@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. @c See the file elisp.texi for copying conditions. @setfilename ../info/text @node Text, Searching and Matching, 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 in the vicinity of 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). @menu * Near Point:: Examining text in the vicinity of point. * Buffer Contents:: Examining text in a general fashion. * Comparing Text:: Comparing substrings of buffers. * Insertion:: Adding new text to a buffer. * Commands for Insertion:: User-level commands to insert text. * Deletion:: Removing text from a buffer. * User-Level Deletion:: User-level commands to delete text. * The Kill Ring:: Where removed text sometimes is saved for later use. * Undo:: Undoing changes to the text of a buffer. * Maintaining Undo:: How to enable and disable undo information. How to control how much information is kept. * Filling:: Functions for explicit filling. * Margins:: How to specify margins for filling commands. * Auto Filling:: How auto-fill mode is implemented to break lines. * Sorting:: Functions for sorting parts of the buffer. * Columns:: Computing horizontal positions, and using them. * Indentation:: Functions to insert or adjust indentation. * Case Changes:: Case conversion of parts of the buffer. * Text Properties:: Assigning Lisp property lists to text characters. * Substitution:: Replacing a given character wherever it appears. * Transposition:: Swapping two portions of a buffer. * Registers:: How registers are implemented. Accessing the text or position stored in a register. * Change Hooks:: Supplying functions to be run when text is changed. @end menu @node Near Point @section Examining 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}. @defun char-after 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}. In the following example, assume that the first character in the buffer is @samp{@@}: @example @group (char-to-string (char-after 1)) @result{} "@@" @end group @end example @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 terminal 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 (char-to-string (preceding-char)) @result{} "a" (char-to-string (following-char)) @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 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 two 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 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. It is not necessary for @var{start} to be less than @var{end}; the arguments can be given in either order. But most often the smaller argument is written first. 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. @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 " @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}. Here's an example of using this function to get a word to look up in an alist: @example (setq flammable (assoc (buffer-substring start end) '(("wood" . t) ("paper" . t) ("steel" . nil) ("asbestos" . nil)))) @end example If this were written using @code{buffer-substring} instead, it would not work reliably; any text properties that happened to be in the word copied from the buffer would make the comparisons fail. @end defun @defun buffer-string This function returns the contents of the accessible portion of the current buffer as a string. This is the portion between @code{(point-min)} and @code{(point-max)} (@pxref{Narrowing}). @example @group ---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-string) @result{} "This is the contents of buffer foo " @end group @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 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-substring nil 6 11 nil 16 21) @result{} 2 @end example @end defun @node Insertion @section Inserting Text @cindex insertion of text @cindex text 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. Insertion relocates markers that point 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 normally doesn't relocate the marker, so that it points to the beginning of the inserted text; however, certain special functions such as @code{insert-before-markers} relocate such markers to point after the inserted text. @cindex insertion before point @cindex before point, insertion 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}. Insertion functions signal an error if the current buffer is read-only. These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text. @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. @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} must be a number, and @var{character} must be a character. The value is @code{nil}. @c It's unfortunate that count comes second. Not like make-string, etc. 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 from @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 @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 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. This command calls @code{auto-fill-function} whenever that is non-@code{nil} and the character inserted is a space or a newline (@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}.) This is also responsible for calling @code{blink-paren-function} when the inserted character has close parenthesis syntax (@pxref{Blinking}). @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 @deffn Command split-line This command splits the current line, moving the portion of the line after point down vertically so that it is on the next line directly below where it was before. Whitespace is inserted as needed at the beginning of the lower line, using the @code{indent-to} function. @code{split-line} returns the position of point. Programs hardly ever use this function. @end deffn @defvar overwrite-mode This variable controls whether overwrite mode is in effect: a non-@code{nil} value enables the mode. It is automatically made buffer-local when set in any fashion. @end defvar @node Deletion @section Deleting Text @cindex deletion 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, and all return a value of @code{nil}. @defun erase-buffer This function deletes the entire text of the current buffer, leaving it empty. If the buffer is read-only, it signals a @code{buffer-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 auto-saving of that buffer ``because it has shrunk''. However, @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 defun @deffn Command delete-region start end This command deletes the text in the current buffer in the region defined by @var{start} and @var{end}. The value is @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 @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 delete 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 @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 @cindex deleting whitespace This function deletes all spaces and tabs around point. It returns @code{nil}. 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 value is @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 @defun fixup-whitespace This function replaces all the white space 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 defun @deffn Command just-one-space @comment !!SourceFile simple.el This command replaces any spaces and tabs around point with a single space. 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 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 entities ``killed''. This is in sharp contrast to ordinary life, in 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. * Yank Commands:: Commands that access the kill ring. * Low-Level Kill Ring:: Functions and variables for kill ring access. * 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 entry in the kill ring, 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 different element as the ``front.'' But this virtual rotation doesn't 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 uses the @code{last-command} variable to determine whether the previous command was a kill command, and if so appends the killed text to the most recent entry. @deffn Command kill-region start end 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. @c Emacs 19 feature If the buffer 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 all the kill commands to copy text into the kill ring from a read-only buffer. @end deffn @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}. It also indicates the extent of the text copied by moving the cursor momentarily, or by displaying a message in the echo area. 