43. 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 (see section 43.9 Undo).

Many text-related functions operate on a region of text defined by two buffer positions passed in arguments named start and end. These arguments should be either markers (see section 42. Markers) or numeric character positions (see section 41. Positions). The order of these arguments does not matter; it is all right for start to be the end of the region and end the beginning. For example, (delete-region 1 10) and (delete-region 10 1) are equivalent. An args-out-of-range error is signaled if either start or end is outside the accessible portion of the buffer. In an interactive call, point and the mark are used for these arguments.

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

43.1 Examining Text Near Point

Many functions are provided to look at the characters around point. Several simple functions are described here. See also looking-at in 44.3 Regular Expression Searching.

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

Function: char-after &optional position buffer

This function returns the character in the buffer at (i.e., immediately after) position position. If position is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is nil. The default for position is point. If optional argument buffer is nil, the current buffer is assumed.

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

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

Function: char-before &optional position buffer

This function returns the character in the current buffer immediately before position position. If position is out of range for this purpose, either at or before the beginning of the buffer, or beyond the end, then the value is nil. The default for position is point. If optional argument buffer is nil, the current buffer is assumed.

Function: following-char &optional buffer

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

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

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

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

Function: preceding-char &optional buffer

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

Function: bobp &optional buffer

This function returns t if point is at the beginning of the buffer. If narrowing is in effect, this means the beginning of the accessible portion of the text. If optional argument buffer is nil, the current buffer is assumed. See also point-min in 41.1 Point.

Function: eobp &optional buffer

This function returns t if point is at the end of the buffer. If narrowing is in effect, this means the end of accessible portion of the text. If optional argument buffer is nil, the current buffer is assumed. See also point-max in See section 41.1 Point.

Function: bolp &optional buffer

This function returns t if point is at the beginning of a line. If optional argument buffer is nil, the current buffer is assumed. See section 41.2.4 Motion by Text Lines. The beginning of the buffer (or its accessible portion) always counts as the beginning of a line.

Function: eolp &optional buffer

This function returns t if point is at the end of a line. The end of the buffer is always considered the end of a line. If optional argument buffer is nil, the current buffer is assumed. The end of the buffer (or of its accessible portion) is always considered the end of a line.

43.2 Examining Buffer Contents

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

Function: buffer-substring start end &optional buffer

Function: buffer-string start end &optional buffer

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

If the region delineated by start and end contains duplicable extents, they will be remembered in the string. See section 47.9 Duplicable Extents.

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

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

43.3 Comparing Text

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

Function: compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2

This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use nil for buffer1, buffer2, or both to stand for the current buffer.

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

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

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

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

43.4 Inserting Text

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

Insertion relocates markers that point at positions after the insertion point, so that they stay with the surrounding text (see section 42. Markers). When a marker points at the place of insertion, insertion normally doesn't relocate the marker, so that it points to the beginning of the inserted text; however, certain special functions such as insert-before-markers relocate such markers to point after the inserted text.

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

If a string with non-nil extent data is inserted, the remembered extents will also be inserted. See section 47.9 Duplicable Extents.

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

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

Function: insert &rest args

This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all args are either strings or characters. The value is nil.

Function: insert-before-markers &rest args

This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. An error is signaled unless all args are either strings or characters. The value is nil.

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

Function: insert-string string &optional buffer

This function inserts string into buffer before point. buffer defaults to the current buffer if omitted. This function is chiefly useful if you want to insert a string in a buffer other than the current one (otherwise you could just use insert).

Function: insert-char character &optional count ignored buffer

This function inserts count instances of character into buffer before point. count must be a number, and character must be a character.

If optional argument buffer is nil, the current buffer is assumed. (In FSF Emacs, the third argument is called inherit and refers to text properties. In XEmacs, it is always ignored.)

This function always returns nil.

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 ----------

43.5 User-Level Insertion Commands

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

Command: insert-buffer from-buffer-or-name

This command inserts the entire contents of from-buffer-or-name (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is nil.

Command: self-insert-command count

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

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

This command calls auto-fill-function whenever that is non-nil and the character inserted is a space or a newline (see section 43.13 Auto Filling).

This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See section 46. Abbrevs And Abbrev Expansion, and 45.2.1 Table of Syntax Classes.)

This is also responsible for calling blink-paren-function when the inserted character has close parenthesis syntax (see section 52.9 Blinking Parentheses).

Command: newline &optional count

This command inserts newlines into the current buffer before point. If count 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 count 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 count is non-nil.

This command indents to the left margin if that is not zero. See section 43.12 Margins for Filling.

The value returned is nil. In an interactive call, count is the numeric prefix argument.

