This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This version is the edition 2.3 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.23. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.  File: elisp, Node: X Connections, Next: Resources, Prev: X Selections, Up: Frames X Connections ============= You can close the connection with the X server with the function `x-close-current-connection', and open a new one with `x-open-connection' (perhaps with a different server and display). - Function: x-close-current-connection This function closes the connection to the X server. It deletes all frames, making Emacs effectively inaccessible to the user; therefore, a Lisp program that closes the connection should open another one. - Function: x-open-connection DISPLAY &optional RESOURCE-STRING This function opens a connection to an X server, for use of display DISPLAY. The optional argument RESOURCE-STRING is a string of resource names and values, in the same format used in the `.Xresources' file. The values you specify override the resource values recorded in the X server itself. Here's an example of what this string might look like: "*BorderWidth: 3\n*InternalBorder: 2\n" *Note Resources::. - Function: x-display-color-p This returns `t' if the connected X display has color, and `nil' otherwise. - Function: x-color-defined-p COLOR This function reports whether a color name is meaningful and supported on the X display Emacs is using. It returns `t' if the display supports that color; otherwise, `nil'. Black-and-white displays support just two colors, `"black"' or `"white"'. Color displays support many other colors. - Function: x-synchronize FLAG The function `x-synchronize' enables or disables synchronous communication with the X server. It enables synchronous communication if FLAG is non-`nil', and disables it if FLAG is `nil'. In synchronous mode, Emacs waits for a response to each X protocol command before doing anything else. This is useful for debugging Emacs, because protocol errors are reported right away, which helps you find the erroneous command. Synchronous mode is not the default because it is much slower.  File: elisp, Node: Resources, Next: Server Data, Prev: X Connections, Up: Frames X Resources =========== - Function: x-get-resource ATTRIBUTE &optional NAME CLASS The function `x-get-resource' retrieves a resource value from the X Windows defaults database. Resources are indexed by a combination of a "key" and a "class". This function searches using a key of the form `INSTANCE.ATTRIBUTE', using the name under which Emacs was invoked as INSTANCE, and using `Emacs' as the class. The optional arguments COMPONENT and SUBCLASS add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is `INSTANCE.COMPONENT.ATTRIBUTE', and the class is `Emacs.SUBCLASS'. *Note X Resources: (emacs)Resources X.  File: elisp, Node: Server Data, Prev: Resources, Up: Frames Data about the X Server ======================= This section describes functions and a variable that you can use to get information about the capabilities and origin of the X server that Emacs is displaying its frames on. - Function: x-display-screens This function returns the number of screens associated with the current display. - Function: x-server-version This function returns the list of version numbers of the X server in use. - Function: x-server-vendor This function returns the vendor supporting the X server in use. - Function: x-display-pixel-height This function returns the height of this X screen in pixels. - Function: x-display-mm-height This function returns the height of this X screen in millimeters. - Function: x-display-pixel-width This function returns the width of this X screen in pixels. - Function: x-display-mm-width This function returns the width of this X screen in millimeters. - Function: x-display-backing-store This function returns the backing store capability of this screen. Values can be the symbols `always', `when-mapped', or `not-useful'. - Function: x-display-save-under This function returns non-`nil' if this X screen supports the SaveUnder feature. - Function: x-display-planes This function returns the number of planes this display supports. - Function: x-display-visual-class This function returns the visual class for this X screen. The value is one of the symbols `static-gray', `gray-scale', `static-color', `pseudo-color', `true-color', and `direct-color'. - Function: x-display-color-p This function returns `t' if the X screen in use is a color screen. - Function: x-display-color-cells This function returns the number of color cells this X screen supports.  File: elisp, Node: Positions, Next: Markers, Prev: Frames, Up: Top Positions ********* A "position" is the index of a character in the text of buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, the we often speak of the character "at" a position, meaning the character after that position. Positions are usually represented as integers starting from 1, but can also be represented as "markers"--special objects which relocate automatically when text is inserted or deleted so they stay with the surrounding characters. *Note Markers::. * Menu: * Point:: The special position where editing takes place. * Motion:: Changing point. * Excursions:: Temporary motion and buffer changes. * Narrowing:: Restricting editing to a portion of the buffer.  File: elisp, Node: Point, Next: Motion, Up: Positions Point ===== "Point" is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places. Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Many terminals display the cursor over the character that immediately follows point; on such terminals, point is actually before the character on which the cursor sits. The value of point is a number between 1 and the buffer size plus 1. If narrowing is in effect (*note Narrowing::.), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it). Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. *Note Window Point::, for more details. - Function: point This function returns the position of point in the current buffer, as an integer. (point) => 175 - Function: point-min This function returns the minimum accessible value of point in the current buffer. This is 1, unless narrowing is in effect, in which case it is the position of the start of the region that you narrowed to. (*Note Narrowing::.) - Function: point-max This function returns the maximum accessible value of point in the current buffer. This is `(1+ (buffer-size))', unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (*Note Narrowing::). - Function: buffer-end FLAG This function returns `(point-min)' if FLAG is less than 1, `(point-max)' otherwise. The argument FLAG must be a number. - Function: buffer-size This function returns the total number of characters in the current buffer. In the absence of any narrowing (*note Narrowing::.), `point-max' returns a value one larger than this. (buffer-size) => 35 (point-max) => 36  File: elisp, Node: Motion, Next: Excursions, Prev: Point, Up: Positions Motion ====== Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. *Note Point::. * Menu: * Character Motion:: Moving in terms of characters. * Word Motion:: Moving in terms of words. * Buffer End Motion:: Moving to the beginning or end of the buffer. * Text Lines:: Moving in terms of lines of text. * Screen Lines:: Moving in terms of lines as displayed. * Vertical Motion:: Implementation of `next-line' and `previous-line'. * List Motion:: Moving by parsing lists and sexps. * Skipping Characters:: Skipping characters belonging to a certain set.  File: elisp, Node: Character Motion, Next: Word Motion, Up: Motion Motion by Characters -------------------- These functions move point based on a count of characters. `goto-char' is the fundamental primitive; the functions others use that. - Command: goto-char POSITION This function sets point in the current buffer to the value POSITION. If POSITION is less than 1, it moves point to the beginning of the buffer. If POSITION is greater than the length of the buffer, it moves point to the end. If narrowing is in effect, POSITION still counts from the beginning of the buffer, but point cannot go outside the accessible portion. If POSITION is out of range, `goto-char' moves point to the beginning or the end of the accessible portion. When this function is called interactively, POSITION is the numeric prefix argument, if provided; otherwise it is read from the minibuffer. `goto-char' returns POSITION. - Command: forward-char &optional COUNT This function moves point COUNT characters forward, towards the end of the buffer (or backward, towards the beginning of the buffer, if COUNT is negative). If the function attempts to move point past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), an error is signaled with error code `beginning-of-buffer' or `end-of-buffer'. In an interactive call, COUNT is the numeric prefix argument. - Command: backward-char &optional COUNT This function moves point COUNT characters backward, towards the beginning of the buffer (or forward, towards the end of the buffer, if COUNT is negative). If the function attempts to move point past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), an error is signaled with error code `beginning-of-buffer' or `end-of-buffer'. In an interactive call, COUNT is the numeric prefix argument.  File: elisp, Node: Word Motion, Next: Buffer End Motion, Prev: Character Motion, Up: Motion Motion by Words --------------- These functions for parsing words use the syntax table to decide whether a given character is part of a word. *Note Syntax Tables::. - Command: forward-word COUNT This function moves point forward COUNT words (or backward if COUNT is negative). Normally it returns `t'. If this motion encounters the beginning or end of the buffer, or the limits of the accessible portion when narrowing is in effect, point stops there and the value is `nil'. In an interactive call, COUNT is set to the numeric prefix argument. - Command: backward-word COUNT This function just like `forward-word', except that it moves backward until encountering the front of a word, rather than forward. In an interactive call, COUNT is set to the numeric prefix argument. This function is rarely used in programs, as it is more efficient to call `forward-word' with negative argument. - Variable: words-include-escapes This variable affects the behavior of `forward-word' and everything that uses it. If it is non-`nil', then characters in the "escape" and "character quote" syntax classes count as part of words. Otherwise, they do not.  