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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
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3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999 |
4 | @c Free Software Foundation, Inc. | |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/positions | |
7 | @node Positions, Markers, Frames, Top | |
8 | @chapter Positions | |
9 | @cindex position (in buffer) | |
10 | ||
29679a81 | 11 | A @dfn{position} is the index of a character in the text of a buffer. |
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12 | More precisely, a position identifies the place between two characters |
13 | (or before the first character, or after the last character), so we can | |
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14 | speak of the character before or after a given position. However, we |
15 | often speak of the character ``at'' a position, meaning the character | |
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16 | after that position. |
17 | ||
18 | Positions are usually represented as integers starting from 1, but can | |
29679a81 | 19 | also be represented as @dfn{markers}---special objects that relocate |
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20 | automatically when text is inserted or deleted so they stay with the |
21 | surrounding characters. @xref{Markers}. | |
22 | ||
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23 | See also the ``field'' feature (@pxref{Fields}), which provides |
24 | functions that are used by many cursur-motion commands. | |
25 | ||
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26 | @menu |
27 | * Point:: The special position where editing takes place. | |
28 | * Motion:: Changing point. | |
29 | * Excursions:: Temporary motion and buffer changes. | |
30 | * Narrowing:: Restricting editing to a portion of the buffer. | |
31 | @end menu | |
32 | ||
33 | @node Point | |
34 | @section Point | |
35 | @cindex point | |
36 | ||
37 | @dfn{Point} is a special buffer position used by many editing | |
38 | commands, including the self-inserting typed characters and text | |
39 | insertion functions. Other commands move point through the text | |
40 | to allow editing and insertion at different places. | |
41 | ||
42 | Like other positions, point designates a place between two characters | |
43 | (or before the first character, or after the last character), rather | |
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44 | than a particular character. Usually terminals display the cursor over |
45 | the character that immediately follows point; point is actually before | |
46 | the character on which the cursor sits. | |
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47 | |
48 | @cindex point with narrowing | |
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49 | The value of point is a number no less than 1, and no greater than the |
50 | buffer size plus 1. If narrowing is in effect (@pxref{Narrowing}), then | |
51 | point is constrained to fall within the accessible portion of the buffer | |
52 | (possibly at one end of it). | |
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53 | |
54 | Each buffer has its own value of point, which is independent of the | |
55 | value of point in other buffers. Each window also has a value of point, | |
56 | which is independent of the value of point in other windows on the same | |
57 | buffer. This is why point can have different values in various windows | |
58 | that display the same buffer. When a buffer appears in only one window, | |
59 | the buffer's point and the window's point normally have the same value, | |
60 | so the distinction is rarely important. @xref{Window Point}, for more | |
61 | details. | |
62 | ||
63 | @defun point | |
64 | @cindex current buffer position | |
29679a81 | 65 | This function returns the value of point in the current buffer, |
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66 | as an integer. |
67 | ||
68 | @need 700 | |
69 | @example | |
70 | @group | |
71 | (point) | |
72 | @result{} 175 | |
73 | @end group | |
74 | @end example | |
75 | @end defun | |
76 | ||
77 | @defun point-min | |
29679a81 RS |
78 | This function returns the minimum accessible value of point in the |
79 | current buffer. This is normally 1, but if narrowing is in effect, it | |
80 | is the position of the start of the region that you narrowed to. | |
81 | (@xref{Narrowing}.) | |
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82 | @end defun |
83 | ||
84 | @defun point-max | |
29679a81 | 85 | This function returns the maximum accessible value of point in the |
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86 | current buffer. This is @code{(1+ (buffer-size))}, unless narrowing is |
87 | in effect, in which case it is the position of the end of the region | |
8241495d | 88 | that you narrowed to. (@xref{Narrowing}.) |
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89 | @end defun |
90 | ||
91 | @defun buffer-end flag | |
29679a81 | 92 | This function returns @code{(point-min)} if @var{flag} is less than 1, |
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93 | @code{(point-max)} otherwise. The argument @var{flag} must be a number. |
94 | @end defun | |
95 | ||
8241495d | 96 | @defun buffer-size &optional buffer |
29679a81 | 97 | This function returns the total number of characters in the current |
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98 | buffer. In the absence of any narrowing (@pxref{Narrowing}), |
99 | @code{point-max} returns a value one larger than this. | |
100 | ||
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101 | If you specify a buffer, @var{buffer}, then the value is the |
102 | size of @var{buffer}. | |
103 | ||
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104 | @example |
105 | @group | |
106 | (buffer-size) | |
107 | @result{} 35 | |
108 | @end group | |
109 | @group | |
110 | (point-max) | |
111 | @result{} 36 | |
112 | @end group | |
113 | @end example | |
114 | @end defun | |
115 | ||
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116 | @node Motion |
117 | @section Motion | |
118 | ||
