2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../../info/modes
6 @node Modes, Documentation, Keymaps, Top
7 @chapter Major and Minor Modes
10 A @dfn{mode} is a set of definitions that customize Emacs and can be
11 turned on and off while you edit. There are two varieties of modes:
12 @dfn{major modes}, which are mutually exclusive and used for editing
13 particular kinds of text, and @dfn{minor modes}, which provide features
14 that users can enable individually.
16 This chapter describes how to write both major and minor modes, how to
17 indicate them in the mode line, and how they run hooks supplied by the
18 user. For related topics such as keymaps and syntax tables, see
19 @ref{Keymaps}, and @ref{Syntax Tables}.
22 * Hooks:: How to use hooks; how to write code that provides hooks.
23 * Major Modes:: Defining major modes.
24 * Minor Modes:: Defining minor modes.
25 * Mode Line Format:: Customizing the text that appears in the mode line.
26 * Imenu:: Providing a menu of definitions made in a buffer.
27 * Font Lock Mode:: How modes can highlight text according to syntax.
28 * Auto-Indentation:: How to teach Emacs to indent for a major mode.
29 * Desktop Save Mode:: How modes can have buffer state saved between
37 A @dfn{hook} is a variable where you can store a function or functions
38 to be called on a particular occasion by an existing program. Emacs
39 provides hooks for the sake of customization. Most often, hooks are set
40 up in the init file (@pxref{Init File}), but Lisp programs can set them also.
41 @xref{Standard Hooks}, for a list of standard hook variables.
44 Most of the hooks in Emacs are @dfn{normal hooks}. These variables
45 contain lists of functions to be called with no arguments. By
46 convention, whenever the hook name ends in @samp{-hook}, that tells
47 you it is normal. We try to make all hooks normal, as much as
48 possible, so that you can use them in a uniform way.
50 Every major mode command is supposed to run a normal hook called the
51 @dfn{mode hook} as the one of the last steps of initialization. This
52 makes it easy for a user to customize the behavior of the mode, by
53 overriding the buffer-local variable assignments already made by the
54 mode. Most minor mode functions also run a mode hook at the end. But
55 hooks are used in other contexts too. For example, the hook
56 @code{suspend-hook} runs just before Emacs suspends itself
57 (@pxref{Suspending Emacs}).
59 The recommended way to add a hook function to a normal hook is by
60 calling @code{add-hook} (see below). The hook functions may be any of
61 the valid kinds of functions that @code{funcall} accepts (@pxref{What
62 Is a Function}). Most normal hook variables are initially void;
63 @code{add-hook} knows how to deal with this. You can add hooks either
64 globally or buffer-locally with @code{add-hook}.
67 If the hook variable's name does not end with @samp{-hook}, that
68 indicates it is probably an @dfn{abnormal hook}. That means the hook
69 functions are called with arguments, or their return values are used
70 in some way. The hook's documentation says how the functions are
71 called. You can use @code{add-hook} to add a function to an abnormal
72 hook, but you must write the function to follow the hook's calling
75 By convention, abnormal hook names end in @samp{-functions} or
76 @samp{-hooks}. If the variable's name ends in @samp{-function}, then
77 its value is just a single function, not a list of functions.
80 * Running Hooks:: How to run a hook.
81 * Setting Hooks:: How to put functions on a hook, or remove them.
85 @subsection Running Hooks
87 In this section, we document the @code{run-hooks} function, which is
88 used to run a normal hook. We also document the functions for running
89 various kinds of abnormal hooks.
91 @defun run-hooks &rest hookvars
92 This function takes one or more normal hook variable names as
93 arguments, and runs each hook in turn. Each argument should be a
94 symbol that is a normal hook variable. These arguments are processed
95 in the order specified.
97 If a hook variable has a non-@code{nil} value, that value should be a
98 list of functions. @code{run-hooks} calls all the functions, one by
99 one, with no arguments.
101 The hook variable's value can also be a single function---either a
102 lambda expression or a symbol with a function definition---which
103 @code{run-hooks} calls. But this usage is obsolete.
105 If the hook variable is buffer-local, the buffer-local variable will
106 be used instead of the global variable. However, if the buffer-local
107 variable contains the element @code{t}, the global hook variable will
111 @defun run-hook-with-args hook &rest args
112 This function runs an abnormal hook by calling all the hook functions in
113 @var{hook}, passing each one the arguments @var{args}.
116 @defun run-hook-with-args-until-failure hook &rest args
117 This function runs an abnormal hook by calling each hook function in
118 turn, stopping if one of them ``fails'' by returning @code{nil}. Each
119 hook function is passed the arguments @var{args}. If this function
120 stops because one of the hook functions fails, it returns @code{nil};
121 otherwise it returns a non-@code{nil} value.
124 @defun run-hook-with-args-until-success hook &rest args
125 This function runs an abnormal hook by calling each hook function,
126 stopping if one of them ``succeeds'' by returning a non-@code{nil}
127 value. Each hook function is passed the arguments @var{args}. If this
128 function stops because one of the hook functions returns a
129 non-@code{nil} value, it returns that value; otherwise it returns
133 @defmac with-wrapper-hook hook args &rest body
134 This macro runs the abnormal hook @code{hook} as a series of nested
135 ``wrapper functions'' around the @var{body} forms. The effect is
136 similar to nested @code{around} advices (@pxref{Around-Advice}).
138 Each hook function must accept an argument list consisting of a function
139 @var{fun}, followed by the additional arguments listed in @var{args}.
140 The function @var{fun} passed to the very first hook function in
141 @var{hook} does the same as @var{body}, if it is called with arguments
142 @var{args}. The @var{fun} passed to each successive hook function is
143 constructed from all the preceding hook functions (and @var{body}); if
144 this @var{fun} is called with arguments @var{args}, it does what the
145 @code{with-wrapper-hook} call would if the preceding hook functions were
146 the only ones in @var{hook}.
148 In the function definition of the hook function, @var{fun} can be called
149 any number of times (including not calling it at all). This function
150 definition is then used to construct the @var{fun} passed to the next
151 hook function in @var{hook}, if any. The last or ``outermost''
152 @var{fun} is called once to produce the effect.
156 @subsection Setting Hooks
158 Here's an example that uses a mode hook to turn on Auto Fill mode when
159 in Lisp Interaction mode:
162 (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
165 @defun add-hook hook function &optional append local
166 This function is the handy way to add function @var{function} to hook
167 variable @var{hook}. You can use it for abnormal hooks as well as for
168 normal hooks. @var{function} can be any Lisp function that can accept
169 the proper number of arguments for @var{hook}. For example,
172 (add-hook 'text-mode-hook 'my-text-hook-function)
176 adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}.
178 If @var{function} is already present in @var{hook} (comparing using
179 @code{equal}), then @code{add-hook} does not add it a second time.
181 If @var{function} has a non-@code{nil} property
182 @code{permanent-local-hook}, then @code{kill-all-local-variables} (or
183 changing major modes) won't delete it from the hook variable's local
186 It is best to design your hook functions so that the order in which
187 they are executed does not matter. Any dependence on the order is
188 asking for trouble. However, the order is predictable: normally,
189 @var{function} goes at the front of the hook list, so it will be
190 executed first (barring another @code{add-hook} call). If the
191 optional argument @var{append} is non-@code{nil}, the new hook
192 function goes at the end of the hook list and will be executed last.
194 @code{add-hook} can handle the cases where @var{hook} is void or its
195 value is a single function; it sets or changes the value to a list of
198 If @var{local} is non-@code{nil}, that says to add @var{function} to the
199 buffer-local hook list instead of to the global hook list. This makes
200 the hook buffer-local and adds @code{t} to the buffer-local value. The
201 latter acts as a flag to run the hook functions in the default value as
202 well as in the local value.
205 @defun remove-hook hook function &optional local
206 This function removes @var{function} from the hook variable
207 @var{hook}. It compares @var{function} with elements of @var{hook}
208 using @code{equal}, so it works for both symbols and lambda
211 If @var{local} is non-@code{nil}, that says to remove @var{function}
212 from the buffer-local hook list instead of from the global hook list.
219 @cindex major mode command
220 Major modes specialize Emacs for editing particular kinds of text.
221 Each buffer has one major mode at a time. Every major mode is
222 associated with a @dfn{major mode command}, whose name should end in
223 @samp{-mode}. This command takes care of switching to that mode in the
224 current buffer, by setting various buffer-local variables such as a
225 local keymap. @xref{Major Mode Conventions}.
227 The least specialized major mode is called @dfn{Fundamental mode},
228 which has no mode-specific definitions or variable settings.
230 @deffn Command fundamental-mode
231 This is the major mode command for Fundamental mode. Unlike other mode
232 commands, it does @emph{not} run any mode hooks (@pxref{Major Mode
233 Conventions}), since you are not supposed to customize this mode.
236 The easiest way to write a major mode is to use the macro
237 @code{define-derived-mode}, which sets up the new mode as a variant of
238 an existing major mode. @xref{Derived Modes}. We recommend using
239 @code{define-derived-mode} even if the new mode is not an obvious
240 derivative of another mode, as it automatically enforces many coding
241 conventions for you. @xref{Basic Major Modes}, for common modes to
244 The standard GNU Emacs Lisp directory tree contains the code for
245 several major modes, in files such as @file{text-mode.el},
246 @file{texinfo.el}, @file{lisp-mode.el}, and @file{rmail.el}. You can
247 study these libraries to see how modes are written.
250 The buffer-local value of this variable holds the symbol for the current
251 major mode. Its default value holds the default major mode for new
252 buffers. The standard default value is @code{fundamental-mode}.
254 If the default value is @code{nil}, then whenever Emacs creates a new
255 buffer via a command such as @kbd{C-x b} (@code{switch-to-buffer}), the
256 new buffer is put in the major mode of the previously current buffer.
257 As an exception, if the major mode of the previous buffer has a
258 @code{mode-class} symbol property with value @code{special}, the new
259 buffer is put in Fundamental mode (@pxref{Major Mode Conventions}).
263 * Major Mode Conventions:: Coding conventions for keymaps, etc.
264 * Auto Major Mode:: How Emacs chooses the major mode automatically.
265 * Mode Help:: Finding out how to use a mode.
266 * Derived Modes:: Defining a new major mode based on another major
268 * Basic Major Modes:: Modes that other modes are often derived from.
269 * Generic Modes:: Defining a simple major mode that supports
270 comment syntax and Font Lock mode.
271 * Mode Hooks:: Hooks run at the end of major mode commands.
272 * Example Major Modes:: Text mode and Lisp modes.
275 @node Major Mode Conventions
276 @subsection Major Mode Conventions
277 @cindex major mode conventions
278 @cindex conventions for writing major modes
280 The code for every major mode should follow various coding
281 conventions, including conventions for local keymap and syntax table
282 initialization, function and variable names, and hooks.
284 If you use the @code{define-derived-mode} macro, it will take care of
285 many of these conventions automatically. @xref{Derived Modes}. Note
286 also that fundamental mode is an exception to many of these conventions,
287 because its definition is to present the global state of Emacs.
289 The following list of conventions is only partial. Each major mode
290 should aim for consistency in general with other Emacs major modes, as
291 this makes Emacs as a whole more coherent. It is impossible to list
292 here all the possible points where this issue might come up; if the
293 Emacs developers point out an area where your major mode deviates from
294 the usual conventions, please make it compatible.
298 Define a major mode command whose name ends in @samp{-mode}. When
299 called with no arguments, this command should switch to the new mode in
300 the current buffer by setting up the keymap, syntax table, and
301 buffer-local variables in an existing buffer. It should not change the
305 Write a documentation string for this command that describes the special
306 commands available in this mode. @xref{Mode Help}.
308 The documentation string may include the special documentation
309 substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and
310 @samp{\<@var{keymap}>}, which allow the help display to adapt
311 automatically to the user's own key bindings. @xref{Keys in
315 The major mode command should start by calling
316 @code{kill-all-local-variables}. This runs the normal hook
317 @code{change-major-mode-hook}, then gets rid of the buffer-local
318 variables of the major mode previously in effect. @xref{Creating
322 The major mode command should set the variable @code{major-mode} to the
323 major mode command symbol. This is how @code{describe-mode} discovers
324 which documentation to print.
327 The major mode command should set the variable @code{mode-name} to the
328 ``pretty'' name of the mode, usually a string (but see @ref{Mode Line
329 Data}, for other possible forms). The name of the mode appears
333 @cindex functions in modes
334 Since all global names are in the same name space, all the global
335 variables, constants, and functions that are part of the mode should
336 have names that start with the major mode name (or with an abbreviation
337 of it if the name is long). @xref{Coding Conventions}.
340 In a major mode for editing some kind of structured text, such as a
341 programming language, indentation of text according to structure is
342 probably useful. So the mode should set @code{indent-line-function}
343 to a suitable function, and probably customize other variables
344 for indentation. @xref{Auto-Indentation}.
347 @cindex keymaps in modes
348 The major mode should usually have its own keymap, which is used as the
349 local keymap in all buffers in that mode. The major mode command should
350 call @code{use-local-map} to install this local map. @xref{Active
351 Keymaps}, for more information.
353 This keymap should be stored permanently in a global variable named
354 @code{@var{modename}-mode-map}. Normally the library that defines the
355 mode sets this variable.
357 @xref{Tips for Defining}, for advice about how to write the code to set
358 up the mode's keymap variable.
361 The key sequences bound in a major mode keymap should usually start with
362 @kbd{C-c}, followed by a control character, a digit, or @kbd{@{},
363 @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation
364 characters are reserved for minor modes, and ordinary letters are
367 A major mode can also rebind the keys @kbd{M-n}, @kbd{M-p} and
368 @kbd{M-s}. The bindings for @kbd{M-n} and @kbd{M-p} should normally
369 be some kind of ``moving forward and backward,'' but this does not
370 necessarily mean cursor motion.
372 It is legitimate for a major mode to rebind a standard key sequence if
373 it provides a command that does ``the same job'' in a way better
374 suited to the text this mode is used for. For example, a major mode
375 for editing a programming language might redefine @kbd{C-M-a} to
376 ``move to the beginning of a function'' in a way that works better for
379 It is also legitimate for a major mode to rebind a standard key
380 sequence whose standard meaning is rarely useful in that mode. For
381 instance, minibuffer modes rebind @kbd{M-r}, whose standard meaning is
382 rarely of any use in the minibuffer. Major modes such as Dired or
383 Rmail that do not allow self-insertion of text can reasonably redefine
384 letters and other printing characters as special commands.
387 Major modes for editing text should not define @key{RET} to do
388 anything other than insert a newline. However, it is ok for
389 specialized modes for text that users don't directly edit, such as
390 Dired and Info modes, to redefine @key{RET} to do something entirely
394 Major modes should not alter options that are primarily a matter of user
395 preference, such as whether Auto-Fill mode is enabled. Leave this to
396 each user to decide. However, a major mode should customize other
397 variables so that Auto-Fill mode will work usefully @emph{if} the user
401 @cindex syntax tables in modes
402 The mode may have its own syntax table or may share one with other
403 related modes. If it has its own syntax table, it should store this in
404 a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax
408 If the mode handles a language that has a syntax for comments, it should
409 set the variables that define the comment syntax. @xref{Options for
410 Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}.
413 @cindex abbrev tables in modes
414 The mode may have its own abbrev table or may share one with other
415 related modes. If it has its own abbrev table, it should store this
416 in a variable named @code{@var{modename}-mode-abbrev-table}. If the
417 major mode command defines any abbrevs itself, it should pass @code{t}
418 for the @var{system-flag} argument to @code{define-abbrev}.
419 @xref{Defining Abbrevs}.
422 The mode should specify how to do highlighting for Font Lock mode, by
423 setting up a buffer-local value for the variable
424 @code{font-lock-defaults} (@pxref{Font Lock Mode}).
427 Each face that the mode defines should, if possible, inherit from an
428 existing Emacs face. @xref{Basic Faces}, and @ref{Faces for Font Lock}.
431 The mode should specify how Imenu should find the definitions or
432 sections of a buffer, by setting up a buffer-local value for the
433 variable @code{imenu-generic-expression}, for the two variables
434 @code{imenu-prev-index-position-function} and
435 @code{imenu-extract-index-name-function}, or for the variable
436 @code{imenu-create-index-function} (@pxref{Imenu}).
439 The mode can specify a local value for
440 @code{eldoc-documentation-function} to tell ElDoc mode how to handle
444 The mode can specify how to complete various keywords by adding
445 to the special hook @code{completion-at-point-functions}.
448 Use @code{defvar} or @code{defcustom} to set mode-related variables, so
449 that they are not reinitialized if they already have a value. (Such
450 reinitialization could discard customizations made by the user.)
453 @cindex buffer-local variables in modes
454 To make a buffer-local binding for an Emacs customization variable, use
455 @code{make-local-variable} in the major mode command, not
456 @code{make-variable-buffer-local}. The latter function would make the
457 variable local to every buffer in which it is subsequently set, which
458 would affect buffers that do not use this mode. It is undesirable for a
459 mode to have such global effects. @xref{Buffer-Local Variables}.
461 With rare exceptions, the only reasonable way to use
462 @code{make-variable-buffer-local} in a Lisp package is for a variable
463 which is used only within that package. Using it on a variable used by
464 other packages would interfere with them.
468 @cindex major mode hook
469 Each major mode should have a normal @dfn{mode hook} named
470 @code{@var{modename}-mode-hook}. The very last thing the major mode command
471 should do is to call @code{run-mode-hooks}. This runs the mode hook,
472 and then runs the normal hook @code{after-change-major-mode-hook}.
476 The major mode command may start by calling some other major mode
477 command (called the @dfn{parent mode}) and then alter some of its
478 settings. A mode that does this is called a @dfn{derived mode}. The
479 recommended way to define one is to use the @code{define-derived-mode}
480 macro, but this is not required. Such a mode should call the parent
481 mode command inside a @code{delay-mode-hooks} form. (Using
482 @code{define-derived-mode} does this automatically.) @xref{Derived
483 Modes}, and @ref{Mode Hooks}.
486 If something special should be done if the user switches a buffer from
487 this mode to any other major mode, this mode can set up a buffer-local
488 value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}).