Command: split-line

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

Programs hardly ever use this function.

Variable: overwrite-mode

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

43.6 Deleting Text

Deletion means removing part of the text in a buffer, without saving it in the kill ring (see section 43.8 The Kill Ring). Deleted text can't be yanked, but can be reinserted using the undo mechanism (see section 43.9 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 &optional buffer

This function deletes the entire text of buffer, leaving it empty. If the buffer is read-only, it signals a buffer-read-only error. Otherwise, it deletes the text without asking for any confirmation. It returns nil. buffer defaults to the current buffer if omitted.

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 &optional buffer

This command deletes the text in buffer in the region defined by start and end. The value is nil. If optional argument buffer is nil, the current buffer is assumed.

Command: delete-char &optional count killp

This command deletes count characters directly after point, or before point if count is negative. count defaults to 1. 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 &optional count killp

This command deletes count characters directly before point, or after point if count is negative. count defaults to 1. 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.

43.7 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 value is 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. See section 43.12 Margins for Filling.

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.

Command: fixup-whitespace

This function replaces all the white space 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. See section 45.2.1 Table of Syntax Classes.

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.

43.8 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. See section 43.6 Deleting Text.

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.

43.8.1 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 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.

43.8.2 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 uses the 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.

Command: kill-region start end &optional verbose

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 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 all the kill commands to copy text into the kill ring from a read-only 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 Emacs 19, it is better to use kill-new or kill-append instead. See section 43.8.4 Low-Level Kill Ring.

43.8.3 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 value is always nil.

43.8.4 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.

Function: current-kill count &optional do-not-move

The function current-kill rotates the yanking pointer which designates the "front" of the kill ring by count 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 countth kill, counting from the current yanking pointer.

If count 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 &optional replace

This function makes the text string the latest entry in the kill ring, and sets kill-ring-yank-pointer to point to it.

Normally, string is added to the front of the kill ring as a new entry. However, if optional argument replace is non-nil, the entry previously at the front of the kill ring is discarded, and string replaces it.

This function runs the functions on kill-hooks, and 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 X server's primary selection as the most recent kill, even if the selection belongs to another X client. See section 58.1 X 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 X server's primary selection to the newly killed text.

43.8.5 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
  |               |
  |     ___ ___    --->  ___ ___      ___ ___
   --> |___|___|------> |___|___|--> |___|___|--> 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.

43.9 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 XEmacs 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:

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.

(start . end)

This kind of element indicates how to delete text that was inserted. Upon insertion, the text occupied the range start--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 start . end)

This kind of element records a change in a text property. Here's how you might undo the change:

(put-text-property start end property value)

position

This element indicates where point was at an earlier time. Undoing this element sets point to position. Deletion normally creates an element of this kind as well as a reinsertion element.

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 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, 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.

43.10 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. It cannot be called interactively.

The name buffer-flush-undo is not considered obsolete, but the preferred name buffer-disable-undo is new as of Emacs versions 19.

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.

43.11 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 (see section 43.13 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 (see section 43.12 Margins for Filling). 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).

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. See section `Paragraphs' in The XEmacs User's Manual.

Command: fill-region start end &optional justify

This command fills each of the paragraphs in the region from start to end. It justifies as well if justify is non-nil.

The variable paragraph-separate controls how to distinguish paragraphs. See section 44.8 Standard Regular Expressions Used in Editing.

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, start and end, are the beginning and end of the region to be filled. The third and fourth arguments, justify and mail-flag, are optional. If justify is non-nil, the paragraphs are justified as well as filled. If mail-flag is non-nil, it means the function is operating on a mail message and therefore should not fill the header lines.

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

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 justify is non-nil.

In an interactive call, any prefix argument requests justification.

In Adaptive Fill mode, which is enabled by default, 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.

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 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 when 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.

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.

43.12 Margins for Filling

User Option: 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.

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 (see section 43.13 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.

The arguments from and to are optional; the default is 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, LFD indents to this column. This variable automatically becomes buffer-local when set in any fashion.

43.13 Auto Filling

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 43.11 Filling.

Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See section 43.12 Margins for Filling.

Variable: 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 nil, in which case nothing special is done in that case.

The value of auto-fill-function is 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.

In older Emacs versions, this variable was named auto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed to auto-fill-function in version 19.

43.14 Sorting Text

The sorting functions described in this section all rearrange text in a buffer. This is in contrast to the function sort, which rearranges the order of the elements of a list (see section 11.6.3 Functions that Rearrange Lists). The values returned by these functions are not meaningful.