119 | Motion functions change the value of point, either relative to the | |
120 | current value of point, relative to the beginning or end of the buffer, | |
121 | or relative to the edges of the selected window. @xref{Point}. | |
122 | ||
123 | @menu | |
124 | * Character Motion:: Moving in terms of characters. | |
125 | * Word Motion:: Moving in terms of words. | |
126 | * Buffer End Motion:: Moving to the beginning or end of the buffer. | |
127 | * Text Lines:: Moving in terms of lines of text. | |
128 | * Screen Lines:: Moving in terms of lines as displayed. | |
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129 | * List Motion:: Moving by parsing lists and sexps. |
130 | * Skipping Characters:: Skipping characters belonging to a certain set. | |
131 | @end menu | |
132 | ||
133 | @node Character Motion | |
134 | @subsection Motion by Characters | |
135 | ||
136 | These functions move point based on a count of characters. | |
29679a81 | 137 | @code{goto-char} is the fundamental primitive; the other functions use |
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138 | that. |
139 | ||
140 | @deffn Command goto-char position | |
141 | This function sets point in the current buffer to the value | |
142 | @var{position}. If @var{position} is less than 1, it moves point to the | |
143 | beginning of the buffer. If @var{position} is greater than the length | |
144 | of the buffer, it moves point to the end. | |
145 | ||
146 | If narrowing is in effect, @var{position} still counts from the | |
147 | beginning of the buffer, but point cannot go outside the accessible | |
148 | portion. If @var{position} is out of range, @code{goto-char} moves | |
149 | point to the beginning or the end of the accessible portion. | |
150 | ||
151 | When this function is called interactively, @var{position} is the | |
152 | numeric prefix argument, if provided; otherwise it is read from the | |
153 | minibuffer. | |
154 | ||
155 | @code{goto-char} returns @var{position}. | |
156 | @end deffn | |
157 | ||
158 | @deffn Command forward-char &optional count | |
159 | @c @kindex beginning-of-buffer | |
160 | @c @kindex end-of-buffer | |
161 | This function moves point @var{count} characters forward, towards the | |
162 | end of the buffer (or backward, towards the beginning of the buffer, if | |
163 | @var{count} is negative). If the function attempts to move point past | |
164 | the beginning or end of the buffer (or the limits of the accessible | |
165 | portion, when narrowing is in effect), an error is signaled with error | |
166 | code @code{beginning-of-buffer} or @code{end-of-buffer}. | |
167 | ||
168 | In an interactive call, @var{count} is the numeric prefix argument. | |
169 | @end deffn | |
170 | ||
171 | @deffn Command backward-char &optional count | |
172 | This function moves point @var{count} characters backward, towards the | |
173 | beginning of the buffer (or forward, towards the end of the buffer, if | |
174 | @var{count} is negative). If the function attempts to move point past | |
175 | the beginning or end of the buffer (or the limits of the accessible | |
176 | portion, when narrowing is in effect), an error is signaled with error | |
177 | code @code{beginning-of-buffer} or @code{end-of-buffer}. | |
178 | ||
179 | In an interactive call, @var{count} is the numeric prefix argument. | |
180 | @end deffn | |
181 | ||
182 | @node Word Motion | |
183 | @subsection Motion by Words | |
184 | ||
185 | These functions for parsing words use the syntax table to decide | |
186 | whether a given character is part of a word. @xref{Syntax Tables}. | |
187 | ||
188 | @deffn Command forward-word count | |
189 | This function moves point forward @var{count} words (or backward if | |
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190 | @var{count} is negative). ``Moving one word'' means moving until point |
191 | crosses a word-constituent character and then encounters a | |
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192 | word-separator character. However, this function cannot move point past |
193 | the boundary of the accessible part of the buffer, or across a field | |
194 | boundary (@pxref{Fields}). The most common case of a field boundary is | |
195 | the end of the prompt in the minibuffer. | |
7015aca4 | 196 | |
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197 | If it is possible to move @var{count} words, without being stopped |
198 | prematurely by the buffer boundary or a field boundary, the value is | |
199 | @code{t}. Otherwise, the return value is @code{nil} and point stops at | |
200 | the buffer boundary or field boundary. | |
8241495d | 201 | |
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202 | If @code{inhibit-field-text-motion} is non-@code{nil}, |
203 | this function ignores field boundaries. | |
204 | ||
2468d0c0 | 205 | In an interactive call, @var{count} is specified by the numeric prefix |
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206 | argument. |
207 | @end deffn | |
208 | ||
209 | @deffn Command backward-word count | |
29679a81 | 210 | This function is just like @code{forward-word}, except that it moves |
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211 | backward until encountering the front of a word, rather than forward. |
212 | ||
213 | In an interactive call, @var{count} is set to the numeric prefix | |
214 | argument. | |
215 | ||
216 | This function is rarely used in programs, as it is more efficient to | |
29679a81 | 217 | call @code{forward-word} with a negative argument. |
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218 | @end deffn |
219 | ||
220 | @defvar words-include-escapes | |
221 | @c Emacs 19 feature | |
222 | This variable affects the behavior of @code{forward-word} and everything | |
223 | that uses it. If it is non-@code{nil}, then characters in the | |
224 | ``escape'' and ``character quote'' syntax classes count as part of | |
225 | words. Otherwise, they do not. | |
226 | @end defvar | |
227 | ||
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228 | @defvar inhibit-field-text-motion |
229 | @tindex inhibit-field-text-motion | |
230 | If this variable is non-@code{nil}, certain motion functions including | |