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. Don't call @code{copy-region-as-kill} in Lisp programs unless you aim to support Emacs 18. For Emacs 19, it is better to use @code{kill-new} or @code{kill-append} instead. @xref{Low-Level Kill Ring}. @end deffn @node Yank Commands @comment node-name, next, previous, up @subsection Functions for Yanking @dfn{Yanking} means reinserting an entry of previously killed text from the kill ring. The text properties are copied too. @deffn Command yank &optional arg @cindex inserting killed text This command inserts before point the text in the first entry in the kill ring. It positions the mark at the beginning of that text, and point at the end. If @var{arg} is a 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 puts the mark after it. 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. @code{yank} does not alter the contents of the kill ring or rotate it. It returns @code{nil}. @end deffn @deffn Command yank-pop 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. 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 value is always @code{nil}. @end deffn @node Low-Level Kill Ring @subsection Low-Level Kill Ring These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs. They take care of interaction with X Window selections. They do not exist in Emacs version 18. @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. @end defun @defun kill-new string This function puts the text @var{string} into the kill ring as a new entry at the front of the ring. It discards the oldest entry if appropriate. It also invokes the value of @code{interprogram-cut-function} (see below). @end defun @defun kill-append string before-p This function appends the text @var{string} to the first entry in the kill ring. 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} (see below). @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 ``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 @code{nil}, then the first element of @code{kill-ring} is used. The normal use of this hook is to get the X server's primary selection as the most recent kill, even if the selection belongs to another X client. @xref{X Selections}. @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 @code{nil} or a function of one argument. If the value is a function, @code{kill-new} and @code{kill-append} call it with the new first element of the kill ring as an argument. The normal use of this hook is to set the X server's primary selection to the newly killed text. @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 | | | ___ ___ ---> ___ ___ ___ ___ --> |___|___|------> |___|___|--> |___|___|--> 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 30. @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.) 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 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{integer} This kind of element records a previous value of point. Ordinary cursor motion does not get any sort of undo record, but deletion commands 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})}. @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 @var{position} This element indicates where point was at an earlier time. Undoing this element sets point to @var{position}. Deletion normally creates an element of this kind as well as a reinsertion element. @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}. The editor command loop automatically creates an undo boundary before each key sequence is executed. Thus, each undo normally undoes the effects of one command. Self-inserting input characters are an exception. The command loop makes a boundary for the first such character; the next 19 consecutive self-inserting input characters do not make boundaries, and then the 20th does, and so on as long as self-inserting characters continue. All buffer modifications add a boundary whenever the previous undoable change was made in some other buffer. This way, a command that modifies several buffers makes a boundary in each buffer it 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 @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}. You could write this function in Lisp, but it is convenient to have it in C. @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. @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 @defun buffer-disable-undo &optional buffer @defunx buffer-flush-undo &optional buffer @cindex disable undo This function discards the undo list of @var{buffer}, 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} is already disabled, this function has no effect. This function returns @code{nil}. It cannot be called interactively. The name @code{buffer-flush-undo} is not considered obsolete, but the preferred name @code{buffer-disable-undo} is new as of Emacs versions 19. @end defun 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.) Two variables control the range of acceptable sizes: @code{undo-limit} and @code{undo-strong-limit}. @defvar 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 defvar @defvar 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 never discarded no matter how big it is. @end defvar @node Filling @comment node-name, next, previous, up @section Filling @cindex filling, explicit @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). When you call the filling functions interactively, using a prefix argument implies the value @code{full} for @var{justify}. @deffn Command fill-paragraph justify @cindex filling a paragraph 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 Emacs Manual}. @end deffn @deffn Command fill-region start end &optional justify 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}. The variable @code{paragraph-separate} controls how to distinguish paragraphs. @xref{Standard Regexps}. @end deffn @deffn Command fill-individual-paragraphs start end &optional justify mail-flag 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{mail-flag}, are optional. If @var{justify} is non-@code{nil}, the paragraphs are justified as well as filled. If @var{mail-flag} is non-@code{nil}, it means the function is operating on a mail message and therefore should not fill the header lines. 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 This command considers a region of text as a 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}. In an interactive call, any prefix argument requests justification. In Adaptive Fill mode, which is enabled by default, @code{fill-region-as-paragraph} on an indented paragraph when there is no fill prefix uses the indentation of the second line of the paragraph as the fill prefix. @end deffn @deffn Command justify-current-line 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 left-justification when @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. @end defun @defvar fill-paragraph-function This variable provides a way for major modes to override the filling of paragraphs. If the value is non-@code{nil}, @code{fill-paragraph} calls this function to do the work. If the function returns a non-@code{nil} 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 @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 variable 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. @end defopt @defvar default-fill-column The value of this variable is the default value for @code{fill-column} in buffers that do not override it. This is the same as @code{(default-value 'fill-column)}. The default value for @code{default-fill-column} is 70. @end defvar @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 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. @end defun @defun indent-to-left-margin This is the default @code{indent-line-function}, used in Fundamental mode, Text mode, etc. Its effect is to adjust the indentation at the beginning of the current line to the value specified by the variable @code{left-margin}. This may involve either inserting or deleting whitespace. @end defun @defvar left-margin This variable specifies the base left margin column. In Fundamental mode, @key{LFD} indents to this column. This variable automatically becomes buffer-local when set in any fashion. @end defvar @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 variable should be a function (of no arguments) to be called after self-inserting a space or a newline. 