1 @c -*- mode: texinfo; coding: utf-8 -*-
2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2015 Free Software
5 @c See the file elisp.texi for copying conditions.
8 @cindex documentation strings
10 GNU Emacs has convenient built-in help facilities, most of which
11 derive their information from documentation strings associated with
12 functions and variables. This chapter describes how to access
13 documentation strings in Lisp programs.
15 The contents of a documentation string should follow certain
16 conventions. In particular, its first line should be a complete
17 sentence (or two complete sentences) that briefly describes what the
18 function or variable does. @xref{Documentation Tips}, for how to
19 write good documentation strings.
21 Note that the documentation strings for Emacs are not the same thing
22 as the Emacs manual. Manuals have their own source files, written in
23 the Texinfo language; documentation strings are specified in the
24 definitions of the functions and variables they apply to. A collection
25 of documentation strings is not sufficient as a manual because a good
26 manual is not organized in that fashion; it is organized in terms of
29 For commands to display documentation strings, see @ref{Help, ,
30 Help, emacs, The GNU Emacs Manual}.
33 * Documentation Basics:: Where doc strings are defined and stored.
34 * Accessing Documentation:: How Lisp programs can access doc strings.
35 * Keys in Documentation:: Substituting current key bindings.
36 * Describing Characters:: Making printable descriptions of
37 non-printing characters and key sequences.
38 * Help Functions:: Subroutines used by Emacs help facilities.
41 @node Documentation Basics
42 @section Documentation Basics
43 @cindex documentation conventions
44 @cindex writing a documentation string
45 @cindex string, writing a doc string
47 A documentation string is written using the Lisp syntax for strings,
48 with double-quote characters surrounding the text. It is, in fact, an
49 actual Lisp string. When the string appears in the proper place in a
50 function or variable definition, it serves as the function's or
51 variable's documentation.
53 @cindex @code{function-documentation} property
54 In a function definition (a @code{lambda} or @code{defun} form), the
55 documentation string is specified after the argument list, and is
56 normally stored directly in the function object. @xref{Function
57 Documentation}. You can also put function documentation in the
58 @code{function-documentation} property of a function name
59 (@pxref{Accessing Documentation}).
61 @cindex @code{variable-documentation} property
62 In a variable definition (a @code{defvar} form), the documentation
63 string is specified after the initial value. @xref{Defining
64 Variables}. The string is stored in the variable's
65 @code{variable-documentation} property.
67 @cindex @file{DOC} (documentation) file
68 Sometimes, Emacs does not keep documentation strings in memory.
69 There are two such circumstances. Firstly, to save memory, the
70 documentation for preloaded functions and variables (including
71 primitives) is kept in a file named @file{DOC}, in the directory
72 specified by @code{doc-directory} (@pxref{Accessing Documentation}).
73 Secondly, when a function or variable is loaded from a byte-compiled
74 file, Emacs avoids loading its documentation string (@pxref{Docs and
75 Compilation}). In both cases, Emacs looks up the documentation string
76 from the file only when needed, such as when the user calls @kbd{C-h
77 f} (@code{describe-function}) for a function.
79 Documentation strings can contain special @dfn{key substitution
80 sequences}, referring to key bindings which are looked up only when
81 the user views the documentation. This allows the help commands to
82 display the correct keys even if a user rearranges the default key
83 bindings. @xref{Keys in Documentation}.
85 In the documentation string of an autoloaded command
86 (@pxref{Autoload}), these key-substitution sequences have an
87 additional special effect: they cause @kbd{C-h f} on the command to
88 trigger autoloading. (This is needed for correctly setting up the
89 hyperlinks in the @file{*Help*} buffer.)
91 @node Accessing Documentation
92 @section Access to Documentation Strings
93 @cindex accessing documentation strings
95 @defun documentation-property symbol property &optional verbatim
96 This function returns the documentation string recorded in
97 @var{symbol}'s property list under property @var{property}. It is
98 most often used to look up the documentation strings of variables, for
99 which @var{property} is @code{variable-documentation}. However, it
100 can also be used to look up other kinds of documentation, such as for
101 customization groups (but for function documentation, use the
102 @code{documentation} function, below).