491 If this mode is appropriate only for specially-prepared text produced by
492 the mode itself (rather than by the user typing at the keyboard or by an
493 external file), then the major mode command symbol should have a
494 property named @code{mode-class} with value @code{special}, put on as
497 @kindex mode-class @r{(property)}
498 @cindex @code{special} modes
500 (put 'funny-mode 'mode-class 'special)
504 This tells Emacs that new buffers created while the current buffer is in
505 Funny mode should not be put in Funny mode, even though the default
506 value of @code{major-mode} is @code{nil}. By default, the value of
507 @code{nil} for @code{major-mode} means to use the current buffer's major
508 mode when creating new buffers (@pxref{Auto Major Mode}), but with such
509 @code{special} modes, Fundamental mode is used instead. Modes such as
510 Dired, Rmail, and Buffer List use this feature.
512 The @code{define-derived-mode} macro automatically marks the derived
513 mode as special if the parent mode is special. Special mode is a
514 convenient parent for such modes to inherit from; @xref{Basic Major
518 If you want to make the new mode the default for files with certain
519 recognizable names, add an element to @code{auto-mode-alist} to select
520 the mode for those file names (@pxref{Auto Major Mode}). If you
521 define the mode command to autoload, you should add this element in
522 the same file that calls @code{autoload}. If you use an autoload
523 cookie for the mode command, you can also use an autoload cookie for
524 the form that adds the element (@pxref{autoload cookie}). If you do
525 not autoload the mode command, it is sufficient to add the element in
526 the file that contains the mode definition.
529 In the comments that document the file, you should provide a sample
530 @code{autoload} form and an example of how to add to
531 @code{auto-mode-alist}, that users can include in their init files
536 The top-level forms in the file defining the mode should be written so
537 that they may be evaluated more than once without adverse consequences.
538 Even if you never load the file more than once, someone else will.
541 @node Auto Major Mode
542 @subsection How Emacs Chooses a Major Mode
543 @cindex major mode, automatic selection
545 Based on information in the file name or in the file itself, Emacs
546 automatically selects a major mode for the new buffer when a file is
547 visited. It also processes local variables specified in the file text.
549 @deffn Command normal-mode &optional find-file
550 This function establishes the proper major mode and buffer-local variable
551 bindings for the current buffer. First it calls @code{set-auto-mode}
552 (see below), then it runs @code{hack-local-variables} to parse, and
553 bind or evaluate as appropriate, the file's local variables
554 (@pxref{File Local Variables}).
556 If the @var{find-file} argument to @code{normal-mode} is non-@code{nil},
557 @code{normal-mode} assumes that the @code{find-file} function is calling
558 it. In this case, it may process local variables in the @samp{-*-}
559 line or at the end of the file. The variable
560 @code{enable-local-variables} controls whether to do so. @xref{File
561 Variables, , Local Variables in Files, emacs, The GNU Emacs Manual},
562 for the syntax of the local variables section of a file.
564 If you run @code{normal-mode} interactively, the argument
565 @var{find-file} is normally @code{nil}. In this case,
566 @code{normal-mode} unconditionally processes any file local variables.
568 The function calls @code{set-auto-mode} to choose a major mode. If this
569 does not specify a mode, the buffer stays in the major mode determined
570 by the default value of @code{major-mode} (see below).
572 @cindex file mode specification error
573 @code{normal-mode} uses @code{condition-case} around the call to the
574 major mode command, so errors are caught and reported as a @samp{File
575 mode specification error}, followed by the original error message.
578 @defun set-auto-mode &optional keep-mode-if-same
579 @cindex visited file mode
580 This function selects the major mode that is appropriate for the
581 current buffer. It bases its decision (in order of precedence) on the
582 @w{@samp{-*-}} line, on any @samp{mode:} local variable near the end of
583 a file, on the @w{@samp{#!}} line (using @code{interpreter-mode-alist}),
584 on the text at the beginning of the buffer (using
585 @code{magic-mode-alist}), and finally on the visited file name (using
586 @code{auto-mode-alist}). @xref{Choosing Modes, , How Major Modes are
587 Chosen, emacs, The GNU Emacs Manual}. If @code{enable-local-variables}
588 is @code{nil}, @code{set-auto-mode} does not check the @w{@samp{-*-}}
589 line, or near the end of the file, for any mode tag.
591 @vindex inhibit-local-variables-regexps
592 There are some file types where it is not appropriate to scan the file
593 contents for a mode specifier. For example, a tar archive may happen to
594 contain, near the end of the file, a member file that has a local
595 variables section specifying a mode for that particular file. This
596 should not be applied to the containing tar file. Similarly, a tiff
597 image file might just happen to contain a first line that seems to
598 match the @w{@samp{-*-}} pattern. For these reasons, both these file
599 extensions are members of the list @var{inhibit-local-variables-regexps}.
600 Add patterns to this list to prevent Emacs searching them for local
601 variables of any kind (not just mode specifiers).
603 If @var{keep-mode-if-same} is non-@code{nil}, this function does not
604 call the mode command if the buffer is already in the proper major
605 mode. For instance, @code{set-visited-file-name} sets this to
606 @code{t} to avoid killing buffer local variables that the user may
610 @defun set-buffer-major-mode buffer
611 This function sets the major mode of @var{buffer} to the default value of
612 @code{major-mode}; if that is @code{nil}, it uses the
613 current buffer's major mode (if that is suitable). As an exception,
614 if @var{buffer}'s name is @samp{*scratch*}, it sets the mode to
615 @code{initial-major-mode}.
617 The low-level primitives for creating buffers do not use this function,
618 but medium-level commands such as @code{switch-to-buffer} and
619 @code{find-file-noselect} use it whenever they create buffers.
622 @defopt initial-major-mode
623 @cindex @samp{*scratch*}
624 The value of this variable determines the major mode of the initial
625 @samp{*scratch*} buffer. The value should be a symbol that is a major
626 mode command. The default value is @code{lisp-interaction-mode}.
629 @defvar interpreter-mode-alist
630 This variable specifies major modes to use for scripts that specify a
631 command interpreter in a @samp{#!} line. Its value is an alist with
632 elements of the form @code{(@var{interpreter} . @var{mode})}; for
633 example, @code{("perl" . perl-mode)} is one element present by
634 default. The element says to use mode @var{mode} if the file
635 specifies an interpreter which matches @var{interpreter}.
638 @defvar magic-mode-alist
639 This variable's value is an alist with elements of the form
640 @code{(@var{regexp} . @var{function})}, where @var{regexp} is a
641 regular expression and @var{function} is a function or @code{nil}.
642 After visiting a file, @code{set-auto-mode} calls @var{function} if
643 the text at the beginning of the buffer matches @var{regexp} and
644 @var{function} is non-@code{nil}; if @var{function} is @code{nil},
645 @code{auto-mode-alist} gets to decide the mode.
648 @defvar magic-fallback-mode-alist
649 This works like @code{magic-mode-alist}, except that it is handled
650 only if @code{auto-mode-alist} does not specify a mode for this file.
653 @defvar auto-mode-alist
654 This variable contains an association list of file name patterns
655 (regular expressions) and corresponding major mode commands. Usually,
656 the file name patterns test for suffixes, such as @samp{.el} and
657 @samp{.c}, but this need not be the case. An ordinary element of the
658 alist looks like @code{(@var{regexp} . @var{mode-function})}.
664 (("\\`/tmp/fol/" . text-mode)
665 ("\\.texinfo\\'" . texinfo-mode)
666 ("\\.texi\\'" . texinfo-mode)
669 ("\\.el\\'" . emacs-lisp-mode)
676 When you visit a file whose expanded file name (@pxref{File Name
677 Expansion}), with version numbers and backup suffixes removed using
678 @code{file-name-sans-versions} (@pxref{File Name Components}), matches
679 a @var{regexp}, @code{set-auto-mode} calls the corresponding
680 @var{mode-function}. This feature enables Emacs to select the proper
681 major mode for most files.
683 If an element of @code{auto-mode-alist} has the form @code{(@var{regexp}
684 @var{function} t)}, then after calling @var{function}, Emacs searches
685 @code{auto-mode-alist} again for a match against the portion of the file
686 name that did not match before. This feature is useful for
687 uncompression packages: an entry of the form @code{("\\.gz\\'"
688 @var{function} t)} can uncompress the file and then put the uncompressed
689 file in the proper mode according to the name sans @samp{.gz}.
691 Here is an example of how to prepend several pattern pairs to
692 @code{auto-mode-alist}. (You might use this sort of expression in your
697 (setq auto-mode-alist
699 ;; @r{File name (within directory) starts with a dot.}
700 '(("/\\.[^/]*\\'" . fundamental-mode)
701 ;; @r{File name has no dot.}
702 ("/[^\\./]*\\'" . fundamental-mode)
703 ;; @r{File name ends in @samp{.C}.}
704 ("\\.C\\'" . c++-mode))
711 @subsection Getting Help about a Major Mode
713 @cindex help for major mode
714 @cindex documentation for major mode
716 The @code{describe-mode} function provides information about major
717 modes. It is normally bound to @kbd{C-h m}. It uses the value of the
718 variable @code{major-mode} (@pxref{Major Modes}), which is why every
719 major mode command needs to set that variable.
721 @deffn Command describe-mode
722 This function displays the documentation of the current major mode.
724 The @code{describe-mode} function calls the @code{documentation}
725 function using the value of @code{major-mode} as an argument. Thus, it
726 displays the documentation string of the major mode command.
727 (@xref{Accessing Documentation}.)
731 @subsection Defining Derived Modes
734 The recommended way to define a new major mode is to derive it from an
735 existing one using @code{define-derived-mode}. If there is no closely
736 related mode, you should inherit from either @code{text-mode},
737 @code{special-mode}, or @code{prog-mode}. @xref{Basic Major Modes}. If
738 none of these are suitable, you can inherit from @code{fundamental-mode}
739 (@pxref{Major Modes}).
741 @defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{}
742 This macro defines @var{variant} as a major mode command, using
743 @var{name} as the string form of the mode name. @var{variant} and
744 @var{parent} should be unquoted symbols.
746 The new command @var{variant} is defined to call the function
747 @var{parent}, then override certain aspects of that parent mode:
751 The new mode has its own sparse keymap, named
752 @code{@var{variant}-map}. @code{define-derived-mode}
753 makes the parent mode's keymap the parent of the new map, unless
754 @code{@var{variant}-map} is already set and already has a parent.
757 The new mode has its own syntax table, kept in the variable
758 @code{@var{variant}-syntax-table}, unless you override this using the
759 @code{:syntax-table} keyword (see below). @code{define-derived-mode}
760 makes the parent mode's syntax-table the parent of
761 @code{@var{variant}-syntax-table}, unless the latter is already set
762 and already has a parent different from the standard syntax table.
765 The new mode has its own abbrev table, kept in the variable
766 @code{@var{variant}-abbrev-table}, unless you override this using the
767 @code{:abbrev-table} keyword (see below).
770 The new mode has its own mode hook, @code{@var{variant}-hook}. It
771 runs this hook, after running the hooks of its ancestor modes, with
772 @code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}.
775 In addition, you can specify how to override other aspects of
776 @var{parent} with @var{body}. The command @var{variant}
777 evaluates the forms in @var{body} after setting up all its usual
778 overrides, just before running the mode hooks.
780 If @var{parent} has a non-@code{nil} @code{mode-class} symbol
781 property, then @code{define-derived-mode} sets the @code{mode-class}
782 property of @var{variant} to the same value. This ensures, for
783 example, that if @var{parent} is a special mode, then @var{variant} is
784 also a special mode (@pxref{Major Mode Conventions}).
786 You can also specify @code{nil} for @var{parent}. This gives the new
787 mode no parent. Then @code{define-derived-mode} behaves as described
788 above, but, of course, omits all actions connected with @var{parent}.
790 The argument @var{docstring} specifies the documentation string for
791 the new mode. @code{define-derived-mode} adds some general
792 information about the mode's hook, followed by the mode's keymap, at
793 the end of this docstring. If you omit @var{docstring},
794 @code{define-derived-mode} generates a documentation string.
796 The @var{keyword-args} are pairs of keywords and values. The values
797 are evaluated. The following keywords are currently supported:
801 You can use this to explicitly specify a syntax table for the new
802 mode. If you specify a @code{nil} value, the new mode uses the same
803 syntax table as @var{parent}, or the standard syntax table if
804 @var{parent} is @code{nil}. (Note that this does @emph{not} follow
805 the convention used for non-keyword arguments that a @code{nil} value
806 is equivalent with not specifying the argument.)
809 You can use this to explicitly specify an abbrev table for the new
810 mode. If you specify a @code{nil} value, the new mode uses the same
811 abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table}
812 if @var{parent} is @code{nil}. (Again, a @code{nil} value is
813 @emph{not} equivalent to not specifying this keyword.)
816 If this is specified, the value should be the customization group for
817 this mode. (Not all major modes have one.) Only the (still
818 experimental and unadvertised) command @code{customize-mode} currently
819 uses this. @code{define-derived-mode} does @emph{not} automatically
820 define the specified customization group.
823 Here is a hypothetical example:
826 (define-derived-mode hypertext-mode
827 text-mode "Hypertext"
828 "Major mode for hypertext.
829 \\@{hypertext-mode-map@}"
830 (setq case-fold-search nil))
832 (define-key hypertext-mode-map
833 [down-mouse-3] 'do-hyper-link)
836 Do not write an @code{interactive} spec in the definition;
837 @code{define-derived-mode} does that automatically.
840 @defun derived-mode-p &rest modes
841 This function returns non-@code{nil} if the current major mode is
842 derived from any of the major modes given by the symbols @var{modes}.
845 @node Basic Major Modes
846 @subsection Basic Major Modes
848 Apart from Fundamental mode, there are three major modes that other
849 major modes commonly derive from: Text mode, Prog mode, and Special
850 mode. While Text mode is useful in its own right (e.g. for editing
851 files ending in @file{.txt}), Prog mode and Special mode exist mainly to
852 let other modes derive from them.
854 @vindex prog-mode-hook
855 As far as possible, new major modes should be derived, either directly
856 or indirectly, from one of these three modes. One reason is that this
857 allows users to customize a single mode hook
858 (e.g. @code{prog-mode-hook}) for an entire family of relevant modes
859 (e.g. all programming language modes).
861 @deffn Command text-mode
862 Text mode is a major mode for editing human languages. It defines the
863 @samp{"} and @samp{\} characters as having punctuation syntax
864 (@pxref{Syntax Class Table}), and binds @kbd{M-@key{TAB}} to
865 @code{ispell-complete-word} (@pxref{Spelling,,, emacs, The GNU Emacs
868 An example of a major mode derived from Text mode is HTML mode.
869 @xref{HTML Mode,,SGML and HTML Modes, emacs, The GNU Emacs Manual}.
872 @deffn Command prog-mode
873 Prog mode is a basic major mode for buffers containing programming
874 language source code. Most of the programming language major modes
875 built into Emacs are derived from it.
877 Prog mode binds @code{parse-sexp-ignore-comments} to @code{t}
878 (@pxref{Motion via Parsing}) and @code{bidi-paragraph-direction} to
879 @code{left-to-right} (@pxref{Bidirectional Display}).
882 @deffn Command special-mode
883 Special mode is a basic major mode for buffers containing text that is
884 produced specially by Emacs, rather than from a file. Major modes
885 derived from Special mode are given a @code{mode-class} property of
886 @code{special} (@pxref{Major Mode Conventions}).
888 Special mode sets the buffer to read-only. Its keymap defines several
889 common bindings, including @kbd{q} for @code{quit-window}, @kbd{z} for
890 @code{kill-this-buffer}, and @kbd{g} for @code{revert-buffer}
893 An example of a major mode derived from Special mode is Buffer Menu
894 mode, which is used by the @samp{*Buffer List*} buffer. @xref{List
895 Buffers,,Listing Existing Buffers, emacs, The GNU Emacs Manual}.
899 @subsection Generic Modes
902 @dfn{Generic modes} are simple major modes with basic support for
903 comment syntax and Font Lock mode. To define a generic mode, use the
904 macro @code{define-generic-mode}. See the file @file{generic-x.el}
905 for some examples of the use of @code{define-generic-mode}.
907 @defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring
908 This macro defines a generic mode command named @var{mode} (a symbol,
909 not quoted). The optional argument @var{docstring} is the
910 documentation for the mode command. If you do not supply it,
911 @code{define-generic-mode} generates one by default.
913 The argument @var{comment-list} is a list in which each element is
914 either a character, a string of one or two characters, or a cons cell.
915 A character or a string is set up in the mode's syntax table as a
916 ``comment starter.'' If the entry is a cons cell, the @sc{car} is set
917 up as a ``comment starter'' and the @sc{cdr} as a ``comment ender.''
918 (Use @code{nil} for the latter if you want comments to end at the end
919 of the line.) Note that the syntax table mechanism has limitations
920 about what comment starters and enders are actually possible.
921 @xref{Syntax Tables}.
923 The argument @var{keyword-list} is a list of keywords to highlight
924 with @code{font-lock-keyword-face}. Each keyword should be a string.
925 Meanwhile, @var{font-lock-list} is a list of additional expressions to
926 highlight. Each element of this list should have the same form as an
927 element of @code{font-lock-keywords}. @xref{Search-based
930 The argument @var{auto-mode-list} is a list of regular expressions to
931 add to the variable @code{auto-mode-alist}. They are added by the execution
932 of the @code{define-generic-mode} form, not by expanding the macro call.
934 Finally, @var{function-list} is a list of functions for the mode
935 command to call for additional setup. It calls these functions just
936 before it runs the mode hook variable @code{@var{mode}-hook}.
940 @subsection Mode Hooks
942 Every major mode command should finish by running its mode hook and
943 the mode-independent normal hook @code{after-change-major-mode-hook}.
944 It does this by calling @code{run-mode-hooks}. If the major mode is a
945 derived mode, that is if it calls another major mode (the parent mode)
946 in its body, it should do this inside @code{delay-mode-hooks} so that
947 the parent won't run these hooks itself. Instead, the derived mode's
948 call to @code{run-mode-hooks} runs the parent's mode hook too.