Function: 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 sort-subr works, consider the whole accessible portion of the buffer as being divided into disjoint pieces called 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 sort-subr function, reverse, is non-nil, the sort records are rearranged in order of descending sort key.

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

1. 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 sort-subr is called. Therefore, you should usually move point to the beginning of the buffer before calling sort-subr.

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

2. endrecfun is called with point within a record. It moves point to the end of the record.

3. 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-nil value to be used as the sort key, or return nil to indicate that the sort key is in the buffer starting at point. In the latter case, endkeyfun is called to find the end of the sort key.

4. 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 startkeyfun returns nil and this argument is omitted (or nil), then the sort key extends to the end of the record. There is no need for endkeyfun if startkeyfun returns a non-nil value.

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

;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user. (defun sort-lines (reverse start end) "Sort lines in region alphabetically. Called from a program, there are three arguments: REVERSE (non-nil means reverse order), and START and END (the region to sort)." (interactive "P\nr") (save-restriction (narrow-to-region start end) (goto-char (point-min)) (sort-subr reverse 'forward-line 'end-of-line)))

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

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

(sort-subr reverse (function (lambda () (skip-chars-forward "\n \t\f"))) 'forward-paragraph)

Command: sort-regexp-fields reverse record-regexp key-regexp start end

This command sorts the region between start and end alphabetically as specified by record-regexp and key-regexp. If 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 ASCII character set, the ordering in that set determines alphabetical order.

The value of the 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 `^.+$', which matches lines with at least one character besides a newline, would make each such line into a sort record. See section 44.2 Regular Expressions, for a description of the syntax and meaning of regular expressions.

The value of the key-regexp argument specifies what part of each record is the sort key. The 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 key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own.

If key-regexp is:

`\digit'

then the text matched by the digitth `\(...\)' parenthesis grouping in record-regexp is the sort key.

`\&'

then the whole record is the sort key.

a regular expression

then 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 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.)

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

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

If you call sort-regexp-fields interactively, it prompts for record-regexp and key-regexp in the minibuffer.

Command: sort-lines reverse start end

This command alphabetically sorts lines in the region between start and end. If reverse is non-nil, the sort is in reverse order.

Command: sort-paragraphs reverse start end

This command alphabetically sorts paragraphs in the region between start and end. If reverse is non-nil, the sort is in reverse order.

Command: sort-pages reverse start end

This command alphabetically sorts pages in the region between start and end. If reverse is non-nil, the sort is in reverse order.

Command: sort-fields field start end

This command sorts lines in the region between start and end, comparing them alphabetically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the -fieldth field from the end of the line. This command is useful for sorting tables.

Command: sort-numeric-fields field start end

This command sorts lines in the region between start and end, comparing them numerically by the fieldth 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 field is negative, sorting is by the -fieldth field from the end of the line. This command is useful for sorting tables.

Command: sort-columns reverse &optional start end

This command sorts the lines in the region between start and end, comparing them alphabetically by a certain range of columns. The column positions of start and end bound the range of columns to sort on.

If reverse is non-nil, the sort is in reverse order.

One unusual thing about this command is that the entire line containing position start, and the entire line containing position end, are included in the region sorted.

Note that sort-columns uses the sort utility program, and so cannot work properly on text containing tab characters. Use M-x untabify to convert tabs to spaces before sorting.

43.15 Counting Columns

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 ctl-arrow, and tabs count as occupying a number of columns that depends on the value of tab-width and on the column where the tab begins. See section 52.10 Usual Display Conventions.

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.

Function: current-column &optional buffer

This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin.

This is calculated by adding together the widths of all the displayed representations of the character between the start of the previous line and point. (e.g. control characters will have a width of 2 or 4, tabs will have a variable width.)

Ignores the finite width of frame displaying the buffer, which means that this function may return values greater than (frame-width).

Whether the line is visible (if selective-display is t) has no effect; however, ^M is treated as end of line when selective-display is t.

If buffer is nil, the current buffer is assumed.

For an example of using current-column, see the description of count-lines in 41.2.4 Motion by Text Lines.

Function: move-to-column column &optional force buffer

This function moves point to column in the current line. The calculation of column takes into account the widths of the displayed representations of the characters between the start of the line and point.

If column column is beyond the end of the line, point moves to the end of the line. If column is negative, point moves to the beginning of the line.

If it is impossible to move to column 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 force is non-nil, and column is in the middle of a tab, then move-to-column converts the tab into spaces so that it can move precisely to column column. Other multicolumn characters can cause anomalies despite force, since there is no way to split them.

The argument force also has an effect if the line isn't long enough to reach column column; in that case, unless the value of force is the special value coerce, it says to add whitespace at the end of the line to reach that column.

