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This is elisp, produced by makeinfo version 4.0f from ./elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This Info file contains edition 2.8 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 21.2. Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Copying", with the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development." File: elisp, Node: Comparing Text, Next: Insertion, Prev: Buffer Contents, Up: Text Comparing Text ============== This function lets you compare portions of the text in a buffer, without copying them into strings first. - Function: compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2 This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use `nil' for BUFFER1, BUFFER2, or both to stand for the current buffer. The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings. This function ignores case when comparing characters if `case-fold-search' is non-`nil'. It always ignores text properties. Suppose the current buffer contains the text `foobarbar haha!rara!'; then in this example the two substrings are `rbar ' and `rara!'. The value is 2 because the first substring is greater at the second character. (compare-buffer-substrings nil 6 11 nil 16 21) => 2 File: elisp, Node: Insertion, Next: Commands for Insertion, Prev: Comparing Text, Up: Text Inserting Text ============== "Insertion" means adding new text to a buffer. The inserted text goes at point--between the character before point and the character after point. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion "after point" and the latter insertion "before point". Insertion relocates markers that point at positions after the insertion point, so that they stay with the surrounding text (*note Markers::). When a marker points at the place of insertion, insertion may or may not relocate the marker, depending on the marker's insertion type (*note Marker Insertion Types::). Certain special functions such as `insert-before-markers' relocate all such markers to point after the inserted text, regardless of the markers' insertion type. Insertion functions signal an error if the current buffer is read-only or if they insert within read-only text. These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text. The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa--if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. *Note Converting Representations::. - Function: insert &rest args This function inserts the strings and/or characters ARGS into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all ARGS are either strings or characters. The value is `nil'. - Function: insert-before-markers &rest args This function inserts the strings and/or characters ARGS into the current buffer, at point, moving point forward. An error is signaled unless all ARGS are either strings or characters. The value is `nil'. This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. If an overlay begins the insertion point, the inserted text falls outside the overlay; if a nonempty overlay ends at the insertion point, the inserted text falls inside that overlay. - Function: insert-char character &optional count inherit This function inserts COUNT instances of CHARACTER into the current buffer before point. The argument COUNT should be a number (`nil' means 1), and CHARACTER must be a character. The value is `nil'. This function does not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. *Note Converting Representations::. If INHERIT is non-`nil', then the inserted characters inherit sticky text properties from the two characters before and after the insertion point. *Note Sticky Properties::. - Function: insert-buffer-substring from-buffer-or-name &optional start end This function inserts a portion of buffer FROM-BUFFER-OR-NAME (which must already exist) into the current buffer before point. The text inserted is the region from START and END. (These arguments default to the beginning and end of the accessible portion of that buffer.) This function returns `nil'. In this example, the form is executed with buffer `bar' as the current buffer. We assume that buffer `bar' is initially empty. ---------- Buffer: foo ---------- We hold these truths to be self-evident, that all ---------- Buffer: foo ---------- (insert-buffer-substring "foo" 1 20) => nil ---------- Buffer: bar ---------- We hold these truth-!- ---------- Buffer: bar ---------- *Note 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. File: elisp, Node: Commands for Insertion, Next: Deletion, Prev: Insertion, Up: Text User-Level Insertion Commands ============================= This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs. - Command: insert-buffer from-buffer-or-name This command inserts the entire contents of FROM-BUFFER-OR-NAME (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is `nil'. - Command: self-insert-command count This command inserts the last character typed; it does so COUNT times, before point, and returns `nil'. Most printing characters are bound to this command. In routine use, `self-insert-command' is the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap. In an interactive call, COUNT is the numeric prefix argument. This command calls `auto-fill-function' whenever that is non-`nil' and the character inserted is in the table `auto-fill-chars' (*note Auto Filling::). This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (*Note