File: elisp, Node: Buffer End Motion, Next: Text Lines, Prev: Word Motion, Up: Motion Motion to an End of the Buffer ------------------------------ To move point to the beginning of the buffer, write: (goto-char (point-min)) Likewise, to move to the end of the buffer, use: (goto-char (point-max)) Here are two commands which users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area. - Command: beginning-of-buffer &optional N This function moves point to the beginning of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position. If N is non-`nil', then it puts point N tenths of the way from the beginning of the buffer. In an interactive call, N is the numeric prefix argument, if provided; otherwise N defaults to `nil'. Don't use this function in Lisp programs! - Command: end-of-buffer &optional N This function moves point to the end of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position. If N is non-`nil', then it puts point N tenths of the way from the end. In an interactive call, N is the numeric prefix argument, if provided; otherwise N defaults to `nil'. Don't use this function in Lisp programs!  File: elisp, Node: Text Lines, Next: Screen Lines, Prev: Buffer End Motion, Up: Motion Motion by Text Lines -------------------- Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed. - Command: goto-line LINE This function moves point to the front of the LINEth line, counting from line 1 at beginning of buffer. If LINE is less than 1, it moves point to the beginning of the buffer. If LINE is greater than the number of lines in the buffer, it moves point to the *end of the last line* of the buffer. If narrowing is in effect, then LINE still counts from the beginning of the buffer, but point cannot go outside the accessible portion. So `goto-line' moves point to the beginning or end of the accessible portion, if the line number specifies an inaccessible position. The return value of `goto-line' is the difference between LINE and the line number of the line to which point actually was able move (in the full buffer, disregarding any narrowing). Thus, the value is positive if the scan encounters the real end of the buffer. In an interactive call, LINE is the numeric prefix argument if one has been provided. Otherwise LINE is read in the minibuffer. - Command: beginning-of-line &optional COUNT This function moves point to the beginning of the current line. With an argument COUNT not `nil' or 1, it moves forward COUNT-1 lines and then to the beginning of the line. If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point at the end of the buffer. No error is signaled. - Command: end-of-line &optional COUNT This function moves point to the end of the current line. With an argument COUNT not `nil' or 1, it moves forward COUNT-1 lines and then to the end of the line. If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point at the end of the buffer. No error is signaled. - Command: forward-line &optional COUNT This function moves point forward COUNT lines, to the beginning of the line. If COUNT is negative, it moves point -COUNT lines backward, to the beginning of the line. If `forward-line' encounters the beginning or end of the buffer (or of the accessible portion) before finding that many lines, it sets point there. No error is signaled. `forward-line' returns the difference between COUNT and the number of lines actually moved. If you attempt to move down five lines from the beginning of a buffer that has only three lines, point stops at the end of the last line, and the value will be 2. In an interactive call, COUNT is the numeric prefix argument. - Function: count-lines START END This function returns the number of lines between the positions START and END in the current buffer. If START and END are equal, then it returns 0. Otherwise it returns at least 1, even if START and END are on the same line. This is because the text between them, considered in isolation, must contain at least one line unless it is empty. Here is an example of using `count-lines': (defun current-line () "Return the vertical position of point..." (+ (count-lines (window-start) (point)) (if (= (current-column) 0) 1 0) -1)) Also see the functions `bolp' and `eolp' in *Note Near Point::. These functions do not move point, but test whether it is already at the beginning or end of a line.  File: elisp, Node: Screen Lines, Next: Vertical Motion, Prev: Text Lines, Up: Motion Motion by Screen Lines ---------------------- The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines. In some cases, text lines are truncated on the screen rather than continued onto additional screen lines. In these cases, `vertical-motion' moves point much like `forward-line'. *Note Truncation::. Because the width of a given string depends on the flags which control the appearance of certain characters, `vertical-motion' behaves differently, for a given piece of text, depending on the buffer it is in, and even on the selected window (because the width, the truncation flag, and display table may vary between windows). *Note Usual Display::. - Function: vertical-motion COUNT &optional WINDOW This function moves point to the start of the screen line COUNT screen lines down from the screen line containing point. If COUNT is negative, it moves up instead. `vertical-motion' returns the number of lines moved. The value may be less in absolute value than COUNT if the beginning or end of the buffer was reached. The window WINDOW is used for obtaining parameters such as the width, the horizontal scrolling, and the display table. But `vertical-motion' always operates on the current buffer, even if WINDOW currently displays some other buffer. - Command: move-to-window-line COUNT This function moves point with respect to the text currently displayed in the