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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f9f59935 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. |
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4 | @c See the file elisp.texi for copying conditions. |
5 | @setfilename ../info/help | |
6 | @node Documentation, Files, Modes, Top | |
7 | @chapter Documentation | |
8 | @cindex documentation strings | |
9 | ||
10 | GNU Emacs Lisp has convenient on-line help facilities, most of which | |
11 | derive their information from the documentation strings associated with | |
12 | functions and variables. This chapter describes how to write good | |
13 | documentation strings for your Lisp programs, as well as how to write | |
14 | programs to access documentation. | |
15 | ||
16 | Note that the documentation strings for Emacs are not the same thing | |
17 | as the Emacs manual. Manuals have their own source files, written in | |
18 | the Texinfo language; documentation strings are specified in the | |
19 | definitions of the functions and variables they apply to. A collection | |
20 | of documentation strings is not sufficient as a manual because a good | |
21 | manual is not organized in that fashion; it is organized in terms of | |
22 | topics of discussion. | |
23 | ||
24 | @menu | |
25 | * Documentation Basics:: Good style for doc strings. | |
26 | Where to put them. How Emacs stores them. | |
27 | * Accessing Documentation:: How Lisp programs can access doc strings. | |
28 | * Keys in Documentation:: Substituting current key bindings. | |
29 | * Describing Characters:: Making printable descriptions of | |
30 | non-printing characters and key sequences. | |
31 | * Help Functions:: Subroutines used by Emacs help facilities. | |
32 | @end menu | |
33 | ||
34 | @node Documentation Basics | |
35 | @comment node-name, next, previous, up | |
36 | @section Documentation Basics | |
37 | @cindex documentation conventions | |
38 | @cindex writing a documentation string | |
39 | @cindex string, writing a doc string | |
40 | ||
41 | A documentation string is written using the Lisp syntax for strings, | |
42 | with double-quote characters surrounding the text of the string. This | |
43 | is because it really is a Lisp string object. The string serves as | |
44 | documentation when it is written in the proper place in the definition | |
45 | of a function or variable. In a function definition, the documentation | |
46 | string follows the argument list. In a variable definition, the | |
47 | documentation string follows the initial value of the variable. | |
48 | ||
49 | When you write a documentation string, make the first line a complete | |
50 | sentence (or two complete sentences) since some commands, such as | |
51 | @code{apropos}, show only the first line of a multi-line documentation | |
52 | string. Also, you should not indent the second line of a documentation | |
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53 | string, if it has one, because that looks odd when you use @kbd{C-h f} |
54 | (@code{describe-function}) or @kbd{C-h v} (@code{describe-variable}) to | |
55 | view the documentation string. @xref{Documentation Tips}. | |
5e8db0c6 | 56 | |
969fe9b5 | 57 | Documentation strings can contain several special substrings, which |
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58 | stand for key bindings to be looked up in the current keymaps when the |
59 | documentation is displayed. This allows documentation strings to refer | |
60 | to the keys for related commands and be accurate even when a user | |
61 | rearranges the key bindings. (@xref{Accessing Documentation}.) | |
62 | ||
f9f59935 | 63 | In Emacs Lisp, a documentation string is accessible through the |
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64 | function or variable that it describes: |
65 | ||
66 | @itemize @bullet | |
67 | @item | |
68 | The documentation for a function is stored in the function definition | |
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69 | itself (@pxref{Lambda Expressions}). The function @code{documentation} |
70 | knows how to extract it. | |
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71 | |
72 | @item | |
73 | @kindex variable-documentation | |
74 | The documentation for a variable is stored in the variable's property | |
75 | list under the property name @code{variable-documentation}. The | |
