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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
73b0cd50 | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2011 |
e9bffc61 | 4 | @c Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/help |
b8d4c8d0 GM |
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 | For commands to display documentation strings, see @ref{Help, , | |
26 | Help, emacs, The GNU Emacs Manual}. For the conventions for writing | |
27 | documentation strings, see @ref{Documentation Tips}. | |
28 | ||
29 | @menu | |
30 | * Documentation Basics:: Good style for doc strings. | |
31 | Where to put them. How Emacs stores them. | |
32 | * Accessing Documentation:: How Lisp programs can access doc strings. | |
33 | * Keys in Documentation:: Substituting current key bindings. | |
34 | * Describing Characters:: Making printable descriptions of | |
35 | non-printing characters and key sequences. | |
36 | * Help Functions:: Subroutines used by Emacs help facilities. | |
37 | @end menu | |
38 | ||
39 | @node Documentation Basics | |
40 | @comment node-name, next, previous, up | |
41 | @section Documentation Basics | |
42 | @cindex documentation conventions | |
43 | @cindex writing a documentation string | |
44 | @cindex string, writing a doc string | |
45 | ||
46 | A documentation string is written using the Lisp syntax for strings, | |
47 | with double-quote characters surrounding the text of the string. This | |
48 | is because it really is a Lisp string object. The string serves as | |
49 | documentation when it is written in the proper place in the definition | |
50 | of a function or variable. In a function definition, the documentation | |
51 | string follows the argument list. In a variable definition, the | |
52 | documentation string follows the initial value of the variable. | |
53 | ||
54 | When you write a documentation string, make the first line a | |
55 | complete sentence (or two complete sentences) since some commands, | |
56 | such as @code{apropos}, show only the first line of a multi-line | |
57 | documentation string. Also, you should not indent the second line of | |
58 | a documentation string, if it has one, because that looks odd when you | |
59 | use @kbd{C-h f} (@code{describe-function}) or @kbd{C-h v} | |
60 | (@code{describe-variable}) to view the documentation string. There | |
61 | are many other conventions for doc strings; see @ref{Documentation | |
62 | Tips}. | |
63 | ||
64 | Documentation strings can contain several special substrings, which | |
65 | stand for key bindings to be looked up in the current keymaps when the | |
66 | documentation is displayed. This allows documentation strings to refer | |
67 | to the keys for related commands and be accurate even when a user | |
68 | rearranges the key bindings. (@xref{Keys in Documentation}.) | |
69 | ||
70 | @vindex emacs-lisp-docstring-fill-column | |
71 | Emacs Lisp mode fills documentation strings to the width | |
72 | specified by @code{emacs-lisp-docstring-fill-column}. | |
73 | ||
74 | In Emacs Lisp, a documentation string is accessible through the | |
75 | function or variable that it describes: | |
76 | ||
77 | @itemize @bullet | |
78 | @item | |
79 | @kindex function-documentation | |
80 | The documentation for a function is usually stored in the function | |
81 | definition itself (@pxref{Lambda Expressions}). The function | |
82 | @code{documentation} knows how to extract it. You can also put | |
83 | function documentation in the @code{function-documentation} property | |
84 | of the function name. That is useful with definitions such as | |
85 | keyboard macros that can't hold a documentation string. | |
86 | ||
87 | @item | |
88 | @kindex variable-documentation | |
89 | The documentation for a variable is stored in the variable's property | |
90 | list under the property name @code{variable-documentation}. The | |
91 | function @code{documentation-property} knows how to retrieve it. | |
92 | @end itemize | |
93 | ||