104 If the property value refers to a documentation string stored in the
105 @file{DOC} file or a byte-compiled file, this function looks up that
106 string and returns it.
108 If the property value isn't @code{nil}, isn't a string, and doesn't
109 refer to text in a file, then it is evaluated as a Lisp expression to
112 Finally, this function passes the string through
113 @code{substitute-command-keys} to substitute key bindings (@pxref{Keys
114 in Documentation}). It skips this step if @var{verbatim} is
119 (documentation-property 'command-line-processed
120 'variable-documentation)
121 @result{} "Non-nil once command line has been processed"
124 (symbol-plist 'command-line-processed)
125 @result{} (variable-documentation 188902)
128 (documentation-property 'emacs 'group-documentation)
129 @result{} "Customization of the One True Editor."
134 @defun documentation function &optional verbatim
135 This function returns the documentation string of @var{function}. It
136 handles macros, named keyboard macros, and special forms, as well as
139 If @var{function} is a symbol, this function first looks for the
140 @code{function-documentation} property of that symbol; if that has a
141 non-@code{nil} value, the documentation comes from that value (if the
142 value is not a string, it is evaluated).
144 If @var{function} is not a symbol, or if it has no
145 @code{function-documentation} property, then @code{documentation}
146 extracts the documentation string from the actual function definition,
147 reading it from a file if called for.
149 Finally, unless @var{verbatim} is non-@code{nil}, this function calls
150 @code{substitute-command-keys}. The result is the documentation
153 The @code{documentation} function signals a @code{void-function} error
154 if @var{function} has no function definition. However, it is OK if
155 the function definition has no documentation string. In that case,
156 @code{documentation} returns @code{nil}.
159 @defun face-documentation face
160 This function returns the documentation string of @var{face} as a
164 Here is an example of using the two functions, @code{documentation} and
165 @code{documentation-property}, to display the documentation strings for
166 several symbols in a @file{*Help*} buffer.
168 @anchor{describe-symbols example}
171 (defun describe-symbols (pattern)
172 "Describe the Emacs Lisp symbols matching PATTERN.
173 All symbols that have PATTERN in their name are described
174 in the *Help* buffer."
175 (interactive "sDescribe symbols matching: ")
181 ;; @r{Print description of symbol.}
182 (if (fboundp s) ; @r{It is a function.}
184 (format "%s\t%s\n%s\n\n" s
186 (let ((keys (where-is-internal s)))
190 (mapconcat 'key-description
196 (or (documentation s)
199 (if (boundp s) ; @r{It is a variable.}
203 (format "%s\t%s\n%s\n\n" s
204 (if (custom-variable-p s)
205 "Option " "Variable")
208 (or (documentation-property
209 s 'variable-documentation)
210 "not documented")))))))
215 ;; @r{Build a list of symbols that match pattern.}
218 (if (string-match pattern (symbol-name sym))
219 (setq sym-list (cons sym sym-list))))))
223 ;; @r{Display the data.}
224 (help-setup-xref (list 'describe-symbols pattern) (interactive-p))
225 (with-help-window (help-buffer)
226 (mapcar describe-func (sort sym-list 'string<)))))
230 The @code{describe-symbols} function works like @code{apropos},
231 but provides more information.
235 (describe-symbols "goal")
237 ---------- Buffer: *Help* ----------
239 Semipermanent goal column for vertical motion, as set by @dots{}
241 @c Do not blithely break or fill these lines.
242 @c That makes them incorrect.
245 minibuffer-temporary-goal-position Variable
250 set-goal-column Keys: C-x C-n
251 Set the current horizontal position as a goal for C-n and C-p.
253 @c DO NOT put a blank line here! That is factually inaccurate!
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 ARG, 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’.
265 temporary-goal-column Variable
266 Current goal column for vertical motion.
267 It is the column where point was at the start of the current run
268 of vertical motion commands.
270 When moving by visual lines via the function ‘line-move-visual’, it is a cons
271 cell (COL . HSCROLL), where COL is the x-position, in pixels,
272 divided by the default column width, and HSCROLL is the number of
273 columns by which window is scrolled from left margin.
