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diff --git a/lispref/positions.texi b/lispref/positions.texi deleted file mode 100644 index 1d02377565a..00000000000 --- a/lispref/positions.texi +++ /dev/null @@ -1,897 +0,0 @@ -@c -*-texinfo-*- -@c This is part of the GNU Emacs Lisp Reference Manual. -@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. -@c See the file elisp.texi for copying conditions. -@setfilename ../info/positions -@node Positions, Markers, Frames, Top -@chapter Positions -@cindex position (in buffer) - - A @dfn{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 @dfn{markers}---special objects that relocate -automatically when text is inserted or deleted so they stay with the -surrounding characters. @xref{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. -@end menu - -@node Point -@section Point -@cindex point - - @dfn{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. - -@cindex point with narrowing - The value of point is a number between 1 and the buffer size plus 1. -If narrowing is in effect (@pxref{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. @xref{Window Point}, for more -details. - -@defun point -@cindex current buffer position -This function returns the value of point in the current buffer, -as an integer. - -@need 700 -@example -@group -(point) - @result{} 175 -@end group -@end example -@end defun - -@defun point-min -This function returns the minimum accessible value of point in the -current 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. -(@xref{Narrowing}.) -@end defun - -@defun point-max -This function returns the maximum accessible value of point in the -current buffer. This is @code{(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. (@xref{Narrowing}). -@end defun - -@defun buffer-end flag -This function returns @code{(point-min)} if @var{flag} is less than 1, -@code{(point-max)} otherwise. The argument @var{flag} must be a number. -@end defun - -@defun buffer-size -This function returns the total number of characters in the current -buffer. In the absence of any narrowing (@pxref{Narrowing}), -@code{point-max} returns a value one larger than this. - -@example -@group -(buffer-size) - @result{} 35 -@end group -@group -(point-max) - @result{} 36 -@end group -@end example -@end defun - -@node Motion -@section 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. @xref{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. -@end menu - -@node Character Motion -@subsection Motion by Characters - - These functions move point based on a count of characters. -@code{goto-char} is the fundamental primitive; the other functions use -that. - -@deffn Command goto-char position -This function sets point in the current buffer to the value -@var{position}. If @var{position} is less than 1, it moves point to the -beginning of the buffer. If @var{position} is greater than the length -of the buffer, it moves point to the end. - -If narrowing is in effect, @var{position} still counts from the -beginning of the buffer, but point cannot go outside the accessible -portion. If @var{position} is out of range, @code{goto-char} moves -point to the beginning or the end of the accessible portion. - -When this function is called interactively, @var{position} is the -numeric prefix argument, if provided; otherwise it is read from the -minibuffer. - -@code{goto-char} returns @var{position}. -@end deffn - -@deffn Command forward-char &optional count -@c @kindex beginning-of-buffer -@c @kindex end-of-buffer -This function moves point @var{count} characters forward, towards the -end of the buffer (or backward, towards the beginning of the buffer, if -@var{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 @code{beginning-of-buffer} or @code{end-of-buffer}. - -In an interactive call, @var{count} is the numeric prefix argument. -@end deffn - -@deffn Command backward-char &optional count -This function moves point @var{count} characters backward, towards the -beginning of the buffer (or forward, towards the end of the buffer, if -@var{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 @code{beginning-of-buffer} or @code{end-of-buffer}. - -In an interactive call, @var{count} is the numeric prefix argument. -@end deffn - -@node Word Motion -@subsection Motion by Words - - These functions for parsing words use the syntax table to decide -whether a given character is part of a word. @xref{Syntax Tables}. - -@deffn Command forward-word count -This function moves point forward @var{count} words (or backward if -@var{count} is negative). Normally it returns @code{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 @code{nil}. - -In an interactive call, @var{count} is set to the numeric prefix -argument. -@end deffn - -@deffn Command backward-word count -This function is just like @code{forward-word}, except that it moves -backward until encountering the front of a word, rather than forward. - -In an interactive call, @var{count} is set to the numeric prefix -argument. - -This function is rarely used in programs, as it is more efficient to -call @code{forward-word} with a negative argument. -@end deffn - -@defvar words-include-escapes -@c Emacs 19 feature -This variable