selected window. It moves point to the beginning of the screen line COUNT screen lines from the top of the window. If COUNT is negative, that specifies a position -COUNT lines from the bottom--or else the last line of the buffer, if the buffer ends above the specified screen position. If COUNT is `nil', then point moves to the beginning of the line in the middle of the window. If the absolute value of COUNT is greater than the size of the window, then point moves to the place which would appear on that screen line if the window were tall enough. This will probably cause the next redisplay to scroll to bring that location onto the screen. In an interactive call, COUNT is the numeric prefix argument. The value returned is the window line number, with the top line in the window numbered 0. - Function: compute-motion FROM FROMPOS TO TOPOS WIDTH OFFSETS WINDOW This function scan through the current buffer, calculating screen position. It scans the current buffer forward from position FROM, assuming that is at screen coordinates FROMPOS, to position TO or coordinates TOPOS, whichever comes first. It returns the ending buffer position and screen coordinates. The coordinate arguments FROMPOS and TOPOS are cons cells of the form `(HPOS . VPOS)'. The argument WIDTH is the number of columns available to display text; this affects handling of continuation lines. Use the value returned by `window-width' for the window of your choice. The argument OFFSETS is either `nil' or a cons cell of the form `(HSCROLL . TAB-OFFSET)'. Here HSCROLL is the number of columns not being displayed at the left margin; most callers get this from `window-hscroll'. Meanwhile, TAB-OFFSET is the offset between column numbers on the screen and column numbers in the buffer. This can be nonzero in a continuation line, when the previous screen lines' widths do not add up to a multiple of `tab-width'. It is always zero in a non-continuation line. The window WINDOW serves to specify which display table to use; that is its only effect. `compute-motion' always operates on the current buffer, regardless of what buffer is displayed in WINDOW. The return value is a list of five elements: (POS VPOS HPOS PREVHPOS CONTIN) Here POS is the buffer position where the scan stopped, VPOS is the vertical position, and HPOS is the horizontal position. The result PREVHPOS is the horizontal position one character back from POS. The result CONTIN is `t' if a line was continued after (or within) the previous character. For example, to find the buffer position of column COL of line LINE of a certain window, pass the window's display start location as FROM and the window's upper-left coordinates as FROMPOS. Pass the buffer's `(point-max)' as TO, to limit the scan to the end of the visible section of the buffer, and pass LINE and COL as TOPOS. Here's a function that does this: (defun coordinates-of-position (col line) (car (compute-motion (window-start) '(0 . 0) (point) (cons col line) (window-width) (cons (window-hscroll) 0)))) When you use `compute-motion' for the minibuffer, you need to use `minibuffer-prompt-width' to get the horizontal position of the beginning of the first screen line. *Note Minibuffer Misc::.  File: elisp, Node: Vertical Motion, Next: List Motion, Prev: Screen Lines, Up: Motion The User-Level Vertical Motion Commands --------------------------------------- A goal column is useful if you want to edit text such as a table in which you want to move point to a certain column on each line. The goal column affects the vertical text line motion commands, `next-line' and `previous-line'. *Note Basic Editing Commands: (emacs)Basic. - User Option: goal-column This variable holds an explicitly specified goal column for vertical line motion commands. If it is an integer, it specifies a column, and these commands try to move to that column on each line. If it is `nil', then the commands set their own goal columns. Any other value is invalid. - Variable: temporary-goal-column This variable holds the temporary goal column during a sequence of consecutive vertical line motion commands. It is overridden by `goal-column' if that is non-`nil'. It is set each time a vertical motion command is invoked, unless the previous command was also a vertical motion command. - User Option: track-eol This variable controls how the vertical line motion commands operate when starting at the end of a line. If `track-eol' is non-`nil', then vertical motion starting at the end of a line will keep to the ends of lines. This means moving to the end of each line moved onto. The value of `track-eol' has no effect if point is not at the end of a line when the first vertical motion command is given. `track-eol' has its effect by telling line motion commands to set `temporary-goal-column' to 9999 instead of to the current column.  