This is ../../info/elisp, produced by makeinfo version 4.11 from elisp.texi. This is edition 3.0 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 23.2. Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License," with the Front-Cover texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License." (a) The FSF's Back-Cover Text is: "You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom." INFO-DIR-SECTION Emacs START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY  File: elisp, Node: Buffer Contents, Next: Comparing Text, Prev: Near Point, Up: Text 32.2 Examining Buffer Contents ============================== This section describes functions that allow a Lisp program to convert any portion of the text in the buffer into a string. -- Function: buffer-substring start end This function returns a string containing a copy of the text of the region defined by positions START and END in the current buffer. If the arguments are not positions in the accessible portion of the buffer, `buffer-substring' signals an `args-out-of-range' error. 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. Here's an example which assumes Font-Lock mode is not enabled: ---------- 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\n" If the text being copied has any text properties, these are copied into the string along with the characters they belong to. *Note Text Properties::. However, overlays (*note Overlays::) in the buffer and their properties are ignored, not copied. For example, if Font-Lock mode is enabled, you might get results like these: (buffer-substring 1 10) => #("This is t" 0 1 (fontified t) 1 9 (fontified t)) -- Function: buffer-substring-no-properties start end This is like `buffer-substring', except that it does not copy text properties, just the characters themselves. *Note Text Properties::. -- Function: filter-buffer-substring start end &optional delete noprops This function passes the buffer text between START and END through the filter functions specified by the variable `buffer-substring-filters', and returns the value from the last filter function. If `buffer-substring-filters' is `nil', the value is the unaltered text from the buffer, what `buffer-substring' would return. If DELETE is non-`nil', this function deletes the text between START and END after copying it, like `delete-and-extract-region'. If NOPROPS is non-`nil', the final string returned does not include text properties, while the string passed through the filters still includes text properties from the buffer text. Lisp code should use this function instead of `buffer-substring', `buffer-substring-no-properties', or `delete-and-extract-region' when copying into user-accessible data structures such as the kill-ring, X clipboard, and registers. Major and minor modes can add functions to `buffer-substring-filters' to alter such text as it is copied out of the buffer. -- Variable: buffer-substring-filters This variable should be a list of functions that accept a single argument, a string, and return a string. `filter-buffer-substring' passes the buffer substring to the first function in this list, and the return value of each function is passed to the next function. The return value of the last function is used as the return value of `filter-buffer-substring'. As a special convention, point is set to the start of the buffer text being operated on (i.e., the START argument for `filter-buffer-substring') before these functions are called. If this variable is `nil', no filtering is performed. -- Function: buffer-string This function returns the contents of the entire accessible portion of the current buffer as a string. It is equivalent to (buffer-substring (point-min) (point-max)) ---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-string) => "This is the contents of buffer foo\n" -- Function: current-word &optional strict really-word This function returns the symbol (or word) at or near point, as a string. The return value includes no text properties. If the optional argument REALLY-WORD is non-`nil', it finds a word; otherwise, it finds a symbol (which includes both word characters and symbol constituent characters). If the optional argument STRICT is non-`nil', then point must be in or next to the symbol or word--if no symbol or word is there, the function returns `nil'. Otherwise, a nearby symbol or word on the same line is acceptable. -- Function: thing-at-point thing Return the THING around or next to point, as a string. The argument THING is a symbol which specifies a kind of syntactic entity. Possibilities include `symbol', `list', `sexp', `defun', `filename', `url', `word', `sentence', `whitespace', `line', `page', and others. ---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (thing-at-point 'word) => "Peace" (thing-at-point 'line) => "Gentlemen may cry ``Peace! Peace!,''\n" (thing-at-point 'whitespace) => nil  File: elisp, Node: Comparing Text, Next: Insertion, Prev: Buffer Contents, Up: Text 32.3 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 (or a buffer name) and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use `nil' for BUFFER1, BUFFER2, or both to stand for the current buffer. The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings. This function ignores case when comparing characters if `case-fold-search' is non-`nil'. It always ignores text properties. Suppose the current buffer contains the text `foobarbar haha!rara!'; then in this example the two substrings are `rbar ' and `rara!'. The value is 2 because the first substring is greater at the second character. (compare-buffer-substrings nil 6 11 nil 16 21) => 2  File: elisp, Node: Insertion, Next: Commands for Insertion, Prev: Comparing Text, Up: Text 32.4 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. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion "after point" and the latter insertion "before point". Insertion relocates markers that point at positions after the insertion point, so that they stay with the surrounding text (*note Markers::). When a marker points at the place of insertion, insertion may or may not relocate the marker, depending on the marker's insertion type (*note Marker Insertion Types::). Certain special functions such as `insert-before-markers' relocate all such markers to point after the inserted text, regardless of the markers' insertion type. Insertion functions signal an error if the current buffer is read-only or if they insert within read-only text. These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text. The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa--if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. *Note Converting Representations::. -- Function: insert &rest args This function inserts the strings and/or characters ARGS into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all ARGS are either strings or characters. The value is `nil'. -- Function: insert-before-markers &rest args This function inserts the strings and/or characters ARGS into the current buffer, at point, moving point forward. An error is signaled unless all ARGS are either strings or characters. The value is `nil'. This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. If an overlay begins at the insertion point, the inserted text falls outside the overlay; if a nonempty overlay ends at the insertion point, the inserted text falls inside that overlay. -- Function: insert-char character count &optional inherit This function inserts COUNT instances of CHARACTER into the current buffer before point. The argument COUNT should be an integer, and CHARACTER must be a character. The value is `nil'. This function does not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. *Note Converting Representations::. If INHERIT is non-`nil', then the inserted characters inherit sticky text properties from the two characters before and after the insertion point. *Note Sticky Properties::. -- Function: insert-buffer-substring from-buffer-or-name &optional start end This function inserts a portion of buffer FROM-BUFFER-OR-NAME (which must already exist) into the current buffer before point. The text inserted is the region between 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 ---------- -- Function: insert-buffer-substring-no-properties from-buffer-or-name &optional start end This is like `insert-buffer-substring' except that it does not copy any text properties. *Note Sticky Properties::, for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties.  File: elisp, Node: Commands for Insertion, Next: Deletion, Prev: Insertion, Up: Text 32.5 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 accessible contents of FROM-BUFFER-OR-NAME (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is `nil'. -- Command: self-insert-command count This command inserts the last character typed; it does so COUNT times, before point, and returns `nil'. Most printing characters are bound to this command. In routine use, `self-insert-command' is the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap. In an interactive call, COUNT is the numeric prefix argument. Self-insertion translates the input character through `translation-table-for-input'. *Note Translation of Characters::. This command calls `auto-fill-function' whenever that is non-`nil' and the character inserted is in the table `auto-fill-chars' (*note Auto Filling::). This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (*Note Abbrevs::, and *note Syntax Class Table::.) It is also responsible for calling `blink-paren-function' when the inserted character has close parenthesis syntax (*note Blinking::). Do not try substituting your own definition of `self-insert-command' for the standard one. The editor command loop handles this function specially. -- Command: newline &optional number-of-newlines This command inserts newlines into the current buffer before point. If NUMBER-OF-NEWLINES is supplied, that many newline characters are inserted. This function calls `auto-fill-function' if the current column number is greater than the value of `fill-column' and NUMBER-OF-NEWLINES is `nil'. Typically what `auto-fill-function' does is insert a newline; thus, the overall result in this case is to insert two newlines at different places: one at point, and another earlier in the line. `newline' does not auto-fill if NUMBER-OF-NEWLINES is non-`nil'. This command indents to the left margin if that is not zero. *Note Margins::. The value returned is `nil'. In an interactive call, COUNT is the numeric prefix argument. -- Variable: overwrite-mode This variable controls whether overwrite mode is in effect. The value should be `overwrite-mode-textual', `overwrite-mode-binary', or `nil'. `overwrite-mode-textual' specifies textual overwrite mode (treats newlines and tabs specially), and `overwrite-mode-binary' specifies binary overwrite mode (treats newlines and tabs like any other characters).  File: elisp, Node: Deletion, Next: User-Level Deletion, Prev: Commands for Insertion, Up: Text 32.6 Deleting Text ================== Deletion means removing part of the text in a buffer, without saving it in the kill ring (*note The Kill Ring::). Deleted text can't be yanked, but can be reinserted using the undo mechanism (*note Undo::). Some deletion functions do save text in the kill ring in some special cases. All of the deletion functions operate on the current buffer. -- Command: erase-buffer This function deletes the entire text of the current buffer (_not_ just the accessible portion), leaving it empty. If the buffer is read-only, it signals a `buffer-read-only' error; if some of the text in it is read-only, it signals a `text-read-only' error. Otherwise, it deletes the text without asking for any confirmation. It returns `nil'. Normally, deleting a large amount of text from a buffer inhibits further auto-saving of that buffer "because it has shrunk." However, `erase-buffer' does not do this, the idea being that the future text is not really related to the former text, and its size should not be compared with that of the former text. -- Command: delete-region start end This command deletes the text between positions START and END in the current buffer, and returns `nil'. If point was inside the deleted region, its value afterward is START. Otherwise, point relocates with the surrounding text, as markers do. -- Function: delete-and-extract-region start end This function deletes the text between positions START and END in the current buffer, and returns a string containing the text just deleted. If point was inside the deleted region, its value afterward is START. Otherwise, point relocates with the surrounding text, as markers do. -- Command: delete-char count &optional killp This command deletes COUNT characters directly after point, or before point if COUNT is negative. If KILLP is non-`nil', then it saves the deleted characters in the kill ring. In an interactive call, COUNT is the numeric prefix argument, and KILLP is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring. The value returned is always `nil'. -- Command: delete-backward-char count &optional killp This command deletes COUNT characters directly before point, or after point if COUNT is negative. If KILLP is non-`nil', then it saves the deleted characters in the kill ring. In an interactive call, COUNT is the numeric prefix argument, and KILLP is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring. The value returned is always `nil'. -- Command: backward-delete-char-untabify count &optional killp This command deletes COUNT characters backward, changing tabs into spaces. When the next character to be deleted is a tab, it is first replaced with the proper number of spaces to preserve alignment and then one of those spaces is deleted instead of the tab. If KILLP is non-`nil', then the command saves the deleted characters in the kill ring. Conversion of tabs to spaces happens only if COUNT is positive. If it is negative, exactly -COUNT characters after point are deleted. In an interactive call, COUNT is the numeric prefix argument, and KILLP is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring. The value returned is always `nil'. -- User Option: backward-delete-char-untabify-method This option specifies how `backward-delete-char-untabify' should deal with whitespace. Possible values include `untabify', the default, meaning convert a tab to many spaces and delete one; `hungry', meaning delete all tabs and spaces before point with one command; `all' meaning delete all tabs, spaces and newlines before point, and `nil', meaning do nothing special for whitespace characters.  File: elisp, Node: User-Level Deletion, Next: The Kill Ring, Prev: Deletion, Up: Text 32.7 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 &optional backward-only This function deletes all spaces and tabs around point. It returns `nil'. If BACKWARD-ONLY is non-`nil', the function deletes spaces and tabs before point, but not after point. In the following examples, we call `delete-horizontal-space' four times, once on each line, with point between the second and third characters on the line each time. ---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. => nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ---------- -- Command: delete-indentation &optional join-following-p This function joins the line point is on to the previous line, deleting any whitespace at the join and in some cases replacing it with one space. If JOIN-FOLLOWING-P is non-`nil', `delete-indentation' joins this line to the following line instead. The function returns `nil'. If there is a fill prefix, and the second of the lines being joined starts with the prefix, then `delete-indentation' deletes the fill prefix before joining the lines. *Note Margins::. In the example below, point is located on the line starting `events', and it makes no difference if there are trailing spaces in the preceding line. ---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) => nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ---------- After the lines are joined, the function `fixup-whitespace' is responsible for deciding whether to leave a space at the junction. -- Command: fixup-whitespace This function replaces all the horizontal whitespace surrounding point with either one space or no space, according to the context. It returns `nil'. At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. *Note Syntax Class Table::. In the example below, `fixup-whitespace' is called the first time with point before the word `spaces' in the first line. For the second invocation, point is directly after the `('. ---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) => nil (fixup-whitespace) => nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ---------- -- Command: just-one-space &optional n This command replaces any spaces and tabs around point with a single space, or N spaces if N is specified. 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 immediately following it. A blank line is defined as a line containing only tabs and spaces. `delete-blank-lines' returns `nil'.  File: elisp, Node: The Kill Ring, Next: Undo, Prev: User-Level Deletion, Up: Text 32.8 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. *Note Deletion::. Killed text is saved for later yanking in the "kill ring". This is a list that holds a number of recent kills, not just the last text kill. We call this a "ring" because yanking treats it as having elements in a cyclic order. The list is kept in the variable `kill-ring', and can be operated on with the usual functions for lists; there are also specialized functions, described in this section, that treat it as a ring. Some people think this use of the word "kill" is unfortunate, since it refers to operations that specifically _do not_ destroy the entities "killed." This is in sharp contrast to ordinary life, in which death is permanent and "killed" entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term "cut ring" makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now. * Menu: * Kill Ring Concepts:: What text looks like in the kill ring. * Kill Functions:: Functions that kill text. * Yanking:: How yanking is done. * Yank Commands:: Commands that access the kill ring. * Low-Level Kill Ring:: Functions and variables for kill ring access. * Internals of Kill Ring:: Variables that hold kill ring data.  File: elisp, Node: Kill Ring Concepts, Next: Kill Functions, Up: The Kill Ring 32.8.1 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 kill ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one. For yanking, one entry in the kill ring is designated the "front" of the ring. Some yank commands "rotate" the ring by designating a different element as the "front." But this virtual rotation doesn't change the list itself--the most recent entry always comes first in the list.  File: elisp, Node: Kill Functions, Next: Yanking, Prev: Kill Ring Concepts, Up: The Kill Ring 32.8.2 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 determines automatically (using `last-command') whether the previous command was a kill command, and if so appends the killed text to the most recent entry. -- Command: kill-region start end &optional yank-handler This function kills the text in the region defined by START and END. The text is deleted but saved in the kill ring, along with its text properties. The value is always `nil'. In an interactive call, START and END are point and the mark. If the buffer or text is read-only, `kill-region' modifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use a series of kill commands to copy text from a read-only buffer into the kill ring. If YANK-HANDLER is non-`nil', this puts that value onto the string of killed text, as a `yank-handler' text property. *Note Yanking::. Note that if YANK-HANDLER is `nil', any `yank-handler' properties present on the killed text are copied onto the kill ring, like other text properties. -- User Option: kill-read-only-ok If this option is non-`nil', `kill-region' does not signal an error if the buffer or text is read-only. Instead, it simply returns, updating the kill ring but not changing the buffer. -- Command: copy-region-as-kill start end This command saves the region defined by START and END on the kill ring (including text properties), but does not delete the text from the buffer. It returns `nil'. The command does not set `this-command' to `kill-region', so a subsequent kill command does not append to the same kill ring entry. Don't call `copy-region-as-kill' in Lisp programs unless you aim to support Emacs 18. For newer Emacs versions, it is better to use `kill-new' or `kill-append' instead. *Note Low-Level Kill Ring::.  File: elisp, Node: Yanking, Next: Yank Commands, Prev: Kill Functions, Up: The Kill Ring 32.8.3 Yanking -------------- Yanking means inserting text from the kill ring, but it does not insert the text blindly. Yank commands and some other commands use `insert-for-yank' to perform special processing on the text that they copy into the buffer. -- Function: insert-for-yank string This function normally works like `insert' except that it doesn't insert the text properties in the `yank-excluded-properties' list. However, if any part of STRING has a non-`nil' `yank-handler' text property, that property can do various special processing on that part of the text being inserted. -- Function: insert-buffer-substring-as-yank buf &optional start end This function resembles `insert-buffer-substring' except that it doesn't insert the text properties in the `yank-excluded-properties' list. You can put a `yank-handler' text property on all or part of the text to control how it will be inserted if it is yanked. The `insert-for-yank' function looks for that property. The property value must be a list of one to four elements, with the following format (where elements after the first may be omitted): (FUNCTION PARAM NOEXCLUDE UNDO) Here is what the elements do: FUNCTION When FUNCTION is present and non-`nil', it is called instead of `insert' to insert the string. FUNCTION takes one argument--the string to insert. PARAM If PARAM is present and non-`nil', it replaces STRING (or the part of STRING being processed) as the object passed to FUNCTION (or `insert'); for example, if FUNCTION is `yank-rectangle', PARAM should be a list of strings to insert as a rectangle. NOEXCLUDE If NOEXCLUDE is present and non-`nil', the normal removal of the yank-excluded-properties is not performed; instead FUNCTION is responsible for removing those properties. This may be necessary if FUNCTION adjusts point before or after inserting the object. UNDO If UNDO is present and non-`nil', it is a function that will be called by `yank-pop' to undo the insertion of the current object. It is called with two arguments, the start and end of the current region. FUNCTION can set `yank-undo-function' to override the UNDO value.  File: elisp, Node: Yank Commands, Next: Low-Level Kill Ring, Prev: Yanking, Up: The Kill Ring 32.8.4 Functions for Yanking ---------------------------- This section describes higher-level commands for yanking, which are intended primarily for the user but useful also in Lisp programs. Both `yank' and `yank-pop' honor the `yank-excluded-properties' variable and `yank-handler' text property (*note Yanking::). -- Command: yank &optional arg This command inserts before point the text at the front of the kill ring. It sets the mark at the beginning of that text, using `push-mark' (*note The Mark::), and puts point at the end. If ARG is a non-`nil' 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 sets 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, counted cyclically from the front, which is considered the first element for this purpose. `yank' does not alter the contents of the kill ring, unless it used text provided by another program, in which case it pushes that text onto the kill ring. However if ARG is an integer different from one, it rotates the kill ring to place the yanked string at the front. `yank' returns `nil'. -- Command: yank-pop &optional arg This command replaces the just-yanked entry from the kill ring with a different entry from the kill ring. This is allowed only immediately after a `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. It does however rotate the kill ring to place the newly yanked string at the front. If ARG is `nil', then the replacement text is the previous element of the kill ring. If ARG is numeric, the replacement is the ARGth previous kill. If ARG is negative, a more recent kill is the replacement. The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest. The return value is always `nil'. -- Variable: yank-undo-function If this variable is non-`nil', the function `yank-pop' uses its value instead of `delete-region' to delete the text inserted by the previous `yank' or `yank-pop' command. The value must be a function of two arguments, the start and end of the current region. The function `insert-for-yank' automatically sets this variable according to the UNDO element of the `yank-handler' text property, if there is one.  File: elisp, Node: Low-Level Kill Ring, Next: Internals of Kill Ring, Prev: Yank Commands, Up: The Kill Ring 32.8.5 Low-Level Kill Ring -------------------------- These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs, because they take care of interaction with window system selections (*note Window System Selections::). -- Function: current-kill n &optional do-not-move The function `current-kill' rotates the yanking pointer, which designates the "front" of the kill ring, by N places (from newer kills to older ones), and returns the text at that place in the ring. If the optional second argument DO-NOT-MOVE is non-`nil', then `current-kill' doesn't alter the yanking pointer; it just returns the Nth kill, counting from the current yanking pointer. If N is zero, indicating a request for the latest kill, `current-kill' calls the value of `interprogram-paste-function' (documented below) before consulting the kill ring. If that value is a function and calling it returns a string or a list of several string, `current-kill' pushes the strings onto the kill ring and returns the first string. It also sets the yanking pointer to point to the kill-ring entry of the first string returned by `interprogram-paste-function', regardless of the value of DO-NOT-MOVE. Otherwise, `current-kill' does not treat a zero value for N specially: it returns the entry pointed at by the yanking pointer and does not move the yanking pointer. -- Function: kill-new string &optional replace yank-handler This function pushes the text STRING onto the kill ring and makes the yanking pointer point to it. It discards the oldest entry if appropriate. It also invokes the value of `interprogram-cut-function' (see below). If REPLACE is non-`nil', then `kill-new' replaces the first element of the kill ring with STRING, rather than pushing STRING onto the kill ring. If YANK-HANDLER is non-`nil', this puts that value onto the string of killed text, as a `yank-handler' property. *Note Yanking::. Note that if YANK-HANDLER is `nil', then `kill-new' copies any `yank-handler' properties present on STRING onto the kill ring, as it does with other text properties. -- Function: kill-append string before-p &optional yank-handler This function appends the text STRING to the first entry in the kill ring and makes the yanking pointer point to the combined entry. 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). This handles YANK-HANDLER just like `kill-new', except that if YANK-HANDLER is different from the `yank-handler' property of the first entry of the kill ring, `kill-append' pushes the concatenated string onto the kill ring, instead of replacing the original first entry with it. -- 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 front of the kill ring is used. To facilitate support for window systems that support multiple selections, this function may also return a list of strings. In that case, the first string is used as the "most recent kill", and all the other strings are pushed onto the kill ring, for easy access by `yank-pop'. The normal use of this function is to get the window system's primary selection as the most recent kill, even if the selection belongs to another application. *Note Window System Selections::. However, if the selection was provided by the current Emacs session, this function should return `nil'. (If it is hard to tell whether Emacs or some other program provided the selection, it should be good enough to use `string=' to compare it with the last text Emacs provided.) -- 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 required and one optional argument. If the value is a function, `kill-new' and `kill-append' call it with the new first element of the kill ring as the first argument. The second, optional, argument has the same meaning as the PUSH argument to `x-set-cut-buffer' (*note Definition of x-set-cut-buffer::) and only affects the second and later cut buffers. The normal use of this function is to set the window system's primary selection (and first cut buffer) from the newly killed text. *Note Window System Selections::.  