This is Info file ../../info/lispref.info, produced by Makeinfo-1.63
from the input file lispref.texi.

   Edition History:

   GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU
Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid
Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994
XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995
GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp
Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp
Reference Manual (for 19.14 and 20.0) v3.1, March 1996

   Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software
Foundation, Inc.  Copyright (C) 1994, 1995 Sun Microsystems, Inc.
Copyright (C) 1995, 1996 Ben Wing.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the section entitled "GNU General Public License" is included
exactly as in the original, and provided that the entire resulting
derived work is distributed under the terms of a permission notice
identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the section entitled "GNU General Public License"
may be included in a translation approved by the Free Software
Foundation instead of in the original English.


File: lispref.info,  Node: Narrowing,  Prev: Excursions,  Up: Positions

Narrowing
=========

   "Narrowing" means limiting the text addressable by XEmacs editing
commands to a limited range of characters in a buffer.  The text that
remains addressable is called the "accessible portion" of the buffer.

   Narrowing is specified with two buffer positions which become the
beginning and end of the accessible portion.  For most editing commands
and most Emacs primitives, these positions replace the values of the
beginning and end of the buffer.  While narrowing is in effect, no text
outside the accessible portion is displayed, and point cannot move
outside the accessible portion.

   Values such as positions or line numbers, which usually count from
the beginning of the buffer, do so despite narrowing, but the functions
which use them refuse to operate on text that is inaccessible.

   The commands for saving buffers are unaffected by narrowing; they
save the entire buffer regardless of any narrowing.

 - Command: narrow-to-region START END &optional BUFFER
     This function sets the accessible portion of BUFFER to start at
     START and end at END.  Both arguments should be character
     positions.  BUFFER defaults to the current buffer if omitted.

     In an interactive call, START and END are set to the bounds of the
     current region (point and the mark, with the smallest first).

 - Command: narrow-to-page &optional MOVE-COUNT
     This function sets the accessible portion of the current buffer to
     include just the current page.  An optional first argument
     MOVE-COUNT non-`nil' means to move forward or backward by
     MOVE-COUNT pages and then narrow.  The variable `page-delimiter'
     specifies where pages start and end (*note Standard Regexps::.).

     In an interactive call, MOVE-COUNT is set to the numeric prefix
     argument.

 - Command: widen &optional BUFFER
     This function cancels any narrowing in BUFFER, so that the entire
     contents are accessible.  This is called "widening".  It is
     equivalent to the following expression:

          (narrow-to-region 1 (1+ (buffer-size)))

     BUFFER defaults to the current buffer if omitted.

 - Special Form: save-restriction BODY...
     This special form saves the current bounds of the accessible
     portion, evaluates the BODY forms, and finally restores the saved
     bounds, thus restoring the same state of narrowing (or absence
     thereof) formerly in effect.  The state of narrowing is restored
     even in the event of an abnormal exit via `throw' or error (*note
     Nonlocal Exits::.).  Therefore, this construct is a clean way to
     narrow a buffer temporarily.

     The value returned by `save-restriction' is that returned by the
     last form in BODY, or `nil' if no body forms were given.

     *Caution:* it is easy to make a mistake when using the
     `save-restriction' construct.  Read the entire description here
     before you try it.

     If BODY changes the current buffer, `save-restriction' still
     restores the restrictions on the original buffer (the buffer whose
     restructions it saved from), but it does not restore the identity
     of the current buffer.

     `save-restriction' does *not* restore point and the mark; use
     `save-excursion' for that.  If you use both `save-restriction' and
     `save-excursion' together, `save-excursion' should come first (on
     the outside).  Otherwise, the old point value would be restored
     with temporary narrowing still in effect.  If the old point value
     were outside the limits of the temporary narrowing, this would
     fail to restore it accurately.

     The `save-restriction' special form records the values of the
     beginning and end of the accessible portion as distances from the
     beginning and end of the buffer.  In other words, it records the
     amount of inaccessible text before and after the accessible
     portion.

     This method yields correct results if BODY does further narrowing.
     However, `save-restriction' can become confused if the body widens
     and then make changes outside the range of the saved narrowing.
     When this is what you want to do, `save-restriction' is not the
     right tool for the job.  Here is what you must use instead:

          (let ((beg (point-min-marker))
                (end (point-max-marker)))
            (unwind-protect
                (progn BODY)
              (save-excursion
                (set-buffer (marker-buffer beg))
                (narrow-to-region beg end))))

     Here is a simple example of correct use of `save-restriction':

          ---------- Buffer: foo ----------
          This is the contents of foo
          This is the contents of foo
          This is the contents of foo-!-
          ---------- Buffer: foo ----------
          
          (save-excursion
            (save-restriction
              (goto-char 1)
              (forward-line 2)
              (narrow-to-region 1 (point))
              (goto-char (point-min))
              (replace-string "foo" "bar")))
          
          ---------- Buffer: foo ----------
          This is the contents of bar
          This is the contents of bar
          This is the contents of foo-!-
          ---------- Buffer: foo ----------


File: lispref.info,  Node: Markers,  Next: Text,  Prev: Positions,  Up: Top

Markers
*******

   A "marker" is a Lisp object used to specify a position in a buffer
relative to the surrounding text.  A marker changes its offset from the
beginning of the buffer automatically whenever text is inserted or
deleted, so that it stays with the two characters on either side of it.

