Commit | Line | Data |
---|---|---|
5e8db0c6 RS |
1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
fd897522 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999 |
177c0ea7 | 4 | @c Free Software Foundation, Inc. |
5e8db0c6 RS |
5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/help | |
7 | @node Documentation, Files, Modes, Top | |
8 | @chapter Documentation | |
9 | @cindex documentation strings | |
10 | ||
11 | GNU Emacs Lisp has convenient on-line help facilities, most of which | |
12 | derive their information from the documentation strings associated with | |
13 | functions and variables. This chapter describes how to write good | |
14 | documentation strings for your Lisp programs, as well as how to write | |
15 | programs to access documentation. | |
16 | ||
17 | Note that the documentation strings for Emacs are not the same thing | |
18 | as the Emacs manual. Manuals have their own source files, written in | |
19 | the Texinfo language; documentation strings are specified in the | |
20 | definitions of the functions and variables they apply to. A collection | |
21 | of documentation strings is not sufficient as a manual because a good | |
22 | manual is not organized in that fashion; it is organized in terms of | |
23 | topics of discussion. | |
24 | ||
25 | @menu | |
26 | * Documentation Basics:: Good style for doc strings. | |
27 | Where to put them. How Emacs stores them. | |
28 | * Accessing Documentation:: How Lisp programs can access doc strings. | |
29 | * Keys in Documentation:: Substituting current key bindings. | |
30 | * Describing Characters:: Making printable descriptions of | |
31 | non-printing characters and key sequences. | |
32 | * Help Functions:: Subroutines used by Emacs help facilities. | |
33 | @end menu | |
34 | ||
35 | @node Documentation Basics | |
36 | @comment node-name, next, previous, up | |
37 | @section Documentation Basics | |
38 | @cindex documentation conventions | |
39 | @cindex writing a documentation string | |
40 | @cindex string, writing a doc string | |
41 | ||
42 | A documentation string is written using the Lisp syntax for strings, | |
43 | with double-quote characters surrounding the text of the string. This | |
44 | is because it really is a Lisp string object. The string serves as | |
45 | documentation when it is written in the proper place in the definition | |
46 | of a function or variable. In a function definition, the documentation | |
47 | string follows the argument list. In a variable definition, the | |
48 | documentation string follows the initial value of the variable. | |
49 | ||
50 | When you write a documentation string, make the first line a complete | |
51 | sentence (or two complete sentences) since some commands, such as | |
52 | @code{apropos}, show only the first line of a multi-line documentation | |
53 | string. Also, you should not indent the second line of a documentation | |
969fe9b5 RS |
54 | string, if it has one, because that looks odd when you use @kbd{C-h f} |
55 | (@code{describe-function}) or @kbd{C-h v} (@code{describe-variable}) to | |
56 | view the documentation string. @xref{Documentation Tips}. | |
5e8db0c6 | 57 | |
969fe9b5 | 58 | Documentation strings can contain several special substrings, which |
5e8db0c6 RS |
59 | stand for key bindings to be looked up in the current keymaps when the |
60 | documentation is displayed. This allows documentation strings to refer | |
61 | to the keys for related commands and be accurate even when a user | |
62 | rearranges the key bindings. (@xref{Accessing Documentation}.) | |
63 | ||
f9f59935 | 64 | In Emacs Lisp, a documentation string is accessible through the |
5e8db0c6 RS |
65 | function or variable that it describes: |
66 | ||
67 | @itemize @bullet | |
68 | @item | |
69 | The documentation for a function is stored in the function definition | |
f9f59935 RS |
70 | itself (@pxref{Lambda Expressions}). The function @code{documentation} |