f9f59935 | 76 | function @code{documentation-property} knows how to retrieve it. |
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77 | @end itemize |
78 | ||
79 | @cindex @file{DOC} (documentation) file | |
80 | @cindex @file{emacs/etc/DOC-@var{version}} | |
81 | @cindex @file{etc/DOC-@var{version}} | |
82 | To save space, the documentation for preloaded functions and variables | |
82a2fe69 | 83 | (including primitive functions and autoloaded functions) is stored in |
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84 | the file @file{emacs/etc/DOC-@var{version}}---not inside Emacs. The |
85 | documentation strings for functions and variables loaded during the | |
86 | Emacs session from byte-compiled files are stored in those files | |
87 | (@pxref{Docs and Compilation}). | |
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88 | |
89 | The data structure inside Emacs has an integer offset into the file, or | |
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90 | a list containing a file name and an integer, in place of the |
91 | documentation string. The functions @code{documentation} and | |
92 | @code{documentation-property} use that information to fetch the | |
93 | documentation string from the appropriate file; this is transparent to | |
94 | the user. | |
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95 | |
96 | For information on the uses of documentation strings, see @ref{Help, , | |
97 | Help, emacs, The GNU Emacs Manual}. | |
98 | ||
99 | @c Wordy to prevent overfull hbox. --rjc 15mar92 | |
b32a6a15 RS |
100 | The @file{emacs/lib-src} directory contains two utilities that you can |
101 | use to print nice-looking hardcopy for the file | |
1911e6e5 RS |
102 | @file{emacs/etc/DOC-@var{version}}. These are @file{sorted-doc} and |
103 | @file{digest-doc}. | |
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104 | |
105 | @node Accessing Documentation | |
106 | @section Access to Documentation Strings | |
107 | ||
108 | @defun documentation-property symbol property &optional verbatim | |
109 | This function returns the documentation string that is recorded | |
1911e6e5 | 110 | in @var{symbol}'s property list under property @var{property}. It |
bfe721d1 KH |
111 | retrieves the text from a file if necessary, and runs |
112 | @code{substitute-command-keys} to substitute actual key bindings. (This | |
f9f59935 | 113 | substitution is not done if @var{verbatim} is non-@code{nil}.) |
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114 | |
115 | @smallexample | |
116 | @group | |
117 | (documentation-property 'command-line-processed | |
118 | 'variable-documentation) | |
1911e6e5 | 119 | @result{} "Non-nil once command line has been processed" |
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120 | @end group |
121 | @group | |
122 | (symbol-plist 'command-line-processed) | |
123 | @result{} (variable-documentation 188902) | |
124 | @end group | |
125 | @end smallexample | |
126 | @end defun | |
127 | ||
128 | @defun documentation function &optional verbatim | |
bfe721d1 KH |
129 | This function returns the documentation string of @var{function}. It |
130 | reads the text from a file if necessary. Then (unless @var{verbatim} is | |
131 | non-@code{nil}) it calls @code{substitute-command-keys}, to return a | |
132 | value containing the actual (current) key bindings. | |
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133 | |
134 | The function @code{documentation} signals a @code{void-function} error | |
969fe9b5 | 135 | if @var{function} has no function definition. However, it is OK if |
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136 | the function definition has no documentation string. In that case, |
137 | @code{documentation} returns @code{nil}. | |
138 | @end defun | |
139 | ||
140 | @c Wordy to prevent overfull hboxes. --rjc 15mar92 | |
82a2fe69 | 141 | Here is an example of using the two functions, @code{documentation} and |
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142 | @code{documentation-property}, to display the documentation strings for |
143 | several symbols in a @samp{*Help*} buffer. | |
144 | ||
145 | @smallexample | |
146 | @group | |
147 | (defun describe-symbols (pattern) | |
148 | "Describe the Emacs Lisp symbols matching PATTERN. | |
149 | All symbols that have PATTERN in their name are described | |
