2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 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 you have one, because that looks odd when you use @kbd{C-h f}
54 (@code{describe-function}) or @kbd{C-h v} (@code{describe-variable}).
55 @xref{Documentation Tips}.
57 Documentation strings may 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 Within the Lisp world, a documentation string 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
70 @code{documentation} 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 extract 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}}. The documentation for
85 functions and variables loaded during the Emacs session from
86 byte-compiled files is stored in those files (@pxref{Docs and
89 The data structure inside Emacs has an integer offset into the file, or
90 a list containing a string and an integer, in place of the documentation
91 string. The functions @code{documentation} and
92 @code{documentation-property} use that information to read the
93 documentation from the appropriate file; this is transparent to the
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}; the
114 @var{verbatim} argument exists only as of Emacs 19.)
118 (documentation-property 'command-line-processed
119 'variable-documentation)
120 @result{} "t once command line has been processed"
123 (symbol-plist 'command-line-processed)
124 @result{} (variable-documentation 188902)
129 @defun documentation function &optional verbatim
130 This function returns the documentation string of @var{function}. It
131 reads the text from a file if necessary. Then (unless @var{verbatim} is
132 non-@code{nil}) it calls @code{substitute-command-keys}, to return a
133 value containing the actual (current) key bindings.
135 The function @code{documentation} signals a @code{void-function} error
136 if @var{function} has no function definition. However, it is ok if
137 the function definition has no documentation string. In that case,
138 @code{documentation} returns @code{nil}.
141 @c Wordy to prevent overfull hboxes. --rjc 15mar92
142 Here is an example of using the two functions, @code{documentation} and
143 @code{documentation-property}, to display the documentation strings for
144 several symbols in a @samp{*Help*} buffer.
148 (defun describe-symbols (pattern)
149 "Describe the Emacs Lisp symbols matching PATTERN.
150 All symbols that have PATTERN in their name are described
151 in the `*Help*' buffer."
152 (interactive "sDescribe symbols matching: ")
158 ;; @r{Print description of symbol.}
159 (if (fboundp s) ; @r{It is a function.}
161 (format "%s\t%s\n%s\n\n" s
163 (let ((keys (where-is-internal s)))
167 (mapconcat 'key-description
173 (or (documentation s)
176 (if (boundp s) ; @r{It is a variable.}
180 (format "%s\t%s\n%s\n\n" s
181 (if (user-variable-p s)
182 "Option " "Variable")
185 (or (documentation-property
186 s 'variable-documentation)
187 "not documented")))))))
192 ;; @r{Build a list of symbols that match pattern.}
195 (if (string-match pattern (symbol-name sym))
196 (setq sym-list (cons sym sym-list))))))
200 ;; @r{Display the data.}
201 (with-output-to-temp-buffer "*Help*"
202 (mapcar describe-func (sort sym-list 'string<))
203 (print-help-return-message))))
207 The @code{describe-symbols} function works like @code{apropos},
208 but provides more information.
212 (describe-symbols "goal")
214 ---------- Buffer: *Help* ----------
216 *Semipermanent goal column for vertical motion, as set by C-x C-n, or nil.
218 @c Do not blithely break or fill these lines.
219 @c That makes them incorrect.
222 set-goal-column Command: C-x C-n
223 Set the current horizontal position as a goal for C-n and C-p.
225 @c DO NOT put a blank line here! That is factually inaccurate!
227 Those commands will move to this position in the line moved to
228 rather than trying to keep the same horizontal position.
229 With a non-nil argument, clears out the goal column
230 so that C-n and C-p resume vertical motion.
231 The goal column is stored in the variable `goal-column'.
235 temporary-goal-column Variable
236 Current goal column for vertical motion.
237 It is the column where point was
238 at the start of current run of vertical motion commands.
239 When the `track-eol' feature is doing its job, the value is 9999.
240 ---------- Buffer: *Help* ----------
244 @defun Snarf-documentation filename
245 This function is used only during Emacs initialization, just before
246 the runnable Emacs is dumped. It finds the file offsets of the
247 documentation strings stored in the file @var{filename}, and records
248 them in the in-core function definitions and variable property lists in
249 place of the actual strings. @xref{Building Emacs}.