94 | @cindex @file{DOC-@var{version}} (documentation) file | |
95 | To save space, the documentation for preloaded functions and variables | |
96 | (including primitive functions and autoloaded functions) is stored in | |
97 | the file @file{emacs/etc/DOC-@var{version}}---not inside Emacs. The | |
98 | documentation strings for functions and variables loaded during the | |
99 | Emacs session from byte-compiled files are stored in those files | |
100 | (@pxref{Docs and Compilation}). | |
101 | ||
102 | The data structure inside Emacs has an integer offset into the file, or | |
103 | a list containing a file name and an integer, in place of the | |
104 | documentation string. The functions @code{documentation} and | |
105 | @code{documentation-property} use that information to fetch the | |
106 | documentation string from the appropriate file; this is transparent to | |
107 | the user. | |
108 | ||
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109 | @node Accessing Documentation |
110 | @section Access to Documentation Strings | |
111 | ||
112 | @defun documentation-property symbol property &optional verbatim | |
113 | This function returns the documentation string that is recorded in | |
114 | @var{symbol}'s property list under property @var{property}. It | |
115 | retrieves the text from a file if the value calls for that. If the | |
116 | property value isn't @code{nil}, isn't a string, and doesn't refer to | |
117 | text in a file, then it is evaluated to obtain a string. | |
118 | ||
119 | The last thing this function does is pass the string through | |
120 | @code{substitute-command-keys} to substitute actual key bindings, | |
121 | unless @var{verbatim} is non-@code{nil}. | |
122 | ||
123 | @smallexample | |
124 | @group | |
125 | (documentation-property 'command-line-processed | |
126 | 'variable-documentation) | |
127 | @result{} "Non-nil once command line has been processed" | |
128 | @end group | |
129 | @group | |
130 | (symbol-plist 'command-line-processed) | |
131 | @result{} (variable-documentation 188902) | |
132 | @end group | |
133 | @group | |
134 | (documentation-property 'emacs 'group-documentation) | |
135 | @result{} "Customization of the One True Editor." | |
136 | @end group | |
137 | @end smallexample | |
138 | @end defun | |
139 | ||
140 | @defun documentation function &optional verbatim | |
141 | This function returns the documentation string of @var{function}. | |
142 | @code{documentation} handles macros, named keyboard macros, and | |
143 | special forms, as well as ordinary functions. | |
144 | ||
145 | If @var{function} is a symbol, this function first looks for the | |
146 | @code{function-documentation} property of that symbol; if that has a | |
147 | non-@code{nil} value, the documentation comes from that value (if the | |
148 | value is not a string, it is evaluated). If @var{function} is not a | |
149 | symbol, or if it has no @code{function-documentation} property, then | |
150 | @code{documentation} extracts the documentation string from the actual | |
151 | function definition, reading it from a file if called for. | |
152 | ||
153 | Finally, unless @var{verbatim} is non-@code{nil}, it calls | |
154 | @code{substitute-command-keys} so as to return a value containing the | |
155 | actual (current) key bindings. | |
156 | ||
157 | The function @code{documentation} signals a @code{void-function} error | |
158 | if @var{function} has no function definition. However, it is OK if | |
159 | the function definition has no documentation string. In that case, | |
160 | @code{documentation} returns @code{nil}. | |
161 | @end defun | |
162 | ||
163 | @defun face-documentation face | |
164 | This function returns the documentation string of @var{face} as a | |
165 | face. | |
166 | @end defun | |
167 | ||
168 | @c Wordy to prevent overfull hboxes. --rjc 15mar92 | |
169 | Here is an example of using the two functions, @code{documentation} and | |
170 | @code{documentation-property}, to display the documentation strings for | |