File: elisp, Node: List Motion, Next: Skipping Characters, Prev: Vertical Motion, Up: Motion Moving over Balanced Expressions -------------------------------- Here are several functions concerned with balanced-parenthesis expressions (also called "sexps" in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see *Note Syntax Tables::. *Note Parsing Expressions::, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see *Note Lists and Sexps: (emacs)Lists and Sexps. - Command: forward-list ARG This function moves forward across ARG balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.) - Command: backward-list ARG This function moves backward across ARG balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.) - Command: up-list ARG This function moves forward out of ARG levels of parentheses. A negative argument means move backward but still to a less deep spot. - Command: down-list ARG This function moves forward down ARG levels of parentheses. A negative argument means move backward but still go down ARG levels. - Command: forward-sexp ARG This function moves forward across ARG balanced expressions. Balanced expressions include both those delimited by parentheses and other kinds, such as words and string constants. For example, ---------- Buffer: foo ---------- (concat-!- "foo " (car x) y z) ---------- Buffer: foo ---------- (forward-sexp 3) => nil ---------- Buffer: foo ---------- (concat "foo " (car x) y-!- z) ---------- Buffer: foo ---------- - Command: backward-sexp ARG This function moves backward across ARG balanced expressions. - Command: beginning-of-defun ARG This function moves back to the ARGth beginning of a defun. If ARG is negative, this actually moves forward, but it still moves to the beginning of a defun, not to the end of one. - Command: end-of-defun ARG Move forward to the ARGth end of a defun. If ARG is negative, this actually moves backward, but it still moves to the end of a defun, not to the beginning of one. - User Option: defun-prompt-regexp If non-`nil', this variable holds a regular expression that specifies what text can appear before the open-parenthesis that starts a defun. That is to say, the a defun begins on a line which starts with a match for this regular expression, followed by a character with open-parenthesis syntax.  File: elisp, Node: Skipping Characters, Prev: List Motion, Up: Motion Skipping Characters ------------------- The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see *Note Motion and Syntax::. - Function: skip-chars-forward CHARACTER-SET &optional LIMIT This function moves point in the current buffer forward, skipping over a given set of characters. It examines the character following point, then advances point if the character matches CHARACTER-SET. This continues until it reaches a character that does not match. The function returns `nil'. The argument CHARACTER-SET is like the inside of a `[...]' in a regular expression except that `]' is never special and `\' quotes `^', `-' or `\'. Thus, `"a-zA-Z"' skips over all letters, stopping before the first nonletter, and `"^a-zA-Z'" skips nonletters stopping before the first letter. *Note Regular Expressions::. If LIMIT is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before LIMIT. In the following example, point is initially located directly before the `T'. After the form is evaluated, point is located at the end of that line (between the `t' of `hat' and the newline). The function skips all letters and spaces, but not newlines. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (skip-chars-forward "a-zA-Z ") => nil ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ---------- - Function: skip-chars-backward CHARACTER-SET &optional LIMIT This function moves point backward, skipping characters that match CHARACTER-SET, until LIMIT. It just like `skip-chars-forward' except for the direction of motion.  File: elisp, Node: Excursions, Next: Narrowing, Prev: Motion, Up: Positions Excursions ========== It is often useful to move point "temporarily" within a localized portion of the program, or to switch buffers temporarily. This is called an "excursion", and it is done with the `save-excursion' special form. This construct saves the current buffer and its values of point and the mark so they can be restored after the completion of the excursion. The forms for saving and restoring the configuration of windows are described elsewhere (see *Note Window Configurations::, and *note Frame Configurations::.). - Special Form: save-excursion FORMS... The `save-excursion' special form saves the identity of the current buffer and the values of point and the mark in it, evaluates FORMS, and finally restores the buffer and its saved values of point and the mark. All three saved values are restored even in case of an abnormal exit via throw or error (*note Nonlocal Exits::.). The `save-excursion' special form is the standard way to switch buffers or move point within one part of a program and avoid affecting the rest of the program. It is used more than 500 times in the Lisp sources of Emacs. `save-excursion' does not save the values of point and the mark for other buffers, so changes in other buffers remain in effect after `save-excursion' exits. Likewise, `save-excursion' does not restore window-buffer correspondences altered by functions such as `switch-to-buffer'. One way to restore these correspondences, and the selected window, is to use `save-window-excursion' inside `save-excursion' (*note Window Configurations::.). The value returned by `save-excursion' is the result of the last of FORMS, or `nil' if no FORMS are given. (save-excursion FORMS) == (let ((old-buf (current-buffer)) (old-pnt (point-marker)) (old-mark (copy-marker (mark-marker)))) (unwind-protect (progn FORMS) (set-buffer old-buf) (goto-char old-pnt) (set-marker (mark-marker) old-mark)))  File: elisp, Node: Narrowing, Prev: Excursions, Up: Positions Narrowing ========= "Narrowing" means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the "accessible portion" of the buffer. Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands and most Emacs primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion. Values such as positions or line numbers, that usually count from the beginning of the buffer, do so despite narrowing, but the functions which use them refuse to operate on text that is inaccessible. The commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of the any narrowing. - Command: narrow-to-region START END This function sets the accessible portion of the current buffer to start at START and end at END. Both arguments should be character positions. In an interactive call, START and END are set to the bounds of the current region (point and the mark, with the smallest first). - Command: narrow-to-page MOVE-COUNT This function sets the accessible portion of the current buffer to include just the current page. An optional first argument MOVE-COUNT non-`nil' means to move forward or backward by MOVE-COUNT pages and then narrow. The variable `page-delimiter' specifies where pages start and end (*note Standard Regexps::.). In an interactive call, MOVE-COUNT is set to the numeric prefix argument. - Command: widen This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called "widening". It is equivalent to the following expression: (narrow-to-region 1 (1+ (buffer-size))) - Special Form: save-restriction BODY... This special form saves the current bounds of the accessible portion, evaluates the BODY forms, and finally restores the saved bounds, thus restoring the same state of narrowing (or absence thereof) formerly in effect. The state of narrowing is restored even in the event of an abnormal exit via throw or error (*note Nonlocal Exits::.). Therefore, this construct is a clean way to narrow a buffer temporarily. The value returned by `save-restriction' is that returned by the last form in BODY, or `nil' if no body forms were given. *Caution:* it is easy to make a mistake when using the `save-restriction' construct. Read the entire description here before you try it. If BODY changes the current buffer, `save-restriction' still restores the restrictions on the original buffer (the buffer whose restructions it saved from), but it does not restore the identity of the current buffer. `save-restriction' does *not* restore point and the mark; use `save-excursion' for that. If you use both `save-restriction' and `save-excursion' together, `save-excursion' should come first (on the outside). Otherwise, the old point value would be restored with temporary narrowing still in effect. If the old point value were outside the limits of the temporary narrowing, this would fail to restore it accurately. The `save-restriction' special form records the values of the beginning and end of the accessible portion as distances from the beginning and end of the buffer. In other words, it records the amount of inaccessible text before and after the accessible portion. This method yields correct results if BODY does further narrowing. However, `save-restriction' can become confused if the body widens and then make changes outside the range of the saved narrowing. When this is what you want to do, `save-restriction' is not the right tool for the job. Here is what you must use instead: (let ((beg (point-min-marker)) (end (point-max-marker))) (unwind-protect (progn BODY) (save-excursion (set-buffer (marker-buffer beg)) (narrow-to-region beg end)))) Here is a simple example of correct use of `save-restriction': ---------- Buffer: foo ---------- This is the contents of foo This is the contents of foo This is the contents of foo-!- ---------- Buffer: foo ---------- (save-excursion (save-restriction (goto-char 1) (forward-line 2) (narrow-to-region 1 (point)) (goto-char (point-min)) (replace-string "foo" "bar"))) ---------- Buffer: foo ---------- This is the contents of bar This is the contents of bar This is the contents of foo-!- ---------- Buffer: foo ----------  File: elisp, Node: Markers, Next: Text, Prev: Positions, Up: Top Markers ******* A "marker" is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it. * Menu: * Overview of Markers:: The components of a marker, and how it relocates. * Predicates on Markers:: Testing whether an object is a marker. * Creating Markers:: Making empty markers or markers at certain places. * Information from Markers:: Finding the marker's buffer or character position. * Changing Markers:: Moving the marker to a new buffer or position. * The Mark:: How "the mark" is implemented with a marker. * The Region:: How to access "the region".  File: elisp, Node: Overview of Markers, Next: Predicates on Markers, Up: Markers Overview of Markers =================== A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. *Note Positions::, for a complete description of positions. A marker has two attributes: the marker position, and the marker buffer. The marker position is an integer which is equivalent (at a given time) to the marker as a position in that buffer. But the marker's position value can change often during the life of the marker. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker. Deleting text around a marker's position leaves the marker between the characters immediately before and after the deleted text. Inserting text at the position of a marker normally leaves the marker in front of the new text--unless it is inserted with `insert-before-markers' (*note Insertion::.). Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Unreferenced markers are garbage collected eventually, but until then will continue to use time if they do point somewhere. Because it is common to perform arithmetic operations on a marker position, most of the arithmetic operations (including `+' and `-') accept markers as arguments. In such cases, the marker stands for its current position. Here are examples of creating markers, setting markers, and moving point to markers: ;; Make a new marker that initially does not point anywhere: (setq m1 (make-marker)) => # ;; Set `m1' to point between the 99th and 100th characters ;; in the current buffer: (set-marker m1 100) => # ;; Now insert one character at the beginning of the buffer: (goto-char (point-min)) => 1 (insert "Q") => nil ;; `m1' is updated appropriately. m1 => # ;; Two markers that point to the same position ;; are not `eq', but they are `equal'. (setq m2 (copy-marker m1)) => # (eq m1 m2) => nil (equal m1 m2) => t ;; When you are finished using a marker, make it point nowhere. (set-marker m1 nil) => #  File: elisp, Node: Predicates on Markers, Next: Creating Markers, Prev: Overview of Markers, Up: Markers Predicates on Markers ===================== You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers. - Function: markerp OBJECT This function returns `t' if OBJECT is a marker, `nil' otherwise. Note that integers are not markers, even though many functions will accept either a marker or an integer. - Function: integer-or-marker-p OBJECT This function returns `t' if OBJECT is an integer or a marker, `nil' otherwise. - Function: number-or-marker-p OBJECT This function returns `t' if OBJECT is a number (either kind) or a marker, `nil' otherwise.  File: elisp, Node: Creating Markers, Next: Information from Markers, Prev: Predicates on Markers, Up: Markers Functions That Create Markers ============================= When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker. - Function: make-marker This functions returns a newly allocated marker that does not point anywhere. (make-marker) => # - Function: point-marker This function returns a new marker that points to the present position of point in the current buffer. *Note Point::. For an example, see `copy-marker', below. - Function: point-min-marker This function returns a new marker that points to the beginning of the accessible portion of the buffer. This will be the beginning of the buffer unless narrowing is in effect. *Note Narrowing::. - Function: point-max-marker This function returns a new marker that points to the end of the accessible portion of the buffer. This will be the end of the buffer unless narrowing is in effect. *Note Narrowing::. Here are examples of this function and `point-min-marker', shown in a buffer containing a version of the source file for the text of this chapter. (point-min-marker) => # (point-max-marker) => # (narrow-to-region 100 200) => nil (point-min-marker) => # (point-max-marker) => # - Function: copy-marker MARKER-OR-INTEGER If passed a marker as its argument, `copy-marker' returns a new marker that points to the same place and the same buffer as does MARKER-OR-INTEGER. If passed an integer as its argument, `copy-marker' returns a new marker that points to position MARKER-OR-INTEGER in the current buffer. If passed an integer argument less than 1, `copy-marker' returns a new marker that points to the beginning of the current buffer. If passed an integer argument greater than the length of the buffer, `copy-marker' returns a new marker that points to the end of the buffer. An error is signaled if MARKER is neither a marker nor an integer. (setq p (point-marker)) => # (setq q (copy-marker p)) => # (eq p q) => nil (equal p q) => t (copy-marker 0) => # (copy-marker 20000) => #  File: elisp, Node: Information from Markers, Next: Changing Markers, Prev: Creating Markers, Up: Markers Information from Markers ======================== This section describes the functions for accessing the components of a marker object. - Function: marker-position MARKER This function returns the position that MARKER points to, or `nil' if it points nowhere. - Function: marker-buffer MARKER This function returns the buffer that MARKER points into, or `nil' if it points nowhere. (setq m (make-marker)) => # (marker-position m) => nil (marker-buffer m) => nil (set-marker m 3770 (current-buffer)) => # (marker-buffer m) => # (marker-position m) => 3770 Two distinct markers are considered `equal' (even though not `eq') to each other if they have the same position and buffer, or if they both point nowhere.  File: elisp, Node: Changing Markers, Next: The Mark, Prev: Information from Markers, Up: Markers Changing Marker Positions ========================= This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it--otherwise, confusing things may happen in other parts of Emacs. - Function: set-marker MARKER POSITION &optional BUFFER This function moves MARKER to POSITION in BUFFER. If BUFFER is not provided, it defaults to the current buffer. If POSITION is less than 1, `set-marker' moves MARKER to the beginning of the buffer. If the value of POSITION is greater than the size of the buffer, `set-marker' moves marker to the end of the buffer. If POSITION is `nil' or a marker that points nowhere, then MARKER is set to point nowhere. The value returned is MARKER. (setq m (point-marker)) => # (set-marker m 55) => # (setq b (get-buffer "foo")) => # (set-marker m 0 b) => # - Function: move-marker MARKER POSITION &optional BUFFER This is another name for `set-marker'.