71 | knows how to extract it. | |
5e8db0c6 RS |
72 | |
73 | @item | |
74 | @kindex variable-documentation | |
75 | The documentation for a variable is stored in the variable's property | |
76 | list under the property name @code{variable-documentation}. The | |
f9f59935 | 77 | function @code{documentation-property} knows how to retrieve it. |
5e8db0c6 RS |
78 | @end itemize |
79 | ||
80 | @cindex @file{DOC} (documentation) file | |
81 | @cindex @file{emacs/etc/DOC-@var{version}} | |
82 | @cindex @file{etc/DOC-@var{version}} | |
83 | To save space, the documentation for preloaded functions and variables | |
82a2fe69 | 84 | (including primitive functions and autoloaded functions) is stored in |
f9f59935 RS |
85 | the file @file{emacs/etc/DOC-@var{version}}---not inside Emacs. The |
86 | documentation strings for functions and variables loaded during the | |
87 | Emacs session from byte-compiled files are stored in those files | |
88 | (@pxref{Docs and Compilation}). | |
bfe721d1 KH |
89 | |
90 | The data structure inside Emacs has an integer offset into the file, or | |
f9f59935 RS |
91 | a list containing a file name and an integer, in place of the |
92 | documentation string. The functions @code{documentation} and | |
93 | @code{documentation-property} use that information to fetch the | |
94 | documentation string from the appropriate file; this is transparent to | |
95 | the user. | |
5e8db0c6 RS |
96 | |
97 | For information on the uses of documentation strings, see @ref{Help, , | |
98 | Help, emacs, The GNU Emacs Manual}. | |
99 | ||
100 | @c Wordy to prevent overfull hbox. --rjc 15mar92 | |
b32a6a15 RS |
101 | The @file{emacs/lib-src} directory contains two utilities that you can |
102 | use to print nice-looking hardcopy for the file | |
1911e6e5 RS |
103 | @file{emacs/etc/DOC-@var{version}}. These are @file{sorted-doc} and |
104 | @file{digest-doc}. | |
5e8db0c6 RS |
105 | |
106 | @node Accessing Documentation | |
107 | @section Access to Documentation Strings | |
108 | ||
109 | @defun documentation-property symbol property &optional verbatim | |
caae20c7 RS |
110 | This function returns the documentation string that is recorded in |
111 | @var{symbol}'s property list under property @var{property}. It | |
112 | retrieves the text from a file if the value calls for that. If the | |
113 | property value isn't @code{nil}, isn't a string, and doesn't refer to | |
114 | text in a file, then it is evaluated to obtain a string. | |
115 | ||
116 | Finally, @code{documentation-property} passes the string through | |
117 | @code{substitute-command-keys} to substitute actual key bindings, | |
118 | unless @var{verbatim} is non-@code{nil}. | |
5e8db0c6 RS |
119 | |
120 | @smallexample | |
121 | @group | |
122 | (documentation-property 'command-line-processed | |
123 | 'variable-documentation) | |
1911e6e5 | 124 | @result{} "Non-nil once command line has been processed" |
5e8db0c6 RS |
125 | @end group |
126 | @group | |
127 | (symbol-plist 'command-line-processed) | |
128 | @result{} (variable-documentation 188902) | |
129 | @end group | |
130 | @end smallexample | |
131 | @end defun | |
132 | ||
133 | @defun documentation function &optional verbatim | |
caae20c7 RS |
134 | This function returns the documentation string of @var{function}. |
135 | ||
136 | If @var{function} is a symbol, this function first looks for the | |
137 | @code{function-documentation} property of that symbol; if that has a | |
138 | non-@code{nil} value, the documentation comes from that value (if the | |
139 | value is not a string, it is evaluated). If @var{function} is not a | |
140 | symbol, or if it has no @code{function-documentation} property, then | |
141 | @code{documentation} extracts the documentation string from the actual | |
142 | function definition, reading it from a file if called for. | |
143 | ||
144 | Finally, unless @var{verbatim} is non-@code{nil}, it calls | |