171 | several symbols in a @samp{*Help*} buffer. | |
172 | ||
173 | @anchor{describe-symbols example} | |
174 | @smallexample | |
175 | @group | |
176 | (defun describe-symbols (pattern) | |
177 | "Describe the Emacs Lisp symbols matching PATTERN. | |
178 | All symbols that have PATTERN in their name are described | |
179 | in the `*Help*' buffer." | |
180 | (interactive "sDescribe symbols matching: ") | |
181 | (let ((describe-func | |
182 | (function | |
183 | (lambda (s) | |
184 | @end group | |
185 | @group | |
186 | ;; @r{Print description of symbol.} | |
187 | (if (fboundp s) ; @r{It is a function.} | |
188 | (princ | |
189 | (format "%s\t%s\n%s\n\n" s | |
190 | (if (commandp s) | |
191 | (let ((keys (where-is-internal s))) | |
192 | (if keys | |
193 | (concat | |
194 | "Keys: " | |
195 | (mapconcat 'key-description | |
196 | keys " ")) | |
197 | "Keys: none")) | |
198 | "Function") | |
199 | @end group | |
200 | @group | |
201 | (or (documentation s) | |
202 | "not documented")))) | |
203 | ||
204 | (if (boundp s) ; @r{It is a variable.} | |
205 | @end group | |
206 | @group | |
207 | (princ | |
208 | (format "%s\t%s\n%s\n\n" s | |
209 | (if (user-variable-p s) | |
210 | "Option " "Variable") | |
211 | @end group | |
212 | @group | |
213 | (or (documentation-property | |
214 | s 'variable-documentation) | |
215 | "not documented"))))))) | |
216 | sym-list) | |
217 | @end group | |
218 | ||
219 | @group | |
220 | ;; @r{Build a list of symbols that match pattern.} | |
221 | (mapatoms (function | |
222 | (lambda (sym) | |
223 | (if (string-match pattern (symbol-name sym)) | |
224 | (setq sym-list (cons sym sym-list)))))) | |
225 | @end group | |
226 | ||
227 | @group | |
228 | ;; @r{Display the data.} | |
b2a77f6d CY |
229 | (help-setup-xref (list 'describe-symbols pattern) (interactive-p)) |
230 | (with-help-window (help-buffer) | |
231 | (mapcar describe-func (sort sym-list 'string<))))) | |
b8d4c8d0 GM |
232 | @end group |
233 | @end smallexample | |
234 | ||
235 | The @code{describe-symbols} function works like @code{apropos}, | |
236 | but provides more information. | |
237 | ||
238 | @smallexample | |
239 | @group | |
240 | (describe-symbols "goal") | |
241 | ||
242 | ---------- Buffer: *Help* ---------- | |
243 | goal-column Option | |
f5c63335 | 244 | Semipermanent goal column for vertical motion, as set by @dots{} |
b8d4c8d0 GM |
245 | @end group |
246 | @c Do not blithely break or fill these lines. | |
247 | @c That makes them incorrect. | |
248 | ||
249 | @group | |
250 | set-goal-column Keys: C-x C-n | |
251 | Set the current horizontal position as a goal for C-n and C-p. | |
252 | @end group | |
253 | @c DO NOT put a blank line here! That is factually inaccurate! | |
254 | @group | |
255 | Those commands will move to this position in the line moved to | |
256 | rather than trying to keep the same horizontal position. | |
257 | With a non-nil argument, clears out the goal column | |
258 | so that C-n and C-p resume vertical motion. | |
259 | The goal column is stored in the variable `goal-column'. | |
260 | @end group | |
261 | ||
262 | @group | |
263 | temporary-goal-column Variable | |
264 | Current goal column for vertical motion. | |
265 | It is the column where point was | |
266 | at the start of current run of vertical motion commands. | |
267 | When the `track-eol' feature is doing its job, the value is 9999. | |
268 | ---------- Buffer: *Help* ---------- | |
269 | @end group | |
270 | @end smallexample | |
271 | ||
b8d4c8d0 GM |
272 | @defun Snarf-documentation filename |
273 | @anchor{Definition of Snarf-documentation} | |
274 | This function is used only during Emacs initialization, just before | |
275 | the runnable Emacs is dumped. It finds the file offsets of the | |
276 | documentation strings stored in the file @var{filename}, and records | |
277 | them in the in-core function definitions and variable property lists in | |
278 | place of the actual strings. @xref{Building Emacs}. | |
279 | ||
280 | Emacs reads the file @var{filename} from the @file{emacs/etc} directory. | |