275 When the ‘track-eol’ feature is doing its job, the value is
276 ‘most-positive-fixnum’.
277 ---------- Buffer: *Help* ----------
281 @anchor{Definition of Snarf-documentation}
282 @defun Snarf-documentation filename
283 This function is used when building Emacs, just before the runnable
284 Emacs is dumped. It finds the positions of the documentation strings
285 stored in the file @var{filename}, and records those positions into
286 memory in the function definitions and variable property lists.
287 @xref{Building Emacs}.
289 Emacs reads the file @var{filename} from the @file{emacs/etc} directory.
290 When the dumped Emacs is later executed, the same file will be looked
291 for in the directory @code{doc-directory}. Usually @var{filename} is
295 @defvar doc-directory
296 This variable holds the name of the directory which should contain the
297 file @code{"DOC"} that contains documentation strings for
298 built-in and preloaded functions and variables.
300 In most cases, this is the same as @code{data-directory}. They may be
301 different when you run Emacs from the directory where you built it,
302 without actually installing it. @xref{Definition of data-directory}.
305 @node Keys in Documentation
306 @section Substituting Key Bindings in Documentation
307 @cindex documentation, keys in
308 @cindex keys in documentation strings
309 @cindex substituting keys in documentation
310 @cindex key substitution sequence
312 When documentation strings refer to key sequences, they should use the
313 current, actual key bindings. They can do so using certain special text
314 sequences described below. Accessing documentation strings in the usual
315 way substitutes current key binding information for these special
316 sequences. This works by calling @code{substitute-command-keys}. You
317 can also call that function yourself.
319 Here is a list of the special sequences and what they mean:
322 @item \[@var{command}]
323 stands for a key sequence that will invoke @var{command}, or @samp{M-x
324 @var{command}} if @var{command} has no key bindings.
326 @item \@{@var{mapvar}@}
327 stands for a summary of the keymap which is the value of the variable
328 @var{mapvar}. The summary is made using @code{describe-bindings}.
330 @item \<@var{mapvar}>
331 stands for no text itself. It is used only for a side effect: it
332 specifies @var{mapvar}'s value as the keymap for any following
333 @samp{\[@var{command}]} sequences in this documentation string.
337 (left single quotation mark and grave accent) both stand for a left quote.
341 (right single quotation mark and apostrophe) both stand for a right quote.
344 quotes the following character and is discarded; thus, @samp{\=`} puts
345 @samp{`} into the output, @samp{\=\[} puts @samp{\[} into the output,
346 and @samp{\=\=} puts @samp{\=} into the output.
349 @strong{Please note:} Each @samp{\} must be doubled when written in a
350 string in Emacs Lisp.
352 @defvar text-quoting-style
353 @cindex curved quotes
355 The value of this variable is a symbol that specifies the style Emacs
356 should use for single quotes in the wording of help and messages.
357 If the variable's value is @code{curve}, the style is
358 @t{‘like this’} with curved single quotes. If the value is
359 @code{straight}, the style is @t{'like this'} with straight
360 apostrophes. If the value is @code{grave}, the style is @t{`like
361 this'} with grave accent and apostrophe. The default value @code{nil}
362 acts like @code{curve} if curved single quotes are displayable, and
363 like @code{grave} otherwise. To use the traditional @code{grave}
364 style, put the line @code{(setq text-quoting-style 'grave)} into your
365 @file{~/.emacs} file.
368 @defun substitute-command-keys string
369 This function scans @var{string} for the above special sequences and
370 replaces them by what they stand for, returning the result as a string.
371 This permits display of documentation that refers accurately to the
372 user's own customized key bindings.
374 @cindex advertised binding
375 If a command has multiple bindings, this function normally uses the
376 first one it finds. You can specify one particular key binding by
377 assigning an @code{:advertised-binding} symbol property to the
381 (put 'undo :advertised-binding [?\C-/])
385 The @code{:advertised-binding} property also affects the binding shown
386 in menu items (@pxref{Menu Bar}). The property is ignored if it
387 specifies a key binding that the command does not actually have.