145 | @code{substitute-command-keys} so as to return a value containing the | |
7f0afecc | 146 | actual (current) key bindings. |
5e8db0c6 RS |
147 | |
148 | The function @code{documentation} signals a @code{void-function} error | |
969fe9b5 | 149 | if @var{function} has no function definition. However, it is OK if |
5e8db0c6 RS |
150 | the function definition has no documentation string. In that case, |
151 | @code{documentation} returns @code{nil}. | |
152 | @end defun | |
153 | ||
154 | @c Wordy to prevent overfull hboxes. --rjc 15mar92 | |
82a2fe69 | 155 | Here is an example of using the two functions, @code{documentation} and |
5e8db0c6 RS |
156 | @code{documentation-property}, to display the documentation strings for |
157 | several symbols in a @samp{*Help*} buffer. | |
158 | ||
73036a68 | 159 | @anchor{describe-symbols example} |
5e8db0c6 RS |
160 | @smallexample |
161 | @group | |
162 | (defun describe-symbols (pattern) | |
163 | "Describe the Emacs Lisp symbols matching PATTERN. | |
164 | All symbols that have PATTERN in their name are described | |
165 | in the `*Help*' buffer." | |
166 | (interactive "sDescribe symbols matching: ") | |
167 | (let ((describe-func | |
177c0ea7 | 168 | (function |
5e8db0c6 RS |
169 | (lambda (s) |
170 | @end group | |
171 | @group | |
172 | ;; @r{Print description of symbol.} | |
173 | (if (fboundp s) ; @r{It is a function.} | |
174 | (princ | |
175 | (format "%s\t%s\n%s\n\n" s | |
177c0ea7 | 176 | (if (commandp s) |
5e8db0c6 RS |
177 | (let ((keys (where-is-internal s))) |
178 | (if keys | |
179 | (concat | |
180 | "Keys: " | |
177c0ea7 | 181 | (mapconcat 'key-description |
5e8db0c6 RS |
182 | keys " ")) |
183 | "Keys: none")) | |
184 | "Function") | |
185 | @end group | |
186 | @group | |
177c0ea7 | 187 | (or (documentation s) |
5e8db0c6 | 188 | "not documented")))) |
177c0ea7 | 189 | |
5e8db0c6 RS |
190 | (if (boundp s) ; @r{It is a variable.} |
191 | @end group | |
192 | @group | |
193 | (princ | |
194 | (format "%s\t%s\n%s\n\n" s | |
177c0ea7 | 195 | (if (user-variable-p s) |
5e8db0c6 RS |
196 | "Option " "Variable") |
197 | @end group | |
198 | @group | |
177c0ea7 | 199 | (or (documentation-property |
5e8db0c6 RS |
200 | s 'variable-documentation) |
201 | "not documented"))))))) | |
202 | sym-list) | |
203 | @end group | |
204 | ||
205 | @group | |
206 | ;; @r{Build a list of symbols that match pattern.} | |
177c0ea7 | 207 | (mapatoms (function |
5e8db0c6 RS |
208 | (lambda (sym) |
209 | (if (string-match pattern (symbol-name sym)) | |
210 | (setq sym-list (cons sym sym-list)))))) | |
211 | @end group | |
212 | ||
213 | @group | |
214 | ;; @r{Display the data.} | |
215 | (with-output-to-temp-buffer "*Help*" | |
216 | (mapcar describe-func (sort sym-list 'string<)) | |
217 | (print-help-return-message)))) | |
218 | @end group | |
219 | @end smallexample | |
220 | ||
221 | The @code{describe-symbols} function works like @code{apropos}, | |
222 | but provides more information. | |
223 | ||
224 | @smallexample | |
225 | @group | |
226 | (describe-symbols "goal") | |
227 | ||
228 | ---------- Buffer: *Help* ---------- | |
177c0ea7 | 229 | goal-column Option |
9e2b495b | 230 | *Semipermanent goal column for vertical motion, as set by @dots{} |
5e8db0c6 RS |
231 | @end group |
232 | @c Do not blithely break or fill these lines. | |
233 | @c That makes them incorrect. | |
234 | ||
235 | @group | |
1911e6e5 | 236 | set-goal-column Keys: C-x C-n |
5e8db0c6 RS |
237 | Set the current horizontal position as a goal for C-n and C-p. |
238 | @end group | |
239 | @c DO NOT put a blank line here! That is factually inaccurate! | |
240 | @group | |
241 | Those commands will move to this position in the line moved to | |
242 | rather than trying to keep the same horizontal position. | |
243 | With a non-nil argument, clears out the goal column | |
244 | so that C-n and C-p resume vertical motion. | |
245 | The goal column is stored in the variable `goal-column'. | |
246 | @end group | |