231 | @code{forward-word}, @code{forward-sentence}, and | |
37680279 | 232 | @code{forward-paragraph} ignore field boundaries. |
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233 | @end defvar |
234 | ||
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235 | @node Buffer End Motion |
236 | @subsection Motion to an End of the Buffer | |
237 | ||
238 | To move point to the beginning of the buffer, write: | |
239 | ||
240 | @example | |
241 | @group | |
242 | (goto-char (point-min)) | |
243 | @end group | |
244 | @end example | |
245 | ||
246 | @noindent | |
247 | Likewise, to move to the end of the buffer, use: | |
248 | ||
249 | @example | |
250 | @group | |
251 | (goto-char (point-max)) | |
252 | @end group | |
253 | @end example | |
254 | ||
29679a81 | 255 | Here are two commands that users use to do these things. They are |
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256 | documented here to warn you not to use them in Lisp programs, because |
257 | they set the mark and display messages in the echo area. | |
258 | ||
259 | @deffn Command beginning-of-buffer &optional n | |
260 | This function moves point to the beginning of the buffer (or the limits | |
261 | of the accessible portion, when narrowing is in effect), setting the | |
262 | mark at the previous position. If @var{n} is non-@code{nil}, then it | |
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263 | puts point @var{n} tenths of the way from the beginning of the |
264 | accessible portion of the buffer. | |
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265 | |
266 | In an interactive call, @var{n} is the numeric prefix argument, | |
267 | if provided; otherwise @var{n} defaults to @code{nil}. | |
268 | ||
969fe9b5 | 269 | @strong{Warning:} Don't use this function in Lisp programs! |
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270 | @end deffn |
271 | ||
272 | @deffn Command end-of-buffer &optional n | |
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273 | This function moves point to the end of the buffer (or the limits of the |
274 | accessible portion, when narrowing is in effect), setting the mark at | |
275 | the previous position. If @var{n} is non-@code{nil}, then it puts point | |
276 | @var{n} tenths of the way from the end of the accessible portion of the | |
277 | buffer. | |
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278 | |
279 | In an interactive call, @var{n} is the numeric prefix argument, | |
280 | if provided; otherwise @var{n} defaults to @code{nil}. | |
281 | ||
969fe9b5 | 282 | @strong{Warning:} Don't use this function in Lisp programs! |
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283 | @end deffn |
284 | ||
285 | @node Text Lines | |
286 | @subsection Motion by Text Lines | |
287 | @cindex lines | |
288 | ||
289 | Text lines are portions of the buffer delimited by newline characters, | |
290 | which are regarded as part of the previous line. The first text line | |
291 | begins at the beginning of the buffer, and the last text line ends at | |
292 | the end of the buffer whether or not the last character is a newline. | |
293 | The division of the buffer into text lines is not affected by the width | |
294 | of the window, by line continuation in display, or by how tabs and | |
295 | control characters are displayed. | |
296 | ||
297 | @deffn Command goto-line line | |
298 | This function moves point to the front of the @var{line}th line, | |
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299 | counting from line 1 at beginning of the buffer. If @var{line} is less |
300 | than 1, it moves point to the beginning of the buffer. If @var{line} is | |
7015aca4 | 301 | greater than the number of lines in the buffer, it moves point to the |
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302 | end of the buffer---that is, the @emph{end of the last line} of the |
303 | buffer. This is the only case in which @code{goto-line} does not | |
304 | necessarily move to the beginning of a line. | |
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305 | |
306 | If narrowing is in effect, then @var{line} still counts from the | |
307 | beginning of the buffer, but point cannot go outside the accessible | |
308 | portion. So @code{goto-line} moves point to the beginning or end of the | |
309 | accessible portion, if the line number specifies an inaccessible | |
310 | position. | |
311 | ||
312 | The return value of @code{goto-line} is the difference between | |
313 | @var{line} and the line number of the line to which point actually was | |
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314 | able to move (in the full buffer, before taking account of narrowing). |
315 | Thus, the value is positive if the scan encounters the real end of the | |
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316 | buffer before finding the specified line. The value is zero if scan |
317 | encounters the end of the accessible portion but not the real end of the | |
318 | buffer. | |
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319 | |
320 | In an interactive call, @var{line} is the numeric prefix argument if | |
321 | one has been provided. Otherwise @var{line} is read in the minibuffer. | |
322 | @end deffn | |
323 | ||
324 | @deffn Command beginning-of-line &optional count | |
325 | This function moves point to the beginning of the current line. With an | |
326 | argument @var{count} not @code{nil} or 1, it moves forward | |
327 | @var{count}@minus{}1 lines and then to the beginning of the line. | |
328 | ||
329 | If this function reaches the end of the buffer (or of the accessible | |
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330 | portion, if narrowing is in effect), it positions point there. No error |
331 | is signaled. | |
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332 | @end deffn |
333 | ||
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334 | @defun line-beginning-position &optional count |
335 | @tindex line-beginning-position | |
336 | Return the position that @code{(beginning-of-line @var{count})} | |
337 | would move to. | |
338 | @end defun | |
339 | ||
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340 | @deffn Command end-of-line &optional count |