affects the behavior of @code{forward-word} and everything -that uses it. If it is non-@code{nil}, then characters in the -``escape'' and ``character quote'' syntax classes count as part of -words. Otherwise, they do not. -@end defvar - -@node Buffer End Motion -@subsection Motion to an End of the Buffer - - To move point to the beginning of the buffer, write: - -@example -@group -(goto-char (point-min)) -@end group -@end example - -@noindent -Likewise, to move to the end of the buffer, use: - -@example -@group -(goto-char (point-max)) -@end group -@end example - - 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. - -@deffn 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 @var{n} is non-@code{nil}, then it -puts point @var{n} tenths of the way from the beginning of the buffer. - -In an interactive call, @var{n} is the numeric prefix argument, -if provided; otherwise @var{n} defaults to @code{nil}. - -Don't use this function in Lisp programs! -@end deffn - -@deffn 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 @var{n} is non-@code{nil}, then it puts -point @var{n} tenths of the way from the end of the buffer. - -In an interactive call, @var{n} is the numeric prefix argument, -if provided; otherwise @var{n} defaults to @code{nil}. - -Don't use this function in Lisp programs! -@end deffn - -@node Text Lines -@subsection Motion by Text Lines -@cindex 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. - -@deffn Command goto-line line -This function moves point to the front of the @var{line}th line, -counting from line 1 at beginning of the buffer. If @var{line} is less -than 1, it moves point to the beginning of the buffer. If @var{line} is -greater than the number of lines in the buffer, it moves point to the -end of the buffer---that is, the @emph{end of the last line} of the -buffer. This is the only case in which @code{goto-line} does not -necessarily move to the beginning of a line. - -If narrowing is in effect, then @var{line} still counts from the -beginning of the buffer, but point cannot go outside the accessible -portion. So @code{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 @code{goto-line} is the difference between -@var{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, @var{line} is the numeric prefix argument if -one has been provided. Otherwise @var{line} is read in the minibuffer. -@end deffn - -@deffn Command beginning-of-line &optional count -This function moves point to the beginning of the current line. With an -argument @var{count} not @code{nil} or 1, it moves forward -@var{count}@minus{}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 there. No error -is signaled. -@end deffn - -@deffn Command end-of-line &optional count -This function moves point to the end of the current line. With an -argument @var{count} not @code{nil} or 1, it moves forward -@var{count}@minus{}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 there. No error -is signaled. -@end deffn - -@deffn Command forward-line &optional count -@cindex beginning of line -This function moves point forward @var{count} lines, to the beginning of -the line. If @var{count} is negative, it moves point -@minus{}@var{count} lines backward, to the beginning of a line. If -@var{count} is zero, it moves point to the beginning of the current -line. - -If @code{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. - -@code{forward-line} returns the difference between @var{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, @var{count} is the numeric prefix argument. -@end deffn - -@defun count-lines start end -@cindex lines in region -This function returns the number of lines between the positions -@var{start} and @var{end} in the current buffer. If @var{start} and -@var{end} are equal, then it returns 0. Otherwise it returns at least -1, even if @var{start} and @var{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 @code{count-lines}: - -@example -@group -(defun current-line () - "Return the vertical position of point@dots{}" - (+ (count-lines (window-start) (point)) - (if (= (current-column) 0) 1 0) - -1)) -@end group -@end example -@end defun - -@ignore -@c ================ -The @code{previous-line} and @code{next-line} commands are functions -that should not be used in programs. They are for users and are -mentioned here only for completeness. - -@deffn Command previous-line count -@cindex goal column -This function moves point up @var{count} lines (down if @var{count} -is negative). In moving, it attempts to keep point in the ``goal column'' -(normally the same column that it was at the beginning of the move). - -If there is no character in the target line exactly under the current -column, point is positioned after the character in that line which -spans this column, or at the end of the line if it is not long enough. - -If it attempts to move beyond the top or bottom of the buffer (or clipped -region), then point is positioned in the goal column in the top or -bottom line. No error is signaled. - -In an interactive call, @var{count} will be the numeric -prefix argument. - -The command @code{set-goal-column} can be used to create a semipermanent -goal column to which this command always moves. Then