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. @quotation In older Emacs versions, this variable was named @code{auto-fill-hook}, but since it is not called with the standard convention for hooks, it was renamed to @code{auto-fill-function} in version 19. @end quotation @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 This function is the general text-sorting routine that divides a buffer into records and 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; they may 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 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. Called from a program, there are three arguments: @end group @group REVERSE (non-nil means reverse order), and BEG and END (the region to sort)." (interactive "P\nr") (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (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 () (skip-chars-forward "\n \t\f"))) 'forward-paragraph) @end group @end example @end defun @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 values. Since Emacs uses the @sc{ASCII} character set, the ordering in that set determines alphabetical order. @c version 19 change 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 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{^.*$} and set @var{key-regexp} to @samp{\}. The resulting expression looks like this: @example @group (sort-regexp-fields nil "^.*$" "\\" (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. The specified field must contain a number in each line of the region. 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-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} uses the @code{sort} utility program, and so cannot work properly on text containing tab characters. Use @kbd{M-x @code{untabify}} to convert tabs to spaces before sorting. @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). A character counts 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. @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 @defun move-to-column column &optional force 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. 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 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}; in that case, it says to add whitespace at the end of the line to reach that column. If @var{column} is not an integer, an error is signaled. The return value is the column number actually moved to. @end defun @node Indentation @section Indentation @cindex indentation The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin. @menu * Primitive Indent:: Functions used to count and insert indentation. * Mode-Specific Indent:: Customize indentation for different modes. * Region Indent:: Indent all the lines in a region. * Relative Indent:: Indent the current line based on previous lines. * Indent Tabs:: Adjustable, typewriter-like tab stops. * Motion by Indent:: Move to first non-blank character. @end menu @node Primitive Indent @subsection Indentation Primitives This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. @defun current-indentation @comment !!Type Primitive Function @comment !!SourceFile indent.c This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line. @end defun @deffn Command indent-to column &optional minimum @comment !!Type Primitive Function @comment !!SourceFile indent.c This function indents from point with tabs and spaces until @var{column} is reached. If @var{minimum} is specified and non-@code{nil}, then at least that many spaces are inserted even if this requires going beyond @var{column}. Otherwise the function does nothing if point is already beyond @var{column}. The value is the column at which the inserted indentation ends. The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). @xref{Sticky Properties}. @end deffn @defopt indent-tabs-mode @comment !!SourceFile indent.c If this variable is non-@code{nil}, indentation functions can insert tabs as well as spaces. Otherwise, they insert only spaces. Setting this variable automatically makes it local to the current buffer. @end defopt @node Mode-Specific Indent @subsection Indentation Controlled by Major Mode An important function of each major mode is to customize the @key{TAB} key to indent properly for the language being edited. This section describes the mechanism of the @key{TAB} key and how to control it. The functions in this section return unpredictable values. @defvar indent-line-function This variable's value is the function to be used by @key{TAB} (and various commands) to indent the current line. The command @code{indent-according-to-mode} does no more than call this function. In Lisp mode, the value is the symbol @code{lisp-indent-line}; in C mode, @code{c-indent-line}; in Fortran mode, @code{fortran-indent-line}. In Fundamental mode, Text mode, and many other modes with no standard for indentation, the value is @code{indent-to-left-margin} (which is the default value). @end defvar @deffn Command indent-according-to-mode This command calls the function in @code{indent-line-function} to indent the current line in a way appropriate for the current major mode. @end deffn @deffn Command indent-for-tab-command This command calls the function in @code{indent-line-function} to indent the current line; except that if that function is @code{indent-to-left-margin}, it calls @code{insert-tab} instead. (That is a trivial command that inserts a tab character.) @end deffn @deffn Command newline-and-indent @comment !!SourceFile simple.el This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode. It does indentation by calling the current @code{indent-line-function}. In programming language modes, this is the same thing @key{TAB} does, but in some text modes, where @key{TAB} inserts a tab, @code{newline-and-indent} indents to the column specified by @code{left-margin}. @end deffn @deffn Command reindent-then-newline-and-indent @comment !!SourceFile simple.el This command reindents the current line, inserts a newline at point, and then reindents the new line (the one following the newline just inserted). This command does indentation on both lines according to the current major mode, by calling the current value of @code{indent-line-function}. In programming language modes, this is the same thing @key{TAB} does, but in some text modes, where @key{TAB} inserts a tab, @code{reindent-then-newline-and-indent} indents to the column specified by @code{left-margin}. @end deffn @node Region Indent @subsection Indenting an Entire Region This section describes commands that indent all the lines in the region. They return unpredictable values. @deffn Command indent-region start end to-column This command indents each nonblank line starting between @var{start} (inclusive) and @var{end} (exclusive). If @var{to-column} is @code{nil}, @code{indent-region} indents each nonblank line by calling the current mode's indentation function, the value of @code{indent-line-function}. If @var{to-column} is non-@code{nil}, it should be an integer specifying the number of columns of indentation; then this function gives each line exactly that much indentation, by either adding or deleting whitespace. If there is a fill prefix, @code{indent-region} indents each line by making it start with the fill prefix. @end deffn @defvar indent-region-function The value of this variable is a function that can be used by @code{indent-region} as a short cut. You should design the function so that it will produce the same results as indenting the lines of the region one by one, but presumably faster. If the value is @code{nil}, there is no short cut, and @code{indent-region} actually works line by line. A short-cut function is useful in modes such as C mode and Lisp mode, where the @code{indent-line-function} must scan from the beginning of the function definition: applying it to each line would be quadratic in time. The short cut can update the scan information as it moves through the lines indenting them; this takes linear time. In a mode where indenting a line individually is fast, there is no need for a short cut. @code{indent-region} with a non-@code{nil} argument @var{to-column} has a different meaning and does not use this variable. @end defvar @deffn Command indent-rigidly start end count @comment !!SourceFile indent.el This command indents all lines starting between @var{start} (inclusive) and @var{end} (exclusive) sideways by @var{count} columns. This ``preserves the shape'' of the affected region, moving it as a rigid unit. Consequently, this command is useful not only for indenting regions of unindented text, but also for indenting regions of formatted code. For example, if @var{count} is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified. In Mail mode, @kbd{C-c C-y} (@code{mail-yank-original}) uses @code{indent-rigidly} to indent the text copied from the message being replied to. @end deffn @defun indent-code-rigidly start end columns &optional nochange-regexp This is like @code{indent-rigidly}, except that it doesn't alter lines that start within strings or comments. In addition, it doesn't alter a line if @var{nochange-regexp} matches at the beginning of the line (if @var{nochange-regexp} is non-@code{nil}). @end defun @node Relative