If column is not a non-negative fixnum, an error is signaled.

The return value is the column number actually moved to.

43.16 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.

43.16.1 Indentation Primitives

This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives.

Function: current-indentation &optional buffer

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.

Command: indent-to column &optional minimum buffer

This function indents from point with tabs and spaces until column is reached. If minimum is specified and non-nil, then at least that many spaces are inserted even if this requires going beyond column. Otherwise the function does nothing if point is already beyond column. The value is the column at which the inserted indentation ends. If buffer is nil, the current buffer is assumed.

User Option: indent-tabs-mode

If this variable is non-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.

43.16.2 Indentation Controlled by Major Mode

An important function of each major mode is to customize the TAB key to indent properly for the language being edited. This section describes the mechanism of the TAB key and how to control it. The functions in this section return unpredictable values.

Variable: indent-line-function

This variable's value is the function to be used by TAB (and various commands) to indent the current line. The command indent-according-to-mode does no more than call this function.

In Lisp mode, the value is the symbol lisp-indent-line; in C mode, c-indent-line; in Fortran mode, fortran-indent-line. In Fundamental mode, Text mode, and many other modes with no standard for indentation, the value is indent-to-left-margin (which is the default value).

Command: indent-according-to-mode

This command calls the function in indent-line-function to indent the current line in a way appropriate for the current major mode.

Command: indent-for-tab-command &optional prefix-arg

This command calls the function in indent-line-function to indent the current line; except that if that function is indent-to-left-margin, it calls insert-tab instead. (That is a trivial command that inserts a tab character.)

Command: newline-and-indent

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 indent-line-function. In programming language modes, this is the same thing TAB does, but in some text modes, where TAB inserts a tab, newline-and-indent indents to the column specified by left-margin.

Command: reindent-then-newline-and-indent

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 indent-line-function. In programming language modes, this is the same thing TAB does, but in some text modes, where TAB inserts a tab, reindent-then-newline-and-indent indents to the column specified by left-margin.

43.16.3 Indenting an Entire Region

This section describes commands that indent all the lines in the region. They return unpredictable values.

Command: indent-region start end to-column

This command indents each nonblank line starting between start (inclusive) and end (exclusive). If to-column is nil, indent-region indents each nonblank line by calling the current mode's indentation function, the value of indent-line-function.

If to-column is non-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, indent-region indents each line by making it start with the fill prefix.

Variable: indent-region-function

The value of this variable is a function that can be used by 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 nil, there is no short cut, and indent-region actually works line by line.

A short-cut function is useful in modes such as C mode and Lisp mode, where the 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.

indent-region with a non-nil argument to-column has a different meaning and does not use this variable.

Command: indent-rigidly start end count

This command indents all lines starting between start (inclusive) and end (exclusive) sideways by 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 count is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified.

In Mail mode, C-c C-y (mail-yank-original) uses indent-rigidly to indent the text copied from the message being replied to.

Command: indent-code-rigidly start end columns &optional nochange-regexp

This is like indent-rigidly, except that it doesn't alter lines that start within strings or comments.

In addition, it doesn't alter a line if nochange-regexp matches at the beginning of the line (if nochange-regexp is non-nil).

43.16.4 Indentation Relative to Previous Lines

This section describes two commands that indent the current line based on the contents of previous lines.

Command: indent-relative &optional unindented-ok

This command inserts whitespace at point, extending to the same column as the next 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), indent-relative either does nothing (if unindented-ok is non-nil) or calls 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 indent-relative is unpredictable.

In the following example, point is at the beginning of the second line:

This line is indented twelve spaces. -!-The quick brown fox jumped.

Evaluation of the expression (indent-relative nil) produces the following:

This line is indented twelve spaces. -!-The quick brown fox jumped.

In this example, point is between the `m' and `p' of `jumped':

This line is indented twelve spaces. The quick brown fox jum-!-ped.

Evaluation of the expression (indent-relative nil) produces the following:

This line is indented twelve spaces. The quick brown fox jum -!-ped.

Command: indent-relative-maybe

This command indents the current line like the previous nonblank line. It calls indent-relative with t as the 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.

43.16.5 Adjustable "Tab Stops"

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 (see section 52.10 Usual Display Conventions). Note that the TAB character as input uses this tab stop feature only in a few major modes, such as Text mode.

Command: tab-to-tab-stop

This command inserts spaces or tabs up to the next tab stop column defined by 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.

User Option: tab-stop-list

This variable is the list of tab stop columns used by tab-to-tab-stops. The elements should be integers in increasing order. The tab stop columns need not be evenly spaced.

Use M-x edit-tab-stops to edit the location of tab stops interactively.