150 | in the `*Help*' buffer." | |
151 | (interactive "sDescribe symbols matching: ") | |
152 | (let ((describe-func | |
153 | (function | |
154 | (lambda (s) | |
155 | @end group | |
156 | @group | |
157 | ;; @r{Print description of symbol.} | |
158 | (if (fboundp s) ; @r{It is a function.} | |
159 | (princ | |
160 | (format "%s\t%s\n%s\n\n" s | |
161 | (if (commandp s) | |
162 | (let ((keys (where-is-internal s))) | |
163 | (if keys | |
164 | (concat | |
165 | "Keys: " | |
166 | (mapconcat 'key-description | |
167 | keys " ")) | |
168 | "Keys: none")) | |
169 | "Function") | |
170 | @end group | |
171 | @group | |
172 | (or (documentation s) | |
173 | "not documented")))) | |
174 | ||
175 | (if (boundp s) ; @r{It is a variable.} | |
176 | @end group | |
177 | @group | |
178 | (princ | |
179 | (format "%s\t%s\n%s\n\n" s | |
180 | (if (user-variable-p s) | |
181 | "Option " "Variable") | |
182 | @end group | |
183 | @group | |
184 | (or (documentation-property | |
185 | s 'variable-documentation) | |
186 | "not documented"))))))) | |
187 | sym-list) | |
188 | @end group | |
189 | ||
190 | @group | |
191 | ;; @r{Build a list of symbols that match pattern.} | |
192 | (mapatoms (function | |
193 | (lambda (sym) | |
194 | (if (string-match pattern (symbol-name sym)) | |
195 | (setq sym-list (cons sym sym-list)))))) | |
196 | @end group | |
197 | ||
198 | @group | |
199 | ;; @r{Display the data.} | |
200 | (with-output-to-temp-buffer "*Help*" | |
201 | (mapcar describe-func (sort sym-list 'string<)) | |
202 | (print-help-return-message)))) | |
203 | @end group | |
204 | @end smallexample | |
205 | ||
206 | The @code{describe-symbols} function works like @code{apropos}, | |
207 | but provides more information. | |
208 | ||
209 | @smallexample | |
210 | @group | |
211 | (describe-symbols "goal") | |
212 | ||
213 | ---------- Buffer: *Help* ---------- | |
214 | goal-column Option | |
9e2b495b | 215 | *Semipermanent goal column for vertical motion, as set by @dots{} |
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216 | @end group |
217 | @c Do not blithely break or fill these lines. | |
218 | @c That makes them incorrect. | |
219 | ||
220 | @group | |
1911e6e5 | 221 | set-goal-column Keys: C-x C-n |
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222 | Set the current horizontal position as a goal for C-n and C-p. |
223 | @end group | |
224 | @c DO NOT put a blank line here! That is factually inaccurate! | |
225 | @group | |
226 | Those commands will move to this position in the line moved to | |
227 | rather than trying to keep the same horizontal position. | |
228 | With a non-nil argument, clears out the goal column | |
229 | so that C-n and C-p resume vertical motion. | |
230 | The goal column is stored in the variable `goal-column'. | |
231 | @end group | |
232 | ||
233 | @group | |
234 | temporary-goal-column Variable | |
235 | Current goal column for vertical motion. | |
236 | It is the column where point was | |
237 | at the start of current run of vertical motion commands. | |
238 | When the `track-eol' feature is doing its job, the value is 9999. | |
239 | ---------- Buffer: *Help* ---------- | |
240 | @end group | |
241 | @end smallexample | |
242 | ||
243 | @defun Snarf-documentation filename | |
f9f59935 | 244 | This function is used only during Emacs initialization, just before |
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245 | the runnable Emacs is dumped. It finds the file offsets of the |
246 | documentation strings stored in the file @var{filename}, and records | |
247 | them in the in-core function definitions and variable property lists in | |
248 | place of the actual strings. @xref{Building Emacs}. | |
249 | ||
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250 | Emacs reads the file @var{filename} from the @file{emacs/etc} directory. |
251 | When the dumped Emacs is later executed, the same file will be looked | |
252 | for in the directory @code{doc-directory}. Usually @var{filename} is | |
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253 | @code{"DOC-@var{version}"}. |
254 | @end defun | |
255 | ||
256 | @c Emacs 19 feature | |
257 | @defvar doc-directory | |
969fe9b5 | 258 | This variable holds the name of the directory which should contain the |
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259 | file @code{"DOC-@var{version}"} that contains documentation strings for |