File: elisp, Node: Internals of Kill Ring, Prev: Low-Level Kill Ring, Up: The Kill Ring 32.8.6 Internals of the Kill Ring --------------------------------- The variable `kill-ring' holds the kill ring contents, in the form of a list of strings. The most recent kill is always at the front of the list. The `kill-ring-yank-pointer' variable points to a link in the kill ring list, whose CAR is the text to yank next. We say it identifies the "front" of the ring. Moving `kill-ring-yank-pointer' to a different link is called "rotating the kill ring". We call the kill ring a "ring" because the functions that move the yank pointer wrap around from the end of the list to the beginning, or vice-versa. Rotation of the kill ring is virtual; it does not change the value of `kill-ring'. Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables whose values are normally lists. The word "pointer" in the name of the `kill-ring-yank-pointer' indicates that the variable's purpose is to identify one element of the list for use by the next yank command. The value of `kill-ring-yank-pointer' is always `eq' to one of the links in the kill ring list. The element it identifies is the CAR of that link. Kill commands, which change the kill ring, also set this variable to the value of `kill-ring'. The effect is to rotate the ring so that the newly killed text is at the front. Here is a diagram that shows the variable `kill-ring-yank-pointer' pointing to the second entry in the kill ring `("some text" "a different piece of text" "yet older text")'. kill-ring ---- kill-ring-yank-pointer | | | v | --- --- --- --- --- --- --> | | |------> | | |--> | | |--> nil --- --- --- --- --- --- | | | | | | | | -->"yet older text" | | | --> "a different piece of text" | --> "some text" This state of affairs might occur after `C-y' (`yank') immediately followed by `M-y' (`yank-pop'). -- Variable: kill-ring This variable holds the list of killed text sequences, most recently killed first. -- Variable: kill-ring-yank-pointer This variable's value indicates which element of the kill ring is at the "front" of the ring for yanking. More precisely, the value is a tail of the value of `kill-ring', and its CAR is the kill string that `C-y' should yank. -- User Option: kill-ring-max The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for `kill-ring-max' is 60.  File: elisp, Node: Undo, Next: Maintaining Undo, Prev: The Kill Ring, Up: Text 32.9 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 Emacs assumes that undoing is not useful. In particular, any buffer whose name begins with a space has its undo recording off by default; see *note Buffer Names::.) All the primitives that modify the text in the buffer automatically add elements to the front of the undo list, which is in the variable `buffer-undo-list'. -- Variable: buffer-undo-list This buffer-local variable's value is the undo list of the current buffer. A value of `t' disables the recording of undo information. Here are the kinds of elements an undo list can have: `POSITION' This kind of element records a previous value of point; undoing this element moves point to POSITION. Ordinary cursor motion does not make any sort of undo record, but deletion operations use these entries to record where point was before the command. `(BEG . END)' This kind of element indicates how to delete text that was inserted. Upon insertion, the text occupied the range BEG-END in the buffer. `(TEXT . POSITION)' This kind of element indicates how to reinsert text that was deleted. The deleted text itself is the string TEXT. The place to reinsert it is `(abs POSITION)'. If POSITION is positive, point was at the beginning of the deleted text, otherwise it was at the end. `(t HIGH . LOW)' This kind of element indicates that an unmodified buffer became modified. The elements HIGH and LOW are two integers, each recording 16 bits of the visited file's modification time as of when it was previously visited or saved. `primitive-undo' uses those values to determine whether to mark the buffer as unmodified once again; it does so only if the file's modification time matches those numbers. `(nil PROPERTY VALUE BEG . END)' This kind of element records a change in a text property. Here's how you might undo the change: (put-text-property BEG END PROPERTY VALUE) `(MARKER . ADJUSTMENT)' This kind of element records the fact that the marker MARKER was relocated due to deletion of surrounding text, and that it moved ADJUSTMENT character positions. Undoing this element moves MARKER - ADJUSTMENT characters. `(apply FUNNAME . ARGS)' This is an extensible undo item, which is undone by calling FUNNAME with arguments ARGS. `(apply DELTA BEG END FUNNAME . ARGS)' This is an extensible undo item, which records a change limited to the range BEG to END, which increased the size of the buffer by DELTA. It is undone by calling FUNNAME with arguments ARGS. This kind of element enables undo limited to a region to determine whether the element pertains to that region. `nil' This element is a boundary. The elements between two boundaries are called a "change group"; normally, each change group corresponds to one keyboard command, and undo commands normally undo an entire group as a unit. -- Function: undo-boundary This function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns `nil'. The editor command loop automatically creates an undo boundary before each key sequence is executed. Thus, each undo normally undoes the effects of one command. Self-inserting input characters are an exception. The command loop makes a boundary for the first such character; the next 19 consecutive self-inserting input characters do not make boundaries, and then the 20th does, and so on as long as self-inserting characters continue. All buffer modifications add a boundary whenever the previous undoable change was made in some other buffer. This is to ensure that each command makes a boundary in each buffer where it makes changes. Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example, `query-replace' calls `undo-boundary' after each replacement, so that the user can undo individual replacements one by one. -- Variable: undo-in-progress This variable is normally `nil', but the undo commands bind it to `t'. This is so that various kinds of change hooks can tell when they're being called for the sake of undoing. -- 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. `primitive-undo' adds elements to the buffer's undo list when it changes the buffer. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing are not part of this saved value, so they don't interfere with continuing to undo. This function does not bind `undo-in-progress'.  File: elisp, Node: Maintaining Undo, Next: Filling, Prev: Undo, Up: Text 32.10 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-or-name This function discards the undo list of BUFFER-OR-NAME, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of BUFFER-OR-NAME is already disabled, this function has no effect. This function returns `nil'. As editing continues, undo lists get longer and longer. To prevent them from using up all available memory space, garbage collection trims them back to size limits you can set. (For this purpose, the "size" of an undo list measures the cons cells that make up the list, plus the strings of deleted text.) Three variables control the range of acceptable sizes: `undo-limit', `undo-strong-limit' and `undo-outer-limit'. In these variables, size is counted as the number of bytes occupied, which includes both saved text and other data. -- User Option: 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. -- User Option: undo-strong-limit This is the upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all older change groups). There is one exception: the very latest change group is only discarded if it exceeds `undo-outer-limit'. -- User Option: undo-outer-limit If at garbage collection time the undo info for the current command exceeds this limit, Emacs discards the info and displays a warning. This is a last ditch limit to prevent memory overflow. -- User Option: undo-ask-before-discard If this variable is non-`nil', when the undo info exceeds `undo-outer-limit', Emacs asks in the echo area whether to discard the info. The default value is `nil', which means to discard it automatically. This option is mainly intended for debugging. Garbage collection is inhibited while the question is asked, which means that Emacs might leak memory if the user waits too long before answering the question.  File: elisp, Node: Filling, Next: Margins, Prev: Maintaining Undo, Up: Text 32.11 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 (*note Auto Filling::) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly. Most of the commands in this section return values that are not meaningful. All the functions that do filling take note of the current left margin, current right margin, and current justification style (*note Margins::). If the current justification style is `none', the filling functions don't actually do anything. Several of the filling functions have an argument JUSTIFY. If it is non-`nil', that requests some kind of justification. It can be `left', `right', `full', or `center', to request a specific style of justification. If it is `t', that means to use the current justification style for this part of the text (see `current-justification', below). Any other value is treated as `full'. When you call the filling functions interactively, using a prefix argument implies the value `full' for JUSTIFY. -- Command: fill-paragraph &optional justify region This command fills the paragraph at or after point. If JUSTIFY is non-`nil', each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. *Note Paragraphs: (emacs)Paragraphs. When REGION is non-`nil', then if Transient Mark mode is enabled and the mark is active, this command calls `fill-region' to fill all the paragraphs in the region, instead of filling only the current paragraph. When this command is called interactively, REGION is `t'. -- Command: fill-region start end &optional justify nosqueeze to-eop This command fills each of the paragraphs in the region from START to END. It justifies as well if JUSTIFY is non-`nil'. If NOSQUEEZE is non-`nil', that means to leave whitespace other than line breaks untouched. If TO-EOP is non-`nil', that means to keep filling to the end of the paragraph--or the next hard newline, if `use-hard-newlines' is enabled (see below). The variable `paragraph-separate' controls how to distinguish paragraphs. *Note Standard Regexps::. -- Command: fill-individual-paragraphs start end &optional justify citation-regexp This command fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph were indented with spaces, the filled paragraph will remain indented in the same fashion. The first two arguments, START and END, are the beginning and end of the region to be filled. The third and fourth arguments, JUSTIFY and CITATION-REGEXP, are optional. If JUSTIFY is non-`nil', the paragraphs are justified as well as filled. If CITATION-REGEXP is non-`nil', it means the function is operating on a mail message and therefore should not fill the header lines. If CITATION-REGEXP is a string, it is used as a regular expression; if it matches the beginning of a line, that line is treated as a citation marker. Ordinarily, `fill-individual-paragraphs' regards each change in indentation as starting a new paragraph. If `fill-individual-varying-indent' is non-`nil', then only separator lines separate paragraphs. That mode can handle indented paragraphs with additional indentation on the first line. -- User Option: fill-individual-varying-indent This variable alters the action of `fill-individual-paragraphs' as described above. -- Command: fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after This command considers a region of text as a single paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when JUSTIFY is non-`nil'. If NOSQUEEZE is non-`nil', that means to leave whitespace other than line breaks untouched. If SQUEEZE-AFTER is non-`nil', it specifies a position in the region, and means don't canonicalize spaces before that position. In Adaptive Fill mode, this command calls `fill-context-prefix' to choose a fill prefix by default. *Note Adaptive Fill::. -- Command: justify-current-line &optional how eop nosqueeze This command inserts spaces between the words of the current line so that the line ends exactly at `fill-column'. It returns `nil'. The argument HOW, if non-`nil' specifies explicitly the style of justification. It can be `left', `right', `full', `center', or `none'. If it is `t', that means to do follow specified justification style (see `current-justification', below). `nil' means to do full justification. If EOP is non-`nil', that means do only left-justification if `current-justification' specifies full justification. This is used for the last line of a paragraph; even if the paragraph as a whole is fully justified, the last line should not be. If NOSQUEEZE is non-`nil', that means do not change interior whitespace. -- User Option: default-justification This variable's value specifies the style of justification to use for text that doesn't specify a style with a text property. The possible values are `left', `right', `full', `center', or `none'. The default value is `left'. -- Function: current-justification This function returns the proper justification style to use for filling the text around point. This returns the value of the `justification' text property at point, or the variable DEFAULT-JUSTIFICATION if there is no such text property. However, it returns `nil' rather than `none' to mean "don't justify". -- User Option: sentence-end-double-space If this variable is non-`nil', a period followed by just one space does not count as the end of a sentence, and the filling functions avoid breaking the line at such a place. -- User Option: sentence-end-without-period If this variable is non-`nil', a sentence can end without a period. This is used for languages like Thai, where sentences end with a double space but without a period. -- User Option: sentence-end-without-space If this variable is non-`nil', it should be a string of characters that can end a sentence without following spaces. -- Variable: fill-paragraph-function This variable provides a way to override the filling of paragraphs. If its 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: fill-forward-paragraph-function This variable provides a way to override how the filling functions, such as `fill-region' and `fill-paragraph', move forward to the next paragraph. Its value should be a function, which is called with a single argument N, the number of paragraphs to move, and should return the difference between N and the number of paragraphs actually moved. The default value of this variable is `forward-paragraph'. *Note Paragraphs: (emacs)Paragraphs. -- Variable: use-hard-newlines If this variable is non-`nil', the filling functions do not delete newlines that have the `hard' text property. These "hard newlines" act as paragraph separators.  File: elisp, Node: Margins, Next: Adaptive Fill, Prev: Filling, Up: Text 32.12 Margins for Filling ========================= -- User Option: fill-prefix This buffer-local variable, if non-`nil', specifies a string of text that appears at the beginning of normal text lines and should be disregarded when filling them. Any line that fails to start with the fill prefix is considered the start of a paragraph; so is any line that starts with the fill prefix followed by additional whitespace. Lines that start with the fill prefix but no additional whitespace are ordinary text lines that can be filled together. The resulting filled lines also start with the fill prefix. The fill prefix follows the left margin whitespace, if any. -- User Option: fill-column This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification, and centering commands are affected by this variable, including Auto Fill mode (*note Auto Filling::). As a practical matter, if you are writing text for other people to read, you should set `fill-column' to no more than 70. Otherwise the line will be too long for people to read comfortably, and this can make the text seem clumsy. The default value for `fill-column' is 70. -- Command: set-left-margin from to margin This sets the `left-margin' property on the text from FROM to TO to the value MARGIN. If Auto Fill mode is enabled, this command also refills the region to fit the new margin. -- Command: set-right-margin from to margin This sets the `right-margin' property on the text from FROM to TO to the value MARGIN. If Auto Fill mode is enabled, this command also refills the region to fit the new margin. -- Function: current-left-margin This function returns the proper left margin value to use for filling the text around point. The value is the sum of the `left-margin' property of the character at the start of the current line (or zero if none), and the value of the variable `left-margin'. -- Function: current-fill-column This function returns the proper fill column value to use for filling the text around point. The value is the value of the `fill-column' variable, minus the value of the `right-margin' property of the character after point. -- Command: move-to-left-margin &optional n force This function moves point to the left margin of the current line. The column moved to is determined by calling the function `current-left-margin'. If the argument N is non-`nil', `move-to-left-margin' moves forward N-1 lines first. If FORCE is non-`nil', that says to fix the line's indentation if that doesn't match the left margin value. -- Function: delete-to-left-margin &optional from to This function removes left margin indentation from the text between FROM and TO. The amount of indentation to delete is determined by calling `current-left-margin'. In no case does this function delete non-whitespace. If FROM and TO are omitted, they default to the whole buffer. -- Function: indent-to-left-margin This function adjusts the indentation at the beginning of the current line to the value specified by the variable `left-margin'. (That may involve either inserting or deleting whitespace.) This function is value of `indent-line-function' in Paragraph-Indent Text mode. -- User Option: left-margin This variable specifies the base left margin column. In Fundamental mode, `C-j' indents to this column. This variable automatically becomes buffer-local when set in any fashion. -- User Option: fill-nobreak-predicate This variable gives major modes a way to specify not to break a line at certain places. Its value should be a list of functions. Whenever filling considers breaking the line at a certain place in the buffer, it calls each of these functions with no arguments and with point located at that place. If any of the functions returns non-`nil', then the line won't be broken there.  File: elisp, Node: Adaptive Fill, Next: Auto Filling, Prev: Margins, Up: Text 32.13 Adaptive Fill Mode ======================== When "Adaptive Fill Mode" is enabled, Emacs determines the fill prefix automatically from the text in each paragraph being filled rather than using a predetermined value. During filling, this fill prefix gets inserted at the start of the second and subsequent lines of the paragraph as described in *note Filling::, and in *note Auto Filling::. -- User Option: adaptive-fill-mode Adaptive Fill mode is enabled when this variable is non-`nil'. It is `t' by default. -- Function: fill-context-prefix from to This function implements the heart of Adaptive Fill mode; it chooses a fill prefix based on the text between FROM and TO, typically the start and end of a paragraph. It does this by looking at the first two lines of the paragraph, based on the variables described below. Usually, this function returns the fill prefix, a string. However, before doing this, the function makes a final check (not specially mentioned in the following) that a line starting with this prefix wouldn't look like the start of a paragraph. Should this happen, the function signals the anomaly by returning `nil' instead. In detail, `fill-context-prefix' does this: 1. It takes a candidate for the fill prefix from the first line--it tries first the function in `adaptive-fill-function' (if any), then the regular expression `adaptive-fill-regexp' (see below). The first non-`nil' result of these, or the empty string if they're both `nil', becomes the first line's candidate. 2. If the paragraph has as yet only one line, the function tests the validity of the prefix candidate just found. The function then returns the candidate if it's valid, or a string of spaces otherwise. (see the description of `adaptive-fill-first-line-regexp' below). 3. When the paragraph already has two lines, the function next looks for a prefix candidate on the second line, in just the same way it did for the first line. If it doesn't find one, it returns `nil'. 4. The function now compares the two candidate prefixes heuristically: if the non-whitespace characters in the line 2 candidate occur in the same order in the line 1 candidate, the function returns the line 2 candidate. Otherwise, it returns the largest initial substring which is common to both candidates (which might be the empty string). -- User Option: adaptive-fill-regexp Adaptive Fill mode matches this regular expression against the text starting after the left margin whitespace (if any) on a line; the characters it matches are that line's candidate for the fill prefix. The default value matches whitespace with certain punctuation characters intermingled. -- User Option: adaptive-fill-first-line-regexp Used only in one-line paragraphs, this regular expression acts as an additional check of the validity of the one available candidate fill prefix: the candidate must match this regular expression, or match `comment-start-skip'. If it doesn't, `fill-context-prefix' replaces the candidate with a string of spaces "of the same width" as it. The default value of this variable is `"\\`[ \t]*\\'"', which matches only a string of whitespace. The effect of this default is to force the fill prefixes found in one-line paragraphs always to be pure whitespace. -- User Option: adaptive-fill-function You can specify more complex ways of choosing a fill prefix automatically by setting this variable to a function. The function is called with point after the left margin (if any) of a line, and it must preserve point. It should return either "that line's" fill prefix or `nil', meaning it has failed to determine a prefix.  File: elisp, Node: Auto Filling, Next: Sorting, Prev: Adaptive Fill, Up: Text 32.14 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 *note Filling::. Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. *Note Margins::. -- Variable: auto-fill-function The value of this buffer-local variable should be a function (of no arguments) to be called after self-inserting a character from the table `auto-fill-chars'. 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. -- Variable: normal-auto-fill-function This variable specifies the function to use for `auto-fill-function', if and when Auto Fill is turned on. Major modes can set buffer-local values for this variable to alter how Auto Fill works. -- Variable: auto-fill-chars A char table of characters which invoke `auto-fill-function' when self-inserted--space and newline in most language environments. They have an entry `t' in the table.  File: elisp, Node: Sorting, Next: Columns, Prev: Auto Filling, Up: Text 32.15 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 (*note Rearrangement::). The values returned by these functions are not meaningful. -- Function: sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate This function is the general text-sorting routine that subdivides a buffer into records and then sorts them. Most of the commands in this section use this function. To understand how `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, but they must not overlap. A portion of each sort record (perhaps all of it) is designated as the sort key. Sorting rearranges the records in order by their sort keys. Usually, the records are rearranged in order of ascending sort key. If the first argument to the `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. The argument PREDICATE is the function to use to compare keys. If keys are numbers, it defaults to `<'; otherwise it defaults to `string<'. 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 beg end) "Sort lines in region alphabetically;\ argument means descending order. Called from a program, there are three arguments: REVERSE (non-nil means reverse order),\ BEG and END (region to sort). The variable `sort-fold-case' determines\ whether alphabetic case affects the sort order." (interactive "P\nr") (save-excursion (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (let ((inhibit-field-text-motion t)) (sort-subr reverse 'forward-line 'end-of-line))))) 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 () (while (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1)))) 'forward-paragraph) Markers pointing into any sort records are left with no useful position after `sort-subr' returns. -- User Option: sort-fold-case If this variable is non-`nil', `sort-subr' and the other buffer sorting functions ignore case when comparing strings. -- 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 character codes in the Emacs character set. 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 taken as 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. *Note 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 `^.*$' and set KEY-REGEXP to `\'. The resulting expression looks like this: (sort-regexp-fields nil "^.*$" "\\" (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. Fields are separated by whitespace and numbered starting from 1. The specified field must contain a number in each line of the region. Numbers starting with 0 are treated as octal, and numbers starting with `0x' are treated as hexadecimal. If FIELD is negative, sorting is by the -FIELDth field from the end of the line. This command is useful for sorting tables. -- User Option: sort-numeric-base This variable specifies the default radix for `sort-numeric-fields' to parse numbers. -- Command: sort-columns reverse &optional beg end This command sorts the lines in the region between BEG and END, comparing them alphabetically by a certain range of columns. The column positions of BEG 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 BEG, and the entire line containing position END, are included in the region sorted. Note that `sort-columns' rejects text that contains tabs, because tabs could be split across the specified columns. Use `M-x untabify' to convert tabs to spaces before sorting. When possible, this command actually works by calling the `sort' utility program.  File: elisp, Node: Columns, Next: Indentation, Prev: Sorting, Up: Text 32.16 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). These functions count each character according to the number of columns it occupies on the screen. This means control characters count as occupying 2 or 4 columns, depending upon the value of `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. *Note Usual Display::. Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0. They also ignore overlays and text properties, aside from invisibility. -- Function: current-column This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column position is the sum of the widths of all the displayed representations of the characters between the start of the current line and point. For an example of using `current-column', see the description of `count-lines' in *note Text Lines::. -- Command: move-to-column column &optional force 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. When called interactively, COLUMN is the value of prefix numeric argument. If COLUMN is not an integer, an error is signaled. 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; if it is `t', that means to add whitespace at the end of the line to reach that column. The return value is the column number actually moved to.  