* Menu:

* Overview of Markers::      The components of a marker, and how it relocates.
* Predicates on Markers::    Testing whether an object is a marker.
* Creating Markers::         Making empty markers or markers at certain places.
* Information from Markers:: Finding the marker's buffer or character position.
* Changing Markers::         Moving the marker to a new buffer or position.
* The Mark::                 How "the mark" is implemented with a marker.
* The Region::               How to access "the region".


File: lispref.info,  Node: Overview of Markers,  Next: Predicates on Markers,  Up: Markers

Overview of Markers
===================

   A marker specifies a buffer and a position in that buffer.  The
marker can be used to represent a position in the functions that
require one, just as an integer could be used.  *Note Positions::, for
a complete description of positions.

   A marker has two attributes: the marker position, and the marker
buffer.  The marker position is an integer that is equivalent (at a
given time) to the marker as a position in that buffer.  But the
marker's position value can change often during the life of the marker.
Insertion and deletion of text in the buffer relocate the marker.  The
idea is that a marker positioned between two characters remains between
those two characters despite insertion and deletion elsewhere in the
buffer.  Relocation changes the integer equivalent of the marker.

   Deleting text around a marker's position leaves the marker between
the characters immediately before and after the deleted text.  Inserting
text at the position of a marker normally leaves the marker in front of
the new text--unless it is inserted with `insert-before-markers' (*note
Insertion::.).

   Insertion and deletion in a buffer must check all the markers and
relocate them if necessary.  This slows processing in a buffer with a
large number of markers.  For this reason, it is a good idea to make a
marker point nowhere if you are sure you don't need it any more.
Unreferenced markers are garbage collected eventually, but until then
will continue to use time if they do point somewhere.

   Because it is common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including `+' and `-')
accept markers as arguments.  In such cases, the marker stands for its
current position.

   Note that you can use extents to achieve the same functionality, and
more, as markers. (Markers were defined before extents, which is why
they both continue to exist.) A zero-length extent with the
`detachable' property removed is almost identical to a marker.  (*Note
Extent Endpoints::, for more information on zero-length extents.)

   In particular:

   * In order to get marker-like behavior in a zero-length extent, the
     `detachable' property must be removed (otherwise, the extent will
     disappear when text near it is deleted) and exactly one endpoint
     must be closed (if both endpoints are closed, the extent will
     expand to contain text inserted where it is located).

   * If a zero-length extent has the `end-open' property but not the
     `start-open' property (this is the default), text inserted at the
     extent's location causes the extent to move forward, just like a
     marker.

   * If a zero-length extent has the `start-open' property but not the
     `end-open' property, text inserted at the extent's location causes
     the extent to remain before the text, like what happens to markers
     when `insert-before-markers' is used.

   * Markers end up after or before inserted text depending on whether
     `insert' or `insert-before-markers' was called.  These functions
     do not affect zero-length extents differently; instead, the
     presence or absence of the `start-open' and `end-open' extent
     properties determines this, as just described.

   * Markers are automatically removed from a buffer when they are no
     longer in use.  Extents remain around until explicitly removed
     from a buffer.

   * Many functions are provided for listing the extents in a buffer or
     in a region of a buffer.  No such functions exist for markers.

   Here are examples of creating markers, setting markers, and moving
point to markers:

     ;; Make a new marker that initially does not point anywhere:
     (setq m1 (make-marker))
          => #<marker in no buffer>
     
     ;; Set `m1' to point between the 99th and 100th characters
     ;;   in the current buffer:
     (set-marker m1 100)
          => #<marker at 100 in markers.texi>
     
     ;; Now insert one character at the beginning of the buffer:
     (goto-char (point-min))
          => 1
     (insert "Q")
          => nil
     
     ;; `m1' is updated appropriately.
     m1
          => #<marker at 101 in markers.texi>
     
     ;; Two markers that point to the same position
     ;;   are not `eq', but they are `equal'.
     (setq m2 (copy-marker m1))
          => #<marker at 101 in markers.texi>
     (eq m1 m2)
          => nil
     (equal m1 m2)
          => t
     
     ;; When you are finished using a marker, make it point nowhere.
     (set-marker m1 nil)
          => #<marker in no buffer>


File: lispref.info,  Node: Predicates on Markers,  Next: Creating Markers,  Prev: Overview of Markers,  Up: Markers

Predicates on Markers
=====================

   You can test an object to see whether it is a marker, or whether it
is either an integer or a marker or either an integer, a character, or a
marker.  The latter tests are useful in connection with the arithmetic
functions that work with any of markers, integers, or characters.

 - Function: markerp OBJECT
     This function returns `t' if OBJECT is a marker, `nil' otherwise.
     Note that integers are not markers, even though many functions
     will accept either a marker or an integer.

 - Function: integer-or-marker-p OBJECT
     This function returns `t' if OBJECT is an integer or a marker,
     `nil' otherwise.

 - Function: integer-char-or-marker-p OBJECT
     This function returns `t' if OBJECT is an integer, a character, or
     a marker, `nil' otherwise.