949 @xref{Major Mode Conventions}.
951 Emacs versions before Emacs 22 did not have @code{delay-mode-hooks}.
952 When user-implemented major modes have not been updated to use it,
953 they won't entirely follow these conventions: they may run the
954 parent's mode hook too early, or fail to run
955 @code{after-change-major-mode-hook}. If you encounter such a major
956 mode, please correct it to follow these conventions.
958 When you defined a major mode using @code{define-derived-mode}, it
959 automatically makes sure these conventions are followed. If you
960 define a major mode ``by hand,'' not using @code{define-derived-mode},
961 use the following functions to handle these conventions automatically.
963 @defun run-mode-hooks &rest hookvars
964 Major modes should run their mode hook using this function. It is
965 similar to @code{run-hooks} (@pxref{Hooks}), but it also runs
966 @code{after-change-major-mode-hook}.
968 When this function is called during the execution of a
969 @code{delay-mode-hooks} form, it does not run the hooks immediately.
970 Instead, it arranges for the next call to @code{run-mode-hooks} to run
974 @defmac delay-mode-hooks body@dots{}
975 When one major mode command calls another, it should do so inside of
976 @code{delay-mode-hooks}.
978 This macro executes @var{body}, but tells all @code{run-mode-hooks}
979 calls during the execution of @var{body} to delay running their hooks.
980 The hooks will actually run during the next call to
981 @code{run-mode-hooks} after the end of the @code{delay-mode-hooks}
985 @defvar after-change-major-mode-hook
986 This is a normal hook run by @code{run-mode-hooks}. It is run at the
987 very end of every properly-written major mode command.
990 @node Example Major Modes
991 @subsection Major Mode Examples
993 Text mode is perhaps the simplest mode besides Fundamental mode.
994 Here are excerpts from @file{text-mode.el} that illustrate many of
995 the conventions listed above:
999 ;; @r{Create the syntax table for this mode.}
1000 (defvar text-mode-syntax-table
1001 (let ((st (make-syntax-table)))
1002 (modify-syntax-entry ?\" ". " st)
1003 (modify-syntax-entry ?\\ ". " st)
1004 ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'.
1005 (modify-syntax-entry ?' "w p" st)
1007 "Syntax table used while in `text-mode'.")
1010 ;; @r{Create the keymap for this mode.}
1012 (defvar text-mode-map
1013 (let ((map (make-sparse-keymap)))
1014 (define-key map "\e\t" 'ispell-complete-word)
1016 "Keymap for `text-mode'.
1017 Many other modes, such as `mail-mode', `outline-mode' and
1018 `indented-text-mode', inherit all the commands defined in this map.")
1022 Here is how the actual mode command is defined now:
1026 (define-derived-mode text-mode nil "Text"
1027 "Major mode for editing text written for humans to read.
1028 In this mode, paragraphs are delimited only by blank or white lines.
1029 You can thus get the full benefit of adaptive filling
1030 (see the variable `adaptive-fill-mode').
1032 Turning on Text mode runs the normal hook `text-mode-hook'."
1035 (set (make-local-variable 'text-mode-variant) t)
1036 (set (make-local-variable 'require-final-newline)
1037 mode-require-final-newline)
1038 (set (make-local-variable 'indent-line-function) 'indent-relative))
1043 (The last line is redundant nowadays, since @code{indent-relative} is
1044 the default value, and we'll delete it in a future version.)
1046 @cindex @file{lisp-mode.el}
1047 The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction
1048 mode) have more features than Text mode and the code is correspondingly
1049 more complicated. Here are excerpts from @file{lisp-mode.el} that
1050 illustrate how these modes are written.
1052 Here is how the Lisp mode syntax and abbrev tables are defined:
1054 @cindex syntax table example
1057 ;; @r{Create mode-specific table variables.}
1058 (defvar lisp-mode-abbrev-table nil)
1059 (define-abbrev-table 'lisp-mode-abbrev-table ())
1061 (defvar lisp-mode-syntax-table
1062 (let ((table (copy-syntax-table emacs-lisp-mode-syntax-table)))
1063 (modify-syntax-entry ?\[ "_ " table)
1064 (modify-syntax-entry ?\] "_ " table)
1065 (modify-syntax-entry ?# "' 14" table)
1066 (modify-syntax-entry ?| "\" 23bn" table)
1068 "Syntax table used in `lisp-mode'.")
1072 The three modes for Lisp share much of their code. For instance,
1073 each calls the following function to set various variables:
1077 (defun lisp-mode-variables (&optional lisp-syntax keywords-case-insensitive)
1079 (set-syntax-table lisp-mode-syntax-table))
1080 (setq local-abbrev-table lisp-mode-abbrev-table)
1086 Amongst other things, this function sets up the @code{comment-start}
1087 variable to handle Lisp comments:
1091 (make-local-variable 'comment-start)
1092 (setq comment-start ";")
1097 Each of the different Lisp modes has a slightly different keymap. For
1098 example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other
1099 Lisp modes do not. However, all Lisp modes have some commands in
1100 common. The following code sets up the common commands:
1104 (defvar lisp-mode-shared-map
1105 (let ((map (make-sparse-keymap)))
1106 (define-key map "\e\C-q" 'indent-sexp)
1107 (define-key map "\177" 'backward-delete-char-untabify)
1109 "Keymap for commands shared by all sorts of Lisp modes.")
1114 And here is the code to set up the keymap for Lisp mode:
1118 (defvar lisp-mode-map
1119 (let ((map (make-sparse-keymap))
1120 (menu-map (make-sparse-keymap "Lisp")))
1121 (set-keymap-parent map lisp-mode-shared-map)
1122 (define-key map "\e\C-x" 'lisp-eval-defun)
1123 (define-key map "\C-c\C-z" 'run-lisp)
1126 "Keymap for ordinary Lisp mode.
1127 All commands in `lisp-mode-shared-map' are inherited by this map.")
1132 Finally, here is the major mode command for Lisp mode:
1136 (define-derived-mode lisp-mode prog-mode "Lisp"
1137 "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
1139 Delete converts tabs to spaces as it moves back.
1140 Blank lines separate paragraphs. Semicolons start comments.
1143 Note that `run-lisp' may be used either to start an inferior Lisp job
1144 or to switch back to an existing one.
1148 Entry to this mode calls the value of `lisp-mode-hook'
1149 if that value is non-nil."
1150 (lisp-mode-variables nil t)
1151 (set (make-local-variable 'find-tag-default-function) 'lisp-find-tag-default)
1152 (make-local-variable 'comment-start-skip)
1153 (setq comment-start-skip
1154 "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *")
1155 (setq imenu-case-fold-search t))
1160 @section Minor Modes
1163 A @dfn{minor mode} provides features that users may enable or disable
1164 independently of the choice of major mode. Minor modes can be enabled
1165 individually or in combination. Minor modes would be better named
1166 ``generally available, optional feature modes,'' except that such a name
1169 A minor mode is not usually meant as a variation of a single major mode.
1170 Usually they are general and can apply to many major modes. For
1171 example, Auto Fill mode works with any major mode that permits text
1172 insertion. To be general, a minor mode must be effectively independent
1173 of the things major modes do.
1175 A minor mode is often much more difficult to implement than a major
1176 mode. One reason is that you should be able to activate and deactivate
1177 minor modes in any order. A minor mode should be able to have its
1178 desired effect regardless of the major mode and regardless of the other
1179 minor modes in effect.
1181 Often the biggest problem in implementing a minor mode is finding a
1182 way to insert the necessary hook into the rest of Emacs. Minor mode
1183 keymaps make this easier than it used to be.
1185 @defvar minor-mode-list
1186 The value of this variable is a list of all minor mode commands.
1190 * Minor Mode Conventions:: Tips for writing a minor mode.
1191 * Keymaps and Minor Modes:: How a minor mode can have its own keymap.
1192 * Defining Minor Modes:: A convenient facility for defining minor modes.
1195 @node Minor Mode Conventions
1196 @subsection Conventions for Writing Minor Modes
1197 @cindex minor mode conventions
1198 @cindex conventions for writing minor modes
1200 There are conventions for writing minor modes just as there are for
1201 major modes. Several of the major mode conventions apply to minor
1202 modes as well: those regarding the name of the mode initialization
1203 function, the names of global symbols, the use of a hook at the end of
1204 the initialization function, and the use of keymaps and other tables.
1206 In addition, there are several conventions that are specific to
1207 minor modes. (The easiest way to follow all the conventions is to use
1208 the macro @code{define-minor-mode}; @ref{Defining Minor Modes}.)
1212 @cindex mode variable
1213 Make a variable whose name ends in @samp{-mode} to control the minor
1214 mode. We call this the @dfn{mode variable}. The minor mode command
1215 should set this variable (@code{nil} to disable; anything else to
1218 If possible, implement the mode so that setting the variable
1219 automatically enables or disables the mode. Then the minor mode command
1220 does not need to do anything except set the variable.
1222 This variable is used in conjunction with the @code{minor-mode-alist} to
1223 display the minor mode name in the mode line. It can also enable
1224 or disable a minor mode keymap. Individual commands or hooks can also
1225 check the variable's value.
1227 If you want the minor mode to be enabled separately in each buffer,
1228 make the variable buffer-local.
1231 Define a command whose name is the same as the mode variable.
1232 Its job is to enable and disable the mode by setting the variable.
1234 The command should accept one optional argument. If the argument is
1235 @code{nil}, it should toggle the mode (turn it on if it is off, and
1236 off if it is on). It should turn the mode on if the argument is a
1237 positive integer, the symbol @code{t}, or a list whose @sc{car} is one
1238 of those. It should turn the mode off if the argument is a negative
1239 integer or zero, the symbol @code{-}, or a list whose @sc{car} is a
1240 negative integer or zero. The meaning of other arguments is not
1243 Here is an example taken from the definition of @code{transient-mark-mode}.
1244 It shows the use of @code{transient-mark-mode} as a variable that enables or
1245 disables the mode's behavior, and also shows the proper way to toggle,
1246 enable or disable the minor mode based on the raw prefix argument value.
1250 (setq transient-mark-mode
1251 (if (null arg) (not transient-mark-mode)
1252 (> (prefix-numeric-value arg) 0)))
1257 Add an element to @code{minor-mode-alist} for each minor mode
1258 (@pxref{Definition of minor-mode-alist}), if you want to indicate the
1259 minor mode in the mode line. This element should be a list of the
1263 (@var{mode-variable} @var{string})
1266 Here @var{mode-variable} is the variable that controls enabling of the
1267 minor mode, and @var{string} is a short string, starting with a space,
1268 to represent the mode in the mode line. These strings must be short so
1269 that there is room for several of them at once.
1271 When you add an element to @code{minor-mode-alist}, use @code{assq} to
1272 check for an existing element, to avoid duplication. For example:
1276 (unless (assq 'leif-mode minor-mode-alist)
1277 (setq minor-mode-alist
1278 (cons '(leif-mode " Leif") minor-mode-alist)))
1283 or like this, using @code{add-to-list} (@pxref{List Variables}):
1287 (add-to-list 'minor-mode-alist '(leif-mode " Leif"))
1292 Global minor modes distributed with Emacs should if possible support
1293 enabling and disabling via Custom (@pxref{Customization}). To do this,
1294 the first step is to define the mode variable with @code{defcustom}, and
1295 specify @code{:type 'boolean}.
1297 If just setting the variable is not sufficient to enable the mode, you
1298 should also specify a @code{:set} method which enables the mode by
1299 invoking the mode command. Note in the variable's documentation string that
1300 setting the variable other than via Custom may not take effect.
1302 Also mark the definition with an autoload cookie (@pxref{autoload cookie}),
1303 and specify a @code{:require} so that customizing the variable will load
1304 the library that defines the mode. This will copy suitable definitions
1305 into @file{loaddefs.el} so that users can use @code{customize-option} to
1306 enable the mode. For example:
1312 (defcustom msb-mode nil
1314 Setting this variable directly does not take effect;
1315 use either \\[customize] or the function `msb-mode'."
1316 :set 'custom-set-minor-mode
1317 :initialize 'custom-initialize-default
1325 @node Keymaps and Minor Modes
1326 @subsection Keymaps and Minor Modes
1328 Each minor mode can have its own keymap, which is active when the mode
1329 is enabled. To set up a keymap for a minor mode, add an element to the
1330 alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}.
1332 @cindex @code{self-insert-command}, minor modes
1333 One use of minor mode keymaps is to modify the behavior of certain
1334 self-inserting characters so that they do something else as well as
1335 self-insert. In general, this is the only way to do that, since the
1336 facilities for customizing @code{self-insert-command} are limited to
1337 special cases (designed for abbrevs and Auto Fill mode). (Do not try
1338 substituting your own definition of @code{self-insert-command} for the
1339 standard one. The editor command loop handles this function specially.)
1341 The key sequences bound in a minor mode should consist of @kbd{C-c}
1342 followed by one of @kbd{.,/?`'"[]\|~!#$%^&*()-_+=}. (The other
1343 punctuation characters are reserved for major modes.)
1345 @node Defining Minor Modes
1346 @subsection Defining Minor Modes
1348 The macro @code{define-minor-mode} offers a convenient way of
1349 implementing a mode in one self-contained definition.
1351 @defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{}
1352 This macro defines a new minor mode whose name is @var{mode} (a
1353 symbol). It defines a command named @var{mode} to toggle the minor
1354 mode, with @var{doc} as its documentation string. By default, it also
1355 defines a variable named @var{mode}, which is set to @code{t} or
1356 @code{nil} by enabling or disabling the mode. The variable is
1357 initialized to @var{init-value}. Except in unusual circumstances (see
1358 below), this value must be @code{nil}.
1360 The string @var{lighter} says what to display in the mode line
1361 when the mode is enabled; if it is @code{nil}, the mode is not displayed
1364 The optional argument @var{keymap} specifies the keymap for the minor
1365 mode. If non-@code{nil}, it should be a variable name (whose value is
1366 a keymap), a keymap, or an alist of the form
1369 (@var{key-sequence} . @var{definition})
1373 where each @var{key-sequence} and @var{definition} are arguments
1374 suitable for passing to @code{define-key} (@pxref{Changing Key
1375 Bindings}). If @var{keymap} is a keymap or an alist, this also
1376 defines the variable @code{@var{mode}-map}.
1378 The above three arguments @var{init-value}, @var{lighter}, and
1379 @var{keymap} can be (partially) omitted when @var{keyword-args} are
1380 used. The @var{keyword-args} consist of keywords followed by
1381 corresponding values. A few keywords have special meanings:
1384 @item :group @var{group}
1385 Custom group name to use in all generated @code{defcustom} forms.
1386 Defaults to @var{mode} without the possible trailing @samp{-mode}.
1387 @strong{Warning:} don't use this default group name unless you have
1388 written a @code{defgroup} to define that group properly. @xref{Group
1391 @item :global @var{global}
1392 If non-@code{nil}, this specifies that the minor mode should be global
1393 rather than buffer-local. It defaults to @code{nil}.
1395 One of the effects of making a minor mode global is that the
1396 @var{mode} variable becomes a customization variable. Toggling it
1397 through the Custom interface turns the mode on and off, and its value
1398 can be saved for future Emacs sessions (@pxref{Saving
1399 Customizations,,, emacs, The GNU Emacs Manual}. For the saved
1400 variable to work, you should ensure that the @code{define-minor-mode}
1401 form is evaluated each time Emacs starts; for packages that are not
1402 part of Emacs, the easiest way to do this is to specify a
1403 @code{:require} keyword.
1405 @item :init-value @var{init-value}
1406 This is equivalent to specifying @var{init-value} positionally.
1408 @item :lighter @var{lighter}
1409 This is equivalent to specifying @var{lighter} positionally.
1411 @item :keymap @var{keymap}
1412 This is equivalent to specifying @var{keymap} positionally.
1414 @item :variable @var{place}
1415 This replaces the default variable @var{mode}, used to store the state
1416 of the mode. If you specify this, the @var{mode} variable is not
1417 defined, and any @var{init-value} argument is unused. @var{place}
1418 can be a different named variable (which you must define yourself), or
1419 anything that can be used with the @code{setf} function
1420 (@pxref{Generalized Variables,,, cl, Common Lisp Extensions}).
1421 @var{place} can also be a cons @code{(@var{get} . @var{set})},
1422 where @var{get} is an expression that returns the current state,
1423 and @var{set} is a function of one argument (a state) that sets it.
1426 Any other keyword arguments are passed directly to the
1427 @code{defcustom} generated for the variable @var{mode}.
1429 The command named @var{mode} first performs the standard actions such
1430 as setting the variable named @var{mode} and then executes the
1431 @var{body} forms, if any. It finishes by running the mode hook
1432 variable @code{@var{mode}-hook}.
1435 The initial value must be @code{nil} except in cases where (1) the
1436 mode is preloaded in Emacs, or (2) it is painless for loading to
1437 enable the mode even though the user did not request it. For
1438 instance, if the mode has no effect unless something else is enabled,
1439 and will always be loaded by that time, enabling it by default is
1440 harmless. But these are unusual circumstances. Normally, the
1441 initial value must be @code{nil}.
1443 @findex easy-mmode-define-minor-mode
1444 The name @code{easy-mmode-define-minor-mode} is an alias
1447 Here is an example of using @code{define-minor-mode}:
1450 (define-minor-mode hungry-mode
1451 "Toggle Hungry mode.
1452 With no argument, this command toggles the mode.
1453 Non-null prefix argument turns on the mode.
1454 Null prefix argument turns off the mode.
1456 When Hungry mode is enabled, the control delete key
1457 gobbles all preceding whitespace except the last.
1458 See the command \\[hungry-electric-delete]."
1459 ;; The initial value.
1461 ;; The indicator for the mode line.
1463 ;; The minor mode bindings.
