from the buffer. It returns `nil'. It also indicates the extent
410 of the text copied by moving the cursor momentarily, or by
411 displaying a message in the echo area.
413 The command does not set `this-command' to `kill-region', so a
414 subsequent kill command does not append to the same kill ring
417 Don't call `copy-region-as-kill' in Lisp programs unless you aim to
418 support Emacs 18. For Emacs 19, it is better to use `kill-new' or
419 `kill-append' instead. *Note Low-Level Kill Ring::.
422 File: lispref.info, Node: Yank Commands, Next: Low-Level Kill Ring, Prev: Kill Functions, Up: The Kill Ring
424 Functions for Yanking
425 ---------------------
427 "Yanking" means reinserting an entry of previously killed text from
428 the kill ring. The text properties are copied too.
430 - Command: yank &optional ARG
431 This command inserts before point the text in the first entry in
432 the kill ring. It positions the mark at the beginning of that
433 text, and point at the end.
435 If ARG is a list (which occurs interactively when the user types
436 `C-u' with no digits), then `yank' inserts the text as described
437 above, but puts point before the yanked text and puts the mark
440 If ARG is a number, then `yank' inserts the ARGth most recently
441 killed text--the ARGth element of the kill ring list.
443 `yank' does not alter the contents of the kill ring or rotate it.
446 - Command: yank-pop ARG
447 This command replaces the just-yanked entry from the kill ring
448 with a different entry from the kill ring.
450 This is allowed only immediately after a `yank' or another
451 `yank-pop'. At such a time, the region contains text that was just
452 inserted by yanking. `yank-pop' deletes that text and inserts in
453 its place a different piece of killed text. It does not add the
454 deleted text to the kill ring, since it is already in the kill
457 If ARG is `nil', then the replacement text is the previous element
458 of the kill ring. If ARG is numeric, the replacement is the ARGth
459 previous kill. If ARG is negative, a more recent kill is the
462 The sequence of kills in the kill ring wraps around, so that after
463 the oldest one comes the newest one, and before the newest one
466 The value is always `nil'.
469 File: lispref.info, Node: Low-Level Kill Ring, Next: Internals of Kill Ring, Prev: Yank Commands, Up: The Kill Ring
474 These functions and variables provide access to the kill ring at a
475 lower level, but still convenient for use in Lisp programs. They take
476 care of interaction with X Window selections. They do not exist in
479 - Function: current-kill N &optional DO-NOT-MOVE
480 The function `current-kill' rotates the yanking pointer which
481 designates the "front" of the kill ring by N places (from newer
482 kills to older ones), and returns the text at that place in the
485 If the optional second argument DO-NOT-MOVE is non-`nil', then
486 `current-kill' doesn't alter the yanking pointer; it just returns
487 the Nth kill, counting from the current yanking pointer.
489 If N is zero, indicating a request for the latest kill,
490 `current-kill' calls the value of `interprogram-paste-function'
491 (documented below) before consulting the kill ring.
493 - Function: kill-new STRING
494 This function puts the text STRING into the kill ring as a new
495 entry at the front of the ring. It discards the oldest entry if
496 appropriate. It also invokes the value of
497 `interprogram-cut-function' (see below).
499 - Function: kill-append STRING BEFORE-P
500 This function appends the text STRING to the first entry in the
501 kill ring. Normally STRING goes at the end of the entry, but if
502 BEFORE-P is non-`nil', it goes at the beginning. This function
503 also invokes the value of `interprogram-cut-function' (see below).
505 - Variable: interprogram-paste-function
506 This variable provides a way of transferring killed text from other
507 programs, when you are using a window system. Its value should be
508 `nil' or a function of no arguments.
510 If the value is a function, `current-kill' calls it to get the
511 "most recent kill". If the function returns a non-`nil' value,
512 then that value is used as the "most recent kill". If it returns
513 `nil', then the first element of `kill-ring' is used.
515 The normal use of this hook is to get the X server's primary
516 selection as the most recent kill, even if the selection belongs
517 to another X client. *Note X Selections::.
519 - Variable: interprogram-cut-function
520 This variable provides a way of communicating killed text to other
521 programs, when you are using a window system. Its value should be
522 `nil' or a function of one argument.
524 If the value is a function, `kill-new' and `kill-append' call it
525 with the new first element of the kill ring as an argument.
527 The normal use of this hook is to set the X server's primary
528 selection to the newly killed text.