Indent @subsection Indentation Relative to Previous Lines This section describes two commands that indent the current line based on the contents of previous lines. @deffn Command indent-relative &optional unindented-ok This command inserts whitespace at point, extending to the same column as the next @dfn{indent point} of the previous nonblank line. An indent point is a non-whitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace. If the previous nonblank line has no next indent point (i.e., none at a great enough column position), @code{indent-relative} either does nothing (if @var{unindented-ok} is non-@code{nil}) or calls @code{tab-to-tab-stop}. Thus, if point is underneath and to the right of the last column of a short line of text, this command ordinarily moves point to the next tab stop by inserting whitespace. The return value of @code{indent-relative} is unpredictable. In the following example, point is at the beginning of the second line: @example @group This line is indented twelve spaces. @point{}The quick brown fox jumped. @end group @end example @noindent Evaluation of the expression @code{(indent-relative nil)} produces the following: @example @group This line is indented twelve spaces. @point{}The quick brown fox jumped. @end group @end example In this example, point is between the @samp{m} and @samp{p} of @samp{jumped}: @example @group This line is indented twelve spaces. The quick brown fox jum@point{}ped. @end group @end example @noindent Evaluation of the expression @code{(indent-relative nil)} produces the following: @example @group This line is indented twelve spaces. The quick brown fox jum @point{}ped. @end group @end example @end deffn @deffn Command indent-relative-maybe @comment !!SourceFile indent.el This command indents the current line like the previous nonblank line. It calls @code{indent-relative} with @code{t} as the @var{unindented-ok} argument. The return value is unpredictable. If the previous nonblank line has no indent points beyond the current column, this command does nothing. @end deffn @node Indent Tabs @comment node-name, next, previous, up @subsection Adjustable ``Tab Stops'' @cindex tabs stops for indentation This section explains the mechanism for user-specified ``tab stops'' and the mechanisms that use and set them. The name ``tab stops'' is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (@pxref{Usual Display}). Note that the @key{TAB} character as input uses this tab stop feature only in a few major modes, such as Text mode. @deffn Command tab-to-tab-stop This command inserts spaces or tabs up to the next tab stop column defined by @code{tab-stop-list}. It searches the list for an element greater than the current column number, and uses that element as the column to indent to. It does nothing if no such element is found. @end deffn @defopt tab-stop-list This variable is the list of tab stop columns used by @code{tab-to-tab-stops}. The elements should be integers in increasing order. The tab stop columns need not be evenly spaced. Use @kbd{M-x edit-tab-stops} to edit the location of tab stops interactively. @end defopt @node Motion by Indent @subsection Indentation-Based Motion Commands These commands, primarily for interactive use, act based on the indentation in the text. @deffn Command back-to-indentation @comment !!SourceFile simple.el This command moves point to the first non-whitespace character in the current line (which is the line in which point is located). It returns @code{nil}. @end deffn @deffn Command backward-to-indentation arg @comment !!SourceFile simple.el This command moves point backward @var{arg} lines and then to the first nonblank character on that line. It returns @code{nil}. @end deffn @deffn Command forward-to-indentation arg @comment !!SourceFile simple.el This command moves point forward @var{arg} lines and then to the first nonblank character on that line. It returns @code{nil}. @end deffn @node Case Changes @comment node-name, next, previous, up @section Case Changes @cindex case changes The case change commands described here work on text in the current buffer. @xref{Character Case}, for case conversion commands that work on strings and characters. @xref{Case Table}, for how to customize which characters are upper or lower case and how to convert them. @deffn Command capitalize-region start end This function capitalizes all words in the region defined by @var{start} and @var{end}. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. The function returns @code{nil}. If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word. When @code{capitalize-region} is called interactively, @var{start} and @var{end} are point and the mark, with the smallest first. @example @group ---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- @end group @group (capitalize-region 1 44) @result{} nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ---------- @end group @end example @end deffn @deffn Command downcase-region start end This function converts all of the letters in the region defined by @var{start} and @var{end} to lower case. The function returns @code{nil}. When @code{downcase-region} is called interactively, @var{start} and @var{end} are point and the mark, with the smallest first. @end deffn @deffn Command upcase-region start end This function converts all of the letters in the region defined by @var{start} and @var{end} to upper case. The function returns @code{nil}. When @code{upcase-region} is called interactively, @var{start} and @var{end} are point and the mark, with the smallest first. @end deffn @deffn Command capitalize-word count This function capitalizes @var{count} words after point, moving point over as it does. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. If @var{count} is negative, the function capitalizes the @minus{}@var{count} previous words but does not move point. The value is @code{nil}. If point is in the middle of a word, the part of the word before point is ignored when moving forward. The rest is treated as an entire word. When @code{capitalize-word} is called interactively, @var{count} is set to the numeric prefix argument. @end deffn @deffn Command downcase-word count This function converts the @var{count} words after point to all lower case, moving point over as it does. If @var{count} is negative, it converts the @minus{}@var{count} previous words but does not move point. The value is @code{nil}. When @code{downcase-word} is called interactively, @var{count} is set to the numeric prefix argument. @end deffn @deffn Command upcase-word count This function converts the @var{count} words after point to all upper case, moving point over as it does. If @var{count} is negative, it converts the @minus{}@var{count} previous words but does not move point. The value is @code{nil}. When @code{upcase-word} is called interactively, @var{count} is set to the numeric prefix argument. @end deffn @node Text Properties @section Text Properties @cindex text properties @cindex attributes of text @cindex properties of text Each character position in a buffer or a string can have a @dfn{text property list}, much like the property list of a symbol (@pxref{Property Lists}). The properties belong to a particular character at a particular place, such as, the letter @samp{T} at the beginning of this sentence or the first @samp{o} in @samp{foo}---if the same character occurs in two different places, the two occurrences generally have different properties. Each property has a name and a value. Both of these can be any Lisp object, but the name is normally a symbol. The usual way to access the property list is to specify a name and ask what value corresponds to it. If a character has a @code{category} property, we call it the @dfn{category} of the character. It should be a symbol. The properties of the symbol serve as defaults for the properties of the character. Copying text between strings and buffers preserves the properties along with the characters; this includes such diverse functions as @code{substring}, @code{insert}, and @code{buffer-substring}. @menu * Examining Properties:: Looking at the properties of one character. * Changing Properties:: Setting the properties of a range of text. * Property Search:: Searching for where a property changes value. * Special Properties:: Particular properties with special meanings. * Format Properties:: Properties for representing formatting of text. * Sticky Properties:: How inserted text gets properties from neighboring text. * Saving Properties:: Saving text properties in files, and reading them back. * Lazy Properties:: Computing text properties in a lazy fashion only when