Abbrevs::, and *Note Syntax Class Table::.) This is also responsible for calling `blink-paren-function' when the inserted character has close parenthesis syntax (*note Blinking::). Do not try substituting your own definition of `self-insert-command' for the standard one. The editor command loop handles this function specially. - Command: newline &optional number-of-newlines This command inserts newlines into the current buffer before point. If NUMBER-OF-NEWLINES is supplied, that many newline characters are inserted. This function calls `auto-fill-function' if the current column number is greater than the value of `fill-column' and NUMBER-OF-NEWLINES is `nil'. Typically what `auto-fill-function' does is insert a newline; thus, the overall result in this case is to insert two newlines at different places: one at point, and another earlier in the line. `newline' does not auto-fill if NUMBER-OF-NEWLINES is non-`nil'. This command indents to the left margin if that is not zero. *Note Margins::. The value returned is `nil'. In an interactive call, COUNT is the numeric prefix argument. - Command: split-line This command splits the current line, moving the portion of the line after point down vertically so that it is on the next line directly below where it was before. Whitespace is inserted as needed at the beginning of the lower line, using the `indent-to' function. `split-line' returns the position of point. Programs hardly ever use this function. - Variable: overwrite-mode This variable controls whether overwrite mode is in effect. The value should be `overwrite-mode-textual', `overwrite-mode-binary', or `nil'. `overwrite-mode-textual' specifies textual overwrite mode (treats newlines and tabs specially), and `overwrite-mode-binary' specifies binary overwrite mode (treats newlines and tabs like any other characters). File: elisp, Node: Deletion, Next: User-Level Deletion, Prev: Commands for Insertion, Up: Text Deleting Text ============= Deletion means removing part of the text in a buffer, without saving it in the kill ring (*note The Kill Ring::). Deleted text can't be yanked, but can be reinserted using the undo mechanism (*note 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 `nil'. - Command: erase-buffer This function deletes the entire text of the current buffer, leaving it empty. If the buffer is read-only, it signals a `buffer-read-only' error; if some of the text in it is read-only, it signals a `text-read-only' error. Otherwise, it deletes the text without asking for any confirmation. It returns `nil'. Normally, deleting a large amount of text from a buffer inhibits further auto-saving of that buffer "because it has shrunk". However, `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. - Command: delete-region start end This command deletes the text between positions START and END in the current buffer, and returns `nil'. If point was inside the deleted region, its value afterward is START. Otherwise, point relocates with the surrounding text, as markers do. - Function: delete-and-extract-region start end This function deletes the text between positions START and END in the current buffer, and returns a string containing the text just deleted. If point was inside the deleted region, its value afterward is START. Otherwise, point relocates with the surrounding text, as markers do. - Command: delete-char count &optional killp This command deletes COUNT characters directly after point, or before point if COUNT is negative. If KILLP is non-`nil', then it saves the deleted characters in the kill ring. In an interactive call, COUNT is the numeric prefix argument, and 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 `nil'. - Command: delete-backward-char count &optional killp This command deletes COUNT characters directly before point, or after point if COUNT is negative. If KILLP is non-`nil', then it saves the deleted characters in the kill ring. In an interactive call, COUNT is the numeric prefix argument, and 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 `nil'. - Command: backward-delete-char-untabify count &optional killp This command deletes 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 KILLP is non-`nil', then the command saves the deleted characters in the kill ring. Conversion of tabs to spaces happens only if COUNT is positive. If it is negative, exactly -COUNT characters after point are deleted. In an interactive call, COUNT is the numeric prefix argument, and 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 `nil'. - User Option: backward-delete-char-untabify-method This option specifies how `backward-delete-char-untabify' should deal with whitespace. Possible values include `untabify', the default, meaning convert a tab to many spaces and delete one; `hungry', meaning delete all the whitespace characters before point with one command, and `nil', meaning do nothing special for whitespace characters. File: elisp, Node: User-Level Deletion, Next: The Kill Ring, Prev: Deletion, Up: Text 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. - Command: delete-horizontal-space This function deletes all spaces and tabs around point. It returns `nil'. In the following examples, we call `delete-horizontal-space' four times, once on each line, with point between the second and third characters on the line each