This is ../info/lispref.info, produced by makeinfo version 4.0 from lispref/lispref.texi. INFO-DIR-SECTION XEmacs Editor START-INFO-DIR-ENTRY * Lispref: (lispref). XEmacs Lisp Reference Manual. END-INFO-DIR-ENTRY Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May, November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 Ben Wing. 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: lispref.info, Node: The Selected Console and Device, Next: Console and Device I/O, Prev: Connecting to a Console or Device, Up: Consoles and Devices The Selected Console and Device =============================== - Function: select-console console This function selects the console CONSOLE. Subsequent editing commands apply to its selected device, selected frame, and selected window. The selection of CONSOLE lasts until the next time the user does something to select a different console, or until the next time this function is called. - Function: selected-console This function returns the console which is currently active. - Function: select-device device This function selects the device DEVICE. - Function: selected-device &optional console This function returns the device which is currently active. If optional CONSOLE is non-`nil', this function returns the device that would be currently active if CONSOLE were the selected console.  File: lispref.info, Node: Console and Device I/O, Prev: The Selected Console and Device, Up: Consoles and Devices Console and Device I/O ====================== - Function: console-disable-input console This function disables input on console CONSOLE. - Function: console-enable-input console This function enables input on console CONSOLE. Each device has a "baud rate" value associated with it. On most systems, changing this value will affect the amount of padding and other strategic decisions made during redisplay. - Function: device-baud-rate &optional device This function returns the output baud rate of DEVICE. - Function: set-device-baud-rate device rate This function sets the output baud rate of DEVICE to RATE.  File: lispref.info, Node: Positions, Next: Markers, Prev: Consoles and Devices, Up: Top Positions ********* A "position" is the index of a character in the text of a 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, 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 that 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: lispref.info, 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. Usually terminals display the cursor over the character that immediately follows point; 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 &optional buffer This function returns the value of point in BUFFER, as an integer. BUFFER defaults to the current buffer if omitted. (point) => 175 - Function: point-min &optional buffer This function returns the minimum accessible value of point in BUFFER. This is normally 1, but if narrowing is in effect, it is the position of the start of the region that you narrowed to. (*Note Narrowing::.) BUFFER defaults to the current buffer if omitted. - Function: point-max &optional buffer This function returns the maximum accessible value of point in BUFFER. This is `(1+ (buffer-size buffer))', unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (*note Narrowing::). BUFFER defaults to the current buffer if omitted. - Function: buffer-end flag &optional buffer This function returns `(point-min buffer)' if FLAG is less than 1, `(point-max buffer)' otherwise. The argument FLAG must be a number. BUFFER defaults to the current buffer if omitted. - Function: buffer-size &optional buffer This function returns the total number of characters in BUFFER. In the absence of any narrowing (*note Narrowing::), `point-max' returns a value one larger than this. BUFFER defaults to the current buffer if omitted. (buffer-size) => 35 (point-max) => 36 - Variable: buffer-saved-size The value of this buffer-local variable is the former length of the current buffer, as of the last time it was read in, saved or auto-saved.  File: lispref.info, 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. * List Motion:: Moving by parsing lists and sexps. * Skipping Characters:: Skipping characters belonging to a certain set.  File: lispref.info, 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 other functions use that. - Command: goto-char position &optional buffer This function sets point in `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. BUFFER defaults to the current buffer if omitted. 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 buffer 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'. BUFFER defaults to the current buffer if omitted. In an interactive call, COUNT is the numeric prefix argument. - Command: backward-char &optional count buffer 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'. BUFFER defaults to the current buffer if omitted. In an interactive call, COUNT is the numeric prefix argument.  File: lispref.info, 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 &optional buffer 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'. BUFFER defaults to the current buffer if omitted. In an interactive call, COUNT is set to the numeric prefix argument. - Command: backward-word count &optional buffer This function is just like `forward-word', except that it moves backward until encountering the front of a word, rather than forward. BUFFER defaults to the current buffer if omitted. 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 a 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: lispref.info, 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 that 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 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!  File: lispref.info, 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 the 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 buffer--that is, the _end of the last line_ of the buffer. This is the only case in which `goto-line' does not necessarily move to the beginning of a line. 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 to move (in the full buffer, before taking account of narrowing). Thus, the value is positive if the scan encounters the real end of the buffer. The value is zero if scan encounters the end of the accessible portion but not 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 buffer 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. BUFFER defaults to the current buffer if omitted. If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled. - Command: end-of-line &optional count buffer 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. BUFFER defaults to the current buffer if omitted. If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled. - Command: forward-line &optional count buffer 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 a line. If COUNT is zero, it moves point to the beginning of the current line. BUFFER defaults to the current buffer if omitted. 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: lispref.info, Node: Screen Lines, Next: List 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 that 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::. These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. *Note cache-long-line-scans: Text Lines. - Function: vertical-motion count &optional window pixels This function moves point to the start of the frame line COUNT frame lines down from the frame line containing point. If COUNT is negative, it moves up instead. The optional second argument WINDOW may be used to specify a window other than the selected window in which to perform the motion. Normally, `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. If the optional third argument, PIXELS is non-`nil', the vertical pixel height of the motion which took place is returned instead of the actual number of lines moved. A motion of zero lines returns the height of the current line. Note that `vertical-motion' sets WINDOW's buffer's point, not WINDOW's point. (This differs from FSF Emacs, which buggily always sets current buffer's point, regardless of WINDOW.) - Function: vertical-motion-pixels count &optional window how This function moves point to the start of the frame line PIXELS vertical pixels down from the frame line containing point, or up if PIXELS is negative. The optional second argument WINDOW is the window to move in, and defaults to the selected window. The optional third argument HOW specifies the stopping condition. A negative integer indicates that the motion should be no more than PIXELS. A positive value indicates that the motion should be at least PIXELS. Any other value indicates that the motion should be as close as possible to PIXELS. - Command: move-to-window-line count &optional window This function moves point with respect to the text currently displayed in WINDOW, which defaults to 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 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 that 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 point has moved to, with the top line in the window numbered 0.  