260 | built-in and preloaded functions and variables. | |
261 | ||
262 | In most cases, this is the same as @code{data-directory}. They may be | |
263 | different when you run Emacs from the directory where you built it, | |
264 | without actually installing it. See @code{data-directory} in @ref{Help | |
265 | Functions}. | |
266 | ||
267 | In older Emacs versions, @code{exec-directory} was used for this. | |
268 | @end defvar | |
269 | ||
270 | @node Keys in Documentation | |
271 | @section Substituting Key Bindings in Documentation | |
272 | @cindex documentation, keys in | |
273 | @cindex keys in documentation strings | |
274 | @cindex substituting keys in documentation | |
275 | ||
82a2fe69 RS |
276 | When documentation strings refer to key sequences, they should use the |
277 | current, actual key bindings. They can do so using certain special text | |
278 | sequences described below. Accessing documentation strings in the usual | |
279 | way substitutes current key binding information for these special | |
280 | sequences. This works by calling @code{substitute-command-keys}. You | |
281 | can also call that function yourself. | |
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282 | |
283 | Here is a list of the special sequences and what they mean: | |
284 | ||
285 | @table @code | |
286 | @item \[@var{command}] | |
287 | stands for a key sequence that will invoke @var{command}, or @samp{M-x | |
288 | @var{command}} if @var{command} has no key bindings. | |
289 | ||
290 | @item \@{@var{mapvar}@} | |
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291 | stands for a summary of the keymap which is the value of the variable |
292 | @var{mapvar}. The summary is made using @code{describe-bindings}. | |
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293 | |
294 | @item \<@var{mapvar}> | |
f9f59935 | 295 | stands for no text itself. It is used only for a side effect: it |
969fe9b5 | 296 | specifies @var{mapvar}'s value as the keymap for any following |
f9f59935 | 297 | @samp{\[@var{command}]} sequences in this documentation string. |
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298 | |
299 | @item \= | |
300 | quotes the following character and is discarded; thus, @samp{\=\[} puts | |
301 | @samp{\[} into the output, and @samp{\=\=} puts @samp{\=} into the | |
302 | output. | |
5e8db0c6 RS |
303 | @end table |
304 | ||
82a2fe69 | 305 | @strong{Please note:} Each @samp{\} must be doubled when written in a |
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306 | string in Emacs Lisp. |
307 | ||
308 | @defun substitute-command-keys string | |
309 | This function scans @var{string} for the above special sequences and | |
310 | replaces them by what they stand for, returning the result as a string. | |
311 | This permits display of documentation that refers accurately to the | |
82a2fe69 | 312 | user's own customized key bindings. |
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313 | @end defun |
314 | ||
315 | Here are examples of the special sequences: | |
316 | ||
317 | @smallexample | |
318 | @group | |
319 | (substitute-command-keys | |
320 | "To abort recursive edit, type: \\[abort-recursive-edit]") | |
321 | @result{} "To abort recursive edit, type: C-]" | |
322 | @end group | |
323 | ||
324 | @group | |
325 | (substitute-command-keys | |
326 | "The keys that are defined for the minibuffer here are: | |
327 | \\@{minibuffer-local-must-match-map@}") | |
328 | @result{} "The keys that are defined for the minibuffer here are: | |
329 | @end group | |
330 | ||
331 | ? minibuffer-completion-help | |
332 | SPC minibuffer-complete-word | |
333 | TAB minibuffer-complete | |
969fe9b5 | 334 | C-j minibuffer-complete-and-exit |
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335 | RET minibuffer-complete-and-exit |
336 | C-g abort-recursive-edit | |
337 | " | |
338 | ||
339 | @group | |
340 | (substitute-command-keys | |
341 | "To abort a recursive edit from the minibuffer, type\ | |
342 | \\<minibuffer-local-must-match-map>\\[abort-recursive-edit].") | |
343 | @result{} "To abort a recursive edit from the minibuffer, type C-g." | |
344 | @end group | |
345 | @end smallexample | |
346 | ||
347 | @node Describing Characters | |
348 | @section Describing Characters for Help Messages | |
349 | ||
f9f59935 RS |
350 | These functions convert events, key sequences, or characters to |
