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@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
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@c Copyright (C) 1990-1995, 1998-2012 Free Software Foundation, Inc.
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@c See the file elisp.texi for copying conditions.
@node Text, Non-ASCII Characters, Markers, Top
@chapter Text
@cindex 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 operating at point or on text adjacent to point.  Many are
interactive.  All the functions that change the text provide for undoing
the changes (@pxref{Undo}).

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

@cindex buffer contents
  Throughout this chapter, ``text'' refers to the characters in the
buffer, together with their properties (when relevant).  Keep in mind
that point is always between two characters, and the cursor appears on
the character after point.

@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.
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                        How to control how much information is kept.
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* Filling::          Functions for explicit filling.
* Margins::          How to specify margins for filling commands.
* Adaptive Fill::    Adaptive Fill mode chooses a fill prefix from context.
* 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.
* Transposition::    Swapping two portions of a buffer.
* Registers::        How registers are implemented.  Accessing the text or
                       position stored in a register.
* Base 64::          Conversion to or from base 64 encoding.
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* Checksum/Hash::    Computing cryptographic hashes.
* Parsing HTML/XML:: Parsing HTML and XML.
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* Atomic Changes::   Installing several buffer changes "atomically".
* Change Hooks::     Supplying functions to be run when text is changed.
@end menu

@node Near Point
@section Examining Text Near Point
@cindex text near point

  Many functions are provided to look at the characters around point.
Several simple functions are described here.  See also @code{looking-at}
in @ref{Regexp Search}.

In the following four functions, ``beginning'' or ``end'' of buffer
refers to the beginning or end of the accessible portion.

@defun char-after &optional position
This function returns the character in the current buffer at (i.e.,
immediately after) position @var{position}.  If @var{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 @code{nil}.  The default for
@var{position} is point.

In the following example, assume that the first character in the
buffer is @samp{@@}:

@example
@group
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(string (char-after 1))
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     @result{} "@@"
@end group
@end example
@end defun

@defun char-before &optional position
This function returns the character in the current buffer immediately
before position @var{position}.  If @var{position} is out of range for
this purpose, either at or before the beginning of the buffer, or beyond
the end, then the value is @code{nil}.  The default for
@var{position} is point.
@end defun

@defun following-char
This function returns the character following point in the current
buffer.  This is similar to @code{(char-after (point))}.  However, if
point is at the end of the buffer, then @code{following-char} returns 0.

Remember that point is always between characters, and the cursor
normally appears over the character following point.  Therefore, the
character returned by @code{following-char} is the character the
cursor is over.

In this example, point is between the @samp{a} and the @samp{c}.

@example
@group
---------- Buffer: foo ----------
Gentlemen may cry ``Pea@point{}ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
@end group

@group
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(string (preceding-char))
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     @result{} "a"
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(string (following-char))
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     @result{} "c"
@end group
@end example
@end defun

@defun preceding-char
This function returns the character preceding point in the current
buffer.  See above, under @code{following-char}, for an example.  If
point is at the beginning of the buffer, @code{preceding-char} returns
0.
@end defun

@defun bobp
This function returns @code{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.  See also @code{point-min} in
@ref{Point}.
@end defun

@defun eobp
This function returns @code{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.  See also @code{point-max} in @xref{Point}.
@end defun

@defun bolp
This function returns @code{t} if point is at the beginning of a line.
@xref{Text Lines}.  The beginning of the buffer (or of its accessible
portion) always counts as the beginning of a line.
@end defun

@defun eolp
This function returns @code{t} if point is at the end of a line.  The
end of the buffer (or of its accessible portion) is always considered
the end of a line.
@end defun

@node Buffer Contents
@section Examining Buffer Contents

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

@defun buffer-substring start end
This function returns a string containing a copy of the text of the
region defined by positions @var{start} and @var{end} in the current
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buffer.  If the arguments are not positions in the accessible portion
of the buffer, @code{buffer-substring} signals an
@code{args-out-of-range} error.
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Here's an example which assumes Font-Lock mode is not enabled:

@example
@group
---------- Buffer: foo ----------
This is the contents of buffer foo

---------- Buffer: foo ----------
@end group

@group
(buffer-substring 1 10)
     @result{} "This is t"
@end group
@group
(buffer-substring (point-max) 10)
     @result{} "he contents of buffer foo\n"
@end group
@end example

If the text being copied has any text properties, these are copied into
the string along with the characters they belong to.  @xref{Text
Properties}.  However, overlays (@pxref{Overlays}) in the buffer and
their properties are ignored, not copied.

For example, if Font-Lock mode is enabled, you might get results like
these:

@example
@group
(buffer-substring 1 10)
     @result{} #("This is t" 0 1 (fontified t) 1 9 (fontified t))
@end group
@end example
@end defun

@defun buffer-substring-no-properties start end
This is like @code{buffer-substring}, except that it does not copy text
properties, just the characters themselves.  @xref{Text Properties}.
@end defun

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@defun buffer-string
This function returns the contents of the entire accessible portion of
the current buffer as a string.  It is equivalent to
@w{@code{(buffer-substring (point-min) (point-max))}}.
@end defun

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@defun filter-buffer-substring start end &optional delete
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This function passes the buffer text between @var{start} and @var{end}
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through the filter functions specified by the wrapper hook
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@code{filter-buffer-substring-functions}, and returns the result.  The
obsolete variable @code{buffer-substring-filters} is also consulted.
If both of these variables are @code{nil}, the value is the unaltered
text from the buffer, i.e.@: what @code{buffer-substring} would
return.
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If @var{delete} is non-@code{nil}, this function deletes the text
between @var{start} and @var{end} after copying it, like
@code{delete-and-extract-region}.

Lisp code should use this function instead of @code{buffer-substring},
@code{buffer-substring-no-properties},
or @code{delete-and-extract-region} when copying into user-accessible
data structures such as the kill-ring, X clipboard, and registers.
Major and minor modes can add functions to
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@code{filter-buffer-substring-functions} to alter such text as it is
copied out of the buffer.
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@end defun

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@defvar filter-buffer-substring-functions
This variable is a wrapper hook (@pxref{Running Hooks}), whose members
should be functions that accept four arguments: @var{fun},
@var{start}, @var{end}, and @var{delete}.  @var{fun} is a function
that takes three arguments (@var{start}, @var{end}, and @var{delete}),
and returns a string.  In both cases, the @var{start}, @var{end}, and
@var{delete} arguments are the same as those of
@code{filter-buffer-substring}.

The first hook function is passed a @var{fun} that is equivalent to
the default operation of @code{filter-buffer-substring}, i.e. it
returns the buffer-substring between @var{start} and @var{end}
(processed by any @code{buffer-substring-filters}) and optionally
deletes the original text from the buffer.  In most cases, the hook
function will call @var{fun} once, and then do its own processing of
the result.  The next hook function receives a @var{fun} equivalent to
this, and so on.  The actual return value is the result of all the
hook functions acting in sequence.
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@end defvar

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@defvar buffer-substring-filters
This variable is obsoleted by
@code{filter-buffer-substring-functions}, but is still supported for
backward compatibility.  Its value should should be a list of
functions which accept a single string argument and return another
string.  @code{filter-buffer-substring} passes the buffer substring to
the first function in this list, and the return value of each function
is passed to the next function.  The return value of the last function
is passed to @code{filter-buffer-substring-functions}.
@end defvar
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@defun current-word &optional strict really-word
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This function returns the symbol (or word) at or near point, as a
string.  The return value includes no text properties.
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If the optional argument @var{really-word} is non-@code{nil}, it finds a
word; otherwise, it finds a symbol (which includes both word
characters and symbol constituent characters).

If the optional argument @var{strict} is non-@code{nil}, then point
must be in or next to the symbol or word---if no symbol or word is
there, the function returns @code{nil}.  Otherwise, a nearby symbol or
word on the same line is acceptable.
@end defun

@defun thing-at-point thing
Return the @var{thing} around or next to point, as a string.

The argument @var{thing} is a symbol which specifies a kind of syntactic
entity.  Possibilities include @code{symbol}, @code{list}, @code{sexp},
@code{defun}, @code{filename}, @code{url}, @code{word}, @code{sentence},
@code{whitespace}, @code{line}, @code{page}, and others.

@example
---------- Buffer: foo ----------
Gentlemen may cry ``Pea@point{}ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------

(thing-at-point 'word)
     @result{} "Peace"
(thing-at-point 'line)
     @result{} "Gentlemen may cry ``Peace! Peace!,''\n"
(thing-at-point 'whitespace)
     @result{} nil
@end example
@end defun

@node Comparing Text
@section Comparing Text
@cindex comparing buffer text

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

@defun 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 (or a buffer name) and two positions within the
buffer.  The last three arguments specify the other substring in the
same way.  You can use @code{nil} for @var{buffer1}, @var{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 @code{case-fold-search} is non-@code{nil}.  It always ignores
text properties.

