2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../info/markers
6 @node Markers, Text, Positions, Top
10 A @dfn{marker} is a Lisp object used to specify a position in a buffer
11 relative to the surrounding text. A marker changes its offset from the
12 beginning of the buffer automatically whenever text is inserted or
13 deleted, so that it stays with the two characters on either side of it.
16 * Overview of Markers:: The components of a marker, and how it relocates.
17 * Predicates on Markers:: Testing whether an object is a marker.
18 * Creating Markers:: Making empty markers or markers at certain places.
19 * Information from Markers:: Finding the marker's buffer or character position.
20 * Marker Insertion Types:: Two ways a marker can relocate when you
21 insert where it points.
22 * Moving Markers:: Moving the marker to a new buffer or position.
23 * The Mark:: How ``the mark'' is implemented with a marker.
24 * The Region:: How to access ``the region''.
27 @node Overview of Markers
28 @section Overview of Markers
30 A marker specifies a buffer and a position in that buffer. The marker
31 can be used to represent a position in the functions that require one,
32 just as an integer could be used. @xref{Positions}, for a complete
33 description of positions.
35 A marker has two attributes: the marker position, and the marker
36 buffer. The marker position is an integer that is equivalent (at a
37 given time) to the marker as a position in that buffer. But the
38 marker's position value can change often during the life of the marker.
39 Insertion and deletion of text in the buffer relocate the marker. The
40 idea is that a marker positioned between two characters remains between
41 those two characters despite insertion and deletion elsewhere in the
42 buffer. Relocation changes the integer equivalent of the marker.
44 @cindex marker relocation
45 Deleting text around a marker's position leaves the marker between the
46 characters immediately before and after the deleted text. Inserting
47 text at the position of a marker normally leaves the marker either in
48 front of or after the new text, depending on the marker's @dfn{insertion
49 type} (@pxref{Marker Insertion Types})---unless the insertion is done
50 with @code{insert-before-markers} (@pxref{Insertion}).
52 @cindex marker garbage collection
53 Insertion and deletion in a buffer must check all the markers and
54 relocate them if necessary. This slows processing in a buffer with a
55 large number of markers. For this reason, it is a good idea to make a
56 marker point nowhere if you are sure you don't need it any more.
57 Unreferenced markers are garbage collected eventually, but until then
58 will continue to use time if they do point somewhere.
60 @cindex markers as numbers
61 Because it is common to perform arithmetic operations on a marker
62 position, most of the arithmetic operations (including @code{+} and
63 @code{-}) accept markers as arguments. In such cases, the marker
64 stands for its current position.
66 Here are examples of creating markers, setting markers, and moving point
71 ;; @r{Make a new marker that initially does not point anywhere:}
72 (setq m1 (make-marker))
73 @result{} #<marker in no buffer>
77 ;; @r{Set @code{m1} to point between the 99th and 100th characters}
78 ;; @r{in the current buffer:}
80 @result{} #<marker at 100 in markers.texi>
84 ;; @r{Now insert one character at the beginning of the buffer:}
85 (goto-char (point-min))
92 ;; @r{@code{m1} is updated appropriately.}
94 @result{} #<marker at 101 in markers.texi>
98 ;; @r{Two markers that point to the same position}
99 ;; @r{are not @code{eq}, but they are @code{equal}.}
100 (setq m2 (copy-marker m1))
101 @result{} #<marker at 101 in markers.texi>
109 ;; @r{When you are finished using a marker, make it point nowhere.}
111 @result{} #<marker in no buffer>
115 @node Predicates on Markers
116 @section Predicates on Markers
118 You can test an object to see whether it is a marker, or whether it is
119 either an integer or a marker. The latter test is useful in connection
120 with the arithmetic functions that work with both markers and integers.
122 @defun markerp object
123 This function returns @code{t} if @var{object} is a marker, @code{nil}
124 otherwise. Note that integers are not markers, even though many
125 functions will accept either a marker or an integer.
128 @defun integer-or-marker-p object
129 This function returns @code{t} if @var{object} is an integer or a marker,
130 @code{nil} otherwise.
133 @defun number-or-marker-p object
134 This function returns @code{t} if @var{object} is a number (either
135 integer or floating point) or a marker, @code{nil} otherwise.