 - Function: number-or-marker-p OBJECT
     This function returns `t' if OBJECT is a number (either kind) or a
     marker, `nil' otherwise.

 - Function: number-char-or-marker-p OBJECT
     This function returns `t' if OBJECT is a number (either kind), a
     character, or a marker, `nil' otherwise.


File: lispref.info,  Node: Creating Markers,  Next: Information from Markers,  Prev: Predicates on Markers,  Up: Markers

Functions That Create Markers
=============================

   When you create a new marker, you can make it point nowhere, or point
to the present position of point, or to the beginning or end of the
accessible portion of the buffer, or to the same place as another given
marker.

 - Function: make-marker
     This functions returns a newly created marker that does not point
     anywhere.

          (make-marker)
               => #<marker in no buffer>

 - Function: point-marker &optional DONT-COPY-P BUFFER
     This function returns a marker that points to the present position
     of point in BUFFER, which defaults to the current buffer.  *Note
     Point::.  For an example, see `copy-marker', below.

     Internally, a marker corresponding to point is always maintained.
     Normally the marker returned by `point-marker' is a copy; you may
     modify it with reckless abandon.  However, if optional argument
     DONT-COPY-P is non-`nil', then the real point-marker is returned;
     modifying the position of this marker will move point.  It is
     illegal to change the buffer of it, or make it point nowhere.

 - Function: point-min-marker &optional BUFFER
     This function returns a new marker that points to the beginning of
     the accessible portion of BUFFER, which defaults to the current
     buffer.  This will be the beginning of the buffer unless narrowing
     is in effect.  *Note Narrowing::.

 - Function: point-max-marker &optional BUFFER
     This function returns a new marker that points to the end of the
     accessible portion of BUFFER, which defaults to the current
     buffer.  This will be the end of the buffer unless narrowing is in
     effect.  *Note Narrowing::.

     Here are examples of this function and `point-min-marker', shown in
     a buffer containing a version of the source file for the text of
     this chapter.

          (point-min-marker)
               => #<marker at 1 in markers.texi>
          (point-max-marker)
               => #<marker at 15573 in markers.texi>
          
          (narrow-to-region 100 200)
               => nil
          (point-min-marker)
               => #<marker at 100 in markers.texi>
          (point-max-marker)
               => #<marker at 200 in markers.texi>

 - Function: copy-marker MARKER-OR-INTEGER
     If passed a marker as its argument, `copy-marker' returns a new
     marker that points to the same place and the same buffer as does
     MARKER-OR-INTEGER.  If passed an integer as its argument,
     `copy-marker' returns a new marker that points to position
     MARKER-OR-INTEGER in the current buffer.

     If passed an integer argument less than 1, `copy-marker' returns a
     new marker that points to the beginning of the current buffer.  If
     passed an integer argument greater than the length of the buffer,
     `copy-marker' returns a new marker that points to the end of the
     buffer.

     An error is signaled if MARKER is neither a marker nor an integer.

          (setq p (point-marker))
               => #<marker at 2139 in markers.texi>
          
          (setq q (copy-marker p))
               => #<marker at 2139 in markers.texi>
          
          (eq p q)
               => nil
          
          (equal p q)
               => t
          
          (point)
               => 2139
          
          (set-marker p 3000)
               => #<marker at 3000 in markers.texi>
          
          (point)
               => 2139
          
          (setq p (point-marker t))
               => #<marker at 2139 in markers.texi>
          
          (set-marker p 3000)
               => #<marker at 3000 in markers.texi>
          
          (point)
               => 3000
          
          (copy-marker 0)
               => #<marker at 1 in markers.texi>
          
          (copy-marker 20000)
               => #<marker at 7572 in markers.texi>


File: lispref.info,  Node: Information from Markers,  Next: Changing Markers,  Prev: Creating Markers,  Up: Markers

Information from Markers
========================

   This section describes the functions for accessing the components of
a marker object.

 - Function: marker-position MARKER
     This function returns the position that MARKER points to, or `nil'
     if it points nowhere.

 - Function: marker-buffer MARKER
     This function returns the buffer that MARKER points into, or `nil'
     if it points nowhere.

          (setq m (make-marker))
               => #<marker in no buffer>
          (marker-position m)
               => nil
          (marker-buffer m)
               => nil
          
          (set-marker m 3770 (current-buffer))
               => #<marker at 3770 in markers.texi>
          (marker-buffer m)
               => #<buffer markers.texi>
          (marker-position m)
               => 3770

   Two distinct markers are considered `equal' (even though not `eq')
to each other if they have the same position and buffer, or if they
both point nowhere.


File: lispref.info,  Node: Changing Markers,  Next: The Mark,  Prev: Information from Markers,  Up: Markers

Changing Marker Positions
=========================

   This section describes how to change the position of an existing
marker.  When you do this, be sure you know whether the marker is used
outside of your program, and, if so, what effects will result from
moving it--otherwise, confusing things may happen in other parts of
Emacs.

 - Function: set-marker MARKER POSITION &optional BUFFER
     This function moves MARKER to POSITION in BUFFER.  If BUFFER is
     not provided, it defaults to the current buffer.