351 | textual descriptions. These descriptions are useful for including | |
352 | arbitrary text characters or key sequences in messages, because they | |
353 | convert non-printing and whitespace characters to sequences of printing | |
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354 | characters. The description of a non-whitespace printing character is |
355 | the character itself. | |
356 | ||
357 | @defun key-description sequence | |
358 | @cindex Emacs event standard notation | |
359 | This function returns a string containing the Emacs standard notation | |
360 | for the input events in @var{sequence}. The argument @var{sequence} may | |
361 | be a string, vector or list. @xref{Input Events}, for more information | |
362 | about valid events. See also the examples for | |
363 | @code{single-key-description}, below. | |
364 | @end defun | |
365 | ||
366 | @defun single-key-description event | |
367 | @cindex event printing | |
368 | @cindex character printing | |
369 | @cindex control character printing | |
370 | @cindex meta character printing | |
371 | This function returns a string describing @var{event} in the standard | |
372 | Emacs notation for keyboard input. A normal printing character appears | |
373 | as itself, but a control character turns into a string starting with | |
374 | @samp{C-}, a meta character turns into a string starting with @samp{M-}, | |
969fe9b5 | 375 | and space, tab, etc.@: appear as @samp{SPC}, @samp{TAB}, etc. A |
82a2fe69 | 376 | function key symbol appears as itself. An event that is a list appears |
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377 | as the name of the symbol in the @sc{car} of the list. |
378 | ||
379 | @smallexample | |
380 | @group | |
381 | (single-key-description ?\C-x) | |
382 | @result{} "C-x" | |
383 | @end group | |
384 | @group | |
385 | (key-description "\C-x \M-y \n \t \r \f123") | |
969fe9b5 | 386 | @result{} "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" |
5e8db0c6 RS |
387 | @end group |
388 | @group | |
389 | (single-key-description 'C-mouse-1) | |
390 | @result{} "C-mouse-1" | |
391 | @end group | |
392 | @end smallexample | |
393 | @end defun | |
394 | ||
395 | @defun text-char-description character | |
396 | This function returns a string describing @var{character} in the | |
397 | standard Emacs notation for characters that appear in text---like | |
398 | @code{single-key-description}, except that control characters are | |
399 | represented with a leading caret (which is how control characters in | |
400 | Emacs buffers are usually displayed). | |
401 | ||
402 | @smallexample | |
403 | @group | |
404 | (text-char-description ?\C-c) | |
405 | @result{} "^C" | |
406 | @end group | |
407 | @group | |
408 | (text-char-description ?\M-m) | |
409 | @result{} "M-m" | |
410 | @end group | |
411 | @group | |
412 | (text-char-description ?\C-\M-m) | |
413 | @result{} "M-^M" | |
414 | @end group | |
415 | @end smallexample | |
416 | @end defun | |
417 | ||
a9f0a989 RS |
418 | @defun read-kbd-macro string |
419 | This function is used mainly for operating on keyboard macros, but it | |
420 | can also be used as a rough inverse for @code{key-description}. You | |
421 | call it with a string containing key descriptions, separated by spaces; | |
422 | it returns a string or vector containing the corresponding events. | |
423 | (This may or may not be a single valid key sequence, depending on what | |
424 | events you use; @pxref{Keymap Terminology}.) | |
425 | @end defun | |
426 | ||
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427 | @node Help Functions |
428 | @section Help Functions | |
429 | ||
430 | Emacs provides a variety of on-line help functions, all accessible to | |
431 | the user as subcommands of the prefix @kbd{C-h}. For more information | |
432 | about them, see @ref{Help, , Help, emacs, The GNU Emacs Manual}. Here | |
433 | we describe some program-level interfaces to the same information. | |
434 | ||
969fe9b5 | 435 | @deffn Command apropos regexp &optional do-all |
82a2fe69 RS |
436 | This function finds all symbols whose names contain a match for the |
437 | regular expression @var{regexp}, and returns a list of them | |
438 | (@pxref{Regular Expressions}). It also displays the symbols in a buffer | |
f9f59935 RS |
439 | named @samp{*Help*}, each with a one-line description taken from the |