247 | ||
248 | @group | |
249 | temporary-goal-column Variable | |
250 | Current goal column for vertical motion. | |
251 | It is the column where point was | |
252 | at the start of current run of vertical motion commands. | |
253 | When the `track-eol' feature is doing its job, the value is 9999. | |
254 | ---------- Buffer: *Help* ---------- | |
255 | @end group | |
256 | @end smallexample | |
257 | ||
bfccb7b3 EZ |
258 | The asterisk @samp{*} as the first character of a variable's doc string, |
259 | as shown above for the @code{goal-column} variable, means that it is a | |
260 | user option; see the description of @code{defvar} in @ref{Defining | |
261 | Variables}. | |
262 | ||
1bff11dc | 263 | @anchor{Definition of Snarf-documentation} |
5e8db0c6 | 264 | @defun Snarf-documentation filename |
f9f59935 | 265 | This function is used only during Emacs initialization, just before |
5e8db0c6 RS |
266 | the runnable Emacs is dumped. It finds the file offsets of the |
267 | documentation strings stored in the file @var{filename}, and records | |
268 | them in the in-core function definitions and variable property lists in | |
269 | place of the actual strings. @xref{Building Emacs}. | |
270 | ||
f9f59935 RS |
271 | Emacs reads the file @var{filename} from the @file{emacs/etc} directory. |
272 | When the dumped Emacs is later executed, the same file will be looked | |
273 | for in the directory @code{doc-directory}. Usually @var{filename} is | |
5e8db0c6 RS |
274 | @code{"DOC-@var{version}"}. |
275 | @end defun | |
276 | ||
277 | @c Emacs 19 feature | |
278 | @defvar doc-directory | |
969fe9b5 | 279 | This variable holds the name of the directory which should contain the |
5e8db0c6 RS |
280 | file @code{"DOC-@var{version}"} that contains documentation strings for |
281 | built-in and preloaded functions and variables. | |
282 | ||
283 | In most cases, this is the same as @code{data-directory}. They may be | |
284 | different when you run Emacs from the directory where you built it, | |
285 | without actually installing it. See @code{data-directory} in @ref{Help | |
286 | Functions}. | |
287 | ||
288 | In older Emacs versions, @code{exec-directory} was used for this. | |
289 | @end defvar | |
290 | ||
291 | @node Keys in Documentation | |
292 | @section Substituting Key Bindings in Documentation | |
293 | @cindex documentation, keys in | |
294 | @cindex keys in documentation strings | |
295 | @cindex substituting keys in documentation | |
296 | ||
82a2fe69 RS |
297 | When documentation strings refer to key sequences, they should use the |
298 | current, actual key bindings. They can do so using certain special text | |
299 | sequences described below. Accessing documentation strings in the usual | |
300 | way substitutes current key binding information for these special | |
301 | sequences. This works by calling @code{substitute-command-keys}. You | |
302 | can also call that function yourself. | |
5e8db0c6 RS |
303 | |
304 | Here is a list of the special sequences and what they mean: | |
305 | ||
306 | @table @code | |
307 | @item \[@var{command}] | |
308 | stands for a key sequence that will invoke @var{command}, or @samp{M-x | |
309 | @var{command}} if @var{command} has no key bindings. | |
310 | ||
177c0ea7 | 311 | @item \@{@var{mapvar}@} |
969fe9b5 RS |
312 | stands for a summary of the keymap which is the value of the variable |
313 | @var{mapvar}. The summary is made using @code{describe-bindings}. | |
5e8db0c6 | 314 | |
177c0ea7 | 315 | @item \<@var{mapvar}> |
f9f59935 | 316 | stands for no text itself. It is used only for a side effect: it |
969fe9b5 | 317 | specifies @var{mapvar}'s value as the keymap for any following |
f9f59935 | 318 | @samp{\[@var{command}]} sequences in this documentation string. |
815c9631 RS |
319 | |
320 | @item \= | |
321 | quotes the following character and is discarded; thus, @samp{\=\[} puts | |
322 | @samp{\[} into the output, and @samp{\=\=} puts @samp{\=} into the | |
