1 @c -*- coding: utf-8 -*-
2 @c This is part of the Emacs manual.
3 @c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2016 Free Software
5 @c See file emacs.texi for copying conditions.
7 @chapter Major and Minor Modes
9 Emacs contains many @dfn{editing modes} that alter its basic
10 behavior in useful ways. These are divided into @dfn{major modes} and
13 Major modes provide specialized facilities for working on a
14 particular file type, such as a C source file (@pxref{Programs}), or a
15 particular type of non-file buffer, such as a shell buffer
16 (@pxref{Shell}). Major modes are mutually exclusive; each buffer has
17 one and only one major mode at any time.
19 Minor modes are optional features which you can turn on or off, not
20 necessarily specific to a type of file or buffer. For example, Auto
21 Fill mode is a minor mode in which @key{SPC} breaks lines between
22 words as you type (@pxref{Auto Fill}). Minor modes are independent of
23 one another, and of the selected major mode.
26 * Major Modes:: Text mode vs. Lisp mode vs. C mode...
27 * Minor Modes:: Each minor mode is a feature you can turn on
28 independently of any others.
29 * Choosing Modes:: How modes are chosen when visiting files.
36 @kindex TAB @r{(and major modes)}
37 @kindex DEL @r{(and major modes)}
38 @kindex C-j @r{(and major modes)}
40 Every buffer possesses a major mode, which determines the editing
41 behavior of Emacs while that buffer is current. The mode line
42 normally shows the name of the current major mode, in parentheses
45 The least specialized major mode is called @dfn{Fundamental mode}.
46 This mode has no mode-specific redefinitions or variable settings, so
47 that each Emacs command behaves in its most general manner, and each
48 user option variable is in its default state.
50 For editing text of a specific type that Emacs knows about, such as
51 Lisp code or English text, you typically use a more specialized major
52 mode, such as Lisp mode or Text mode. Most major modes fall into
53 three major groups. The first group contains modes for normal text,
54 either plain or with mark-up. It includes Text mode, HTML mode, SGML
55 mode, @TeX{} mode and Outline mode. The second group contains modes
56 for specific programming languages. These include Lisp mode (which
57 has several variants), C mode, Fortran mode, and others. The third
58 group consists of major modes that are not associated directly with
59 files; they are used in buffers created for specific purposes by
60 Emacs, such as Dired mode for buffers made by Dired (@pxref{Dired}),
61 Message mode for buffers made by @kbd{C-x m} (@pxref{Sending Mail}),
62 and Shell mode for buffers used to communicate with an inferior shell
63 process (@pxref{Interactive Shell}).
65 Usually, the major mode is automatically set by Emacs, when you
66 first visit a file or create a buffer (@pxref{Choosing Modes}). You
67 can explicitly select a new major mode by using an @kbd{M-x} command.
68 Take the name of the mode and add @code{-mode} to get the name of the
69 command to select that mode (e.g., @kbd{M-x lisp-mode} enters Lisp mode).
72 The value of the buffer-local variable @code{major-mode} is a symbol
73 with the same name as the major mode command (e.g., @code{lisp-mode}).
74 This variable is set automatically; you should not change it yourself.
76 The default value of @code{major-mode} determines the major mode to
77 use for files that do not specify a major mode, and for new buffers
78 created with @kbd{C-x b}. Normally, this default value is the symbol
79 @code{fundamental-mode}, which specifies Fundamental mode. You can
80 change this default value via the Customization interface (@pxref{Easy
81 Customization}), or by adding a line like this to your init file
85 (setq-default major-mode 'text-mode)
89 If the default value of @code{major-mode} is @code{nil}, the major
90 mode is taken from the previously current buffer.
92 Specialized major modes often change the meanings of certain keys to
93 do something more suitable for the mode. For instance, programming
94 language modes bind @key{TAB} to indent the current line according to
95 the rules of the language (@pxref{Indentation}). The keys that are
96 commonly changed are @key{TAB}, @key{DEL}, and @kbd{C-j}. Many modes
97 also define special commands of their own, usually bound in the prefix
98 key @kbd{C-c}. Major modes can also alter user options and variables;
99 for instance, programming language modes typically set a buffer-local
100 value for the variable @code{comment-start}, which determines how
101 source code comments are delimited (@pxref{Comments}).