it does not try to -move vertically. - -If you are thinking of using this in a Lisp program, consider using -@code{forward-line} with a negative argument instead. It is usually easier -to use and more reliable (no dependence on goal column, etc.). -@end deffn - -@deffn Command next-line count -This function moves point down @var{count} lines (up if @var{count} -is negative). In moving, it attempts to keep point in the ``goal column'' -(normally the same column that it was at the beginning of the move). - -If there is no character in the target line exactly under the current -column, point is positioned after the character in that line which -spans this column, or at the end of the line if it is not long enough. - -If it attempts to move beyond the top or bottom of the buffer (or clipped -region), then point is positioned in the goal column in the top or -bottom line. No error is signaled. - -In the case where the @var{count} is 1, and point is on the last -line of the buffer (or clipped region), a new empty line is inserted at the -end of the buffer (or clipped region) and point moved there. - -In an interactive call, @var{count} will be the numeric -prefix argument. - -The command @code{set-goal-column} can be used to create a semipermanent -goal column to which this command always moves. Then it does not try to -move vertically. - -If you are thinking of using this in a Lisp program, consider using -@code{forward-line} instead. It is usually easier -to use and more reliable (no dependence on goal column, etc.). -@end deffn - -@c ================ -@end ignore - - Also see the functions @code{bolp} and @code{eolp} in @ref{Near Point}. -These functions do not move point, but test whether it is already at the -beginning or end of a line. - -@node Screen Lines -@subsection 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, -@code{vertical-motion} moves point much like @code{forward-line}. -@xref{Truncation}. - - Because the width of a given string depends on the flags that control -the appearance of certain characters, @code{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). @xref{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. @xref{Text Lines, cache-long-line-scans}. - - -@defun vertical-motion count &optional window -This function moves point to the start of the screen line @var{count} -screen lines down from the screen line containing point. If @var{count} -is negative, it moves up instead. - -@code{vertical-motion} returns the number of lines moved. The value may -be less in absolute value than @var{count} if the beginning or end of -the buffer was reached. - -The window @var{window} is used for obtaining parameters such as the -width, the horizontal scrolling, and the display table. But -@code{vertical-motion} always operates on the current buffer, even if -@var{window} currently displays some other buffer. -@end defun - -@deffn 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 @var{count} screen lines from the top of the window. If -@var{count} is negative, that specifies a position -@w{@minus{}@var{count}} lines from the bottom (or the last line of the -buffer, if the buffer ends above the specified screen position). - -If @var{count} is @code{nil}, then point moves to the beginning of the -line in the middle of the window. If the absolute value of @var{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, @var{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. -@end deffn - -@defun compute-motion from frompos to topos width offsets window -This function scans the current buffer, calculating screen positions. -It scans the buffer forward from position @var{from}, assuming that is -at screen coordinates @var{frompos}, to position @var{to} or coordinates -@var{topos}, whichever comes first. It returns the ending buffer -position and screen coordinates. - -The coordinate arguments @var{frompos} and @var{topos} are cons cells of -the form @code{(@var{hpos} . @var{vpos})}. - -The argument @var{width} is the number of columns available to display -text; this affects handling of continuation lines. Use the value -returned by @code{window-width} for the window of your choice; -normally, use @code{(window-width @var{window})}. - -The argument @var{offsets} is either @code{nil} or a cons cell of the -form @code{(@var{hscroll} . @var{tab-offset})}. Here @var{hscroll} is -the number of columns not being displayed at the left margin; most -callers get this from @code{window-hscroll}. Meanwhile, -@var{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 @code{tab-width}. It is always zero in a non-continuation line. - -The window @var{window} serves only to specify which display table to -use. @code{compute-motion} always operates on the current buffer, -regardless of what buffer is displayed in @var{window}. - -The return value is a list of five elements: - -@example -(@var{pos} @var{vpos} @var{hpos} @var{prevhpos} @var{contin}) -@end example - -@noindent -Here @var{pos} is the buffer position where the scan stopped, @var{vpos} -is the vertical screen position, and @var{hpos} is the horizontal screen -position. - -The result @var{prevhpos} is the horizontal position one character back -from @var{pos}. The result @var{contin} is @code{t} if the last line -was continued after (or within) the previous character. - -For example, to find the buffer position of column @var{col} of line -@var{line} of a certain window, pass the window's display start location -as @var{from} and the window's upper-left coordinates as @var{frompos}. -Pass the buffer's @code{(point-max)} as @var{to}, to limit the scan to -the end of the accessible portion of the buffer, and pass @var{line} and -@var{col} as @var{topos}. Here's a function that does this: - -@example -(defun coordinates-of-position (col line) - (car (compute-motion (window-start) - '(0 . 