1464 '(([C-backspace] . hungry-electric-delete))
1469 This defines a minor mode named ``Hungry mode,'' a command named
1470 @code{hungry-mode} to toggle it, a variable named @code{hungry-mode}
1471 which indicates whether the mode is enabled, and a variable named
1472 @code{hungry-mode-map} which holds the keymap that is active when the
1473 mode is enabled. It initializes the keymap with a key binding for
1474 @kbd{C-@key{DEL}}. It puts the variable @code{hungry-mode} into
1475 custom group @code{hunger}. There are no @var{body} forms---many
1476 minor modes don't need any.
1478 Here's an equivalent way to write it:
1481 (define-minor-mode hungry-mode
1482 "Toggle Hungry mode.
1483 With no argument, this command toggles the mode.
1484 Non-null prefix argument turns on the mode.
1485 Null prefix argument turns off the mode.
1487 When Hungry mode is enabled, the control delete key
1488 gobbles all preceding whitespace except the last.
1489 See the command \\[hungry-electric-delete]."
1490 ;; The initial value.
1492 ;; The indicator for the mode line.
1494 ;; The minor mode bindings.
1496 '(([C-backspace] . hungry-electric-delete)
1500 (hungry-electric-delete t))))
1504 @defmac define-globalized-minor-mode global-mode mode turn-on keyword-args@dots{}
1505 This defines a global toggle named @var{global-mode} whose meaning is
1506 to enable or disable the buffer-local minor mode @var{mode} in all
1507 buffers. To turn on the minor mode in a buffer, it uses the function
1508 @var{turn-on}; to turn off the minor mode, it calls @code{mode} with
1509 @minus{}1 as argument.
1511 Globally enabling the mode also affects buffers subsequently created
1512 by visiting files, and buffers that use a major mode other than
1513 Fundamental mode; but it does not detect the creation of a new buffer
1514 in Fundamental mode.
1516 This defines the customization option @var{global-mode} (@pxref{Customization}),
1517 which can be toggled in the Custom interface to turn the minor mode on
1518 and off. As with @code{define-minor-mode}, you should ensure that the
1519 @code{define-globalized-minor-mode} form is evaluated each time Emacs
1520 starts, for example by providing a @code{:require} keyword.
1522 Use @code{:group @var{group}} in @var{keyword-args} to specify the
1523 custom group for the mode variable of the global minor mode.
1525 When you define a globalized minor mode, you should generally also
1526 define a non-globalized version to toggle the mode on an individual
1527 buffer basis. This allows users to disable a globally enabled minor
1528 mode in a specific major mode if they wish, by deactivating the local
1529 minor mode in the major mode's hook.
1533 @node Mode Line Format
1534 @section Mode-Line Format
1537 Each Emacs window (aside from minibuffer windows) typically has a mode
1538 line at the bottom, which displays status information about the buffer
1539 displayed in the window. The mode line contains information about the
1540 buffer, such as its name, associated file, depth of recursive editing,
1541 and major and minor modes. A window can also have a @dfn{header
1542 line}, which is much like the mode line but appears at the top of the
1545 This section describes how to control the contents of the mode line
1546 and header line. We include it in this chapter because much of the
1547 information displayed in the mode line relates to the enabled major and
1551 * Base: Mode Line Basics. Basic ideas of mode line control.
1552 * Data: Mode Line Data. The data structure that controls the mode line.
1553 * Top: Mode Line Top. The top level variable, mode-line-format.
1554 * Mode Line Variables:: Variables used in that data structure.
1555 * %-Constructs:: Putting information into a mode line.
1556 * Properties in Mode:: Using text properties in the mode line.
1557 * Header Lines:: Like a mode line, but at the top.
1558 * Emulating Mode Line:: Formatting text as the mode line would.
1561 @node Mode Line Basics
1562 @subsection Mode Line Basics
1564 @code{mode-line-format} is a buffer-local variable that holds a
1565 @dfn{mode line construct}, a kind of template, which controls what is
1566 displayed on the mode line of the current buffer. The value of
1567 @code{header-line-format} specifies the buffer's header line in the
1568 same way. All windows for the same buffer use the same
1569 @code{mode-line-format} and @code{header-line-format}.
1571 For efficiency, Emacs does not continuously recompute the mode
1572 line and header line of a window. It does so when circumstances
1573 appear to call for it---for instance, if you change the window
1574 configuration, switch buffers, narrow or widen the buffer, scroll, or
1575 change the buffer's modification status. If you modify any of the
1576 variables referenced by @code{mode-line-format} (@pxref{Mode Line
1577 Variables}), or any other variables and data structures that affect
1578 how text is displayed (@pxref{Display}), you may want to force an
1579 update of the mode line so as to display the new information or
1580 display it in the new way.
1582 @defun force-mode-line-update &optional all
1583 Force redisplay of the current buffer's mode line and header line.
1584 The next redisplay will update the mode line and header line based on
1585 the latest values of all relevant variables. With optional
1586 non-@code{nil} @var{all}, force redisplay of all mode lines and header
1589 This function also forces recomputation of the menu bar menus
1590 and the frame title.
1593 The selected window's mode line is usually displayed in a different
1594 color using the face @code{mode-line}. Other windows' mode lines
1595 appear in the face @code{mode-line-inactive} instead. @xref{Faces}.
1597 @node Mode Line Data
1598 @subsection The Data Structure of the Mode Line
1599 @cindex mode-line construct
1601 The mode-line contents are controlled by a data structure called a
1602 @dfn{mode-line construct}, made up of lists, strings, symbols, and
1603 numbers kept in buffer-local variables. Each data type has a specific
1604 meaning for the mode-line appearance, as described below. The same
1605 data structure is used for constructing frame titles (@pxref{Frame
1606 Titles}) and header lines (@pxref{Header Lines}).
1608 A mode-line construct may be as simple as a fixed string of text,
1609 but it usually specifies how to combine fixed strings with variables'
1610 values to construct the text. Many of these variables are themselves
1611 defined to have mode-line constructs as their values.
1613 Here are the meanings of various data types as mode-line constructs:
1616 @cindex percent symbol in mode line
1618 A string as a mode-line construct appears verbatim except for
1619 @dfn{@code{%}-constructs} in it. These stand for substitution of
1620 other data; see @ref{%-Constructs}.
1622 If parts of the string have @code{face} properties, they control
1623 display of the text just as they would text in the buffer. Any
1624 characters which have no @code{face} properties are displayed, by
1625 default, in the face @code{mode-line} or @code{mode-line-inactive}
1626 (@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}). The
1627 @code{help-echo} and @code{local-map} properties in @var{string} have
1628 special meanings. @xref{Properties in Mode}.
1631 A symbol as a mode-line construct stands for its value. The value of
1632 @var{symbol} is used as a mode-line construct, in place of @var{symbol}.
1633 However, the symbols @code{t} and @code{nil} are ignored, as is any
1634 symbol whose value is void.
1636 There is one exception: if the value of @var{symbol} is a string, it is
1637 displayed verbatim: the @code{%}-constructs are not recognized.
1639 Unless @var{symbol} is marked as ``risky'' (i.e., it has a
1640 non-@code{nil} @code{risky-local-variable} property), all text
1641 properties specified in @var{symbol}'s value are ignored. This
1642 includes the text properties of strings in @var{symbol}'s value, as
1643 well as all @code{:eval} and @code{:propertize} forms in it. (The
1644 reason for this is security: non-risky variables could be set
1645 automatically from file variables without prompting the user.)
1647 @item (@var{string} @var{rest}@dots{})
1648 @itemx (@var{list} @var{rest}@dots{})
1649 A list whose first element is a string or list means to process all the
1650 elements recursively and concatenate the results. This is the most
1651 common form of mode-line construct.
1653 @item (:eval @var{form})
1654 A list whose first element is the symbol @code{:eval} says to evaluate
1655 @var{form}, and use the result as a string to display. Make sure this
1656 evaluation cannot load any files, as doing so could cause infinite
1659 @item (:propertize @var{elt} @var{props}@dots{})
1660 A list whose first element is the symbol @code{:propertize} says to
1661 process the mode-line construct @var{elt} recursively, then add the text
1662 properties specified by @var{props} to the result. The argument
1663 @var{props} should consist of zero or more pairs @var{text-property}
1664 @var{value}. (This feature is new as of Emacs 22.1.)
1666 @item (@var{symbol} @var{then} @var{else})
1667 A list whose first element is a symbol that is not a keyword specifies
1668 a conditional. Its meaning depends on the value of @var{symbol}. If
1669 @var{symbol} has a non-@code{nil} value, the second element,
1670 @var{then}, is processed recursively as a mode-line element.
1671 Otherwise, the third element, @var{else}, is processed recursively.
1672 You may omit @var{else}; then the mode-line element displays nothing
1673 if the value of @var{symbol} is @code{nil} or void.
1675 @item (@var{width} @var{rest}@dots{})
1676 A list whose first element is an integer specifies truncation or
1677 padding of the results of @var{rest}. The remaining elements
1678 @var{rest} are processed recursively as mode-line constructs and
1679 concatenated together. When @var{width} is positive, the result is
1680 space filled on the right if its width is less than @var{width}. When
1681 @var{width} is negative, the result is truncated on the right to
1682 @minus{}@var{width} columns if its width exceeds @minus{}@var{width}.
1684 For example, the usual way to show what percentage of a buffer is above
1685 the top of the window is to use a list like this: @code{(-3 "%p")}.
1689 @subsection The Top Level of Mode Line Control
1691 The variable in overall control of the mode line is
1692 @code{mode-line-format}.
1694 @defopt mode-line-format
1695 The value of this variable is a mode-line construct that controls the
1696 contents of the mode-line. It is always buffer-local in all buffers.
1698 If you set this variable to @code{nil} in a buffer, that buffer does
1699 not have a mode line. (A window that is just one line tall never
1700 displays a mode line.)
1703 The default value of @code{mode-line-format} is designed to use the
1704 values of other variables such as @code{mode-line-position} and
1705 @code{mode-line-modes} (which in turn incorporates the values of the
1706 variables @code{mode-name} and @code{minor-mode-alist}). Very few
1707 modes need to alter @code{mode-line-format} itself. For most
1708 purposes, it is sufficient to alter some of the variables that
1709 @code{mode-line-format} either directly or indirectly refers to.
1711 If you do alter @code{mode-line-format} itself, the new value should
1712 use the same variables that appear in the default value (@pxref{Mode
1713 Line Variables}), rather than duplicating their contents or displaying
1714 the information in another fashion. This way, customizations made by
1715 the user or by Lisp programs (such as @code{display-time} and major
1716 modes) via changes to those variables remain effective.
1718 Here is an example of a @code{mode-line-format} that might be
1719 useful for @code{shell-mode}, since it contains the host name and default
1724 (setq mode-line-format
1726 'mode-line-mule-info
1728 'mode-line-frame-identification
1732 ;; @r{Note that this is evaluated while making the list.}
1733 ;; @r{It makes a mode-line construct which is just a string.}
1741 '(:eval (mode-line-mode-name))
1747 '(which-func-mode ("" which-func-format "--"))
1748 '(line-number-mode "L%l--")
1749 '(column-number-mode "C%c--")
1756 (The variables @code{line-number-mode}, @code{column-number-mode}
1757 and @code{which-func-mode} enable particular minor modes; as usual,
1758 these variable names are also the minor mode command names.)
1760 @node Mode Line Variables
1761 @subsection Variables Used in the Mode Line
1763 This section describes variables incorporated by the standard value
1764 of @code{mode-line-format} into the text of the mode line. There is
1765 nothing inherently special about these variables; any other variables
1766 could have the same effects on the mode line if
1767 @code{mode-line-format}'s value were changed to use them. However,
1768 various parts of Emacs set these variables on the understanding that
1769 they will control parts of the mode line; therefore, practically
1770 speaking, it is essential for the mode line to use them.
1772 @defvar mode-line-mule-info
1773 This variable holds the value of the mode-line construct that displays
1774 information about the language environment, buffer coding system, and
1775 current input method. @xref{Non-ASCII Characters}.
1778 @defvar mode-line-modified
1779 This variable holds the value of the mode-line construct that displays
1780 whether the current buffer is modified. Its default value displays
1781 @samp{**} if the buffer is modified, @samp{--} if the buffer is not
1782 modified, @samp{%%} if the buffer is read only, and @samp{%*} if the
1783 buffer is read only and modified.
1785 Changing this variable does not force an update of the mode line.
1788 @defvar mode-line-frame-identification
1789 This variable identifies the current frame. Its default value
1790 displays @code{" "} if you are using a window system which can show
1791 multiple frames, or @code{"-%F "} on an ordinary terminal which shows
1792 only one frame at a time.
1795 @defvar mode-line-buffer-identification
1796 This variable identifies the buffer being displayed in the window.
1797 Its default value displays the buffer name, padded with spaces to at
1801 @defopt mode-line-position
1802 This variable indicates the position in the buffer. Its default value
1803 displays the buffer percentage and, optionally, the buffer size, the
1804 line number and the column number.
1808 The variable @code{vc-mode}, buffer-local in each buffer, records
1809 whether the buffer's visited file is maintained with version control,
1810 and, if so, which kind. Its value is a string that appears in the mode
1811 line, or @code{nil} for no version control.
1814 @defopt mode-line-modes
1815 This variable displays the buffer's major and minor modes. Its
1816 default value also displays the recursive editing level, information
1817 on the process status, and whether narrowing is in effect.
1820 @defopt mode-line-remote
1821 This variable is used to show whether @code{default-directory} for the
1822 current buffer is remote.
1825 @defopt mode-line-client
1826 This variable is used to identify @code{emacsclient} frames.
1829 The following three variables are used in @code{mode-line-modes}:
1832 This buffer-local variable holds the ``pretty'' name of the current
1833 buffer's major mode. Each major mode should set this variable so that
1834 the mode name will appear in the mode line. The value does not have
1835 to be a string, but can use any of the data types valid in a mode-line
1836 construct (@pxref{Mode Line Data}). To compute the string that will
1837 identify the mode name in the mode line, use @code{format-mode-line}
1838 (@pxref{Emulating Mode Line}).
1841 @defvar mode-line-process
1842 This buffer-local variable contains the mode-line information on process
1843 status in modes used for communicating with subprocesses. It is
1844 displayed immediately following the major mode name, with no intervening
1845 space. For example, its value in the @samp{*shell*} buffer is
1846 @code{(":%s")}, which allows the shell to display its status along
1847 with the major mode as: @samp{(Shell:run)}. Normally this variable
1851 @defvar minor-mode-alist
1852 @anchor{Definition of minor-mode-alist}
1853 This variable holds an association list whose elements specify how the
1854 mode line should indicate that a minor mode is active. Each element of
1855 the @code{minor-mode-alist} should be a two-element list:
1858 (@var{minor-mode-variable} @var{mode-line-string})
1861 More generally, @var{mode-line-string} can be any mode-line spec. It
1862 appears in the mode line when the value of @var{minor-mode-variable}
1863 is non-@code{nil}, and not otherwise. These strings should begin with
1864 spaces so that they don't run together. Conventionally, the
1865 @var{minor-mode-variable} for a specific mode is set to a
1866 non-@code{nil} value when that minor mode is activated.
1868 @code{minor-mode-alist} itself is not buffer-local. Each variable
1869 mentioned in the alist should be buffer-local if its minor mode can be
1870 enabled separately in each buffer.
1873 @defvar global-mode-string
1874 This variable holds a mode-line spec that, by default, appears in the
1875 mode line just after the @code{which-func-mode} minor mode if set,
1876 else after @code{mode-line-modes}. The command @code{display-time}
1877 sets @code{global-mode-string} to refer to the variable
1878 @code{display-time-string}, which holds a string containing the time
1879 and load information.
1881 The @samp{%M} construct substitutes the value of
1882 @code{global-mode-string}, but that is obsolete, since the variable is
1883 included in the mode line from @code{mode-line-format}.
1886 Here is a simplified version of the default value of
1887 @code{mode-line-format}. The real default value also
1888 specifies addition of text properties.
1895 mode-line-frame-identification
1896 mode-line-buffer-identification
1904 (which-func-mode ("" which-func-format "--"))
1905 (global-mode-string ("--" global-mode-string))
1911 @subsection @code{%}-Constructs in the Mode Line
1913 Strings used as mode-line constructs can use certain
1914 @code{%}-constructs to substitute various kinds of data. Here is a
1915 list of the defined @code{%}-constructs, and what they mean. In any
1916 construct except @samp{%%}, you can add a decimal integer after the
1917 @samp{%} to specify a minimum field width. If the width is less, the
1918 field is padded with spaces to the right.
1922 The current buffer name, obtained with the @code{buffer-name} function.
1923 @xref{Buffer Names}.
1926 The current column number of point.
1929 When Emacs is nearly out of memory for Lisp objects, a brief message
1930 saying so. Otherwise, this is empty.
1933 The visited file name, obtained with the @code{buffer-file-name}
1934 function. @xref{Buffer File Name}.
1937 The title (only on a window system) or the name of the selected frame.
1938 @xref{Basic Parameters}.
1941 The size of the accessible part of the current buffer; basically
1942 @code{(- (point-max) (point-min))}.
1945 Like @samp{%i}, but the size is printed in a more readable way by using
1946 @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., to
1950 The current line number of point, counting within the accessible portion
1954 @samp{Narrow} when narrowing is in effect; nothing otherwise (see
1955 @code{narrow-to-region} in @ref{Narrowing}).
1958 The percentage of the buffer text above the @strong{top} of window, or
1959 @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default
1960 mode-line specification truncates this to three characters.
1963 The percentage of the buffer text that is above the @strong{bottom} of
1964 the window (which includes the text visible in the window, as well as
1965 the text above the top), plus @samp{Top} if the top of the buffer is
1966 visible on screen; or @samp{Bottom} or @samp{All}.
1969 The status of the subprocess belonging to the current buffer, obtained with
1970 @code{process-status}. @xref{Process Information}.
1973 Whether the visited file is a text file or a binary file. This is a
1974 meaningful distinction only on certain operating systems (@pxref{MS-DOS
1978 The mnemonics of keyboard, terminal, and buffer coding systems.
1981 Like @samp{%z}, but including the end-of-line format.
1984 @samp{%} if the buffer is read only (see @code{buffer-read-only}); @*
1985 @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @*
1986 @samp{-} otherwise. @xref{Buffer Modification}.