138 @node Creating Markers
139 @section Functions that Create Markers
141 When you create a new marker, you can make it point nowhere, or point
142 to the present position of point, or to the beginning or end of the
143 accessible portion of the buffer, or to the same place as another given
147 This function returns a newly created marker that does not point
153 @result{} #<marker in no buffer>
159 This function returns a new marker that points to the present position
160 of point in the current buffer. @xref{Point}. For an example, see
161 @code{copy-marker}, below.
164 @defun point-min-marker
165 This function returns a new marker that points to the beginning of the
166 accessible portion of the buffer. This will be the beginning of the
167 buffer unless narrowing is in effect. @xref{Narrowing}.
170 @defun point-max-marker
171 @cindex end of buffer marker
172 This function returns a new marker that points to the end of the
173 accessible portion of the buffer. This will be the end of the buffer
174 unless narrowing is in effect. @xref{Narrowing}.
176 Here are examples of this function and @code{point-min-marker}, shown in
177 a buffer containing a version of the source file for the text of this
183 @result{} #<marker at 1 in markers.texi>
185 @result{} #<marker at 15573 in markers.texi>
189 (narrow-to-region 100 200)
194 @result{} #<marker at 100 in markers.texi>
198 @result{} #<marker at 200 in markers.texi>
203 @defun copy-marker marker-or-integer insertion-type
204 If passed a marker as its argument, @code{copy-marker} returns a
205 new marker that points to the same place and the same buffer as does
206 @var{marker-or-integer}. If passed an integer as its argument,
207 @code{copy-marker} returns a new marker that points to position
208 @var{marker-or-integer} in the current buffer.
210 The new marker's insertion type is specified by the argument
211 @var{insertion-type}. @xref{Marker Insertion Types}.
213 If passed an integer argument less than 1, @code{copy-marker} returns a
214 new marker that points to the beginning of the current buffer. If
215 passed an integer argument greater than the length of the buffer,
216 @code{copy-marker} returns a new marker that points to the end of the
222 @result{} #<marker at 1 in markers.texi>
227 @result{} #<marker at 7572 in markers.texi>
231 An error is signaled if @var{marker} is neither a marker nor an
235 Two distinct markers are considered @code{equal} (even though not
236 @code{eq}) to each other if they have the same position and buffer, or
237 if they both point nowhere.
241 (setq p (point-marker))
242 @result{} #<marker at 2139 in markers.texi>
246 (setq q (copy-marker p))
247 @result{} #<marker at 2139 in markers.texi>
261 @node Information from Markers
262 @section Information from Markers
264 This section describes the functions for accessing the components of a
267 @defun marker-position marker
268 This function returns the position that @var{marker} points to, or
269 @code{nil} if it points nowhere.
272 @defun marker-buffer marker
273 This function returns the buffer that @var{marker} points into, or
274 @code{nil} if it points nowhere.
278 (setq m (make-marker))
279 @result{} #<marker in no buffer>
291 (set-marker m 3770 (current-buffer))
292 @result{} #<marker at 3770 in markers.texi>
296 @result{} #<buffer markers.texi>
305 @defun buffer-has-markers-at position
306 @tindex buffer-has-markers-at
307 This function returns @code{t} if one or more markers
308 point at position @var{position} in the current buffer.
311 @node Marker Insertion Types
312 @section Marker Insertion Types
314 @cindex insertion type of a marker
315 When you insert text directly at the place where a marker points,
316 there are two possible ways to relocate that marker: it can point before
317 the inserted text, or point after it. You can specify which one a given
318 marker should do by setting its @dfn{insertion type}. Note that use of
319 @code{insert-before-markers} ignores markers' insertion types, always
320 relocating a marker to point after the inserted text.
322 @defun set-marker-insertion-type marker type
323 @tindex set-marker-insertion-type
324 This function sets the insertion type of marker @var{marker} to
325 @var{type}. If @var{type} is @code{t}, @var{marker} will advance when
326 text is inserted at its position. If @var{type} is @code{nil},
327 @var{marker} does not advance when text is inserted there.
330 @defun marker-insertion-type marker
331 @tindex marker-insertion-type
332 This function reports the current insertion type of @var{marker}.
336 @section Moving Marker Positions
338 This section describes how to change the position of an existing
339 marker. When you do this, be sure you know whether the marker is used
340 outside of your program, and, if so, what effects will result from
341 moving it---otherwise, confusing things may happen in other parts of
344 @defun set-marker marker position &optional buffer
345 This function moves @var{marker} to @var{position}
346 in @var{buffer}. If @var{buffer} is not provided, it defaults to
349 If @var{position} is less than 1, @code{set-marker} moves @var{marker}
350 to the beginning of the buffer. If @var{position} is greater than the
351 size of the buffer, @code{set-marker} moves marker to the end of the
352 buffer. If @var{position} is @code{nil} or a marker that points
353 nowhere, then @var{marker} is set to point nowhere.