File: elisp, Node: Indentation, Next: Case Changes, Prev: Columns, Up: Text 32.17 Indentation ================= The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin. * Menu: * Primitive Indent:: Functions used to count and insert indentation. * Mode-Specific Indent:: Customize indentation for different modes. * Region Indent:: Indent all the lines in a region. * Relative Indent:: Indent the current line based on previous lines. * Indent Tabs:: Adjustable, typewriter-like tab stops. * Motion by Indent:: Move to first non-blank character.  File: elisp, Node: Primitive Indent, Next: Mode-Specific Indent, Up: Indentation 32.17.1 Indentation Primitives ------------------------------ This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. *Note Width::, for related functions. -- Function: current-indentation 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 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. The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). *Note Sticky Properties::. -- 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 buffer-local in the current buffer.  File: elisp, Node: Mode-Specific Indent, Next: Region Indent, Prev: Primitive Indent, Up: Indentation 32.17.2 Indentation Controlled by Major Mode -------------------------------------------- An important function of each major mode is to customize the key to indent properly for the language being edited. This section describes the mechanism of the 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 (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'. The default value is `indent-relative'. -- 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 rigid This command calls the function in `indent-line-function' to indent the current line; however, if that function is `indent-to-left-margin', `insert-tab' is called instead. (That is a trivial command that inserts a tab character.) If RIGID is non-`nil', this function also rigidly indents the entire balanced expression that starts at the beginning of the current line, to reflect change in indentation of the current line. -- 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 does, but in some text modes, where 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 indents 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 does, but in some text modes, where inserts a tab, `reindent-then-newline-and-indent' indents to the column specified by `left-margin'.  File: elisp, Node: Region Indent, Next: Relative Indent, Prev: Mode-Specific Indent, Up: Indentation 32.17.3 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 &optional 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. It should take two arguments, the start and end of the region. 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').  File: elisp, Node: Relative Indent, Next: Indent Tabs, Prev: Region Indent, Up: Indentation 32.17.4 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 next 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, by calling `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.  File: elisp, Node: Indent Tabs, Next: Motion by Indent, Prev: Relative Indent, Up: Indentation 32.17.5 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 (*note Usual Display::). Note that the character as input uses this tab stop feature only in a few major modes, such as Text mode. *Note Tab Stops: (emacs)Tab Stops. -- Command: tab-to-tab-stop This command inserts spaces or tabs before point, 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.  File: elisp, Node: Motion by Indent, Prev: Indent Tabs, Up: Indentation 32.17.6 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 &optional arg This command moves point backward ARG lines and then to the first nonblank character on that line. It returns `nil'. If ARG is omitted or `nil', it defaults to 1. -- Command: forward-to-indentation &optional arg This command moves point forward ARG lines and then to the first nonblank character on that line. It returns `nil'. If ARG is omitted or `nil', it defaults to 1.  File: elisp, Node: Case Changes, Next: Text Properties, Prev: Indentation, Up: Text 32.18 Case Changes ================== The case change commands described here work on text in the current buffer. *Note Case Conversion::, for case conversion functions that work on strings and characters. *Note Case Tables::, for how to customize which characters are upper or lower case and how to convert them. -- Command: capitalize-region start end 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 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 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 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 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 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.  File: elisp, Node: Text Properties, Next: Substitution, Prev: Case Changes, Up: Text 32.19 Text Properties ===================== Each character position in a buffer or a string can have a "text property list", much like the property list of a symbol (*note 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 in general 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. Typically each property name symbol is used for a particular purpose; for instance, the text property `face' specifies the faces for displaying the character (*note Special Properties::). The usual way to access the property list is to specify a name and ask what value corresponds to it. If a character has a `category' property, we call it the "property category" of the character. It should be a symbol. The properties of the symbol serve as defaults for the properties of the character. Copying text between strings and buffers preserves the properties along with the characters; this includes such diverse functions as `substring', `insert', and `buffer-substring'. * Menu: * Examining Properties:: Looking at the properties of one character. * Changing Properties:: Setting the properties of a range of text. * Property Search:: Searching for where a property changes value. * Special Properties:: Particular properties with special meanings. * Format Properties:: Properties for representing formatting of text. * Sticky Properties:: How inserted text gets properties from neighboring text. * Lazy Properties:: Computing text properties in a lazy fashion only when text is examined. * Clickable Text:: Using text properties to make regions of text do something when you click on them. * Fields:: The `field' property defines fields within the buffer. * Not Intervals:: Why text properties do not use Lisp-visible text intervals.  File: elisp, Node: Examining Properties, Next: Changing Properties, Up: Text Properties 32.19.1 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. *Note Property Search::, for functions to examine the properties of a number of characters at once. These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1. -- Function: get-text-property pos prop &optional object 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. If there is no PROP property strictly speaking, but the character has a property category that is a symbol, then `get-text-property' returns the PROP property of that symbol. -- Function: get-char-property position prop &optional object This function is like `get-text-property', except that it checks overlays first and then text properties. *Note Overlays::. The argument OBJECT may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If OBJECT is a buffer, then overlays in that buffer are considered first, in order of decreasing priority, followed by the text properties. If OBJECT is a string, only text properties are considered, since strings never have overlays. -- Function: get-char-property-and-overlay position prop &optional object This is like `get-char-property', but gives extra information about the overlay that the property value comes from. Its value is a cons cell whose CAR is the property value, the same value `get-char-property' would return with the same arguments. Its CDR is the overlay in which the property was found, or `nil', if it was found as a text property or not found at all. If POSITION is at the end of OBJECT, both the CAR and the CDR of the value are `nil'. -- Variable: char-property-alias-alist This variable holds an alist which maps property names to a list of alternative property names. If a character does not specify a direct value for a property, the alternative property names are consulted in order; the first non-`nil' value is used. This variable takes precedence over `default-text-properties', and `category' properties take precedence over this variable. -- 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, neither directly, through a category symbol, or through `char-property-alias-alist', the value stored in this list is used instead. Here is an example: (setq default-text-properties '(foo 69) char-property-alias-alist nil) ;; 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  File: elisp, Node: Changing Properties, Next: Property Search, Prev: Examining Properties, Up: Text Properties 32.19.2 Changing Text Properties -------------------------------- The primitives for changing properties apply to a specified range of text in a buffer or string. 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 contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties marks the buffer as modified. Buffer text property changes are undoable also (*note Undo::). Positions in a string start from 0, whereas positions in a buffer start from 1. -- 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 adds or overrides 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 add. It should have the form of a property list (*note 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 (*note 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). To remove all text properties from certain text, use `set-text-properties' and specify `nil' for the new property list. -- Function: remove-list-of-text-properties start end list-of-properties &optional object Like `remove-text-properties' except that LIST-OF-PROPERTIES is a list of property names only, not an alternating list of property names and values. -- 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) Do not rely on the return value of this function. The easiest way to make a string with text properties is with `propertize': -- Function: propertize string &rest properties This function returns a copy of STRING which has the text properties PROPERTIES. These properties apply to all the characters in the string that is returned. Here is an example that constructs a string with a `face' property and a `mouse-face' property: (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) => #("foo" 0 3 (mouse-face bold-italic face italic)) To put different properties on various parts of a string, you can construct each part with `propertize' and then combine them with `concat': (concat (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) " and " (propertize "bar" 'face 'italic 'mouse-face 'bold-italic)) => #("foo and bar" 0 3 (face italic mouse-face bold-italic) 3 8 nil 8 11 (face italic mouse-face bold-italic)) See also the function `buffer-substring-no-properties' (*note Buffer Contents::) which copies text from the buffer but does not copy its properties.  File: elisp, Node: Property Search, Next: Special Properties, Prev: Changing Properties, Up: Text Properties 32.19.3 Text 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. These functions do not move point; instead, they return a position (or `nil'). 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: previous-property-change pos &optional object limit This is like `next-property-change', but scans back 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: next-single-property-change pos prop &optional object limit The function scans text for a change in the PROP property, then returns the position of the change. The scan goes forward from position POS in the string or buffer OBJECT. In other words, this function 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-single-property-change pos prop &optional object limit This is like `next-single-property-change', but scans back 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: next-char-property-change pos &optional limit This is like `next-property-change' except that it considers overlay properties as well as text properties, and if no change is found before the end of the buffer, it returns the maximum buffer position rather than `nil' (in this sense, it resembles the corresponding overlay function `next-overlay-change', rather than `next-property-change'). There is no OBJECT operand because this function operates only on the current buffer. It returns the next address at which either kind of property changes. -- Function: previous-char-property-change pos &optional limit This is like `next-char-property-change', but scans back from POS instead of forward, and returns the minimum buffer position if no change is found. -- Function: next-single-char-property-change pos prop &optional object limit This is like `next-single-property-change' except that it considers overlay properties as well as text properties, and if no change is found before the end of the OBJECT, it returns the maximum valid position in OBJECT rather than `nil'. Unlike `next-char-property-change', this function _does_ have an OBJECT operand; if OBJECT is not a buffer, only text-properties are considered. -- Function: previous-single-char-property-change pos prop &optional object limit This is like `next-single-char-property-change', but scans back from POS instead of forward, and returns the minimum valid position in OBJECT if no change is found. -- 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 does not have a property PROP with value 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.  File: elisp, Node: Special Properties, Next: Format Properties, Prev: Property Search, Up: Text Properties 32.19.4 Properties with Special Meanings ---------------------------------------- Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like. Note: the properties `composition', `display', `invisible' and `intangible' can also cause point to move to an acceptable place, after each Emacs command. *Note Adjusting Point::. `category' If a character has a `category' property, we call it the "property category" of the character. It should be a symbol. The properties of this symbol serve as defaults for the properties of the character. `face' You can use the property `face' to control the font and color of text. *Note Faces::, for more information. In the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities; * A face name (a symbol or string). * A property list of face attributes. This has the form (KEYWORD VALUE ...), where each KEYWORD is a face attribute name and VALUE is a meaningful value for that attribute. With this feature, you do not need to create a face each time you want to specify a particular attribute for certain text. *Note Face Attributes::. * A cons cell with the form `(foreground-color . COLOR-NAME)' or `(background-color . COLOR-NAME)'. These are old, deprecated equivalents for `(:foreground COLOR-NAME)' and `(:background COLOR-NAME)'. Please convert code that uses them. It works to use the latter two forms directly as the value of the `face' property. Font Lock mode (*note Font Lock Mode::) works in most buffers by dynamically updating the `face' property of characters based on the context. `font-lock-face' The `font-lock-face' property is equivalent to the `face' property when Font Lock mode is enabled. When Font Lock mode is disabled, `font-lock-face' has no effect. The `font-lock-mode' property is useful for special modes that implement their own highlighting. *Note Precalculated Fontification::. `mouse-face' The property `mouse-face' is used instead of `face' when the mouse is on or near the character. For this purpose, "near" means that all text between the character and where the mouse is have the same `mouse-face' property value. `fontified' This property says whether the text is ready for display. If `nil', Emacs's redisplay routine calls the functions in `fontification-functions' (*note Auto Faces::) to prepare this part of the buffer before it is displayed. It is used internally by the "just in time" font locking code. `display' This property activates various features that change the way text is displayed. For example, it can make text appear taller or shorter, higher or lower, wider or narrow, or replaced with an image. *Note Display Property::. `help-echo' If text has a string as its `help-echo' property, then when you move the mouse onto that text, Emacs displays that string in the echo area, or in the tooltip window (*note Tooltips: (emacs)Tooltips.). If the value of the `help-echo' property is a function, that function is called with three arguments, WINDOW, OBJECT and POS and should return a help string or `nil' for none. The first argument, WINDOW is the window in which the help was found. The second, OBJECT, is the buffer, overlay or string which had the `help-echo' property. The POS argument is as follows: * If OBJECT is a buffer, POS is the position in the buffer. * If OBJECT is an overlay, that overlay has a `help-echo' property, and POS is the position in the overlay's buffer. * If OBJECT is a string (an overlay string or a string displayed with the `display' property), POS is the position in that string. If the value of the `help-echo' property is neither a function nor a string, it is evaluated to obtain a help string. You can alter the way help text is displayed by setting the variable `show-help-function' (*note Help display::). This feature is used in the mode line and for other active text. `keymap' The `keymap' property specifies an additional keymap for commands. When this keymap applies, it is used for key lookup before the minor mode keymaps and before the buffer's local map. *Note Active Keymaps::. If the property value is a symbol, the symbol's function definition is used as the keymap. The property's value for the character before point applies if it is non-`nil' and rear-sticky, and the property's value for the character after point applies if it is non-`nil' and front-sticky. (For mouse clicks, the position of the click is used instead of the position of point.) `local-map' This property works like `keymap' except that it specifies a keymap to use _instead of_ the buffer's local map. For most purposes (perhaps all purposes), it is better to use the `keymap' property. `syntax-table' The `syntax-table' property overrides what the syntax table says about this particular character. *Note Syntax Properties::. `read-only' If a character has the property `read-only', then modifying that character is not allowed. Any command that would do so gets an error, `text-read-only'. If the property value is a string, that string is used as the error message. Insertion next to a read-only character is an error if inserting ordinary text there would inherit the `read-only' property due to stickiness. Thus, you can control permission to insert next to read-only text by controlling the stickiness. *Note Sticky Properties::. Since changing properties counts as modifying the buffer, it is not possible to remove a `read-only' property unless you know the special trick: bind `inhibit-read-only' to a non-`nil' value and then remove the property. *Note Read Only Buffers::. `invisible' A non-`nil' `invisible' property can make a character invisible on the screen. *Note Invisible Text::, for details. `intangible' If a group of consecutive characters have equal and non-`nil' `intangible' properties, then you cannot place point between them. If you try to move point forward into the group, point actually moves to the end of the group. If you try to move point backward into the group, point actually moves to the start of the group. If consecutive characters have unequal non-`nil' `intangible' properties, they belong to separate groups; each group is separately treated as described above. When the variable `inhibit-point-motion-hooks' is non-`nil', the `intangible' property is ignored. `field' Consecutive characters with the same `field' property constitute a "field". Some motion functions including `forward-word' and `beginning-of-line' stop moving at a field boundary. *Note Fields::. `cursor' Normally, the cursor is displayed at the end of any overlay and text property strings present at the current buffer position. You can place the cursor on any desired character of these strings by giving that character a non-`nil' `cursor' text property. In addition, if the value of the `cursor' property of an overlay string is an integer number, it specifies the number of buffer's character positions associated with the overlay string; this way, Emacs will display the cursor on the character with that property regardless of whether the current buffer position is actually covered by the overlay. Specifically, if the value of the `cursor' property of a character is the number N, the cursor will be displayed on this character for any buffer position in the range `[OVPOS..OVPOS+N]', where OVPOS is the starting buffer position covered by the overlay (*note Managing Overlays::). `pointer' This specifies a specific pointer shape when the mouse pointer is over this text or image. *Note Pointer Shape::, for possible pointer shapes. `line-spacing' A newline can have a `line-spacing' text or overlay property that controls the height of the display line ending with that newline. The property value overrides the default frame line spacing and the buffer local `line-spacing' variable. *Note Line Height::. `line-height' A newline can have a `line-height' text or overlay property that controls the total height of the display line ending in that newline. *Note Line Height::. `wrap-prefix' If text has a `wrap-prefix' property, the prefix it defines will be added at display-time to the beginning of every continuation line due to text wrapping (so if lines are truncated, the wrap-prefix is never used). It may be a string, an image, or a stretch-glyph such as used by the `display' text-property. *Note Display Property::. A wrap-prefix may also be specified for an entire buffer using the `wrap-prefix' buffer-local variable (however, a `wrap-prefix' text-property takes precedence over the value of the `wrap-prefix' variable). *Note Truncation::. `line-prefix' If text has a `line-prefix' property, the prefix it defines will be added at display-time to the beginning of every non-continuation line. It may be a string, an image, or a stretch-glyph such as used by the `display' text-property. *Note Display Property::. A line-prefix may also be specified for an entire buffer using the `line-prefix' buffer-local variable (however, a `line-prefix' text-property takes precedence over the value of the `line-prefix' variable). *Note Truncation::. `modification-hooks' If a character has the property `modification-hooks', then its value should be a list of functions; modifying that character calls all of those functions. Each function receives two arguments: the beginning and end of the part of the buffer being modified. Note that if a particular modification hook function appears on several characters being modified by a single primitive, you can't predict how many times the function will be called. If these functions modify the buffer, they should bind `inhibit-modification-hooks' to `t' around doing so, to avoid confusing the internal mechanism that calls these hooks. Overlays also support the `modification-hooks' property, but the details are somewhat different (*note Overlay Properties::). `insert-in-front-hooks' `insert-behind-hooks' The operation of inserting text in a buffer also calls the functions listed in the `insert-in-front-hooks' property of the following character and in the `insert-behind-hooks' property of the preceding character. These functions receive two arguments, the beginning and end of the inserted text. The functions are called _after_ the actual insertion takes place. See also *note Change Hooks::, for other hooks that are called when you change text in a buffer. `point-entered' `point-left' The special properties `point-entered' and `point-left' record hook functions that report motion of point. Each time point moves, Emacs compares these two property values: * the `point-left' property of the character after the old location, and * the `point-entered' property of the character after the new location. If these two values differ, each of them is called (if not `nil') with two arguments: the old value of point, and the new one. The same comparison is made for the characters before the old and new locations. The result may be to execute two `point-left' functions (which may be the same function) and/or two `point-entered' functions (which may be the same function). In any case, all the `point-left' functions are called first, followed by all the `point-entered' functions. It is possible with `char-after' to examine characters at various buffer positions without moving point to those positions. Only an actual change in the value of point runs these hook functions. -- Variable: inhibit-point-motion-hooks When this variable is non-`nil', `point-left' and `point-entered' hooks are not run, and the `intangible' property has no effect. Do not set this variable globally; bind it with `let'. -- Variable: show-help-function If this variable is non-`nil', it specifies a function called to display help strings. These may be `help-echo' properties, menu help strings (*note Simple Menu Items::, *note Extended Menu Items::), or tool bar help strings (*note Tool Bar::). The specified function is called with one argument, the help string to display. Tooltip mode (*note Tooltips: (emacs)Tooltips.) provides an example. `composition' This text property is used to display a sequence of characters as a single glyph composed from components. But the value of the property itself is completely internal to Emacs and should not be manipulated directly by, for instance, `put-text-property'.  File: elisp, Node: Format Properties, Next: Sticky Properties, Prev: Special Properties, Up: Text Properties 32.19.5 Formatted Text Properties --------------------------------- These text properties affect the behavior of the fill commands. They are used for representing formatted text. *Note Filling::, and *note Margins::. `hard' If a newline character has this property, it is a "hard" newline. The fill commands do not alter hard newlines and do not move words across them. However, this property takes effect only if the `use-hard-newlines' minor mode is enabled. *Note Hard and Soft Newlines: (emacs)Hard and Soft Newlines. `right-margin' This property specifies an extra right margin for filling this part of the text. `left-margin' This property specifies an extra left margin for filling this part of the text. `justification' This property specifies the style of justification for filling this part of the text.  