531 File: lispref.info, Node: Internals of Kill Ring, Prev: Low-Level Kill Ring, Up: The Kill Ring
533 Internals of the Kill Ring
534 --------------------------
536 The variable `kill-ring' holds the kill ring contents, in the form
537 of a list of strings. The most recent kill is always at the front of
540 The `kill-ring-yank-pointer' variable points to a link in the kill
541 ring list, whose CAR is the text to yank next. We say it identifies
542 the "front" of the ring. Moving `kill-ring-yank-pointer' to a
543 different link is called "rotating the kill ring". We call the kill
544 ring a "ring" because the functions that move the yank pointer wrap
545 around from the end of the list to the beginning, or vice-versa.
546 Rotation of the kill ring is virtual; it does not change the value of
549 Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables
550 whose values are normally lists. The word "pointer" in the name of the
551 `kill-ring-yank-pointer' indicates that the variable's purpose is to
552 identify one element of the list for use by the next yank command.
554 The value of `kill-ring-yank-pointer' is always `eq' to one of the
555 links in the kill ring list. The element it identifies is the CAR of
556 that link. Kill commands, which change the kill ring, also set this
557 variable to the value of `kill-ring'. The effect is to rotate the ring
558 so that the newly killed text is at the front.
560 Here is a diagram that shows the variable `kill-ring-yank-pointer'
561 pointing to the second entry in the kill ring `("some text" "a
562 different piece of text" "yet older text")'.
564 kill-ring kill-ring-yank-pointer
566 | ___ ___ ---> ___ ___ ___ ___
567 --> |___|___|------> |___|___|--> |___|___|--> nil
570 | | -->"yet older text"
572 | --> "a different piece of text"
576 This state of affairs might occur after `C-y' (`yank') immediately
577 followed by `M-y' (`yank-pop').
579 - Variable: kill-ring
580 This variable holds the list of killed text sequences, most
581 recently killed first.
583 - Variable: kill-ring-yank-pointer
584 This variable's value indicates which element of the kill ring is
585 at the "front" of the ring for yanking. More precisely, the value
586 is a tail of the value of `kill-ring', and its CAR is the kill
587 string that `C-y' should yank.
589 - User Option: kill-ring-max
590 The value of this variable is the maximum length to which the kill
591 ring can grow, before elements are thrown away at the end. The
592 default value for `kill-ring-max' is 30.
595 File: lispref.info, Node: Undo, Next: Maintaining Undo, Prev: The Kill Ring, Up: Text
600 Most buffers have an "undo list", which records all changes made to
601 the buffer's text so that they can be undone. (The buffers that don't
602 have one are usually special-purpose buffers for which XEmacs assumes
603 that undoing is not useful.) All the primitives that modify the text
604 in the buffer automatically add elements to the front of the undo list,
605 which is in the variable `buffer-undo-list'.
607 - Variable: buffer-undo-list
608 This variable's value is the undo list of the current buffer. A
609 value of `t' disables the recording of undo information.
611 Here are the kinds of elements an undo list can have:
614 This kind of element records a previous value of point. Ordinary
615 cursor motion does not get any sort of undo record, but deletion
616 commands use these entries to record where point was before the
620 This kind of element indicates how to delete text that was
621 inserted. Upon insertion, the text occupied the range BEG-END in
625 This kind of element indicates how to reinsert text that was
626 deleted. The deleted text itself is the string TEXT. The place to
627 reinsert it is `(abs POSITION)'.
630 This kind of element indicates that an unmodified buffer became
631 modified. The elements HIGH and LOW are two integers, each
632 recording 16 bits of the visited file's modification time as of
633 when it was previously visited or saved. `primitive-undo' uses
634 those values to determine whether to mark the buffer as unmodified
635 once again; it does so only if the file's modification time
636 matches those numbers.
638 `(nil PROPERTY VALUE BEG . END)'
639 This kind of element records a change in a text property. Here's
640 how you might undo the change:
642 (put-text-property BEG END PROPERTY VALUE)
645 This element indicates where point was at an earlier time.
646 Undoing this element sets point to POSITION. Deletion normally
647 creates an element of this kind as well as a reinsertion element.
650 This element is a boundary. The elements between two boundaries
651 are called a "change group"; normally, each change group
652 corresponds to one keyboard command, and undo commands normally
653 undo an entire group as a unit.
