2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../info/help
6 @node Documentation, Files, Modes, Top
8 @cindex documentation strings
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.
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
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.
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
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.
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
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}.
57 Documentation strings can contain several special substrings, which
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}.)
63 In Emacs Lisp, a documentation string is accessible through the
64 function or variable that it describes:
68 The documentation for a function is stored in the function definition
69 itself (@pxref{Lambda Expressions}). The function @code{documentation}
70 knows how to extract it.
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
76 function @code{documentation-property} knows how to retrieve it.
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
83 (including primitive functions and autoloaded functions) is stored in
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}).
89 The data structure inside Emacs has an integer offset into the file, or
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
96 For information on the uses of documentation strings, see @ref{Help, ,
97 Help, emacs, The GNU Emacs Manual}.
99 @c Wordy to prevent overfull hbox. --rjc 15mar92
100 The @file{emacs/lib-src} directory contains two utilities that you can
101 use to print nice-looking hardcopy for the file
102 @file{emacs/etc/DOC-@var{version}}. These are @file{sorted-doc.c} and
105 @node Accessing Documentation
106 @section Access to Documentation Strings
108 @defun documentation-property symbol property &optional verbatim
109 This function returns the documentation string that is recorded
110 @var{symbol}'s property list under property @var{property}. It
111 retrieves the text from a file if necessary, and runs
112 @code{substitute-command-keys} to substitute actual key bindings. (This
113 substitution is not done if @var{verbatim} is non-@code{nil}.)
117 (documentation-property 'command-line-processed
118 'variable-documentation)
119 @result{} "t once command line has been processed"
122 (symbol-plist 'command-line-processed)
123 @result{} (variable-documentation 188902)
128 @defun documentation function &optional verbatim
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.
134 The function @code{documentation} signals a @code{void-function} error
135 if @var{function} has no function definition. However, it is OK if
136 the function definition has no documentation string. In that case,
137 @code{documentation} returns @code{nil}.
140 @c Wordy to prevent overfull hboxes. --rjc 15mar92
141 Here is an example of using the two functions, @code{documentation} and
142 @code{documentation-property}, to display the documentation strings for
143 several symbols in a @samp{*Help*} buffer.
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: ")
157 ;; @r{Print description of symbol.}
158 (if (fboundp s) ; @r{It is a function.}
160 (format "%s\t%s\n%s\n\n" s
162 (let ((keys (where-is-internal s)))
166 (mapconcat 'key-description
172 (or (documentation s)
175 (if (boundp s) ; @r{It is a variable.}
179 (format "%s\t%s\n%s\n\n" s
180 (if (user-variable-p s)
181 "Option " "Variable")
184 (or (documentation-property
185 s 'variable-documentation)
186 "not documented")))))))
191 ;; @r{Build a list of symbols that match pattern.}
194 (if (string-match pattern (symbol-name sym))
195 (setq sym-list (cons sym sym-list))))))
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))))
206 The @code{describe-symbols} function works like @code{apropos},
207 but provides more information.
211 (describe-symbols "goal")
213 ---------- Buffer: *Help* ----------
215 *Semipermanent goal column for vertical motion, as set by @dots{}
217 @c Do not blithely break or fill these lines.
218 @c That makes them incorrect.
221 set-goal-column Command: C-x C-n
222 Set the current horizontal position as a goal for C-n and C-p.
224 @c DO NOT put a blank line here! That is factually inaccurate!
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'.
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* ----------
243 @defun Snarf-documentation filename
244 This function is used only during Emacs initialization, just before
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}.
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
253 @code{"DOC-@var{version}"}.
257 @defvar doc-directory
258 This variable holds the name of the directory which should contain the
259 file @code{"DOC-@var{version}"} that contains documentation strings for
260 built-in and preloaded functions and variables.
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
267 In older Emacs versions, @code{exec-directory} was used for this.
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
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.
283 Here is a list of the special sequences and what they mean:
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.
290 @item \@{@var{mapvar}@}
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}.