251 Emacs finds the file @var{filename} in the @file{emacs/etc} directory.
252 When the dumped Emacs is later executed, the same file is found in the
253 directory @code{doc-directory}. Usually @var{filename} is
254 @code{"DOC-@var{version}"}.
258 @defvar doc-directory
259 This variable holds the name of the directory which should contion the
260 file @code{"DOC-@var{version}"} that contains documentation strings for
261 built-in and preloaded functions and variables.
263 In most cases, this is the same as @code{data-directory}. They may be
264 different when you run Emacs from the directory where you built it,
265 without actually installing it. See @code{data-directory} in @ref{Help
268 In older Emacs versions, @code{exec-directory} was used for this.
271 @node Keys in Documentation
272 @section Substituting Key Bindings in Documentation
273 @cindex documentation, keys in
274 @cindex keys in documentation strings
275 @cindex substituting keys in documentation
277 When documentation strings refer to key sequences, they should use the
278 current, actual key bindings. They can do so using certain special text
279 sequences described below. Accessing documentation strings in the usual
280 way substitutes current key binding information for these special
281 sequences. This works by calling @code{substitute-command-keys}. You
282 can also call that function yourself.
284 Here is a list of the special sequences and what they mean:
287 @item \[@var{command}]
288 stands for a key sequence that will invoke @var{command}, or @samp{M-x
289 @var{command}} if @var{command} has no key bindings.
291 @item \@{@var{mapvar}@}
292 stands for a summary of the value of @var{mapvar}, which should be a
293 keymap. The summary is made by @code{describe-bindings}.
295 @item \<@var{mapvar}>
296 stands for no text itself. It is used for a side effect: it specifies
297 @var{mapvar} as the keymap for any following @samp{\[@var{command}]}
298 sequences in this documentation string.
301 @strong{Please note:} Each @samp{\} must be doubled when written in a
302 string in Emacs Lisp.
304 @defun substitute-command-keys string
305 This function scans @var{string} for the above special sequences and
306 replaces them by what they stand for, returning the result as a string.
307 This permits display of documentation that refers accurately to the
308 user's own customized key bindings.
311 Here are examples of the special sequences:
315 (substitute-command-keys
316 "To abort recursive edit, type: \\[abort-recursive-edit]")
317 @result{} "To abort recursive edit, type: C-]"
321 (substitute-command-keys
322 "The keys that are defined for the minibuffer here are:
323 \\@{minibuffer-local-must-match-map@}")
324 @result{} "The keys that are defined for the minibuffer here are:
327 ? minibuffer-completion-help
328 SPC minibuffer-complete-word
329 TAB minibuffer-complete
330 LFD minibuffer-complete-and-exit
331 RET minibuffer-complete-and-exit
332 C-g abort-recursive-edit
336 (substitute-command-keys
337 "To abort a recursive edit from the minibuffer, type\
338 \\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
339 @result{} "To abort a recursive edit from the minibuffer, type C-g."
343 @node Describing Characters
344 @section Describing Characters for Help Messages
346 These functions convert events, key sequences or characters to textual
347 descriptions. These descriptions are useful for including arbitrary
348 text characters or key sequences in messages, because they convert
349 non-printing and whitespace characters to sequences of printing
350 characters. The description of a non-whitespace printing character is
351 the character itself.
353 @defun key-description sequence
354 @cindex Emacs event standard notation
355 This function returns a string containing the Emacs standard notation
356 for the input events in @var{sequence}. The argument @var{sequence} may
357 be a string, vector or list. @xref{Input Events}, for more information
358 about valid events. See also the examples for
359 @code{single-key-description}, below.
362 @defun single-key-description event
363 @cindex event printing
364 @cindex character printing
365 @cindex control character printing
366 @cindex meta character printing
367 This function returns a string describing @var{event} in the standard
368 Emacs notation for keyboard input. A normal printing character appears
369 as itself, but a control character turns into a string starting with
370 @samp{C-}, a meta character turns into a string starting with @samp{M-},
371 and space, linefeed, etc.@: appear as @samp{SPC}, @samp{LFD}, etc. A
372 function key symbol appears as itself. An event that is a list appears
373 as the name of the symbol in the @sc{car} of the list.