655 - Function: undo-boundary
656 This function places a boundary element in the undo list. The undo
657 command stops at such a boundary, and successive undo commands undo
658 to earlier and earlier boundaries. This function returns `nil'.
660 The editor command loop automatically creates an undo boundary
661 before each key sequence is executed. Thus, each undo normally
662 undoes the effects of one command. Self-inserting input
663 characters are an exception. The command loop makes a boundary
664 for the first such character; the next 19 consecutive
665 self-inserting input characters do not make boundaries, and then
666 the 20th does, and so on as long as self-inserting characters
669 All buffer modifications add a boundary whenever the previous
670 undoable change was made in some other buffer. This way, a
671 command that modifies several buffers makes a boundary in each
674 Calling this function explicitly is useful for splitting the
675 effects of a command into more than one unit. For example,
676 `query-replace' calls `undo-boundary' after each replacement, so
677 that the user can undo individual replacements one by one.
679 - Function: primitive-undo COUNT LIST
680 This is the basic function for undoing elements of an undo list.
681 It undoes the first COUNT elements of LIST, returning the rest of
682 LIST. You could write this function in Lisp, but it is convenient
685 `primitive-undo' adds elements to the buffer's undo list when it
686 changes the buffer. Undo commands avoid confusion by saving the
687 undo list value at the beginning of a sequence of undo operations.
688 Then the undo operations use and update the saved value. The new
689 elements added by undoing are not part of this saved value, so
690 they don't interfere with continuing to undo.
693 File: lispref.info, Node: Maintaining Undo, Next: Filling, Prev: Undo, Up: Text
695 Maintaining Undo Lists
696 ======================
698 This section describes how to enable and disable undo information for
699 a given buffer. It also explains how the undo list is truncated
700 automatically so it doesn't get too big.
702 Recording of undo information in a newly created buffer is normally
703 enabled to start with; but if the buffer name starts with a space, the
704 undo recording is initially disabled. You can explicitly enable or
705 disable undo recording with the following two functions, or by setting
706 `buffer-undo-list' yourself.
708 - Command: buffer-enable-undo &optional BUFFER-OR-NAME
709 This command enables recording undo information for buffer
710 BUFFER-OR-NAME, so that subsequent changes can be undone. If no
711 argument is supplied, then the current buffer is used. This
712 function does nothing if undo recording is already enabled in the
713 buffer. It returns `nil'.
715 In an interactive call, BUFFER-OR-NAME is the current buffer. You
716 cannot specify any other buffer.
718 - Function: buffer-disable-undo &optional BUFFER
719 - Function: buffer-flush-undo &optional BUFFER
720 This function discards the undo list of BUFFER, and disables
721 further recording of undo information. As a result, it is no
722 longer possible to undo either previous changes or any subsequent
723 changes. If the undo list of BUFFER is already disabled, this
724 function has no effect.
726 This function returns `nil'. It cannot be called interactively.
728 The name `buffer-flush-undo' is not considered obsolete, but the
729 preferred name `buffer-disable-undo' is new as of Emacs versions
732 As editing continues, undo lists get longer and longer. To prevent
733 them from using up all available memory space, garbage collection trims
734 them back to size limits you can set. (For this purpose, the "size" of
735 an undo list measures the cons cells that make up the list, plus the
736 strings of deleted text.) Two variables control the range of acceptable
737 sizes: `undo-limit' and `undo-strong-limit'.
739 - Variable: undo-limit
740 This is the soft limit for the acceptable size of an undo list.
741 The change group at which this size is exceeded is the last one
744 - Variable: undo-strong-limit
745 This is the upper limit for the acceptable size of an undo list.
746 The change group at which this size is exceeded is discarded
747 itself (along with all older change groups). There is one
748 exception: the very latest change group is never discarded no
749 matter how big it is.
752 File: lispref.info, Node: Filling, Next: Margins, Prev: Maintaining Undo, Up: Text
757 "Filling" means adjusting the lengths of lines (by moving the line
758 breaks) so that they are nearly (but no greater than) a specified
759 maximum width. Additionally, lines can be "justified", which means
760 inserting spaces to make the left and/or right margins line up
761 precisely. The width is controlled by the variable `fill-column'. For
762 ease of reading, lines should be no longer than 70 or so columns.
764 You can use Auto Fill mode (*note Auto Filling::.) to fill text
765 automatically as you insert it, but changes to existing text may leave
766 it improperly filled. Then you must fill the text explicitly.