294 @item \<@var{mapvar}>
295 stands for no text itself. It is used only for a side effect: it
296 specifies @var{mapvar}'s value as the keymap for any following
297 @samp{\[@var{command}]} sequences in this documentation string.
300 quotes the following character and is discarded; thus, @samp{\=\[} puts
301 @samp{\[} into the output, and @samp{\=\=} puts @samp{\=} into the
305 @strong{Please note:} Each @samp{\} must be doubled when written in a
306 string in Emacs Lisp.
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
312 user's own customized key bindings.
315 Here are examples of the special sequences:
319 (substitute-command-keys
320 "To abort recursive edit, type: \\[abort-recursive-edit]")
321 @result{} "To abort recursive edit, type: C-]"
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:
331 ? minibuffer-completion-help
332 SPC minibuffer-complete-word
333 TAB minibuffer-complete
334 C-j minibuffer-complete-and-exit
335 RET minibuffer-complete-and-exit
336 C-g abort-recursive-edit
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."
347 @node Describing Characters
348 @section Describing Characters for Help Messages
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
354 characters. The description of a non-whitespace printing character is
355 the character itself.
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.
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-},
375 and space, tab, etc.@: appear as @samp{SPC}, @samp{TAB}, etc. A
376 function key symbol appears as itself. An event that is a list appears
377 as the name of the symbol in the @sc{car} of the list.
381 (single-key-description ?\C-x)
385 (key-description "\C-x \M-y \n \t \r \f123")
386 @result{} "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
389 (single-key-description 'C-mouse-1)
390 @result{} "C-mouse-1"
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).
404 (text-char-description ?\C-c)
408 (text-char-description ?\M-m)
412 (text-char-description ?\C-\M-m)
419 @section Help Functions
421 Emacs provides a variety of on-line help functions, all accessible to
422 the user as subcommands of the prefix @kbd{C-h}. For more information
423 about them, see @ref{Help, , Help, emacs, The GNU Emacs Manual}. Here
424 we describe some program-level interfaces to the same information.
426 @deffn Command apropos regexp &optional do-all
427 This function finds all symbols whose names contain a match for the
428 regular expression @var{regexp}, and returns a list of them
429 (@pxref{Regular Expressions}). It also displays the symbols in a buffer
430 named @samp{*Help*}, each with a one-line description taken from the
431 beginning of its documentation string.
434 If @var{do-all} is non-@code{nil}, then @code{apropos} also shows
435 key bindings for the functions that are found.
437 In the first of the following examples, @code{apropos} finds all the
438 symbols with names containing @samp{exec}. (We don't show here the
439 output that results in the @samp{*Help*} buffer.)
444 @result{} (Buffer-menu-execute command-execute exec-directory
445 exec-path execute-extended-command execute-kbd-macro
446 executing-kbd-macro executing-macro)
452 The value of this variable is a local keymap for characters following the
456 @deffn {Prefix Command} help-command
457 This symbol is not a function; its function definition cell holds the
458 keymap known as @code{help-map}. It is defined in @file{help.el} as
463 (define-key global-map "\C-h" 'help-command)
464 (fset 'help-command help-map)
469 @defun print-help-return-message &optional function
470 This function builds a string that explains how to restore the previous
471 state of the windows after a help command. After building the message,
472 it applies @var{function} to it if @var{function} is non-@code{nil}.
473 Otherwise it calls @code{message} to display it in the echo area.
475 This function expects to be called inside a
476 @code{with-output-to-temp-buffer} special form, and expects
477 @code{standard-output} to have the value bound by that special form.
478 For an example of its use, see the long example in @ref{Accessing
483 The value of this variable is the help character---the character that
484 Emacs recognizes as meaning Help. By default, it stands for 8, which is
485 @kbd{C-h}. When Emacs reads this character, if @code{help-form} is
486 non-@code{nil} Lisp expression, it evaluates that expression, and
487 displays the result in a window if it is a string.