time. ---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. => nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ---------- - 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 JOIN-FOLLOWING-P is non-`nil', `delete-indentation' joins this line to the following line instead. The function returns `nil'. If there is a fill prefix, and the second of the lines being joined starts with the prefix, then `delete-indentation' deletes the fill prefix before joining the lines. *Note Margins::. In the example below, point is located on the line starting `events', and it makes no difference if there are trailing spaces in the preceding line. ---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) => nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ---------- After the lines are joined, the function `fixup-whitespace' is responsible for deciding whether to leave a space at the junction. - Function: fixup-whitespace This function replaces all the whitespace surrounding point with either one space or no space, according to the context. It returns `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. *Note Syntax Class Table::. In the example below, `fixup-whitespace' is called the first time with point before the word `spaces' in the first line. For the second invocation, point is directly after the `('. ---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) => nil (fixup-whitespace) => nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ---------- - Command: just-one-space This command replaces any spaces and tabs around point with a single space. It returns `nil'. - 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. `delete-blank-lines' returns `nil'. File: elisp, Node: The Kill Ring, Next: Undo, Prev: User-Level Deletion, Up: Text The Kill Ring ============= "Kill functions" delete text like the deletion functions, but save it so that the user can reinsert it by "yanking". Most of these functions have `kill-' in their name. By contrast, the functions whose names start with `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. *Note Deletion::. Killed text is saved for later yanking in the "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 `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 _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. File: elisp, Node: Kill Ring Concepts, Next: Kill Functions, Up: The Kill Ring 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: ("some text" "a different piece of text" "even older text") When the list reaches `kill-ring-max' entries in length, adding a new entry automatically deletes the last entry. When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single kill-ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one. For yanking, one entry in the kill ring is designated the "front" of the ring. Some yank commands "rotate" the ring by designating a 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. File: elisp, Node: Kill Functions, Next: Yank Commands, Prev: Kill Ring Concepts, Up: The Kill Ring Functions for Killing --------------------- `kill-region' is the usual subroutine for killing text. Any command that calls this function is a "kill command" (and should probably have `kill' in its name). `kill-region' puts the newly killed text in a new element at the beginning of the kill ring or adds it to the most recent element. It determines automatically (using `last-command') whether the previous command was a kill command, and if so appends the killed text to the most recent entry. - Command: kill-region start end This function kills the text in the region defined by START and END. The text is deleted but saved in the kill ring, along with its text properties. The value is always `nil'. In an interactive call, START and END are point and the mark. If the buffer or text is read-only, `kill-region' modifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use a series of kill commands to copy text from a read-only buffer into the kill ring. - User Option: kill-read-only-ok If this option is non-`nil', `kill-region' does not signal an error if the buffer or text is read-only. Instead, it simply returns, updating the kill ring but not changing the buffer. - Command: copy-region-as-kill start end This command saves the region defined by START and END on the kill ring (including text properties), but does not delete the text from the buffer. It returns `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 `this-command' to `kill-region', so a subsequent kill command does not append to the same kill ring entry. Don't call `copy-region-as-kill' in Lisp programs unless you aim to support Emacs 18. For newer Emacs versions, it is better to use `kill-new' or `kill-append' instead. *Note Low-Level Kill Ring::. File: elisp, Node: Yank Commands, Next: Low-Level Kill Ring, Prev: Kill Functions, Up: The Kill Ring Functions for Yanking --------------------- "Yanking" means reinserting an entry of previously killed text from the kill ring. The text properties are copied too. - Command: yank &optional arg 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 ARG is a list (which occurs interactively when the user types `C-u' with no digits), then `yank' inserts the text as described above, but puts point before the yanked text and puts the mark after it. If ARG is a number, then `yank' inserts the ARGth most recently killed text--the ARGth element of the kill ring list. `yank' does not alter the