377 (single-key-description ?\C-x)
381 (key-description "\C-x \M-y \n \t \r \f123")
382 @result{} "C-x SPC M-y SPC LFD SPC TAB SPC RET SPC C-l 1 2 3"
385 (single-key-description 'C-mouse-1)
386 @result{} "C-mouse-1"
391 @defun text-char-description character
392 This function returns a string describing @var{character} in the
393 standard Emacs notation for characters that appear in text---like
394 @code{single-key-description}, except that control characters are
395 represented with a leading caret (which is how control characters in
396 Emacs buffers are usually displayed).
400 (text-char-description ?\C-c)
404 (text-char-description ?\M-m)
408 (text-char-description ?\C-\M-m)
415 @section Help Functions
417 Emacs provides a variety of on-line help functions, all accessible to
418 the user as subcommands of the prefix @kbd{C-h}. For more information
419 about them, see @ref{Help, , Help, emacs, The GNU Emacs Manual}. Here
420 we describe some program-level interfaces to the same information.
422 @deffn Command apropos regexp &optional do-all predicate
423 This function finds all symbols whose names contain a match for the
424 regular expression @var{regexp}, and returns a list of them
425 (@pxref{Regular Expressions}). It also displays the symbols in a buffer
426 named @samp{*Help*}, each with a one-line description.
429 If @var{do-all} is non-@code{nil}, then @code{apropos} also shows
430 key bindings for the functions that are found.
432 If @var{predicate} is non-@code{nil}, it should be a function to be
433 called on each symbol that has matched @var{regexp}. Only symbols for
434 which @var{predicate} returns a non-@code{nil} value are listed or
437 In the first of the following examples, @code{apropos} finds all the
438 symbols with names containing @samp{exec}. In the second example, it
439 finds and returns only those symbols that are also commands.
440 (We don't show the output that results in the @samp{*Help*} buffer.)
445 @result{} (Buffer-menu-execute command-execute exec-directory
446 exec-path execute-extended-command execute-kbd-macro
447 executing-kbd-macro executing-macro)
451 (apropos "exec" nil 'commandp)
452 @result{} (Buffer-menu-execute execute-extended-command)
456 ---------- Buffer: *Help* ----------
458 Function: Save and/or delete buffers marked with
459 M-x Buffer-menu-save or M-x Buffer-menu-delete commands.
460 execute-extended-command ESC x
461 Function: Read function name, then read its
462 arguments and call it.
463 ---------- Buffer: *Help* ----------
468 The command @kbd{C-h a} (@code{command-apropos}) calls @code{apropos},
469 but specifies a @var{predicate} to restrict the output to symbols that
470 are commands. The call to @code{apropos} looks like this:
473 (apropos string t 'commandp)
478 @deffn Command super-apropos regexp &optional do-all
479 This function differs from @code{apropos} in that it searches
480 documentation strings as well as symbol names for matches for
481 @var{regexp}. By default, it searches the documentation strings only
482 for preloaded functions and variables. If @var{do-all} is
483 non-@code{nil}, it scans the names and documentation strings of all
484 functions and variables.
488 The value of this variable is a local keymap for characters following the
492 @deffn {Prefix Command} help-command
493 This symbol is not a function; its function definition is actually the
494 keymap known as @code{help-map}. It is defined in @file{help.el} as
499 (define-key global-map "\C-h" 'help-command)
500 (fset 'help-command help-map)
505 @defun print-help-return-message &optional function
506 This function builds a string that explains how to restore the previous
507 state of the windows after a help command. After building the message,
508 it applies @var{function} to it if @var{function} is non-@code{nil}.
509 Otherwise it calls @code{message} to display it in the echo area.
511 This function expects to be called inside a
512 @code{with-output-to-temp-buffer} special form, and expects
513 @code{standard-output} to have the value bound by that special form.