489 Usually the value of @code{help-form}'s value is @code{nil}. Then the
490 help character has no special meaning at the level of command input, and
491 it becomes part of a key sequence in the normal way. The standard key
492 binding of @kbd{C-h} is a prefix key for several general-purpose help
495 The help character is special after prefix keys, too. If it has no
496 binding as a subcommand of the prefix key, it runs
497 @code{describe-prefix-bindings}, which displays a list of all the
498 subcommands of the prefix key.
501 @tindex help-event-list
502 @defvar help-event-list
503 The value of this variable is a list of event types that serve as
504 alternative ``help characters.'' These events are handled just like the
505 event specified by @code{help-char}.
509 If this variable is non-@code{nil}, its value is a form to evaluate
510 whenever the character @code{help-char} is read. If evaluating the form
511 produces a string, that string is displayed.
513 A command that calls @code{read-event} or @code{read-char} probably
514 should bind @code{help-form} to a non-@code{nil} expression while it
515 does input. (The time when you should not do this is when @kbd{C-h} has
516 some other meaning.) Evaluating this expression should result in a
517 string that explains what the input is for and how to enter it properly.
519 Entry to the minibuffer binds this variable to the value of
520 @code{minibuffer-help-form} (@pxref{Minibuffer Misc}).
523 @defvar prefix-help-command
524 This variable holds a function to print help for a prefix key. The
525 function is called when the user types a prefix key followed by the help
526 character, and the help character has no binding after that prefix. The
527 variable's default value is @code{describe-prefix-bindings}.
530 @defun describe-prefix-bindings
531 This function calls @code{describe-bindings} to display a list of all
532 the subcommands of the prefix key of the most recent key sequence. The
533 prefix described consists of all but the last event of that key
534 sequence. (The last event is, presumably, the help character.)
537 The following two functions are found in the library @file{helper}.
538 They are for modes that want to provide help without relinquishing
539 control, such as the ``electric'' modes. You must load that library
540 with @code{(require 'helper)} in order to use them. Their names begin
541 with @samp{Helper} to distinguish them from the ordinary help functions.
543 @deffn Command Helper-describe-bindings
544 This command pops up a window displaying a help buffer containing a
545 listing of all of the key bindings from both the local and global keymaps.
546 It works by calling @code{describe-bindings}.
549 @deffn Command Helper-help
550 This command provides help for the current mode. It prompts the user
551 in the minibuffer with the message @samp{Help (Type ? for further
552 options)}, and then provides assistance in finding out what the key
553 bindings are, and what the mode is intended for. It returns @code{nil}.
555 This can be customized by changing the map @code{Helper-help-map}.
559 @defvar data-directory
560 This variable holds the name of the directory in which Emacs finds
561 certain documentation and text files that come with Emacs. In older
562 Emacs versions, @code{exec-directory} was used for this.
566 @defmac make-help-screen fname help-line help-text help-map
567 This macro defines a help command named @var{fname} that acts like a
568 prefix key that shows a list of the subcommands it offers.
570 When invoked, @var{fname} displays @var{help-text} in a window, then
571 reads and executes a key sequence according to @var{help-map}. The
572 string @var{help-text} should describe the bindings available in
575 The command @var{fname} is defined to handle a few events itself, by
576 scrolling the display of @var{help-text}. When @var{fname} reads one of
577 those special events, it does the scrolling and then reads another
578 event. When it reads an event that is not one of those few, and which
579 has a binding in @var{help-map}, it executes that key's binding and
582 The argument @var{help-line} should be a single-line summary of the
583 alternatives in @var{help-map}. In the current version of Emacs, this
584 argument is used only if you set the option @code{three-step-help} to
587 This macro is used in the command @code{help-for-help} which is the
588 binding of @kbd{C-h C-h}.
591 @defopt three-step-help
592 If this variable is non-@code{nil}, commands defined with
593 @code{make-help-screen} display their @var{help-line} strings in the
594 echo area at first, and display the longer @var{help-text} strings only
595 if the user types the help character again.