File: elisp, Node: Sticky Properties, Next: Lazy Properties, Prev: Format Properties, Up: Text Properties 32.19.6 Stickiness of Text Properties ------------------------------------- Self-inserting characters normally take on the same properties as the preceding character. This is called "inheritance" of properties. In a Lisp program, you can do insertion with inheritance or without, depending on your choice of insertion primitive. The ordinary text insertion functions such as `insert' do not inherit any properties. They insert text with precisely the properties of the string being inserted, and no others. This is correct for programs that copy text from one context to another--for example, into or out of the kill ring. To insert with inheritance, use the special primitives described in this section. Self-inserting characters inherit properties because they work using these primitives. When you do insertion with inheritance, _which_ properties are inherited, and from where, depends on which properties are "sticky". Insertion after a character inherits those of its properties that are "rear-sticky". Insertion before a character inherits those of its properties that are "front-sticky". When both sides offer different sticky values for the same property, the previous character's value takes precedence. By default, a text property is rear-sticky but not front-sticky; thus, the default is to inherit all the properties of the preceding character, and nothing from the following character. You can control the stickiness of various text properties with two specific text properties, `front-sticky' and `rear-nonsticky', and with the variable `text-property-default-nonsticky'. You can use the variable to specify a different default for a given property. You can use those two text properties to make any specific properties sticky or nonsticky in any particular part of the text. If a character's `front-sticky' property is `t', then all its properties are front-sticky. If the `front-sticky' property is a list, then the sticky properties of the character are those whose names are in the list. For example, if a character has a `front-sticky' property whose value is `(face read-only)', then insertion before the character can inherit its `face' property and its `read-only' property, but no others. The `rear-nonsticky' property works the opposite way. Most properties are rear-sticky by default, so the `rear-nonsticky' property says which properties are _not_ rear-sticky. If a character's `rear-nonsticky' property is `t', then none of its properties are rear-sticky. If the `rear-nonsticky' property is a list, properties are rear-sticky _unless_ their names are in the list. -- Variable: text-property-default-nonsticky This variable holds an alist which defines the default rear-stickiness of various text properties. Each element has the form `(PROPERTY . NONSTICKINESS)', and it defines the stickiness of a particular text property, PROPERTY. If NONSTICKINESS is non-`nil', this means that the property PROPERTY is rear-nonsticky by default. Since all properties are front-nonsticky by default, this makes PROPERTY nonsticky in both directions by default. The text properties `front-sticky' and `rear-nonsticky', when used, take precedence over the default NONSTICKINESS specified in `text-property-default-nonsticky'. Here are the functions that insert text with inheritance of properties: -- Function: insert-and-inherit &rest strings Insert the strings STRINGS, just like the function `insert', but inherit any sticky properties from the adjoining text. -- Function: insert-before-markers-and-inherit &rest strings Insert the strings STRINGS, just like the function `insert-before-markers', but inherit any sticky properties from the adjoining text. *Note Insertion::, for the ordinary insertion functions which do not inherit.  File: elisp, Node: Lazy Properties, Next: Clickable Text, Prev: Sticky Properties, Up: Text Properties 32.19.7 Lazy Computation of Text Properties ------------------------------------------- Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them. The primitive that extracts text from the buffer along with its properties is `buffer-substring'. Before examining the properties, this function runs the abnormal hook `buffer-access-fontify-functions'. -- Variable: buffer-access-fontify-functions This variable holds a list of functions for computing text properties. Before `buffer-substring' copies the text and text properties for a portion of the buffer, it calls all the functions in this list. Each of the functions receives two arguments that specify the range of the buffer being accessed. (The buffer itself is always the current buffer.) The function `buffer-substring-no-properties' does not call these functions, since it ignores text properties anyway. In order to prevent the hook functions from being called more than once for the same part of the buffer, you can use the variable `buffer-access-fontified-property'. -- Variable: buffer-access-fontified-property If this variable's value is non-`nil', it is a symbol which is used as a text property name. A non-`nil' value for that text property means, "the other text properties for this character have already been computed." If all the characters in the range specified for `buffer-substring' have a non-`nil' value for this property, `buffer-substring' does not call the `buffer-access-fontify-functions' functions. It assumes these characters already have the right text properties, and just copies the properties they already have. The normal way to use this feature is that the `buffer-access-fontify-functions' functions add this property, as well as others, to the characters they operate on. That way, they avoid being called over and over for the same text.  File: elisp, Node: Clickable Text, Next: Fields, Prev: Lazy Properties, Up: Text Properties 32.19.8 Defining Clickable Text ------------------------------- "Clickable text" is text that can be clicked, with either the mouse or via a keyboard command, to produce some result. Many major modes use clickable text to implement textual hyper-links, or "links" for short. The easiest way to insert and manipulate links is to use the `button' package. *Note Buttons::. In this section, we will explain how to manually set up clickable text in a buffer, using text properties. For simplicity, we will refer to the clickable text as a "link". Implementing a link involves three separate steps: (1) indicating clickability when the mouse moves over the link; (2) making `RET' or `Mouse-2' on that link do something; and (3) setting up a `follow-link' condition so that the link obeys `mouse-1-click-follows-link'. To indicate clickability, add the `mouse-face' text property to the text of the link; then Emacs will highlight the link when the mouse moves over it. In addition, you should define a tooltip or echo area message, using the `help-echo' text property. *Note Special Properties::. For instance, here is how Dired indicates that file names are clickable: (if (dired-move-to-filename) (add-text-properties (point) (save-excursion (dired-move-to-end-of-filename) (point)) '(mouse-face highlight help-echo "mouse-2: visit this file in other window"))) To make the link clickable, bind and `Mouse-2' to commands that perform the desired action. Each command should check to see whether it was called on a link, and act accordingly. For instance, Dired's major mode keymap binds `Mouse-2' to the following command: (defun dired-mouse-find-file-other-window (event) "In Dired, visit the file or directory name you click on." (interactive "e") (let ((window (posn-window (event-end event))) (pos (posn-point (event-end event))) file) (if (not (windowp window)) (error "No file chosen")) (with-current-buffer (window-buffer window) (goto-char pos) (setq file (dired-get-file-for-visit))) (if (file-directory-p file) (or (and (cdr dired-subdir-alist) (dired-goto-subdir file)) (progn (select-window window) (dired-other-window file))) (select-window window) (find-file-other-window (file-name-sans-versions file t))))) This command uses the functions `posn-window' and `posn-point' to determine where the click occurred, and `dired-get-file-for-visit' to determine which file to visit. Instead of binding the mouse command in a major mode keymap, you can bind it within the link text, using the `keymap' text property (*note Special Properties::). For instance: (let ((map (make-sparse-keymap))) (define-key map [mouse-2] 'operate-this-button) (put-text-property link-start link-end 'keymap map)) With this method, you can easily define different commands for different links. Furthermore, the global definition of and `Mouse-2' remain available for the rest of the text in the buffer. The basic Emacs command for clicking on links is `Mouse-2'. However, for compatibility with other graphical applications, Emacs also recognizes `Mouse-1' clicks on links, provided the user clicks on the link quickly without moving the mouse. This behavior is controlled by the user option `mouse-1-click-follows-link'. *Note Mouse References: (emacs)Mouse References. To set up the link so that it obeys `mouse-1-click-follows-link', you must either (1) apply a `follow-link' text or overlay property to the link text, or (2) bind the `follow-link' event to a keymap (which can be a major mode keymap or a local keymap specified via the `keymap' text property). The value of the `follow-link' property, or the binding for the `follow-link' event, acts as a "condition" for the link action. This condition tells Emacs two things: the circumstances under which a `Mouse-1' click should be regarded as occurring "inside" the link, and how to compute an "action code" that says what to translate the `Mouse-1' click into. The link action condition can be one of the following: `mouse-face' If the condition is the symbol `mouse-face', a position is inside a link if there is a non-`nil' `mouse-face' property at that position. The action code is always `t'. For example, here is how Info mode handles : (define-key Info-mode-map [follow-link] 'mouse-face) a function If the condition is a function, FUNC, then a position POS is inside a link if `(FUNC POS)' evaluates to non-`nil'. The value returned by FUNC serves as the action code. For example, here is how pcvs enables `Mouse-1' to follow links on file names only: (define-key map [follow-link] (lambda (pos) (eq (get-char-property pos 'face) 'cvs-filename-face))) anything else If the condition value is anything else, then the position is inside a link and the condition itself is the action code. Clearly, you should specify this kind of condition only when applying the condition via a text or property overlay on the link text (so that it does not apply to the entire buffer). The action code tells `Mouse-1' how to follow the link: a string or vector If the action code is a string or vector, the `Mouse-1' event is translated into the first element of the string or vector; i.e., the action of the `Mouse-1' click is the local or global binding of that character or symbol. Thus, if the action code is `"foo"', `Mouse-1' translates into `f'. If it is `[foo]', `Mouse-1' translates into . anything else For any other non-`nil' action code, the `Mouse-1' event is translated into a `Mouse-2' event at the same position. To define `Mouse-1' to activate a button defined with `define-button-type', give the button a `follow-link' property. The property value should be a link action condition, as described above. *Note Buttons::. For example, here is how Help mode handles `Mouse-1': (define-button-type 'help-xref 'follow-link t 'action #'help-button-action) To define `Mouse-1' on a widget defined with `define-widget', give the widget a `:follow-link' property. The property value should be a link action condition, as described above. For example, here is how the `link' widget specifies that a click shall be translated to : (define-widget 'link 'item "An embedded link." :button-prefix 'widget-link-prefix :button-suffix 'widget-link-suffix :follow-link "\C-m" :help-echo "Follow the link." :format "%[%t%]") -- Function: mouse-on-link-p pos This function returns non-`nil' if position POS in the current buffer is on a link. POS can also be a mouse event location, as returned by `event-start' (*note Accessing Mouse::).  File: elisp, Node: Fields, Next: Not Intervals, Prev: Clickable Text, Up: Text Properties 32.19.9 Defining and Using Fields --------------------------------- A field is a range of consecutive characters in the buffer that are identified by having the same value (comparing with `eq') of the `field' property (either a text-property or an overlay property). This section describes special functions that are available for operating on fields. You specify a field with a buffer position, POS. We think of each field as containing a range of buffer positions, so the position you specify stands for the field containing that position. When the characters before and after POS are part of the same field, there is no doubt which field contains POS: the one those characters both belong to. When POS is at a boundary between fields, which field it belongs to depends on the stickiness of the `field' properties of the two surrounding characters (*note Sticky Properties::). The field whose property would be inherited by text inserted at POS is the field that contains POS. There is an anomalous case where newly inserted text at POS would not inherit the `field' property from either side. This happens if the previous character's `field' property is not rear-sticky, and the following character's `field' property is not front-sticky. In this case, POS belongs to neither the preceding field nor the following field; the field functions treat it as belonging to an empty field whose beginning and end are both at POS. In all of these functions, if POS is omitted or `nil', the value of point is used by default. If narrowing is in effect, then POS should fall within the accessible portion. *Note Narrowing::. -- Function: field-beginning &optional pos escape-from-edge limit This function returns the beginning of the field specified by POS. If POS is at the beginning of its field, and ESCAPE-FROM-EDGE is non-`nil', then the return value is always the beginning of the preceding field that _ends_ at POS, regardless of the stickiness of the `field' properties around POS. If LIMIT is non-`nil', it is a buffer position; if the beginning of the field is before LIMIT, then LIMIT will be returned instead. -- Function: field-end &optional pos escape-from-edge limit This function returns the end of the field specified by POS. If POS is at the end of its field, and ESCAPE-FROM-EDGE is non-`nil', then the return value is always the end of the following field that _begins_ at POS, regardless of the stickiness of the `field' properties around POS. If LIMIT is non-`nil', it is a buffer position; if the end of the field is after LIMIT, then LIMIT will be returned instead. -- Function: field-string &optional pos This function returns the contents of the field specified by POS, as a string. -- Function: field-string-no-properties &optional pos This function returns the contents of the field specified by POS, as a string, discarding text properties. -- Function: delete-field &optional pos This function deletes the text of the field specified by POS. -- Function: constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property This function "constrains" NEW-POS to the field that OLD-POS belongs to--in other words, it returns the position closest to NEW-POS that is in the same field as OLD-POS. If NEW-POS is `nil', then `constrain-to-field' uses the value of point instead, and moves point to the resulting position as well as returning it. If OLD-POS is at the boundary of two fields, then the acceptable final positions depend on the argument ESCAPE-FROM-EDGE. If ESCAPE-FROM-EDGE is `nil', then NEW-POS must be in the field whose `field' property equals what new characters inserted at OLD-POS would inherit. (This depends on the stickiness of the `field' property for the characters before and after OLD-POS.) If ESCAPE-FROM-EDGE is non-`nil', NEW-POS can be anywhere in the two adjacent fields. Additionally, if two fields are separated by another field with the special value `boundary', then any point within this special field is also considered to be "on the boundary." Commands like `C-a' with no argumemt, that normally move backward to a specific kind of location and stay there once there, probably should specify `nil' for ESCAPE-FROM-EDGE. Other motion commands that check fields should probably pass `t'. If the optional argument ONLY-IN-LINE is non-`nil', and constraining NEW-POS in the usual way would move it to a different line, NEW-POS is returned unconstrained. This used in commands that move by line, such as `next-line' and `beginning-of-line', so that they respect field boundaries only in the case where they can still move to the right line. If the optional argument INHIBIT-CAPTURE-PROPERTY is non-`nil', and OLD-POS has a non-`nil' property of that name, then any field boundaries are ignored. You can cause `constrain-to-field' to ignore all field boundaries (and so never constrain anything) by binding the variable `inhibit-field-text-motion' to a non-`nil' value.  File: elisp, Node: Not Intervals, Prev: Fields, Up: Text Properties 32.19.10 Why Text Properties are not Intervals ---------------------------------------------- Some editors that support adding attributes to text in the buffer do so by letting the user specify "intervals" within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification. If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property. Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two. Suppose we "fix" this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two. Insertion of text at the border between intervals also raises questions that have no satisfactory answer. However, it is easy to arrange for editing to behave consistently for questions of the form, "What are the properties of this character?" So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end. In practice, you can usually use the text property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. *Note Property Search::. Emacs also provides explicit intervals as a presentation feature; see *note Overlays::.  File: elisp, Node: Substitution, Next: Transposition, Prev: Text Properties, Up: Text 32.20 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 was useful for controlling the old selective display feature (*note 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 ---------- -- Command: 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 is a string or a char-table; `(aref TABLE OCHAR)' gives the translated character corresponding to OCHAR. If TABLE is a string, 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.  File: elisp, Node: Registers, Next: Base 64, Prev: Transposition, Up: Text 32.21 Registers =============== A register is a sort of variable used in Emacs editing that can hold a variety of different kinds of values. Each register is named by a single character. All ASCII characters and their meta variants (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 the character that is its name. -- Variable: register-alist This variable is an alist of elements of the form `(NAME . CONTENTS)'. Normally, there is one element for each Emacs register that has been used. The object NAME is a character (an integer) identifying the register. The CONTENTS of a register can have several possible types: a number A number stands for itself. If `insert-register' finds a number in the register, it converts the number to decimal. a marker A marker represents a buffer position to jump to. a string A string is text saved in the register. a rectangle A rectangle is represented by a list of strings. `(WINDOW-CONFIGURATION POSITION)' This represents a window configuration to restore in one frame, and a position to jump to in the current buffer. `(FRAME-CONFIGURATION POSITION)' This represents a frame configuration to restore, and a position to jump to in the current buffer. (file FILENAME) This represents a file to visit; jumping to this value visits file FILENAME. (file-query FILENAME POSITION) This represents a file to visit and a position in it; jumping to this value visits file FILENAME and goes to buffer position POSITION. Restoring this type of position asks the user for confirmation first. The functions in this section return unpredictable values unless otherwise stated. -- Function: get-register reg This function returns the contents of the register REG, or `nil' if it has no contents. -- Function: set-register reg value This function sets the contents of register REG 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 reg This command displays what is contained in register REG. -- Command: insert-register reg &optional beforep This command inserts contents of register REG into the current buffer. Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument 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.  File: elisp, Node: Transposition, Next: Registers, Prev: Substitution, Up: Text 32.22 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.  File: elisp, Node: Base 64, Next: MD5 Checksum, Prev: Registers, Up: Text 32.23 Base 64 Encoding ====================== Base 64 code is used in email to encode a sequence of 8-bit bytes as a longer sequence of ASCII graphic characters. It is defined in Internet RFC(1)2045. This section describes the functions for converting to and from this code. -- Command: base64-encode-region beg end &optional no-line-break This function converts the region from BEG to END into base 64 code. It returns the length of the encoded text. An error is signaled if a character in the region is multibyte, i.e. in a multibyte buffer the region must contain only characters from the charsets `ascii', `eight-bit-control' and `eight-bit-graphic'. Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument NO-LINE-BREAK is non-`nil', these newlines are not added, so the output is just one long line. -- Command: base64-encode-string string &optional no-line-break This function converts the string STRING into base 64 code. It returns a string containing the encoded text. As for `base64-encode-region', an error is signaled if a character in the string is multibyte. Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument NO-LINE-BREAK is non-`nil', these newlines are not added, so the result string is just one long line. -- Function: base64-decode-region beg end This function converts the region from BEG to END from base 64 code into the corresponding decoded text. It returns the length of the decoded text. The decoding functions ignore newline characters in the encoded text. -- Function: base64-decode-string string This function converts the string STRING from base 64 code into the corresponding decoded text. It returns a unibyte string containing the decoded text. The decoding functions ignore newline characters in the encoded text. ---------- Footnotes ---------- (1) An RFC, an acronym for "Request for Comments", is a numbered Internet informational document describing a standard. RFCs are usually written by technical experts acting on their own initiative, and are traditionally written in a pragmatic, experience-driven manner.  File: elisp, Node: MD5 Checksum, Next: Atomic Changes, Prev: Base 64, Up: Text 32.24 MD5 Checksum ================== MD5 cryptographic checksums, or "message digests", are 128-bit "fingerprints" of a document or program. They are used to verify that you have an exact and unaltered copy of the data. The algorithm to calculate the MD5 message digest is defined in Internet RFC(1)1321. This section describes the Emacs facilities for computing message digests. -- Function: md5 object &optional start end coding-system noerror This function returns the MD5 message digest of OBJECT, which should be a buffer or a string. The two optional arguments START and END are character positions specifying the portion of OBJECT to compute the message digest for. If they are `nil' or omitted, the digest is computed for the whole of OBJECT. The function `md5' does not compute the message digest directly from the internal Emacs representation of the text (*note Text Representations::). Instead, it encodes the text using a coding system, and computes the message digest from the encoded text. The optional fourth argument CODING-SYSTEM specifies which coding system to use for encoding the text. It should be the same coding system that you used to read the text, or that you used or will use when saving or sending the text. *Note Coding Systems::, for more information about coding systems. If CODING-SYSTEM is `nil' or omitted, the default depends on OBJECT. If OBJECT is a buffer, the default for CODING-SYSTEM is whatever coding system would be chosen by default for writing this text into a file. If OBJECT is a string, the user's most preferred coding system (*note prefer-coding-system: (emacs)Recognize Coding.) is used. Normally, `md5' signals an error if the text can't be encoded using the specified or chosen coding system. However, if NOERROR is non-`nil', it silently uses `raw-text' coding instead. ---------- Footnotes ---------- (1) For an explanation of what is an RFC, see the footnote in *note Base 64::.  File: elisp, Node: Atomic Changes, Next: Change Hooks, Prev: MD5 Checksum, Up: Text 32.25 Atomic Change Groups ========================== In data base terminology, an "atomic" change is an indivisible change--it can succeed entirely or it can fail entirely, but it cannot partly succeed. A Lisp program can make a series of changes to one or several buffers as an "atomic change group", meaning that either the entire series of changes will be installed in their buffers or, in case of an error, none of them will be. To do this for one buffer, the one already current, simply write a call to `atomic-change-group' around the code that makes the changes, like this: (atomic-change-group (insert foo) (delete-region x y)) If an error (or other nonlocal exit) occurs inside the body of `atomic-change-group', it unmakes all the changes in that buffer that were during the execution of the body. This kind of change group has no effect on any other buffers--any such changes remain. If you need something more sophisticated, such as to make changes in various buffers constitute one atomic group, you must directly call lower-level functions that `atomic-change-group' uses. -- Function: prepare-change-group &optional buffer This function sets up a change group for buffer BUFFER, which defaults to the current buffer. It returns a "handle" that represents the change group. You must use this handle to activate the change group and subsequently to finish it. To use the change group, you must "activate" it. You must do this before making any changes in the text of BUFFER. -- Function: activate-change-group handle This function activates the change group that HANDLE designates. After you activate the change group, any changes you make in that buffer become part of it. Once you have made all the desired changes in the buffer, you must "finish" the change group. There are two ways to do this: you can either accept (and finalize) all the changes, or cancel them all. -- Function: accept-change-group handle This function accepts all the changes in the change group specified by HANDLE, making them final. -- Function: cancel-change-group handle This function cancels and undoes all the changes in the change group specified by HANDLE. Your code should use `unwind-protect' to make sure the group is always finished. The call to `activate-change-group' should be inside the `unwind-protect', in case the user types `C-g' just after it runs. (This is one reason why `prepare-change-group' and `activate-change-group' are separate functions, because normally you would call `prepare-change-group' before the start of that `unwind-protect'.) Once you finish the group, don't use the handle again--in particular, don't try to finish the same group twice. To make a multibuffer change group, call `prepare-change-group' once for each buffer you want to cover, then use `nconc' to combine the returned values, like this: (nconc (prepare-change-group buffer-1) (prepare-change-group buffer-2)) You can then activate the multibuffer change group with a single call to `activate-change-group', and finish it with a single call to `accept-change-group' or `cancel-change-group'. Nested use of several change groups for the same buffer works as you would expect. Non-nested use of change groups for the same buffer will get Emacs confused, so don't let it happen; the first change group you start for any given buffer should be the last one finished.  File: elisp, Node: Change Hooks, Prev: Atomic Changes, Up: Text 32.26 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). See also *note Special Properties::, for how to detect changes to specific parts of the text. The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them. -- Variable: before-change-functions This variable holds a list of 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 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. All three arguments are integers. The buffer that's about to change is always the current buffer. The length of the old text is the difference between the buffer positions before and after that text as it was before the change. As for the changed text, its length is simply the difference between the first two arguments. Output of messages into the `*Messages*' buffer does not call these functions. -- Macro: combine-after-change-calls body... The macro executes BODY normally, but arranges to call the after-change functions just once for a series of several changes--if that seems safe. If a program makes several text changes in the same area of the buffer, using the macro `combine-after-change-calls' around that part of the program can make it run considerably faster when after-change hooks are in use. When the after-change hooks are ultimately called, the arguments specify a portion of the buffer including all of the changes made within the `combine-after-change-calls' body. *Warning:* You must not alter the values of `after-change-functions' within the body of a `combine-after-change-calls' form. *Warning:* if the changes you combine occur in widely scattered parts of the buffer, this will still work, but it is not advisable, because it may lead to inefficient behavior for some change hook 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. -- Variable: inhibit-modification-hooks If this variable is non-`nil', all of the change hooks are disabled; none of them run. This affects all the hook variables described above in this section, as well as the hooks attached to certain special text properties (*note Special Properties::) and overlay properties (*note Overlay Properties::). Also, this variable is bound to non-`nil' while running those same hook variables, so that by default modifying the buffer from a modification hook does not cause other modification hooks to be run. If you do want modification hooks to be run in a particular piece of code that is itself run from a modification hook, then rebind locally `inhibit-modification-hooks' to `nil'.  