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

@example
(compare-buffer-substrings nil 6 11 nil 16 21)
     @result{} 2
@end example
@end defun

@node Insertion
@section Inserting Text
@cindex insertion of text
@cindex text insertion

@cindex insertion before point
@cindex before point, insertion
  @dfn{Insertion} means adding new text to a buffer.  The inserted text
goes at point---between the character before point and the character
after point.  Some insertion functions leave point before the inserted
text, while other functions leave it after.  We call the former
insertion @dfn{after point} and the latter insertion @dfn{before point}.

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  Insertion moves markers located at positions after the insertion
point, so that they stay with the surrounding text (@pxref{Markers}).
When a marker points at the place of insertion, insertion may or may
not relocate the marker, depending on the marker's insertion type
(@pxref{Marker Insertion Types}).  Certain special functions such as
@code{insert-before-markers} relocate all such markers to point after
the inserted text, regardless of the markers' insertion type.
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  Insertion functions signal an error if the current buffer is
read-only or if they insert within read-only text.

  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.

  The insertion functions convert text from unibyte to multibyte in
order to insert in a multibyte buffer, and vice versa---if the text
comes from a string or from a buffer.  However, they do not convert
unibyte character codes 128 through 255 to multibyte characters, not
even if the current buffer is a multibyte buffer.  @xref{Converting
Representations}.

@defun insert &rest args
This function inserts the strings and/or characters @var{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
@var{args} are either strings or characters.  The value is @code{nil}.
@end defun

@defun insert-before-markers &rest args
This function inserts the strings and/or characters @var{args} into the
current buffer, at point, moving point forward.  An error is signaled
unless all @var{args} are either strings or characters.  The value is
@code{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.  If an overlay begins at the insertion point,
the inserted text falls outside the overlay; if a nonempty overlay
ends at the insertion point, the inserted text falls inside that
overlay.
@end defun

@defun insert-char character count &optional inherit
This function inserts @var{count} instances of @var{character} into the
current buffer before point.  The argument @var{count} should be an
integer, and @var{character} must be a character.  The value is @code{nil}.

This function does not convert unibyte character codes 128 through 255
to multibyte characters, not even if the current buffer is a multibyte
buffer.  @xref{Converting Representations}.

If @var{inherit} is non-@code{nil}, then the inserted characters inherit
sticky text properties from the two characters before and after the
insertion point.  @xref{Sticky Properties}.
@end defun

@defun insert-buffer-substring from-buffer-or-name &optional start end
This function inserts a portion of buffer @var{from-buffer-or-name}
(which must already exist) into the current buffer before point.  The
text inserted is the region between @var{start} and @var{end}.  (These
arguments default to the beginning and end of the accessible portion of
that buffer.)  This function returns @code{nil}.

In this example, the form is executed with buffer @samp{bar} as the
current buffer.  We assume that buffer @samp{bar} is initially empty.

@example
@group
---------- Buffer: foo ----------
We hold these truths to be self-evident, that all
---------- Buffer: foo ----------
@end group

@group
(insert-buffer-substring "foo" 1 20)
     @result{} nil

---------- Buffer: bar ----------
We hold these truth@point{}
---------- Buffer: bar ----------
@end group
@end example
@end defun

@defun insert-buffer-substring-no-properties from-buffer-or-name &optional start end
This is like @code{insert-buffer-substring} except that it does not
copy any text properties.
@end defun

  @xref{Sticky Properties}, for other insertion functions that inherit
text properties from the nearby text in addition to inserting it.
Whitespace inserted by indentation functions also inherits text
properties.

@node Commands for Insertion
@section 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.

@deffn Command insert-buffer from-buffer-or-name
This command inserts the entire accessible contents of
@var{from-buffer-or-name} (which must exist) into the current buffer
after point.  It leaves the mark after the inserted text.  The value
is @code{nil}.
@end deffn

@deffn Command self-insert-command count
@cindex character insertion
@cindex self-insertion
This command inserts the last character typed; it does so @var{count}
times, before point, and returns @code{nil}.  Most printing characters
are bound to this command.  In routine use, @code{self-insert-command}
is the most frequently called function in Emacs, but programs rarely use
it except to install it on a keymap.

In an interactive call, @var{count} is the numeric prefix argument.

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Self-insertion translates the input character through
@code{translation-table-for-input}.  @xref{Translation of Characters}.

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This command calls @code{auto-fill-function} whenever that is
non-@code{nil} and the character inserted is in the table
@code{auto-fill-chars} (@pxref{Auto Filling}).

@c Cross refs reworded to prevent overfull hbox.  --rjc 15mar92
This command performs abbrev expansion if Abbrev mode is enabled and
the inserted character does not have word-constituent
syntax. (@xref{Abbrevs}, and @ref{Syntax Class Table}.)  It is also
responsible for calling @code{blink-paren-function} when the inserted
character has close parenthesis syntax (@pxref{Blinking}).

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@vindex post-self-insert-hook
The final thing this command does is to run the hook
@code{post-self-insert-hook}.  You could use this to automatically
reindent text as it is typed, for example.

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Do not try substituting your own definition of
@code{self-insert-command} for the standard one.  The editor command
loop handles this function specially.
@end deffn

@deffn Command newline &optional number-of-newlines
This command inserts newlines into the current buffer before point.
If @var{number-of-newlines} is supplied, that many newline characters
are inserted.

@cindex newline and Auto Fill mode
This function calls @code{auto-fill-function} if the current column
number is greater than the value of @code{fill-column} and
@var{number-of-newlines} is @code{nil}.  Typically what
@code{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.  @code{newline} does not
auto-fill if @var{number-of-newlines} is non-@code{nil}.

This command indents to the left margin if that is not zero.
@xref{Margins}.

The value returned is @code{nil}.  In an interactive call, @var{count}
is the numeric prefix argument.
@end deffn

@defvar overwrite-mode
This variable controls whether overwrite mode is in effect.  The value
should be @code{overwrite-mode-textual}, @code{overwrite-mode-binary},
or @code{nil}.  @code{overwrite-mode-textual} specifies textual
overwrite mode (treats newlines and tabs specially), and
@code{overwrite-mode-binary} specifies binary overwrite mode (treats
newlines and tabs like any other characters).
@end defvar

@node Deletion
@section Deleting Text
@cindex text deletion

@cindex deleting text vs killing
  Deletion means removing part of the text in a buffer, without saving
it in the kill ring (@pxref{The Kill Ring}).  Deleted text can't be
yanked, but can be reinserted using the undo mechanism (@pxref{Undo}).
Some deletion functions do save text in the kill ring in some special
cases.

  All of the deletion functions operate on the current buffer.

@deffn Command erase-buffer
This function deletes the entire text of the current buffer
(@emph{not} just the accessible portion), leaving it
empty.  If the buffer is read-only, it signals a @code{buffer-read-only}
error; if some of the text in it is read-only, it signals a
@code{text-read-only} error.  Otherwise, it deletes the text without
asking for any confirmation.  It returns @code{nil}.

Normally, deleting a large amount of text from a buffer inhibits further
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auto-saving of that buffer ``because it has shrunk''.  However,
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@code{erase-buffer} does not do this, the idea being that the future
text is not really related to the former text, and its size should not
be compared with that of the former text.
@end deffn

@deffn Command delete-region start end
This command deletes the text between positions @var{start} and
@var{end} in the current buffer, and returns @code{nil}.  If point was
inside the deleted region, its value afterward is @var{start}.
Otherwise, point relocates with the surrounding text, as markers do.
@end deffn

@defun delete-and-extract-region start end
This function deletes the text between positions @var{start} and
@var{end} in the current buffer, and returns a string containing the
text just deleted.

If point was inside the deleted region, its value afterward is
@var{start}.  Otherwise, point relocates with the surrounding text, as
markers do.
@end defun

@deffn Command delete-char count &optional killp
This command deletes @var{count} characters directly after point, or
before point if @var{count} is negative.  If @var{killp} is
non-@code{nil}, then it saves the deleted characters in the kill ring.

In an interactive call, @var{count} is the numeric prefix argument, and
@var{killp} is the unprocessed prefix argument.  Therefore, if a prefix
argument is supplied, the text is saved in the kill ring.  If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.

The value returned is always @code{nil}.
@end deffn

@deffn Command delete-backward-char count &optional killp
@cindex deleting previous char
This command deletes @var{count} characters directly before point, or
after point if @var{count} is negative.  If @var{killp} is
non-@code{nil}, then it saves the deleted characters in the kill ring.

In an interactive call, @var{count} is the numeric prefix argument, and
@var{killp} is the unprocessed prefix argument.  Therefore, if a prefix
argument is supplied, the text is saved in the kill ring.  If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.