355 The value returned is @var{marker}.
359 (setq m (point-marker))
360 @result{} #<marker at 4714 in markers.texi>
364 @result{} #<marker at 55 in markers.texi>
367 (setq b (get-buffer "foo"))
368 @result{} #<buffer foo>
372 @result{} #<marker at 1 in foo>
377 @defun move-marker marker position &optional buffer
378 This is another name for @code{set-marker}.
386 One special marker in each buffer is designated @dfn{the mark}. It
387 records a position for the user for the sake of commands such as
388 @code{kill-region} and @code{indent-rigidly}. Lisp programs should set
389 the mark only to values that have a potential use to the user, and never
390 for their own internal purposes. For example, the @code{replace-regexp}
391 command sets the mark to the value of point before doing any
392 replacements, because this enables the user to move back there
393 conveniently after the replace is finished.
395 Many commands are designed so that when called interactively they
396 operate on the text between point and the mark. If you are writing such
397 a command, don't examine the mark directly; instead, use
398 @code{interactive} with the @samp{r} specification. This provides the
399 values of point and the mark as arguments to the command in an
400 interactive call, but permits other Lisp programs to specify arguments
401 explicitly. @xref{Interactive Codes}.
403 Each buffer has its own value of the mark that is independent of the
404 value of the mark in other buffers. When a buffer is created, the mark
405 exists but does not point anywhere. We consider this state as ``the
406 absence of a mark in that buffer.''
408 Once the mark ``exists'' in a buffer, it normally never ceases to
409 exist. However, it may become @dfn{inactive}, if Transient Mark mode is
410 enabled. The variable @code{mark-active}, which is always buffer-local
411 in all buffers, indicates whether the mark is active: non-@code{nil}
412 means yes. A command can request deactivation of the mark upon return
413 to the editor command loop by setting @code{deactivate-mark} to a
414 non-@code{nil} value (but this causes deactivation only if Transient
415 Mark mode is enabled).
417 The main motivation for using Transient Mark mode is that this mode
418 also enables highlighting of the region when the mark is active.
421 In addition to the mark, each buffer has a @dfn{mark ring} which is a
422 list of markers containing previous values of the mark. When editing
423 commands change the mark, they should normally save the old value of the
424 mark on the mark ring. The variable @code{mark-ring-max} specifies the
425 maximum number of entries in the mark ring; once the list becomes this
426 long, adding a new element deletes the last element.
428 There is also a separate global mark ring, but that is used only in a
429 few particular user-level commands, and is not relevant to Lisp
430 programming. So we do not describe it here.
432 @defun mark &optional force
433 @cindex current buffer mark
434 This function returns the current buffer's mark position as an integer.
436 If the mark is inactive, @code{mark} normally signals an error.
437 However, if @var{force} is non-@code{nil}, then @code{mark} returns the
438 mark position anyway---or @code{nil}, if the mark is not yet set for
443 This function returns the current buffer's mark. This is the very marker
444 that records the mark location inside Emacs, not a copy. Therefore,
445 changing this marker's position will directly affect the position of the mark.
446 Don't do it unless that is the effect you want.
450 (setq m (mark-marker))
451 @result{} #<marker at 3420 in markers.texi>
455 @result{} #<marker at 100 in markers.texi>
459 @result{} #<marker at 100 in markers.texi>
463 Like any marker, this marker can be set to point at any buffer you like.
464 We don't recommend that you make it point at any buffer other than the
465 one of which it is the mark. If you do, it will yield perfectly
466 consistent, but rather odd, results.
470 @deffn Command set-mark-command jump
471 If @var{jump} is @code{nil}, this command sets the mark to the value
472 of point and pushes the previous value of the mark on the mark ring. The
473 message @samp{Mark set} is also displayed in the echo area.
475 If @var{jump} is not @code{nil}, this command sets point to the value
476 of the mark, and sets the mark to the previous saved mark value, which
477 is popped off the mark ring.