323 | output. | |
5e8db0c6 RS |
324 | @end table |
325 | ||
82a2fe69 | 326 | @strong{Please note:} Each @samp{\} must be doubled when written in a |
5e8db0c6 RS |
327 | string in Emacs Lisp. |
328 | ||
329 | @defun substitute-command-keys string | |
330 | This function scans @var{string} for the above special sequences and | |
331 | replaces them by what they stand for, returning the result as a string. | |
332 | This permits display of documentation that refers accurately to the | |
82a2fe69 | 333 | user's own customized key bindings. |
5e8db0c6 RS |
334 | @end defun |
335 | ||
336 | Here are examples of the special sequences: | |
337 | ||
338 | @smallexample | |
339 | @group | |
177c0ea7 | 340 | (substitute-command-keys |
5e8db0c6 RS |
341 | "To abort recursive edit, type: \\[abort-recursive-edit]") |
342 | @result{} "To abort recursive edit, type: C-]" | |
343 | @end group | |
344 | ||
345 | @group | |
177c0ea7 | 346 | (substitute-command-keys |
5e8db0c6 RS |
347 | "The keys that are defined for the minibuffer here are: |
348 | \\@{minibuffer-local-must-match-map@}") | |
349 | @result{} "The keys that are defined for the minibuffer here are: | |
350 | @end group | |
351 | ||
352 | ? minibuffer-completion-help | |
353 | SPC minibuffer-complete-word | |
354 | TAB minibuffer-complete | |
969fe9b5 | 355 | C-j minibuffer-complete-and-exit |
5e8db0c6 RS |
356 | RET minibuffer-complete-and-exit |
357 | C-g abort-recursive-edit | |
358 | " | |
359 | ||
360 | @group | |
361 | (substitute-command-keys | |
362 | "To abort a recursive edit from the minibuffer, type\ | |
363 | \\<minibuffer-local-must-match-map>\\[abort-recursive-edit].") | |
364 | @result{} "To abort a recursive edit from the minibuffer, type C-g." | |
365 | @end group | |
366 | @end smallexample | |
367 | ||
368 | @node Describing Characters | |
369 | @section Describing Characters for Help Messages | |
370 | ||
f9f59935 RS |
371 | These functions convert events, key sequences, or characters to |
372 | textual descriptions. These descriptions are useful for including | |
373 | arbitrary text characters or key sequences in messages, because they | |
374 | convert non-printing and whitespace characters to sequences of printing | |
5e8db0c6 RS |
375 | characters. The description of a non-whitespace printing character is |
376 | the character itself. | |
377 | ||
378 | @defun key-description sequence | |
379 | @cindex Emacs event standard notation | |
380 | This function returns a string containing the Emacs standard notation | |
381 | for the input events in @var{sequence}. The argument @var{sequence} may | |
382 | be a string, vector or list. @xref{Input Events}, for more information | |
383 | about valid events. See also the examples for | |
384 | @code{single-key-description}, below. | |
385 | @end defun | |
386 | ||
7f0afecc | 387 | @defun single-key-description event &optional no-angles |
5e8db0c6 RS |
388 | @cindex event printing |
389 | @cindex character printing | |
390 | @cindex control character printing | |
391 | @cindex meta character printing | |
392 | This function returns a string describing @var{event} in the standard | |
caae20c7 RS |
393 | Emacs notation for keyboard input. A normal printing character |
394 | appears as itself, but a control character turns into a string | |
395 | starting with @samp{C-}, a meta character turns into a string starting | |
396 | with @samp{M-}, and space, tab, etc.@: appear as @samp{SPC}, | |
397 | @samp{TAB}, etc. A function key symbol appears inside angle brackets | |
398 | @samp{<@dots{}>}. An event that is a list appears as the name of the | |
399 | symbol in the @sc{car} of the list, inside angle brackets. | |
7f0afecc EZ |
400 | |
401 | If the optional argument @var{no-angles} is non-@code{nil}, the angle | |
402 | brackets around function keys and event symbols are omitted; this is | |
caae20c7 | 403 | for compatibility with old versions of Emacs which didn't use the |