The value returned is always @code{nil}.
@end deffn

@deffn Command backward-delete-char-untabify count &optional killp
@cindex tab deletion
This command deletes @var{count} characters backward, changing tabs
into spaces.  When the next character to be deleted is a tab, it is
first replaced with the proper number of spaces to preserve alignment
and then one of those spaces is deleted instead of the tab.  If
@var{killp} is non-@code{nil}, then the command saves the deleted
characters in the kill ring.

Conversion of tabs to spaces happens only if @var{count} is positive.
If it is negative, exactly @minus{}@var{count} characters after point
are deleted.

In an interactive call, @var{count} is the numeric prefix argument, and
@var{killp} is the unprocessed prefix argument.  Therefore, if a prefix
argument is supplied, the text is saved in the kill ring.  If no prefix
argument is supplied, then one character is deleted, but not saved in
the kill ring.

The value returned is always @code{nil}.
@end deffn

@defopt backward-delete-char-untabify-method
This option specifies how @code{backward-delete-char-untabify} should
deal with whitespace.  Possible values include @code{untabify}, the
default, meaning convert a tab to many spaces and delete one;
@code{hungry}, meaning delete all tabs and spaces before point with
one command; @code{all} meaning delete all tabs, spaces and newlines
before point, and @code{nil}, meaning do nothing special for
whitespace characters.
@end defopt

@node User-Level Deletion
@section User-Level Deletion Commands

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

@deffn Command delete-horizontal-space &optional backward-only
@cindex deleting whitespace
This function deletes all spaces and tabs around point.  It returns
@code{nil}.

If @var{backward-only} is non-@code{nil}, the function deletes
spaces and tabs before point, but not after point.

In the following examples, we call @code{delete-horizontal-space} four
times, once on each line, with point between the second and third
characters on the line each time.

@example
@group
---------- Buffer: foo ----------
I @point{}thought
I @point{}     thought
We@point{} thought
Yo@point{}u thought
---------- Buffer: foo ----------
@end group

@group
(delete-horizontal-space)   ; @r{Four times.}
     @result{} nil

---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------
@end group
@end example
@end deffn

@deffn Command delete-indentation &optional join-following-p
This function joins the line point is on to the previous line, deleting
any whitespace at the join and in some cases replacing it with one
space.  If @var{join-following-p} is non-@code{nil},
@code{delete-indentation} joins this line to the following line
instead.  The function returns @code{nil}.

If there is a fill prefix, and the second of the lines being joined
starts with the prefix, then @code{delete-indentation} deletes the
fill prefix before joining the lines.  @xref{Margins}.

In the example below, point is located on the line starting
@samp{events}, and it makes no difference if there are trailing spaces
in the preceding line.

@smallexample
@group
---------- Buffer: foo ----------
When in the course of human
@point{}    events, it becomes necessary
---------- Buffer: foo ----------
@end group

(delete-indentation)
     @result{} nil

@group
---------- Buffer: foo ----------
When in the course of human@point{} events, it becomes necessary
---------- Buffer: foo ----------
@end group
@end smallexample

After the lines are joined, the function @code{fixup-whitespace} is
responsible for deciding whether to leave a space at the junction.
@end deffn

@deffn Command fixup-whitespace
This function replaces all the horizontal whitespace surrounding point
with either one space or no space, according to the context.  It
returns @code{nil}.

At the beginning or end of a line, the appropriate amount of space is
none.  Before a character with close parenthesis syntax, or after a
character with open parenthesis or expression-prefix syntax, no space is
also appropriate.  Otherwise, one space is appropriate.  @xref{Syntax
Class Table}.

In the example below, @code{fixup-whitespace} is called the first time
with point before the word @samp{spaces} in the first line.  For the
second invocation, point is directly after the @samp{(}.

@smallexample
@group
---------- Buffer: foo ----------
This has too many     @point{}spaces
This has too many spaces at the start of (@point{}   this list)
---------- Buffer: foo ----------
@end group

@group
(fixup-whitespace)
     @result{} nil
(fixup-whitespace)
     @result{} nil
@end group

@group
---------- Buffer: foo ----------
This has too many spaces
This has too many spaces at the start of (this list)
---------- Buffer: foo ----------
@end group
@end smallexample
@end deffn

@deffn Command just-one-space &optional n
@comment !!SourceFile simple.el
This command replaces any spaces and tabs around point with a single
space, or @var{n} spaces if @var{n} is specified.  It returns
@code{nil}.
@end deffn

@deffn Command delete-blank-lines
This function deletes blank lines surrounding point.  If point is on a
blank line with one or more blank lines before or after it, then all but
one of them are deleted.  If point is on an isolated blank line, then it
is deleted.  If point is on a nonblank line, the command deletes all
blank lines immediately following it.

A blank line is defined as a line containing only tabs and spaces.

@code{delete-blank-lines} returns @code{nil}.
@end deffn

@node The Kill Ring
@section The Kill Ring
@cindex kill ring

  @dfn{Kill functions} delete text like the deletion functions, but save
it so that the user can reinsert it by @dfn{yanking}.  Most of these
functions have @samp{kill-} in their name.  By contrast, the functions
whose names start with @samp{delete-} normally do not save text for
yanking (though they can still be undone); these are ``deletion''
functions.

  Most of the kill commands are primarily for interactive use, and are
not described here.  What we do describe are the functions provided for
use in writing such commands.  You can use these functions to write
commands for killing text.  When you need to delete text for internal
purposes within a Lisp function, you should normally use deletion
functions, so as not to disturb the kill ring contents.
@xref{Deletion}.

  Killed text is saved for later yanking in the @dfn{kill ring}.  This
is a list that holds a number of recent kills, not just the last text
kill.  We call this a ``ring'' because yanking treats it as having
elements in a cyclic order.  The list is kept in the variable
@code{kill-ring}, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.

  Some people think this use of the word ``kill'' is unfortunate, since
it refers to operations that specifically @emph{do not} destroy the
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entities ``killed''.  This is in sharp contrast to ordinary life, in
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which death is permanent and ``killed'' entities do not come back to
life.  Therefore, other metaphors have been proposed.  For example, the
term ``cut ring'' makes sense to people who, in pre-computer days, used
scissors and paste to cut up and rearrange manuscripts.  However, it
would be difficult to change the terminology now.

@menu
* Kill Ring Concepts::     What text looks like in the kill ring.
* Kill Functions::         Functions that kill text.
* Yanking::                How yanking is done.
* Yank Commands::          Commands that access the kill ring.
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* Low-Level Kill Ring::    Functions and variables for kill ring access.
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* Internals of Kill Ring:: Variables that hold kill ring data.
@end menu

@node Kill Ring Concepts
@comment  node-name,  next,  previous,  up
@subsection Kill Ring Concepts

  The kill ring records killed text as strings in a list, most recent
first.  A short kill ring, for example, might look like this:

@example
("some text" "a different piece of text" "even older text")
@end example

@noindent
When the list reaches @code{kill-ring-max} entries in length, adding a
new entry automatically deletes the last entry.

  When kill commands are interwoven with other commands, each kill
command makes a new entry in the kill ring.  Multiple kill commands in
succession build up a single kill ring entry, which would be yanked as a
unit; the second and subsequent consecutive kill commands add text to
the entry made by the first one.

  For yanking, one entry in the kill ring is designated the ``front'' of
the ring.  Some yank commands ``rotate'' the ring by designating a
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different element as the ``front''.  But this virtual rotation doesn't
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change the list itself---the most recent entry always comes first in the
list.

@node Kill Functions
@comment  node-name,  next,  previous,  up
@subsection Functions for Killing

  @code{kill-region} is the usual subroutine for killing text.  Any
command that calls this function is a ``kill command'' (and should
probably have @samp{kill} in its name).  @code{kill-region} puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element.  It determines automatically (using
@code{last-command}) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.

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@deffn Command kill-region start end
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This function kills the text in the region defined by @var{start} and
@var{end}.  The text is deleted but saved in the kill ring, along with
its text properties.  The value is always @code{nil}.

In an interactive call, @var{start} and @var{end} are point and
the mark.

If the buffer or text is read-only, @code{kill-region} modifies the kill
ring just the same, then signals an error without modifying the buffer.
This is convenient because it lets the user use a series of kill
commands to copy text from a read-only buffer into the kill ring.
@end deffn

@defopt kill-read-only-ok
If this option is non-@code{nil}, @code{kill-region} does not signal an
error if the buffer or text is read-only.  Instead, it simply returns,
updating the kill ring but not changing the buffer.
@end defopt

@deffn Command copy-region-as-kill start end
This command saves the region defined by @var{start} and @var{end} on
the kill ring (including text properties), but does not delete the text
from the buffer.  It returns @code{nil}.

The command does not set @code{this-command} to @code{kill-region}, so a
subsequent kill command does not append to the same kill ring entry.