281 | When the dumped Emacs is later executed, the same file will be looked | |
282 | for in the directory @code{doc-directory}. Usually @var{filename} is | |
283 | @code{"DOC-@var{version}"}. | |
284 | @end defun | |
285 | ||
b8d4c8d0 GM |
286 | @defvar doc-directory |
287 | This variable holds the name of the directory which should contain the | |
288 | file @code{"DOC-@var{version}"} that contains documentation strings for | |
289 | built-in and preloaded functions and variables. | |
290 | ||
291 | In most cases, this is the same as @code{data-directory}. They may be | |
292 | different when you run Emacs from the directory where you built it, | |
293 | without actually installing it. @xref{Definition of data-directory}. | |
b8d4c8d0 GM |
294 | @end defvar |
295 | ||
296 | @node Keys in Documentation | |
297 | @section Substituting Key Bindings in Documentation | |
298 | @cindex documentation, keys in | |
299 | @cindex keys in documentation strings | |
300 | @cindex substituting keys in documentation | |
301 | ||
302 | When documentation strings refer to key sequences, they should use the | |
303 | current, actual key bindings. They can do so using certain special text | |
304 | sequences described below. Accessing documentation strings in the usual | |
305 | way substitutes current key binding information for these special | |
306 | sequences. This works by calling @code{substitute-command-keys}. You | |
307 | can also call that function yourself. | |
308 | ||
309 | Here is a list of the special sequences and what they mean: | |
310 | ||
311 | @table @code | |
312 | @item \[@var{command}] | |
313 | stands for a key sequence that will invoke @var{command}, or @samp{M-x | |
314 | @var{command}} if @var{command} has no key bindings. | |
315 | ||
316 | @item \@{@var{mapvar}@} | |
317 | stands for a summary of the keymap which is the value of the variable | |
318 | @var{mapvar}. The summary is made using @code{describe-bindings}. | |
319 | ||
320 | @item \<@var{mapvar}> | |
321 | stands for no text itself. It is used only for a side effect: it | |
322 | specifies @var{mapvar}'s value as the keymap for any following | |
323 | @samp{\[@var{command}]} sequences in this documentation string. | |
324 | ||
325 | @item \= | |
326 | quotes the following character and is discarded; thus, @samp{\=\[} puts | |
327 | @samp{\[} into the output, and @samp{\=\=} puts @samp{\=} into the | |
328 | output. | |
329 | @end table | |
330 | ||
331 | @strong{Please note:} Each @samp{\} must be doubled when written in a | |
332 | string in Emacs Lisp. | |
333 | ||
334 | @defun substitute-command-keys string | |
335 | This function scans @var{string} for the above special sequences and | |
336 | replaces them by what they stand for, returning the result as a string. | |
337 | This permits display of documentation that refers accurately to the | |
338 | user's own customized key bindings. | |
339 | @end defun | |
340 | ||
341 | Here are examples of the special sequences: | |
342 | ||
343 | @smallexample | |
344 | @group | |
345 | (substitute-command-keys | |
346 | "To abort recursive edit, type: \\[abort-recursive-edit]") | |
347 | @result{} "To abort recursive edit, type: C-]" | |
348 | @end group | |
349 | ||
350 | @group | |
351 | (substitute-command-keys | |
352 | "The keys that are defined for the minibuffer here are: | |
353 | \\@{minibuffer-local-must-match-map@}") | |
354 | @result{} "The keys that are defined for the minibuffer here are: | |
355 | @end group | |
356 | ||
357 | ? minibuffer-completion-help | |
358 | SPC minibuffer-complete-word | |
359 | TAB minibuffer-complete | |
360 | C-j minibuffer-complete-and-exit | |
361 | RET minibuffer-complete-and-exit | |
362 | C-g abort-recursive-edit | |
363 | " | |
364 | ||
365 | @group | |
366 | (substitute-command-keys | |
367 | "To abort a recursive edit from the minibuffer, type\ | |
368 | \\<minibuffer-local-must-match-map>\\[abort-recursive-edit].") | |