390 Here are examples of the special sequences:
394 (substitute-command-keys
395 "To abort recursive edit, type `\\[abort-recursive-edit]'.")
396 @result{} "To abort recursive edit, type ‘C-]’."
400 (substitute-command-keys
401 "The keys that are defined for the minibuffer here are:
402 \\@{minibuffer-local-must-match-map@}")
403 @result{} "The keys that are defined for the minibuffer here are:
406 ? minibuffer-completion-help
407 SPC minibuffer-complete-word
408 TAB minibuffer-complete
409 C-j minibuffer-complete-and-exit
410 RET minibuffer-complete-and-exit
411 C-g abort-recursive-edit
415 (substitute-command-keys
416 "To abort a recursive edit from the minibuffer, type \
417 `\\<minibuffer-local-must-match-map>\\[abort-recursive-edit]'.")
418 @result{} "To abort a recursive edit from the minibuffer, type ‘C-g’."
422 There are other special conventions for the text in documentation
423 strings---for instance, you can refer to functions, variables, and
424 sections of this manual. @xref{Documentation Tips}, for details.
426 @node Describing Characters
427 @section Describing Characters for Help Messages
428 @cindex describe characters and events
430 These functions convert events, key sequences, or characters to
431 textual descriptions. These descriptions are useful for including
432 arbitrary text characters or key sequences in messages, because they
433 convert non-printing and whitespace characters to sequences of printing
434 characters. The description of a non-whitespace printing character is
435 the character itself.
437 @defun key-description sequence &optional prefix
438 @cindex Emacs event standard notation
439 This function returns a string containing the Emacs standard notation
440 for the input events in @var{sequence}. If @var{prefix} is
441 non-@code{nil}, it is a sequence of input events leading up to
442 @var{sequence} and is included in the return value. Both arguments
443 may be strings, vectors or lists. @xref{Input Events}, for more
444 information about valid events.
448 (key-description [?\M-3 delete])
449 @result{} "M-3 <delete>"
452 (key-description [delete] "\M-3")
453 @result{} "M-3 <delete>"
457 See also the examples for @code{single-key-description}, below.
460 @defun single-key-description event &optional no-angles
461 @cindex event printing
462 @cindex character printing
463 @cindex control character printing
464 @cindex meta character printing
465 This function returns a string describing @var{event} in the standard
466 Emacs notation for keyboard input. A normal printing character
467 appears as itself, but a control character turns into a string
468 starting with @samp{C-}, a meta character turns into a string starting
469 with @samp{M-}, and space, tab, etc., appear as @samp{SPC},
470 @samp{TAB}, etc. A function key symbol appears inside angle brackets
471 @samp{<@dots{}>}. An event that is a list appears as the name of the
472 symbol in the @sc{car} of the list, inside angle brackets.
474 If the optional argument @var{no-angles} is non-@code{nil}, the angle
475 brackets around function keys and event symbols are omitted; this is
476 for compatibility with old versions of Emacs which didn't use the
481 (single-key-description ?\C-x)
485 (key-description "\C-x \M-y \n \t \r \f123")
486 @result{} "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
489 (single-key-description 'delete)
493 (single-key-description 'C-mouse-1)
494 @result{} "<C-mouse-1>"
497 (single-key-description 'C-mouse-1 t)
498 @result{} "C-mouse-1"
503 @defun text-char-description character
504 This function returns a string describing @var{character} in the
505 standard Emacs notation for characters that appear in text---like
506 @code{single-key-description}, except that control characters are
507 represented with a leading caret (which is how control characters in
508 Emacs buffers are usually displayed). Another difference is that
509 @code{text-char-description} recognizes the 2**7 bit as the Meta
510 character, whereas @code{single-key-description} uses the 2**27 bit
515 (text-char-description ?\C-c)
519 (text-char-description ?\M-m)
523 (text-char-description ?\C-\M-m)
527 (text-char-description (+ 128 ?m))
531 (text-char-description (+ 128 ?\C-m))
537 @deffn Command read-kbd-macro string &optional need-vector
538 This function is used mainly for operating on keyboard macros, but it
539 can also be used as a rough inverse for @code{key-description}. You
540 call it with a string containing key descriptions, separated by spaces;
541 it returns a string or vector containing the corresponding events.