43.16.6 Indentation-Based Motion Commands

These commands, primarily for interactive use, act based on the indentation in the text.

Command: back-to-indentation

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 nil.

Command: backward-to-indentation arg

This command moves point backward arg lines and then to the first nonblank character on that line. It returns nil.

Command: forward-to-indentation arg

This command moves point forward arg lines and then to the first nonblank character on that line. It returns nil.

43.17 Case Changes

The case change commands described here work on text in the current buffer. See section 10.11 Character Case, for case conversion commands that work on strings and characters. See section 10.12 The Case Table, for how to customize which characters are upper or lower case and how to convert them.

Command: capitalize-region start end &optional buffer

This function capitalizes all words in the region defined by start and 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 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 capitalize-region is called interactively, start and end are point and the mark, with the smallest first.

---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ----------

Command: downcase-region start end &optional buffer

This function converts all of the letters in the region defined by start and end to lower case. The function returns nil.

When downcase-region is called interactively, start and end are point and the mark, with the smallest first.

Command: upcase-region start end &optional buffer

This function converts all of the letters in the region defined by start and end to upper case. The function returns nil.

When upcase-region is called interactively, start and end are point and the mark, with the smallest first.

Command: capitalize-word count &optional buffer

This function capitalizes 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 count is negative, the function capitalizes the -count previous words but does not move point. The value is 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 capitalize-word is called interactively, count is set to the numeric prefix argument.

Command: downcase-word count &optional buffer

This function converts the count words after point to all lower case, moving point over as it does. If count is negative, it converts the -count previous words but does not move point. The value is nil.

When downcase-word is called interactively, count is set to the numeric prefix argument.

Command: upcase-word count &optional buffer

This function converts the count words after point to all upper case, moving point over as it does. If count is negative, it converts the -count previous words but does not move point. The value is nil.

When upcase-word is called interactively, count is set to the numeric prefix argument.

43.18 Text Properties

Text properties are an alternative interface to extents (see section 47. Extents), and are built on top of them. They are useful when you want to view textual properties as being attached to the characters themselves rather than to intervals of characters. The text property interface is compatible with FSF Emacs.

Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see section 11.9 Property Lists). The properties belong to a particular character at a particular place, such as, the letter `T' at the beginning of this sentence or the first `o' in `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.

Note that FSF Emacs also looks at the category property to find defaults for text properties. We consider this too bogus to implement.

Copying text between strings and buffers preserves the properties along with the characters; this includes such diverse functions as subseq, insert, and buffer-substring.

43.18.1 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 get-text-property. Use text-properties-at to get the entire property list of a character. See section 43.18.3 Property Search Functions, 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.)

Function: get-text-property pos prop &optional object at-flag

This function returns the value of the prop property of the character after position pos in object (a buffer or string). The argument object is optional and defaults to the current buffer.

Function: get-char-property pos prop &optional object at-flag

This function is like get-text-property, except that it checks all extents, not just text-property extents.

Function: text-properties-at position &optional object

This function returns the entire property list of the character at position in the string or buffer object. If object is nil, it defaults to the current buffer.

Variable: 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, the value stored in this list is used instead. Here is an example:

(setq default-text-properties '(foo 69)) ;; Make sure character 1 has no properties of its own. (set-text-properties 1 2 nil) ;; What we get, when we ask, is the default value. (get-text-property 1 'foo) => 69

43.18.2 Changing Text Properties

The primitives for changing properties apply to a specified range of text. The function 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 (see section 43.9 Undo).

Function: put-text-property start end prop value &optional object

This function sets the prop property to value for the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer.

Function: add-text-properties start end props &optional object

This function modifies the text properties for the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer.

The argument props specifies which properties to change. It should have the form of a property list (see section 11.9 Property Lists): a list whose elements include the property names followed alternately by the corresponding values.

The return value is t if the function actually changed some property's value; nil otherwise (if props is nil or its values agree with those in the text).

For example, here is how to set the comment and face properties of a range of text:

(add-text-properties start end '(comment t face highlight))

Function: remove-text-properties start end props &optional object

This function deletes specified text properties from the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer.

The argument props specifies which properties to delete. It should have the form of a property list (see section 11.9 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 face property.

(remove-text-properties start end '(face nil))

The return value is t if the function actually changed some property's value; nil otherwise (if props is nil or if no character in the specified text had any of those properties).

Function: set-text-properties start end props &optional object

This function completely replaces the text property list for the text between start and end in the string or buffer object. If object is nil, it defaults to the current buffer.

The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values.

After set-text-properties returns, all the characters in the specified range have identical properties.