1989 @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @*
1990 @samp{%} if the buffer is read only (see @code{buffer-read-only}); @*
1991 @samp{-} otherwise. This differs from @samp{%*} only for a modified
1992 read-only buffer. @xref{Buffer Modification}.
1995 @samp{*} if the buffer is modified, and @samp{-} otherwise.
1998 An indication of the depth of recursive editing levels (not counting
1999 minibuffer levels): one @samp{[} for each editing level.
2000 @xref{Recursive Editing}.
2003 One @samp{]} for each recursive editing level (not counting minibuffer
2007 Dashes sufficient to fill the remainder of the mode line.
2010 The character @samp{%}---this is how to include a literal @samp{%} in a
2011 string in which @code{%}-constructs are allowed.
2014 The following two @code{%}-constructs are still supported, but they are
2015 obsolete, since you can get the same results with the variables
2016 @code{mode-name} and @code{global-mode-string}.
2020 The value of @code{mode-name}.
2023 The value of @code{global-mode-string}.
2026 @node Properties in Mode
2027 @subsection Properties in the Mode Line
2028 @cindex text properties in the mode line
2030 Certain text properties are meaningful in the
2031 mode line. The @code{face} property affects the appearance of text; the
2032 @code{help-echo} property associates help strings with the text, and
2033 @code{local-map} can make the text mouse-sensitive.
2035 There are four ways to specify text properties for text in the mode
2040 Put a string with a text property directly into the mode-line data
2044 Put a text property on a mode-line %-construct such as @samp{%12b}; then
2045 the expansion of the %-construct will have that same text property.
2048 Use a @code{(:propertize @var{elt} @var{props}@dots{})} construct to
2049 give @var{elt} a text property specified by @var{props}.
2052 Use a list containing @code{:eval @var{form}} in the mode-line data
2053 structure, and make @var{form} evaluate to a string that has a text
2057 You can use the @code{local-map} property to specify a keymap. This
2058 keymap only takes real effect for mouse clicks; binding character keys
2059 and function keys to it has no effect, since it is impossible to move
2060 point into the mode line.
2062 When the mode line refers to a variable which does not have a
2063 non-@code{nil} @code{risky-local-variable} property, any text
2064 properties given or specified within that variable's values are
2065 ignored. This is because such properties could otherwise specify
2066 functions to be called, and those functions could come from file
2070 @subsection Window Header Lines
2071 @cindex header line (of a window)
2072 @cindex window header line
2074 A window can have a @dfn{header line} at the
2075 top, just as it can have a mode line at the bottom. The header line
2076 feature works just like the mode-line feature, except that it's
2077 controlled by different variables.
2079 @defvar header-line-format
2080 This variable, local in every buffer, specifies how to display the
2081 header line, for windows displaying the buffer. The format of the value
2082 is the same as for @code{mode-line-format} (@pxref{Mode Line Data}).
2083 It is normally @code{nil}, so that ordinary buffers have no header line.
2086 A window that is just one line tall never displays a header line. A
2087 window that is two lines tall cannot display both a mode line and a
2088 header line at once; if it has a mode line, then it does not display a
2091 @node Emulating Mode Line
2092 @subsection Emulating Mode-Line Formatting
2094 You can use the function @code{format-mode-line} to compute
2095 the text that would appear in a mode line or header line
2096 based on a certain mode-line specification.
2098 @defun format-mode-line format &optional face window buffer
2099 This function formats a line of text according to @var{format} as if it
2100 were generating the mode line for @var{window}, but it also returns the
2101 text as a string. The argument @var{window} defaults to the selected
2102 window. If @var{buffer} is non-@code{nil}, all the information used is
2103 taken from @var{buffer}; by default, it comes from @var{window}'s
2106 The value string normally has text properties that correspond to the
2107 faces, keymaps, etc., that the mode line would have. Any character for
2108 which no @code{face} property is specified by @var{format} gets a
2109 default value determined by @var{face}. If @var{face} is @code{t}, that
2110 stands for either @code{mode-line} if @var{window} is selected,
2111 otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or
2112 omitted, that stands for the default face. If @var{face} is an integer,
2113 the value returned by this function will have no text properties.
2115 You can also specify other valid faces as the value of @var{face}.
2116 If specified, that face provides the @code{face} property for characters
2117 whose face is not specified by @var{format}.
2119 Note that using @code{mode-line}, @code{mode-line-inactive}, or
2120 @code{header-line} as @var{face} will actually redisplay the mode line
2121 or the header line, respectively, using the current definitions of the
2122 corresponding face, in addition to returning the formatted string.
2123 (Other faces do not cause redisplay.)
2125 For example, @code{(format-mode-line header-line-format)} returns the
2126 text that would appear in the selected window's header line (@code{""}
2127 if it has no header line). @code{(format-mode-line header-line-format
2128 'header-line)} returns the same text, with each character
2129 carrying the face that it will have in the header line itself, and also
2130 redraws the header line.
2137 @dfn{Imenu} is a feature that lets users select a definition or
2138 section in the buffer, from a menu which lists all of them, to go
2139 directly to that location in the buffer. Imenu works by constructing
2140 a buffer index which lists the names and buffer positions of the
2141 definitions, or other named portions of the buffer; then the user can
2142 choose one of them and move point to it. Major modes can add a menu
2143 bar item to use Imenu using @code{imenu-add-to-menubar}.
2145 @defun imenu-add-to-menubar name
2146 This function defines a local menu bar item named @var{name}
2150 The user-level commands for using Imenu are described in the Emacs
2151 Manual (@pxref{Imenu,, Imenu, emacs, the Emacs Manual}). This section
2152 explains how to customize Imenu's method of finding definitions or
2153 buffer portions for a particular major mode.
2155 The usual and simplest way is to set the variable
2156 @code{imenu-generic-expression}:
2158 @defvar imenu-generic-expression
2159 This variable, if non-@code{nil}, is a list that specifies regular
2160 expressions for finding definitions for Imenu. Simple elements of
2161 @code{imenu-generic-expression} look like this:
2164 (@var{menu-title} @var{regexp} @var{index})
2167 Here, if @var{menu-title} is non-@code{nil}, it says that the matches
2168 for this element should go in a submenu of the buffer index;
2169 @var{menu-title} itself specifies the name for the submenu. If
2170 @var{menu-title} is @code{nil}, the matches for this element go directly
2171 in the top level of the buffer index.
2173 The second item in the list, @var{regexp}, is a regular expression
2174 (@pxref{Regular Expressions}); anything in the buffer that it matches
2175 is considered a definition, something to mention in the buffer index.
2176 The third item, @var{index}, is a non-negative integer that indicates
2177 which subexpression in @var{regexp} matches the definition's name.
2179 An element can also look like this:
2182 (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{})
2185 Each match for this element creates an index item, and when the index
2186 item is selected by the user, it calls @var{function} with arguments
2187 consisting of the item name, the buffer position, and @var{arguments}.
2189 For Emacs Lisp mode, @code{imenu-generic-expression} could look like
2192 @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+]
2195 ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\
2196 \\s-+\\([-A-Za-z0-9+]+\\)" 2)
2199 ("*Vars*" "^\\s-*(def\\(var\\|const\\)\
2200 \\s-+\\([-A-Za-z0-9+]+\\)" 2)
2205 (def\\(type\\|struct\\|class\\|ine-condition\\)\
2206 \\s-+\\([-A-Za-z0-9+]+\\)" 2))
2210 Setting this variable makes it buffer-local in the current buffer.
2213 @defvar imenu-case-fold-search
2214 This variable controls whether matching against the regular
2215 expressions in the value of @code{imenu-generic-expression} is
2216 case-sensitive: @code{t}, the default, means matching should ignore
2219 Setting this variable makes it buffer-local in the current buffer.
2222 @defvar imenu-syntax-alist
2223 This variable is an alist of syntax table modifiers to use while
2224 processing @code{imenu-generic-expression}, to override the syntax table
2225 of the current buffer. Each element should have this form:
2228 (@var{characters} . @var{syntax-description})
2231 The @sc{car}, @var{characters}, can be either a character or a string.
2232 The element says to give that character or characters the syntax
2233 specified by @var{syntax-description}, which is passed to
2234 @code{modify-syntax-entry} (@pxref{Syntax Table Functions}).
2236 This feature is typically used to give word syntax to characters which
2237 normally have symbol syntax, and thus to simplify
2238 @code{imenu-generic-expression} and speed up matching.
2239 For example, Fortran mode uses it this way:
2242 (setq imenu-syntax-alist '(("_$" . "w")))
2245 The @code{imenu-generic-expression} regular expressions can then use
2246 @samp{\\sw+} instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this
2247 technique may be inconvenient when the mode needs to limit the initial
2248 character of a name to a smaller set of characters than are allowed in
2251 Setting this variable makes it buffer-local in the current buffer.
2254 Another way to customize Imenu for a major mode is to set the
2255 variables @code{imenu-prev-index-position-function} and
2256 @code{imenu-extract-index-name-function}:
2258 @defvar imenu-prev-index-position-function
2259 If this variable is non-@code{nil}, its value should be a function that
2260 finds the next ``definition'' to put in the buffer index, scanning
2261 backward in the buffer from point. It should return @code{nil} if it
2262 doesn't find another ``definition'' before point. Otherwise it should
2263 leave point at the place it finds a ``definition'' and return any
2264 non-@code{nil} value.
2266 Setting this variable makes it buffer-local in the current buffer.
2269 @defvar imenu-extract-index-name-function
2270 If this variable is non-@code{nil}, its value should be a function to
2271 return the name for a definition, assuming point is in that definition
2272 as the @code{imenu-prev-index-position-function} function would leave
2275 Setting this variable makes it buffer-local in the current buffer.
2278 The last way to customize Imenu for a major mode is to set the
2279 variable @code{imenu-create-index-function}:
2281 @defvar imenu-create-index-function
2282 This variable specifies the function to use for creating a buffer
2283 index. The function should take no arguments, and return an index
2284 alist for the current buffer. It is called within
2285 @code{save-excursion}, so where it leaves point makes no difference.
2287 The index alist can have three types of elements. Simple elements
2291 (@var{index-name} . @var{index-position})
2294 Selecting a simple element has the effect of moving to position
2295 @var{index-position} in the buffer. Special elements look like this:
2298 (@var{index-name} @var{index-position} @var{function} @var{arguments}@dots{})
2301 Selecting a special element performs:
2304 (funcall @var{function}
2305 @var{index-name} @var{index-position} @var{arguments}@dots{})
2308 A nested sub-alist element looks like this:
2311 (@var{menu-title} @var{sub-alist})
2314 It creates the submenu @var{menu-title} specified by @var{sub-alist}.
2316 The default value of @code{imenu-create-index-function} is
2317 @code{imenu-default-create-index-function}. This function calls the
2318 value of @code{imenu-prev-index-position-function} and the value of
2319 @code{imenu-extract-index-name-function} to produce the index alist.
2320 However, if either of these two variables is @code{nil}, the default
2321 function uses @code{imenu-generic-expression} instead.
2323 Setting this variable makes it buffer-local in the current buffer.
2326 @node Font Lock Mode
2327 @section Font Lock Mode
2328 @cindex Font Lock mode
2330 @dfn{Font Lock mode} is a feature that automatically attaches
2331 @code{face} properties to certain parts of the buffer based on their
2332 syntactic role. How it parses the buffer depends on the major mode;
2333 most major modes define syntactic criteria for which faces to use in
2334 which contexts. This section explains how to customize Font Lock for a
2335 particular major mode.
2337 Font Lock mode finds text to highlight in two ways: through
2338 syntactic parsing based on the syntax table, and through searching
2339 (usually for regular expressions). Syntactic fontification happens
2340 first; it finds comments and string constants and highlights them.
2341 Search-based fontification happens second.
2344 * Font Lock Basics:: Overview of customizing Font Lock.
2345 * Search-based Fontification:: Fontification based on regexps.
2346 * Customizing Keywords:: Customizing search-based fontification.
2347 * Other Font Lock Variables:: Additional customization facilities.
2348 * Levels of Font Lock:: Each mode can define alternative levels
2349 so that the user can select more or less.
2350 * Precalculated Fontification:: How Lisp programs that produce the buffer
2351 contents can also specify how to fontify it.
2352 * Faces for Font Lock:: Special faces specifically for Font Lock.
2353 * Syntactic Font Lock:: Fontification based on syntax tables.
2354 * Setting Syntax Properties:: Defining character syntax based on context
2355 using the Font Lock mechanism.
2356 * Multiline Font Lock:: How to coerce Font Lock into properly
2357 highlighting multiline constructs.
2360 @node Font Lock Basics
2361 @subsection Font Lock Basics
2363 There are several variables that control how Font Lock mode highlights
2364 text. But major modes should not set any of these variables directly.
2365 Instead, they should set @code{font-lock-defaults} as a buffer-local
2366 variable. The value assigned to this variable is used, if and when Font
2367 Lock mode is enabled, to set all the other variables.
2369 @defvar font-lock-defaults
2370 This variable is set by major modes, as a buffer-local variable, to
2371 specify how to fontify text in that mode. It automatically becomes
2372 buffer-local when you set it. If its value is @code{nil}, Font-Lock
2373 mode does no highlighting, and you can use the @samp{Faces} menu
2374 (under @samp{Edit} and then @samp{Text Properties} in the menu bar) to
2375 assign faces explicitly to text in the buffer.
2377 If non-@code{nil}, the value should look like this:
2380 (@var{keywords} [@var{keywords-only} [@var{case-fold}
2381 [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]])
2384 The first element, @var{keywords}, indirectly specifies the value of
2385 @code{font-lock-keywords} which directs search-based fontification.
2386 It can be a symbol, a variable or a function whose value is the list
2387 to use for @code{font-lock-keywords}. It can also be a list of
2388 several such symbols, one for each possible level of fontification.
2389 The first symbol specifies the @samp{mode default} level of
2390 fontification, the next symbol level 1 fontification, the next level 2,
2391 and so on. The @samp{mode default} level is normally the same as level
2392 1. It is used when @code{font-lock-maximum-decoration} has a @code{nil}
2393 value. @xref{Levels of Font Lock}.
2395 The second element, @var{keywords-only}, specifies the value of the
2396 variable @code{font-lock-keywords-only}. If this is omitted or
2397 @code{nil}, syntactic fontification (of strings and comments) is also
2398 performed. If this is non-@code{nil}, such fontification is not
2399 performed. @xref{Syntactic Font Lock}.
2401 The third element, @var{case-fold}, specifies the value of
2402 @code{font-lock-keywords-case-fold-search}. If it is non-@code{nil},
2403 Font Lock mode ignores case when searching as directed by
2404 @code{font-lock-keywords}.
2406 If the fourth element, @var{syntax-alist}, is non-@code{nil}, it
2407 should be a list of cons cells of the form @code{(@var{char-or-string}
2408 . @var{string})}. These are used to set up a syntax table for
2409 syntactic fontification (@pxref{Syntax Table Functions}). The
2410 resulting syntax table is stored in @code{font-lock-syntax-table}.
2412 The fifth element, @var{syntax-begin}, specifies the value of
2413 @code{font-lock-beginning-of-syntax-function}. We recommend setting
2414 this variable to @code{nil} and using @code{syntax-begin-function}
2417 All the remaining elements (if any) are collectively called
2418 @var{other-vars}. Each of these elements should have the form
2419 @code{(@var{variable} . @var{value})}---which means, make
2420 @var{variable} buffer-local and then set it to @var{value}. You can
2421 use these @var{other-vars} to set other variables that affect
2422 fontification, aside from those you can control with the first five
2423 elements. @xref{Other Font Lock Variables}.
2426 If your mode fontifies text explicitly by adding
2427 @code{font-lock-face} properties, it can specify @code{(nil t)} for
2428 @code{font-lock-defaults} to turn off all automatic fontification.
2429 However, this is not required; it is possible to fontify some things
2430 using @code{font-lock-face} properties and set up automatic
2431 fontification for other parts of the text.
2433 @node Search-based Fontification
2434 @subsection Search-based Fontification
2436 The most important variable for customizing Font Lock mode is
2437 @code{font-lock-keywords}. It specifies the search criteria for
2438 search-based fontification. You should specify the value of this
2439 variable with @var{keywords} in @code{font-lock-defaults}.
2441 @defvar font-lock-keywords
2442 This variable's value is a list of the keywords to highlight. Be
2443 careful when composing regular expressions for this list; a poorly
2444 written pattern can dramatically slow things down!
2447 Each element of @code{font-lock-keywords} specifies how to find
2448 certain cases of text, and how to highlight those cases. Font Lock mode
2449 processes the elements of @code{font-lock-keywords} one by one, and for
2450 each element, it finds and handles all matches. Ordinarily, once
2451 part of the text has been fontified already, this cannot be overridden
2452 by a subsequent match in the same text; but you can specify different
2453 behavior using the @var{override} element of a @var{subexp-highlighter}.
2455 Each element of @code{font-lock-keywords} should have one of these
2460 Highlight all matches for @var{regexp} using
2461 @code{font-lock-keyword-face}. For example,
2464 ;; @r{Highlight occurrences of the word @samp{foo}}
2465 ;; @r{using @code{font-lock-keyword-face}.}
2469 The function @code{regexp-opt} (@pxref{Regexp Functions}) is useful
2470 for calculating optimal regular expressions to match a number of
2473 @item @var{function}
2474 Find text by calling @var{function}, and highlight the matches
2475 it finds using @code{font-lock-keyword-face}.
2477 When @var{function} is called, it receives one argument, the limit of
2478 the search; it should begin searching at point, and not search beyond the
2479 limit. It should return non-@code{nil} if it succeeds, and set the
2480 match data to describe the match that was found. Returning @code{nil}
2481 indicates failure of the search.
2483 Fontification will call @var{function} repeatedly with the same limit,
2484 and with point where the previous invocation left it, until
2485 @var{function} fails. On failure, @var{function} need not reset point
2486 in any particular way.