File: lispref.info, Node: List Motion, Next: Skipping Characters, Prev: Screen Lines, 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 XEmacs). 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 &optional arg This function moves forward across ARG balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.) ARG defaults to 1 if omitted. If ARG is negative, move backward across that many groups of parentheses. - Command: backward-list &optional arg This function moves backward across ARG balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.) ARG defaults to 1 if omitted. If ARG is negative, move forward across that many groups of parentheses. - 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 into ARG levels of parentheses. A negative argument means move backward but still go deeper in parentheses (-ARG levels). - Command: forward-sexp &optional 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. ARG defaults to 1 if omitted. If ARG is negative, move backward across that many balanced expressions. 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 &optional arg This function moves backward across ARG balanced expressions. ARG defaults to 1 if omitted. If ARG is negative, move forward across that many balanced expressions. - Command: beginning-of-defun &optional 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. ARG defaults to 1 if omitted. - Command: end-of-defun &optional arg This function moves 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. ARG defaults to 1 if omitted. - 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, a defun begins on a line that starts with a match for this regular expression, followed by a character with open-parenthesis syntax.  File: lispref.info, 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 buffer This function moves point in 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'. BUFFER defaults to the current buffer if omitted. 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 non-letter, and `"^a-zA-Z'" skips non-letters 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 buffer 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: lispref.info, 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 XEmacs. `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))) - Special Form: save-current-buffer forms... This special form is similar to `save-excursion' but it only saves and restores the current buffer. Beginning with XEmacs 20.3, `save-current-buffer' is a primitive. - Special Form: with-current-buffer buffer forms... This special form evaluates FORMS with BUFFER as the current buffer. It returns the value of the last form. - Special Form: with-temp-file file forms... This special form creates a new buffer, evaluates FORMS there, and writes the buffer to FILE. It returns the value of the last form evaluated. - Special Form: save-selected-window forms... This special form is similar to `save-excursion' but it saves and restores the selected window and nothing else.  File: lispref.info, Node: Narrowing, Prev: Excursions, Up: Positions Narrowing ========= "Narrowing" means limiting the text addressable by XEmacs 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, which 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 any narrowing. - Command: narrow-to-region start end &optional buffer This function sets the accessible portion of BUFFER to start at START and end at END. Both arguments should be character positions. BUFFER defaults to the current buffer if omitted. 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 &optional 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 &optional buffer This function cancels any narrowing in 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))) BUFFER defaults to the current buffer if omitted. - 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 restrictions 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: lispref.info, 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: lispref.info, 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 that 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. Note that you can use extents to achieve the same functionality, and more, as markers. (Markers were defined before extents, which is why they both continue to exist.) A zero-length extent with the `detachable' property removed is almost identical to a marker. (*Note Extent Endpoints::, for more information on zero-length extents.) In particular: * In order to get marker-like behavior in a zero-length extent, the `detachable' property must be removed (otherwise, the extent will disappear when text near it is deleted) and exactly one endpoint must be closed (if both endpoints are closed, the extent will expand to contain text inserted where it is located). * If a zero-length extent has the `end-open' property but not the `start-open' property (this is the default), text inserted at the extent's location causes the extent to move forward, just like a marker. * If a zero-length extent has the `start-open' property but not the `end-open' property, text inserted at the extent's location causes the extent to remain before the text, like what happens to markers when `insert-before-markers' is used. * Markers end up after or before inserted text depending on whether `insert' or `insert-before-markers' was called. These functions do not affect zero-length extents differently; instead, the presence or absence of the `start-open' and `end-open' extent properties determines this, as just described. * Markers are automatically removed from a buffer when they are no longer in use. Extents remain around until explicitly removed from a buffer. * Many functions are provided for listing the extents in a buffer or in a region of a buffer. No such functions exist for markers. 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: lispref.info, 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 or either an integer, a character, or a marker. The latter tests are useful in connection with the arithmetic functions that work with any of markers, integers, or characters. - 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: integer-char-or-marker-p object This function returns `t' if OBJECT is an integer, a character, 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. - Function: number-char-or-marker-p object This function returns `t' if OBJECT is a number (either kind), a character, or a marker, `nil' otherwise.  File: lispref.info, 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 created marker that does not point anywhere. (make-marker) => # - Function: point-marker &optional dont-copy-p buffer This function returns a marker that points to the present position of point in BUFFER, which defaults to the current buffer. *Note Point::. For an example, see `copy-marker', below. Internally, a marker corresponding to point is always maintained. Normally the marker returned by `point-marker' is a copy; you may modify it with reckless abandon. However, if optional argument DONT-COPY-P is non-`nil', then the real point-marker is returned; modifying the position of this marker will move point. It is illegal to change the buffer of it, or make it point nowhere. - Function: point-min-marker &optional buffer This function returns a new marker that points to the beginning of the accessible portion of BUFFER, which defaults to the current buffer. This will be the beginning of the buffer unless narrowing is in effect. *Note Narrowing::. - Function: point-max-marker &optional buffer This function returns a new marker that points to the end of the accessible portion of BUFFER, which defaults to the current 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 (point) => 2139 (set-marker p 3000) => # (point) => 2139 (setq p (point-marker t)) => # (set-marker p 3000) => # (point) => 3000 (copy-marker 0) => # (copy-marker 20000) => #  File: lispref.info, 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: lispref.info, 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 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'.