369 | @result{} "To abort a recursive edit from the minibuffer, type C-g." | |
370 | @end group | |
371 | @end smallexample | |
372 | ||
373 | There are other special conventions for the text in documentation | |
374 | strings---for instance, you can refer to functions, variables, and | |
375 | sections of this manual. @xref{Documentation Tips}, for details. | |
376 | ||
377 | @node Describing Characters | |
378 | @section Describing Characters for Help Messages | |
379 | @cindex describe characters and events | |
380 | ||
381 | These functions convert events, key sequences, or characters to | |
382 | textual descriptions. These descriptions are useful for including | |
383 | arbitrary text characters or key sequences in messages, because they | |
384 | convert non-printing and whitespace characters to sequences of printing | |
385 | characters. The description of a non-whitespace printing character is | |
386 | the character itself. | |
387 | ||
388 | @defun key-description sequence &optional prefix | |
389 | @cindex Emacs event standard notation | |
390 | This function returns a string containing the Emacs standard notation | |
391 | for the input events in @var{sequence}. If @var{prefix} is | |
392 | non-@code{nil}, it is a sequence of input events leading up to | |
393 | @var{sequence} and is included in the return value. Both arguments | |
394 | may be strings, vectors or lists. @xref{Input Events}, for more | |
395 | information about valid events. | |
396 | ||
397 | @smallexample | |
398 | @group | |
399 | (key-description [?\M-3 delete]) | |
400 | @result{} "M-3 <delete>" | |
401 | @end group | |
402 | @group | |
403 | (key-description [delete] "\M-3") | |
404 | @result{} "M-3 <delete>" | |
405 | @end group | |
406 | @end smallexample | |
407 | ||
408 | See also the examples for @code{single-key-description}, below. | |
409 | @end defun | |
410 | ||
411 | @defun single-key-description event &optional no-angles | |
412 | @cindex event printing | |
413 | @cindex character printing | |
414 | @cindex control character printing | |
415 | @cindex meta character printing | |
416 | This function returns a string describing @var{event} in the standard | |
417 | Emacs notation for keyboard input. A normal printing character | |
418 | appears as itself, but a control character turns into a string | |
419 | starting with @samp{C-}, a meta character turns into a string starting | |
420 | with @samp{M-}, and space, tab, etc.@: appear as @samp{SPC}, | |
421 | @samp{TAB}, etc. A function key symbol appears inside angle brackets | |
422 | @samp{<@dots{}>}. An event that is a list appears as the name of the | |
423 | symbol in the @sc{car} of the list, inside angle brackets. | |
424 | ||
425 | If the optional argument @var{no-angles} is non-@code{nil}, the angle | |
426 | brackets around function keys and event symbols are omitted; this is | |
427 | for compatibility with old versions of Emacs which didn't use the | |
428 | brackets. | |
429 | ||
430 | @smallexample | |
431 | @group | |
432 | (single-key-description ?\C-x) | |
433 | @result{} "C-x" | |
434 | @end group | |
435 | @group | |
436 | (key-description "\C-x \M-y \n \t \r \f123") | |
437 | @result{} "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" | |
438 | @end group | |
439 | @group | |
440 | (single-key-description 'delete) | |
441 | @result{} "<delete>" | |
442 | @end group | |
443 | @group | |
444 | (single-key-description 'C-mouse-1) | |
445 | @result{} "<C-mouse-1>" | |
446 | @end group | |
447 | @group | |
448 | (single-key-description 'C-mouse-1 t) | |
449 | @result{} "C-mouse-1" | |
450 | @end group | |
451 | @end smallexample | |
452 | @end defun | |
453 | ||
454 | @defun text-char-description character | |
455 | This function returns a string describing @var{character} in the | |
456 | standard Emacs notation for characters that appear in text---like | |
457 | @code{single-key-description}, except that control characters are | |
458 | represented with a leading caret (which is how control characters in | |