contents of the kill ring or rotate it. It returns `nil'. - 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 `yank' or another `yank-pop'. At such a time, the region contains text that was just inserted by yanking. `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 ARG is `nil', then the replacement text is the previous element of the kill ring. If ARG is numeric, the replacement is the ARGth previous kill. If ARG is negative, a more recent kill is the replacement. The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest. The return value is always `nil'. File: elisp, Node: Low-Level Kill Ring, Next: Internals of Kill Ring, Prev: Yank Commands, Up: The Kill Ring 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, because they take care of interaction with window system selections (*note Window System Selections::). - Function: current-kill n &optional do-not-move The function `current-kill' rotates the yanking pointer, which designates the "front" of the kill ring, by N places (from newer kills to older ones), and returns the text at that place in the ring. If the optional second argument DO-NOT-MOVE is non-`nil', then `current-kill' doesn't alter the yanking pointer; it just returns the Nth kill, counting from the current yanking pointer. If N is zero, indicating a request for the latest kill, `current-kill' calls the value of `interprogram-paste-function' (documented below) before consulting the kill ring. - Function: kill-new string This function puts the text 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 `interprogram-cut-function' (see below). - Function: kill-append string before-p This function appends the text STRING to the first entry in the kill ring. Normally STRING goes at the end of the entry, but if BEFORE-P is non-`nil', it goes at the beginning. This function also invokes the value of `interprogram-cut-function' (see below). - Variable: 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 `nil' or a function of no arguments. If the value is a function, `current-kill' calls it to get the "most recent kill". If the function returns a non-`nil' value, then that value is used as the "most recent kill". If it returns `nil', then the first element of `kill-ring' is used. The normal use of this hook is to get the window system's primary selection as the most recent kill, even if the selection belongs to another application. *Note Window System Selections::. - Variable: 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 `nil' or a function of one argument. If the value is a function, `kill-new' and `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 window system's primary selection from the newly killed text. *Note Window System Selections::. File: elisp, Node: Internals of Kill Ring, Prev: Low-Level Kill Ring, Up: The Kill Ring Internals of the Kill Ring -------------------------- The variable `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 `kill-ring-yank-pointer' variable points to a link in the kill ring list, whose CAR is the text to yank next. We say it identifies the "front" of the ring. Moving `kill-ring-yank-pointer' to a different link is called "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 `kill-ring'. Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables whose values are normally lists. The word "pointer" in the name of the `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 `kill-ring-yank-pointer' is always `eq' to one of the links in the kill ring list. The element it identifies is the CAR of that link. Kill commands, which change the kill ring, also set this variable to the value of `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 `kill-ring-yank-pointer' pointing to the second entry in the kill ring `("some text" "a different piece of text" "yet older text")'. kill-ring ---- kill-ring-yank-pointer | | | v | --- --- --- --- --- --- --> | | |------> | | |--> | | |--> nil --- --- --- --- --- --- | | | | | | | | -->"yet older text" | | | --> "a different piece of text" | --> "some text" This state of affairs might occur after `C-y' (`yank') immediately followed by `M-y' (`yank-pop'). - Variable: kill-ring This variable holds the list of killed text sequences, most recently killed first. - Variable: 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 `kill-ring', and its CAR is the kill string that `C-y' should yank. - User Option: 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 `kill-ring-max' is 30. File: elisp, Node: Undo, Next: Maintaining Undo, Prev: The Kill Ring, Up: Text Undo ==== Most buffers have an "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 `buffer-undo-list'. - Variable: buffer-undo-list This variable's value is the undo list of the current buffer. A value of `t' disables the recording of undo information. Here are the kinds of elements an undo list can have: `POSITION' This kind of element records a previous value of point; undoing this element moves point to POSITION. Ordinary cursor motion does not make any sort of undo record, but deletion operations use these entries to record where point was before the command. `(BEG . END)' This kind of element indicates how to delete text that was inserted. Upon insertion, the text occupied the range BEG-END in the buffer. `(TEXT . POSITION)' This kind of element indicates how to reinsert text that was deleted. The deleted text itself is the string TEXT. The place to reinsert