0) - (point-max) - (cons col line) - (window-width) - (cons (window-hscroll) 0) - (selected-window)))) -@end example - -When you use @code{compute-motion} for the minibuffer, you need to use -@code{minibuffer-prompt-width} to get the horizontal position of the -beginning of the first screen line. @xref{Minibuffer Misc}. -@end defun - -@node List Motion -@comment node-name, next, previous, up -@subsection Moving over Balanced Expressions -@cindex sexp motion -@cindex Lisp expression motion -@cindex list motion - - Here are several functions concerned with balanced-parenthesis -expressions (also called @dfn{sexps} in connection with moving across -them in Emacs). The syntax table controls how these functions interpret -various characters; see @ref{Syntax Tables}. @xref{Parsing -Expressions}, for lower-level primitives for scanning sexps or parts of -sexps. For user-level commands, see @ref{Lists Commands,,, emacs, GNU -Emacs Manual}. - -@deffn Command forward-list arg -This function moves forward across @var{arg} balanced groups of -parentheses. (Other syntactic entities such as words or paired string -quotes are ignored.) -@end deffn - -@deffn Command backward-list arg -This function moves backward across @var{arg} balanced groups of -parentheses. (Other syntactic entities such as words or paired string -quotes are ignored.) -@end deffn - -@deffn Command up-list arg -This function moves forward out of @var{arg} levels of parentheses. -A negative argument means move backward but still to a less deep spot. -@end deffn - -@deffn Command down-list arg -This function moves forward into @var{arg} levels of parentheses. A -negative argument means move backward but still go -deeper in parentheses (@minus{}@var{arg} levels). -@end deffn - -@deffn Command forward-sexp arg -This function moves forward across @var{arg} balanced expressions. -Balanced expressions include both those delimited by parentheses and -other kinds, such as words and string constants. For example, - -@example -@group ----------- Buffer: foo ---------- -(concat@point{} "foo " (car x) y z) ----------- Buffer: foo ---------- -@end group - -@group -(forward-sexp 3) - @result{} nil - ----------- Buffer: foo ---------- -(concat "foo " (car x) y@point{} z) ----------- Buffer: foo ---------- -@end group -@end example -@end deffn - -@deffn Command backward-sexp arg -This function moves backward across @var{arg} balanced expressions. -@end deffn - -@deffn Command beginning-of-defun arg -This function moves back to the @var{arg}th beginning of a defun. If -@var{arg} is negative, this actually moves forward, but it still moves -to the beginning of a defun, not to the end of one. -@end deffn - -@deffn Command end-of-defun arg -This function moves forward to the @var{arg}th end of a defun. If -@var{arg} is negative, this actually moves backward, but it still moves -to the end of a defun, not to the beginning of one. -@end deffn - -@defopt defun-prompt-regexp -If non-@code{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. -@end defopt - -@node Skipping Characters -@comment node-name, next, previous, up -@subsection Skipping Characters -@cindex 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 @ref{Motion and Syntax}. - -@defun 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 @var{character-set}. This -continues until it reaches a character that does not match. The -function returns @code{nil}. - -The argument @var{character-set} is like the inside of a -@samp{[@dots{}]} in a regular expression except that @samp{]} is never -special and @samp{\} quotes @samp{^}, @samp{-} or @samp{\}. Thus, -@code{"a-zA-Z"} skips over all letters, stopping before the first -nonletter, and @code{"^a-zA-Z"} skips nonletters stopping before the -first letter. @xref{Regular Expressions}. - -If @var{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 @var{limit}. - -In the following example, point is initially located directly before the -@samp{T}. After the form is evaluated, point is located at the end of -that line (between the @samp{t} of @samp{hat} and the newline). The -function skips all letters and spaces, but not newlines. - -@example -@group ----------- Buffer: foo ---------- -I read "@point{}The cat in the hat -comes back" twice. ----------- Buffer: foo ---------- -@end group - -@group -(skip-chars-forward "a-zA-Z ") - @result{} nil - ----------- Buffer: foo ---------- -I read "The cat in the hat@point{} -comes back" twice. ----------- Buffer: foo ---------- -@end group -@end example -@end defun - -@defun skip-chars-backward