459 | Emacs buffers are usually displayed). Another difference is that | |
460 | @code{text-char-description} recognizes the 2**7 bit as the Meta | |
461 | character, whereas @code{single-key-description} uses the 2**27 bit | |
462 | for Meta. | |
463 | ||
464 | @smallexample | |
465 | @group | |
466 | (text-char-description ?\C-c) | |
467 | @result{} "^C" | |
468 | @end group | |
469 | @group | |
470 | (text-char-description ?\M-m) | |
471 | @result{} "\xed" | |
472 | @end group | |
473 | @group | |
474 | (text-char-description ?\C-\M-m) | |
475 | @result{} "\x8d" | |
476 | @end group | |
477 | @group | |
478 | (text-char-description (+ 128 ?m)) | |
479 | @result{} "M-m" | |
480 | @end group | |
481 | @group | |
482 | (text-char-description (+ 128 ?\C-m)) | |
483 | @result{} "M-^M" | |
484 | @end group | |
485 | @end smallexample | |
486 | @end defun | |
487 | ||
488 | @defun read-kbd-macro string &optional need-vector | |
489 | This function is used mainly for operating on keyboard macros, but it | |
490 | can also be used as a rough inverse for @code{key-description}. You | |
491 | call it with a string containing key descriptions, separated by spaces; | |
492 | it returns a string or vector containing the corresponding events. | |
493 | (This may or may not be a single valid key sequence, depending on what | |
494 | events you use; @pxref{Key Sequences}.) If @var{need-vector} is | |
495 | non-@code{nil}, the return value is always a vector. | |
496 | @end defun | |
497 | ||
498 | @node Help Functions | |
499 | @section Help Functions | |
500 | ||
501 | Emacs provides a variety of on-line help functions, all accessible to | |
502 | the user as subcommands of the prefix @kbd{C-h}. For more information | |
503 | about them, see @ref{Help, , Help, emacs, The GNU Emacs Manual}. Here | |
504 | we describe some program-level interfaces to the same information. | |
505 | ||
506 | @deffn Command apropos pattern &optional do-all | |
507 | This function finds all ``meaningful'' symbols whose names contain a | |
508 | match for the apropos pattern @var{pattern}. An apropos pattern is | |
509 | either a word to match, a space-separated list of words of which at | |
510 | least two must match, or a regular expression (if any special regular | |
511 | expression characters occur). A symbol is ``meaningful'' if it has a | |
512 | definition as a function, variable, or face, or has properties. | |
513 | ||
514 | The function returns a list of elements that look like this: | |
515 | ||
516 | @example | |
517 | (@var{symbol} @var{score} @var{fn-doc} @var{var-doc} | |
518 | @var{plist-doc} @var{widget-doc} @var{face-doc} @var{group-doc}) | |
519 | @end example | |
520 | ||
521 | Here, @var{score} is an integer measure of how important the symbol | |
522 | seems to be as a match, and the remaining elements are documentation | |
523 | strings for @var{symbol}'s various roles (or @code{nil}). | |
524 | ||
525 | It also displays the symbols in a buffer named @samp{*Apropos*}, each | |
526 | with a one-line description taken from the beginning of its | |
527 | documentation string. | |
528 | ||
b8d4c8d0 GM |
529 | If @var{do-all} is non-@code{nil}, or if the user option |
530 | @code{apropos-do-all} is non-@code{nil}, then @code{apropos} also | |
531 | shows key bindings for the functions that are found; it also shows | |
532 | @emph{all} interned symbols, not just meaningful ones (and it lists | |
533 | them in the return value as well). | |
534 | @end deffn | |
535 | ||
536 | @defvar help-map | |
537 | The value of this variable is a local keymap for characters following the | |
538 | Help key, @kbd{C-h}. | |
539 | @end defvar | |
540 | ||
541 | @deffn {Prefix Command} help-command | |
542 | This symbol is not a function; its function definition cell holds the | |
543 | keymap known as @code{help-map}. It is defined in @file{help.el} as | |
544 | follows: | |
545 | ||
546 | @smallexample | |
547 | @group | |
3e99b825 | 548 | (define-key global-map (string help-char) 'help-command) |
b8d4c8d0 GM |