7f0afecc | 404 | brackets. |
5e8db0c6 RS |
405 | |
406 | @smallexample | |
407 | @group | |
408 | (single-key-description ?\C-x) | |
409 | @result{} "C-x" | |
410 | @end group | |
411 | @group | |
412 | (key-description "\C-x \M-y \n \t \r \f123") | |
969fe9b5 | 413 | @result{} "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" |
5e8db0c6 RS |
414 | @end group |
415 | @group | |
7f0afecc EZ |
416 | (single-key-description 'delete) |
417 | @result{} "<delete>" | |
418 | @end group | |
419 | @group | |
5e8db0c6 | 420 | (single-key-description 'C-mouse-1) |
7f0afecc EZ |
421 | @result{} "<C-mouse-1>" |
422 | @end group | |
423 | @group | |
424 | (single-key-description 'C-mouse-1 t) | |
5e8db0c6 RS |
425 | @result{} "C-mouse-1" |
426 | @end group | |
427 | @end smallexample | |
428 | @end defun | |
429 | ||
430 | @defun text-char-description character | |
431 | This function returns a string describing @var{character} in the | |
432 | standard Emacs notation for characters that appear in text---like | |
433 | @code{single-key-description}, except that control characters are | |
434 | represented with a leading caret (which is how control characters in | |
a48d10ae RS |
435 | Emacs buffers are usually displayed) and character codes 128 |
436 | and above are not treated as Meta characters. | |
5e8db0c6 RS |
437 | |
438 | @smallexample | |
439 | @group | |
440 | (text-char-description ?\C-c) | |
441 | @result{} "^C" | |
442 | @end group | |
443 | @group | |
444 | (text-char-description ?\M-m) | |
a48d10ae | 445 | @result{} "\xed" |
5e8db0c6 RS |
446 | @end group |
447 | @group | |
448 | (text-char-description ?\C-\M-m) | |
a48d10ae | 449 | @result{} "\x8d" |
5e8db0c6 RS |
450 | @end group |
451 | @end smallexample | |
452 | @end defun | |
453 | ||
a9f0a989 RS |
454 | @defun read-kbd-macro string |
455 | This function is used mainly for operating on keyboard macros, but it | |
456 | can also be used as a rough inverse for @code{key-description}. You | |
457 | call it with a string containing key descriptions, separated by spaces; | |
458 | it returns a string or vector containing the corresponding events. | |
459 | (This may or may not be a single valid key sequence, depending on what | |
460 | events you use; @pxref{Keymap Terminology}.) | |
461 | @end defun | |
462 | ||
5e8db0c6 RS |
463 | @node Help Functions |
464 | @section Help Functions | |
465 | ||
466 | Emacs provides a variety of on-line help functions, all accessible to | |
467 | the user as subcommands of the prefix @kbd{C-h}. For more information | |
468 | about them, see @ref{Help, , Help, emacs, The GNU Emacs Manual}. Here | |
469 | we describe some program-level interfaces to the same information. | |
470 | ||
969fe9b5 | 471 | @deffn Command apropos regexp &optional do-all |
82a2fe69 RS |
472 | This function finds all symbols whose names contain a match for the |
473 | regular expression @var{regexp}, and returns a list of them | |
474 | (@pxref{Regular Expressions}). It also displays the symbols in a buffer | |
f9f59935 RS |
475 | named @samp{*Help*}, each with a one-line description taken from the |
476 | beginning of its documentation string. | |
5e8db0c6 RS |
477 | |
478 | @c Emacs 19 feature | |
a9f0a989 RS |
479 | If @var{do-all} is non-@code{nil}, then @code{apropos} also shows key |
480 | bindings for the functions that are found; it also shows all symbols, | |
481 | even those that are neither functions nor variables. | |
5e8db0c6 | 482 | |
82a2fe69 | 483 | In the first of the following examples, @code{apropos} finds all the |
969fe9b5 RS |
484 | symbols with names containing @samp{exec}. (We don't show here the |
485 | output that results in the @samp{*Help*} buffer.) | |
5e8db0c6 RS |
486 | |
487 | @smallexample | |
488 | @group | |
489 | (apropos "exec") | |
490 | @result{} (Buffer-menu-execute command-execute exec-directory | |
491 | exec-path execute-extended-command execute-kbd-macro | |