text is examined. * Not Intervals:: Why text properties do not use Lisp-visible text intervals. @end menu @node Examining Properties @subsection Examining Text Properties The simplest way to examine text properties is to ask for the value of a particular property of a particular character. For that, use @code{get-text-property}. Use @code{text-properties-at} to get the entire property list of a character. @xref{Property Search}, for functions to examine the properties of a number of characters at once. These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1. @defun get-text-property pos prop &optional object This function returns the value of the @var{prop} property of the character after position @var{pos} in @var{object} (a buffer or string). The argument @var{object} is optional and defaults to the current buffer. If there is no @var{prop} property strictly speaking, but the character has a category that is a symbol, then @code{get-text-property} returns the @var{prop} property of that symbol. @end defun @defun get-char-property pos prop &optional object This function is like @code{get-text-property}, except that it checks overlays first and then text properties. @xref{Overlays}. The argument @var{object} may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If @var{object} is a buffer, then all overlays in that buffer are considered, as well as text properties. If @var{object} is a string, only text properties are considered, since strings never have overlays. @end defun @defun text-properties-at position &optional object This function returns the entire property list of the character at @var{position} in the string or buffer @var{object}. If @var{object} is @code{nil}, it defaults to the current buffer. @end defun @defvar default-text-properties This variable holds a property list giving default values for text properties. Whenever a character does not specify a value for a property, neither directly nor through a category symbol, the value stored in this list is used instead. Here is an example: @example (setq default-text-properties '(foo 69)) ;; @r{Make sure character 1 has no properties of its own.} (set-text-properties 1 2 nil) ;; @r{What we get, when we ask, is the default value.} (get-text-property 1 'foo) @result{} 69 @end example @end defvar @node Changing Properties @subsection Changing Text Properties The primitives for changing properties apply to a specified range of text. The function @code{set-text-properties} (see end of section) sets the entire property list of the text in that range; more often, it is useful to add, change, or delete just certain properties specified by name. Since text properties are considered part of the buffer's contents, and can affect how the buffer looks on the screen, any change in the text properties is considered a buffer modification. Buffer text property changes are undoable (@pxref{Undo}). @defun put-text-property start end prop value &optional object This function sets the @var{prop} property to @var{value} for the text between @var{start} and @var{end} in the string or buffer @var{object}. If @var{object} is @code{nil}, it defaults to the current buffer. @end defun @defun add-text-properties start end props &optional object This function modifies the text properties for the text between @var{start} and @var{end} in the string or buffer @var{object}. If @var{object} is @code{nil}, it defaults to the current buffer. The argument @var{props} specifies which properties to change. It should have the form of a property list (@pxref{Property Lists}): a list whose elements include the property names followed alternately by the corresponding values. The return value is @code{t} if the function actually changed some property's value; @code{nil} otherwise (if @var{props} is @code{nil} or its values agree with those in the text). For example, here is how to set the @code{comment} and @code{face} properties of a range of text: @example (add-text-properties @var{start} @var{end} '(comment t face highlight)) @end example @end defun @defun remove-text-properties start end props &optional object This function deletes specified text properties from the text between @var{start} and @var{end} in the string or buffer @var{object}. If @var{object} is @code{nil}, it defaults to the current buffer. The argument @var{props} specifies which properties to delete. It should have the form of a property list (@pxref{Property Lists}): a list whose elements are property names alternating with corresponding values. But only the names matter---the values that accompany them are ignored. For example, here's how to remove the @code{face} property. @example (remove-text-properties @var{start} @var{end} '(face nil)) @end example The return value is @code{t} if the function actually changed some property's value; @code{nil} otherwise (if @var{props} is @code{nil} or if no character in the specified text had any of those properties). @end defun @defun set-text-properties start end props &optional object This function completely replaces the text property list for the text between @var{start} and @var{end} in the string or buffer @var{object}. If @var{object} is @code{nil}, it defaults to the current buffer. The argument @var{props} is the new property list. It should be a list whose elements are property names alternating with corresponding values. After @code{set-text-properties} returns, all the characters in the specified range have identical properties. If @var{props} is @code{nil}, the effect is to get rid of all properties from the specified range of text. Here's an example: @example (set-text-properties @var{start} @var{end} nil) @end example @end defun See also the function @code{buffer-substring-no-properties} (@pxref{Buffer Contents}) which copies text from the buffer but does not copy its properties. @node Property Search @subsection Property Search Functions In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value. Here are functions you can use to do this. They use @code{eq} for comparing property values. In all cases, @var{object} defaults to the current buffer. For high performance, it's very important to use the @var{limit} argument to these functions, especially the ones that search for a single property---otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change. Remember that a position is always between two characters; the position returned by these functions is between two characters with different properties. @defun next-property-change pos &optional object limit The function scans the text forward from position @var{pos} in the string or buffer @var{object} till it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond @var{pos} whose properties are not identical to those of the character just after @var{pos}. If @var{limit} is non-@code{nil}, then the scan ends at position @var{limit}. If there is no property change before that point, @code{next-property-change} returns @var{limit}. The value is @code{nil} if the properties remain unchanged all the way to the end of @var{object} and @var{limit} is @code{nil}. If the value is non-@code{nil}, it is a position greater than or equal to @var{pos}. The value equals @var{pos} only when @var{limit} equals @var{pos}. Here is an example of how to scan the buffer by chunks of text within which all properties are constant: @smallexample (while (not (eobp)) (let ((plist (text-properties-at (point))) (next-change (or (next-property-change (point) (current-buffer)) (point-max)))) @r{Process text from point to @var{next-change}@dots{}} (goto-char next-change))) @end smallexample @end defun @defun next-single-property-change pos prop &optional object limit The function scans the text forward from position @var{pos} in the string or buffer @var{object} till it finds a change in the @var{prop} property, then returns the position of the change. In other words, it returns the position of the first character beyond @var{pos} whose @var{prop} property differs from that of the character just after @var{pos}. If @var{limit} is non-@code{nil}, then the scan ends at position @var{limit}. If there is no property change before that point, @code{next-single-property-change} returns @var{limit}. The value is @code{nil} if the property remains unchanged all the way to the end of @var{object} and @var{limit} is @code{nil}. If the value is non-@code{nil}, it is a position greater than or equal to @var{pos}; it equals @var{pos} only if @var{limit} equals @var{pos}. @end defun @defun previous-property-change pos &optional object limit This is like @code{next-property-change}, but scans back from @var{pos} instead of forward. If the value is