542 (This may or may not be a single valid key sequence, depending on what
543 events you use; @pxref{Key Sequences}.) If @var{need-vector} is
544 non-@code{nil}, the return value is always a vector.
548 @section Help Functions
549 @cindex help functions
551 Emacs provides a variety of built-in help functions, all accessible to
552 the user as subcommands of the prefix @kbd{C-h}. For more information
553 about them, see @ref{Help, , Help, emacs, The GNU Emacs Manual}. Here
554 we describe some program-level interfaces to the same information.
556 @deffn Command apropos pattern &optional do-all
557 This function finds all meaningful symbols whose names contain a
558 match for the apropos pattern @var{pattern}. An apropos pattern is
559 either a word to match, a space-separated list of words of which at
560 least two must match, or a regular expression (if any special regular
561 expression characters occur). A symbol is meaningful if it has a
562 definition as a function, variable, or face, or has properties.
564 The function returns a list of elements that look like this:
567 (@var{symbol} @var{score} @var{function-doc} @var{variable-doc}
568 @var{plist-doc} @var{widget-doc} @var{face-doc} @var{group-doc})
571 Here, @var{score} is an integer measure of how important the symbol
572 seems to be as a match. Each of the remaining elements is a
573 documentation string, or @code{nil}, for @var{symbol} as a function,
576 It also displays the symbols in a buffer named @file{*Apropos*}, each
577 with a one-line description taken from the beginning of its
578 documentation string.
580 If @var{do-all} is non-@code{nil}, or if the user option
581 @code{apropos-do-all} is non-@code{nil}, then @code{apropos} also
582 shows key bindings for the functions that are found; it also shows
583 @emph{all} interned symbols, not just meaningful ones (and it lists
584 them in the return value as well).
588 The value of this variable is a local keymap for characters following the
592 @deffn {Prefix Command} help-command
593 This symbol is not a function; its function definition cell holds the
594 keymap known as @code{help-map}. It is defined in @file{help.el} as
599 (define-key global-map (string help-char) 'help-command)
600 (fset 'help-command help-map)
606 The value of this variable is the help character---the character that
607 Emacs recognizes as meaning Help. By default, its value is 8, which
608 stands for @kbd{C-h}. When Emacs reads this character, if
609 @code{help-form} is a non-@code{nil} Lisp expression, it evaluates that
610 expression, and displays the result in a window if it is a string.
612 Usually the value of @code{help-form} is @code{nil}. Then the
613 help character has no special meaning at the level of command input, and
614 it becomes part of a key sequence in the normal way. The standard key
615 binding of @kbd{C-h} is a prefix key for several general-purpose help
618 The help character is special after prefix keys, too. If it has no
619 binding as a subcommand of the prefix key, it runs
620 @code{describe-prefix-bindings}, which displays a list of all the
621 subcommands of the prefix key.
624 @defopt help-event-list
625 The value of this variable is a list of event types that serve as
626 alternative help characters. These events are handled just like the
627 event specified by @code{help-char}.
631 If this variable is non-@code{nil}, its value is a form to evaluate
632 whenever the character @code{help-char} is read. If evaluating the form
633 produces a string, that string is displayed.
635 A command that calls @code{read-event}, @code{read-char-choice}, or
636 @code{read-char} probably should bind @code{help-form} to a
637 non-@code{nil} expression while it does input. (The time when you
638 should not do this is when @kbd{C-h} has some other meaning.)
639 Evaluating this expression should result in a string that explains
640 what the input is for and how to enter it properly.
642 Entry to the minibuffer binds this variable to the value of
643 @code{minibuffer-help-form} (@pxref{Definition of minibuffer-help-form}).
646 @defvar prefix-help-command
647 This variable holds a function to print help for a prefix key. The
648 function is called when the user types a prefix key followed by the help
649 character, and the help character has no binding after that prefix. The
650 variable's default value is @code{describe-prefix-bindings}.