492 | executing-kbd-macro executing-macro) | |
493 | @end group | |
5e8db0c6 | 494 | @end smallexample |
5e8db0c6 RS |
495 | @end deffn |
496 | ||
497 | @defvar help-map | |
498 | The value of this variable is a local keymap for characters following the | |
499 | Help key, @kbd{C-h}. | |
500 | @end defvar | |
501 | ||
502 | @deffn {Prefix Command} help-command | |
f9f59935 | 503 | This symbol is not a function; its function definition cell holds the |
5e8db0c6 RS |
504 | keymap known as @code{help-map}. It is defined in @file{help.el} as |
505 | follows: | |
506 | ||
507 | @smallexample | |
508 | @group | |
509 | (define-key global-map "\C-h" 'help-command) | |
510 | (fset 'help-command help-map) | |
511 | @end group | |
512 | @end smallexample | |
513 | @end deffn | |
514 | ||
515 | @defun print-help-return-message &optional function | |
82a2fe69 RS |
516 | This function builds a string that explains how to restore the previous |
517 | state of the windows after a help command. After building the message, | |
518 | it applies @var{function} to it if @var{function} is non-@code{nil}. | |
519 | Otherwise it calls @code{message} to display it in the echo area. | |
5e8db0c6 RS |
520 | |
521 | This function expects to be called inside a | |
522 | @code{with-output-to-temp-buffer} special form, and expects | |
523 | @code{standard-output} to have the value bound by that special form. | |
524 | For an example of its use, see the long example in @ref{Accessing | |
525 | Documentation}. | |
526 | @end defun | |
527 | ||
528 | @defvar help-char | |
529 | The value of this variable is the help character---the character that | |
a9f0a989 RS |
530 | Emacs recognizes as meaning Help. By default, its value is 8, which |
531 | stands for @kbd{C-h}. When Emacs reads this character, if | |
532 | @code{help-form} is a non-@code{nil} Lisp expression, it evaluates that | |
533 | expression, and displays the result in a window if it is a string. | |
5e8db0c6 | 534 | |
1911e6e5 | 535 | Usually the value of @code{help-form} is @code{nil}. Then the |
5e8db0c6 RS |
536 | help character has no special meaning at the level of command input, and |
537 | it becomes part of a key sequence in the normal way. The standard key | |
538 | binding of @kbd{C-h} is a prefix key for several general-purpose help | |
539 | features. | |
540 | ||
541 | The help character is special after prefix keys, too. If it has no | |
542 | binding as a subcommand of the prefix key, it runs | |
543 | @code{describe-prefix-bindings}, which displays a list of all the | |
544 | subcommands of the prefix key. | |
545 | @end defvar | |
546 | ||
969fe9b5 RS |
547 | @defvar help-event-list |
548 | The value of this variable is a list of event types that serve as | |
549 | alternative ``help characters.'' These events are handled just like the | |
550 | event specified by @code{help-char}. | |
551 | @end defvar | |
552 | ||
5e8db0c6 RS |
553 | @defvar help-form |
554 | If this variable is non-@code{nil}, its value is a form to evaluate | |
555 | whenever the character @code{help-char} is read. If evaluating the form | |
556 | produces a string, that string is displayed. | |
557 | ||
558 | A command that calls @code{read-event} or @code{read-char} probably | |
559 | should bind @code{help-form} to a non-@code{nil} expression while it | |
969fe9b5 RS |
560 | does input. (The time when you should not do this is when @kbd{C-h} has |
561 | some other meaning.) Evaluating this expression should result in a | |
562 | string that explains what the input is for and how to enter it properly. | |
5e8db0c6 RS |
563 | |
564 | Entry to the minibuffer binds this variable to the value of | |
565 | @code{minibuffer-help-form} (@pxref{Minibuffer Misc}). | |
566 | @end defvar | |
567 | ||
568 | @defvar prefix-help-command | |
969fe9b5 RS |
569 | This variable holds a function to print help for a prefix key. The |