it is `(abs POSITION)'. `(t HIGH . LOW)' This kind of element indicates that an unmodified buffer became modified. The elements HIGH and LOW are two integers, each recording 16 bits of the visited file's modification time as of when it was previously visited or saved. `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. `(nil PROPERTY VALUE BEG . END)' This kind of element records a change in a text property. Here's how you might undo the change: (put-text-property BEG END PROPERTY VALUE) `(MARKER . ADJUSTMENT)' This kind of element records the fact that the marker MARKER was relocated due to deletion of surrounding text, and that it moved ADJUSTMENT character positions. Undoing this element moves MARKER - ADJUSTMENT characters. `nil' This element is a boundary. The elements between two boundaries are called a "change group"; normally, each change group corresponds to one keyboard command, and undo commands normally undo an entire group as a unit. - Function: 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 `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 is to ensure that each command makes a boundary in each buffer where it makes changes. Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example, `query-replace' calls `undo-boundary' after each replacement, so that the user can undo individual replacements one by one. - Function: primitive-undo count list This is the basic function for undoing elements of an undo list. It undoes the first COUNT elements of LIST, returning the rest of LIST. You could write this function in Lisp, but it is convenient to have it in C. `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. File: elisp, Node: Maintaining Undo, Next: Filling, Prev: Undo, Up: Text 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 `buffer-undo-list' yourself. - Command: buffer-enable-undo &optional buffer-or-name This command enables recording undo information for buffer 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 `nil'. In an interactive call, BUFFER-OR-NAME is the current buffer. You cannot specify any other buffer. - Command: buffer-disable-undo &optional buffer - Command: buffer-flush-undo &optional buffer This function discards the undo list of 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 BUFFER is already disabled, this function has no effect. This function returns `nil'. The name `buffer-flush-undo' is not considered obsolete, but the preferred name is `buffer-disable-undo'. 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: `undo-limit' and `undo-strong-limit'. - Variable: 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. - Variable: 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. File: elisp, Node: Filling, Next: Margins, Prev: Maintaining Undo, Up: Text Filling ======= "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 "justified", which means inserting spaces to make the left and/or right margins line up precisely. The width is controlled by the variable `fill-column'. For ease of reading, lines should be no longer than 70 or so columns. You can use Auto Fill mode (*note 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 (*note Margins::). If the current justification style is `none', the filling functions don't actually do anything. Several of the filling functions have an argument JUSTIFY. If it is non-`nil', that requests some kind of justification. It can be `left', `right', `full', or `center', to request a specific style of justification. If it is `t', that means to use the current justification style for this part of the text (see `current-justification', below). Any other value is treated as `full'. When you call the filling functions interactively, using a prefix argument implies the value `full' for JUSTIFY. - Command: fill-paragraph justify This command fills the paragraph at or after point. If JUSTIFY is non-`nil', each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. *Note Paragraphs: (emacs)Paragraphs. - Command: fill-region start end &optional justify nosqueeze to-eop This command fills each of the paragraphs in the region from START to END. It justifies as well if JUSTIFY is non-`nil'. If NOSQUEEZE is non-`nil', that means to leave whitespace other than line breaks untouched. If TO-EOP is non-`nil', that means to keep filling to the end of the paragraph--or the next hard newline, if `use-hard-newlines' is enabled (see below). The variable `paragraph-separate' controls how to distinguish paragraphs. *Note Standard Regexps::. - Command: fill-individual-paragraphs start end &optional justify citation-regexp This command fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph were indented with spaces, the filled paragraph will remain indented in the same fashion. The first two arguments, START and END, are the beginning and end of the region to be filled. The third and fourth arguments, JUSTIFY and CITATION-REGEXP, are optional. If JUSTIFY is non-`nil', the paragraphs are justified as well as filled. If CITATION-REGEXP is non-`nil', it means the function is operating on a mail message and therefore should not fill the header lines. If CITATION-REGEXP is a string, it is used as a regular expression; if it matches the beginning of a line, that line is treated as a citation marker. Ordinarily, `fill-individual-paragraphs' regards each change in indentation as starting a new paragraph. If `fill-individual-varying-indent' is