     If POSITION is less than 1, `set-marker' moves MARKER to the
     beginning of the buffer.  If POSITION is greater than the size of
     the buffer, `set-marker' moves marker to the end of the buffer.
     If POSITION is `nil' or a marker that points nowhere, then MARKER
     is set to point nowhere.

     The value returned is MARKER.

          (setq m (point-marker))
               => #<marker at 4714 in markers.texi>
          (set-marker m 55)
               => #<marker at 55 in markers.texi>
          (setq b (get-buffer "foo"))
               => #<buffer foo>
          (set-marker m 0 b)
               => #<marker at 1 in foo>

 - Function: move-marker MARKER POSITION &optional BUFFER
     This is another name for `set-marker'.


File: lispref.info,  Node: The Mark,  Next: The Region,  Prev: Changing Markers,  Up: Markers

The Mark
========

   One special marker in each buffer is designated "the mark".  It
records a position for the user for the sake of commands such as `C-w'
and `C-x TAB'.  Lisp programs should set the mark only to values that
have a potential use to the user, and never for their own internal
purposes.  For example, the `replace-regexp' command sets the mark to
the value of point before doing any replacements, because this enables
the user to move back there conveniently after the replace is finished.

   Once the mark "exists" in a buffer, it normally never ceases to
exist.  However, it may become "inactive", and usually does so after
each command (other than simple motion commands and some commands that
explicitly activate the mark).  When the mark is active, the region
between point and the mark is called the "active region" and is
highlighted specially.

   Many commands are designed so that when called interactively they
operate on the text between point and the mark.  Such commands work
only when an active region exists, i.e. when the mark is active.  (The
reason for this is to prevent you from accidentally deleting or
changing large chunks of your text.) If you are writing such a command,
don't examine the mark directly; instead, use `interactive' with the
`r' specification.  This provides the values of point and the mark as
arguments to the command in an interactive call, but permits other Lisp
programs to specify arguments explicitly, and automatically signals an
error if the command is called interactively when no active region
exists.  *Note Interactive Codes::.

   Each buffer has its own value of the mark that is independent of the
value of the mark in other buffers. (When a buffer is created, the mark
exists but does not point anywhere.  We consider this state as "the
absence of a mark in that buffer.") However, only one active region can
exist at a time.  Activating the mark in one buffer automatically
deactivates an active mark in any other buffer.  Note that the user can
explicitly activate a mark at any time by using the command
`activate-region' (normally bound to `M-C-z') or by using the command
`exchange-point-and-mark' (normally bound to `C-x C-x'), which has the
side effect of activating the mark.

   Some people do not like active regions, so they disable this behavior
by setting the variable `zmacs-regions' to `nil'.  This makes the mark
always active (except when a buffer is just created and the mark points
nowhere), and turns off the highlighting of the region between point
and the mark.  Commands that explicitly retrieve the value of the mark
should make sure that they behave correctly and consistently
irrespective of the setting of `zmacs-regions'; some primitives are
provided to ensure this behavior.

   In addition to the mark, each buffer has a "mark ring" which is a
list of markers containing previous values of the mark.  When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring.  The variable `mark-ring-max' specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.

 - Function: mark &optional FORCE BUFFER
     This function returns BUFFER's mark position as an integer.
     BUFFER defaults to the current buffer if omitted.

     If the mark is inactive, `mark' normally returns `nil'.  However,
     if FORCE is non-`nil', then `mark' returns the mark position
     anyway--or `nil', if the mark is not yet set for the buffer.

     (Remember that if ZMACS-REGIONS is `nil', the mark is always
     active as long as it exists, and the FORCE argument will have no
     effect.)

     If you are using this in an editing command, you are most likely
     making a mistake; see the documentation of `set-mark' below.

 - Function: mark-marker INACTIVE-P BUFFER
     This function returns BUFFER's mark.  BUFFER defaults to the
     current buffer if omitted.  This is the very marker that records
     the mark location inside XEmacs, not a copy.  Therefore, changing
     this marker's position will directly affect the position of the
     mark.  Don't do it unless that is the effect you want.

     If the mark is inactive, `mark-marker' normally returns `nil'.
     However, if FORCE is non-`nil', then `mark-marker' returns the
     mark anyway.
          (setq m (mark-marker))
               => #<marker at 3420 in markers.texi>
          (set-marker m 100)
               => #<marker at 100 in markers.texi>
          (mark-marker)
               => #<marker at 100 in markers.texi>

     Like any marker, this marker can be set to point at any buffer you
     like.  We don't recommend that you make it point at any buffer
     other than the one of which it is the mark.  If you do, it will
     yield perfectly consistent, but rather odd, results.

 - Function: set-mark POSITION &optional BUFFER
     This function sets `buffer''s mark to POSITION, and activates the
     mark.  BUFFER defaults to the current buffer if omitted.  The old
     value of the mark is *not* pushed onto the mark ring.

     *Please note:* Use this function only if you want the user to see
     that the mark has moved, and you want the previous mark position to
     be lost.  Normally, when a new mark is set, the old one should go
     on the `mark-ring'.  For this reason, most applications should use
     `push-mark' and `pop-mark', not `set-mark'.