570 | function is called when the user types a prefix key followed by the help | |
571 | character, and the help character has no binding after that prefix. The | |
572 | variable's default value is @code{describe-prefix-bindings}. | |
5e8db0c6 RS |
573 | @end defvar |
574 | ||
575 | @defun describe-prefix-bindings | |
576 | This function calls @code{describe-bindings} to display a list of all | |
577 | the subcommands of the prefix key of the most recent key sequence. The | |
578 | prefix described consists of all but the last event of that key | |
82a2fe69 | 579 | sequence. (The last event is, presumably, the help character.) |
5e8db0c6 RS |
580 | @end defun |
581 | ||
a9f0a989 RS |
582 | The following two functions are meant for modes that want to provide |
583 | help without relinquishing control, such as the ``electric'' modes. | |
584 | Their names begin with @samp{Helper} to distinguish them from the | |
585 | ordinary help functions. | |
5e8db0c6 RS |
586 | |
587 | @deffn Command Helper-describe-bindings | |
588 | This command pops up a window displaying a help buffer containing a | |
589 | listing of all of the key bindings from both the local and global keymaps. | |
590 | It works by calling @code{describe-bindings}. | |
591 | @end deffn | |
592 | ||
593 | @deffn Command Helper-help | |
594 | This command provides help for the current mode. It prompts the user | |
595 | in the minibuffer with the message @samp{Help (Type ? for further | |
596 | options)}, and then provides assistance in finding out what the key | |
597 | bindings are, and what the mode is intended for. It returns @code{nil}. | |
598 | ||
599 | This can be customized by changing the map @code{Helper-help-map}. | |
600 | @end deffn | |
601 | ||
602 | @c Emacs 19 feature | |
603 | @defvar data-directory | |
604 | This variable holds the name of the directory in which Emacs finds | |
605 | certain documentation and text files that come with Emacs. In older | |
606 | Emacs versions, @code{exec-directory} was used for this. | |
607 | @end defvar | |
608 | ||
609 | @c Emacs 19 feature | |
610 | @defmac make-help-screen fname help-line help-text help-map | |
177c0ea7 | 611 | This macro defines a help command named @var{fname} that acts like a |
82a2fe69 | 612 | prefix key that shows a list of the subcommands it offers. |
5e8db0c6 RS |
613 | |
614 | When invoked, @var{fname} displays @var{help-text} in a window, then | |
615 | reads and executes a key sequence according to @var{help-map}. The | |
82a2fe69 | 616 | string @var{help-text} should describe the bindings available in |
5e8db0c6 RS |
617 | @var{help-map}. |
618 | ||
619 | The command @var{fname} is defined to handle a few events itself, by | |
620 | scrolling the display of @var{help-text}. When @var{fname} reads one of | |
621 | those special events, it does the scrolling and then reads another | |
82a2fe69 | 622 | event. When it reads an event that is not one of those few, and which |
5e8db0c6 RS |
623 | has a binding in @var{help-map}, it executes that key's binding and |
624 | then returns. | |
625 | ||
626 | The argument @var{help-line} should be a single-line summary of the | |
627 | alternatives in @var{help-map}. In the current version of Emacs, this | |
628 | argument is used only if you set the option @code{three-step-help} to | |
629 | @code{t}. | |
f9f59935 RS |
630 | |
631 | This macro is used in the command @code{help-for-help} which is the | |
632 | binding of @kbd{C-h C-h}. | |
5e8db0c6 RS |
633 | @end defmac |
634 | ||
635 | @defopt three-step-help | |
636 | If this variable is non-@code{nil}, commands defined with | |
637 | @code{make-help-screen} display their @var{help-line} strings in the | |
638 | echo area at first, and display the longer @var{help-text} strings only | |
639 | if the user types the help character again. | |
640 | @end defopt | |
ab5796a9 MB |
641 | |
642 | @ignore | |
643 | arch-tag: ba36b4c2-e60f-49e2-bc25-61158fdcd815 | |
644 | @end ignore |