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@c FIXME Why is it better?  Why isn't copy-region-as-kill obsolete then?
@c Why is it used in many places in Emacs?
In Lisp programs, it is better to use @code{kill-new} or
@code{kill-append} instead of this command.  @xref{Low-Level Kill Ring}.
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@end deffn

@node Yanking
@subsection Yanking

  Yanking means inserting text from the kill ring, but it does
not insert the text blindly.  Yank commands and some other commands
use @code{insert-for-yank} to perform special processing on the
text that they copy into the buffer.

@defun insert-for-yank string
This function normally works like @code{insert} except that it doesn't
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insert the text properties (@pxref{Text Properties}) in the list
variable @code{yank-excluded-properties}.  However, if any part of
@var{string} has a non-@code{nil} @code{yank-handler} text property,
that property can do various special processing on that part of the
text being inserted.
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@end defun

@defun insert-buffer-substring-as-yank buf &optional start end
This function resembles @code{insert-buffer-substring} except that it
doesn't insert the text properties in the
@code{yank-excluded-properties} list.
@end defun

  You can put a @code{yank-handler} text property on all or part of
the text to control how it will be inserted if it is yanked.  The
@code{insert-for-yank} function looks for that property.  The property
value must be a list of one to four elements, with the following
format (where elements after the first may be omitted):

@example
(@var{function} @var{param} @var{noexclude} @var{undo})
@end example

  Here is what the elements do:

@table @var
@item function
When @var{function} is present and non-@code{nil}, it is called instead of
@code{insert} to insert the string.  @var{function} takes one
argument---the string to insert.

@item param
If @var{param} is present and non-@code{nil}, it replaces @var{string}
(or the part of @var{string} being processed) as the object passed to
@var{function} (or @code{insert}); for example, if @var{function} is
@code{yank-rectangle}, @var{param} should be a list of strings to
insert as a rectangle.

@item noexclude
If @var{noexclude} is present and non-@code{nil}, the normal removal of the
yank-excluded-properties is not performed; instead @var{function} is
responsible for removing those properties.  This may be necessary
if @var{function} adjusts point before or after inserting the object.

@item undo
If @var{undo} is present and non-@code{nil}, it is a function that will be
called by @code{yank-pop} to undo the insertion of the current object.
It is called with two arguments, the start and end of the current
region.  @var{function} can set @code{yank-undo-function} to override
the @var{undo} value.
@end table

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@cindex yanking and text properties
@defopt yank-excluded-properties
Yanking discards certain text properties from the yanked text, as
described above.  The value of this variable is the list of properties
to discard.  Its default value contains properties that might lead to
annoying results, such as causing the text to respond to the mouse or
specifying key bindings.
@end defopt

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@node Yank Commands
@comment  node-name,  next,  previous,  up
@subsection Functions for Yanking

  This section describes higher-level commands for yanking, which are
intended primarily for the user but useful also in Lisp programs.
Both @code{yank} and @code{yank-pop} honor the
@code{yank-excluded-properties} variable and @code{yank-handler} text
property (@pxref{Yanking}).

@deffn Command yank &optional arg
@cindex inserting killed text
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This command inserts before point the text at the front of the kill
ring.  It sets the mark at the beginning of that text, using
@code{push-mark} (@pxref{The Mark}), and puts point at the end.
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If @var{arg} is a non-@code{nil} list (which occurs interactively when
the user types @kbd{C-u} with no digits), then @code{yank} inserts the
text as described above, but puts point before the yanked text and
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sets the mark after it.
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If @var{arg} is a number, then @code{yank} inserts the @var{arg}th
most recently killed text---the @var{arg}th element of the kill ring
list, counted cyclically from the front, which is considered the
first element for this purpose.

@code{yank} does not alter the contents of the kill ring, unless it
used text provided by another program, in which case it pushes that text
onto the kill ring.  However if @var{arg} is an integer different from
one, it rotates the kill ring to place the yanked string at the front.

@code{yank} returns @code{nil}.
@end deffn

@deffn Command yank-pop &optional arg
This command replaces the just-yanked entry from the kill ring with a
different entry from the kill ring.

This is allowed only immediately after a @code{yank} or another
@code{yank-pop}.  At such a time, the region contains text that was just
inserted by yanking.  @code{yank-pop} deletes that text and inserts in
its place a different piece of killed text.  It does not add the deleted
text to the kill ring, since it is already in the kill ring somewhere.
It does however rotate the kill ring to place the newly yanked string at
the front.

If @var{arg} is @code{nil}, then the replacement text is the previous
element of the kill ring.  If @var{arg} is numeric, the replacement is
the @var{arg}th previous kill.  If @var{arg} is negative, a more recent
kill is the replacement.

The sequence of kills in the kill ring wraps around, so that after the
oldest one comes the newest one, and before the newest one goes the
oldest.

The return value is always @code{nil}.
@end deffn

@defvar yank-undo-function
If this variable is non-@code{nil}, the function @code{yank-pop} uses
its value instead of @code{delete-region} to delete the text
inserted by the previous @code{yank} or
@code{yank-pop} command.  The value must be a function of two
arguments, the start and end of the current region.

The function @code{insert-for-yank} automatically sets this variable
according to the @var{undo} element of the @code{yank-handler}
text property, if there is one.
@end defvar

@node Low-Level Kill Ring
@subsection Low-Level Kill Ring

  These functions and variables provide access to the kill ring at a
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lower level, but are still convenient for use in Lisp programs,
because they take care of interaction with window system selections
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(@pxref{Window System Selections}).

@defun current-kill n &optional do-not-move
The function @code{current-kill} rotates the yanking pointer, which
designates the ``front'' of the kill ring, by @var{n} places (from newer
kills to older ones), and returns the text at that place in the ring.

If the optional second argument @var{do-not-move} is non-@code{nil},
then @code{current-kill} doesn't alter the yanking pointer; it just
returns the @var{n}th kill, counting from the current yanking pointer.

If @var{n} is zero, indicating a request for the latest kill,
@code{current-kill} calls the value of
@code{interprogram-paste-function} (documented below) before
consulting the kill ring.  If that value is a function and calling it
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returns a string or a list of several string, @code{current-kill}
pushes the strings onto the kill ring and returns the first string.
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It also sets the yanking pointer to point to the kill-ring entry of
the first string returned by @code{interprogram-paste-function},
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regardless of the value of @var{do-not-move}.  Otherwise,
@code{current-kill} does not treat a zero value for @var{n} specially:
it returns the entry pointed at by the yanking pointer and does not
move the yanking pointer.
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@end defun

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@defun kill-new string &optional replace
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This function pushes the text @var{string} onto the kill ring and
makes the yanking pointer point to it.  It discards the oldest entry
if appropriate.  It also invokes the value of
@code{interprogram-cut-function} (see below).

If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
first element of the kill ring with @var{string}, rather than pushing
@var{string} onto the kill ring.
@end defun

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@defun kill-append string before-p
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This function appends the text @var{string} to the first entry in the
kill ring and makes the yanking pointer point to the combined entry.
Normally @var{string} goes at the end of the entry, but if
@var{before-p} is non-@code{nil}, it goes at the beginning.  This
function also invokes the value of @code{interprogram-cut-function}
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(see below).
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@end defun

@defvar interprogram-paste-function
This variable provides a way of transferring killed text from other
programs, when you are using a window system.  Its value should be
@code{nil} or a function of no arguments.

If the value is a function, @code{current-kill} calls it to get the
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``most recent kill''.  If the function returns a non-@code{nil} value,
then that value is used as the ``most recent kill''.  If it returns
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@code{nil}, then the front of the kill ring is used.

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To facilitate support for window systems that support multiple
selections, this function may also return a list of strings.  In that
case, the first string is used as the ``most recent kill'', and all
the other strings are pushed onto the kill ring, for easy access by
@code{yank-pop}.

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The normal use of this function is to get the window system's
clipboard as the most recent kill, even if the selection belongs to
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another application.  @xref{Window System Selections}.  However, if
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the clipboard contents come from the current Emacs session, this
function should return @code{nil}.
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@end defvar

@defvar interprogram-cut-function
This variable provides a way of communicating killed text to other
programs, when you are using a window system.  Its value should be
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@code{nil} or a function of one required argument.
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If the value is a function, @code{kill-new} and @code{kill-append} call
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it with the new first element of the kill ring as the argument.
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The normal use of this function is to put newly killed text in the
window system's clipboard.  @xref{Window System Selections}.
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@end defvar

@node Internals of Kill Ring
@comment  node-name,  next,  previous,  up
@subsection Internals of the Kill Ring

  The variable @code{kill-ring} holds the kill ring contents, in the
form of a list of strings.  The most recent kill is always at the front
of the list.