103 @findex describe-mode
105 To view the documentation for the current major mode, including a
106 list of its key bindings, type @code{C-h m} (@code{describe-mode}).
109 @vindex text-mode-hook
110 @vindex prog-mode-hook
111 Every major mode, apart from Fundamental mode, defines a @dfn{mode
112 hook}, a customizable list of Lisp functions to run each time the mode
113 is enabled in a buffer. @xref{Hooks}, for more information about
114 hooks. Each mode hook is named after its major mode, e.g., Fortran
115 mode has @code{fortran-mode-hook}. Furthermore, all text-based major
116 modes run @code{text-mode-hook}, and all programming language modes
117 run @code{prog-mode-hook}, prior to running their own mode hooks.
118 Hook functions can look at the value of the variable @code{major-mode}
119 to see which mode is actually being entered.
121 Mode hooks are commonly used to enable minor modes (@pxref{Minor
122 Modes}). For example, you can put the following lines in your init
123 file to enable Flyspell minor mode in all text-based major modes
124 (@pxref{Spelling}), and Eldoc minor mode in Emacs Lisp mode
128 (add-hook 'text-mode-hook 'flyspell-mode)
129 (add-hook 'emacs-lisp-mode-hook 'eldoc-mode)
137 A minor mode is an optional editing mode that alters the behavior of
138 Emacs in some well-defined way. Unlike major modes, any number of
139 minor modes can be in effect at any time. Some minor modes are
140 @dfn{buffer-local}, and can be turned on (enabled) in certain buffers
141 and off (disabled) in others. Other minor modes are @dfn{global}:
142 while enabled, they affect everything you do in the Emacs session, in
143 all buffers. Most minor modes are disabled by default, but a few are
146 Most buffer-local minor modes say in the mode line when they are
147 enabled, just after the major mode indicator. For example,
148 @samp{Fill} in the mode line means that Auto Fill mode is enabled.
151 @cindex mode commands for minor modes
152 Like major modes, each minor mode is associated with a @dfn{mode
153 command}, whose name consists of the mode name followed by
154 @samp{-mode}. For instance, the mode command for Auto Fill mode is
155 @code{auto-fill-mode}. But unlike a major mode command, which simply
156 enables the mode, the mode command for a minor mode can either enable
161 If you invoke the mode command directly with no prefix argument
162 (either via @kbd{M-x}, or by binding it to a key and typing that key;
163 @pxref{Key Bindings}), that @dfn{toggles} the minor mode. The minor
164 mode is turned on if it was off, and turned off if it was on.
167 If you invoke the mode command with a prefix argument, the minor mode
168 is unconditionally turned off if that argument is zero or negative;
169 otherwise, it is unconditionally turned on.
172 If the mode command is called via Lisp, the minor mode is
173 unconditionally turned on if the argument is omitted or @code{nil}.
174 This makes it easy to turn on a minor mode from a major mode's mode
175 hook (@pxref{Major Modes}). A non-@code{nil} argument is handled like
176 an interactive prefix argument, as described above.
179 Most minor modes also have a @dfn{mode variable}, with the same name
180 as the mode command. Its value is non-@code{nil} if the mode is
181 enabled, and @code{nil} if it is disabled. In general, you should not
182 try to enable or disable the mode by changing the value of the mode
183 variable directly in Lisp; you should run the mode command instead.
184 However, setting the mode variable through the Customize interface
185 (@pxref{Easy Customization}) will always properly enable or disable
186 the mode, since Customize automatically runs the mode command for you.
188 The following is a list of some buffer-local minor modes:
192 Abbrev mode automatically expands text based on pre-defined
193 abbreviation definitions. @xref{Abbrevs}.
196 Auto Fill mode inserts newlines as you type to prevent lines from
197 becoming too long. @xref{Filling}.
200 Auto Save mode saves the buffer contents periodically to reduce the
201 amount of work you can lose in case of a crash. @xref{Auto Save}.
204 Electric Quote mode automatically converts quotation marks. For
205 example, it requotes text typed @t{`like this'} to text @t{‘like
206 this’}. You can control what kind of text it operates in, and you can
207 disable it entirely in individual buffers. @xref{Quotation Marks}.
210 Enriched mode enables editing and saving of formatted text.
211 @xref{Enriched Text}.
214 Flyspell mode automatically highlights misspelled words.
218 Font-Lock mode automatically highlights certain textual units found in
219 programs. It is enabled globally by default, but you can disable it
220 in individual buffers. @xref{Faces}.