If props is nil, the effect is to get rid of all properties from the specified range of text. Here's an example:

(set-text-properties start end nil)

See also the function buffer-substring-without-properties (see section 43.2 Examining Buffer Contents) which copies text from the buffer but does not copy its properties.

43.18.3 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 eq for comparing property values. In all cases, object defaults to the current buffer.

For high performance, it's very important to use the 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.

Function: next-property-change pos &optional object limit

The function scans the text forward from position pos in the string or buffer 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 pos whose properties are not identical to those of the character just after pos.

If limit is non-nil, then the scan ends at position limit. If there is no property change before that point, next-property-change returns limit.

The value is nil if the properties remain unchanged all the way to the end of object and limit is nil. If the value is non-nil, it is a position greater than or equal to pos. The value equals pos only when limit equals pos.

Here is an example of how to scan the buffer by chunks of text within which all properties are constant:

(while (not (eobp)) (let ((plist (text-properties-at (point))) (next-change (or (next-property-change (point) (current-buffer)) (point-max)))) Process text from point to next-change... (goto-char next-change)))

Function: next-single-property-change pos prop &optional object limit

The function scans the text forward from position pos in the string or buffer object till it finds a change in the prop property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose prop property differs from that of the character just after pos.

If limit is non-nil, then the scan ends at position limit. If there is no property change before that point, next-single-property-change returns limit.

The value is nil if the property remains unchanged all the way to the end of object and limit is nil. If the value is non-nil, it is a position greater than or equal to pos; it equals pos only if limit equals pos.

Function: previous-property-change pos &optional object limit

This is like next-property-change, but scans backward from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.

Function: previous-single-property-change pos prop &optional object limit

This is like next-single-property-change, but scans backward from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.

Function: text-property-any start end prop value &optional object

This function returns non-nil if at least one character between start and end has a property prop whose value is value. More precisely, it returns the position of the first such character. Otherwise, it returns nil.

The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.

Function: text-property-not-all start end prop value &optional object

This function returns non-nil if at least one character between start and end has a property prop whose value differs from value. More precisely, it returns the position of the first such character. Otherwise, it returns nil.

The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.

43.18.4 Properties with Special Meanings

The predefined properties are the same as those for extents. See section 47.6 Properties of Extents.

43.18.5 Saving Text Properties in Files

You can save text properties in files, and restore text properties when inserting the files, using these two hooks:

Variable: write-region-annotate-functions

This variable's value is a list of functions for write-region to run to encode text properties in some fashion as annotations to the text being written in the file. See section 35.4 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 (position . string), where position is an integer specifying the relative position in the text to be written, and string is the annotation to add there.

Each list returned by one of these functions must be already sorted in increasing order by position. If there is more than one function, write-region merges the lists destructively into one sorted list.

When 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.

Variable: after-insert-file-functions

This variable holds a list of functions for 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 after-insert-file-functions is for converting some sort of textual annotations into actual text properties. But other uses may be possible.

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.

See section 35.13 File Format Conversion, for a related feature.

43.18.6 Fields

Emacs supplies a notion of a text field, which is a region of text where every character has the same value of the field property. It is used to identify regions of a buffer used for communicating with an external process, for example. XEmacs supplies a compatible interface. In XEmacs, the field property can be set as either an extent property or a text property, mirroring the Emacs capability of using either overlays or text properties.

The field manipulating functions take a buffer position as the field-identifying argument, defaulting to point. This really means the field containing that buffer position. Consecutive buffer positions with no field property are considered an "empty" field. There is some ambiguity when a specified buffer position falls at the very beginning or the very end of a field: does it belong to the preceding or the following field? The answer depends on the openness or closedness of the corresponding extents (see section 47.3 Extent Endpoints). A buffer position corresponds to the field whose property would be inherited by a character inserted at that position. If the buffer position is between an end-open and a start-open extent, then it corresponds to an empty field at that position, since an inserted character will belong to neither extent.

Variable: inhibit-field-text-motion

This variable controls whether the text motion commands notice fields or not. When it is nil (the default), commands such as beginning-of-line will try to move only within fields.

Function: make-field value from to &optional buffer

There is no Emacs counterpart to this function. The default open and closedness of extents in XEmacs is opposite to the default for Emacs overlays. Hence, fields based on extents in XEmacs behave differently from the equivalent fields based on overlays in Emacs. This function creates a field with value value over the region from to to in buffer, which defaults to the current buffer, with the default Emacs open and closedness.

Function: find-field &optional pos merge-at-boundary beg-limit end-limit

There is no (Lisp-visible) Emacs counterpart to this function. It is the workhorse for the other functions. It returns a dotted pair (start . stop) holding the endpoints of the field matching a specification. If pos is non-nil, it specifies a buffer position whose enclosing field should be found; otherwise, the value of point is used.