  The @code{kill-ring-yank-pointer} variable points to a link in the
kill ring list, whose @sc{car} is the text to yank next.  We say it
identifies the ``front'' of the ring.  Moving
@code{kill-ring-yank-pointer} to a different link is called
@dfn{rotating the kill ring}.  We call the kill ring a ``ring'' because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa.  Rotation of the kill ring is
virtual; it does not change the value of @code{kill-ring}.

  Both @code{kill-ring} and @code{kill-ring-yank-pointer} are Lisp
variables whose values are normally lists.  The word ``pointer'' in the
name of the @code{kill-ring-yank-pointer} indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.

  The value of @code{kill-ring-yank-pointer} is always @code{eq} to one
of the links in the kill ring list.  The element it identifies is the
@sc{car} of that link.  Kill commands, which change the kill ring, also
set this variable to the value of @code{kill-ring}.  The effect is to
rotate the ring so that the newly killed text is at the front.

  Here is a diagram that shows the variable @code{kill-ring-yank-pointer}
pointing to the second entry in the kill ring @code{("some text" "a
different piece of text" "yet older text")}.

@example
@group
kill-ring                  ---- kill-ring-yank-pointer
  |                       |
  |                       v
  |     --- ---          --- ---      --- ---
   --> |   |   |------> |   |   |--> |   |   |--> nil
        --- ---          --- ---      --- ---
         |                |            |
         |                |            |
         |                |             -->"yet older text"
         |                |
         |                 --> "a different piece of text"
         |
          --> "some text"
@end group
@end example

@noindent
This state of affairs might occur after @kbd{C-y} (@code{yank})
immediately followed by @kbd{M-y} (@code{yank-pop}).

@defvar kill-ring
This variable holds the list of killed text sequences, most recently
killed first.
@end defvar

@defvar kill-ring-yank-pointer
This variable's value indicates which element of the kill ring is at the
``front'' of the ring for yanking.  More precisely, the value is a tail
of the value of @code{kill-ring}, and its @sc{car} is the kill string
that @kbd{C-y} should yank.
@end defvar

@defopt kill-ring-max
The value of this variable is the maximum length to which the kill
ring can grow, before elements are thrown away at the end.  The default
value for @code{kill-ring-max} is 60.
@end defopt

@node Undo
@comment  node-name,  next,  previous,  up
@section Undo
@cindex redo

  Most buffers have an @dfn{undo list}, which records all changes made
to the buffer's text so that they can be undone.  (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful.  In particular, any buffer whose
name begins with a space has its undo recording off by default;
see @ref{Buffer Names}.)  All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable @code{buffer-undo-list}.

@defvar buffer-undo-list
This buffer-local variable's value is the undo list of the current
buffer. A value of @code{t} disables the recording of undo information.
@end defvar

Here are the kinds of elements an undo list can have:

@table @code
@item @var{position}
This kind of element records a previous value of point; undoing this
element moves point to @var{position}.  Ordinary cursor motion does not
make any sort of undo record, but deletion operations use these entries
to record where point was before the command.

@item (@var{beg} . @var{end})
This kind of element indicates how to delete text that was inserted.
Upon insertion, the text occupied the range @var{beg}--@var{end} in the
buffer.

@item (@var{text} . @var{position})
This kind of element indicates how to reinsert text that was deleted.
The deleted text itself is the string @var{text}.  The place to
reinsert it is @code{(abs @var{position})}.  If @var{position} is
positive, point was at the beginning of the deleted text, otherwise it
was at the end.

@item (t @var{high} . @var{low})
This kind of element indicates that an unmodified buffer became
modified.  The elements @var{high} and @var{low} are two integers, each
recording 16 bits of the visited file's modification time as of when it
was previously visited or saved.  @code{primitive-undo} uses those
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's modification time matches those numbers.

@item (nil @var{property} @var{value} @var{beg} . @var{end})
This kind of element records a change in a text property.
Here's how you might undo the change:

@example
(put-text-property @var{beg} @var{end} @var{property} @var{value})
@end example

@item (@var{marker} . @var{adjustment})
This kind of element records the fact that the marker @var{marker} was
relocated due to deletion of surrounding text, and that it moved
@var{adjustment} character positions.  Undoing this element moves
@var{marker} @minus{} @var{adjustment} characters.

@item (apply @var{funname} . @var{args})
This is an extensible undo item, which is undone by calling
@var{funname} with arguments @var{args}.

@item (apply @var{delta} @var{beg} @var{end} @var{funname} . @var{args})
This is an extensible undo item, which records a change limited to the
range @var{beg} to @var{end}, which increased the size of the buffer
by @var{delta}.  It is undone by calling @var{funname} with arguments
@var{args}.

This kind of element enables undo limited to a region to determine
whether the element pertains to that region.

@item nil
This element is a boundary.  The elements between two boundaries are
called a @dfn{change group}; normally, each change group corresponds to
one keyboard command, and undo commands normally undo an entire group as
a unit.
@end table

@defun undo-boundary
This function places a boundary element in the undo list.  The undo
command stops at such a boundary, and successive undo commands undo
to earlier and earlier boundaries.  This function returns @code{nil}.

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The editor command loop automatically calls @code{undo-boundary} just
before executing each key sequence, so that each undo normally undoes
the effects of one command.  As an exception, the command
@code{self-insert-command}, which produces self-inserting input
characters (@pxref{Commands for Insertion}), may remove the boundary
inserted by the command loop: a boundary is accepted for the first
such character, the next 19 consecutive self-inserting input
characters do not have boundaries, and then the 20th does; and so on
as long as the self-inserting characters continue.  Hence, sequences
of consecutive character insertions can be undone as a group.
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All buffer modifications add a boundary whenever the previous undoable
change was made in some other buffer.  This is to ensure that
each command makes a boundary in each buffer where it makes changes.

Calling this function explicitly is useful for splitting the effects of
a command into more than one unit.  For example, @code{query-replace}
calls @code{undo-boundary} after each replacement, so that the user can
undo individual replacements one by one.
@end defun

@defvar undo-in-progress
This variable is normally @code{nil}, but the undo commands bind it to
@code{t}.  This is so that various kinds of change hooks can tell when
they're being called for the sake of undoing.
@end defvar

@defun primitive-undo count list
This is the basic function for undoing elements of an undo list.
It undoes the first @var{count} elements of @var{list}, returning
the rest of @var{list}.

@code{primitive-undo} adds elements to the buffer's undo list when it
changes the buffer.  Undo commands avoid confusion by saving the undo
list value at the beginning of a sequence of undo operations.  Then the
undo operations use and update the saved value.  The new elements added
by undoing are not part of this saved value, so they don't interfere with
continuing to undo.

This function does not bind @code{undo-in-progress}.
@end defun

@node Maintaining Undo
@section Maintaining Undo Lists

  This section describes how to enable and disable undo information for
a given buffer.  It also explains how the undo list is truncated
automatically so it doesn't get too big.

  Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled.  You can explicitly enable or
disable undo recording with the following two functions, or by setting
@code{buffer-undo-list} yourself.

@deffn Command buffer-enable-undo &optional buffer-or-name
This command enables recording undo information for buffer
@var{buffer-or-name}, so that subsequent changes can be undone.  If no
argument is supplied, then the current buffer is used.  This function
does nothing if undo recording is already enabled in the buffer.  It
returns @code{nil}.

In an interactive call, @var{buffer-or-name} is the current buffer.
You cannot specify any other buffer.
@end deffn

@deffn Command buffer-disable-undo &optional buffer-or-name
@cindex disabling undo
This function discards the undo list of @var{buffer-or-name}, and disables
further recording of undo information.  As a result, it is no longer
possible to undo either previous changes or any subsequent changes.  If
the undo list of @var{buffer-or-name} is already disabled, this function
has no effect.

This function returns @code{nil}.
@end deffn

  As editing continues, undo lists get longer and longer.  To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set.  (For this purpose, the ``size''
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.)  Three variables control the range of acceptable
sizes: @code{undo-limit}, @code{undo-strong-limit} and
@code{undo-outer-limit}.  In these variables, size is counted as the
number of bytes occupied, which includes both saved text and other
data.

@defopt undo-limit
This is the soft limit for the acceptable size of an undo list.  The
change group at which this size is exceeded is the last one kept.
@end defopt

@defopt undo-strong-limit
This is the upper limit for the acceptable size of an undo list.  The
change group at which this size is exceeded is discarded itself (along
with all older change groups).  There is one exception: the very latest
change group is only discarded if it exceeds @code{undo-outer-limit}.
@end defopt

@defopt undo-outer-limit
If at garbage collection time the undo info for the current command
exceeds this limit, Emacs discards the info and displays a warning.
This is a last ditch limit to prevent memory overflow.
@end defopt

@defopt undo-ask-before-discard
If this variable is non-@code{nil}, when the undo info exceeds
@code{undo-outer-limit}, Emacs asks in the echo area whether to
discard the info.  The default value is @code{nil}, which means to
discard it automatically.