653 @deffn Command describe-prefix-bindings
654 This function calls @code{describe-bindings} to display a list of all
655 the subcommands of the prefix key of the most recent key sequence. The
656 prefix described consists of all but the last event of that key
657 sequence. (The last event is, presumably, the help character.)
660 The following two functions are meant for modes that want to provide
661 help without relinquishing control, such as the electric modes.
662 Their names begin with @samp{Helper} to distinguish them from the
663 ordinary help functions.
665 @deffn Command Helper-describe-bindings
666 This command pops up a window displaying a help buffer containing a
667 listing of all of the key bindings from both the local and global keymaps.
668 It works by calling @code{describe-bindings}.
671 @deffn Command Helper-help
672 This command provides help for the current mode. It prompts the user
673 in the minibuffer with the message @samp{Help (Type ? for further
674 options)}, and then provides assistance in finding out what the key
675 bindings are, and what the mode is intended for. It returns @code{nil}.
677 @vindex Helper-help-map
678 This can be customized by changing the map @code{Helper-help-map}.
681 @defvar data-directory
682 @anchor{Definition of data-directory}
683 This variable holds the name of the directory in which Emacs finds
684 certain documentation and text files that come with Emacs.
688 This function returns the name of the help buffer, which is normally
689 @file{*Help*}; if such a buffer does not exist, it is first created.
692 @vindex help-window-select
693 @defmac with-help-window buffer-name body@dots{}
694 This macro evaluates @var{body} like @code{with-output-to-temp-buffer}
695 (@pxref{Temporary Displays}), inserting any output produced by its forms
696 into a buffer named @var{buffer-name}. (Usually, @var{buffer-name}
697 should be the value returned by the function @code{help-buffer}.) It
698 also puts the specified buffer into Help mode and displays a message
699 telling the user how to quit and scroll the help window. It selects the
700 help window if the current value of the user option
701 @code{help-window-select} has been set accordingly. It returns the last
705 @defun help-setup-xref item interactive-p
706 This function updates the cross reference data in the @file{*Help*}
707 buffer, which is used to regenerate the help information when the user
708 clicks on the @samp{Back} or @samp{Forward} buttons. Most commands
709 that use the @file{*Help*} buffer should invoke this function before
710 clearing the buffer. The @var{item} argument should have the form
711 @code{(@var{function} . @var{args})}, where @var{function} is a function
712 to call, with argument list @var{args}, to regenerate the help buffer.
713 The @var{interactive-p} argument is non-@code{nil} if the calling
714 command was invoked interactively; in that case, the stack of items
715 for the @file{*Help*} buffer's @samp{Back} buttons is cleared.
718 @xref{describe-symbols example}, for an example of using
719 @code{help-buffer}, @code{with-help-window}, and
720 @code{help-setup-xref}.
722 @defmac make-help-screen fname help-line help-text help-map
723 This macro defines a help command named @var{fname} that acts like a
724 prefix key that shows a list of the subcommands it offers.
726 When invoked, @var{fname} displays @var{help-text} in a window, then
727 reads and executes a key sequence according to @var{help-map}. The
728 string @var{help-text} should describe the bindings available in
731 The command @var{fname} is defined to handle a few events itself, by
732 scrolling the display of @var{help-text}. When @var{fname} reads one of
733 those special events, it does the scrolling and then reads another
734 event. When it reads an event that is not one of those few, and which
735 has a binding in @var{help-map}, it executes that key's binding and
738 The argument @var{help-line} should be a single-line summary of the
739 alternatives in @var{help-map}. In the current version of Emacs, this
740 argument is used only if you set the option @code{three-step-help} to
743 This macro is used in the command @code{help-for-help} which is the
744 binding of @kbd{C-h C-h}.
747 @defopt three-step-help
748 If this variable is non-@code{nil}, commands defined with
749 @code{make-help-screen} display their @var{help-line} strings in the
750 echo area at first, and display the longer @var{help-text} strings only
751 if the user types the help character again.