File: elisp, Node: Non-ASCII Characters, Next: Searching and Matching, Prev: Text, Up: Top 33 Non-ASCII Characters *********************** This chapter covers the special issues relating to characters and how they are stored in strings and buffers. * Menu: * Text Representations:: How Emacs represents text. * Converting Representations:: Converting unibyte to multibyte and vice versa. * Selecting a Representation:: Treating a byte sequence as unibyte or multi. * Character Codes:: How unibyte and multibyte relate to codes of individual characters. * Character Properties:: Character attributes that define their behavior and handling. * Character Sets:: The space of possible character codes is divided into various character sets. * Scanning Charsets:: Which character sets are used in a buffer? * Translation of Characters:: Translation tables are used for conversion. * Coding Systems:: Coding systems are conversions for saving files. * Input Methods:: Input methods allow users to enter various non-ASCII characters without special keyboards. * Locales:: Interacting with the POSIX locale.  File: elisp, Node: Text Representations, Next: Converting Representations, Up: Non-ASCII Characters 33.1 Text Representations ========================= Emacs buffers and strings support a large repertoire of characters from many different scripts, allowing users to type and display text in almost any known written language. To support this multitude of characters and scripts, Emacs closely follows the "Unicode Standard". The Unicode Standard assigns a unique number, called a "codepoint", to each and every character. The range of codepoints defined by Unicode, or the Unicode "codespace", is `0..#x10FFFF' (in hexadecimal notation), inclusive. Emacs extends this range with codepoints in the range `#x110000..#x3FFFFF', which it uses for representing characters that are not unified with Unicode and "raw 8-bit bytes" that cannot be interpreted as characters. Thus, a character codepoint in Emacs is a 22-bit integer number. To conserve memory, Emacs does not hold fixed-length 22-bit numbers that are codepoints of text characters within buffers and strings. Rather, Emacs uses a variable-length internal representation of characters, that stores each character as a sequence of 1 to 5 8-bit bytes, depending on the magnitude of its codepoint(1). For example, any ASCII character takes up only 1 byte, a Latin-1 character takes up 2 bytes, etc. We call this representation of text "multibyte". Outside Emacs, characters can be represented in many different encodings, such as ISO-8859-1, GB-2312, Big-5, etc. Emacs converts between these external encodings and its internal representation, as appropriate, when it reads text into a buffer or a string, or when it writes text to a disk file or passes it to some other process. Occasionally, Emacs needs to hold and manipulate encoded text or binary non-text data in its buffers or strings. For example, when Emacs visits a file, it first reads the file's text verbatim into a buffer, and only then converts it to the internal representation. Before the conversion, the buffer holds encoded text. Encoded text is not really text, as far as Emacs is concerned, but rather a sequence of raw 8-bit bytes. We call buffers and strings that hold encoded text "unibyte" buffers and strings, because Emacs treats them as a sequence of individual bytes. Usually, Emacs displays unibyte buffers and strings as octal codes such as `\237'. We recommend that you never use unibyte buffers and strings except for manipulating encoded text or binary non-text data. In a buffer, the buffer-local value of the variable `enable-multibyte-characters' specifies the representation used. The representation for a string is determined and recorded in the string when the string is constructed. -- Variable: enable-multibyte-characters This variable specifies the current buffer's text representation. If it is non-`nil', the buffer contains multibyte text; otherwise, it contains unibyte encoded text or binary non-text data. You cannot set this variable directly; instead, use the function `set-buffer-multibyte' to change a buffer's representation. The `--unibyte' command line option does its job by setting the default value to `nil' early in startup. -- Function: position-bytes position Buffer positions are measured in character units. This function returns the byte-position corresponding to buffer position POSITION in the current buffer. This is 1 at the start of the buffer, and counts upward in bytes. If POSITION is out of range, the value is `nil'. -- Function: byte-to-position byte-position Return the buffer position, in character units, corresponding to given BYTE-POSITION in the current buffer. If BYTE-POSITION is out of range, the value is `nil'. In a multibyte buffer, an arbitrary value of BYTE-POSITION can be not at character boundary, but inside a multibyte sequence representing a single character; in this case, this function returns the buffer position of the character whose multibyte sequence includes BYTE-POSITION. In other words, the value does not change for all byte positions that belong to the same character. -- Function: multibyte-string-p string Return `t' if STRING is a multibyte string, `nil' otherwise. -- Function: string-bytes string This function returns the number of bytes in STRING. If STRING is a multibyte string, this can be greater than `(length STRING)'. -- Function: unibyte-string &rest bytes This function concatenates all its argument BYTES and makes the result a unibyte string. ---------- Footnotes ---------- (1) This internal representation is based on one of the encodings defined by the Unicode Standard, called "UTF-8", for representing any Unicode codepoint, but Emacs extends UTF-8 to represent the additional codepoints it uses for raw 8-bit bytes and characters not unified with Unicode.  File: elisp, Node: Converting Representations, Next: Selecting a Representation, Prev: Text Representations, Up: Non-ASCII Characters 33.2 Converting Text Representations ==================================== Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte, provided that the multibyte text contains only ASCII and 8-bit raw bytes. In general, these conversions happen when inserting text into a buffer, or when putting text from several strings together in one string. You can also explicitly convert a string's contents to either representation. Emacs chooses the representation for a string based on the text from which it is constructed. The general rule is to convert unibyte text to multibyte text when combining it with other multibyte text, because the multibyte representation is more general and can hold whatever characters the unibyte text has. When inserting text into a buffer, Emacs converts the text to the buffer's representation, as specified by `enable-multibyte-characters' in that buffer. In particular, when you insert multibyte text into a unibyte buffer, Emacs converts the text to unibyte, even though this conversion cannot in general preserve all the characters that might be in the multibyte text. The other natural alternative, to convert the buffer contents to multibyte, is not acceptable because the buffer's representation is a choice made by the user that cannot be overridden automatically. Converting unibyte text to multibyte text leaves ASCII characters unchanged, and converts bytes with codes 128 through 159 to the multibyte representation of raw eight-bit bytes. Converting multibyte text to unibyte converts all ASCII and eight-bit characters to their single-byte form, but loses information for non-ASCII characters by discarding all but the low 8 bits of each character's codepoint. Converting unibyte text to multibyte and back to unibyte reproduces the original unibyte text. The next two functions either return the argument STRING, or a newly created string with no text properties. -- Function: string-to-multibyte string This function returns a multibyte string containing the same sequence of characters as STRING. If STRING is a multibyte string, it is returned unchanged. The function assumes that STRING includes only ASCII characters and raw 8-bit bytes; the latter are converted to their multibyte representation corresponding to the codepoints `#x3FFF80' through `#x3FFFFF', inclusive (*note codepoints: Text Representations.). -- Function: string-to-unibyte string This function returns a unibyte string containing the same sequence of characters as STRING. It signals an error if STRING contains a non-ASCII character. If STRING is a unibyte string, it is returned unchanged. Use this function for STRING arguments that contain only ASCII and eight-bit characters. -- Function: multibyte-char-to-unibyte char This converts the multibyte character CHAR to a unibyte character, and returns that character. If CHAR is neither ASCII nor eight-bit, the function returns -1. -- Function: unibyte-char-to-multibyte char This convert the unibyte character CHAR to a multibyte character, assuming CHAR is either ASCII or raw 8-bit byte.  File: elisp, Node: Selecting a Representation, Next: Character Codes, Prev: Converting Representations, Up: Non-ASCII Characters 33.3 Selecting a Representation =============================== Sometimes it is useful to examine an existing buffer or string as multibyte when it was unibyte, or vice versa. -- Function: set-buffer-multibyte multibyte Set the representation type of the current buffer. If MULTIBYTE is non-`nil', the buffer becomes multibyte. If MULTIBYTE is `nil', the buffer becomes unibyte. This function leaves the buffer contents unchanged when viewed as a sequence of bytes. As a consequence, it can change the contents viewed as characters; for instance, a sequence of three bytes which is treated as one character in multibyte representation will count as three characters in unibyte representation. Eight-bit characters representing raw bytes are an exception. They are represented by one byte in a unibyte buffer, but when the buffer is set to multibyte, they are converted to two-byte sequences, and vice versa. This function sets `enable-multibyte-characters' to record which representation is in use. It also adjusts various data in the buffer (including overlays, text properties and markers) so that they cover the same text as they did before. You cannot use `set-buffer-multibyte' on an indirect buffer, because indirect buffers always inherit the representation of the base buffer. -- Function: string-as-unibyte string If STRING is already a unibyte string, this function returns STRING itself. Otherwise, it returns a new string with the same bytes as STRING, but treating each byte as a separate character (so that the value may have more characters than STRING); as an exception, each eight-bit character representing a raw byte is converted into a single byte. The newly-created string contains no text properties. -- Function: string-as-multibyte string If STRING is a multibyte string, this function returns STRING itself. Otherwise, it returns a new string with the same bytes as STRING, but treating each multibyte sequence as one character. This means that the value may have fewer characters than STRING has. If a byte sequence in STRING is invalid as a multibyte representation of a single character, each byte in the sequence is treated as a raw 8-bit byte. The newly-created string contains no text properties.  File: elisp, Node: Character Codes, Next: Character Properties, Prev: Selecting a Representation, Up: Non-ASCII Characters 33.4 Character Codes ==================== The unibyte and multibyte text representations use different character codes. The valid character codes for unibyte representation range from 0 to `#xFF' (255)--the values that can fit in one byte. The valid character codes for multibyte representation range from 0 to `#x3FFFFF'. In this code space, values 0 through `#x7F' (127) are for ASCII characters, and values `#x80' (128) through `#x3FFF7F' (4194175) are for non-ASCII characters. Emacs character codes are a superset of the Unicode standard. Values 0 through `#x10FFFF' (1114111) correspond to Unicode characters of the same codepoint; values `#x110000' (1114112) through `#x3FFF7F' (4194175) represent characters that are not unified with Unicode; and values `#x3FFF80' (4194176) through `#x3FFFFF' (4194303) represent eight-bit raw bytes. -- Function: characterp charcode This returns `t' if CHARCODE is a valid character, and `nil' otherwise. (characterp 65) => t (characterp 4194303) => t (characterp 4194304) => nil -- Function: max-char This function returns the largest value that a valid character codepoint can have. (characterp (max-char)) => t (characterp (1+ (max-char))) => nil -- Function: get-byte &optional pos string This function returns the byte at character position POS in the current buffer. If the current buffer is unibyte, this is literally the byte at that position. If the buffer is multibyte, byte values of ASCII characters are the same as character codepoints, whereas eight-bit raw bytes are converted to their 8-bit codes. The function signals an error if the character at POS is non-ASCII. The optional argument STRING means to get a byte value from that string instead of the current buffer.  File: elisp, Node: Character Properties, Next: Character Sets, Prev: Character Codes, Up: Non-ASCII Characters 33.5 Character Properties ========================= A "character property" is a named attribute of a character that specifies how the character behaves and how it should be handled during text processing and display. Thus, character properties are an important part of specifying the character's semantics. On the whole, Emacs follows the Unicode Standard in its implementation of character properties. In particular, Emacs supports the Unicode Character Property Model (http://www.unicode.org/reports/tr23/), and the Emacs character property database is derived from the Unicode Character Database (UCD). See the Character Properties chapter of the Unicode Standard (http://www.unicode.org/versions/Unicode5.0.0/ch04.pdf), for a detailed description of Unicode character properties and their meaning. This section assumes you are already familiar with that chapter of the Unicode Standard, and want to apply that knowledge to Emacs Lisp programs. In Emacs, each property has a name, which is a symbol, and a set of possible values, whose types depend on the property; if a character does not have a certain property, the value is `nil'. As a general rule, the names of character properties in Emacs are produced from the corresponding Unicode properties by downcasing them and replacing each `_' character with a dash `-'. For example, `Canonical_Combining_Class' becomes `canonical-combining-class'. However, sometimes we shorten the names to make their use easier. Here is the full list of value types for all the character properties that Emacs knows about: `name' This property corresponds to the Unicode `Name' property. The value is a string consisting of upper-case Latin letters A to Z, digits, spaces, and hyphen `-' characters. `general-category' This property corresponds to the Unicode `General_Category' property. The value is a symbol whose name is a 2-letter abbreviation of the character's classification. `canonical-combining-class' Corresponds to the Unicode `Canonical_Combining_Class' property. The value is an integer number. `bidi-class' Corresponds to the Unicode `Bidi_Class' property. The value is a symbol whose name is the Unicode "directional type" of the character. `decomposition' Corresponds to the Unicode `Decomposition_Type' and `Decomposition_Value' properties. The value is a list, whose first element may be a symbol representing a compatibility formatting tag, such as `small'(1); the other elements are characters that give the compatibility decomposition sequence of this character. `decimal-digit-value' Corresponds to the Unicode `Numeric_Value' property for characters whose `Numeric_Type' is `Digit'. The value is an integer number. `digit' Corresponds to the Unicode `Numeric_Value' property for characters whose `Numeric_Type' is `Decimal'. The value is an integer number. Examples of such characters include compatibility subscript and superscript digits, for which the value is the corresponding number. `numeric-value' Corresponds to the Unicode `Numeric_Value' property for characters whose `Numeric_Type' is `Numeric'. The value of this property is an integer or a floating-point number. Examples of characters that have this property include fractions, subscripts, superscripts, Roman numerals, currency numerators, and encircled numbers. For example, the value of this property for the character `U+2155' (VULGAR FRACTION ONE FIFTH) is `0.2'. `mirrored' Corresponds to the Unicode `Bidi_Mirrored' property. The value of this property is a symbol, either `Y' or `N'. `old-name' Corresponds to the Unicode `Unicode_1_Name' property. The value is a string. `iso-10646-comment' Corresponds to the Unicode `ISO_Comment' property. The value is a string. `uppercase' Corresponds to the Unicode `Simple_Uppercase_Mapping' property. The value of this property is a single character. `lowercase' Corresponds to the Unicode `Simple_Lowercase_Mapping' property. The value of this property is a single character. `titlecase' Corresponds to the Unicode `Simple_Titlecase_Mapping' property. "Title case" is a special form of a character used when the first character of a word needs to be capitalized. The value of this property is a single character. -- Function: get-char-code-property char propname This function returns the value of CHAR's PROPNAME property. (get-char-code-property ? 'general-category) => Zs (get-char-code-property ?1 'general-category) => Nd (get-char-code-property ?\u2084 'digit-value) ; subscript 4 => 4 (get-char-code-property ?\u2155 'numeric-value) ; one fifth => 1/5 (get-char-code-property ?\u2163 'numeric-value) ; Roman IV => \4 -- Function: char-code-property-description prop value This function returns the description string of property PROP's VALUE, or `nil' if VALUE has no description. (char-code-property-description 'general-category 'Zs) => "Separator, Space" (char-code-property-description 'general-category 'Nd) => "Number, Decimal Digit" (char-code-property-description 'numeric-value '1/5) => nil -- Function: put-char-code-property char propname value This function stores VALUE as the value of the property PROPNAME for the character CHAR. -- Variable: char-script-table The value of this variable is a char-table (*note Char-Tables::) that specifies, for each character, a symbol whose name is the script to which the character belongs, according to the Unicode Standard classification of the Unicode code space into script-specific blocks. This char-table has a single extra slot whose value is the list of all script symbols. -- Variable: char-width-table The value of this variable is a char-table that specifies the width of each character in columns that it will occupy on the screen. -- Variable: printable-chars The value of this variable is a char-table that specifies, for each character, whether it is printable or not. That is, if evaluating `(aref printable-chars char)' results in `t', the character is printable, and if it results in `nil', it is not. ---------- Footnotes ---------- (1) Note that the Unicode spec writes these tag names inside `<..>' brackets. The tag names in Emacs do not include the brackets; e.g., Unicode specifies `' where Emacs uses `small'.  File: elisp, Node: Character Sets, Next: Scanning Charsets, Prev: Character Properties, Up: Non-ASCII Characters 33.6 Character Sets =================== An Emacs "character set", or "charset", is a set of characters in which each character is assigned a numeric code point. (The Unicode Standard calls this a "coded character set".) Each Emacs charset has a name which is a symbol. A single character can belong to any number of different character sets, but it will generally have a different code point in each charset. Examples of character sets include `ascii', `iso-8859-1', `greek-iso8859-7', and `windows-1255'. The code point assigned to a character in a charset is usually different from its code point used in Emacs buffers and strings. Emacs defines several special character sets. The character set `unicode' includes all the characters whose Emacs code points are in the range `0..#x10FFFF'. The character set `emacs' includes all ASCII and non-ASCII characters. Finally, the `eight-bit' charset includes the 8-bit raw bytes; Emacs uses it to represent raw bytes encountered in text. -- Function: charsetp object Returns `t' if OBJECT is a symbol that names a character set, `nil' otherwise. -- Variable: charset-list The value is a list of all defined character set names. -- Function: charset-priority-list &optional highestp This functions returns a list of all defined character sets ordered by their priority. If HIGHESTP is non-`nil', the function returns a single character set of the highest priority. -- Function: set-charset-priority &rest charsets This function makes CHARSETS the highest priority character sets. -- Function: char-charset character &optional restriction This function returns the name of the character set of highest priority that CHARACTER belongs to. ASCII characters are an exception: for them, this function always returns `ascii'. If RESTRICTION is non-`nil', it should be a list of charsets to search. Alternatively, it can be a coding system, in which case the returned charset must be supported by that coding system (*note Coding Systems::). -- Function: charset-plist charset This function returns the property list of the character set CHARSET. Although CHARSET is a symbol, this is not the same as the property list of that symbol. Charset properties include important information about the charset, such as its documentation string, short name, etc. -- Function: put-charset-property charset propname value This function sets the PROPNAME property of CHARSET to the given VALUE. -- Function: get-charset-property charset propname This function returns the value of CHARSETs property PROPNAME. -- Command: list-charset-chars charset This command displays a list of characters in the character set CHARSET. Emacs can convert between its internal representation of a character and the character's codepoint in a specific charset. The following two functions support these conversions. -- Function: decode-char charset code-point This function decodes a character that is assigned a CODE-POINT in CHARSET, to the corresponding Emacs character, and returns it. If CHARSET doesn't contain a character of that code point, the value is `nil'. If CODE-POINT doesn't fit in a Lisp integer (*note most-positive-fixnum: Integer Basics.), it can be specified as a cons cell `(HIGH . LOW)', where LOW are the lower 16 bits of the value and HIGH are the high 16 bits. -- Function: encode-char char charset This function returns the code point assigned to the character CHAR in CHARSET. If the result does not fit in a Lisp integer, it is returned as a cons cell `(HIGH . LOW)' that fits the second argument of `decode-char' above. If CHARSET doesn't have a codepoint for CHAR, the value is `nil'. The following function comes in handy for applying a certain function to all or part of the characters in a charset: -- Function: map-charset-chars function charset &optional arg from-code to-code Call FUNCTION for characters in CHARSET. FUNCTION is called with two arguments. The first one is a cons cell `(FROM . TO)', where FROM and TO indicate a range of characters contained in charset. The second argument passed to FUNCTION is ARG. By default, the range of codepoints passed to FUNCTION includes all the characters in CHARSET, but optional arguments FROM-CODE and TO-CODE limit that to the range of characters between these two codepoints of CHARSET. If either of them is `nil', it defaults to the first or last codepoint of CHARSET, respectively.  File: elisp, Node: Scanning Charsets, Next: Translation of Characters, Prev: Character Sets, Up: Non-ASCII Characters 33.7 Scanning for Character Sets ================================ Sometimes it is useful to find out which character set a particular character belongs to. One use for this is in determining which coding systems (*note Coding Systems::) are capable of representing all of the text in question; another is to determine the font(s) for displaying that text. -- Function: charset-after &optional pos This function returns the charset of highest priority containing the character at position POS in the current buffer. If POS is omitted or `nil', it defaults to the current value of point. If POS is out of range, the value is `nil'. -- Function: find-charset-region beg end &optional translation This function returns a list of the character sets of highest priority that contain characters in the current buffer between positions BEG and END. The optional argument TRANSLATION specifies a translation table to use for scanning the text (*note Translation of Characters::). If it is non-`nil', then each character in the region is translated through this table, and the value returned describes the translated characters instead of the characters actually in the buffer. -- Function: find-charset-string string &optional translation This function returns a list of character sets of highest priority that contain characters in STRING. It is just like `find-charset-region', except that it applies to the contents of STRING instead of part of the current buffer.  File: elisp, Node: Translation of Characters, Next: Coding Systems, Prev: Scanning Charsets, Up: Non-ASCII Characters 33.8 Translation of Characters ============================== A "translation table" is a char-table (*note Char-Tables::) that specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems. A translation table has two extra slots. The first is either `nil' or a translation table that performs the reverse translation; the second is the maximum number of characters to look up for translating sequences of characters (see the description of `make-translation-table-from-alist' below). -- Function: make-translation-table &rest translations This function returns a translation table based on the argument TRANSLATIONS. Each element of TRANSLATIONS should be a list of elements of the form `(FROM . TO)'; this says to translate the character FROM into TO. The arguments and the forms in each argument are processed in order, and if a previous form already translates TO to some other character, say TO-ALT, FROM is also translated to TO-ALT. During decoding, the translation table's translations are applied to the characters that result from ordinary decoding. If a coding system has the property `:decode-translation-table', that specifies the translation table to use, or a list of translation tables to apply in sequence. (This is a property of the coding system, as returned by `coding-system-get', not a property of the symbol that is the coding system's name. *Note Basic Concepts of Coding Systems: Coding System Basics.) Finally, if `standard-translation-table-for-decode' is non-`nil', the resulting characters are translated by that table. During encoding, the translation table's translations are applied to the characters in the buffer, and the result of translation is actually encoded. If a coding system has property `:encode-translation-table', that specifies the translation table to use, or a list of translation tables to apply in sequence. In addition, if the variable `standard-translation-table-for-encode' is non-`nil', it specifies the translation table to use for translating the result. -- Variable: standard-translation-table-for-decode This is the default translation table for decoding. If a coding systems specifies its own translation tables, the table that is the value of this variable, if non-`nil', is applied after them. -- Variable: standard-translation-table-for-encode This is the default translation table for encoding. If a coding systems specifies its own translation tables, the table that is the value of this variable, if non-`nil', is applied after them. -- Variable: translation-table-for-input Self-inserting characters are translated through this translation table before they are inserted. Search commands also translate their input through this table, so they can compare more reliably with what's in the buffer. This variable automatically becomes buffer-local when set. -- Function: make-translation-table-from-vector vec This function returns a translation table made from VEC that is an array of 256 elements to map bytes (values 0 through #xFF) to characters. Elements may be `nil' for untranslated bytes. The returned table has a translation table for reverse mapping in the first extra slot, and the value `1' in the second extra slot. This function provides an easy way to make a private coding system that maps each byte to a specific character. You can specify the returned table and the reverse translation table using the properties `:decode-translation-table' and `:encode-translation-table' respectively in the PROPS argument to `define-coding-system'. -- Function: make-translation-table-from-alist alist This function is similar to `make-translation-table' but returns a complex translation table rather than a simple one-to-one mapping. Each element of ALIST is of the form `(FROM . TO)', where FROM and TO are either characters or vectors specifying a sequence of characters. If FROM is a character, that character is translated to TO (i.e. to a character or a character sequence). If FROM is a vector of characters, that sequence is translated to TO. The returned table has a translation table for reverse mapping in the first extra slot, and the maximum length of all the FROM character sequences in the second extra slot.  