225 Linum mode displays each line's line number in the window's left margin.
228 Outline minor mode provides similar facilities to the major mode
229 called Outline mode. @xref{Outline Mode}.
231 @cindex Overwrite mode
232 @cindex mode, Overwrite
233 @findex overwrite-mode
236 Overwrite mode causes ordinary printing characters to replace existing
237 text instead of shoving it to the right. For example, if point is in
238 front of the @samp{B} in @samp{FOOBAR}, then in Overwrite mode typing
239 a @kbd{G} changes it to @samp{FOOGAR}, instead of producing
240 @samp{FOOGBAR} as usual. In Overwrite mode, the command @kbd{C-q}
241 inserts the next character whatever it may be, even if it is a
242 digit---this gives you a way to insert a character instead of
243 replacing an existing character. The mode command,
244 @code{overwrite-mode}, is bound to the @key{Insert} key.
246 @findex binary-overwrite-mode
248 Binary Overwrite mode is a variant of Overwrite mode for editing
249 binary files; it treats newlines and tabs like other characters, so
250 that they overwrite other characters and can be overwritten by them.
251 In Binary Overwrite mode, digits after @kbd{C-q} specify an octal
252 character code, as usual.
255 Visual Line mode performs word wrapping, causing long lines to be
256 wrapped at word boundaries. @xref{Visual Line Mode}.
260 And here are some useful global minor modes:
264 Column Number mode enables display of the current column number in the
265 mode line. @xref{Mode Line}.
268 Delete Selection mode causes text insertion to first delete the text
269 in the region, if the region is active. @xref{Using Region}.
272 Icomplete mode displays an indication of available completions when
273 you are in the minibuffer and completion is active. @xref{Icomplete}.
276 Line Number mode enables display of the current line number in the
277 mode line. It is enabled by default. @xref{Mode Line}.
280 Menu Bar mode gives each frame a menu bar. It is enabled by default.
284 Scroll Bar mode gives each window a scroll bar. It is enabled by
285 default, but the scroll bar is only displayed on graphical terminals.
289 Tool Bar mode gives each frame a tool bar. It is enabled by default,
290 but the tool bar is only displayed on graphical terminals. @xref{Tool
294 Transient Mark mode highlights the region, and makes many Emacs
295 commands operate on the region when the mark is active. It is enabled
296 by default. @xref{Mark}.
300 @section Choosing File Modes
302 @cindex choosing a major mode
303 @cindex choosing a minor mode
304 @vindex auto-mode-alist
305 When you visit a file, Emacs chooses a major mode automatically.
306 Normally, it makes the choice based on the file name---for example,
307 files whose names end in @samp{.c} are normally edited in C mode---but
308 sometimes it chooses the major mode based on special text in the file.
309 This special text can also be used to enable buffer-local minor modes.
311 Here is the exact procedure:
313 First, Emacs checks whether the file contains file-local mode
314 variables. @xref{File Variables}. If there is a file-local variable
315 that specifies a major mode, then Emacs uses that major mode, ignoring
316 all other criteria. There are several methods to specify a major mode
317 using a file-local variable; the simplest is to put the mode name in
318 the first nonblank line, preceded and followed by @samp{-*-}. Other
319 text may appear on the line as well. For example,
326 tells Emacs to use Lisp mode. Note how the semicolon is used to make
327 Lisp treat this line as a comment. You could equivalently write
334 You can also use file-local variables to specify buffer-local minor
335 modes, by using @code{eval} specifications. For example, this first
336 nonblank line puts the buffer in Lisp mode and enables Auto-Fill mode:
339 ; -*- mode: Lisp; eval: (auto-fill-mode 1); -*-
343 Note, however, that it is usually inappropriate to enable minor modes
344 this way, since most minor modes represent individual user
345 preferences. If you personally want to use a minor mode for a
346 particular file type, it is better to enable the minor mode via a
347 major mode hook (@pxref{Major Modes}).
349 @vindex interpreter-mode-alist
350 Second, if there is no file variable specifying a major mode, Emacs
351 checks whether the file's contents begin with @samp{#!}. If so, that
352 indicates that the file can serve as an executable shell command,
353 which works by running an interpreter named on the file's first line
354 (the rest of the file is used as input to the interpreter).