768 Most of the commands in this section return values that are not
769 meaningful. All the functions that do filling take note of the current
770 left margin, current right margin, and current justification style
771 (*note Margins::.). If the current justification style is `none', the
772 filling functions don't actually do anything.
774 Several of the filling functions have an argument JUSTIFY. If it is
775 non-`nil', that requests some kind of justification. It can be `left',
776 `right', `full', or `center', to request a specific style of
777 justification. If it is `t', that means to use the current
778 justification style for this part of the text (see
779 `current-justification', below).
781 When you call the filling functions interactively, using a prefix
782 argument implies the value `full' for JUSTIFY.
784 - Command: fill-paragraph JUSTIFY
785 This command fills the paragraph at or after point. If JUSTIFY is
786 non-`nil', each line is justified as well. It uses the ordinary
787 paragraph motion commands to find paragraph boundaries. *Note
788 Paragraphs: (xemacs)Paragraphs.
790 - Command: fill-region START END &optional JUSTIFY
791 This command fills each of the paragraphs in the region from START
792 to END. It justifies as well if JUSTIFY is non-`nil'.
794 The variable `paragraph-separate' controls how to distinguish
795 paragraphs. *Note Standard Regexps::.
797 - Command: fill-individual-paragraphs START END &optional JUSTIFY
799 This command fills each paragraph in the region according to its
800 individual fill prefix. Thus, if the lines of a paragraph were
801 indented with spaces, the filled paragraph will remain indented in
804 The first two arguments, START and END, are the beginning and end
805 of the region to be filled. The third and fourth arguments,
806 JUSTIFY and MAIL-FLAG, are optional. If JUSTIFY is non-`nil', the
807 paragraphs are justified as well as filled. If MAIL-FLAG is
808 non-`nil', it means the function is operating on a mail message
809 and therefore should not fill the header lines.
811 Ordinarily, `fill-individual-paragraphs' regards each change in
812 indentation as starting a new paragraph. If
813 `fill-individual-varying-indent' is non-`nil', then only separator
814 lines separate paragraphs. That mode can handle indented
815 paragraphs with additional indentation on the first line.
817 - User Option: fill-individual-varying-indent
818 This variable alters the action of `fill-individual-paragraphs' as
821 - Command: fill-region-as-paragraph START END &optional JUSTIFY
822 This command considers a region of text as a paragraph and fills
823 it. If the region was made up of many paragraphs, the blank lines
824 between paragraphs are removed. This function justifies as well
825 as filling when JUSTIFY is non-`nil'.
827 In an interactive call, any prefix argument requests justification.
829 In Adaptive Fill mode, which is enabled by default,
830 `fill-region-as-paragraph' on an indented paragraph when there is
831 no fill prefix uses the indentation of the second line of the
832 paragraph as the fill prefix.
834 - Command: justify-current-line HOW EOP NOSQUEEZE
835 This command inserts spaces between the words of the current line
836 so that the line ends exactly at `fill-column'. It returns `nil'.
838 The argument HOW, if non-`nil' specifies explicitly the style of
839 justification. It can be `left', `right', `full', `center', or
840 `none'. If it is `t', that means to do follow specified
841 justification style (see `current-justification', below). `nil'
842 means to do full justification.
844 If EOP is non-`nil', that means do left-justification when
845 `current-justification' specifies full justification. This is used
846 for the last line of a paragraph; even if the paragraph as a whole
847 is fully justified, the last line should not be.
849 If NOSQUEEZE is non-`nil', that means do not change interior
852 - User Option: default-justification
853 This variable's value specifies the style of justification to use
854 for text that doesn't specify a style with a text property. The
855 possible values are `left', `right', `full', `center', or `none'.
856 The default value is `left'.
858 - Function: current-justification
859 This function returns the proper justification style to use for
860 filling the text around point.
862 - Variable: fill-paragraph-function
863 This variable provides a way for major modes to override the
864 filling of paragraphs. If the value is non-`nil',
865 `fill-paragraph' calls this function to do the work. If the
866 function returns a non-`nil' value, `fill-paragraph' assumes the
867 job is done, and immediately returns that value.
869 The usual use of this feature is to fill comments in programming
870 language modes. If the function needs to fill a paragraph in the
871 usual way, it can do so as follows:
873 (let ((fill-paragraph-function nil))
874 (fill-paragraph arg))
876 - Variable: use-hard-newlines
877 If this variable is non-`nil', the filling functions do not delete
878 newlines that have the `hard' text property. These "hard
879 newlines" act as paragraph separators.