If merge-at-boundary is non-nil, then two changes are made to the search algorithm. First, if pos is at the very first position of a field, then the beginning of the previous field is returned instead of the beginning of pos's field. Second, if the value of the field property at pos is the symbol boundary, then the beginning of the field before the boundary field and the end of the field after the boundary field are returned.

If beg-limit is a buffer position, and the start position that would be returned is less than beg-limit, then beg-limit is returned instead. Likewise, if end-limit is a buffer position, and the stop position that would be returned is greater than end-limit, then end-limit is returned instead.

Function: delete-field &optional pos

Delete the text of the field at pos.

Function: field-string &optional pos

Return the contents of the field at pos as a string.

Function: field-string-no-properties &optional pos

Return the contents of the field at pos as a string, without text properties.

Function: field-beginning &optional pos escape-from-edge limit

Return the beginning of the field at pos. If escape-from-edge is non-nil and pos is at the beginning of a field, then the beginning of the field that ends at pos is returned instead. If limit is a buffer position and the returned value would be less than limit, then limit is returned instead.

Function: field-end &optional pos escape-from-edge limit

Return the end of the field at pos. If escape-from-edge is non-nil and pos is at the end of a field, then the end of the field that begins at pos is returned instead. If limit is a buffer position and the returned value would be greater than limit, then limit is returned instead.

Function: constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property

Return the position closest to new-pos that is in the same field as old-pos. If new-pos is nil, then the value of point is used instead and point is set to the value that is returned.

If escape-from-edge is non-nil and old-pos is at the boundary of two fields, then the two adjacent fields are considered one field. Furthermore, if new-pos is in a field whose field property is the symbol boundary, then the preceding field, the boundary field, and the following field are considered one field.

If only-in-line is non-nil and the returned position would be on a different line than new-pos, return new-pos instead.

If inhibit-capture-property is non-nil and the character at old-pos has a property of the same name as the value of inhibit-capture-property, then all field boundaries are ignored; i.e., new-pos is returned.

If inhibit-field-text-motion is non-nil, then all field boundaries are ignored and this function always returns new-pos.

43.19 Substituting for a Character Code

The following functions replace characters within a specified region based on their character codes.

Function: subst-char-in-region start end old-char new-char &optional noundo

This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.

If noundo is non-nil, then 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 (see section 52.6 Selective Display).

subst-char-in-region does not move point and returns nil.

---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- (subst-char-in-region 1 20 ?i ?X) => nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ----------

Function: translate-region start end table

This function applies a translation table to the characters in the buffer between positions start and end. The translation table table can be either a string, a vector, or a char-table.

If table is a string, its nth element is the mapping for the character with code n.

If table is a vector, its nth element is the mapping for character with code n. Legal mappings are characters, strings, or nil (meaning don't replace.)

If table is a char-table, its elements describe the mapping between characters and their replacements. The char-table should be of type char or generic.

When the table is a string or vector and its length is less than the total number of characters (256 without Mule), any characters with codes larger than the length of table are not altered by the translation.

The return value of 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.

NOTE: Prior to XEmacs 21.2, the table argument was allowed only to be a string. This is still the case in FSF Emacs.

The following example creates a char-table that is passed to translate-region, which translates character `a' to `the letter a', removes character `b', and translates character `c' to newline.

---------- Buffer: foo ---------- Here is a sentence in the buffer. ---------- Buffer: foo ---------- (let ((table (make-char-table 'generic))) (put-char-table ?a "the letter a" table) (put-char-table ?b "" table) (put-char-table ?c ?\n table) (translate-region (point-min) (point-max) table)) => 3 ---------- Buffer: foo ---------- Here is the letter a senten e in the uffer. ---------- Buffer: foo ----------

43.20 Registers

A register is a sort of variable used in XEmacs 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 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.

Variable: register-alist

This variable is an alist of elements of the form (name . contents). Normally, there is one element for each XEmacs register that has been used.

The object name is a character identifying the register. The object 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.

Function: get-register register

This function returns the contents of the register register, or nil if it has no contents.

Function: set-register register value

This function sets the contents of register register to value. A register can be set to any value, but the other register functions expect only certain data types. The return value is value.

Command: view-register register

This command displays what is contained in register register.

Command: insert-register register &optional beforep

This command inserts contents of register register into the current buffer.

Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument beforep is non-nil, it puts the mark before and point after. You can pass a non-nil second argument 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.

43.21 Transposition of Text

This subroutine is used by the transposition commands.