     Novice XEmacs Lisp programmers often try to use the mark for the
     wrong purposes.  The mark saves a location for the user's
     convenience.  An editing command should not alter the mark unless
     altering the mark is part of the user-level functionality of the
     command.  (And, in that case, this effect should be documented.)
     To remember a location for internal use in the Lisp program, store
     it in a Lisp variable.  For example:

          (let ((beg (point)))
            (forward-line 1)
            (delete-region beg (point))).

 - Command: exchange-point-and-mark &optional DONT-ACTIVATE-REGION
     This function exchanges the positions of point and the mark.  It
     is intended for interactive use.  The mark is also activated
     unless DONT-ACTIVATE-REGION is non-`nil'.

 - Function: push-mark &optional POSITION NOMSG ACTIVATE BUFFER
     This function sets BUFFER's mark to POSITION, and pushes a copy of
     the previous mark onto `mark-ring'.  BUFFER defaults to the
     current buffer if omitted.  If POSITION is `nil', then the value
     of point is used.  `push-mark' returns `nil'.

     If the last global mark pushed was not in BUFFER, also push
     POSITION on the global mark ring (see below).

     The function `push-mark' normally *does not* activate the mark.
     To do that, specify `t' for the argument ACTIVATE.

     A `Mark set' message is displayed unless NOMSG is non-`nil'.

 - Function: pop-mark
     This function pops off the top element of `mark-ring' and makes
     that mark become the buffer's actual mark.  This does not move
     point in the buffer, and it does nothing if `mark-ring' is empty.
     It deactivates the mark.

     The return value is not meaningful.

 - Variable: mark-ring
     The value of this buffer-local variable is the list of saved former
     marks of the current buffer, most recent first.

          mark-ring
          => (#<marker at 11050 in markers.texi>
              #<marker at 10832 in markers.texi>
              ...)

 - User Option: mark-ring-max
     The value of this variable is the maximum size of `mark-ring'.  If
     more marks than this are pushed onto the `mark-ring', `push-mark'
     discards an old mark when it adds a new one.

   In additional to a per-buffer mark ring, there is a "global mark
ring".  Marks are pushed onto the global mark ring the first time you
set a mark after switching buffers.

 - Variable: global-mark-ring
     The value of this variable is the list of saved former global
     marks, most recent first.

 - User Option: mark-ring-max
     The value of this variable is the maximum size of
     `global-mark-ring'.  If more marks than this are pushed onto the
     `global-mark-ring', `push-mark' discards an old mark when it adds
     a new one.

 - Command: pop-global-mark
     This function pops a mark off the global mark ring and jumps to
     that location.


File: lispref.info,  Node: The Region,  Prev: The Mark,  Up: Markers

The Region
==========

   The text between point and the mark is known as "the region".
Various functions operate on text delimited by point and the mark, but
only those functions specifically related to the region itself are
described here.

   When `zmacs-regions' is non-`nil' (this is the default), the concept
of an "active region" exists.  The region is active when the
corresponding mark is active.  Note that only one active region at a
time can exist - i.e. only one buffer's region is active at a time.
*Note The Mark:: for more information about active regions.

 - User Option: zmacs-regions
     If non-`nil' (the default), active regions are used.  *Note The
     Mark::, for a detailed explanation of what this means.

   A number of functions are provided for explicitly determining the
bounds of the region and whether it is active.  Few programs need to use
these functions, however.  A command designed to operate on a region
should normally use `interactive' with the `r' specification to find
the beginning and end of the region.  This lets other Lisp programs
specify the bounds explicitly as arguments and automatically respects
the user's setting for ZMACS-REGIONS.  (*Note Interactive Codes::.)

 - Function: region-beginning &optional BUFFER
     This function returns the position of the beginning of BUFFER's
     region (as an integer).  This is the position of either point or
     the mark, whichever is smaller.  BUFFER defaults to the current
     buffer if omitted.

     If the mark does not point anywhere, an error is signaled.  Note
     that this function ignores whether the region is active.

 - Function: region-end &optional BUFFER
     This function returns the position of the end of BUFFER's region
     (as an integer).  This is the position of either point or the mark,
     whichever is larger.  BUFFER defaults to the current buffer if
     omitted.

     If the mark does not point anywhere, an error is signaled.  Note
     that this function ignores whether the region is active.

 - Function: region-exists-p
     This function is non-`nil' if the region exists.  If active regions
     are in use (i.e. `zmacs-regions' is true), this means that the
     region is active.  Otherwise, this means that the user has pushed
     a mark in this buffer at some point in the past.  If this function
     returns `nil', a function that uses the `r' interactive
     specification will cause an error when called interactively.

 - Function: region-active-p
     If `zmacs-regions' is true, this is equivalent to
     `region-exists-p'.  Otherwise, this function always returns false.
     This function is used by commands such as
     `fill-paragraph-or-region' and `capitalize-region-or-word', which
     operate either on the active region or on something else (e.g. the
     word or paragraph at point).