341 | This function moves point to the end of the current line. With an | |
342 | argument @var{count} not @code{nil} or 1, it moves forward | |
343 | @var{count}@minus{}1 lines and then to the end of the line. | |
344 | ||
345 | If this function reaches the end of the buffer (or of the accessible | |
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346 | portion, if narrowing is in effect), it positions point there. No error |
347 | is signaled. | |
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348 | @end deffn |
349 | ||
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350 | @defun line-end-position &optional count |
351 | @tindex line-end-position | |
352 | Return the position that @code{(end-of-line @var{count})} | |
353 | would move to. | |
354 | @end defun | |
355 | ||
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356 | @deffn Command forward-line &optional count |
357 | @cindex beginning of line | |
358 | This function moves point forward @var{count} lines, to the beginning of | |
359 | the line. If @var{count} is negative, it moves point | |
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360 | @minus{}@var{count} lines backward, to the beginning of a line. If |
361 | @var{count} is zero, it moves point to the beginning of the current | |
362 | line. | |
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363 | |
364 | If @code{forward-line} encounters the beginning or end of the buffer (or | |
365 | of the accessible portion) before finding that many lines, it sets point | |
366 | there. No error is signaled. | |
367 | ||
368 | @code{forward-line} returns the difference between @var{count} and the | |
369 | number of lines actually moved. If you attempt to move down five lines | |
370 | from the beginning of a buffer that has only three lines, point stops at | |
371 | the end of the last line, and the value will be 2. | |
372 | ||
373 | In an interactive call, @var{count} is the numeric prefix argument. | |
374 | @end deffn | |
375 | ||
376 | @defun count-lines start end | |
377 | @cindex lines in region | |
378 | This function returns the number of lines between the positions | |
379 | @var{start} and @var{end} in the current buffer. If @var{start} and | |
380 | @var{end} are equal, then it returns 0. Otherwise it returns at least | |
381 | 1, even if @var{start} and @var{end} are on the same line. This is | |
382 | because the text between them, considered in isolation, must contain at | |
383 | least one line unless it is empty. | |
384 | ||
385 | Here is an example of using @code{count-lines}: | |
386 | ||
387 | @example | |
388 | @group | |
389 | (defun current-line () | |
390 | "Return the vertical position of point@dots{}" | |
391 | (+ (count-lines (window-start) (point)) | |
392 | (if (= (current-column) 0) 1 0) | |
393 | -1)) | |
394 | @end group | |
395 | @end example | |
396 | @end defun | |
397 | ||
398 | @ignore | |
399 | @c ================ | |
400 | The @code{previous-line} and @code{next-line} commands are functions | |
401 | that should not be used in programs. They are for users and are | |
402 | mentioned here only for completeness. | |
403 | ||
404 | @deffn Command previous-line count | |
405 | @cindex goal column | |
406 | This function moves point up @var{count} lines (down if @var{count} | |
407 | is negative). In moving, it attempts to keep point in the ``goal column'' | |
408 | (normally the same column that it was at the beginning of the move). | |
409 | ||
410 | If there is no character in the target line exactly under the current | |
411 | column, point is positioned after the character in that line which | |
412 | spans this column, or at the end of the line if it is not long enough. | |
413 | ||
414 | If it attempts to move beyond the top or bottom of the buffer (or clipped | |
415 | region), then point is positioned in the goal column in the top or | |
416 | bottom line. No error is signaled. | |
417 | ||
418 | In an interactive call, @var{count} will be the numeric | |
419 | prefix argument. | |
420 | ||
421 | The command @code{set-goal-column} can be used to create a semipermanent | |
422 | goal column to which this command always moves. Then it does not try to | |
423 | move vertically. | |
424 | ||
425 | If you are thinking of using this in a Lisp program, consider using | |
426 | @code{forward-line} with a negative argument instead. It is usually easier | |
427 | to use and more reliable (no dependence on goal column, etc.). | |
428 | @end deffn | |
429 | ||
430 | @deffn Command next-line count | |
431 | This function moves point down @var{count} lines (up if @var{count} | |
432 | is negative). In moving, it attempts to keep point in the ``goal column'' | |
433 | (normally the same column that it was at the beginning of the move). | |
434 | ||
435 | If there is no character in the target line exactly under the current | |
436 | column, point is positioned after the character in that line which | |
437 | spans this column, or at the end of the line if it is not long enough. | |
438 | ||
439 | If it attempts to move beyond the top or bottom of the buffer (or clipped | |
440 | region), then point is positioned in the goal column in the top or | |
441 | bottom line. No error is signaled. | |
442 | ||
443 | In the case where the @var{count} is 1, and point is on the last | |
444 | line of the buffer (or clipped region), a new empty line is inserted at the | |
445 | end of the buffer (or clipped region) and point moved there. | |
446 | ||
447 | In an interactive call, @var{count} will be the numeric | |
448 | prefix argument. | |
449 | ||
450 | The command @code{set-goal-column} can be used to create a semipermanent | |
451 | goal column to which this command always moves. Then it does not try to | |
452 | move vertically. | |
453 | ||
454 | If you are thinking of using this in a Lisp program, consider using | |
455 | @code{forward-line} instead. It is usually easier | |
456 | to use and more reliable (no dependence on goal column, etc.). | |
457 | @end deffn | |
458 | ||
459 | @c ================ | |
460 | @end ignore | |
461 | ||
462 | Also see the functions @code{bolp} and @code{eolp} in @ref{Near Point}. | |