479 This function is @emph{only} intended for interactive use.
483 @defun set-mark position
484 This function sets the mark to @var{position}, and activates the mark.
485 The old value of the mark is @emph{not} pushed onto the mark ring.
487 @strong{Please note:} Use this function only if you want the user to
488 see that the mark has moved, and you want the previous mark position to
489 be lost. Normally, when a new mark is set, the old one should go on the
490 @code{mark-ring}. For this reason, most applications should use
491 @code{push-mark} and @code{pop-mark}, not @code{set-mark}.
493 Novice Emacs Lisp programmers often try to use the mark for the wrong
494 purposes. The mark saves a location for the user's convenience. An
495 editing command should not alter the mark unless altering the mark is
496 part of the user-level functionality of the command. (And, in that
497 case, this effect should be documented.) To remember a location for
498 internal use in the Lisp program, store it in a Lisp variable. For
505 (delete-region beg (point))).
510 @c for interactive use only
512 @deffn Command exchange-point-and-mark
513 This function exchanges the positions of point and the mark.
514 It is intended for interactive use.
518 @defun push-mark &optional position nomsg activate
519 This function sets the current buffer's mark to @var{position}, and
520 pushes a copy of the previous mark onto @code{mark-ring}. If
521 @var{position} is @code{nil}, then the value of point is used.
522 @code{push-mark} returns @code{nil}.
524 The function @code{push-mark} normally @emph{does not} activate the
525 mark. To do that, specify @code{t} for the argument @var{activate}.
527 A @samp{Mark set} message is displayed unless @var{nomsg} is
532 This function pops off the top element of @code{mark-ring} and makes
533 that mark become the buffer's actual mark. This does not move point in
534 the buffer, and it does nothing if @code{mark-ring} is empty. It
535 deactivates the mark.
537 The return value is not meaningful.
540 @defopt transient-mark-mode
541 @cindex Transient Mark mode
542 This variable if non-@code{nil} enables Transient Mark mode, in which
543 every buffer-modifying primitive sets @code{deactivate-mark}. The
544 consequence of this is that commands that modify the buffer normally
545 make the mark inactive.
548 @defopt mark-even-if-inactive
549 If this is non-@code{nil}, Lisp programs and the Emacs user can use the
550 mark even when it is inactive. This option affects the behavior of
551 Transient Mark mode. When the option is non-@code{nil}, deactivation of
552 the mark turns off region highlighting, but commands that use the mark
553 behave as if the mark were still active.
556 @defvar deactivate-mark
557 If an editor command sets this variable non-@code{nil}, then the editor
558 command loop deactivates the mark after the command returns (if
559 Transient Mark mode is enabled). All the primitives that change the
560 buffer set @code{deactivate-mark}, to deactivate the mark when the
564 @defun deactivate-mark
565 This function deactivates the mark, if Transient Mark mode is enabled.
566 Otherwise it does nothing.
570 The mark is active when this variable is non-@code{nil}. This variable
571 is always buffer-local in each buffer.
574 @defvar activate-mark-hook
575 @defvarx deactivate-mark-hook
576 These normal hooks are run, respectively, when the mark becomes active
577 and when it becomes inactive. The hook @code{activate-mark-hook} is
578 also run at the end of a command if the mark is active and it is
579 possible that the region may have changed.
583 The value of this buffer-local variable is the list of saved former
584 marks of the current buffer, most recent first.
589 @result{} (#<marker at 11050 in markers.texi>
590 #<marker at 10832 in markers.texi>
596 @defopt mark-ring-max
597 The value of this variable is the maximum size of @code{mark-ring}. If
598 more marks than this are pushed onto the @code{mark-ring},
599 @code{push-mark} discards an old mark when it adds a new one.
606 The text between point and the mark is known as @dfn{the region}.
607 Various functions operate on text delimited by point and the mark, but
608 only those functions specifically related to the region itself are
611 @defun region-beginning
612 This function returns the position of the beginning of the region (as
613 an integer). This is the position of either point or the mark,
614 whichever is smaller.
616 If the mark does not point anywhere, an error is signaled.
620 This function returns the position of the end of the region (as an
621 integer). This is the position of either point or the mark, whichever is
624 If the mark does not point anywhere, an error is signaled.
627 Few programs need to use the @code{region-beginning} and
628 @code{region-end} functions. A command designed to operate on a region
629 should normally use @code{interactive} with the @samp{r} specification
630 to find the beginning and end of the region. This lets other Lisp
631 programs specify the bounds explicitly as arguments. (@xref{Interactive