This option is mainly intended for debugging.  Garbage collection is
inhibited while the question is asked, which means that Emacs might
leak memory if the user waits too long before answering the question.
@end defopt

@node Filling
@comment  node-name,  next,  previous,  up
@section Filling
@cindex filling text

  @dfn{Filling} means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width.  Additionally, lines can be @dfn{justified}, which means
inserting spaces to make the left and/or right margins line up
precisely.  The width is controlled by the variable @code{fill-column}.
For ease of reading, lines should be no longer than 70 or so columns.

  You can use Auto Fill mode (@pxref{Auto Filling}) to fill text
automatically as you insert it, but changes to existing text may leave
it improperly filled.  Then you must fill the text explicitly.

  Most of the commands in this section return values that are not
meaningful.  All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(@pxref{Margins}).  If the current justification style is
@code{none}, the filling functions don't actually do anything.

  Several of the filling functions have an argument @var{justify}.
If it is non-@code{nil}, that requests some kind of justification.  It
can be @code{left}, @code{right}, @code{full}, or @code{center}, to
request a specific style of justification.  If it is @code{t}, that
means to use the current justification style for this part of the text
(see @code{current-justification}, below).  Any other value is treated
as @code{full}.

  When you call the filling functions interactively, using a prefix
argument implies the value @code{full} for @var{justify}.

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@deffn Command fill-paragraph &optional justify region
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This command fills the paragraph at or after point.  If
@var{justify} is non-@code{nil}, each line is justified as well.
It uses the ordinary paragraph motion commands to find paragraph
boundaries.  @xref{Paragraphs,,, emacs, The GNU Emacs Manual}.
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When @var{region} is non-@code{nil}, then if Transient Mark mode is
enabled and the mark is active, this command calls @code{fill-region}
to fill all the paragraphs in the region, instead of filling only the
current paragraph.  When this command is called interactively,
@var{region} is @code{t}.
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@end deffn

@deffn Command fill-region start end &optional justify nosqueeze to-eop
This command fills each of the paragraphs in the region from @var{start}
to @var{end}.  It justifies as well if @var{justify} is
non-@code{nil}.

If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
other than line breaks untouched.  If @var{to-eop} is non-@code{nil},
that means to keep filling to the end of the paragraph---or the next hard
newline, if @code{use-hard-newlines} is enabled (see below).

The variable @code{paragraph-separate} controls how to distinguish
paragraphs.  @xref{Standard Regexps}.
@end deffn

@deffn Command fill-individual-paragraphs start end &optional justify citation-regexp
This command fills each paragraph in the region according to its
individual fill prefix.  Thus, if the lines of a paragraph were indented
with spaces, the filled paragraph will remain indented in the same
fashion.

The first two arguments, @var{start} and @var{end}, are the beginning
and end of the region to be filled.  The third and fourth arguments,
@var{justify} and @var{citation-regexp}, are optional.  If
@var{justify} is non-@code{nil}, the paragraphs are justified as
well as filled.  If @var{citation-regexp} is non-@code{nil}, it means the
function is operating on a mail message and therefore should not fill
the header lines.  If @var{citation-regexp} is a string, it is used as
a regular expression; if it matches the beginning of a line, that line
is treated as a citation marker.

Ordinarily, @code{fill-individual-paragraphs} regards each change in
indentation as starting a new paragraph.  If
@code{fill-individual-varying-indent} is non-@code{nil}, then only
separator lines separate paragraphs.  That mode can handle indented
paragraphs with additional indentation on the first line.
@end deffn

@defopt fill-individual-varying-indent
This variable alters the action of @code{fill-individual-paragraphs} as
described above.
@end defopt

@deffn Command fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after
This command considers a region of text as a single paragraph and fills
it.  If the region was made up of many paragraphs, the blank lines
between paragraphs are removed.  This function justifies as well as
filling when @var{justify} is non-@code{nil}.

If @var{nosqueeze} is non-@code{nil}, that means to leave whitespace
other than line breaks untouched.  If @var{squeeze-after} is
non-@code{nil}, it specifies a position in the region, and means don't
canonicalize spaces before that position.

In Adaptive Fill mode, this command calls @code{fill-context-prefix} to
choose a fill prefix by default.  @xref{Adaptive Fill}.
@end deffn

@deffn Command justify-current-line &optional how eop nosqueeze
This command inserts spaces between the words of the current line so
that the line ends exactly at @code{fill-column}.  It returns
@code{nil}.

The argument @var{how}, if non-@code{nil} specifies explicitly the style
of justification.  It can be @code{left}, @code{right}, @code{full},
@code{center}, or @code{none}.  If it is @code{t}, that means to do
follow specified justification style (see @code{current-justification},
below).  @code{nil} means to do full justification.

If @var{eop} is non-@code{nil}, that means do only left-justification
if @code{current-justification} specifies full justification.  This is
used for the last line of a paragraph; even if the paragraph as a
whole is fully justified, the last line should not be.

If @var{nosqueeze} is non-@code{nil}, that means do not change interior
whitespace.
@end deffn

@defopt default-justification
This variable's value specifies the style of justification to use for
text that doesn't specify a style with a text property.  The possible
values are @code{left}, @code{right}, @code{full}, @code{center}, or
@code{none}.  The default value is @code{left}.
@end defopt

@defun current-justification
This function returns the proper justification style to use for filling
the text around point.

This returns the value of the @code{justification} text property at
point, or the variable @var{default-justification} if there is no such
text property.  However, it returns @code{nil} rather than @code{none}
to mean ``don't justify''.
@end defun

@defopt sentence-end-double-space
@anchor{Definition of sentence-end-double-space}
If this variable is non-@code{nil}, a period followed by just one space
does not count as the end of a sentence, and the filling functions
avoid breaking the line at such a place.
@end defopt

@defopt sentence-end-without-period
If this variable is non-@code{nil}, a sentence can end without a
period.  This is used for languages like Thai, where sentences end
with a double space but without a period.
@end defopt

@defopt sentence-end-without-space
If this variable is non-@code{nil}, it should be a string of
characters that can end a sentence without following spaces.
@end defopt

@defvar fill-paragraph-function
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This variable provides a way to override the filling of paragraphs.
If its value is non-@code{nil}, @code{fill-paragraph} calls this
function to do the work.  If the function returns a non-@code{nil}
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value, @code{fill-paragraph} assumes the job is done, and immediately
returns that value.

The usual use of this feature is to fill comments in programming
language modes.  If the function needs to fill a paragraph in the usual
way, it can do so as follows:

@example
(let ((fill-paragraph-function nil))
  (fill-paragraph arg))
@end example
@end defvar

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@defvar fill-forward-paragraph-function
This variable provides a way to override how the filling functions,
such as @code{fill-region} and @code{fill-paragraph}, move forward to
the next paragraph.  Its value should be a function, which is called
with a single argument @var{n}, the number of paragraphs to move, and
should return the difference between @var{n} and the number of
paragraphs actually moved.  The default value of this variable is
@code{forward-paragraph}.  @xref{Paragraphs,,, emacs, The GNU Emacs
Manual}.
@end defvar

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@defvar use-hard-newlines
If this variable is non-@code{nil}, the filling functions do not delete
newlines that have the @code{hard} text property.  These ``hard
newlines'' act as paragraph separators.
@end defvar

@node Margins
@section Margins for Filling

@defopt fill-prefix
This buffer-local variable, if non-@code{nil}, specifies a string of
text that appears at the beginning of normal text lines and should be
disregarded when filling them.  Any line that fails to start with the
fill prefix is considered the start of a paragraph; so is any line
that starts with the fill prefix followed by additional whitespace.
Lines that start with the fill prefix but no additional whitespace are
ordinary text lines that can be filled together.  The resulting filled
lines also start with the fill prefix.

The fill prefix follows the left margin whitespace, if any.
@end defopt

@defopt fill-column
This buffer-local variable specifies the maximum width of filled lines.
Its value should be an integer, which is a number of columns.  All the
filling, justification, and centering commands are affected by this
variable, including Auto Fill mode (@pxref{Auto Filling}).

As a practical matter, if you are writing text for other people to
read, you should set @code{fill-column} to no more than 70.  Otherwise
the line will be too long for people to read comfortably, and this can
make the text seem clumsy.