463 | These functions do not move point, but test whether it is already at the | |
464 | beginning or end of a line. | |
465 | ||
466 | @node Screen Lines | |
467 | @subsection Motion by Screen Lines | |
468 | ||
469 | The line functions in the previous section count text lines, delimited | |
470 | only by newline characters. By contrast, these functions count screen | |
471 | lines, which are defined by the way the text appears on the screen. A | |
472 | text line is a single screen line if it is short enough to fit the width | |
473 | of the selected window, but otherwise it may occupy several screen | |
474 | lines. | |
475 | ||
476 | In some cases, text lines are truncated on the screen rather than | |
477 | continued onto additional screen lines. In these cases, | |
478 | @code{vertical-motion} moves point much like @code{forward-line}. | |
479 | @xref{Truncation}. | |
480 | ||
29679a81 | 481 | Because the width of a given string depends on the flags that control |
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482 | the appearance of certain characters, @code{vertical-motion} behaves |
483 | differently, for a given piece of text, depending on the buffer it is | |
484 | in, and even on the selected window (because the width, the truncation | |
485 | flag, and display table may vary between windows). @xref{Usual | |
486 | Display}. | |
487 | ||
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488 | These functions scan text to determine where screen lines break, and |
489 | thus take time proportional to the distance scanned. If you intend to | |
490 | use them heavily, Emacs provides caches which may improve the | |
a9f0a989 | 491 | performance of your code. @xref{Truncation, cache-long-line-scans}. |
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492 | |
493 | ||
a890e1b0 | 494 | @defun vertical-motion count &optional window |
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495 | This function moves point to the start of the screen line @var{count} |
496 | screen lines down from the screen line containing point. If @var{count} | |
497 | is negative, it moves up instead. | |
498 | ||
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499 | @code{vertical-motion} returns the number of screen lines over which it |
500 | moved point. The value may be less in absolute value than @var{count} | |
501 | if the beginning or end of the buffer was reached. | |
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502 | |
503 | The window @var{window} is used for obtaining parameters such as the | |
504 | width, the horizontal scrolling, and the display table. But | |
505 | @code{vertical-motion} always operates on the current buffer, even if | |
506 | @var{window} currently displays some other buffer. | |
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507 | @end defun |
508 | ||
509 | @deffn Command move-to-window-line count | |
510 | This function moves point with respect to the text currently displayed | |
511 | in the selected window. It moves point to the beginning of the screen | |
512 | line @var{count} screen lines from the top of the window. If | |
513 | @var{count} is negative, that specifies a position | |
29679a81 RS |
514 | @w{@minus{}@var{count}} lines from the bottom (or the last line of the |
515 | buffer, if the buffer ends above the specified screen position). | |
7015aca4 RS |
516 | |
517 | If @var{count} is @code{nil}, then point moves to the beginning of the | |
518 | line in the middle of the window. If the absolute value of @var{count} | |
519 | is greater than the size of the window, then point moves to the place | |
29679a81 | 520 | that would appear on that screen line if the window were tall enough. |
7015aca4 RS |
521 | This will probably cause the next redisplay to scroll to bring that |
522 | location onto the screen. | |
523 | ||
524 | In an interactive call, @var{count} is the numeric prefix argument. | |
525 | ||
29679a81 RS |
526 | The value returned is the window line number point has moved to, with |
527 | the top line in the window numbered 0. | |
7015aca4 RS |
528 | @end deffn |
529 | ||
a890e1b0 | 530 | @defun compute-motion from frompos to topos width offsets window |
29679a81 RS |
531 | This function scans the current buffer, calculating screen positions. |
532 | It scans the buffer forward from position @var{from}, assuming that is | |
533 | at screen coordinates @var{frompos}, to position @var{to} or coordinates | |
534 | @var{topos}, whichever comes first. It returns the ending buffer | |
535 | position and screen coordinates. | |
7015aca4 RS |
536 | |
537 | The coordinate arguments @var{frompos} and @var{topos} are cons cells of | |
538 | the form @code{(@var{hpos} . @var{vpos})}. | |
539 | ||
540 | The argument @var{width} is the number of columns available to display | |
541 | text; this affects handling of continuation lines. Use the value | |
bfe721d1 KH |
542 | returned by @code{window-width} for the window of your choice; |
543 | normally, use @code{(window-width @var{window})}. | |
7015aca4 RS |
544 | |
545 | The argument @var{offsets} is either @code{nil} or a cons cell of the | |
546 | form @code{(@var{hscroll} . @var{tab-offset})}. Here @var{hscroll} is | |
a890e1b0 | 547 | the number of columns not being displayed at the left margin; most |
a9f0a989 | 548 | callers get this by calling @code{window-hscroll}. Meanwhile, |
a890e1b0 RS |
549 | @var{tab-offset} is the offset between column numbers on the screen and |
550 | column numbers in the buffer. This can be nonzero in a continuation | |
551 | line, when the previous screen lines' widths do not add up to a multiple | |
552 | of @code{tab-width}. It is always zero in a non-continuation line. | |
553 | ||
29679a81 RS |
554 | The window @var{window} serves only to specify which display table to |
555 | use. @code{compute-motion} always operates on the current buffer, | |
556 | regardless of what buffer is displayed in @var{window}. | |
7015aca4 RS |
557 | |
558 | The return value is a list of five elements: | |
559 | ||
560 | @example | |
561 | (@var{pos} @var{vpos} @var{hpos} @var{prevhpos} @var{contin}) | |
562 | @end example | |