File: elisp, Node: Coding Systems, Next: Input Methods, Prev: Translation of Characters, Up: Non-ASCII Characters 33.9 Coding Systems =================== When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives text from a subprocess, it normally performs character code conversion and end-of-line conversion as specified by a particular "coding system". How to define a coding system is an arcane matter, and is not documented here. * Menu: * Coding System Basics:: Basic concepts. * Encoding and I/O:: How file I/O functions handle coding systems. * Lisp and Coding Systems:: Functions to operate on coding system names. * User-Chosen Coding Systems:: Asking the user to choose a coding system. * Default Coding Systems:: Controlling the default choices. * Specifying Coding Systems:: Requesting a particular coding system for a single file operation. * Explicit Encoding:: Encoding or decoding text without doing I/O. * Terminal I/O Encoding:: Use of encoding for terminal I/O. * MS-DOS File Types:: How DOS "text" and "binary" files relate to coding systems.  File: elisp, Node: Coding System Basics, Next: Encoding and I/O, Up: Coding Systems 33.9.1 Basic Concepts of Coding Systems --------------------------------------- "Character code conversion" involves conversion between the internal representation of characters used inside Emacs and some other encoding. Emacs supports many different encodings, in that it can convert to and from them. For example, it can convert text to or from encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some cases, Emacs supports several alternative encodings for the same characters; for example, there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and KOI8. Every coding system specifies a particular set of character code conversions, but the coding system `undecided' is special: it leaves the choice unspecified, to be chosen heuristically for each file, based on the file's data. In general, a coding system doesn't guarantee roundtrip identity: decoding a byte sequence using coding system, then encoding the resulting text in the same coding system, can produce a different byte sequence. But some coding systems do guarantee that the byte sequence will be the same as what you originally decoded. Here are a few examples: iso-8859-1, utf-8, big5, shift_jis, euc-jp Encoding buffer text and then decoding the result can also fail to reproduce the original text. For instance, if you encode a character with a coding system which does not support that character, the result is unpredictable, and thus decoding it using the same coding system may produce a different text. Currently, Emacs can't report errors that result from encoding unsupported characters. "End of line conversion" handles three different conventions used on various systems for representing end of line in files. The Unix convention, used on GNU and Unix systems, is to use the linefeed character (also called newline). The DOS convention, used on MS-Windows and MS-DOS systems, is to use a carriage-return and a linefeed at the end of a line. The Mac convention is to use just carriage-return. "Base coding systems" such as `latin-1' leave the end-of-line conversion unspecified, to be chosen based on the data. "Variant coding systems" such as `latin-1-unix', `latin-1-dos' and `latin-1-mac' specify the end-of-line conversion explicitly as well. Most base coding systems have three corresponding variants whose names are formed by adding `-unix', `-dos' and `-mac'. The coding system `raw-text' is special in that it prevents character code conversion, and causes the buffer visited with this coding system to be a unibyte buffer. For historical reasons, you can save both unibyte and multibyte text with this coding system. When you use `raw-text' to encode multibyte text, it does perform one character code conversion: it converts eight-bit characters to their single-byte external representation. `raw-text' does not specify the end-of-line conversion, allowing that to be determined as usual by the data, and has the usual three variants which specify the end-of-line conversion. `no-conversion' (and its alias `binary') is equivalent to `raw-text-unix': it specifies no conversion of either character codes or end-of-line. The coding system `utf-8-emacs' specifies that the data is represented in the internal Emacs encoding (*note Text Representations::). This is like `raw-text' in that no code conversion happens, but different in that the result is multibyte data. The name `emacs-internal' is an alias for `utf-8-emacs'. -- Function: coding-system-get coding-system property This function returns the specified property of the coding system CODING-SYSTEM. Most coding system properties exist for internal purposes, but one that you might find useful is `:mime-charset'. That property's value is the name used in MIME for the character coding which this coding system can read and write. Examples: (coding-system-get 'iso-latin-1 :mime-charset) => iso-8859-1 (coding-system-get 'iso-2022-cn :mime-charset) => iso-2022-cn (coding-system-get 'cyrillic-koi8 :mime-charset) => koi8-r The value of the `:mime-charset' property is also defined as an alias for the coding system. -- Function: coding-system-aliases coding-system This function returns the list of aliases of CODING-SYSTEM.  File: elisp, Node: Encoding and I/O, Next: Lisp and Coding Systems, Prev: Coding System Basics, Up: Coding Systems 33.9.2 Encoding and I/O ----------------------- The principal purpose of coding systems is for use in reading and writing files. The function `insert-file-contents' uses a coding system to decode the file data, and `write-region' uses one to encode the buffer contents. You can specify the coding system to use either explicitly (*note Specifying Coding Systems::), or implicitly using a default mechanism (*note Default Coding Systems::). But these methods may not completely specify what to do. For example, they may choose a coding system such as `undefined' which leaves the character code conversion to be determined from the data. In these cases, the I/O operation finishes the job of choosing a coding system. Very often you will want to find out afterwards which coding system was chosen. -- Variable: buffer-file-coding-system This buffer-local variable records the coding system used for saving the buffer and for writing part of the buffer with `write-region'. If the text to be written cannot be safely encoded using the coding system specified by this variable, these operations select an alternative encoding by calling the function `select-safe-coding-system' (*note User-Chosen Coding Systems::). If selecting a different encoding requires to ask the user to specify a coding system, `buffer-file-coding-system' is updated to the newly selected coding system. `buffer-file-coding-system' does _not_ affect sending text to a subprocess. -- Variable: save-buffer-coding-system This variable specifies the coding system for saving the buffer (by overriding `buffer-file-coding-system'). Note that it is not used for `write-region'. When a command to save the buffer starts out to use `buffer-file-coding-system' (or `save-buffer-coding-system'), and that coding system cannot handle the actual text in the buffer, the command asks the user to choose another coding system (by calling `select-safe-coding-system'). After that happens, the command also updates `buffer-file-coding-system' to represent the coding system that the user specified. -- Variable: last-coding-system-used I/O operations for files and subprocesses set this variable to the coding system name that was used. The explicit encoding and decoding functions (*note Explicit Encoding::) set it too. *Warning:* Since receiving subprocess output sets this variable, it can change whenever Emacs waits; therefore, you should copy the value shortly after the function call that stores the value you are interested in. The variable `selection-coding-system' specifies how to encode selections for the window system. *Note Window System Selections::. -- Variable: file-name-coding-system The variable `file-name-coding-system' specifies the coding system to use for encoding file names. Emacs encodes file names using that coding system for all file operations. If `file-name-coding-system' is `nil', Emacs uses a default coding system determined by the selected language environment. In the default language environment, any non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation. *Warning:* if you change `file-name-coding-system' (or the language environment) in the middle of an Emacs session, problems can result if you have already visited files whose names were encoded using the earlier coding system and are handled differently under the new coding system. If you try to save one of these buffers under the visited file name, saving may use the wrong file name, or it may get an error. If such a problem happens, use `C-x C-w' to specify a new file name for that buffer.  File: elisp, Node: Lisp and Coding Systems, Next: User-Chosen Coding Systems, Prev: Encoding and I/O, Up: Coding Systems 33.9.3 Coding Systems in Lisp ----------------------------- Here are the Lisp facilities for working with coding systems: -- Function: coding-system-list &optional base-only This function returns a list of all coding system names (symbols). If BASE-ONLY is non-`nil', the value includes only the base coding systems. Otherwise, it includes alias and variant coding systems as well. -- Function: coding-system-p object This function returns `t' if OBJECT is a coding system name or `nil'. -- Function: check-coding-system coding-system This function checks the validity of CODING-SYSTEM. If that is valid, it returns CODING-SYSTEM. If CODING-SYSTEM is `nil', the function return `nil'. For any other values, it signals an error whose `error-symbol' is `coding-system-error' (*note signal: Signaling Errors.). -- Function: coding-system-eol-type coding-system This function returns the type of end-of-line (a.k.a. "eol") conversion used by CODING-SYSTEM. If CODING-SYSTEM specifies a certain eol conversion, the return value is an integer 0, 1, or 2, standing for `unix', `dos', and `mac', respectively. If CODING-SYSTEM doesn't specify eol conversion explicitly, the return value is a vector of coding systems, each one with one of the possible eol conversion types, like this: (coding-system-eol-type 'latin-1) => [latin-1-unix latin-1-dos latin-1-mac] If this function returns a vector, Emacs will decide, as part of the text encoding or decoding process, what eol conversion to use. For decoding, the end-of-line format of the text is auto-detected, and the eol conversion is set to match it (e.g., DOS-style CRLF format will imply `dos' eol conversion). For encoding, the eol conversion is taken from the appropriate default coding system (e.g., default value of `buffer-file-coding-system' for `buffer-file-coding-system'), or from the default eol conversion appropriate for the underlying platform. -- Function: coding-system-change-eol-conversion coding-system eol-type This function returns a coding system which is like CODING-SYSTEM except for its eol conversion, which is specified by `eol-type'. EOL-TYPE should be `unix', `dos', `mac', or `nil'. If it is `nil', the returned coding system determines the end-of-line conversion from the data. EOL-TYPE may also be 0, 1 or 2, standing for `unix', `dos' and `mac', respectively. -- Function: coding-system-change-text-conversion eol-coding text-coding This function returns a coding system which uses the end-of-line conversion of EOL-CODING, and the text conversion of TEXT-CODING. If TEXT-CODING is `nil', it returns `undecided', or one of its variants according to EOL-CODING. -- Function: find-coding-systems-region from to This function returns a list of coding systems that could be used to encode a text between FROM and TO. All coding systems in the list can safely encode any multibyte characters in that portion of the text. If the text contains no multibyte characters, the function returns the list `(undecided)'. -- Function: find-coding-systems-string string This function returns a list of coding systems that could be used to encode the text of STRING. All coding systems in the list can safely encode any multibyte characters in STRING. If the text contains no multibyte characters, this returns the list `(undecided)'. -- Function: find-coding-systems-for-charsets charsets This function returns a list of coding systems that could be used to encode all the character sets in the list CHARSETS. -- Function: check-coding-systems-region start end coding-system-list This function checks whether coding systems in the list `coding-system-list' can encode all the characters in the region between START and END. If all of the coding systems in the list can encode the specified text, the function returns `nil'. If some coding systems cannot encode some of the characters, the value is an alist, each element of which has the form `(CODING-SYSTEM1 POS1 POS2 ...)', meaning that CODING-SYSTEM1 cannot encode characters at buffer positions POS1, POS2, .... START may be a string, in which case END is ignored and the returned value references string indices instead of buffer positions. -- Function: detect-coding-region start end &optional highest This function chooses a plausible coding system for decoding the text from START to END. This text should be a byte sequence, i.e. unibyte text or multibyte text with only ASCII and eight-bit characters (*note Explicit Encoding::). Normally this function returns a list of coding systems that could handle decoding the text that was scanned. They are listed in order of decreasing priority. But if HIGHEST is non-`nil', then the return value is just one coding system, the one that is highest in priority. If the region contains only ASCII characters except for such ISO-2022 control characters ISO-2022 as `ESC', the value is `undecided' or `(undecided)', or a variant specifying end-of-line conversion, if that can be deduced from the text. If the region contains null bytes, the value is `no-conversion', even if the region contains text encoded in some coding system. -- Function: detect-coding-string string &optional highest This function is like `detect-coding-region' except that it operates on the contents of STRING instead of bytes in the buffer. -- Variable: inhibit-null-byte-detection If this variable has a non-`nil' value, null bytes are ignored when detecting the encoding of a region or a string. This allows to correctly detect the encoding of text that contains null bytes, such as Info files with Index nodes. -- Variable: inhibit-iso-escape-detection If this variable has a non-`nil' value, ISO-2022 escape sequences are ignored when detecting the encoding of a region or a string. The result is that no text is ever detected as encoded in some ISO-2022 encoding, and all escape sequences become visible in a buffer. *Warning:* _Use this variable with extreme caution, because many files in the Emacs distribution use ISO-2022 encoding._ -- Function: coding-system-charset-list coding-system This function returns the list of character sets (*note Character Sets::) supported by CODING-SYSTEM. Some coding systems that support too many character sets to list them all yield special values: * If CODING-SYSTEM supports all the ISO-2022 charsets, the value is `iso-2022'. * If CODING-SYSTEM supports all Emacs characters, the value is `(emacs)'. * If CODING-SYSTEM supports all emacs-mule characters, the value is `emacs-mule'. * If CODING-SYSTEM supports all Unicode characters, the value is `(unicode)'. *Note Process Information: Coding systems for a subprocess, in particular the description of the functions `process-coding-system' and `set-process-coding-system', for how to examine or set the coding systems used for I/O to a subprocess.  File: elisp, Node: User-Chosen Coding Systems, Next: Default Coding Systems, Prev: Lisp and Coding Systems, Up: Coding Systems 33.9.4 User-Chosen Coding Systems --------------------------------- -- Function: select-safe-coding-system from to &optional default-coding-system accept-default-p file This function selects a coding system for encoding specified text, asking the user to choose if necessary. Normally the specified text is the text in the current buffer between FROM and TO. If FROM is a string, the string specifies the text to encode, and TO is ignored. If the specified text includes raw bytes (*note Text Representations::), `select-safe-coding-system' suggests `raw-text' for its encoding. If DEFAULT-CODING-SYSTEM is non-`nil', that is the first coding system to try; if that can handle the text, `select-safe-coding-system' returns that coding system. It can also be a list of coding systems; then the function tries each of them one by one. After trying all of them, it next tries the current buffer's value of `buffer-file-coding-system' (if it is not `undecided'), then the default value of `buffer-file-coding-system' and finally the user's most preferred coding system, which the user can set using the command `prefer-coding-system' (*note Recognizing Coding Systems: (emacs)Recognize Coding.). If one of those coding systems can safely encode all the specified text, `select-safe-coding-system' chooses it and returns it. Otherwise, it asks the user to choose from a list of coding systems which can encode all the text, and returns the user's choice. DEFAULT-CODING-SYSTEM can also be a list whose first element is t and whose other elements are coding systems. Then, if no coding system in the list can handle the text, `select-safe-coding-system' queries the user immediately, without trying any of the three alternatives described above. The optional argument ACCEPT-DEFAULT-P, if non-`nil', should be a function to determine whether a coding system selected without user interaction is acceptable. `select-safe-coding-system' calls this function with one argument, the base coding system of the selected coding system. If ACCEPT-DEFAULT-P returns `nil', `select-safe-coding-system' rejects the silently selected coding system, and asks the user to select a coding system from a list of possible candidates. If the variable `select-safe-coding-system-accept-default-p' is non-`nil', it should be a function taking a single argument. It is used in place of ACCEPT-DEFAULT-P, overriding any value supplied for this argument. As a final step, before returning the chosen coding system, `select-safe-coding-system' checks whether that coding system is consistent with what would be selected if the contents of the region were read from a file. (If not, this could lead to data corruption in a file subsequently re-visited and edited.) Normally, `select-safe-coding-system' uses `buffer-file-name' as the file for this purpose, but if FILE is non-`nil', it uses that file instead (this can be relevant for `write-region' and similar functions). If it detects an apparent inconsistency, `select-safe-coding-system' queries the user before selecting the coding system. Here are two functions you can use to let the user specify a coding system, with completion. *Note Completion::. -- Function: read-coding-system prompt &optional default This function reads a coding system using the minibuffer, prompting with string PROMPT, and returns the coding system name as a symbol. If the user enters null input, DEFAULT specifies which coding system to return. It should be a symbol or a string. -- Function: read-non-nil-coding-system prompt This function reads a coding system using the minibuffer, prompting with string PROMPT, and returns the coding system name as a symbol. If the user tries to enter null input, it asks the user to try again. *Note Coding Systems::.  File: elisp, Node: Default Coding Systems, Next: Specifying Coding Systems, Prev: User-Chosen Coding Systems, Up: Coding Systems 33.9.5 Default Coding Systems ----------------------------- This section describes variables that specify the default coding system for certain files or when running certain subprograms, and the function that I/O operations use to access them. The idea of these variables is that you set them once and for all to the defaults you want, and then do not change them again. To specify a particular coding system for a particular operation in a Lisp program, don't change these variables; instead, override them using `coding-system-for-read' and `coding-system-for-write' (*note Specifying Coding Systems::). -- User Option: auto-coding-regexp-alist This variable is an alist of text patterns and corresponding coding systems. Each element has the form `(REGEXP . CODING-SYSTEM)'; a file whose first few kilobytes match REGEXP is decoded with CODING-SYSTEM when its contents are read into a buffer. The settings in this alist take priority over `coding:' tags in the files and the contents of `file-coding-system-alist' (see below). The default value is set so that Emacs automatically recognizes mail files in Babyl format and reads them with no code conversions. -- User Option: file-coding-system-alist This variable is an alist that specifies the coding systems to use for reading and writing particular files. Each element has the form `(PATTERN . CODING)', where PATTERN is a regular expression that matches certain file names. The element applies to file names that match PATTERN. The CDR of the element, CODING, should be either a coding system, a cons cell containing two coding systems, or a function name (a symbol with a function definition). If CODING is a coding system, that coding system is used for both reading the file and writing it. If CODING is a cons cell containing two coding systems, its CAR specifies the coding system for decoding, and its CDR specifies the coding system for encoding. If CODING is a function name, the function should take one argument, a list of all arguments passed to `find-operation-coding-system'. It must return a coding system or a cons cell containing two coding systems. This value has the same meaning as described above. If CODING (or what returned by the above function) is `undecided', the normal code-detection is performed. -- User Option: auto-coding-alist This variable is an alist that specifies the coding systems to use for reading and writing particular files. Its form is like that of `file-coding-system-alist', but, unlike the latter, this variable takes priority over any `coding:' tags in the file. -- Variable: process-coding-system-alist This variable is an alist specifying which coding systems to use for a subprocess, depending on which program is running in the subprocess. It works like `file-coding-system-alist', except that PATTERN is matched against the program name used to start the subprocess. The coding system or systems specified in this alist are used to initialize the coding systems used for I/O to the subprocess, but you can specify other coding systems later using `set-process-coding-system'. *Warning:* Coding systems such as `undecided', which determine the coding system from the data, do not work entirely reliably with asynchronous subprocess output. This is because Emacs handles asynchronous subprocess output in batches, as it arrives. If the coding system leaves the character code conversion unspecified, or leaves the end-of-line conversion unspecified, Emacs must try to detect the proper conversion from one batch at a time, and this does not always work. Therefore, with an asynchronous subprocess, if at all possible, use a coding system which determines both the character code conversion and the end of line conversion--that is, one like `latin-1-unix', rather than `undecided' or `latin-1'. -- Variable: network-coding-system-alist This variable is an alist that specifies the coding system to use for network streams. It works much like `file-coding-system-alist', with the difference that the PATTERN in an element may be either a port number or a regular expression. If it is a regular expression, it is matched against the network service name used to open the network stream. -- Variable: default-process-coding-system This variable specifies the coding systems to use for subprocess (and network stream) input and output, when nothing else specifies what to do. The value should be a cons cell of the form `(INPUT-CODING . OUTPUT-CODING)'. Here INPUT-CODING applies to input from the subprocess, and OUTPUT-CODING applies to output to it. -- User Option: auto-coding-functions This variable holds a list of functions that try to determine a coding system for a file based on its undecoded contents. Each function in this list should be written to look at text in the current buffer, but should not modify it in any way. The buffer will contain undecoded text of parts of the file. Each function should take one argument, SIZE, which tells it how many characters to look at, starting from point. If the function succeeds in determining a coding system for the file, it should return that coding system. Otherwise, it should return `nil'. If a file has a `coding:' tag, that takes precedence, so these functions won't be called. -- Function: find-auto-coding filename size This function tries to determine a suitable coding system for FILENAME. It examines the buffer visiting the named file, using the variables documented above in sequence, until it finds a match for one of the rules specified by these variables. It then returns a cons cell of the form `(CODING . SOURCE)', where CODING is the coding system to use and SOURCE is a symbol, one of `auto-coding-alist', `auto-coding-regexp-alist', `:coding', or `auto-coding-functions', indicating which one supplied the matching rule. The value `:coding' means the coding system was specified by the `coding:' tag in the file (*note coding tag: (emacs)Specify Coding.). The order of looking for a matching rule is `auto-coding-alist' first, then `auto-coding-regexp-alist', then the `coding:' tag, and lastly `auto-coding-functions'. If no matching rule was found, the function returns `nil'. The second argument SIZE is the size of text, in characters, following point. The function examines text only within SIZE characters after point. Normally, the buffer should be positioned at the beginning when this function is called, because one of the places for the `coding:' tag is the first one or two lines of the file; in that case, SIZE should be the size of the buffer. -- Function: set-auto-coding filename size This function returns a suitable coding system for file FILENAME. It uses `find-auto-coding' to find the coding system. If no coding system could be determined, the function returns `nil'. The meaning of the argument SIZE is like in `find-auto-coding'. -- Function: find-operation-coding-system operation &rest arguments This function returns the coding system to use (by default) for performing OPERATION with ARGUMENTS. The value has this form: (DECODING-SYSTEM . ENCODING-SYSTEM) The first element, DECODING-SYSTEM, is the coding system to use for decoding (in case OPERATION does decoding), and ENCODING-SYSTEM is the coding system for encoding (in case OPERATION does encoding). The argument OPERATION is a symbol, one of `write-region', `start-process', `call-process', `call-process-region', `insert-file-contents', or `open-network-stream'. These are the names of the Emacs I/O primitives that can do character code and eol conversion. The remaining arguments should be the same arguments that might be given to the corresponding I/O primitive. Depending on the primitive, one of those arguments is selected as the "target". For example, if OPERATION does file I/O, whichever argument specifies the file name is the target. For subprocess primitives, the process name is the target. For `open-network-stream', the target is the service name or port number. Depending on OPERATION, this function looks up the target in `file-coding-system-alist', `process-coding-system-alist', or `network-coding-system-alist'. If the target is found in the alist, `find-operation-coding-system' returns its association in the alist; otherwise it returns `nil'. If OPERATION is `insert-file-contents', the argument corresponding to the target may be a cons cell of the form `(FILENAME . BUFFER)'). In that case, FILENAME is a file name to look up in `file-coding-system-alist', and BUFFER is a buffer that contains the file's contents (not yet decoded). If `file-coding-system-alist' specifies a function to call for this file, and that function needs to examine the file's contents (as it usually does), it should examine the contents of BUFFER instead of reading the file.  