 - Variable: zmacs-region-stays
     If a command sets this variable to true, the currently active
     region will remain activated when the command finishes. (Normally
     the region is deactivated when each command terminates.) If
     ZMACS-REGIONS is false, however, this has no effect.  Under normal
     circumstances, you do not need to set this; use the interactive
     specification `_' instead, if you want the region to remain active.

 - Function: zmacs-activate-region
     This function activates the region in the current buffer (this is
     equivalent to activating the current buffer's mark).  This will
     normally also highlight the text in the active region and set
     ZMACS-REGION-STAYS to `t'. (If ZMACS-REGIONS is false, however,
     this function has no effect.)

 - Function: zmacs-deactivate-region
     This function deactivates the region in the current buffer (this is
     equivalent to deactivating the current buffer's mark).  This will
     normally also unhighlight the text in the active region and set
     ZMACS-REGION-STAYS to `nil'. (If ZMACS-REGIONS is false, however,
     this function has no effect.)

 - Function: zmacs-update-region
     This function updates the active region, if it's currently active.
     (If there is no active region, this function does nothing.) This
     has the effect of updating the highlighting on the text in the
     region; but you should never need to call this except under rather
     strange circumstances.  The command loop automatically calls it
     when appropriate.  Calling this function will call the hook
     `zmacs-update-region-hook', if the region is active.

 - Variable: zmacs-activate-region-hook
     This normal hook is called when a region becomes active. (Usually
     this happens as a result of a command that activates the region,
     such as `set-mark-command', `activate-region', or
     `exchange-point-and-mark'.) Note that calling
     `zmacs-activate-region' will call this hook, even if the region is
     already active.  If ZMACS-REGIONS is false, however, this hook
     will never get called under any circumstances.

 - Variable: zmacs-deactivate-region-hook
     This normal hook is called when an active region becomes inactive.
     (Calling `zmacs-deactivate-region' when the region is inactive will
     *not* cause this hook to be called.)  If ZMACS-REGIONS is false,
     this hook will never get called.

 - Variable: zmacs-update-region-hook
     This normal hook is called when an active region is "updated" by
     `zmacs-update-region'.  This normally gets called at the end of
     each command that sets ZMACS-REGION-STAYS to `t', indicating that
     the region should remain activated.  The motion commands do this.


File: lispref.info,  Node: Text,  Next: Searching and Matching,  Prev: Markers,  Up: Top

Text
****

   This chapter describes the functions that deal with the text in a
buffer.  Most examine, insert, or delete text in the current buffer,
often in the vicinity of point.  Many are interactive.  All the
functions that change the text provide for undoing the changes (*note
Undo::.).

   Many text-related functions operate on a region of text defined by
two buffer positions passed in arguments named START and END.  These
arguments should be either markers (*note Markers::.) or numeric
character positions (*note Positions::.).  The order of these arguments
does not matter; it is all right for START to be the end of the region
and END the beginning.  For example, `(delete-region 1 10)' and
`(delete-region 10 1)' are equivalent.  An `args-out-of-range' error is
signaled if either START or END is outside the accessible portion of
the buffer.  In an interactive call, point and the mark are used for
these arguments.

   Throughout this chapter, "text" refers to the characters in the
buffer, together with their properties (when relevant).

* Menu:

* Near Point::       Examining text in the vicinity of point.
* Buffer Contents::  Examining text in a general fashion.
* Comparing Text::   Comparing substrings of buffers.
* Insertion::        Adding new text to a buffer.
* Commands for Insertion::  User-level commands to insert text.
* Deletion::         Removing text from a buffer.
* User-Level Deletion::     User-level commands to delete text.
* The Kill Ring::    Where removed text sometimes is saved for later use.
* Undo::             Undoing changes to the text of a buffer.
* Maintaining Undo:: How to enable and disable undo information.
			How to control how much information is kept.
* Filling::          Functions for explicit filling.
* Margins::          How to specify margins for filling commands.
* Auto Filling::     How auto-fill mode is implemented to break lines.
* Sorting::          Functions for sorting parts of the buffer.
* Columns::          Computing horizontal positions, and using them.
* Indentation::      Functions to insert or adjust indentation.
* Case Changes::     Case conversion of parts of the buffer.
* Text Properties::  Assigning Lisp property lists to text characters.
* Substitution::     Replacing a given character wherever it appears.
* Registers::        How registers are implemented.  Accessing the text or
                       position stored in a register.
* Transposition::    Swapping two portions of a buffer.
* Change Hooks::     Supplying functions to be run when text is changed.


File: lispref.info,  Node: Near Point,  Next: Buffer Contents,  Up: Text

Examining Text Near Point
=========================

   Many functions are provided to look at the characters around point.
Several simple functions are described here.  See also `looking-at' in
*Note Regexp Search::.

   Many of these functions take an optional BUFFER argument.  In all
such cases, the current buffer will be used if this argument is
omitted. (In FSF Emacs, and earlier versions of XEmacs, these functions
usually did not have these optional BUFFER arguments and always
operated on the current buffer.)

 - Function: char-after POSITION &optional BUFFER
     This function returns the character in the buffer at (i.e.,
     immediately after) position POSITION.  If POSITION is out of range
     for this purpose, either before the beginning of the buffer, or at
     or beyond the end, then the value is `nil'.  If optional argument
     BUFFER is `nil', the current buffer is assumed.