non-@code{nil}, it is a position less than or equal to @var{pos}; it equals @var{pos} only if @var{limit} equals @var{pos}. @end defun @defun previous-single-property-change pos prop &optional object limit This is like @code{next-single-property-change}, but scans back from @var{pos} instead of forward. If the value is non-@code{nil}, it is a position less than or equal to @var{pos}; it equals @var{pos} only if @var{limit} equals @var{pos}. @end defun @defun text-property-any start end prop value &optional object This function returns non-@code{nil} if at least one character between @var{start} and @var{end} has a property @var{prop} whose value is @var{value}. More precisely, it returns the position of the first such character. Otherwise, it returns @code{nil}. The optional fifth argument, @var{object}, specifies the string or buffer to scan. Positions are relative to @var{object}. The default for @var{object} is the current buffer. @end defun @defun text-property-not-all start end prop value &optional object This function returns non-@code{nil} if at least one character between @var{start} and @var{end} has a property @var{prop} whose value differs from @var{value}. More precisely, it returns the position of the first such character. Otherwise, it returns @code{nil}. The optional fifth argument, @var{object}, specifies the string or buffer to scan. Positions are relative to @var{object}. The default for @var{object} is the current buffer. @end defun @node Special Properties @subsection Properties with Special Meanings Here is a table of text property names that have special built-in meanings. The following section lists a few more special property names that are used to control filling. All other names have no standard meaning, and you can use them as you like. @table @code @cindex category of text character @kindex category @r{(text property)} @item category If a character has a @code{category} property, we call it the @dfn{category} of the character. It should be a symbol. The properties of the symbol serve as defaults for the properties of the character. @item face @cindex face codes of text @kindex face @r{(text property)} You can use the property @code{face} to control the font and color of text. Its value is a face name or a list of face names. @xref{Faces}, for more information. This feature may be temporary; in the future, we may replace it with other ways of specifying how to display text. @item mouse-face @kindex mouse-face @r{(text property)} The property @code{mouse-face} is used instead of @code{face} when the mouse is on or near the character. For this purpose, ``near'' means that all text between the character and where the mouse is have the same @code{mouse-face} property value. @item local-map @cindex keymap of character @kindex local-map @r{(text property)} You can specify a different keymap for a portion of the text by means of a @code{local-map} property. The property's value for the character after point, if non-@code{nil}, replaces the buffer's local map. @xref{Active Keymaps}. @item read-only @cindex read-only character @kindex read-only @r{(text property)} If a character has the property @code{read-only}, then modifying that character is not allowed. Any command that would do so gets an error. Insertion next to a read-only character is an error if inserting ordinary text there would inherit the @code{read-only} property due to stickiness. Thus, you can control permission to insert next to read-only text by controlling the stickiness. @xref{Sticky Properties}. Since changing properties counts as modifying the buffer, it is not possible to remove a @code{read-only} property unless you know the special trick: bind @code{inhibit-read-only} to a non-@code{nil} value and then remove the property. @xref{Read Only Buffers}. @item invisible @kindex invisible @r{(text property)} A non-@code{nil} @code{invisible} property can make a character invisible on the screen. @xref{Invisible Text}, for details. @item intangible @kindex intangible @r{(text property)} If a group of consecutive characters have equal and non-@code{nil} @code{intangible} properties, then you cannot place point between them. If you try to move point forward into the group, point actually moves to the end of the group. If you try to move point backward into the group, point actually moves to the start of the group. When the variable @code{inhibit-point-motion-hooks} is non-@code{nil}, the @code{intangible} property is ignored. @item modification-hooks @cindex change hooks for a character @cindex hooks for changing a character @kindex modification-hooks @r{(text property)} If a character has the property @code{modification-hooks}, then its value should be a list of functions; modifying that character calls all of those functions. Each function receives two arguments: the beginning and end of the part of the buffer being modified. Note that if a particular modification hook function appears on several characters being modified by a single primitive, you can't predict how many times the function will be called. @item insert-in-front-hooks @itemx insert-behind-hooks @kindex insert-in-front-hooks @r{(text property)} @kindex insert-behind-hooks @r{(text property)} The operation of inserting text in a buffer, before actually modifying the buffer, calls the functions listed in the @code{insert-in-front-hooks} property of the following character and in the @code{insert-behind-hooks} property of the preceding character. These functions receive two arguments, the beginning and end of the inserted text. See also @ref{Change Hooks}, for other hooks that are called when you change text in a buffer. @item point-entered @itemx point-left @cindex hooks for motion of point @kindex point-entered @r{(text property)} @kindex point-left @r{(text property)} The special properties @code{point-entered} and @code{point-left} record hook functions that report motion of point. Each time point moves, Emacs compares these two property values: @itemize @bullet @item the @code{point-left} property of the character after the old location, and @item the @code{point-entered} property of the character after the new location. @end itemize @noindent If these two values differ, each of them is called (if not @code{nil}) with two arguments: the old value of point, and the new one. The same comparison is made for the characters before the old and new locations. The result may be to execute two @code{point-left} functions (which may be the same function) and/or two @code{point-entered} functions (which may be the same function). In any case, all the @code{point-left} functions are called first, followed by all the @code{point-entered} functions. A primitive function may examine characters at various positions without moving point to those positions. Only an actual change in the value of point runs these hook functions. @end table @defvar inhibit-point-motion-hooks When this variable is non-@code{nil}, @code{point-left} and @code{point-entered} hooks are not run, and the @code{intangible} property has no effect. @end defvar @node Format Properties @subsection Formatted Text Properties These text properties affect the behavior of the fill commands. They are used for representing formatted text. @xref{Filling}, and @ref{Margins}. @table @code @item hard If a newline character has this property, it is a ``hard'' newline. The fill commands do not alter hard newlines and do not move words across them. However, this property takes effect only if the variable @code{use-hard-newlines} is non-@code{nil}. @item right-margin This property specifies an extra right margin for filling this part of the text. @item left-margin This property specifies an extra left margin for filling this part of the text. @item justification This property specifies the style of justification for filling this part of the text. @end table @node Sticky Properties @subsection Stickiness of Text Properties @cindex sticky text properties @cindex inheritance of text properties Self-inserting characters normally take on the same properties as the preceding character. This is called @dfn{inheritance} of properties. In a Lisp program, you can do insertion with inheritance or without, depending on your choice of insertion primitive. The ordinary text insertion functions such as @code{insert} do not inherit any properties. They insert text with precisely the properties of the string being inserted, and no others. This is correct for programs that copy text from one context to another---for example, into or out of the kill ring. To insert with inheritance, use the special primitives described in this section. Self-inserting