440 | beginning of its documentation string. | |
5e8db0c6 RS |
441 | |
442 | @c Emacs 19 feature | |
a9f0a989 RS |
443 | If @var{do-all} is non-@code{nil}, then @code{apropos} also shows key |
444 | bindings for the functions that are found; it also shows all symbols, | |
445 | even those that are neither functions nor variables. | |
5e8db0c6 | 446 | |
82a2fe69 | 447 | In the first of the following examples, @code{apropos} finds all the |
969fe9b5 RS |
448 | symbols with names containing @samp{exec}. (We don't show here the |
449 | output that results in the @samp{*Help*} buffer.) | |
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450 | |
451 | @smallexample | |
452 | @group | |
453 | (apropos "exec") | |
454 | @result{} (Buffer-menu-execute command-execute exec-directory | |
455 | exec-path execute-extended-command execute-kbd-macro | |
456 | executing-kbd-macro executing-macro) | |
457 | @end group | |
5e8db0c6 | 458 | @end smallexample |
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459 | @end deffn |
460 | ||
461 | @defvar help-map | |
462 | The value of this variable is a local keymap for characters following the | |
463 | Help key, @kbd{C-h}. | |
464 | @end defvar | |
465 | ||
466 | @deffn {Prefix Command} help-command | |
f9f59935 | 467 | This symbol is not a function; its function definition cell holds the |
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468 | keymap known as @code{help-map}. It is defined in @file{help.el} as |
469 | follows: | |
470 | ||
471 | @smallexample | |
472 | @group | |
473 | (define-key global-map "\C-h" 'help-command) | |
474 | (fset 'help-command help-map) | |
475 | @end group | |
476 | @end smallexample | |
477 | @end deffn | |
478 | ||
479 | @defun print-help-return-message &optional function | |
82a2fe69 RS |
480 | This function builds a string that explains how to restore the previous |
481 | state of the windows after a help command. After building the message, | |
482 | it applies @var{function} to it if @var{function} is non-@code{nil}. | |
483 | Otherwise it calls @code{message} to display it in the echo area. | |
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484 | |
485 | This function expects to be called inside a | |
486 | @code{with-output-to-temp-buffer} special form, and expects | |
487 | @code{standard-output} to have the value bound by that special form. | |
488 | For an example of its use, see the long example in @ref{Accessing | |
489 | Documentation}. | |
490 | @end defun | |
491 | ||
492 | @defvar help-char | |
493 | The value of this variable is the help character---the character that | |
a9f0a989 RS |
494 | Emacs recognizes as meaning Help. By default, its value is 8, which |
495 | stands for @kbd{C-h}. When Emacs reads this character, if | |
496 | @code{help-form} is a non-@code{nil} Lisp expression, it evaluates that | |
497 | expression, and displays the result in a window if it is a string. | |
5e8db0c6 | 498 | |
1911e6e5 | 499 | Usually the value of @code{help-form} is @code{nil}. Then the |
5e8db0c6 RS |
500 | help character has no special meaning at the level of command input, and |
501 | it becomes part of a key sequence in the normal way. The standard key | |
502 | binding of @kbd{C-h} is a prefix key for several general-purpose help | |
503 | features. | |
504 | ||
505 | The help character is special after prefix keys, too. If it has no | |
506 | binding as a subcommand of the prefix key, it runs | |
507 | @code{describe-prefix-bindings}, which displays a list of all the | |
508 | subcommands of the prefix key. | |
509 | @end defvar | |
510 | ||
969fe9b5 | 511 | @defvar help-event-list |
a9f0a989 | 512 | @tindex help-event-list |
969fe9b5 RS |
513 | The value of this variable is a list of event types that serve as |
514 | alternative ``help characters.'' These events are handled just like the | |
515 | event specified by @code{help-char}. | |
516 | @end defvar | |
517 | ||
5e8db0c6 RS |
518 | @defvar help-form |
519 | If this variable is non-@code{nil}, its value is a form to evaluate | |
520 | whenever the character @code{help-char} is read. If evaluating the form | |
521 | produces a string, that string is displayed. | |
522 | ||
523 | A command that calls @code{read-event} or @code{read-char} probably | |
524 | should bind @code{help-form} to a non-@code{nil} expression while it | |
969fe9b5 RS |