2488 @item (@var{matcher} . @var{subexp})
2489 In this kind of element, @var{matcher} is either a regular
2490 expression or a function, as described above. The @sc{cdr},
2491 @var{subexp}, specifies which subexpression of @var{matcher} should be
2492 highlighted (instead of the entire text that @var{matcher} matched).
2495 ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},}
2496 ;; @r{using @code{font-lock-keyword-face}.}
2500 If you use @code{regexp-opt} to produce the regular expression
2501 @var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp
2502 Functions}) to calculate the value for @var{subexp}.
2504 @item (@var{matcher} . @var{facespec})
2505 In this kind of element, @var{facespec} is an expression whose value
2506 specifies the face to use for highlighting. In the simplest case,
2507 @var{facespec} is a Lisp variable (a symbol) whose value is a face
2511 ;; @r{Highlight occurrences of @samp{fubar},}
2512 ;; @r{using the face which is the value of @code{fubar-face}.}
2513 ("fubar" . fubar-face)
2516 However, @var{facespec} can also evaluate to a list of this form:
2519 (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{})
2523 to specify the face @var{face} and various additional text properties
2524 to put on the text that matches. If you do this, be sure to add the
2525 other text property names that you set in this way to the value of
2526 @code{font-lock-extra-managed-props} so that the properties will also
2527 be cleared out when they are no longer appropriate. Alternatively,
2528 you can set the variable @code{font-lock-unfontify-region-function} to
2529 a function that clears these properties. @xref{Other Font Lock
2532 @item (@var{matcher} . @var{subexp-highlighter})
2533 In this kind of element, @var{subexp-highlighter} is a list
2534 which specifies how to highlight matches found by @var{matcher}.
2538 (@var{subexp} @var{facespec} [@var{override} [@var{laxmatch}]])
2541 The @sc{car}, @var{subexp}, is an integer specifying which subexpression
2542 of the match to fontify (0 means the entire matching text). The second
2543 subelement, @var{facespec}, is an expression whose value specifies the
2544 face, as described above.
2546 The last two values in @var{subexp-highlighter}, @var{override} and
2547 @var{laxmatch}, are optional flags. If @var{override} is @code{t},
2548 this element can override existing fontification made by previous
2549 elements of @code{font-lock-keywords}. If it is @code{keep}, then
2550 each character is fontified if it has not been fontified already by
2551 some other element. If it is @code{prepend}, the face specified by
2552 @var{facespec} is added to the beginning of the @code{font-lock-face}
2553 property. If it is @code{append}, the face is added to the end of the
2554 @code{font-lock-face} property.
2556 If @var{laxmatch} is non-@code{nil}, it means there should be no error
2557 if there is no subexpression numbered @var{subexp} in @var{matcher}.
2558 Obviously, fontification of the subexpression numbered @var{subexp} will
2559 not occur. However, fontification of other subexpressions (and other
2560 regexps) will continue. If @var{laxmatch} is @code{nil}, and the
2561 specified subexpression is missing, then an error is signaled which
2562 terminates search-based fontification.
2564 Here are some examples of elements of this kind, and what they do:
2567 ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar}, using}
2568 ;; @r{@code{foo-bar-face}, even if they have already been highlighted.}
2569 ;; @r{@code{foo-bar-face} should be a variable whose value is a face.}
2570 ("foo\\|bar" 0 foo-bar-face t)
2572 ;; @r{Highlight the first subexpression within each occurrence}
2573 ;; @r{that the function @code{fubar-match} finds,}
2574 ;; @r{using the face which is the value of @code{fubar-face}.}
2575 (fubar-match 1 fubar-face)
2578 @item (@var{matcher} . @var{anchored-highlighter})
2579 In this kind of element, @var{anchored-highlighter} specifies how to
2580 highlight text that follows a match found by @var{matcher}. So a
2581 match found by @var{matcher} acts as the anchor for further searches
2582 specified by @var{anchored-highlighter}. @var{anchored-highlighter}
2583 is a list of the following form:
2586 (@var{anchored-matcher} @var{pre-form} @var{post-form}
2587 @var{subexp-highlighters}@dots{})
2590 Here, @var{anchored-matcher}, like @var{matcher}, is either a regular
2591 expression or a function. After a match of @var{matcher} is found,
2592 point is at the end of the match. Now, Font Lock evaluates the form
2593 @var{pre-form}. Then it searches for matches of
2594 @var{anchored-matcher} and uses @var{subexp-highlighters} to highlight
2595 these. A @var{subexp-highlighter} is as described above. Finally,
2596 Font Lock evaluates @var{post-form}.
2598 The forms @var{pre-form} and @var{post-form} can be used to initialize
2599 before, and cleanup after, @var{anchored-matcher} is used. Typically,
2600 @var{pre-form} is used to move point to some position relative to the
2601 match of @var{matcher}, before starting with @var{anchored-matcher}.
2602 @var{post-form} might be used to move back, before resuming with
2605 After Font Lock evaluates @var{pre-form}, it does not search for
2606 @var{anchored-matcher} beyond the end of the line. However, if
2607 @var{pre-form} returns a buffer position that is greater than the
2608 position of point after @var{pre-form} is evaluated, then the position
2609 returned by @var{pre-form} is used as the limit of the search instead.
2610 It is generally a bad idea to return a position greater than the end
2611 of the line; in other words, the @var{anchored-matcher} search should
2617 ;; @r{Highlight occurrences of the word @samp{item} following}
2618 ;; @r{an occurrence of the word @samp{anchor} (on the same line)}
2619 ;; @r{in the value of @code{item-face}.}
2620 ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face))
2623 Here, @var{pre-form} and @var{post-form} are @code{nil}. Therefore
2624 searching for @samp{item} starts at the end of the match of
2625 @samp{anchor}, and searching for subsequent instances of @samp{anchor}
2626 resumes from where searching for @samp{item} concluded.
2628 @item (@var{matcher} @var{highlighters}@dots{})
2629 This sort of element specifies several @var{highlighter} lists for a
2630 single @var{matcher}. A @var{highlighter} list can be of the type
2631 @var{subexp-highlighter} or @var{anchored-highlighter} as described
2637 ;; @r{Highlight occurrences of the word @samp{anchor} in the value}
2638 ;; @r{of @code{anchor-face}, and subsequent occurrences of the word}
2639 ;; @r{@samp{item} (on the same line) in the value of @code{item-face}.}
2640 ("\\<anchor\\>" (0 anchor-face)
2641 ("\\<item\\>" nil nil (0 item-face)))
2644 @item (eval . @var{form})
2645 Here @var{form} is an expression to be evaluated the first time
2646 this value of @code{font-lock-keywords} is used in a buffer.
2647 Its value should have one of the forms described in this table.
2650 @strong{Warning:} Do not design an element of @code{font-lock-keywords}
2651 to match text which spans lines; this does not work reliably.
2652 For details, see @xref{Multiline Font Lock}.
2654 You can use @var{case-fold} in @code{font-lock-defaults} to specify
2655 the value of @code{font-lock-keywords-case-fold-search} which says
2656 whether search-based fontification should be case-insensitive.
2658 @defvar font-lock-keywords-case-fold-search
2659 Non-@code{nil} means that regular expression matching for the sake of
2660 @code{font-lock-keywords} should be case-insensitive.
2663 @node Customizing Keywords
2664 @subsection Customizing Search-Based Fontification
2666 You can use @code{font-lock-add-keywords} to add additional
2667 search-based fontification rules to a major mode, and
2668 @code{font-lock-remove-keywords} to remove rules.
2670 @defun font-lock-add-keywords mode keywords &optional how
2671 This function adds highlighting @var{keywords}, for the current buffer
2672 or for major mode @var{mode}. The argument @var{keywords} should be a
2673 list with the same format as the variable @code{font-lock-keywords}.
2675 If @var{mode} is a symbol which is a major mode command name, such as
2676 @code{c-mode}, the effect is that enabling Font Lock mode in
2677 @var{mode} will add @var{keywords} to @code{font-lock-keywords}.
2678 Calling with a non-@code{nil} value of @var{mode} is correct only in
2679 your @file{~/.emacs} file.
2681 If @var{mode} is @code{nil}, this function adds @var{keywords} to
2682 @code{font-lock-keywords} in the current buffer. This way of calling
2683 @code{font-lock-add-keywords} is usually used in mode hook functions.
2685 By default, @var{keywords} are added at the beginning of
2686 @code{font-lock-keywords}. If the optional argument @var{how} is
2687 @code{set}, they are used to replace the value of
2688 @code{font-lock-keywords}. If @var{how} is any other non-@code{nil}
2689 value, they are added at the end of @code{font-lock-keywords}.
2691 Some modes provide specialized support you can use in additional
2692 highlighting patterns. See the variables
2693 @code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types},
2694 and @code{java-font-lock-extra-types}, for example.
2696 @strong{Warning:} major mode commands must not call
2697 @code{font-lock-add-keywords} under any circumstances, either directly
2698 or indirectly, except through their mode hooks. (Doing so would lead to
2699 incorrect behavior for some minor modes.) They should set up their
2700 rules for search-based fontification by setting
2701 @code{font-lock-keywords}.
2704 @defun font-lock-remove-keywords mode keywords
2705 This function removes @var{keywords} from @code{font-lock-keywords}
2706 for the current buffer or for major mode @var{mode}. As in
2707 @code{font-lock-add-keywords}, @var{mode} should be a major mode
2708 command name or @code{nil}. All the caveats and requirements for
2709 @code{font-lock-add-keywords} apply here too.
2712 For example, this code
2715 (font-lock-add-keywords 'c-mode
2716 '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
2717 ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face)))
2721 adds two fontification patterns for C mode: one to fontify the word
2722 @samp{FIXME}, even in comments, and another to fontify the words
2723 @samp{and}, @samp{or} and @samp{not} as keywords.
2726 That example affects only C mode proper. To add the same patterns to
2727 C mode @emph{and} all modes derived from it, do this instead:
2730 (add-hook 'c-mode-hook
2732 (font-lock-add-keywords nil
2733 '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
2734 ("\\<\\(and\\|or\\|not\\)\\>" .
2735 font-lock-keyword-face)))))
2738 @node Other Font Lock Variables
2739 @subsection Other Font Lock Variables
2741 This section describes additional variables that a major mode can
2742 set by means of @var{other-vars} in @code{font-lock-defaults}
2743 (@pxref{Font Lock Basics}).
2745 @defvar font-lock-mark-block-function
2746 If this variable is non-@code{nil}, it should be a function that is
2747 called with no arguments, to choose an enclosing range of text for
2748 refontification for the command @kbd{M-o M-o}
2749 (@code{font-lock-fontify-block}).
2751 The function should report its choice by placing the region around it.
2752 A good choice is a range of text large enough to give proper results,
2753 but not too large so that refontification becomes slow. Typical values
2754 are @code{mark-defun} for programming modes or @code{mark-paragraph} for
2758 @defvar font-lock-extra-managed-props
2759 This variable specifies additional properties (other than
2760 @code{font-lock-face}) that are being managed by Font Lock mode. It
2761 is used by @code{font-lock-default-unfontify-region}, which normally
2762 only manages the @code{font-lock-face} property. If you want Font
2763 Lock to manage other properties as well, you must specify them in a
2764 @var{facespec} in @code{font-lock-keywords} as well as add them to
2765 this list. @xref{Search-based Fontification}.
2768 @defvar font-lock-fontify-buffer-function
2769 Function to use for fontifying the buffer. The default value is
2770 @code{font-lock-default-fontify-buffer}.
2773 @defvar font-lock-unfontify-buffer-function
2774 Function to use for unfontifying the buffer. This is used when
2775 turning off Font Lock mode. The default value is
2776 @code{font-lock-default-unfontify-buffer}.
2779 @defvar font-lock-fontify-region-function
2780 Function to use for fontifying a region. It should take two
2781 arguments, the beginning and end of the region, and an optional third
2782 argument @var{verbose}. If @var{verbose} is non-@code{nil}, the
2783 function should print status messages. The default value is
2784 @code{font-lock-default-fontify-region}.
2787 @defvar font-lock-unfontify-region-function
2788 Function to use for unfontifying a region. It should take two
2789 arguments, the beginning and end of the region. The default value is
2790 @code{font-lock-default-unfontify-region}.
2793 @defun jit-lock-register function &optional contextual
2794 This function tells Font Lock mode to run the Lisp function
2795 @var{function} any time it has to fontify or refontify part of the
2796 current buffer. It calls @var{function} before calling the default
2797 fontification functions, and gives it two arguments, @var{start} and
2798 @var{end}, which specify the region to be fontified or refontified.
2800 The optional argument @var{contextual}, if non-@code{nil}, forces Font
2801 Lock mode to always refontify a syntactically relevant part of the
2802 buffer, and not just the modified lines. This argument can usually be
2806 @defun jit-lock-unregister function
2807 If @var{function} was previously registered as a fontification
2808 function using @code{jit-lock-register}, this function unregisters it.
2811 @node Levels of Font Lock
2812 @subsection Levels of Font Lock
2814 Many major modes offer three different levels of fontification. You
2815 can define multiple levels by using a list of symbols for @var{keywords}
2816 in @code{font-lock-defaults}. Each symbol specifies one level of
2817 fontification; it is up to the user to choose one of these levels,
2818 normally by setting @code{font-lock-maximum-decoration} (@pxref{Font
2819 Lock,,, emacs, the GNU Emacs Manual}). The chosen level's symbol
2820 value is used to initialize @code{font-lock-keywords}.
2822 Here are the conventions for how to define the levels of
2827 Level 1: highlight function declarations, file directives (such as include or
2828 import directives), strings and comments. The idea is speed, so only
2829 the most important and top-level components are fontified.
2832 Level 2: in addition to level 1, highlight all language keywords,
2833 including type names that act like keywords, as well as named constant
2834 values. The idea is that all keywords (either syntactic or semantic)
2835 should be fontified appropriately.
2838 Level 3: in addition to level 2, highlight the symbols being defined in
2839 function and variable declarations, and all builtin function names,
2840 wherever they appear.
2843 @node Precalculated Fontification
2844 @subsection Precalculated Fontification
2846 Some major modes such as @code{list-buffers} and @code{occur}
2847 construct the buffer text programmatically. The easiest way for them
2848 to support Font Lock mode is to specify the faces of text when they
2849 insert the text in the buffer.
2851 The way to do this is to specify the faces in the text with the
2852 special text property @code{font-lock-face} (@pxref{Special
2853 Properties}). When Font Lock mode is enabled, this property controls
2854 the display, just like the @code{face} property. When Font Lock mode
2855 is disabled, @code{font-lock-face} has no effect on the display.
2857 It is ok for a mode to use @code{font-lock-face} for some text and
2858 also use the normal Font Lock machinery. But if the mode does not use
2859 the normal Font Lock machinery, it should not set the variable
2860 @code{font-lock-defaults}.
2862 @node Faces for Font Lock
2863 @subsection Faces for Font Lock
2864 @cindex faces for font lock
2865 @cindex font lock faces
2867 Font Lock mode can highlight using any face, but Emacs defines several
2868 faces specifically for syntactic highlighting. These @dfn{Font Lock
2869 faces} are listed below. They can also be used by major modes for
2870 syntactic highlighting outside of Font Lock mode (@pxref{Major Mode
2873 Each of these symbols is both a face name, and a variable whose
2874 default value is the symbol itself. Thus, the default value of
2875 @code{font-lock-comment-face} is @code{font-lock-comment-face}.
2877 The faces are listed with descriptions of their typical usage, and in
2878 order of greater to lesser ``prominence''. If a mode's syntactic
2879 categories do not fit well with the usage descriptions, the faces can be
2880 assigned using the ordering as a guide.
2883 @item font-lock-warning-face
2884 @vindex font-lock-warning-face
2885 for a construct that is peculiar, or that greatly changes the meaning of
2886 other text, like @samp{;;;###autoload} in Emacs Lisp and @samp{#error}
2889 @item font-lock-function-name-face
2890 @vindex font-lock-function-name-face
2891 for the name of a function being defined or declared.
2893 @item font-lock-variable-name-face
2894 @vindex font-lock-variable-name-face
2895 for the name of a variable being defined or declared.
2897 @item font-lock-keyword-face
2898 @vindex font-lock-keyword-face
2899 for a keyword with special syntactic significance, like @samp{for} and
2902 @item font-lock-comment-face
2903 @vindex font-lock-comment-face
2906 @item font-lock-comment-delimiter-face
2907 @vindex font-lock-comment-delimiter-face
2908 for comments delimiters, like @samp{/*} and @samp{*/} in C. On most
2909 terminals, this inherits from @code{font-lock-comment-face}.
2911 @item font-lock-type-face
2912 @vindex font-lock-type-face
2913 for the names of user-defined data types.
2915 @item font-lock-constant-face
2916 @vindex font-lock-constant-face
2917 for the names of constants, like @samp{NULL} in C.
2919 @item font-lock-builtin-face
2920 @vindex font-lock-builtin-face
2921 for the names of built-in functions.
2923 @item font-lock-preprocessor-face
2924 @vindex font-lock-preprocessor-face
2925 for preprocessor commands. This inherits, by default, from
2926 @code{font-lock-builtin-face}.
2928 @item font-lock-string-face
2929 @vindex font-lock-string-face
2930 for string constants.
2932 @item font-lock-doc-face
2933 @vindex font-lock-doc-face
2934 for documentation strings in the code. This inherits, by default, from
2935 @code{font-lock-string-face}.
2937 @item font-lock-negation-char-face
2938 @vindex font-lock-negation-char-face
2939 for easily-overlooked negation characters.
2942 @node Syntactic Font Lock
2943 @subsection Syntactic Font Lock
2944 @cindex syntactic font lock
2946 Syntactic fontification uses the syntax table to find comments and
2947 string constants (@pxref{Syntax Tables}). It highlights them using
2948 @code{font-lock-comment-face} and @code{font-lock-string-face}
2949 (@pxref{Faces for Font Lock}), or whatever
2950 @code{font-lock-syntactic-face-function} chooses. There are several
2951 variables that affect syntactic fontification; you should set them by
2952 means of @code{font-lock-defaults} (@pxref{Font Lock Basics}).