549 | (fset 'help-command help-map) |
550 | @end group | |
551 | @end smallexample | |
552 | @end deffn | |
553 | ||
01f17ae2 | 554 | @defopt help-char |
b8d4c8d0 GM |
555 | The value of this variable is the help character---the character that |
556 | Emacs recognizes as meaning Help. By default, its value is 8, which | |
557 | stands for @kbd{C-h}. When Emacs reads this character, if | |
558 | @code{help-form} is a non-@code{nil} Lisp expression, it evaluates that | |
559 | expression, and displays the result in a window if it is a string. | |
560 | ||
561 | Usually the value of @code{help-form} is @code{nil}. Then the | |
562 | help character has no special meaning at the level of command input, and | |
563 | it becomes part of a key sequence in the normal way. The standard key | |
564 | binding of @kbd{C-h} is a prefix key for several general-purpose help | |
565 | features. | |
566 | ||
567 | The help character is special after prefix keys, too. If it has no | |
568 | binding as a subcommand of the prefix key, it runs | |
569 | @code{describe-prefix-bindings}, which displays a list of all the | |
570 | subcommands of the prefix key. | |
01f17ae2 | 571 | @end defopt |
b8d4c8d0 | 572 | |
01f17ae2 | 573 | @defopt help-event-list |
b8d4c8d0 GM |
574 | The value of this variable is a list of event types that serve as |
575 | alternative ``help characters.'' These events are handled just like the | |
576 | event specified by @code{help-char}. | |
01f17ae2 | 577 | @end defopt |
b8d4c8d0 GM |
578 | |
579 | @defvar help-form | |
580 | If this variable is non-@code{nil}, its value is a form to evaluate | |
581 | whenever the character @code{help-char} is read. If evaluating the form | |
582 | produces a string, that string is displayed. | |
583 | ||
584 | A command that calls @code{read-event} or @code{read-char} probably | |
585 | should bind @code{help-form} to a non-@code{nil} expression while it | |
586 | does input. (The time when you should not do this is when @kbd{C-h} has | |
587 | some other meaning.) Evaluating this expression should result in a | |
588 | string that explains what the input is for and how to enter it properly. | |
589 | ||
590 | Entry to the minibuffer binds this variable to the value of | |
591 | @code{minibuffer-help-form} (@pxref{Definition of minibuffer-help-form}). | |
592 | @end defvar | |
593 | ||
594 | @defvar prefix-help-command | |
595 | This variable holds a function to print help for a prefix key. The | |
596 | function is called when the user types a prefix key followed by the help | |
597 | character, and the help character has no binding after that prefix. The | |
598 | variable's default value is @code{describe-prefix-bindings}. | |
599 | @end defvar | |
600 | ||
601 | @defun describe-prefix-bindings | |
602 | This function calls @code{describe-bindings} to display a list of all | |
603 | the subcommands of the prefix key of the most recent key sequence. The | |
604 | prefix described consists of all but the last event of that key | |
605 | sequence. (The last event is, presumably, the help character.) | |
606 | @end defun | |
607 | ||
608 | The following two functions are meant for modes that want to provide | |
609 | help without relinquishing control, such as the ``electric'' modes. | |
610 | Their names begin with @samp{Helper} to distinguish them from the | |
611 | ordinary help functions. | |
612 | ||
613 | @deffn Command Helper-describe-bindings | |
614 | This command pops up a window displaying a help buffer containing a | |
615 | listing of all of the key bindings from both the local and global keymaps. | |
616 | It works by calling @code{describe-bindings}. | |
617 | @end deffn | |
618 | ||
619 | @deffn Command Helper-help | |
620 | This command provides help for the current mode. It prompts the user | |
621 | in the minibuffer with the message @samp{Help (Type ? for further | |
622 | options)}, and then provides assistance in finding out what the key | |
623 | bindings are, and what the mode is intended for. It returns @code{nil}. | |