514 For an example of its use, see the long example in @ref{Accessing
519 The value of this variable is the help character---the character that
520 Emacs recognizes as meaning Help. By default, it is 8, which is
521 @kbd{C-h}. When Emacs reads this character, if @code{help-form} is
522 non-@code{nil} Lisp expression, it evaluates that expression, and
523 displays the result in a window if it is a string.
525 Usually the value of @code{help-form}'s value is @code{nil}. Then the
526 help character has no special meaning at the level of command input, and
527 it becomes part of a key sequence in the normal way. The standard key
528 binding of @kbd{C-h} is a prefix key for several general-purpose help
531 The help character is special after prefix keys, too. If it has no
532 binding as a subcommand of the prefix key, it runs
533 @code{describe-prefix-bindings}, which displays a list of all the
534 subcommands of the prefix key.
538 If this variable is non-@code{nil}, its value is a form to evaluate
539 whenever the character @code{help-char} is read. If evaluating the form
540 produces a string, that string is displayed.
542 A command that calls @code{read-event} or @code{read-char} probably
543 should bind @code{help-form} to a non-@code{nil} expression while it
544 does input. (The exception is when @kbd{C-h} is meaningful input.)
545 Evaluating this expression should result in a string that explains what
546 the input is for and how to enter it properly.
548 Entry to the minibuffer binds this variable to the value of
549 @code{minibuffer-help-form} (@pxref{Minibuffer Misc}).
552 @defvar prefix-help-command
553 This variable holds a function to print help for a prefix character.
554 The function is called when the user types a prefix key followed by the
555 help character, and the help character has no binding after that prefix.
556 The variable's default value is @code{describe-prefix-bindings}.
559 @defun describe-prefix-bindings
560 This function calls @code{describe-bindings} to display a list of all
561 the subcommands of the prefix key of the most recent key sequence. The
562 prefix described consists of all but the last event of that key
563 sequence. (The last event is, presumably, the help character.)
566 The following two functions are found in the library @file{helper}.
567 They are for modes that want to provide help without relinquishing
568 control, such as the ``electric'' modes. You must load that library
569 with @code{(require 'helper)} in order to use them. Their names begin
570 with @samp{Helper} to distinguish them from the ordinary help functions.
572 @deffn Command Helper-describe-bindings
573 This command pops up a window displaying a help buffer containing a
574 listing of all of the key bindings from both the local and global keymaps.
575 It works by calling @code{describe-bindings}.
578 @deffn Command Helper-help
579 This command provides help for the current mode. It prompts the user
580 in the minibuffer with the message @samp{Help (Type ? for further
581 options)}, and then provides assistance in finding out what the key
582 bindings are, and what the mode is intended for. It returns @code{nil}.
584 This can be customized by changing the map @code{Helper-help-map}.
588 @defvar data-directory
589 This variable holds the name of the directory in which Emacs finds
590 certain documentation and text files that come with Emacs. In older
591 Emacs versions, @code{exec-directory} was used for this.
595 @defmac make-help-screen fname help-line help-text help-map
596 This macro defines a help command named @var{fname} that acts like a
597 prefix key that shows a list of the subcommands it offers.
599 When invoked, @var{fname} displays @var{help-text} in a window, then
600 reads and executes a key sequence according to @var{help-map}. The
601 string @var{help-text} should describe the bindings available in
604 The command @var{fname} is defined to handle a few events itself, by
605 scrolling the display of @var{help-text}. When @var{fname} reads one of
606 those special events, it does the scrolling and then reads another
607 event. When it reads an event that is not one of those few, and which
608 has a binding in @var{help-map}, it executes that key's binding and
611 The argument @var{help-line} should be a single-line summary of the
612 alternatives in @var{help-map}. In the current version of Emacs, this
613 argument is used only if you set the option @code{three-step-help} to
617 @defopt three-step-help
618 If this variable is non-@code{nil}, commands defined with
619 @code{make-help-screen} display their @var{help-line} strings in the
620 echo area at first, and display the longer @var{help-text} strings only
621 if the user types the help character again.