563 | ||
564 | @noindent | |
565 | Here @var{pos} is the buffer position where the scan stopped, @var{vpos} | |
29679a81 RS |
566 | is the vertical screen position, and @var{hpos} is the horizontal screen |
567 | position. | |
7015aca4 RS |
568 | |
569 | The result @var{prevhpos} is the horizontal position one character back | |
29679a81 RS |
570 | from @var{pos}. The result @var{contin} is @code{t} if the last line |
571 | was continued after (or within) the previous character. | |
7015aca4 | 572 | |
f9f59935 | 573 | For example, to find the buffer position of column @var{col} of screen line |
7015aca4 RS |
574 | @var{line} of a certain window, pass the window's display start location |
575 | as @var{from} and the window's upper-left coordinates as @var{frompos}. | |
576 | Pass the buffer's @code{(point-max)} as @var{to}, to limit the scan to | |
29679a81 | 577 | the end of the accessible portion of the buffer, and pass @var{line} and |
7015aca4 RS |
578 | @var{col} as @var{topos}. Here's a function that does this: |
579 | ||
580 | @example | |
581 | (defun coordinates-of-position (col line) | |
582 | (car (compute-motion (window-start) | |
583 | '(0 . 0) | |
29679a81 | 584 | (point-max) |
7015aca4 RS |
585 | (cons col line) |
586 | (window-width) | |
29679a81 RS |
587 | (cons (window-hscroll) 0) |
588 | (selected-window)))) | |
7015aca4 | 589 | @end example |
a890e1b0 RS |
590 | |
591 | When you use @code{compute-motion} for the minibuffer, you need to use | |
592 | @code{minibuffer-prompt-width} to get the horizontal position of the | |
593 | beginning of the first screen line. @xref{Minibuffer Misc}. | |
7015aca4 RS |
594 | @end defun |
595 | ||
7015aca4 RS |
596 | @node List Motion |
597 | @comment node-name, next, previous, up | |
598 | @subsection Moving over Balanced Expressions | |
599 | @cindex sexp motion | |
600 | @cindex Lisp expression motion | |
601 | @cindex list motion | |
602 | ||
603 | Here are several functions concerned with balanced-parenthesis | |
604 | expressions (also called @dfn{sexps} in connection with moving across | |
605 | them in Emacs). The syntax table controls how these functions interpret | |
606 | various characters; see @ref{Syntax Tables}. @xref{Parsing | |
607 | Expressions}, for lower-level primitives for scanning sexps or parts of | |
8241495d | 608 | sexps. For user-level commands, see @ref{Lists Commands,,, emacs, The GNU |
7015aca4 RS |
609 | Emacs Manual}. |
610 | ||
611 | @deffn Command forward-list arg | |
a890e1b0 RS |
612 | This function moves forward across @var{arg} balanced groups of |
613 | parentheses. (Other syntactic entities such as words or paired string | |
614 | quotes are ignored.) | |
7015aca4 RS |
615 | @end deffn |
616 | ||
617 | @deffn Command backward-list arg | |
a890e1b0 RS |
618 | This function moves backward across @var{arg} balanced groups of |
619 | parentheses. (Other syntactic entities such as words or paired string | |
620 | quotes are ignored.) | |
7015aca4 RS |
621 | @end deffn |
622 | ||
623 | @deffn Command up-list arg | |
a890e1b0 | 624 | This function moves forward out of @var{arg} levels of parentheses. |
7015aca4 RS |
625 | A negative argument means move backward but still to a less deep spot. |
626 | @end deffn | |
627 | ||
628 | @deffn Command down-list arg | |
29679a81 | 629 | This function moves forward into @var{arg} levels of parentheses. A |
ec221d13 RS |
630 | negative argument means move backward but still go |
631 | deeper in parentheses (@minus{}@var{arg} levels). | |
7015aca4 RS |
632 | @end deffn |
633 | ||
634 | @deffn Command forward-sexp arg | |
a890e1b0 RS |
635 | This function moves forward across @var{arg} balanced expressions. |
636 | Balanced expressions include both those delimited by parentheses and | |
637 | other kinds, such as words and string constants. For example, | |
7015aca4 RS |
638 | |
639 | @example | |
640 | @group | |
641 | ---------- Buffer: foo ---------- | |
642 | (concat@point{} "foo " (car x) y z) | |
643 | ---------- Buffer: foo ---------- | |
644 | @end group | |
645 | ||
646 | @group | |
647 | (forward-sexp 3) | |
648 | @result{} nil | |
649 | ||
650 | ---------- Buffer: foo ---------- | |
651 | (concat "foo " (car x) y@point{} z) | |
652 | ---------- Buffer: foo ---------- | |
653 | @end group | |
654 | @end example | |
655 | @end deffn | |
656 | ||
657 | @deffn Command backward-sexp arg | |
a890e1b0 | 658 | This function moves backward across @var{arg} balanced expressions. |
7015aca4 RS |
659 | @end deffn |
660 | ||
a890e1b0 RS |
661 | @deffn Command beginning-of-defun arg |
662 | This function moves back to the @var{arg}th beginning of a defun. If | |
663 | @var{arg} is negative, this actually moves forward, but it still moves | |
664 | to the beginning of a defun, not to the end of one. | |
665 | @end deffn | |
666 | ||
667 | @deffn Command end-of-defun arg | |
29679a81 RS |
668 | This function moves forward to the @var{arg}th end of a defun. If |
669 | @var{arg} is negative, this actually moves backward, but it still moves | |
670 | to the end of a defun, not to the beginning of one. | |
a890e1b0 RS |
671 | @end deffn |
672 | ||
673 | @defopt defun-prompt-regexp | |
674 | If non-@code{nil}, this variable holds a regular expression that | |
675 | specifies what text can appear before the open-parenthesis that starts a | |
29679a81 RS |
676 | defun. That is to say, a defun begins on a line that starts with a |
677 | match for this regular expression, followed by a character with | |
678 | open-parenthesis syntax. | |
a890e1b0 RS |
679 | @end defopt |
680 | ||
7015aca4 RS |
681 | @node Skipping Characters |
682 | @comment node-name, next, previous, up | |
683 | @subsection Skipping Characters | |
684 | @cindex skipping characters | |
685 | ||
686 | The following two functions move point over a specified set of | |
687 | characters. For example, they are often used to skip whitespace. For | |
688 | related functions, see @ref{Motion and Syntax}. | |
689 | ||
690 | @defun skip-chars-forward character-set &optional limit | |
691 | This function moves point in the current buffer forward, skipping over a | |
692 | given set of characters. It examines the character following point, | |