non-`nil', then only separator lines separate paragraphs. That mode can handle indented paragraphs with additional indentation on the first line. - User Option: fill-individual-varying-indent This variable alters the action of `fill-individual-paragraphs' as described above. - Command: fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after This command considers a region of text as a single paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when JUSTIFY is non-`nil'. In an interactive call, any prefix argument requests justification. If NOSQUEEZE is non-`nil', that means to leave whitespace other than line breaks untouched. If SQUEEZE-AFTER is non-`nil', it specifies a position in the region, and means don't canonicalize spaces before that position. In Adaptive Fill mode, this command calls `fill-context-prefix' to choose a fill prefix by default. *Note Adaptive Fill::. - Command: justify-current-line &optional how eop nosqueeze This command inserts spaces between the words of the current line so that the line ends exactly at `fill-column'. It returns `nil'. The argument HOW, if non-`nil' specifies explicitly the style of justification. It can be `left', `right', `full', `center', or `none'. If it is `t', that means to do follow specified justification style (see `current-justification', below). `nil' means to do full justification. If EOP is non-`nil', that means do left-justification if `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 NOSQUEEZE is non-`nil', that means do not change interior whitespace. - User Option: 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 `left', `right', `full', `center', or `none'. The default value is `left'. - Function: current-justification This function returns the proper justification style to use for filling the text around point. - User Option: sentence-end-double-space If this variable is non-`nil', a period followed by just one space does not count as the end of a sentence, and the filling functions avoid breaking the line at such a place. - Variable: fill-paragraph-function This variable provides a way for major modes to override the filling of paragraphs. If the value is non-`nil', `fill-paragraph' calls this function to do the work. If the function returns a non-`nil' value, `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: (let ((fill-paragraph-function nil)) (fill-paragraph arg)) - Variable: use-hard-newlines If this variable is non-`nil', the filling functions do not delete newlines that have the `hard' text property. These "hard newlines" act as paragraph separators. File: elisp, Node: Margins, Next: Adaptive Fill, Prev: Filling, Up: Text Margins for Filling =================== - User Option: fill-prefix This buffer-local 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. - User Option: 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 (*note Auto Filling::). As a practical matter, if you are writing text for other people to read, you should set `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. - Variable: default-fill-column The value of this variable is the default value for `fill-column' in buffers that do not override it. This is the same as `(default-value 'fill-column)'. The default value for `default-fill-column' is 70. - Command: set-left-margin from to margin This sets the `left-margin' property on the text from FROM to TO to the value MARGIN. If Auto Fill mode is enabled, this command also refills the region to fit the new margin. - Command: set-right-margin from to margin This sets the `right-margin' property on the text from FROM to TO to the value MARGIN. If Auto Fill mode is enabled, this command also refills the region to fit the new margin. - Function: 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 `left-margin' property of the character at the start of the current line (or zero if none), and the value of the variable `left-margin'. - Function: 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 `fill-column' variable, minus the value of the `right-margin' property of the character after point. - 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 `current-left-margin'. If the argument N is non-`nil', `move-to-left-margin' moves forward N-1 lines first. If FORCE is non-`nil', that says to fix the line's indentation if that doesn't match the left margin value. - Function: delete-to-left-margin &optional from to This function removes left margin indentation from the text between FROM and TO. The amount of indentation to delete is determined by calling `current-left-margin'. In no case does this function delete non-whitespace. If FROM and TO are omitted, they default to the whole buffer. - Function: indent-to-left-margin This is the default `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 `left-margin'. This may involve either inserting or deleting whitespace. - Variable: left-margin This variable specifies the base left margin column. In Fundamental mode, `C-j' indents to this column. This variable automatically becomes buffer-local when set in any fashion. - Variable: fill-nobreak-predicate This variable gives major modes a way to specify not to break a line at certain places. Its value should be a function. This function is called during filling, with no arguments and with point located at the place where a break is being considered. If the function returns non-`nil', then the line won't be broken there.