2954 @defvar font-lock-keywords-only
2955 Non-@code{nil} means Font Lock should not do syntactic fontification;
2956 it should only fontify based on @code{font-lock-keywords}. The normal
2957 way for a mode to set this variable to @code{t} is with
2958 @var{keywords-only} in @code{font-lock-defaults}.
2961 @defvar font-lock-syntax-table
2962 This variable holds the syntax table to use for fontification of
2963 comments and strings. Specify it using @var{syntax-alist} in
2964 @code{font-lock-defaults}. If this is @code{nil}, fontification uses
2965 the buffer's syntax table.
2968 @defvar font-lock-beginning-of-syntax-function
2969 If this variable is non-@code{nil}, it should be a function to move
2970 point back to a position that is syntactically at ``top level'' and
2971 outside of strings or comments. Font Lock uses this when necessary
2972 to get the right results for syntactic fontification.
2974 This function is called with no arguments. It should leave point at
2975 the beginning of any enclosing syntactic block. Typical values are
2976 @code{beginning-of-line} (used when the start of the line is known to
2977 be outside a syntactic block), or @code{beginning-of-defun} for
2978 programming modes, or @code{backward-paragraph} for textual modes.
2980 If the value is @code{nil}, Font Lock uses
2981 @code{syntax-begin-function} to move back outside of any comment,
2982 string, or sexp. This variable is semi-obsolete; we recommend setting
2983 @code{syntax-begin-function} instead.
2985 Specify this variable using @var{syntax-begin} in
2986 @code{font-lock-defaults}.
2989 @defvar font-lock-syntactic-face-function
2990 A function to determine which face to use for a given syntactic
2991 element (a string or a comment). The function is called with one
2992 argument, the parse state at point returned by
2993 @code{parse-partial-sexp}, and should return a face. The default
2994 value returns @code{font-lock-comment-face} for comments and
2995 @code{font-lock-string-face} for strings.
2997 This can be used to highlighting different kinds of strings or
2998 comments differently. It is also sometimes abused together with
2999 @code{font-lock-syntactic-keywords} to highlight constructs that span
3000 multiple lines, but this is too esoteric to document here.
3002 Specify this variable using @var{other-vars} in
3003 @code{font-lock-defaults}.
3006 @node Setting Syntax Properties
3007 @subsection Setting Syntax Properties
3009 Font Lock mode can be used to update @code{syntax-table} properties
3010 automatically (@pxref{Syntax Properties}). This is useful in
3011 languages for which a single syntax table by itself is not sufficient.
3013 @defvar font-lock-syntactic-keywords
3014 This variable enables and controls updating @code{syntax-table}
3015 properties by Font Lock. Its value should be a list of elements of
3019 (@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch})
3022 The parts of this element have the same meanings as in the corresponding
3023 sort of element of @code{font-lock-keywords},
3026 (@var{matcher} @var{subexp} @var{facespec} @var{override} @var{laxmatch})
3029 However, instead of specifying the value @var{facespec} to use for the
3030 @code{face} property, it specifies the value @var{syntax} to use for
3031 the @code{syntax-table} property. Here, @var{syntax} can be a string
3032 (as taken by @code{modify-syntax-entry}), a syntax table, a cons cell
3033 (as returned by @code{string-to-syntax}), or an expression whose value
3034 is one of those two types. @var{override} cannot be @code{prepend} or
3037 For example, an element of the form:
3040 ("\\$\\(#\\)" 1 ".")
3043 highlights syntactically a hash character when following a dollar
3044 character, with a SYNTAX of @code{"."} (meaning punctuation syntax).
3045 Assuming that the buffer syntax table specifies hash characters to
3046 have comment start syntax, the element will only highlight hash
3047 characters that do not follow dollar characters as comments
3050 An element of the form:
3058 highlights syntactically both single quotes which surround a single
3059 character, with a SYNTAX of @code{"\""} (meaning string quote syntax).
3060 Assuming that the buffer syntax table does not specify single quotes
3061 to have quote syntax, the element will only highlight single quotes of
3062 the form @samp{'@var{c}'} as strings syntactically. Other forms, such
3063 as @samp{foo'bar} or @samp{'fubar'}, will not be highlighted as
3066 Major modes normally set this variable with @var{other-vars} in
3067 @code{font-lock-defaults}.
3070 @node Multiline Font Lock
3071 @subsection Multiline Font Lock Constructs
3072 @cindex multiline font lock
3074 Normally, elements of @code{font-lock-keywords} should not match
3075 across multiple lines; that doesn't work reliably, because Font Lock
3076 usually scans just part of the buffer, and it can miss a multi-line
3077 construct that crosses the line boundary where the scan starts. (The
3078 scan normally starts at the beginning of a line.)
3080 Making elements that match multiline constructs work properly has
3081 two aspects: correct @emph{identification} and correct
3082 @emph{rehighlighting}. The first means that Font Lock finds all
3083 multiline constructs. The second means that Font Lock will correctly
3084 rehighlight all the relevant text when a multiline construct is
3085 changed---for example, if some of the text that was previously part of
3086 a multiline construct ceases to be part of it. The two aspects are
3087 closely related, and often getting one of them to work will appear to
3088 make the other also work. However, for reliable results you must
3089 attend explicitly to both aspects.
3091 There are three ways to ensure correct identification of multiline
3096 Add a function to @code{font-lock-extend-region-functions} that does
3097 the @emph{identification} and extends the scan so that the scanned
3098 text never starts or ends in the middle of a multiline construct.
3100 Use the @code{font-lock-fontify-region-function} hook similarly to
3101 extend the scan so that the scanned text never starts or ends in the
3102 middle of a multiline construct.
3104 Somehow identify the multiline construct right when it gets inserted
3105 into the buffer (or at any point after that but before font-lock
3106 tries to highlight it), and mark it with a @code{font-lock-multiline}
3107 which will instruct font-lock not to start or end the scan in the
3108 middle of the construct.
3111 There are three ways to do rehighlighting of multiline constructs:
3115 Place a @code{font-lock-multiline} property on the construct. This
3116 will rehighlight the whole construct if any part of it is changed. In
3117 some cases you can do this automatically by setting the
3118 @code{font-lock-multiline} variable, which see.
3120 Make sure @code{jit-lock-contextually} is set and rely on it doing its
3121 job. This will only rehighlight the part of the construct that
3122 follows the actual change, and will do it after a short delay.
3123 This only works if the highlighting of the various parts of your
3124 multiline construct never depends on text in subsequent lines.
3125 Since @code{jit-lock-contextually} is activated by default, this can
3126 be an attractive solution.
3128 Place a @code{jit-lock-defer-multiline} property on the construct.
3129 This works only if @code{jit-lock-contextually} is used, and with the
3130 same delay before rehighlighting, but like @code{font-lock-multiline},
3131 it also handles the case where highlighting depends on
3136 * Font Lock Multiline:: Marking multiline chunks with a text property.
3137 * Region to Refontify:: Controlling which region gets refontified
3138 after a buffer change.
3141 @node Font Lock Multiline
3142 @subsubsection Font Lock Multiline
3144 One way to ensure reliable rehighlighting of multiline Font Lock
3145 constructs is to put on them the text property @code{font-lock-multiline}.
3146 It should be present and non-@code{nil} for text that is part of a
3147 multiline construct.
3149 When Font Lock is about to highlight a range of text, it first
3150 extends the boundaries of the range as necessary so that they do not
3151 fall within text marked with the @code{font-lock-multiline} property.
3152 Then it removes any @code{font-lock-multiline} properties from the
3153 range, and highlights it. The highlighting specification (mostly
3154 @code{font-lock-keywords}) must reinstall this property each time,
3155 whenever it is appropriate.
3157 @strong{Warning:} don't use the @code{font-lock-multiline} property
3158 on large ranges of text, because that will make rehighlighting slow.
3160 @defvar font-lock-multiline
3161 If the @code{font-lock-multiline} variable is set to @code{t}, Font
3162 Lock will try to add the @code{font-lock-multiline} property
3163 automatically on multiline constructs. This is not a universal
3164 solution, however, since it slows down Font Lock somewhat. It can
3165 miss some multiline constructs, or make the property larger or smaller
3168 For elements whose @var{matcher} is a function, the function should
3169 ensure that submatch 0 covers the whole relevant multiline construct,
3170 even if only a small subpart will be highlighted. It is often just as
3171 easy to add the @code{font-lock-multiline} property by hand.
3174 The @code{font-lock-multiline} property is meant to ensure proper
3175 refontification; it does not automatically identify new multiline
3176 constructs. Identifying the requires that Font-Lock operate on large
3177 enough chunks at a time. This will happen by accident on many cases,
3178 which may give the impression that multiline constructs magically work.
3179 If you set the @code{font-lock-multiline} variable non-@code{nil},
3180 this impression will be even stronger, since the highlighting of those
3181 constructs which are found will be properly updated from then on.
3182 But that does not work reliably.
3184 To find multiline constructs reliably, you must either manually
3185 place the @code{font-lock-multiline} property on the text before
3186 Font-Lock looks at it, or use
3187 @code{font-lock-fontify-region-function}.
3189 @node Region to Refontify
3190 @subsubsection Region to Fontify after a Buffer Change
3192 When a buffer is changed, the region that Font Lock refontifies is
3193 by default the smallest sequence of whole lines that spans the change.
3194 While this works well most of the time, sometimes it doesn't---for
3195 example, when a change alters the syntactic meaning of text on an
3198 You can enlarge (or even reduce) the region to refontify by setting
3199 the following variable:
3201 @defvar font-lock-extend-after-change-region-function
3202 This buffer-local variable is either @code{nil} or a function for
3203 Font-Lock to call to determine the region to scan and fontify.
3205 The function is given three parameters, the standard @var{beg},
3206 @var{end}, and @var{old-len} from @code{after-change-functions}
3207 (@pxref{Change Hooks}). It should return either a cons of the
3208 beginning and end buffer positions (in that order) of the region to
3209 fontify, or @code{nil} (which means choose the region in the standard
3210 way). This function needs to preserve point, the match-data, and the
3211 current restriction. The region it returns may start or end in the
3214 Since this function is called after every buffer change, it should be
3218 @node Auto-Indentation
3219 @section Auto-indentation of code
3221 For programming languages, an important feature of a major mode is to
3222 provide automatic indentation. This is controlled in Emacs by
3223 @code{indent-line-function} (@pxref{Mode-Specific Indent}).
3224 Writing a good indentation function can be difficult and to a large
3225 extent it is still a black art.
3227 Many major mode authors will start by writing a simple indentation
3228 function that works for simple cases, for example by comparing with the
3229 indentation of the previous text line. For most programming languages
3230 that are not really line-based, this tends to scale very poorly:
3231 improving such a function to let it handle more diverse situations tends
3232 to become more and more difficult, resulting in the end with a large,
3233 complex, unmaintainable indentation function which nobody dares to touch.
3235 A good indentation function will usually need to actually parse the
3236 text, according to the syntax of the language. Luckily, it is not
3237 necessary to parse the text in as much detail as would be needed
3238 for a compiler, but on the other hand, the parser embedded in the
3239 indentation code will want to be somewhat friendly to syntactically
3242 Good maintainable indentation functions usually fall into 2 categories:
3243 either parsing forward from some ``safe'' starting point until the
3244 position of interest, or parsing backward from the position of interest.
3245 Neither of the two is a clearly better choice than the other: parsing
3246 backward is often more difficult than parsing forward because
3247 programming languages are designed to be parsed forward, but for the
3248 purpose of indentation it has the advantage of not needing to
3249 guess a ``safe'' starting point, and it generally enjoys the property
3250 that only a minimum of text will be analyzed to decide the indentation
3251 of a line, so indentation will tend to be unaffected by syntax errors in
3252 some earlier unrelated piece of code. Parsing forward on the other hand
3253 is usually easier and has the advantage of making it possible to
3254 reindent efficiently a whole region at a time, with a single parse.
3256 Rather than write your own indentation function from scratch, it is
3257 often preferable to try and reuse some existing ones or to rely
3258 on a generic indentation engine. There are sadly few such
3259 engines. The CC-mode indentation code (used with C, C++, Java, Awk
3260 and a few other such modes) has been made more generic over the years,
3261 so if your language seems somewhat similar to one of those languages,
3262 you might try to use that engine. @c FIXME: documentation?
3263 Another one is SMIE which takes an approach in the spirit
3264 of Lisp sexps and adapts it to non-Lisp languages.
3267 * SMIE:: A simple minded indentation engine
3271 @subsection Simple Minded Indentation Engine
3273 SMIE is a package that provides a generic navigation and indentation
3274 engine. Based on a very simple parser using an ``operator precedence
3275 grammar'', it lets major modes extend the sexp-based navigation of Lisp
3276 to non-Lisp languages as well as provide a simple to use but reliable
3279 Operator precedence grammar is a very primitive technology for parsing
3280 compared to some of the more common techniques used in compilers.
3281 It has the following characteristics: its parsing power is very limited,
3282 and it is largely unable to detect syntax errors, but it has the
3283 advantage of being algorithmically efficient and able to parse forward
3284 just as well as backward. In practice that means that SMIE can use it
3285 for indentation based on backward parsing, that it can provide both
3286 @code{forward-sexp} and @code{backward-sexp} functionality, and that it
3287 will naturally work on syntactically incorrect code without any extra
3288 effort. The downside is that it also means that most programming
3289 languages cannot be parsed correctly using SMIE, at least not without
3290 resorting to some special tricks (@pxref{SMIE Tricks}).
3293 * SMIE setup:: SMIE setup and features
3294 * Operator Precedence Grammars:: A very simple parsing technique
3295 * SMIE Grammar:: Defining the grammar of a language
3296 * SMIE Lexer:: Defining tokens
3297 * SMIE Tricks:: Working around the parser's limitations
3298 * SMIE Indentation:: Specifying indentation rules
3299 * SMIE Indentation Helpers:: Helper functions for indentation rules
3300 * SMIE Indentation Example:: Sample indentation rules
3304 @subsubsection SMIE Setup and Features
3306 SMIE is meant to be a one-stop shop for structural navigation and
3307 various other features which rely on the syntactic structure of code, in
3308 particular automatic indentation. The main entry point is
3309 @code{smie-setup} which is a function typically called while setting
3312 @defun smie-setup grammar rules-function &rest keywords
3313 Setup SMIE navigation and indentation.
3314 @var{grammar} is a grammar table generated by @code{smie-prec2->grammar}.
3315 @var{rules-function} is a set of indentation rules for use on
3316 @code{smie-rules-function}.
3317 @var{keywords} are additional arguments, which can include the following
3321 @code{:forward-token} @var{fun}: Specify the forward lexer to use.
3323 @code{:backward-token} @var{fun}: Specify the backward lexer to use.
3327 Calling this function is sufficient to make commands such as
3328 @code{forward-sexp}, @code{backward-sexp}, and @code{transpose-sexps} be
3329 able to properly handle structural elements other than just the paired
3330 parentheses already handled by syntax tables. For example, if the
3331 provided grammar is precise enough, @code{transpose-sexps} can correctly
3332 transpose the two arguments of a @code{+} operator, taking into account
3333 the precedence rules of the language.
3335 Calling `smie-setup' is also sufficient to make TAB indentation work in
3336 the expected way, extends @code{blink-matching-paren} to apply to
3337 elements like @code{begin...end}, and provides some commands that you
3338 can bind in the major mode keymap.
3340 @deffn Command smie-close-block
3341 This command closes the most recently opened (and not yet closed) block.
3344 @deffn Command smie-down-list &optional arg
3345 This command is like @code{down-list} but it also pays attention to
3346 nesting of tokens other than parentheses, such as @code{begin...end}.
3349 @node Operator Precedence Grammars
3350 @subsubsection Operator Precedence Grammars
3352 SMIE's precedence grammars simply give to each token a pair of
3353 precedences: the left-precedence and the right-precedence. We say
3354 @code{T1 < T2} if the right-precedence of token @code{T1} is less than
3355 the left-precedence of token @code{T2}. A good way to read this
3356 @code{<} is as a kind of parenthesis: if we find @code{... T1 something
3357 T2 ...} then that should be parsed as @code{... T1 (something T2 ...}
3358 rather than as @code{... T1 something) T2 ...}. The latter
3359 interpretation would be the case if we had @code{T1 > T2}. If we have
3360 @code{T1 = T2}, it means that token T2 follows token T1 in the same
3361 syntactic construction, so typically we have @code{"begin" = "end"}.
3362 Such pairs of precedences are sufficient to express left-associativity
3363 or right-associativity of infix operators, nesting of tokens like
3364 parentheses and many other cases.
3366 @c Let's leave this undocumented to leave it more open for change!
3367 @c @defvar smie-grammar
3368 @c The value of this variable is an alist specifying the left and right
3369 @c precedence of each token. It is meant to be initialized by using one of
3370 @c the functions below.
3373 @defun smie-prec2->grammar table
3374 This function takes a @emph{prec2} grammar @var{table} and returns an
3375 alist suitable for use in @code{smie-setup}. The @emph{prec2}
3376 @var{table} is itself meant to be built by one of the functions below.
3379 @defun smie-merge-prec2s &rest tables
3380 This function takes several @emph{prec2} @var{tables} and merges them
3381 into a new @emph{prec2} table.
3384 @defun smie-precs->prec2 precs
3385 This function builds a @emph{prec2} table from a table of precedences
3386 @var{precs}. @var{precs} should be a list, sorted by precedence (for
3387 example @code{"+"} will come before @code{"*"}), of elements of the form
3388 @code{(@var{assoc} @var{op} ...)}, where each @var{op} is a token that
3389 acts as an operator; @var{assoc} is their associativity, which can be
3390 either @code{left}, @code{right}, @code{assoc}, or @code{nonassoc}.
3391 All operators in a given element share the same precedence level
3395 @defun smie-bnf->prec2 bnf &rest resolvers
3396 This function lets you specify the grammar using a BNF notation.
3397 It accepts a @var{bnf} description of the grammar along with a set of
3398 conflict resolution rules @var{resolvers}, and
3399 returns a @emph{prec2} table.