525 | does input. (The time when you should not do this is when @kbd{C-h} has |
526 | some other meaning.) Evaluating this expression should result in a | |
527 | string that explains what the input is for and how to enter it properly. | |
5e8db0c6 RS |
528 | |
529 | Entry to the minibuffer binds this variable to the value of | |
530 | @code{minibuffer-help-form} (@pxref{Minibuffer Misc}). | |
531 | @end defvar | |
532 | ||
533 | @defvar prefix-help-command | |
969fe9b5 RS |
534 | This variable holds a function to print help for a prefix key. The |
535 | function is called when the user types a prefix key followed by the help | |
536 | character, and the help character has no binding after that prefix. The | |
537 | variable's default value is @code{describe-prefix-bindings}. | |
5e8db0c6 RS |
538 | @end defvar |
539 | ||
540 | @defun describe-prefix-bindings | |
541 | This function calls @code{describe-bindings} to display a list of all | |
542 | the subcommands of the prefix key of the most recent key sequence. The | |
543 | prefix described consists of all but the last event of that key | |
82a2fe69 | 544 | sequence. (The last event is, presumably, the help character.) |
5e8db0c6 RS |
545 | @end defun |
546 | ||
a9f0a989 RS |
547 | The following two functions are meant for modes that want to provide |
548 | help without relinquishing control, such as the ``electric'' modes. | |
549 | Their names begin with @samp{Helper} to distinguish them from the | |
550 | ordinary help functions. | |
5e8db0c6 RS |
551 | |
552 | @deffn Command Helper-describe-bindings | |
553 | This command pops up a window displaying a help buffer containing a | |
554 | listing of all of the key bindings from both the local and global keymaps. | |
555 | It works by calling @code{describe-bindings}. | |
556 | @end deffn | |
557 | ||
558 | @deffn Command Helper-help | |
559 | This command provides help for the current mode. It prompts the user | |
560 | in the minibuffer with the message @samp{Help (Type ? for further | |
561 | options)}, and then provides assistance in finding out what the key | |
562 | bindings are, and what the mode is intended for. It returns @code{nil}. | |
563 | ||
564 | This can be customized by changing the map @code{Helper-help-map}. | |
565 | @end deffn | |
566 | ||
567 | @c Emacs 19 feature | |
568 | @defvar data-directory | |
569 | This variable holds the name of the directory in which Emacs finds | |
570 | certain documentation and text files that come with Emacs. In older | |
571 | Emacs versions, @code{exec-directory} was used for this. | |
572 | @end defvar | |
573 | ||
574 | @c Emacs 19 feature | |
575 | @defmac make-help-screen fname help-line help-text help-map | |
82a2fe69 RS |
576 | This macro defines a help command named @var{fname} that acts like a |
577 | prefix key that shows a list of the subcommands it offers. | |
5e8db0c6 RS |
578 | |
579 | When invoked, @var{fname} displays @var{help-text} in a window, then | |
580 | reads and executes a key sequence according to @var{help-map}. The | |
82a2fe69 | 581 | string @var{help-text} should describe the bindings available in |
5e8db0c6 RS |
582 | @var{help-map}. |
583 | ||
584 | The command @var{fname} is defined to handle a few events itself, by | |
585 | scrolling the display of @var{help-text}. When @var{fname} reads one of | |
586 | those special events, it does the scrolling and then reads another | |
82a2fe69 | 587 | event. When it reads an event that is not one of those few, and which |
5e8db0c6 RS |
588 | has a binding in @var{help-map}, it executes that key's binding and |
589 | then returns. | |
590 | ||
591 | The argument @var{help-line} should be a single-line summary of the | |
592 | alternatives in @var{help-map}. In the current version of Emacs, this | |
593 | argument is used only if you set the option @code{three-step-help} to | |
594 | @code{t}. | |
f9f59935 RS |
595 | |
596 | This macro is used in the command @code{help-for-help} which is the | |
597 | binding of @kbd{C-h C-h}. | |
5e8db0c6 RS |
598 | @end defmac |
599 | ||
600 | @defopt three-step-help | |
601 | If this variable is non-@code{nil}, commands defined with | |
602 | @code{make-help-screen} display their @var{help-line} strings in the | |
603 | echo area at first, and display the longer @var{help-text} strings only | |
604 | if the user types the help character again. | |
605 | @end defopt |