624 | ||
625 | This can be customized by changing the map @code{Helper-help-map}. | |
626 | @end deffn | |
627 | ||
b8d4c8d0 GM |
628 | @defvar data-directory |
629 | @anchor{Definition of data-directory} | |
630 | This variable holds the name of the directory in which Emacs finds | |
bbe45ef7 | 631 | certain documentation and text files that come with Emacs. |
b8d4c8d0 GM |
632 | @end defvar |
633 | ||
77c7e2e1 | 634 | @defun help-buffer |
b2a77f6d CY |
635 | This function returns the name of the help buffer, which is normally |
636 | @samp{*Help*}; if such a buffer does not exist, it is first created. | |
77c7e2e1 | 637 | @end defun |
b2a77f6d CY |
638 | |
639 | @defmac with-help-window buffer-name body@dots{} | |
640 | This macro evaluates the @var{body} forms, inserting any output they | |
641 | produce into a buffer named @var{buffer-name} like | |
642 | @code{with-output-to-temp-buffer} (@pxref{Temporary Displays}). | |
643 | (Usually, @var{buffer-name} should be the value returned by the | |
644 | function @code{help-buffer}.) It also puts the specified buffer into | |
645 | Help mode and displays a message telling the user how to quit and | |
646 | scroll the help window. | |
647 | @end defmac | |
648 | ||
77c7e2e1 | 649 | @defun help-setup-xref item interactive-p |
b2a77f6d CY |
650 | This function updates the cross reference data in the @samp{*Help*} |
651 | buffer, which is used to regenerate the help information when the user | |
652 | clicks on the @samp{Back} or @samp{Forward} buttons. Most commands | |
653 | that use the @samp{*Help*} buffer should invoke this function before | |
654 | clearing the buffer. The @var{item} argument should have the form | |
655 | @code{(@var{funtion} . @var{args})}, where @var{funtion} is a function | |
656 | to call, with argument list @var{args}, to regenerate the help buffer. | |
657 | The @var{interactive-p} argument is non-@code{nil} if the calling | |
658 | command was invoked interactively; in that case, the stack of items | |
659 | for the @samp{*Help*} buffer's @samp{Back} buttons is cleared. | |
77c7e2e1 | 660 | @end defun |
b2a77f6d CY |
661 | |
662 | @xref{describe-symbols example}, for an example of using | |
663 | @code{help-buffer}, @code{with-help-window}, and | |
664 | @code{help-setup-xref}. | |
665 | ||
b8d4c8d0 GM |
666 | @defmac make-help-screen fname help-line help-text help-map |
667 | This macro defines a help command named @var{fname} that acts like a | |
668 | prefix key that shows a list of the subcommands it offers. | |
669 | ||
670 | When invoked, @var{fname} displays @var{help-text} in a window, then | |
671 | reads and executes a key sequence according to @var{help-map}. The | |
672 | string @var{help-text} should describe the bindings available in | |
673 | @var{help-map}. | |
674 | ||
675 | The command @var{fname} is defined to handle a few events itself, by | |
676 | scrolling the display of @var{help-text}. When @var{fname} reads one of | |
677 | those special events, it does the scrolling and then reads another | |
678 | event. When it reads an event that is not one of those few, and which | |
679 | has a binding in @var{help-map}, it executes that key's binding and | |
680 | then returns. | |
681 | ||
682 | The argument @var{help-line} should be a single-line summary of the | |
683 | alternatives in @var{help-map}. In the current version of Emacs, this | |
684 | argument is used only if you set the option @code{three-step-help} to | |
685 | @code{t}. | |
686 | ||
687 | This macro is used in the command @code{help-for-help} which is the | |
688 | binding of @kbd{C-h C-h}. | |
689 | @end defmac | |
690 | ||
691 | @defopt three-step-help | |
692 | If this variable is non-@code{nil}, commands defined with | |
693 | @code{make-help-screen} display their @var{help-line} strings in the | |
694 | echo area at first, and display the longer @var{help-text} strings only | |
695 | if the user types the help character again. | |
696 | @end defopt | |
697 |