Function: transpose-regions start1 end1 start2 end2 &optional leave-markers

This function exchanges two nonoverlapping portions of the buffer. Arguments start1 and end1 specify the bounds of one portion and arguments start2 and end2 specify the bounds of the other portion.

Normally, 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 leave-markers is non-nil, transpose-regions does not do this--it leaves all markers unrelocated.

43.22 Change Hooks

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).

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.

Buffer changes made while executing the following hooks don't themselves cause any change hooks to be invoked.

Variable: 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.

Variable: 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.

Variable: before-change-function

This obsolete variable holds one function to call before any buffer modification (or nil for no function). It is called just like the functions in before-change-functions.

Variable: after-change-function

This obsolete variable holds one function to call after any buffer modification (or nil for no function). It is called just like the functions in after-change-functions.

Variable: first-change-hook

This variable is a normal hook that is run whenever a buffer is changed that was previously in the unmodified state.

43.23 Textual transformations--MD5 and base64 support

Some textual operations inherently require examining each character in turn, and performing arithmetic operations on them. Such operations can, of course, be implemented in Emacs Lisp, but tend to be very slow for large portions of text or data. This is why some of them are implemented in C, with an appropriate interface for Lisp programmers. Examples of algorithms thus provided are MD5 and base64 support.

MD5 is an algorithm for calculating message digests, as described in rfc1321. Given a message of arbitrary length, MD5 produces a 128-bit "fingerprint" ("message digest") corresponding to that message. It is considered computationally infeasible to produce two messages having the same MD5 digest, or to produce a message having a prespecified target digest. MD5 is used heavily by various authentication schemes.

Emacs Lisp interface to MD5 consists of a single function md5:

Function: md5 object &optional start end coding noerror

This function returns the MD5 message digest of object, a buffer or string.

Optional arguments start and end denote positions for computing the digest of a portion of object.

The optional coding argument specifies the coding system the text is to be represented in while computing the digest. If unspecified, it defaults to the current format of the data, or is guessed.

If noerror is non-nil, silently assume binary coding if the guesswork fails. Normally, an error is signaled in such case.

coding and noerror arguments are meaningful only in XEmacsen with file-coding or Mule support. Otherwise, they are ignored. Some examples of usage:

;; Calculate the digest of the entire buffer (md5 (current-buffer)) => "8842b04362899b1cda8d2d126dc11712" ;; Calculate the digest of the current line (md5 (current-buffer) (point-at-bol) (point-at-eol)) => "60614d21e9dee27dfdb01fa4e30d6d00" ;; Calculate the digest of your name and email address (md5 (concat (format "%s <%s>" (user-full-name) user-mail-address))) => "0a2188c40fd38922d941fe6032fce516"

Base64 is a portable encoding for arbitrary sequences of octets, in a form that need not be readable by humans. It uses a 65-character subset of US-ASCII, as described in rfc2045. Base64 is used by MIME to encode binary bodies, and to encode binary characters in message headers.

The Lisp interface to base64 consists of four functions:

Command: base64-encode-region start end &optional no-line-break

This function encodes the region between start and end of the current buffer to base64 format. This means that the original region is deleted, and replaced with its base64 equivalent.

Normally, encoded base64 output is multi-line, with 76-character lines. If no-line-break is non-nil, newlines will not be inserted, resulting in single-line output.

Mule note: you should make sure that you convert the multibyte characters (those that do not fit into 0--255 range) to something else, because they cannot be meaningfully converted to base64. If the base64-encode-region encounters such characters, it will signal an error.

base64-encode-region returns the length of the encoded text.

;; Encode the whole buffer in base64 (base64-encode-region (point-min) (point-max))

The function can also be used interactively, in which case it works on the currently active region.

Function: base64-encode-string string &optional no-line-break

This function encodes string to base64, and returns the encoded string.

Normally, encoded base64 output is multi-line, with 76-character lines. If no-line-break is non-nil, newlines will not be inserted, resulting in single-line output.

For Mule, the same considerations apply as for base64-encode-region.

(base64-encode-string "fubar") => "ZnViYXI="

Command: base64-decode-region start end

This function decodes the region between start and end of the current buffer. The region should be in base64 encoding.

If the region was decoded correctly, base64-decode-region returns the length of the decoded region. If the decoding failed, nil is returned.

;; Decode a base64 buffer, and replace it with the decoded version (base64-decode-region (point-min) (point-max))

Function: base64-decode-string string

This function decodes string to base64, and returns the decoded string. string should be valid base64-encoded text.

If encoding was not possible, nil is returned.

(base64-decode-string "ZnViYXI=") => "fubar" (base64-decode-string "totally bogus") => nil