882 File: lispref.info, Node: Margins, Next: Auto Filling, Prev: Filling, Up: Text
887 - User Option: fill-prefix
888 This variable specifies a string of text that appears at the
889 beginning of normal text lines and should be disregarded when
890 filling them. Any line that fails to start with the fill prefix
891 is considered the start of a paragraph; so is any line that starts
892 with the fill prefix followed by additional whitespace. Lines
893 that start with the fill prefix but no additional whitespace are
894 ordinary text lines that can be filled together. The resulting
895 filled lines also start with the fill prefix.
897 The fill prefix follows the left margin whitespace, if any.
899 - User Option: fill-column
900 This buffer-local variable specifies the maximum width of filled
901 lines. Its value should be an integer, which is a number of
902 columns. All the filling, justification and centering commands
903 are affected by this variable, including Auto Fill mode (*note
906 As a practical matter, if you are writing text for other people to
907 read, you should set `fill-column' to no more than 70. Otherwise
908 the line will be too long for people to read comfortably, and this
909 can make the text seem clumsy.
911 - Variable: default-fill-column
912 The value of this variable is the default value for `fill-column'
913 in buffers that do not override it. This is the same as
914 `(default-value 'fill-column)'.
916 The default value for `default-fill-column' is 70.
918 - Command: set-left-margin FROM TO MARGIN
919 This sets the `left-margin' property on the text from FROM to TO
920 to the value MARGIN. If Auto Fill mode is enabled, this command
921 also refills the region to fit the new margin.
923 - Command: set-right-margin FROM TO MARGIN
924 This sets the `right-margin' property on the text from FROM to TO
925 to the value MARGIN. If Auto Fill mode is enabled, this command
926 also refills the region to fit the new margin.
928 - Function: current-left-margin
929 This function returns the proper left margin value to use for
930 filling the text around point. The value is the sum of the
931 `left-margin' property of the character at the start of the
932 current line (or zero if none), and the value of the variable
935 - Function: current-fill-column
936 This function returns the proper fill column value to use for
937 filling the text around point. The value is the value of the
938 `fill-column' variable, minus the value of the `right-margin'
939 property of the character after point.
941 - Command: move-to-left-margin &optional N FORCE
942 This function moves point to the left margin of the current line.
943 The column moved to is determined by calling the function
944 `current-left-margin'. If the argument N is non-`nil',
945 `move-to-left-margin' moves forward N-1 lines first.
947 If FORCE is non-`nil', that says to fix the line's indentation if
948 that doesn't match the left margin value.
950 - Function: delete-to-left-margin FROM TO
951 This function removes left margin indentation from the text
952 between FROM and TO. The amount of indentation to delete is
953 determined by calling `current-left-margin'. In no case does this
954 function delete non-whitespace.
956 - Function: indent-to-left-margin
957 This is the default `indent-line-function', used in Fundamental
958 mode, Text mode, etc. Its effect is to adjust the indentation at
959 the beginning of the current line to the value specified by the
960 variable `left-margin'. This may involve either inserting or
963 - Variable: left-margin
964 This variable specifies the base left margin column. In
965 Fundamental mode, <LFD> indents to this column. This variable
966 automatically becomes buffer-local when set in any fashion.
969 File: lispref.info, Node: Auto Filling, Next: Sorting, Prev: Margins, Up: Text
974 Auto Fill mode is a minor mode that fills lines automatically as text
975 is inserted. This section describes the hook used by Auto Fill mode.
976 For a description of functions that you can call explicitly to fill and
977 justify existing text, see *Note Filling::.
979 Auto Fill mode also enables the functions that change the margins and
980 justification style to refill portions of the text. *Note Margins::.
982 - Variable: auto-fill-function
983 The value of this variable should be a function (of no arguments)
984 to be called after self-inserting a space or a newline. It may be
985 `nil', in which case nothing special is done in that case.
987 The value of `auto-fill-function' is `do-auto-fill' when Auto-Fill
988 mode is enabled. That is a function whose sole purpose is to
989 implement the usual strategy for breaking a line.
991 In older Emacs versions, this variable was named
992 `auto-fill-hook', but since it is not called with the
993 standard convention for hooks, it was renamed to
994 `auto-fill-function' in version 19.
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