character-set &optional limit -This function moves point backward, skipping characters that match -@var{character-set}, until @var{limit}. It just like -@code{skip-chars-forward} except for the direction of motion. -@end defun - -@node Excursions -@section Excursions -@cindex excursion - - It is often useful to move point ``temporarily'' within a localized -portion of the program, or to switch buffers temporarily. This is -called an @dfn{excursion}, and it is done with the @code{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 @ref{Window Configurations}, and @pxref{Frame -Configurations}). - -@defspec save-excursion forms@dots{} -@cindex mark excursion -@cindex point excursion -@cindex current buffer excursion -The @code{save-excursion} special form saves the identity of the current -buffer and the values of point and the mark in it, evaluates -@var{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 @code{throw} or error (@pxref{Nonlocal Exits}). - -The @code{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. - -@code{save-excursion} does not save the values of point and the mark for -other buffers, so changes in other buffers remain in effect after -@code{save-excursion} exits. - -@cindex window excursions -Likewise, @code{save-excursion} does not restore window-buffer -correspondences altered by functions such as @code{switch-to-buffer}. -One way to restore these correspondences, and the selected window, is to -use @code{save-window-excursion} inside @code{save-excursion} -(@pxref{Window Configurations}). - -The value returned by @code{save-excursion} is the result of the last of -@var{forms}, or @code{nil} if no @var{forms} are given. - -@example -@group -(save-excursion - @var{forms}) -@equiv{} -(let ((old-buf (current-buffer)) - (old-pnt (point-marker)) - (old-mark (copy-marker (mark-marker)))) - (unwind-protect - (progn @var{forms}) - (set-buffer old-buf) - (goto-char old-pnt) - (set-marker (mark-marker) old-mark))) -@end group -@end example -@end defspec - -@node Narrowing -@section Narrowing -@cindex narrowing -@cindex restriction (in a buffer) -@cindex accessible portion (of a buffer) - - @dfn{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 @dfn{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. - -@deffn Command narrow-to-region start end -This function sets the accessible portion of the current buffer to start -at @var{start} and end at @var{end}. Both arguments should be character -positions. - -In an interactive call, @var{start} and @var{end} are set to the bounds -of the current region (point and the mark, with the smallest first). -@end deffn - -@deffn 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 -@var{move-count} non-@code{nil} means to move forward or backward by -@var{move-count} pages and then narrow. The variable -@code{page-delimiter} specifies where pages start and end -(@pxref{Standard Regexps}). - -In an interactive call, @var{move-count} is set to the numeric prefix -argument. -@end deffn - -@deffn Command widen -@cindex widening -This function cancels any narrowing in the current buffer, so that the -entire contents are accessible. This is called @dfn{widening}. -It is equivalent to the following expression: - -@example -(narrow-to-region 1 (1+ (buffer-size))) -@end example -@end deffn - -@defspec save-restriction body@dots{} -This special form saves the current bounds of the accessible portion, -evaluates the @var{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 @code{throw} or error (@pxref{Nonlocal Exits}). -Therefore, this construct is a clean way to narrow a buffer temporarily. - -The value returned by @code{save-restriction} is that returned by the -last form in @var{body}, or @code{nil} if no body forms were given. - -@c Wordy to avoid overfull hbox. --rjc 16mar92 -@strong{Caution:} it is easy to make a mistake when using the -@code{save-restriction} construct. Read the entire description here -before you try it. - -If @var{body} changes the current buffer, @code{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. - -@code{save-restriction} does @emph{not} restore point and the mark; use -@code{save-excursion} for that. If you use both @code{save-restriction} -and @code{save-excursion} together, @code{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 @code{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 @var{body} does further narrowing. -However, @code{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, @code{save-restriction} is not the right -tool for the job. Here is what you must use instead: - -@example -@group -(let ((beg (point-min-marker)) - (end (point-max-marker))) - (unwind-protect - (progn @var{body}) - (save-excursion - (set-buffer (marker-buffer beg)) - (narrow-to-region beg end)))) -@end group -@end example - -Here is a simple example of correct use of @code{save-restriction}: - -@example -@group ----------- Buffer: foo ---------- -This is the contents of foo -This is the contents of foo -This is the contents of foo@point{} ----------- Buffer: foo ---------- -@end group - -@group -(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@point{} ----------- Buffer: foo ---------- -@end group -@end example -@end defspec |