characters inherit properties because they work using these primitives. When you do insertion with inheritance, @emph{which} properties are inherited depends on two specific properties: @code{front-sticky} and @code{rear-nonsticky}. Insertion after a character inherits those of its properties that are @dfn{rear-sticky}. Insertion before a character inherits those of its properties that are @dfn{front-sticky}. By default, a text property is rear-sticky but not front-sticky. Thus, the default is to inherit all the properties of the preceding character, and nothing from the following character. You can request different behavior by specifying the stickiness of certain properties. If a character's @code{front-sticky} property is @code{t}, then all its properties are front-sticky. If the @code{front-sticky} property is a list, then the sticky properties of the character are those whose names are in the list. For example, if a character has a @code{front-sticky} property whose value is @code{(face read-only)}, then insertion before the character can inherit its @code{face} property and its @code{read-only} property, but no others. The @code{rear-nonsticky} works the opposite way. Every property is rear-sticky by default, so the @code{rear-nonsticky} property says which properties are @emph{not} rear-sticky. If a character's @code{rear-nonsticky} property is @code{t}, then none of its properties are rear-sticky. If the @code{rear-nonsticky} property is a list, properties are rear-sticky @emph{unless} their names are in the list. When you insert text with inheritance, it inherits all the rear-sticky properties of the preceding character, and all the front-sticky properties of the following character. The previous character's properties take precedence when both sides offer different sticky values for the same property. Here are the functions that insert text with inheritance of properties: @defun insert-and-inherit &rest strings Insert the strings @var{strings}, just like the function @code{insert}, but inherit any sticky properties from the adjoining text. @end defun @defun insert-before-markers-and-inherit &rest strings Insert the strings @var{strings}, just like the function @code{insert-before-markers}, but inherit any sticky properties from the adjoining text. @end defun @node Saving Properties @subsection Saving Text Properties in Files @cindex text properties in files @cindex saving text properties You can save text properties in files, and restore text properties when inserting the files, using these two hooks: @defvar write-region-annotate-functions This variable's value is a list of functions for @code{write-region} to run to encode text properties in some fashion as annotations to the text being written in the file. @xref{Writing to Files}. Each function in the list is called with two arguments: the start and end of the region to be written. These functions should not alter the contents of the buffer. Instead, they should return lists indicating annotations to write in the file in addition to the text in the buffer. Each function should return a list of elements of the form @code{(@var{position} . @var{string})}, where @var{position} is an integer specifying the relative position in the text to be written, and @var{string} is the annotation to add there. Each list returned by one of these functions must be already sorted in increasing order by @var{position}. If there is more than one function, @code{write-region} merges the lists destructively into one sorted list. When @code{write-region} actually writes the text from the buffer to the file, it intermixes the specified annotations at the corresponding positions. All this takes place without modifying the buffer. @end defvar @defvar after-insert-file-functions This variable holds a list of functions for @code{insert-file-contents} to call after inserting a file's contents. These functions should scan the inserted text for annotations, and convert them to the text properties they stand for. Each function receives one argument, the length of the inserted text; point indicates the start of that text. The function should scan that text for annotations, delete them, and create the text properties that the annotations specify. The function should return the updated length of the inserted text, as it stands after those changes. The value returned by one function becomes the argument to the next function. These functions should always return with point at the beginning of the inserted text. The intended use of @code{after-insert-file-functions} is for converting some sort of textual annotations into actual text properties. But other uses may be possible. @end defvar We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs. We suggest not trying to handle arbitrary Lisp objects as property names or property values---because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode. @xref{Format Conversion}, for a related feature. @c ??? In next edition, merge this info Format Conversion. @node Lazy Properties @subsection Lazy Computation of Text Properties Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them. The primitive that extracts text from the buffer along with its properties is @code{buffer-substring}. Before examining the properties, this function runs the abnormal hook @code{buffer-access-fontify-functions}. @defvar buffer-access-fontify-functions This variable holds a list of functions for computing text properties. Before @code{buffer-substring} copies the text and text properties for a portion of the buffer, it calls all the functions in this list. Each of the functions receives two arguments that specify the range of the buffer being accessed. (The buffer itself is always the current buffer.) @end defvar The function @code{buffer-substring-no-properties} does not call these functions, since it ignores text properties anyway. In order to prevent the hook functions from being called more than once for the same part of the buffer, you can use the variable @code{buffer-access-fontified-property}. @defvar buffer-access-fontified-property If this value's variable is non-@code{nil}, it is a symbol which is used as a text property name. A non-@code{nil} value for that text property means, ``the other text properties for this character have already been computed.'' If all the characters in the range specified for @code{buffer-substring} have a non-@code{nil} value for this property, @code{buffer-substring} does not call the @code{buffer-access-fontify-functions} functions. It assumes these characters already have the right text properties, and just copies the properties they already have. The normal way to use this feature is that the @code{buffer-access-fontify-functions} functions add this property, as well as others, to the characters they operate on. That way, they avoid being called over and over for the same text. @end defvar @node Not Intervals @subsection Why Text Properties are not Intervals @cindex intervals Some editors that support adding attributes to text in the buffer do so by letting the user specify ``intervals'' within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification. If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property. Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two. Suppose we ``fix'' this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two. Insertion of text at the border between intervals also raises questions that have no satisfactory answer. However, it is easy to arrange for editing to behave consistently for questions of the form, ``What are the properties of this character?'' So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end. In practice, you can usually use the property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. @xref{Property Search}. Emacs also provides explicit intervals as a presentation feature; see @ref{Overlays}. @node Substitution @section Substituting for a Character Code The following functions replace characters within a specified region based on their character codes. @defun subst-char-in-region start end old-char new-char &optional noundo @cindex replace characters This function replaces all occurrences of the character @var{old-char} with the character @var{new-char} in the region of the current buffer defined by @var{start} and @var{end}. @cindex Outline mode @cindex undo avoidance If @var{noundo} is non-@code{nil}, then @code{subst-char-in-region} does not record the change for undo and does not mark the buffer as modified. This feature is used for controlling selective display (@pxref{Selective Display}). @code{subst-char-in-region} does not move point and