File: elisp, Node: Specifying Coding Systems, Next: Explicit Encoding, Prev: Default Coding Systems, Up: Coding Systems 33.9.6 Specifying a Coding System for One Operation --------------------------------------------------- You can specify the coding system for a specific operation by binding the variables `coding-system-for-read' and/or `coding-system-for-write'. -- Variable: coding-system-for-read If this variable is non-`nil', it specifies the coding system to use for reading a file, or for input from a synchronous subprocess. It also applies to any asynchronous subprocess or network stream, but in a different way: the value of `coding-system-for-read' when you start the subprocess or open the network stream specifies the input decoding method for that subprocess or network stream. It remains in use for that subprocess or network stream unless and until overridden. The right way to use this variable is to bind it with `let' for a specific I/O operation. Its global value is normally `nil', and you should not globally set it to any other value. Here is an example of the right way to use the variable: ;; Read the file with no character code conversion. ;; Assume crlf represents end-of-line. (let ((coding-system-for-read 'emacs-mule-dos)) (insert-file-contents filename)) When its value is non-`nil', this variable takes precedence over all other methods of specifying a coding system to use for input, including `file-coding-system-alist', `process-coding-system-alist' and `network-coding-system-alist'. -- Variable: coding-system-for-write This works much like `coding-system-for-read', except that it applies to output rather than input. It affects writing to files, as well as sending output to subprocesses and net connections. When a single operation does both input and output, as do `call-process-region' and `start-process', both `coding-system-for-read' and `coding-system-for-write' affect it. -- User Option: inhibit-eol-conversion When this variable is non-`nil', no end-of-line conversion is done, no matter which coding system is specified. This applies to all the Emacs I/O and subprocess primitives, and to the explicit encoding and decoding functions (*note Explicit Encoding::). Sometimes, you need to prefer several coding systems for some operation, rather than fix a single one. Emacs lets you specify a priority order for using coding systems. This ordering affects the sorting of lists of coding sysems returned by functions such as `find-coding-systems-region' (*note Lisp and Coding Systems::). -- Function: coding-system-priority-list &optional highestp This function returns the list of coding systems in the order of their current priorities. Optional argument HIGHESTP, if non-`nil', means return only the highest priority coding system. -- Function: set-coding-system-priority &rest coding-systems This function puts CODING-SYSTEMS at the beginning of the priority list for coding systems, thus making their priority higher than all the rest. -- Macro: with-coding-priority coding-systems &rest body... This macro execute BODY, like `progn' does (*note progn: Sequencing.), with CODING-SYSTEMS at the front of the priority list for coding systems. CODING-SYSTEMS should be a list of coding systems to prefer during execution of BODY.  File: elisp, Node: Explicit Encoding, Next: Terminal I/O Encoding, Prev: Specifying Coding Systems, Up: Coding Systems 33.9.7 Explicit Encoding and Decoding ------------------------------------- All the operations that transfer text in and out of Emacs have the ability to use a coding system to encode or decode the text. You can also explicitly encode and decode text using the functions in this section. The result of encoding, and the input to decoding, are not ordinary text. They logically consist of a series of byte values; that is, a series of ASCII and eight-bit characters. In unibyte buffers and strings, these characters have codes in the range 0 through #xFF (255). In a multibyte buffer or string, eight-bit characters have character codes higher than #xFF (*note Text Representations::), but Emacs transparently converts them to their single-byte values when you encode or decode such text. The usual way to read a file into a buffer as a sequence of bytes, so you can decode the contents explicitly, is with `insert-file-contents-literally' (*note Reading from Files::); alternatively, specify a non-`nil' RAWFILE argument when visiting a file with `find-file-noselect'. These methods result in a unibyte buffer. The usual way to use the byte sequence that results from explicitly encoding text is to copy it to a file or process--for example, to write it with `write-region' (*note Writing to Files::), and suppress encoding by binding `coding-system-for-write' to `no-conversion'. Here are the functions to perform explicit encoding or decoding. The encoding functions produce sequences of bytes; the decoding functions are meant to operate on sequences of bytes. All of these functions discard text properties. They also set `last-coding-system-used' to the precise coding system they used. -- Command: encode-coding-region start end coding-system &optional destination This command encodes the text from START to END according to coding system CODING-SYSTEM. Normally, the encoded text replaces the original text in the buffer, but the optional argument DESTINATION can change that. If DESTINATION is a buffer, the encoded text is inserted in that buffer after point (point does not move); if it is `t', the command returns the encoded text as a unibyte string without inserting it. If encoded text is inserted in some buffer, this command returns the length of the encoded text. The result of encoding is logically a sequence of bytes, but the buffer remains multibyte if it was multibyte before, and any 8-bit bytes are converted to their multibyte representation (*note Text Representations::). Do _not_ use `undecided' for CODING-SYSTEM when encoding text, since that may lead to unexpected results. Instead, use `select-safe-coding-system' (*note select-safe-coding-system: User-Chosen Coding Systems.) to suggest a suitable encoding, if there's no obvious pertinent value for CODING-SYSTEM. -- Function: encode-coding-string string coding-system &optional nocopy buffer This function encodes the text in STRING according to coding system CODING-SYSTEM. It returns a new string containing the encoded text, except when NOCOPY is non-`nil', in which case the function may return STRING itself if the encoding operation is trivial. The result of encoding is a unibyte string. -- Command: decode-coding-region start end coding-system &optional destination This command decodes the text from START to END according to coding system CODING-SYSTEM. To make explicit decoding useful, the text before decoding ought to be a sequence of byte values, but both multibyte and unibyte buffers are acceptable (in the multibyte case, the raw byte values should be represented as eight-bit characters). Normally, the decoded text replaces the original text in the buffer, but the optional argument DESTINATION can change that. If DESTINATION is a buffer, the decoded text is inserted in that buffer after point (point does not move); if it is `t', the command returns the decoded text as a multibyte string without inserting it. If decoded text is inserted in some buffer, this command returns the length of the decoded text. This command puts a `charset' text property on the decoded text. The value of the property states the character set used to decode the original text. -- Function: decode-coding-string string coding-system &optional nocopy buffer This function decodes the text in STRING according to CODING-SYSTEM. It returns a new string containing the decoded text, except when NOCOPY is non-`nil', in which case the function may return STRING itself if the decoding operation is trivial. To make explicit decoding useful, the contents of STRING ought to be a unibyte string with a sequence of byte values, but a multibyte string is also acceptable (assuming it contains 8-bit bytes in their multibyte form). If optional argument BUFFER specifies a buffer, the decoded text is inserted in that buffer after point (point does not move). In this case, the return value is the length of the decoded text. This function puts a `charset' text property on the decoded text. The value of the property states the character set used to decode the original text: (decode-coding-string "Gr\374ss Gott" 'latin-1) => #("Gru"ss Gott" 0 9 (charset iso-8859-1)) -- Function: decode-coding-inserted-region from to filename &optional visit beg end replace This function decodes the text from FROM to TO as if it were being read from file FILENAME using `insert-file-contents' using the rest of the arguments provided. The normal way to use this function is after reading text from a file without decoding, if you decide you would rather have decoded it. Instead of deleting the text and reading it again, this time with decoding, you can call this function.  File: elisp, Node: Terminal I/O Encoding, Next: MS-DOS File Types, Prev: Explicit Encoding, Up: Coding Systems 33.9.8 Terminal I/O Encoding ---------------------------- Emacs can decode keyboard input using a coding system, and encode terminal output. This is useful for terminals that transmit or display text using a particular encoding such as Latin-1. Emacs does not set `last-coding-system-used' for encoding or decoding of terminal I/O. -- Function: keyboard-coding-system &optional terminal This function returns the coding system that is in use for decoding keyboard input from TERMINAL--or `nil' if no coding system is to be used for that terminal. If TERMINAL is omitted or `nil', it means the selected frame's terminal. *Note Multiple Terminals::. -- Command: set-keyboard-coding-system coding-system &optional terminal This command specifies CODING-SYSTEM as the coding system to use for decoding keyboard input from TERMINAL. If CODING-SYSTEM is `nil', that means do not decode keyboard input. If TERMINAL is a frame, it means that frame's terminal; if it is `nil', that means the currently selected frame's terminal. *Note Multiple Terminals::. -- Function: terminal-coding-system &optional terminal This function returns the coding system that is in use for encoding terminal output from TERMINAL--or `nil' if the output is not encoded. If TERMINAL is a frame, it means that frame's terminal; if it is `nil', that means the currently selected frame's terminal. -- Command: set-terminal-coding-system coding-system &optional terminal This command specifies CODING-SYSTEM as the coding system to use for encoding terminal output from TERMINAL. If CODING-SYSTEM is `nil', terminal output is not encoded. If TERMINAL is a frame, it means that frame's terminal; if it is `nil', that means the currently selected frame's terminal.  File: elisp, Node: MS-DOS File Types, Prev: Terminal I/O Encoding, Up: Coding Systems 33.9.9 MS-DOS File Types ------------------------ On MS-DOS and Microsoft Windows, Emacs guesses the appropriate end-of-line conversion for a file by looking at the file's name. This feature classifies files as "text files" and "binary files". By "binary file" we mean a file of literal byte values that are not necessarily meant to be characters; Emacs does no end-of-line conversion and no character code conversion for them. On the other hand, the bytes in a text file are intended to represent characters; when you create a new file whose name implies that it is a text file, Emacs uses DOS end-of-line conversion. -- Variable: buffer-file-type This variable, automatically buffer-local in each buffer, records the file type of the buffer's visited file. When a buffer does not specify a coding system with `buffer-file-coding-system', this variable is used to determine which coding system to use when writing the contents of the buffer. It should be `nil' for text, `t' for binary. If it is `t', the coding system is `no-conversion'. Otherwise, `undecided-dos' is used. Normally this variable is set by visiting a file; it is set to `nil' if the file was visited without any actual conversion. Its default value is used to decide how to handle files for which `file-name-buffer-file-type-alist' says nothing about the type: If the default value is non-`nil', then these files are treated as binary: the coding system `no-conversion' is used. Otherwise, nothing special is done for them--the coding system is deduced solely from the file contents, in the usual Emacs fashion. -- User Option: file-name-buffer-file-type-alist This variable holds an alist for recognizing text and binary files. Each element has the form (REGEXP . TYPE), where REGEXP is matched against the file name, and TYPE may be `nil' for text, `t' for binary, or a function to call to compute which. If it is a function, then it is called with a single argument (the file name) and should return `t' or `nil'. When running on MS-DOS or MS-Windows, Emacs checks this alist to decide which coding system to use when reading a file. For a text file, `undecided-dos' is used. For a binary file, `no-conversion' is used. If no element in this alist matches a given file name, then the default value of `buffer-file-type' says how to treat the file.  File: elisp, Node: Input Methods, Next: Locales, Prev: Coding Systems, Up: Non-ASCII Characters 33.10 Input Methods =================== "Input methods" provide convenient ways of entering non-ASCII characters from the keyboard. Unlike coding systems, which translate non-ASCII characters to and from encodings meant to be read by programs, input methods provide human-friendly commands. (*Note Input Methods: (emacs)Input Methods, for information on how users use input methods to enter text.) How to define input methods is not yet documented in this manual, but here we describe how to use them. Each input method has a name, which is currently a string; in the future, symbols may also be usable as input method names. -- Variable: current-input-method This variable holds the name of the input method now active in the current buffer. (It automatically becomes local in each buffer when set in any fashion.) It is `nil' if no input method is active in the buffer now. -- User Option: default-input-method This variable holds the default input method for commands that choose an input method. Unlike `current-input-method', this variable is normally global. -- Command: set-input-method input-method This command activates input method INPUT-METHOD for the current buffer. It also sets `default-input-method' to INPUT-METHOD. If INPUT-METHOD is `nil', this command deactivates any input method for the current buffer. -- Function: read-input-method-name prompt &optional default inhibit-null This function reads an input method name with the minibuffer, prompting with PROMPT. If DEFAULT is non-`nil', that is returned by default, if the user enters empty input. However, if INHIBIT-NULL is non-`nil', empty input signals an error. The returned value is a string. -- Variable: input-method-alist This variable defines all the supported input methods. Each element defines one input method, and should have the form: (INPUT-METHOD LANGUAGE-ENV ACTIVATE-FUNC TITLE DESCRIPTION ARGS...) Here INPUT-METHOD is the input method name, a string; LANGUAGE-ENV is another string, the name of the language environment this input method is recommended for. (That serves only for documentation purposes.) ACTIVATE-FUNC is a function to call to activate this method. The ARGS, if any, are passed as arguments to ACTIVATE-FUNC. All told, the arguments to ACTIVATE-FUNC are INPUT-METHOD and the ARGS. TITLE is a string to display in the mode line while this method is active. DESCRIPTION is a string describing this method and what it is good for. The fundamental interface to input methods is through the variable `input-method-function'. *Note Reading One Event::, and *note Invoking the Input Method::.  File: elisp, Node: Locales, Prev: Input Methods, Up: Non-ASCII Characters 33.11 Locales ============= POSIX defines a concept of "locales" which control which language to use in language-related features. These Emacs variables control how Emacs interacts with these features. -- Variable: locale-coding-system This variable specifies the coding system to use for decoding system error messages and--on X Window system only--keyboard input, for encoding the format argument to `format-time-string', and for decoding the return value of `format-time-string'. -- Variable: system-messages-locale This variable specifies the locale to use for generating system error messages. Changing the locale can cause messages to come out in a different language or in a different orthography. If the variable is `nil', the locale is specified by environment variables in the usual POSIX fashion. -- Variable: system-time-locale This variable specifies the locale to use for formatting time values. Changing the locale can cause messages to appear according to the conventions of a different language. If the variable is `nil', the locale is specified by environment variables in the usual POSIX fashion. -- Function: locale-info item This function returns locale data ITEM for the current POSIX locale, if available. ITEM should be one of these symbols: `codeset' Return the character set as a string (locale item `CODESET'). `days' Return a 7-element vector of day names (locale items `DAY_1' through `DAY_7'); `months' Return a 12-element vector of month names (locale items `MON_1' through `MON_12'). `paper' Return a list `(WIDTH HEIGHT)' for the default paper size measured in millimeters (locale items `PAPER_WIDTH' and `PAPER_HEIGHT'). If the system can't provide the requested information, or if ITEM is not one of those symbols, the value is `nil'. All strings in the return value are decoded using `locale-coding-system'. *Note Locales: (libc)Locales, for more information about locales and locale items.  File: elisp, Node: Searching and Matching, Next: Syntax Tables, Prev: Non-ASCII Characters, Up: Top 34 Searching and Matching ************************* GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the "match data" to determine which text matched the whole regular expression or various portions of it. * Menu: * String Search:: Search for an exact match. * Searching and Case:: Case-independent or case-significant searching. * Regular Expressions:: Describing classes of strings. * Regexp Search:: Searching for a match for a regexp. * POSIX Regexps:: Searching POSIX-style for the longest match. * Match Data:: Finding out which part of the text matched, after a string or regexp search. * Search and Replace:: Commands that loop, searching and replacing. * Standard Regexps:: Useful regexps for finding sentences, pages,... The `skip-chars...' functions also perform a kind of searching. *Note Skipping Characters::. To search for changes in character properties, see *note Property Search::.  File: elisp, Node: String Search, Next: Searching and Case, Up: Searching and Matching 34.1 Searching for Strings ========================== These are the primitive functions for searching through the text in a buffer. They are meant for use in programs, but you may call them interactively. If you do so, they prompt for the search string; the arguments LIMIT and NOERROR are `nil', and REPEAT is 1. These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. *Note Text Representations::. -- Command: search-forward string &optional limit noerror repeat This function searches forward from point for an exact match for STRING. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on NOERROR (see below). In the following example, point is initially at the beginning of the line. Then `(search-forward "fox")' moves point after the last letter of `fox': ---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") => 20 ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ---------- The argument LIMIT specifies the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. If LIMIT is omitted or `nil', it defaults to the end of the accessible portion of the buffer. What happens when the search fails depends on the value of NOERROR. If NOERROR is `nil', a `search-failed' error is signaled. If NOERROR is `t', `search-forward' returns `nil' and does nothing. If NOERROR is neither `nil' nor `t', then `search-forward' moves point to the upper bound and returns `nil'. (It would be more consistent now to return the new position of point in that case, but some existing programs may depend on a value of `nil'.) The argument NOERROR only affects valid searches which fail to find a match. Invalid arguments cause errors regardless of NOERROR. If REPEAT is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails, with results depending on the value of NOERROR, as described above. -- Command: search-backward string &optional limit noerror repeat This function searches backward from point for STRING. It is just like `search-forward' except that it searches backwards and leaves point at the beginning of the match. -- Command: word-search-forward string &optional limit noerror repeat This function searches forward from point for a "word" match for STRING. If it finds a match, it sets point to the end of the match found, and returns the new value of point. Word matching regards STRING as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word `ball' does not match the word `balls'), but the details of punctuation and spacing are ignored (searching for `ball boy' does match `ball. Boy!'). In this example, point is initially at the beginning of the buffer; the search leaves it between the `y' and the `!'. ---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") => 35 ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ---------- If LIMIT is non-`nil', it must be a position in the current buffer; it specifies the upper bound to the search. The match found must not extend after that position. If NOERROR is `nil', then `word-search-forward' signals an error if the search fails. If NOERROR is `t', then it returns `nil' instead of signaling an error. If NOERROR is neither `nil' nor `t', it moves point to LIMIT (or the end of the accessible portion of the buffer) and returns `nil'. If REPEAT is non-`nil', then the search is repeated that many times. Point is positioned at the end of the last match. -- Command: word-search-forward-lax string &optional limit noerror repeat This command is identical to `word-search-forward', except that the end of `string' need not match a word boundary unless it ends in whitespace. For instance, searching for `ball boy' matches `ball boyee', but does not match `aball boy'. -- Command: word-search-backward string &optional limit noerror repeat This function searches backward from point for a word match to STRING. This function is just like `word-search-forward' except that it searches backward and normally leaves point at the beginning of the match. -- Command: word-search-backward-lax string &optional limit noerror repeat This command is identical to `word-search-backward', except that the end of `string' need not match a word boundary unless it ends in whitespace.  File: elisp, Node: Searching and Case, Next: Regular Expressions, Prev: String Search, Up: Searching and Matching 34.2 Searching and Case ======================= By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' or `foo' is also considered a match. This applies to regular expressions, too; thus, `[aB]' would match `a' or `A' or `b' or `B'. If you do not want this feature, set the variable `case-fold-search' to `nil'. Then all letters must match exactly, including case. This is a buffer-local variable; altering the variable affects only the current buffer. (*Note Intro to Buffer-Local::.) Alternatively, you may change the default value of `case-fold-search'. Note that the user-level incremental search feature handles case distinctions differently. When the search string contains only lower case letters, the search ignores case, but when the search string contains one or more upper case letters, the search becomes case-sensitive. But this has nothing to do with the searching functions used in Lisp code. -- User Option: case-fold-search This buffer-local variable determines whether searches should ignore case. If the variable is `nil' they do not ignore case; otherwise they do ignore case. -- User Option: case-replace This variable determines whether the higher level replacement functions should preserve case. If the variable is `nil', that means to use the replacement text verbatim. A non-`nil' value means to convert the case of the replacement text according to the text being replaced. This variable is used by passing it as an argument to the function `replace-match'. *Note Replacing Match::.  File: elisp, Node: Regular Expressions, Next: Regexp Search, Prev: Searching and Case, Up: Searching and Matching 34.3 Regular Expressions ======================== A "regular expression", or "regexp" for short, is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them. For convenient interactive development of regular expressions, you can use the `M-x re-builder' command. It provides a convenient interface for creating regular expressions, by giving immediate visual feedback in a separate buffer. As you edit the regexp, all its matches in the target buffer are highlighted. Each parenthesized sub-expression of the regexp is shown in a distinct face, which makes it easier to verify even very complex regexps. * Menu: * Syntax of Regexps:: Rules for writing regular expressions. * Regexp Example:: Illustrates regular expression syntax. * Regexp Functions:: Functions for operating on regular expressions.  File: elisp, Node: Syntax of Regexps, Next: Regexp Example, Up: Regular Expressions 34.3.1 Syntax of Regular Expressions ------------------------------------ Regular expressions have a syntax in which a few characters are special constructs and the rest are "ordinary". An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are `.', `*', `+', `?', `[', `^', `$', and `\'; no new special characters will be defined in the future. The character `]' is special if it ends a character alternative (see later). The character `-' is special inside a character alternative. A `[:' and balancing `:]' enclose a character class inside a character alternative. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it. For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does _not_ match the string `fg', but it does match a _part_ of that string.) Likewise, `o' is a regular expression that matches only `o'. Any two regular expressions A and B can be concatenated. The result is a regular expression that matches a string if A matches some amount of the beginning of that string and B matches the rest of the string. As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something more powerful, you need to use one of the special regular expression constructs. * Menu: * Regexp Special:: Special characters in regular expressions. * Char Classes:: Character classes used in regular expressions. * Regexp Backslash:: Backslash-sequences in regular expressions.  