     In the following example, assume that the first character in the
     buffer is `@':

          (char-to-string (char-after 1))
               => "@"

 - Function: following-char &optional BUFFER
     This function returns the character following point in the buffer.
     This is similar to `(char-after (point))'.  However, if point is at
     the end of the buffer, then the result of `following-char' is 0.
     If optional argument BUFFER is `nil', the current buffer is
     assumed.

     Remember that point is always between characters, and the terminal
     cursor normally appears over the character following point.
     Therefore, the character returned by `following-char' is the
     character the cursor is over.

     In this example, point is between the `a' and the `c'.

          ---------- Buffer: foo ----------
          Gentlemen may cry ``Pea-!-ce! Peace!,''
          but there is no peace.
          ---------- Buffer: foo ----------
          
          (char-to-string (preceding-char))
               => "a"
          (char-to-string (following-char))
               => "c"

 - Function: preceding-char &optional BUFFER
     This function returns the character preceding point in the buffer.
     See above, under `following-char', for an example.  If point is at
     the beginning of the buffer, `preceding-char' returns 0.  If
     optional argument BUFFER is `nil', the current buffer is assumed.

 - Function: bobp &optional BUFFER
     This function returns `t' if point is at the beginning of the
     buffer.  If narrowing is in effect, this means the beginning of the
     accessible portion of the text.  If optional argument BUFFER is
     `nil', the current buffer is assumed.  See also `point-min' in
     *Note Point::.

 - Function: eobp &optional BUFFER
     This function returns `t' if point is at the end of the buffer.
     If narrowing is in effect, this means the end of accessible
     portion of the text.  If optional argument BUFFER is `nil', the
     current buffer is assumed.  See also `point-max' in *Note Point::.

 - Function: bolp &optional BUFFER
     This function returns `t' if point is at the beginning of a line.
     If optional argument BUFFER is `nil', the current buffer is
     assumed.  *Note Text Lines::.  The beginning of the buffer (or its
     accessible portion) always counts as the beginning of a line.

 - Function: eolp &optional BUFFER
     This function returns `t' if point is at the end of a line.  The
     end of the buffer is always considered the end of a line.  If
     optional argument BUFFER is `nil', the current buffer is assumed.
     The end of the buffer (or of its accessible portion) is always
     considered the end of a line.


File: lispref.info,  Node: Buffer Contents,  Next: Comparing Text,  Prev: Near Point,  Up: Text

Examining Buffer Contents
=========================

   This section describes two functions that allow a Lisp program to
convert any portion of the text in the buffer into a string.

 - Function: buffer-substring START END &optional BUFFER
 - Function: buffer-string START END &optional BUFFER
     These functions are equivalent and return a string containing a
     copy of the text of the region defined by positions START and END
     in the buffer.  If the arguments are not positions in the
     accessible portion of the buffer, `buffer-substring' signals an
     `args-out-of-range' error.  If optional argument BUFFER is `nil',
     the current buffer is assumed.

     If the region delineated by START and END contains duplicable
     extents, they will be remembered in the string.  *Note Duplicable
     Extents::.

     It is not necessary for START to be less than END; the arguments
     can be given in either order.  But most often the smaller argument
     is written first.

          ---------- Buffer: foo ----------
          This is the contents of buffer foo
          
          ---------- Buffer: foo ----------
          
          (buffer-substring 1 10)
          => "This is t"
          (buffer-substring (point-max) 10)
          => "he contents of buffer foo
          "


File: lispref.info,  Node: Comparing Text,  Next: Insertion,  Prev: Buffer Contents,  Up: Text

Comparing Text
==============

   This function lets you compare portions of the text in a buffer,
without copying them into strings first.

 - Function: compare-buffer-substrings BUFFER1 START1 END1 BUFFER2
          START2 END2
     This function lets you compare two substrings of the same buffer
     or two different buffers.  The first three arguments specify one
     substring, giving a buffer and two positions within the buffer.
     The last three arguments specify the other substring in the same
     way.  You can use `nil' for BUFFER1, BUFFER2, or both to stand for
     the current buffer.

     The value is negative if the first substring is less, positive if
     the first is greater, and zero if they are equal.  The absolute
     value of the result is one plus the index of the first differing
     characters within the substrings.

     This function ignores case when comparing characters if
     `case-fold-search' is non-`nil'.  It always ignores text
     properties.

     Suppose the current buffer contains the text `foobarbar
     haha!rara!'; then in this example the two substrings are `rbar '
     and `rara!'.  The value is 2 because the first substring is greater
     at the second character.

          (compare-buffer-substring nil 6 11 nil 16 21)
               => 2


File: lispref.info,  Node: Insertion,  Next: Commands for Insertion,  Prev: Comparing Text,  Up: Text

Inserting Text
==============

   "Insertion" means adding new text to a buffer.  The inserted text
goes at point--between the character before point and the character
after point.

   Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text (*note
Markers::.).  When a marker points at the place of insertion, insertion
normally doesn't relocate the marker, so that it points to the
beginning of the inserted text; however, certain special functions such
as `insert-before-markers' relocate such markers to point after the
inserted text.