returns @code{nil}. @example @group ---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- @end group @group (subst-char-in-region 1 20 ?i ?X) @result{} nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ---------- @end group @end example @end defun @defun translate-region start end table This function applies a translation table to the characters in the buffer between positions @var{start} and @var{end}. The translation table @var{table} is a string; @code{(aref @var{table} @var{ochar})} gives the translated character corresponding to @var{ochar}. If the length of @var{table} is less than 256, any characters with codes larger than the length of @var{table} are not altered by the translation. The return value of @code{translate-region} is the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table. @end defun @node Registers @section Registers @cindex registers A register is a sort of variable used in Emacs editing that can hold a marker, a string, a rectangle, a window configuration (of one frame), or a frame configuration (of all frames). Each register is named by a single character. All characters, including control and meta characters (but with the exception of @kbd{C-g}), can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by a character that is its name. The functions in this section return unpredictable values unless otherwise stated. @c Will change in version 19 @defvar register-alist This variable is an alist of elements of the form @code{(@var{name} . @var{contents})}. Normally, there is one element for each Emacs register that has been used. The object @var{name} is a character (an integer) identifying the register. The object @var{contents} is a string, marker, or list representing the register contents. A string represents text stored in the register. A marker represents a position. A list represents a rectangle; its elements are strings, one per line of the rectangle. @end defvar @defun get-register reg This function returns the contents of the register @var{reg}, or @code{nil} if it has no contents. @end defun @defun set-register reg value This function sets the contents of register @var{reg} to @var{value}. A register can be set to any value, but the other register functions expect only certain data types. The return value is @var{value}. @end defun @deffn Command view-register reg This command displays what is contained in register @var{reg}. @end deffn @ignore @deffn Command point-to-register reg This command stores both the current location of point and the current buffer in register @var{reg} as a marker. @end deffn @deffn Command jump-to-register reg @deffnx Command register-to-point reg @comment !!SourceFile register.el This command restores the status recorded in register @var{reg}. If @var{reg} contains a marker, it moves point to the position stored in the marker. Since both the buffer and the location within the buffer are stored by the @code{point-to-register} function, this command can switch you to another buffer. If @var{reg} contains a window configuration or a frame configuration. @code{jump-to-register} restores that configuration. @end deffn @end ignore @deffn Command insert-register reg &optional beforep This command inserts contents of register @var{reg} into the current buffer. Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument @var{beforep} is non-@code{nil}, it puts the mark before and point after. You can pass a non-@code{nil} second argument @var{beforep} to this function interactively by supplying any prefix argument. If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines. If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future. @end deffn @ignore @deffn Command copy-to-register reg start end &optional delete-flag This command copies the region from @var{start} to @var{end} into register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes the region from the buffer after copying it into the register. @end deffn @deffn Command prepend-to-register reg start end &optional delete-flag This command prepends the region from @var{start} to @var{end} into register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes the region from the buffer after copying it to the register. @end deffn @deffn Command append-to-register reg start end &optional delete-flag This command appends the region from @var{start} to @var{end} to the text already in register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes the region from the buffer after copying it to the register. @end deffn @deffn Command copy-rectangle-to-register reg start end &optional delete-flag This command copies a rectangular region from @var{start} to @var{end} into register @var{reg}. If @var{delete-flag} is non-@code{nil}, it deletes the region from the buffer after copying it to the register. @end deffn @deffn Command window-configuration-to-register reg This function stores the window configuration of the selected frame in register @var{reg}. @end deffn @deffn Command frame-configuration-to-register reg This function stores the current frame configuration in register @var{reg}. @end deffn @end ignore @node Transposition @section Transposition of Text This subroutine is used by the transposition commands. @defun transpose-regions start1 end1 start2 end2 &optional leave-markers This function exchanges two nonoverlapping portions of the buffer. Arguments @var{start1} and @var{end1} specify the bounds of one portion and arguments @var{start2} and @var{end2} specify the bounds of the other portion. Normally, @code{transpose-regions} relocates markers with the transposed text; a marker previously positioned within one of the two transposed portions moves along with that portion, thus remaining between the same two characters in their new position. However, if @var{leave-markers} is non-@code{nil}, @code{transpose-regions} does not do this---it leaves all markers unrelocated. @end defun @node Change Hooks @section Change Hooks @cindex change hooks @cindex hooks for text changes These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also @ref{Special Properties}, for how to detect changes to specific parts of the text. The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them. @defvar before-change-functions This variable holds a list of a functions to call before any buffer modification. Each function gets two arguments, the beginning and end of the region that is about to change, represented as integers. The buffer that is about to change is always the current buffer. @end defvar @defvar after-change-functions This variable holds a list of a functions to call after any buffer modification. Each function receives three arguments: the beginning and end of the region just changed, and the length of the text that existed before the change. (To get the current length, subtract the region beginning from the region end.) All three arguments are integers. The buffer that's about to change is always the current buffer. @end defvar @defvar before-change-function This obsolete variable holds one function to call before any buffer modification (or @code{nil} for no function). It is called just like the functions in @code{before-change-functions}. @end defvar @defvar after-change-function This obsolete variable holds one function to call after any buffer modification (or @code{nil} for no function). It is called just like the functions in @code{after-change-functions}. @end defvar The four variables above are temporarily bound to @code{nil} during the time that any of these functions is running. This means that if one of these functions changes the buffer, that change won't run these functions. If you do want a hook function to make changes that run these functions, make it bind these variables back to their usual values. One inconvenient result of this protective feature is that you cannot have a function in @code{after-change-functions} or @code{before-change-functions} which changes the value of that variable. But that's not a real limitation. If you want those functions to change the list of functions to run, simply add one fixed function to the hook, and code that function to look in another variable for other functions to call. Here is an example: @example (setq my-own-after-change-functions nil) (defun indirect-after-change-function (beg end len) (let ((list my-own-after-change-functions)) (while list (funcall (car list) beg end len) (setq list (cdr list))))) (add-hooks 'after-change-functions 'indirect-after-change-function) @end example @defvar first-change-hook This variable is a normal hook that is run whenever a buffer is changed that was previously in the unmodified state. @end defvar