File: elisp, Node: Regexp Special, Next: Char Classes, Up: Syntax of Regexps 34.3.1.1 Special Characters in Regular Expressions .................................................. Here is a list of the characters that are special in a regular expression. `.' (Period) is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like `a.b', which matches any three-character string that begins with `a' and ends with `b'. `*' is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively as many times as possible. Thus, `o*' matches any number of `o's (including no `o's). `*' always applies to the _smallest_ possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. It matches `f', `fo', `foo', and so on. The matcher processes a `*' construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the `*'-modified construct in the hope that that will make it possible to match the rest of the pattern. For example, in matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully. *Warning:* Nested repetition operators can run for an indefinitely long time, if they lead to ambiguous matching. For example, trying to match the regular expression `\(x+y*\)*a' against the string `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz' could take hours before it ultimately fails. Emacs must try each way of grouping the `x's before concluding that none of them can work. Even worse, `\(x*\)*' can match the null string in infinitely many ways, so it causes an infinite loop. To avoid these problems, check nested repetitions carefully, to make sure that they do not cause combinatorial explosions in backtracking. `+' is a postfix operator, similar to `*' except that it must match the preceding expression at least once. So, for example, `ca+r' matches the strings `car' and `caaaar' but not the string `cr', whereas `ca*r' matches all three strings. `?' is a postfix operator, similar to `*' except that it must match the preceding expression either once or not at all. For example, `ca?r' matches `car' or `cr'; nothing else. `*?', `+?', `??' These are "non-greedy" variants of the operators `*', `+' and `?'. Where those operators match the largest possible substring (consistent with matching the entire containing expression), the non-greedy variants match the smallest possible substring (consistent with matching the entire containing expression). For example, the regular expression `c[ad]*a' when applied to the string `cdaaada' matches the whole string; but the regular expression `c[ad]*?a', applied to that same string, matches just `cda'. (The smallest possible match here for `[ad]*?' that permits the whole expression to match is `d'.) `[ ... ]' is a "character alternative", which begins with `[' and is terminated by `]'. In the simplest case, the characters between the two brackets are what this character alternative can match. Thus, `[ad]' matches either one `a' or one `d', and `[ad]*' matches any string composed of just `a's and `d's (including the empty string), from which it follows that `c[ad]*r' matches `cr', `car', `cdr', `caddaar', etc. You can also include character ranges in a character alternative, by writing the starting and ending characters with a `-' between them. Thus, `[a-z]' matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower case ASCII letter or `$', `%' or period. Note that the usual regexp special characters are not special inside a character alternative. A completely different set of characters is special inside character alternatives: `]', `-' and `^'. To include a `]' in a character alternative, you must make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first or last character of the character alternative, or put it after a range. Thus, `[]-]' matches both `]' and `-'. To include `^' in a character alternative, put it anywhere but at the beginning. The beginning and end of a range of multibyte characters must be in the same character set (*note Character Sets::). Thus, `"[\x8e0-\x97c]"' is invalid because character 0x8e0 (`a' with grave accent) is in the Emacs character set for Latin-1 but the character 0x97c (`u' with diaeresis) is in the Emacs character set for Latin-2. (We use Lisp string syntax to write that example, and a few others in the next few paragraphs, in order to include hex escape sequences in them.) If a range starts with a unibyte character C and ends with a multibyte character C2, the range is divided into two parts: one is `C..?\377', the other is `C1..C2', where C1 is the first character of the charset to which C2 belongs. You cannot always match all non-ASCII characters with the regular expression `"[\200-\377]"'. This works when searching a unibyte buffer or string (*note Text Representations::), but not in a multibyte buffer or string, because many non-ASCII characters have codes above octal 0377. However, the regular expression `"[^\000-\177]"' does match all non-ASCII characters (see below regarding `^'), in both multibyte and unibyte representations, because only the ASCII characters are excluded. A character alternative can also specify named character classes (*note Char Classes::). This is a POSIX feature whose syntax is `[:CLASS:]'. Using a character class is equivalent to mentioning each of the characters in that class; but the latter is not feasible in practice, since some classes include thousands of different characters. `[^ ... ]' `[^' begins a "complemented character alternative". This matches any character except the ones specified. Thus, `[^a-z0-9A-Z]' matches all characters _except_ letters and digits. `^' is not special in a character alternative unless it is the first character. The character following the `^' is treated as if it were first (in other words, `-' and `]' are not special there). A complemented character alternative can match a newline, unless newline is mentioned as one of the characters not to match. This is in contrast to the handling of regexps in programs such as `grep'. `^' When matching a buffer, `^' matches the empty string, but only at the beginning of a line in the text being matched (or the beginning of the accessible portion of the buffer). Otherwise it fails to match anything. Thus, `^foo' matches a `foo' that occurs at the beginning of a line. When matching a string instead of a buffer, `^' matches at the beginning of the string or after a newline character. For historical compatibility reasons, `^' can be used only at the beginning of the regular expression, or after `\(', `\(?:' or `\|'. `$' is similar to `^' but matches only at the end of a line (or the end of the accessible portion of the buffer). Thus, `x+$' matches a string of one `x' or more at the end of a line. When matching a string instead of a buffer, `$' matches at the end of the string or before a newline character. For historical compatibility reasons, `$' can be used only at the end of the regular expression, or before `\)' or `\|'. `\' has two functions: it quotes the special characters (including `\'), and it introduces additional special constructs. Because `\' quotes special characters, `\$' is a regular expression that matches only `$', and `\[' is a regular expression that matches only `[', and so on. Note that `\' also has special meaning in the read syntax of Lisp strings (*note String Type::), and must be quoted with `\'. For example, the regular expression that matches the `\' character is `\\'. To write a Lisp string that contains the characters `\\', Lisp syntax requires you to quote each `\' with another `\'. Therefore, the read syntax for a regular expression matching `\' is `"\\\\"'. *Please note:* For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears. As a `\' is not special inside a character alternative, it can never remove the special meaning of `-' or `]'. So you should not quote these characters when they have no special meaning either. This would not clarify anything, since backslashes can legitimately precede these characters where they _have_ special meaning, as in `[^\]' (`"[^\\]"' for Lisp string syntax), which matches any single character except a backslash. In practice, most `]' that occur in regular expressions close a character alternative and hence are special. However, occasionally a regular expression may try to match a complex pattern of literal `[' and `]'. In such situations, it sometimes may be necessary to carefully parse the regexp from the start to determine which square brackets enclose a character alternative. For example, `[^][]]' consists of the complemented character alternative `[^][]' (which matches any single character that is not a square bracket), followed by a literal `]'. The exact rules are that at the beginning of a regexp, `[' is special and `]' not. This lasts until the first unquoted `[', after which we are in a character alternative; `[' is no longer special (except when it starts a character class) but `]' is special, unless it immediately follows the special `[' or that `[' followed by a `^'. This lasts until the next special `]' that does not end a character class. This ends the character alternative and restores the ordinary syntax of regular expressions; an unquoted `[' is special again and a `]' not.  File: elisp, Node: Char Classes, Next: Regexp Backslash, Prev: Regexp Special, Up: Syntax of Regexps 34.3.1.2 Character Classes .......................... Here is a table of the classes you can use in a character alternative, and what they mean: `[:ascii:]' This matches any ASCII character (codes 0-127). `[:alnum:]' This matches any letter or digit. (At present, for multibyte characters, it matches anything that has word syntax.) `[:alpha:]' This matches any letter. (At present, for multibyte characters, it matches anything that has word syntax.) `[:blank:]' This matches space and tab only. `[:cntrl:]' This matches any ASCII control character. `[:digit:]' This matches `0' through `9'. Thus, `[-+[:digit:]]' matches any digit, as well as `+' and `-'. `[:graph:]' This matches graphic characters--everything except ASCII control characters, space, and the delete character. `[:lower:]' This matches any lower-case letter, as determined by the current case table (*note Case Tables::). If `case-fold-search' is non-`nil', this also matches any upper-case letter. `[:multibyte:]' This matches any multibyte character (*note Text Representations::). `[:nonascii:]' This matches any non-ASCII character. `[:print:]' This matches printing characters--everything except ASCII control characters and the delete character. `[:punct:]' This matches any punctuation character. (At present, for multibyte characters, it matches anything that has non-word syntax.) `[:space:]' This matches any character that has whitespace syntax (*note Syntax Class Table::). `[:unibyte:]' This matches any unibyte character (*note Text Representations::). `[:upper:]' This matches any upper-case letter, as determined by the current case table (*note Case Tables::). If `case-fold-search' is non-`nil', this also matches any lower-case letter. `[:word:]' This matches any character that has word syntax (*note Syntax Class Table::). `[:xdigit:]' This matches the hexadecimal digits: `0' through `9', `a' through `f' and `A' through `F'.  File: elisp, Node: Regexp Backslash, Prev: Char Classes, Up: Syntax of Regexps 34.3.1.3 Backslash Constructs in Regular Expressions .................................................... For the most part, `\' followed by any character matches only that character. However, there are several exceptions: certain two-character sequences starting with `\' that have special meanings. (The character after the `\' in such a sequence is always ordinary when used on its own.) Here is a table of the special `\' constructs. `\|' specifies an alternative. Two regular expressions A and B with `\|' in between form an expression that matches anything that either A or B matches. Thus, `foo\|bar' matches either `foo' or `bar' but no other string. `\|' applies to the largest possible surrounding expressions. Only a surrounding `\( ... \)' grouping can limit the grouping power of `\|'. If you need full backtracking capability to handle multiple uses of `\|', use the POSIX regular expression functions (*note POSIX Regexps::). `\{M\}' is a postfix operator that repeats the previous pattern exactly M times. Thus, `x\{5\}' matches the string `xxxxx' and nothing else. `c[ad]\{3\}r' matches string such as `caaar', `cdddr', `cadar', and so on. `\{M,N\}' is a more general postfix operator that specifies repetition with a minimum of M repeats and a maximum of N repeats. If M is omitted, the minimum is 0; if N is omitted, there is no maximum. For example, `c[ad]\{1,2\}r' matches the strings `car', `cdr', `caar', `cadr', `cdar', and `cddr', and nothing else. `\{0,1\}' or `\{,1\}' is equivalent to `?'. `\{0,\}' or `\{,\}' is equivalent to `*'. `\{1,\}' is equivalent to `+'. `\( ... \)' is a grouping construct that serves three purposes: 1. To enclose a set of `\|' alternatives for other operations. Thus, the regular expression `\(foo\|bar\)x' matches either `foox' or `barx'. 2. To enclose a complicated expression for the postfix operators `*', `+' and `?' to operate on. Thus, `ba\(na\)*' matches `ba', `bana', `banana', `bananana', etc., with any number (zero or more) of `na' strings. 3. To record a matched substring for future reference with `\DIGIT' (see below). This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that was assigned as a second meaning to the same `\( ... \)' construct because, in practice, there was usually no conflict between the two meanings. But occasionally there is a conflict, and that led to the introduction of shy groups. `\(?: ... \)' is the "shy group" construct. A shy group serves the first two purposes of an ordinary group (controlling the nesting of other operators), but it does not get a number, so you cannot refer back to its value with `\DIGIT'. Shy groups are particularly useful for mechanically-constructed regular expressions, because they can be added automatically without altering the numbering of ordinary, non-shy groups. Shy groups are also called "non-capturing" or "unnumbered groups". `\(?NUM: ... \)' is the "explicitly numbered group" construct. Normal groups get their number implicitly, based on their position, which can be inconvenient. This construct allows you to force a particular group number. There is no particular restriction on the numbering, e.g. you can have several groups with the same number in which case the last one to match (i.e. the rightmost match) will win. Implicitly numbered groups always get the smallest integer larger than the one of any previous group. `\DIGIT' matches the same text that matched the DIGITth occurrence of a grouping (`\( ... \)') construct. In other words, after the end of a group, the matcher remembers the beginning and end of the text matched by that group. Later on in the regular expression you can use `\' followed by DIGIT to match that same text, whatever it may have been. The strings matching the first nine grouping constructs appearing in the entire regular expression passed to a search or matching function are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use `\1' through `\9' to refer to the text matched by the corresponding grouping constructs. For example, `\(.*\)\1' matches any newline-free string that is composed of two identical halves. The `\(.*\)' matches the first half, which may be anything, but the `\1' that follows must match the same exact text. If a `\( ... \)' construct matches more than once (which can happen, for instance, if it is followed by `*'), only the last match is recorded. If a particular grouping construct in the regular expression was never matched--for instance, if it appears inside of an alternative that wasn't used, or inside of a repetition that repeated zero times--then the corresponding `\DIGIT' construct never matches anything. To use an artificial example, `\(foo\(b*\)\|lose\)\2' cannot match `lose': the second alternative inside the larger group matches it, but then `\2' is undefined and can't match anything. But it can match `foobb', because the first alternative matches `foob' and `\2' matches `b'. `\w' matches any word-constituent character. The editor syntax table determines which characters these are. *Note Syntax Tables::. `\W' matches any character that is not a word constituent. `\sCODE' matches any character whose syntax is CODE. Here CODE is a character that represents a syntax code: thus, `w' for word constituent, `-' for whitespace, `(' for open parenthesis, etc. To represent whitespace syntax, use either `-' or a space character. *Note Syntax Class Table::, for a list of syntax codes and the characters that stand for them. `\SCODE' matches any character whose syntax is not CODE. `\cC' matches any character whose category is C. Here C is a character that represents a category: thus, `c' for Chinese characters or `g' for Greek characters in the standard category table. `\CC' matches any character whose category is not C. The following regular expression constructs match the empty string--that is, they don't use up any characters--but whether they match depends on the context. For all, the beginning and end of the accessible portion of the buffer are treated as if they were the actual beginning and end of the buffer. `\`' matches the empty string, but only at the beginning of the buffer or string being matched against. `\'' matches the empty string, but only at the end of the buffer or string being matched against. `\=' matches the empty string, but only at point. (This construct is not defined when matching against a string.) `\b' matches the empty string, but only at the beginning or end of a word. Thus, `\bfoo\b' matches any occurrence of `foo' as a separate word. `\bballs?\b' matches `ball' or `balls' as a separate word. `\b' matches at the beginning or end of the buffer (or string) regardless of what text appears next to it. `\B' matches the empty string, but _not_ at the beginning or end of a word, nor at the beginning or end of the buffer (or string). `\<' matches the empty string, but only at the beginning of a word. `\<' matches at the beginning of the buffer (or string) only if a word-constituent character follows. `\>' matches the empty string, but only at the end of a word. `\>' matches at the end of the buffer (or string) only if the contents end with a word-constituent character. `\_<' matches the empty string, but only at the beginning of a symbol. A symbol is a sequence of one or more word or symbol constituent characters. `\_<' matches at the beginning of the buffer (or string) only if a symbol-constituent character follows. `\_>' matches the empty string, but only at the end of a symbol. `\_>' matches at the end of the buffer (or string) only if the contents end with a symbol-constituent character. Not every string is a valid regular expression. For example, a string that ends inside a character alternative without terminating `]' is invalid, and so is a string that ends with a single `\'. If an invalid regular expression is passed to any of the search functions, an `invalid-regexp' error is signaled.  File: elisp, Node: Regexp Example, Next: Regexp Functions, Prev: Syntax of Regexps, Up: Regular Expressions 34.3.2 Complex Regexp Example ----------------------------- Here is a complicated regexp which was formerly used by Emacs to recognize the end of a sentence together with any whitespace that follows. (Nowadays Emacs uses a similar but more complex default regexp constructed by the function `sentence-end'. *Note Standard Regexps::.) First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the string, `\\' for a backslash as part of the string, `\t' for a tab and `\n' for a newline. "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" In contrast, if you evaluate this string, you will see the following: "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" => "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[ ]*" In this output, tab and newline appear as themselves. This regular expression contains four parts in succession and can be deciphered as follows: `[.?!]' The first part of the pattern is a character alternative that matches any one of three characters: period, question mark, and exclamation mark. The match must begin with one of these three characters. (This is one point where the new default regexp used by Emacs differs from the old. The new value also allows some non-ASCII characters that end a sentence without any following whitespace.) `[]\"')}]*' The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The `\"' is Lisp syntax for a double-quote in a string. The `*' at the end indicates that the immediately preceding regular expression (a character alternative, in this case) may be repeated zero or more times. `\\($\\| $\\|\t\\| \\)' The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line (optionally with a space), or a tab, or two spaces. The double backslashes mark the parentheses and vertical bars as regular expression syntax; the parentheses delimit a group and the vertical bars separate alternatives. The dollar sign is used to match the end of a line. `[ \t\n]*' Finally, the last part of the pattern matches any additional whitespace beyond the minimum needed to end a sentence.  File: elisp, Node: Regexp Functions, Prev: Regexp Example, Up: Regular Expressions 34.3.3 Regular Expression Functions ----------------------------------- These functions operate on regular expressions. -- Function: regexp-quote string This function returns a regular expression whose only exact match is STRING. Using this regular expression in `looking-at' will succeed only if the next characters in the buffer are STRING; using it in a search function will succeed if the text being searched contains STRING. This allows you to request an exact string match or search when calling a function that wants a regular expression. (regexp-quote "^The cat$") => "\\^The cat\\$" One use of `regexp-quote' is to combine an exact string match with context described as a regular expression. For example, this searches for the string that is the value of STRING, surrounded by whitespace: (re-search-forward (concat "\\s-" (regexp-quote string) "\\s-")) -- Function: regexp-opt strings &optional paren This function returns an efficient regular expression that will match any of the strings in the list STRINGS. This is useful when you need to make matching or searching as fast as possible--for example, for Font Lock mode. If the optional argument PAREN is non-`nil', then the returned regular expression is always enclosed by at least one parentheses-grouping construct. If PAREN is `words', then that construct is additionally surrounded by `\<' and `\>'. This simplified definition of `regexp-opt' produces a regular expression which is equivalent to the actual value (but not as efficient): (defun regexp-opt (strings paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren))) -- Function: regexp-opt-depth regexp This function returns the total number of grouping constructs (parenthesized expressions) in REGEXP. This does not include shy groups (*note Regexp Backslash::).  File: elisp, Node: Regexp Search, Next: POSIX Regexps, Prev: Regular Expressions, Up: Searching and Matching 34.4 Regular Expression Searching ================================= In GNU Emacs, you can search for the next match for a regular expression either incrementally or not. For incremental search commands, see *note Regular Expression Search: (emacs)Regexp Search. Here we describe only the search functions useful in programs. The principal one is `re-search-forward'. These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. *Note Text Representations::. -- Command: re-search-forward regexp &optional limit noerror repeat This function searches forward in the current buffer for a string of text that is matched by the regular expression REGEXP. The function skips over any amount of text that is not matched by REGEXP, and leaves point at the end of the first match found. It returns the new value of point. If LIMIT is non-`nil', it must be a position in the current buffer. It specifies the upper bound to the search. No match extending after that position is accepted. If REPEAT is supplied, it must be a positive number; the search is repeated that many times; each repetition starts at the end of the previous match. If all these successive searches succeed, the search succeeds, moving point and returning its new value. Otherwise the search fails. What `re-search-forward' does when the search fails depends on the value of NOERROR: `nil' Signal a `search-failed' error. `t' Do nothing and return `nil'. anything else Move point to LIMIT (or the end of the accessible portion of the buffer) and return `nil'. In the following example, point is initially before the `T'. Evaluating the search call moves point to the end of that line (between the `t' of `hat' and the newline). ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) => 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ---------- -- Command: re-search-backward regexp &optional limit noerror repeat This function searches backward in the current buffer for a string of text that is matched by the regular expression REGEXP, leaving point at the beginning of the first text found. This function is analogous to `re-search-forward', but they are not simple mirror images. `re-search-forward' finds the match whose beginning is as close as possible to the starting point. If `re-search-backward' were a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible (and yet ends before the starting point). The reason for this is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position. A true mirror-image of `re-search-forward' would require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that. -- Function: string-match regexp string &optional start This function returns the index of the start of the first match for the regular expression REGEXP in STRING, or `nil' if there is no match. If START is non-`nil', the search starts at that index in STRING. For example, (string-match "quick" "The quick brown fox jumped quickly.") => 4 (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 The index of the first character of the string is 0, the index of the second character is 1, and so on. After this function returns, the index of the first character beyond the match is available as `(match-end 0)'. *Note Match Data::. (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 (match-end 0) => 32 -- Function: string-match-p regexp string &optional start This predicate function does what `string-match' does, but it avoids modifying the match data. -- Function: looking-at regexp This function determines whether the text in the current buffer directly following point matches the regular expression REGEXP. "Directly following" means precisely that: the search is "anchored" and it can succeed only starting with the first character following point. The result is `t' if so, `nil' otherwise. This function does not move point, but it updates the match data, which you can access using `match-beginning' and `match-end'. *Note Match Data::. If you need to test for a match without modifying the match data, use `looking-at-p', described below. In this example, point is located directly before the `T'. If it were anywhere else, the result would be `nil'. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") => t -- Function: looking-back regexp &optional limit greedy This function returns `t' if REGEXP matches text before point, ending at point, and `nil' otherwise. Because regular expression matching works only going forward, this is implemented by searching backwards from point for a match that ends at point. That can be quite slow if it has to search a long distance. You can bound the time required by specifying LIMIT, which says not to search before LIMIT. In this case, the match that is found must begin at or after LIMIT. If GREEDY is non-`nil', this function extends the match backwards as far as possible, stopping when a single additional previous character cannot be part of a match for regexp. When the match is extended, its starting position is allowed to occur before LIMIT. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-back "read \"" 3) => t (looking-back "read \"" 4) => nil -- Function: looking-at-p regexp This predicate function works like `looking-at', but without updating the match data. -- Variable: search-spaces-regexp If this variable is non-`nil', it should be a regular expression that says how to search for whitespace. In that case, any group of spaces in a regular expression being searched for stands for use of this regular expression. However, spaces inside of constructs such as `[...]' and `*', `+', `?' are not affected by `search-spaces-regexp'. Since this variable affects all regular expression search and match constructs, you should bind it temporarily for as small as possible a part of the code.