   Some insertion functions leave point before the inserted text, while
other functions leave it after.  We call the former insertion "after
point" and the latter insertion "before point".

   If a string with non-`nil' extent data is inserted, the remembered
extents will also be inserted.  *Note Duplicable Extents::.

   Insertion functions signal an error if the current buffer is
read-only.

   These functions copy text characters from strings and buffers along
with their properties.  The inserted characters have exactly the same
properties as the characters they were copied from.  By contrast,
characters specified as separate arguments, not part of a string or
buffer, inherit their text properties from the neighboring text.

 - Function: insert &rest ARGS
     This function inserts the strings and/or characters ARGS into the
     current buffer, at point, moving point forward.  In other words, it
     inserts the text before point.  An error is signaled unless all
     ARGS are either strings or characters.  The value is `nil'.

 - Function: insert-before-markers &rest ARGS
     This function inserts the strings and/or characters ARGS into the
     current buffer, at point, moving point forward.  An error is
     signaled unless all ARGS are either strings or characters.  The
     value is `nil'.

     This function is unlike the other insertion functions in that it
     relocates markers initially pointing at the insertion point, to
     point after the inserted text.

 - Function: insert-string STRING &optional BUFFER
     This function inserts STRING into BUFFER before point.  BUFFER
     defaults to the current buffer if omitted.  This function is
     chiefly useful if you want to insert a string in a buffer other
     than the current one (otherwise you could just use `insert').

 - Function: insert-char CHARACTER COUNT &optional BUFFER
     This function inserts COUNT instances of CHARACTER into BUFFER
     before point.  COUNT must be a number, and CHARACTER must be a
     character.  The value is `nil'.  If optional argument BUFFER is
     `nil', the current buffer is assumed. (In FSF Emacs, the third
     argument is called INHERIT and refers to text properties.)

 - Function: insert-buffer-substring FROM-BUFFER-OR-NAME &optional
          START END
     This function inserts a portion of buffer FROM-BUFFER-OR-NAME
     (which must already exist) into the current buffer before point.
     The text inserted is the region from START and END.  (These
     arguments default to the beginning and end of the accessible
     portion of that buffer.)  This function returns `nil'.

     In this example, the form is executed with buffer `bar' as the
     current buffer.  We assume that buffer `bar' is initially empty.

          ---------- Buffer: foo ----------
          We hold these truths to be self-evident, that all
          ---------- Buffer: foo ----------
          
          (insert-buffer-substring "foo" 1 20)
               => nil
          
          ---------- Buffer: bar ----------
          We hold these truth-!-
          ---------- Buffer: bar ----------


File: lispref.info,  Node: Commands for Insertion,  Next: Deletion,  Prev: Insertion,  Up: Text

User-Level Insertion Commands
=============================

   This section describes higher-level commands for inserting text,
commands intended primarily for the user but useful also in Lisp
programs.

 - Command: insert-buffer FROM-BUFFER-OR-NAME
     This command inserts the entire contents of FROM-BUFFER-OR-NAME
     (which must exist) into the current buffer after point.  It leaves
     the mark after the inserted text.  The value is `nil'.

 - Command: self-insert-command COUNT
     This command inserts the last character typed; it does so COUNT
     times, before point, and returns `nil'.  Most printing characters
     are bound to this command.  In routine use, `self-insert-command'
     is the most frequently called function in XEmacs, but programs
     rarely use it except to install it on a keymap.

     In an interactive call, COUNT is the numeric prefix argument.

     This command calls `auto-fill-function' whenever that is non-`nil'
     and the character inserted is a space or a newline (*note Auto
     Filling::.).

     This command performs abbrev expansion if Abbrev mode is enabled
     and the inserted character does not have word-constituent syntax.
     (*Note Abbrevs::, and *Note Syntax Class Table::.)

     This is also responsible for calling `blink-paren-function' when
     the inserted character has close parenthesis syntax (*note
     Blinking::.).

 - Command: newline &optional NUMBER-OF-NEWLINES
     This command inserts newlines into the current buffer before point.
     If NUMBER-OF-NEWLINES is supplied, that many newline characters
     are inserted.

     This function calls `auto-fill-function' if the current column
     number is greater than the value of `fill-column' and
     NUMBER-OF-NEWLINES is `nil'.  Typically what `auto-fill-function'
     does is insert a newline; thus, the overall result in this case is
     to insert two newlines at different places: one at point, and
     another earlier in the line.  `newline' does not auto-fill if
     NUMBER-OF-NEWLINES is non-`nil'.

     This command indents to the left margin if that is not zero.
     *Note Margins::.

     The value returned is `nil'.  In an interactive call, COUNT is the
     numeric prefix argument.

 - Command: split-line
     This command splits the current line, moving the portion of the
     line after point down vertically so that it is on the next line
     directly below where it was before.  Whitespace is inserted as
     needed at the beginning of the lower line, using the `indent-to'
     function.  `split-line' returns the position of point.

     Programs hardly ever use this function.

 - Variable: overwrite-mode
     This variable controls whether overwrite mode is in effect: a
     non-`nil' value enables the mode.  It is automatically made
     buffer-local when set in any fashion.