693 | then advances point if the character matches @var{character-set}. This | |
694 | continues until it reaches a character that does not match. The | |
1911e6e5 | 695 | function returns the number of characters moved over. |
7015aca4 RS |
696 | |
697 | The argument @var{character-set} is like the inside of a | |
698 | @samp{[@dots{}]} in a regular expression except that @samp{]} is never | |
699 | special and @samp{\} quotes @samp{^}, @samp{-} or @samp{\}. Thus, | |
700 | @code{"a-zA-Z"} skips over all letters, stopping before the first | |
67f09a62 | 701 | nonletter, and @code{"^a-zA-Z"} skips nonletters stopping before the |
7015aca4 RS |
702 | first letter. @xref{Regular Expressions}. |
703 | ||
704 | If @var{limit} is supplied (it must be a number or a marker), it | |
705 | specifies the maximum position in the buffer that point can be skipped | |
706 | to. Point will stop at or before @var{limit}. | |
707 | ||
708 | In the following example, point is initially located directly before the | |
709 | @samp{T}. After the form is evaluated, point is located at the end of | |
710 | that line (between the @samp{t} of @samp{hat} and the newline). The | |
711 | function skips all letters and spaces, but not newlines. | |
712 | ||
713 | @example | |
714 | @group | |
715 | ---------- Buffer: foo ---------- | |
716 | I read "@point{}The cat in the hat | |
717 | comes back" twice. | |
718 | ---------- Buffer: foo ---------- | |
719 | @end group | |
720 | ||
721 | @group | |
722 | (skip-chars-forward "a-zA-Z ") | |
723 | @result{} nil | |
724 | ||
725 | ---------- Buffer: foo ---------- | |
726 | I read "The cat in the hat@point{} | |
727 | comes back" twice. | |
728 | ---------- Buffer: foo ---------- | |
729 | @end group | |
730 | @end example | |
731 | @end defun | |
732 | ||
733 | @defun skip-chars-backward character-set &optional limit | |
734 | This function moves point backward, skipping characters that match | |
f9f59935 | 735 | @var{character-set}, until @var{limit}. It is just like |
7015aca4 | 736 | @code{skip-chars-forward} except for the direction of motion. |
1911e6e5 RS |
737 | |
738 | The return value indicates the distance traveled. It is an integer that | |
739 | is zero or less. | |
7015aca4 RS |
740 | @end defun |
741 | ||
742 | @node Excursions | |
743 | @section Excursions | |
744 | @cindex excursion | |
745 | ||
746 | It is often useful to move point ``temporarily'' within a localized | |
747 | portion of the program, or to switch buffers temporarily. This is | |
748 | called an @dfn{excursion}, and it is done with the @code{save-excursion} | |
8241495d RS |
749 | special form. This construct initially remembers the identity of the |
750 | current buffer, and its values of point and the mark, and restores them | |
751 | after the completion of the excursion. | |
7015aca4 RS |
752 | |
753 | The forms for saving and restoring the configuration of windows are | |
754 | described elsewhere (see @ref{Window Configurations}, and @pxref{Frame | |
755 | Configurations}). | |
756 | ||
757 | @defspec save-excursion forms@dots{} | |
758 | @cindex mark excursion | |
759 | @cindex point excursion | |
760 | @cindex current buffer excursion | |
761 | The @code{save-excursion} special form saves the identity of the current | |
29679a81 RS |
762 | buffer and the values of point and the mark in it, evaluates |
763 | @var{forms}, and finally restores the buffer and its saved values of | |
764 | point and the mark. All three saved values are restored even in case of | |
765 | an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). | |
7015aca4 RS |
766 | |
767 | The @code{save-excursion} special form is the standard way to switch | |
768 | buffers or move point within one part of a program and avoid affecting | |
a9f0a989 | 769 | the rest of the program. It is used more than 4000 times in the Lisp |
7015aca4 RS |
770 | sources of Emacs. |
771 | ||
772 | @code{save-excursion} does not save the values of point and the mark for | |
773 | other buffers, so changes in other buffers remain in effect after | |
774 | @code{save-excursion} exits. | |
775 | ||
776 | @cindex window excursions | |
777 | Likewise, @code{save-excursion} does not restore window-buffer | |
778 | correspondences altered by functions such as @code{switch-to-buffer}. | |
779 | One way to restore these correspondences, and the selected window, is to | |
780 | use @code{save-window-excursion} inside @code{save-excursion} | |
781 | (@pxref{Window Configurations}). | |
782 | ||
783 | The value returned by @code{save-excursion} is the result of the last of | |
784 | @var{forms}, or @code{nil} if no @var{forms} are given. | |
785 | ||
786 | @example | |
787 | @group | |
7dd3d99f | 788 | (save-excursion @var{forms}) |
7015aca4 RS |
789 | @equiv{} |
790 | (let ((old-buf (current-buffer)) | |
791 | (old-pnt (point-marker)) | |
7dd3d99f | 792 | @end group |
7015aca4 RS |
793 | (old-mark (copy-marker (mark-marker)))) |
794 | (unwind-protect | |
795 | (progn @var{forms}) | |
796 | (set-buffer old-buf) | |
7dd3d99f | 797 | @group |
7015aca4 RS |
798 | (goto-char old-pnt) |
799 | (set-marker (mark-marker) old-mark))) | |
800 | @end group | |
801 | @end example | |
802 | @end defspec | |
803 | ||
a9f0a989 RS |
804 | @strong{Warning:} Ordinary insertion of text adjacent to the saved |
805 | point value relocates the saved value, just as it relocates all markers. | |
806 | Therefore, when the saved point value is restored, it normally comes | |
1911e6e5 | 807 | before the inserted text. |
a9f0a989 | 808 | |
969fe9b5 RS |
809 | Although @code{save-excursion} saves the location of the mark, it does |
810 | not prevent functions which modify the buffer from setting | |
811 | @code{deactivate-mark}, and thus causing the deactivation of the mark | |
812 | after the command finishes. @xref{The Mark}. | |
813 | ||
7015aca4 RS |
814 | @node Narrowing |
815 | @section Narrowing | |
816 | @cindex narrowing | |
817 | @cindex restriction (in a buffer) | |
818 | @cindex accessible portion (of a buffer) | |
819 | ||
820 | @dfn{Narrowing} means limiting the text addressable by Emacs editing | |
821 | commands to a limited range of characters in a buffer. The text that | |