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The default value for @code{fill-column} is 70.
@end defopt
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@deffn Command set-left-margin from to margin
This sets the @code{left-margin} property on the text from @var{from} to
@var{to} to the value @var{margin}.  If Auto Fill mode is enabled, this
command also refills the region to fit the new margin.
@end deffn

@deffn Command set-right-margin from to margin
This sets the @code{right-margin} property on the text from @var{from}
to @var{to} to the value @var{margin}.  If Auto Fill mode is enabled,
this command also refills the region to fit the new margin.
@end deffn

@defun current-left-margin
This function returns the proper left margin value to use for filling
the text around point.  The value is the sum of the @code{left-margin}
property of the character at the start of the current line (or zero if
none), and the value of the variable @code{left-margin}.
@end defun

@defun current-fill-column
This function returns the proper fill column value to use for filling
the text around point.  The value is the value of the @code{fill-column}
variable, minus the value of the @code{right-margin} property of the
character after point.
@end defun

@deffn Command move-to-left-margin &optional n force
This function moves point to the left margin of the current line.  The
column moved to is determined by calling the function
@code{current-left-margin}.  If the argument @var{n} is non-@code{nil},
@code{move-to-left-margin} moves forward @var{n}@minus{}1 lines first.

If @var{force} is non-@code{nil}, that says to fix the line's
indentation if that doesn't match the left margin value.
@end deffn

@defun delete-to-left-margin &optional from to
This function removes left margin indentation from the text between
@var{from} and @var{to}.  The amount of indentation to delete is
determined by calling @code{current-left-margin}.  In no case does this
function delete non-whitespace.  If @var{from} and @var{to} are omitted,
they default to the whole buffer.
@end defun

@defun indent-to-left-margin
This function adjusts the indentation at the beginning of the current
line to the value specified by the variable @code{left-margin}.  (That
may involve either inserting or deleting whitespace.)  This function
is value of @code{indent-line-function} in Paragraph-Indent Text mode.
@end defun

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@defopt left-margin
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This variable specifies the base left margin column.  In Fundamental
mode, @kbd{C-j} indents to this column.  This variable automatically
becomes buffer-local when set in any fashion.
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@end defopt
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@defopt fill-nobreak-predicate
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This variable gives major modes a way to specify not to break a line
at certain places.  Its value should be a list of functions.  Whenever
filling considers breaking the line at a certain place in the buffer,
it calls each of these functions with no arguments and with point
located at that place.  If any of the functions returns
non-@code{nil}, then the line won't be broken there.
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@end defopt
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@node Adaptive Fill
@section Adaptive Fill Mode
@c @cindex Adaptive Fill mode  "adaptive-fill-mode" is adjacent.

  When @dfn{Adaptive Fill Mode} is enabled, Emacs determines the fill
prefix automatically from the text in each paragraph being filled
rather than using a predetermined value.  During filling, this fill
prefix gets inserted at the start of the second and subsequent lines
of the paragraph as described in @ref{Filling}, and in @ref{Auto
Filling}.

@defopt adaptive-fill-mode
Adaptive Fill mode is enabled when this variable is non-@code{nil}.
It is @code{t} by default.
@end defopt

@defun fill-context-prefix from to
This function implements the heart of Adaptive Fill mode; it chooses a
fill prefix based on the text between @var{from} and @var{to},
typically the start and end of a paragraph.  It does this by looking
at the first two lines of the paragraph, based on the variables
described below.
@c The optional argument first-line-regexp is not documented
@c because it exists for internal purposes and might be eliminated
@c in the future.

Usually, this function returns the fill prefix, a string.  However,
before doing this, the function makes a final check (not specially
mentioned in the following) that a line starting with this prefix
wouldn't look like the start of a paragraph.  Should this happen, the
function signals the anomaly by returning @code{nil} instead.

In detail, @code{fill-context-prefix} does this:

@enumerate
@item
It takes a candidate for the fill prefix from the first line---it
tries first the function in @code{adaptive-fill-function} (if any),
then the regular expression @code{adaptive-fill-regexp} (see below).
The first non-@code{nil} result of these, or the empty string if
they're both @code{nil}, becomes the first line's candidate.
@item
If the paragraph has as yet only one line, the function tests the
validity of the prefix candidate just found.  The function then
returns the candidate if it's valid, or a string of spaces otherwise.
(see the description of @code{adaptive-fill-first-line-regexp} below).
@item
When the paragraph already has two lines, the function next looks for
a prefix candidate on the second line, in just the same way it did for
the first line.  If it doesn't find one, it returns @code{nil}.
@item
The function now compares the two candidate prefixes heuristically: if
the non-whitespace characters in the line 2 candidate occur in the
same order in the line 1 candidate, the function returns the line 2
candidate.  Otherwise, it returns the largest initial substring which
is common to both candidates (which might be the empty string).
@end enumerate
@end defun

@defopt adaptive-fill-regexp
Adaptive Fill mode matches this regular expression against the text
starting after the left margin whitespace (if any) on a line; the
characters it matches are that line's candidate for the fill prefix.

The default value matches whitespace with certain punctuation
characters intermingled.
@end defopt

@defopt adaptive-fill-first-line-regexp
Used only in one-line paragraphs, this regular expression acts as an
additional check of the validity of the one available candidate fill
prefix: the candidate must match this regular expression, or match
@code{comment-start-skip}.  If it doesn't, @code{fill-context-prefix}
replaces the candidate with a string of spaces ``of the same width''
as it.

The default value of this variable is @w{@code{"\\`[ \t]*\\'"}}, which
matches only a string of whitespace.  The effect of this default is to
force the fill prefixes found in one-line paragraphs always to be pure
whitespace.
@end defopt

@defopt adaptive-fill-function
You can specify more complex ways of choosing a fill prefix
automatically by setting this variable to a function.  The function is
called with point after the left margin (if any) of a line, and it
must preserve point.  It should return either ``that line's'' fill
prefix or @code{nil}, meaning it has failed to determine a prefix.
@end defopt

@node Auto Filling
@comment  node-name,  next,  previous,  up
@section Auto Filling
@cindex filling, automatic
@cindex Auto Fill mode

  Auto Fill mode is a minor mode that fills lines automatically as text
is inserted.  This section describes the hook used by Auto Fill mode.
For a description of functions that you can call explicitly to fill and
justify existing text, see @ref{Filling}.

  Auto Fill mode also enables the functions that change the margins and
justification style to refill portions of the text.  @xref{Margins}.

@defvar auto-fill-function
The value of this buffer-local variable should be a function (of no
arguments) to be called after self-inserting a character from the table
@code{auto-fill-chars}.  It may be @code{nil}, in which case nothing
special is done in that case.

The value of @code{auto-fill-function} is @code{do-auto-fill} when
Auto-Fill mode is enabled.  That is a function whose sole purpose is to
implement the usual strategy for breaking a line.
@end defvar

@defvar normal-auto-fill-function
This variable specifies the function to use for
@code{auto-fill-function}, if and when Auto Fill is turned on.  Major
modes can set buffer-local values for this variable to alter how Auto
Fill works.
@end defvar

@defvar auto-fill-chars
A char table of characters which invoke @code{auto-fill-function} when
self-inserted---space and newline in most language environments.  They
have an entry @code{t} in the table.
@end defvar

@node Sorting
@section Sorting Text
@cindex sorting text

  The sorting functions described in this section all rearrange text in
a buffer.  This is in contrast to the function @code{sort}, which
rearranges the order of the elements of a list (@pxref{Rearrangement}).
The values returned by these functions are not meaningful.

@defun sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate
This function is the general text-sorting routine that subdivides a
buffer into records and then sorts them.  Most of the commands in this
section use this function.

To understand how @code{sort-subr} works, consider the whole accessible
portion of the buffer as being divided into disjoint pieces called
@dfn{sort records}.  The records may or may not be contiguous, but they
must not overlap.  A portion of each sort record (perhaps all of it) is
designated as the sort key.  Sorting rearranges the records in order by
their sort keys.

Usually, the records are rearranged in order of ascending sort key.
If the first argument to the @code{sort-subr} function, @var{reverse},
is non-@code{nil}, the sort records are rearranged in order of
descending sort key.

The next four arguments to @code{sort-subr} are functions that are
called to move point across a sort record.  They are called many times
from within @code{sort-subr}.

@enumerate
@item
@var{nextrecfun} is called with point at the end of a record.  This
function moves point to the start of the next record.  The first record
is assumed to start at the position of point when @code{sort-subr} is
called.  Therefore, you should usually move point to the beginning of
the buffer before calling @code{sort-subr}.

This function can indicate there are no more sort records by leaving
point at the end of the buffer.

@item
@var{endrecfun} is called with point within a record.  It moves point to
the end of the record.

@item
@var{startkeyfun} is called to move point from the start of a record to
the start of the sort key.  This argument is optional; if it is omitted,
the whole record is the sort key.  If supplied, the function should
either return a non-@code{nil} value to be used as the sort key, or
return @code{nil} to indicate that the sort key is in the buffer
starting at point.  In the latter case, @var{endkeyfun} is called to
find the end of the sort key.