3401 @var{bnf} is a list of nonterminal definitions of the form
3402 @code{(@var{nonterm} @var{rhs1} @var{rhs2} ...)} where each @var{rhs}
3403 is a (non-empty) list of terminals (aka tokens) or non-terminals.
3405 Not all grammars are accepted:
3408 An @var{rhs} cannot be an empty list (an empty list is never needed,
3409 since SMIE allows all non-terminals to match the empty string anyway).
3411 An @var{rhs} cannot have 2 consecutive non-terminals: each pair of
3412 non-terminals needs to be separated by a terminal (aka token).
3413 This is a fundamental limitation of operator precedence grammars.
3416 Additionally, conflicts can occur:
3419 The returned @emph{prec2} table holds constraints between pairs of tokens, and
3420 for any given pair only one constraint can be present: T1 < T2,
3421 T1 = T2, or T1 > T2.
3423 A token can be an @code{opener} (something similar to an open-paren),
3424 a @code{closer} (like a close-paren), or @code{neither} of the two
3425 (e.g. an infix operator, or an inner token like @code{"else"}).
3428 Precedence conflicts can be resolved via @var{resolvers}, which
3429 is a list of @emph{precs} tables (see @code{smie-precs->prec2}): for
3430 each precedence conflict, if those @code{precs} tables
3431 specify a particular constraint, then the conflict is resolved by using
3432 this constraint instead, else a conflict is reported and one of the
3433 conflicting constraints is picked arbitrarily and the others are
3438 @subsubsection Defining the Grammar of a Language
3440 The usual way to define the SMIE grammar of a language is by
3441 defining a new global variable that holds the precedence table by
3442 giving a set of BNF rules.
3443 For example, the grammar definition for a small Pascal-like language
3448 (defvar sample-smie-grammar
3449 (smie-prec2->grammar
3454 (inst ("begin" insts "end")
3455 ("if" exp "then" inst "else" inst)
3458 (insts (insts ";" insts) (inst))
3462 (exps (exps "," exps) (exp)))
3467 '((assoc "+") (assoc "*")))))
3472 A few things to note:
3476 The above grammar does not explicitly mention the syntax of function
3477 calls: SMIE will automatically allow any sequence of sexps, such as
3478 identifiers, balanced parentheses, or @code{begin ... end} blocks
3479 to appear anywhere anyway.
3481 The grammar category @code{id} has no right hand side: this does not
3482 mean that it can match only the empty string, since as mentioned any
3483 sequence of sexps can appear anywhere anyway.
3485 Because non terminals cannot appear consecutively in the BNF grammar, it
3486 is difficult to correctly handle tokens that act as terminators, so the
3487 above grammar treats @code{";"} as a statement @emph{separator} instead,
3488 which SMIE can handle very well.
3490 Separators used in sequences (such as @code{","} and @code{";"} above)
3491 are best defined with BNF rules such as @code{(foo (foo "separator" foo) ...)}
3492 which generate precedence conflicts which are then resolved by giving
3493 them an explicit @code{(assoc "separator")}.
3495 The @code{("(" exps ")")} rule was not needed to pair up parens, since
3496 SMIE will pair up any characters that are marked as having paren syntax
3497 in the syntax table. What this rule does instead (together with the
3498 definition of @code{exps}) is to make it clear that @code{","} should
3499 not appear outside of parentheses.
3501 Rather than have a single @emph{precs} table to resolve conflicts, it is
3502 preferable to have several tables, so as to let the BNF part of the
3503 grammar specify relative precedences where possible.
3505 Unless there is a very good reason to prefer @code{left} or
3506 @code{right}, it is usually preferable to mark operators as associative,
3507 using @code{assoc}. For that reason @code{"+"} and @code{"*"} are
3508 defined above as @code{assoc}, although the language defines them
3509 formally as left associative.
3513 @subsubsection Defining Tokens
3515 SMIE comes with a predefined lexical analyzer which uses syntax tables
3516 in the following way: any sequence of characters that have word or
3517 symbol syntax is considered a token, and so is any sequence of
3518 characters that have punctuation syntax. This default lexer is
3519 often a good starting point but is rarely actually correct for any given
3520 language. For example, it will consider @code{"2,+3"} to be composed
3521 of 3 tokens: @code{"2"}, @code{",+"}, and @code{"3"}.
3523 To describe the lexing rules of your language to SMIE, you need
3524 2 functions, one to fetch the next token, and another to fetch the
3525 previous token. Those functions will usually first skip whitespace and
3526 comments and then look at the next chunk of text to see if it
3527 is a special token. If so it should skip the token and
3528 return a description of this token. Usually this is simply the string
3529 extracted from the buffer, but it can be anything you want.
3533 (defvar sample-keywords-regexp
3534 (regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "=")))
3537 (defun sample-smie-forward-token ()
3538 (forward-comment (point-max))
3540 ((looking-at sample-keywords-regexp)
3541 (goto-char (match-end 0))
3542 (match-string-no-properties 0))
3543 (t (buffer-substring-no-properties
3545 (progn (skip-syntax-forward "w_")
3549 (defun sample-smie-backward-token ()
3550 (forward-comment (- (point)))
3552 ((looking-back sample-keywords-regexp (- (point) 2) t)
3553 (goto-char (match-beginning 0))
3554 (match-string-no-properties 0))
3555 (t (buffer-substring-no-properties
3557 (progn (skip-syntax-backward "w_")
3562 Notice how those lexers return the empty string when in front of
3563 parentheses. This is because SMIE automatically takes care of the
3564 parentheses defined in the syntax table. More specifically if the lexer
3565 returns nil or an empty string, SMIE tries to handle the corresponding
3566 text as a sexp according to syntax tables.
3569 @subsubsection Living With a Weak Parser
3571 The parsing technique used by SMIE does not allow tokens to behave
3572 differently in different contexts. For most programming languages, this
3573 manifests itself by precedence conflicts when converting the
3576 Sometimes, those conflicts can be worked around by expressing the
3577 grammar slightly differently. For example, for Modula-2 it might seem
3578 natural to have a BNF grammar that looks like this:
3582 (inst ("IF" exp "THEN" insts "ELSE" insts "END")
3583 ("CASE" exp "OF" cases "END")
3585 (cases (cases "|" cases)
3586 (caselabel ":" insts)
3591 But this will create conflicts for @code{"ELSE"}: on the one hand, the
3592 IF rule implies (among many other things) that @code{"ELSE" = "END"};
3593 but on the other hand, since @code{"ELSE"} appears within @code{cases},
3594 which appears left of @code{"END"}, we also have @code{"ELSE" > "END"}.
3595 We can solve the conflict either by using:
3598 (inst ("IF" exp "THEN" insts "ELSE" insts "END")
3599 ("CASE" exp "OF" cases "END")
3600 ("CASE" exp "OF" cases "ELSE" insts "END")
3602 (cases (cases "|" cases) (caselabel ":" insts))
3608 (inst ("IF" exp "THEN" else "END")
3609 ("CASE" exp "OF" cases "END")
3611 (else (insts "ELSE" insts))
3612 (cases (cases "|" cases) (caselabel ":" insts) (else))
3616 Reworking the grammar to try and solve conflicts has its downsides, tho,
3617 because SMIE assumes that the grammar reflects the logical structure of
3618 the code, so it is preferable to keep the BNF closer to the intended
3619 abstract syntax tree.
3621 Other times, after careful consideration you may conclude that those
3622 conflicts are not serious and simply resolve them via the
3623 @var{resolvers} argument of @code{smie-bnf->prec2}. Usually this is
3624 because the grammar is simply ambiguous: the conflict does not affect
3625 the set of programs described by the grammar, but only the way those
3626 programs are parsed. This is typically the case for separators and
3627 associative infix operators, where you want to add a resolver like
3628 @code{'((assoc "|"))}. Another case where this can happen is for the
3629 classic @emph{dangling else} problem, where you will use @code{'((assoc
3630 "else" "then"))}. It can also happen for cases where the conflict is
3631 real and cannot really be resolved, but it is unlikely to pose a problem
3634 Finally, in many cases some conflicts will remain despite all efforts to
3635 restructure the grammar. Do not despair: while the parser cannot be
3636 made more clever, you can make the lexer as smart as you want. So, the
3637 solution is then to look at the tokens involved in the conflict and to
3638 split one of those tokens into 2 (or more) different tokens. E.g. if
3639 the grammar needs to distinguish between two incompatible uses of the
3640 token @code{"begin"}, make the lexer return different tokens (say
3641 @code{"begin-fun"} and @code{"begin-plain"}) depending on which kind of
3642 @code{"begin"} it finds. This pushes the work of distinguishing the
3643 different cases to the lexer, which will thus have to look at the
3644 surrounding text to find ad-hoc clues.
3646 @node SMIE Indentation
3647 @subsubsection Specifying Indentation Rules
3649 Based on the provided grammar, SMIE will be able to provide automatic
3650 indentation without any extra effort. But in practice, this default
3651 indentation style will probably not be good enough. You will want to
3652 tweak it in many different cases.
3654 SMIE indentation is based on the idea that indentation rules should be
3655 as local as possible. To this end, it relies on the idea of
3656 @emph{virtual} indentation, which is the indentation that a particular
3657 program point would have if it were at the beginning of a line.
3658 Of course, if that program point is indeed at the beginning of a line,
3659 its virtual indentation is its current indentation. But if not, then
3660 SMIE uses the indentation algorithm to compute the virtual indentation
3661 of that point. Now in practice, the virtual indentation of a program
3662 point does not have to be identical to the indentation it would have if
3663 we inserted a newline before it. To see how this works, the SMIE rule
3664 for indentation after a @code{@{} in C does not care whether the
3665 @code{@{} is standing on a line of its own or is at the end of the
3666 preceding line. Instead, these different cases are handled in the
3667 indentation rule that decides how to indent before a @code{@{}.
3669 Another important concept is the notion of @emph{parent}: The
3670 @emph{parent} of a token, is the head token of the nearest enclosing
3671 syntactic construct. For example, the parent of an @code{else} is the
3672 @code{if} to which it belongs, and the parent of an @code{if}, in turn,
3673 is the lead token of the surrounding construct. The command
3674 @code{backward-sexp} jumps from a token to its parent, but there are
3675 some caveats: for @emph{openers} (tokens which start a construct, like
3676 @code{if}), you need to start with point before the token, while for
3677 others you need to start with point after the token.
3678 @code{backward-sexp} stops with point before the parent token if that is
3679 the @emph{opener} of the token of interest, and otherwise it stops with
3680 point after the parent token.
3682 SMIE indentation rules are specified using a function that takes two
3683 arguments @var{method} and @var{arg} where the meaning of @var{arg} and the
3684 expected return value depend on @var{method}.
3686 @var{method} can be:
3689 @code{:after}, in which case @var{arg} is a token and the function
3690 should return the @var{offset} to use for indentation after @var{arg}.
3692 @code{:before}, in which case @var{arg} is a token and the function
3693 should return the @var{offset} to use to indent @var{arg} itself.
3695 @code{:elem}, in which case the function should return either the offset
3696 to use to indent function arguments (if @var{arg} is the symbol
3697 @code{arg}) or the basic indentation step (if @var{arg} is the symbol
3700 @code{:list-intro}, in which case @var{arg} is a token and the function
3701 should return non-@code{nil} if the token is followed by a list of
3702 expressions (not separated by any token) rather than an expression.
3705 When @var{arg} is a token, the function is called with point just before
3706 that token. A return value of nil always means to fallback on the
3707 default behavior, so the function should return nil for arguments it
3710 @var{offset} can be:
3713 @code{nil}: use the default indentation rule.
3715 @code{(column . @var{column})}: indent to column @var{column}.
3717 @var{number}: offset by @var{number}, relative to a base token which is
3718 the current token for @code{:after} and its parent for @code{:before}.
3721 @node SMIE Indentation Helpers
3722 @subsubsection Helper Functions for Indentation Rules
3724 SMIE provides various functions designed specifically for use in the
3725 indentation rules function (several of those functions break if used in
3726 another context). These functions all start with the prefix
3729 @defun smie-rule-bolp
3730 Return non-@code{nil} if the current token is the first on the line.
3733 @defun smie-rule-hanging-p
3734 Return non-@code{nil} if the current token is @emph{hanging}.
3735 A token is @emph{hanging} if it is the last token on the line
3736 and if it is preceded by other tokens: a lone token on a line is not
3740 @defun smie-rule-next-p &rest tokens
3741 Return non-@code{nil} if the next token is among @var{tokens}.
3744 @defun smie-rule-prev-p &rest tokens
3745 Return non-@code{nil} if the previous token is among @var{tokens}.
3748 @defun smie-rule-parent-p &rest parents
3749 Return non-@code{nil} if the current token's parent is among @var{parents}.
3752 @defun smie-rule-sibling-p
3753 Return non-nil if the current token's parent is actually a sibling.
3754 This is the case for example when the parent of a @code{","} is just the
3755 previous @code{","}.
3758 @defun smie-rule-parent &optional offset
3759 Return the proper offset to align the current token with the parent.
3760 If non-@code{nil}, @var{offset} should be an integer giving an
3761 additional offset to apply.
3764 @defun smie-rule-separator method
3765 Indent current token as a @emph{separator}.
3767 By @emph{separator}, we mean here a token whose sole purpose is to
3768 separate various elements within some enclosing syntactic construct, and
3769 which does not have any semantic significance in itself (i.e. it would
3770 typically not exist as a node in an abstract syntax tree).
3772 Such a token is expected to have an associative syntax and be closely
3773 tied to its syntactic parent. Typical examples are @code{","} in lists
3774 of arguments (enclosed inside parentheses), or @code{";"} in sequences
3775 of instructions (enclosed in a @code{@{...@}} or @code{begin...end}
3778 @var{method} should be the method name that was passed to
3779 `smie-rules-function'.
3782 @node SMIE Indentation Example
3783 @subsubsection Sample Indentation Rules
3785 Here is an example of an indentation function:
3788 (defun sample-smie-rules (kind token)
3789 (pcase (cons kind token)
3790 (`(:elem . basic) sample-indent-basic)
3791 (`(,_ . ",") (smie-rule-separator kind))
3792 (`(:after . ":=") sample-indent-basic)
3793 (`(:before . ,(or `"begin" `"(" `"@{")))
3794 (if (smie-rule-hanging-p) (smie-rule-parent)))
3796 (and (not (smie-rule-bolp)) (smie-rule-prev-p "else")
3797 (smie-rule-parent)))))
3801 A few things to note:
3805 The first case indicates the basic indentation increment to use.
3806 If @code{sample-indent-basic} is nil, then SMIE uses the global
3807 setting @code{smie-indent-basic}. The major mode could have set
3808 @code{smie-indent-basic} buffer-locally instead, but that
3812 The rule for the token @code{","} make SMIE try to be more clever when
3813 the comma separator is placed at the beginning of lines. It tries to
3814 outdent the separator so as to align the code after the comma; for
3818 x = longfunctionname (
3825 The rule for indentation after @code{":="} exists because otherwise
3826 SMIE would treat @code{":="} as an infix operator and would align the
3827 right argument with the left one.
3830 The rule for indentation before @code{"begin"} is an example of the use
3831 of virtual indentation: This rule is used only when @code{"begin"} is
3832 hanging, which can happen only when @code{"begin"} is not at the
3833 beginning of a line. So this is not used when indenting
3834 @code{"begin"} itself but only when indenting something relative to this
3835 @code{"begin"}. Concretely, this rule changes the indentation from:
3850 The rule for indentation before @code{"if"} is similar to the one for
3851 @code{"begin"}, but where the purpose is to treat @code{"else if"}
3852 as a single unit, so as to align a sequence of tests rather than indent
3853 each test further to the right. This function does this only in the
3854 case where the @code{"if"} is not placed on a separate line, hence the
3855 @code{smie-rule-bolp} test.
3857 If we know that the @code{"else"} is always aligned with its @code{"if"}
3858 and is always at the beginning of a line, we can use a more efficient
3862 (and (not (smie-rule-bolp))
3863 (smie-rule-prev-p "else")
3865 (sample-smie-backward-token)
3866 (cons 'column (current-column)))))
3869 The advantage of this formulation is that it reuses the indentation of
3870 the previous @code{"else"}, rather than going all the way back to the
3871 first @code{"if"} of the sequence.
3874 @node Desktop Save Mode
3875 @section Desktop Save Mode
3876 @cindex desktop save mode
3878 @dfn{Desktop Save Mode} is a feature to save the state of Emacs from
3879 one session to another. The user-level commands for using Desktop
3880 Save Mode are described in the GNU Emacs Manual (@pxref{Saving Emacs
3881 Sessions,,, emacs, the GNU Emacs Manual}). Modes whose buffers visit
3882 a file, don't have to do anything to use this feature.
3884 For buffers not visiting a file to have their state saved, the major
3885 mode must bind the buffer local variable @code{desktop-save-buffer} to
3886 a non-@code{nil} value.
3888 @defvar desktop-save-buffer
3889 If this buffer-local variable is non-@code{nil}, the buffer will have
3890 its state saved in the desktop file at desktop save. If the value is
3891 a function, it is called at desktop save with argument
3892 @var{desktop-dirname}, and its value is saved in the desktop file along
3893 with the state of the buffer for which it was called. When file names
3894 are returned as part of the auxiliary information, they should be
3895 formatted using the call
3898 (desktop-file-name @var{file-name} @var{desktop-dirname})
3903 For buffers not visiting a file to be restored, the major mode must
3904 define a function to do the job, and that function must be listed in
3905 the alist @code{desktop-buffer-mode-handlers}.
3907 @defvar desktop-buffer-mode-handlers
3911 (@var{major-mode} . @var{restore-buffer-function})
3914 The function @var{restore-buffer-function} will be called with
3918 (@var{buffer-file-name} @var{buffer-name} @var{desktop-buffer-misc})
3921 and it should return the restored buffer.
3922 Here @var{desktop-buffer-misc} is the value returned by the function
3923 optionally bound to @code{desktop-save-buffer}.