822 | remains addressable is called the @dfn{accessible portion} of the | |
823 | buffer. | |
824 | ||
825 | Narrowing is specified with two buffer positions which become the | |
826 | beginning and end of the accessible portion. For most editing commands | |
827 | and most Emacs primitives, these positions replace the values of the | |
828 | beginning and end of the buffer. While narrowing is in effect, no text | |
829 | outside the accessible portion is displayed, and point cannot move | |
830 | outside the accessible portion. | |
831 | ||
29679a81 | 832 | Values such as positions or line numbers, which usually count from the |
7015aca4 RS |
833 | beginning of the buffer, do so despite narrowing, but the functions |
834 | which use them refuse to operate on text that is inaccessible. | |
835 | ||
836 | The commands for saving buffers are unaffected by narrowing; they save | |
29679a81 | 837 | the entire buffer regardless of any narrowing. |
7015aca4 RS |
838 | |
839 | @deffn Command narrow-to-region start end | |
840 | This function sets the accessible portion of the current buffer to start | |
841 | at @var{start} and end at @var{end}. Both arguments should be character | |
842 | positions. | |
843 | ||
844 | In an interactive call, @var{start} and @var{end} are set to the bounds | |
845 | of the current region (point and the mark, with the smallest first). | |
846 | @end deffn | |
847 | ||
848 | @deffn Command narrow-to-page move-count | |
849 | This function sets the accessible portion of the current buffer to | |
850 | include just the current page. An optional first argument | |
851 | @var{move-count} non-@code{nil} means to move forward or backward by | |
f9f59935 | 852 | @var{move-count} pages and then narrow to one page. The variable |
7015aca4 RS |
853 | @code{page-delimiter} specifies where pages start and end |
854 | (@pxref{Standard Regexps}). | |
855 | ||
856 | In an interactive call, @var{move-count} is set to the numeric prefix | |
857 | argument. | |
858 | @end deffn | |
859 | ||
860 | @deffn Command widen | |
861 | @cindex widening | |
862 | This function cancels any narrowing in the current buffer, so that the | |
863 | entire contents are accessible. This is called @dfn{widening}. | |
864 | It is equivalent to the following expression: | |
865 | ||
866 | @example | |
867 | (narrow-to-region 1 (1+ (buffer-size))) | |
868 | @end example | |
869 | @end deffn | |
870 | ||
871 | @defspec save-restriction body@dots{} | |
872 | This special form saves the current bounds of the accessible portion, | |
873 | evaluates the @var{body} forms, and finally restores the saved bounds, | |
874 | thus restoring the same state of narrowing (or absence thereof) formerly | |
875 | in effect. The state of narrowing is restored even in the event of an | |
29679a81 RS |
876 | abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). |
877 | Therefore, this construct is a clean way to narrow a buffer temporarily. | |
7015aca4 RS |
878 | |
879 | The value returned by @code{save-restriction} is that returned by the | |
880 | last form in @var{body}, or @code{nil} if no body forms were given. | |
881 | ||
882 | @c Wordy to avoid overfull hbox. --rjc 16mar92 | |
883 | @strong{Caution:} it is easy to make a mistake when using the | |
884 | @code{save-restriction} construct. Read the entire description here | |
885 | before you try it. | |
886 | ||
887 | If @var{body} changes the current buffer, @code{save-restriction} still | |
888 | restores the restrictions on the original buffer (the buffer whose | |
f9f59935 | 889 | restrictions it saved from), but it does not restore the identity of the |
7015aca4 RS |
890 | current buffer. |
891 | ||
892 | @code{save-restriction} does @emph{not} restore point and the mark; use | |
893 | @code{save-excursion} for that. If you use both @code{save-restriction} | |
894 | and @code{save-excursion} together, @code{save-excursion} should come | |
895 | first (on the outside). Otherwise, the old point value would be | |
896 | restored with temporary narrowing still in effect. If the old point | |
897 | value were outside the limits of the temporary narrowing, this would | |
898 | fail to restore it accurately. | |
899 | ||
900 | The @code{save-restriction} special form records the values of the | |
901 | beginning and end of the accessible portion as distances from the | |
902 | beginning and end of the buffer. In other words, it records the amount | |
903 | of inaccessible text before and after the accessible portion. | |
904 | ||
905 | This method yields correct results if @var{body} does further narrowing. | |
906 | However, @code{save-restriction} can become confused if the body widens | |
a9f0a989 | 907 | and then makes changes outside the range of the saved narrowing. When |
7015aca4 RS |
908 | this is what you want to do, @code{save-restriction} is not the right |
909 | tool for the job. Here is what you must use instead: | |
910 | ||
911 | @example | |
912 | @group | |
913 | (let ((beg (point-min-marker)) | |
914 | (end (point-max-marker))) | |
915 | (unwind-protect | |
916 | (progn @var{body}) | |
917 | (save-excursion | |
918 | (set-buffer (marker-buffer beg)) | |
919 | (narrow-to-region beg end)))) | |
920 | @end group | |
921 | @end example | |
922 | ||
923 | Here is a simple example of correct use of @code{save-restriction}: | |
924 | ||
925 | @example | |
926 | @group | |
927 | ---------- Buffer: foo ---------- | |
928 | This is the contents of foo | |
929 | This is the contents of foo | |
930 | This is the contents of foo@point{} | |
931 | ---------- Buffer: foo ---------- | |
932 | @end group | |
933 | ||
934 | @group | |
935 | (save-excursion | |
936 | (save-restriction | |
937 | (goto-char 1) | |
938 | (forward-line 2) | |
939 | (narrow-to-region 1 (point)) | |
940 | (goto-char (point-min)) | |
941 | (replace-string "foo" "bar"))) | |
942 | ||
943 | ---------- Buffer: foo ---------- | |
944 | This is the contents of bar | |
945 | This is the contents of bar | |
946 | This is the contents of foo@point{} | |
947 | ---------- Buffer: foo ---------- | |
948 | @end group | |
949 | @end example | |
950 | @end defspec |