@item
@var{endkeyfun} is called to move point from the start of the sort key
to the end of the sort key.  This argument is optional.  If
@var{startkeyfun} returns @code{nil} and this argument is omitted (or
@code{nil}), then the sort key extends to the end of the record.  There
is no need for @var{endkeyfun} if @var{startkeyfun} returns a
non-@code{nil} value.
@end enumerate

The argument @var{predicate} is the function to use to compare keys.
If keys are numbers, it defaults to @code{<}; otherwise it defaults to
@code{string<}.

As an example of @code{sort-subr}, here is the complete function
definition for @code{sort-lines}:

@example
@group
;; @r{Note that the first two lines of doc string}
;; @r{are effectively one line when viewed by a user.}
(defun sort-lines (reverse beg end)
  "Sort lines in region alphabetically;\
 argument means descending order.
Called from a program, there are three arguments:
@end group
@group
REVERSE (non-nil means reverse order),\
 BEG and END (region to sort).
The variable `sort-fold-case' determines\
 whether alphabetic case affects
the sort order."
@end group
@group
  (interactive "P\nr")
  (save-excursion
    (save-restriction
      (narrow-to-region beg end)
      (goto-char (point-min))
      (let ((inhibit-field-text-motion t))
        (sort-subr reverse 'forward-line 'end-of-line)))))
@end group
@end example

Here @code{forward-line} moves point to the start of the next record,
and @code{end-of-line} moves point to the end of record.  We do not pass
the arguments @var{startkeyfun} and @var{endkeyfun}, because the entire
record is used as the sort key.

The @code{sort-paragraphs} function is very much the same, except that
its @code{sort-subr} call looks like this:

@example
@group
(sort-subr reverse
           (function
             (lambda ()
               (while (and (not (eobp))
                      (looking-at paragraph-separate))
                 (forward-line 1))))
           'forward-paragraph)
@end group
@end example

Markers pointing into any sort records are left with no useful
position after @code{sort-subr} returns.
@end defun

@defopt sort-fold-case
If this variable is non-@code{nil}, @code{sort-subr} and the other
buffer sorting functions ignore case when comparing strings.
@end defopt

@deffn Command sort-regexp-fields reverse record-regexp key-regexp start end
This command sorts the region between @var{start} and @var{end}
alphabetically as specified by @var{record-regexp} and @var{key-regexp}.
If @var{reverse} is a negative integer, then sorting is in reverse
order.

Alphabetical sorting means that two sort keys are compared by
comparing the first characters of each, the second characters of each,
and so on.  If a mismatch is found, it means that the sort keys are
unequal; the sort key whose character is less at the point of first
mismatch is the lesser sort key.  The individual characters are compared
according to their numerical character codes in the Emacs character set.

The value of the @var{record-regexp} argument specifies how to divide
the buffer into sort records.  At the end of each record, a search is
done for this regular expression, and the text that matches it is taken
as the next record.  For example, the regular expression @samp{^.+$},
which matches lines with at least one character besides a newline, would
make each such line into a sort record.  @xref{Regular Expressions}, for
a description of the syntax and meaning of regular expressions.

The value of the @var{key-regexp} argument specifies what part of each
record is the sort key.  The @var{key-regexp} could match the whole
record, or only a part.  In the latter case, the rest of the record has
no effect on the sorted order of records, but it is carried along when
the record moves to its new position.

The @var{key-regexp} argument can refer to the text matched by a
subexpression of @var{record-regexp}, or it can be a regular expression
on its own.

If @var{key-regexp} is:

@table @asis
@item @samp{\@var{digit}}
then the text matched by the @var{digit}th @samp{\(...\)} parenthesis
grouping in @var{record-regexp} is the sort key.

@item @samp{\&}
then the whole record is the sort key.

@item a regular expression
then @code{sort-regexp-fields} searches for a match for the regular
expression within the record.  If such a match is found, it is the sort
key.  If there is no match for @var{key-regexp} within a record then
that record is ignored, which means its position in the buffer is not
changed.  (The other records may move around it.)
@end table

For example, if you plan to sort all the lines in the region by the
first word on each line starting with the letter @samp{f}, you should
set @var{record-regexp} to @samp{^.*$} and set @var{key-regexp} to
@samp{\<f\w*\>}.  The resulting expression looks like this:

@example
@group
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
                    (region-beginning)
                    (region-end))
@end group
@end example

If you call @code{sort-regexp-fields} interactively, it prompts for
@var{record-regexp} and @var{key-regexp} in the minibuffer.
@end deffn

@deffn Command sort-lines reverse start end
This command alphabetically sorts lines in the region between
@var{start} and @var{end}.  If @var{reverse} is non-@code{nil}, the sort
is in reverse order.
@end deffn

@deffn Command sort-paragraphs reverse start end
This command alphabetically sorts paragraphs in the region between
@var{start} and @var{end}.  If @var{reverse} is non-@code{nil}, the sort
is in reverse order.
@end deffn

@deffn Command sort-pages reverse start end
This command alphabetically sorts pages in the region between
@var{start} and @var{end}.  If @var{reverse} is non-@code{nil}, the sort
is in reverse order.
@end deffn

@deffn Command sort-fields field start end
This command sorts lines in the region between @var{start} and
@var{end}, comparing them alphabetically by the @var{field}th field
of each line.  Fields are separated by whitespace and numbered starting
from 1.  If @var{field} is negative, sorting is by the
@w{@minus{}@var{field}th} field from the end of the line.  This command
is useful for sorting tables.
@end deffn

@deffn Command sort-numeric-fields field start end
This command sorts lines in the region between @var{start} and
@var{end}, comparing them numerically by the @var{field}th field of
each line.  Fields are separated by whitespace and numbered starting
from 1.  The specified field must contain a number in each line of the
region.  Numbers starting with 0 are treated as octal, and numbers
starting with @samp{0x} are treated as hexadecimal.

If @var{field} is negative, sorting is by the
@w{@minus{}@var{field}th} field from the end of the line.  This
command is useful for sorting tables.
@end deffn

@defopt sort-numeric-base
This variable specifies the default radix for
@code{sort-numeric-fields} to parse numbers.
@end defopt

@deffn Command sort-columns reverse &optional beg end
This command sorts the lines in the region between @var{beg} and
@var{end}, comparing them alphabetically by a certain range of
columns.  The column positions of @var{beg} and @var{end} bound the
range of columns to sort on.

If @var{reverse} is non-@code{nil}, the sort is in reverse order.

One unusual thing about this command is that the entire line
containing position @var{beg}, and the entire line containing position
@var{end}, are included in the region sorted.

Note that @code{sort-columns} rejects text that contains tabs, because
tabs could be split across the specified columns.  Use @kbd{M-x
untabify} to convert tabs to spaces before sorting.

When possible, this command actually works by calling the @code{sort}
utility program.
@end deffn

@node Columns
@comment  node-name,  next,  previous,  up
@section Counting Columns
@cindex columns
@cindex counting columns
@cindex horizontal position

  The column functions convert between a character position (counting
characters from the beginning of the buffer) and a column position
(counting screen characters from the beginning of a line).

  These functions count each character according to the number of
columns it occupies on the screen.  This means control characters count
as occupying 2 or 4 columns, depending upon the value of
@code{ctl-arrow}, and tabs count as occupying a number of columns that
depends on the value of @code{tab-width} and on the column where the tab
begins.  @xref{Usual Display}.

  Column number computations ignore the width of the window and the
amount of horizontal scrolling.  Consequently, a column value can be
arbitrarily high.  The first (or leftmost) column is numbered 0.  They
also ignore overlays and text properties, aside from invisibility.

@defun current-column
This function returns the horizontal position of point, measured in
columns, counting from 0 at the left margin.  The column position is the
sum of the widths of all the displayed representations of the characters
between the start of the current line and point.

For an example of using @code{current-column}, see the description of
@code{count-lines} in @ref{Text Lines}.
@end defun

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@deffn Command move-to-column column &optional force
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This function moves point to @var{column} in the current line.  The
calculation of @var{column} takes into account the widths of the
displayed representations of the characters between the start of the
line and point.

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When called interactively, @var{column} is the value of prefix numeric
argument.  If @var{column} is not an integer, an error is signaled.

If column @var{column} is beyond the end of the line, point moves to
the end of the line.  If @var{column} is negative, point moves to the
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beginning of the line.

If it is impossible to move to column @var{column} because that is in
the middle of a multicolumn character such as a tab, point moves to the
end of that character.  However, if @var{force} is non-@code{nil}, and
@var{column} is in the middle of a tab, then @code{move-to-column}
converts the tab into spaces so that it can move precisely to column
@var{column}.  Other multicolumn characters can cause anomalies despite
@var{force}, since there is no way to split them.

The argument @var{force} also has an effect if the line isn't long
enough to reach column @var{column}; if it is @code{t}, that means to
add whitespace at the end of the line to reach that column.

The return value is the column number actually moved to.
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@end deffn
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