355 Therefore, Emacs tries to use the interpreter name to choose a mode.
356 For instance, a file that begins with @samp{#!/usr/bin/perl} is opened
357 in Perl mode. The variable @code{interpreter-mode-alist} specifies
358 the correspondence between interpreter program names and major modes.
360 When the first line starts with @samp{#!}, you usually cannot use
361 the @samp{-*-} feature on the first line, because the system would get
362 confused when running the interpreter. So Emacs looks for @samp{-*-}
363 on the second line in such files as well as on the first line. The
364 same is true for man pages which start with the magic string
365 @samp{'\"} to specify a list of troff preprocessors.
367 @vindex magic-mode-alist
368 Third, Emacs tries to determine the major mode by looking at the
369 text at the start of the buffer, based on the variable
370 @code{magic-mode-alist}. By default, this variable is @code{nil} (an
371 empty list), so Emacs skips this step; however, you can customize it
372 in your init file (@pxref{Init File}). The value should be a list of
376 (@var{regexp} . @var{mode-function})
380 where @var{regexp} is a regular expression (@pxref{Regexps}), and
381 @var{mode-function} is a major mode command. If the text at the
382 beginning of the file matches @var{regexp}, Emacs chooses the major
383 mode specified by @var{mode-function}.
385 Alternatively, an element of @code{magic-mode-alist} may have the form
388 (@var{match-function} . @var{mode-function})
392 where @var{match-function} is a Lisp function that is called at the
393 beginning of the buffer; if the function returns non-@code{nil}, Emacs
394 set the major mode with @var{mode-function}.
396 Fourth---if Emacs still hasn't found a suitable major mode---it
397 looks at the file's name. The correspondence between file names and
398 major modes is controlled by the variable @code{auto-mode-alist}. Its
399 value is a list in which each element has this form,
402 (@var{regexp} . @var{mode-function})
409 (@var{regexp} @var{mode-function} @var{flag})
413 For example, one element normally found in the list has the form
414 @code{(@t{"\\.c\\'"} . c-mode)}, and it is responsible for selecting C
415 mode for files whose names end in @file{.c}. (Note that @samp{\\} is
416 needed in Lisp syntax to include a @samp{\} in the string, which must
417 be used to suppress the special meaning of @samp{.} in regexps.) If
418 the element has the form @code{(@var{regexp} @var{mode-function}
419 @var{flag})} and @var{flag} is non-@code{nil}, then after calling
420 @var{mode-function}, Emacs discards the suffix that matched
421 @var{regexp} and searches the list again for another match.
423 @vindex auto-mode-case-fold
424 On GNU/Linux and other systems with case-sensitive file names, Emacs
425 performs a case-sensitive search through @code{auto-mode-alist}; if
426 this search fails, it performs a second case-insensitive search
427 through the alist. To suppress the second search, change the variable
428 @code{auto-mode-case-fold} to @code{nil}. On systems with
429 case-insensitive file names, such as Microsoft Windows, Emacs performs
430 a single case-insensitive search through @code{auto-mode-alist}.
432 @vindex magic-fallback-mode-alist
433 Finally, if Emacs @emph{still} hasn't found a major mode to use, it
434 compares the text at the start of the buffer to the variable
435 @code{magic-fallback-mode-alist}. This variable works like
436 @code{magic-mode-alist}, described above, except that is consulted
437 only after @code{auto-mode-alist}. By default,
438 @code{magic-fallback-mode-alist} contains forms that check for image
439 files, HTML/XML/SGML files, PostScript files, and Unix style Conf
443 If you have changed the major mode of a buffer, you can return to
444 the major mode Emacs would have chosen automatically, by typing
445 @kbd{M-x normal-mode}. This is the same function that
446 @code{find-file} calls to choose the major mode. It also processes
447 the file's @samp{-*-} line or local variables list (if any).
448 @xref{File Variables}.
450 @vindex change-major-mode-with-file-name
451 The commands @kbd{C-x C-w} and @code{set-visited-file-name} change to
452 a new major mode if the new file name implies a mode (@pxref{Saving}).
453 (@kbd{C-x C-s} does this too, if the buffer wasn't visiting a file.)
454 However, this does not happen if the buffer contents specify a major
455 mode, and certain special major modes do not allow the mode to
456 change. You can turn off this mode-changing feature by setting
457 @code{change-major-mode-with-file-name} to @code{nil}.