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date Mon, 13 Aug 2007 08:45:50 +0200
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1
2 @node Major Modes, Indentation, Windows, Top
3 @chapter Major Modes
4 @cindex major modes
5 @kindex TAB
6 @kindex DEL
7 @kindex LFD
8
9 Emacs has many different @dfn{major modes}, each of which customizes
10 Emacs for editing text of a particular sort. The major modes are mutually
11 exclusive; at any time, each buffer has one major mode. The mode line
12 normally contains the name of the current major mode in parentheses.
13 @xref{Mode Line}.
14
15 The least specialized major mode is called @dfn{Fundamental mode}. This
16 mode has no mode-specific redefinitions or variable settings. Each
17 Emacs command behaves in its most general manner, and each option is in its
18 default state. For editing any specific type of text, such as Lisp code or
19 English text, you should switch to the appropriate major mode, such as Lisp
20 mode or Text mode.
21
22 Selecting a major mode changes the meanings of a few keys to become
23 more specifically adapted to the language being edited. @key{TAB},
24 @key{DEL}, and @key{LFD} are changed frequently. In addition, commands
25 which handle comments use the mode to determine how to delimit comments.
26 Many major modes redefine the syntactical properties of characters
27 appearing in the buffer. @xref{Syntax}.
28
29 The major modes fall into three major groups. Lisp mode (which has
30 several variants), C mode, and Muddle mode are for specific programming
31 languages. Text mode, Nroff mode, @TeX{} mode, and Outline mode are for
32 editing English text. The remaining major modes are not intended for use
33 on users' files; they are used in buffers created by Emacs for specific
34 purposes and include Dired mode for buffers made by Dired (@pxref{Dired}),
35 Mail mode for buffers made by @kbd{C-x m} (@pxref{Sending Mail}), and Shell
36 mode for buffers used for communicating with an inferior shell process
37 (@pxref{Interactive Shell}).
38
39 Most programming language major modes specify that only blank lines
40 separate paragraphs. This is so that the paragraph commands remain useful.
41 @xref{Paragraphs}. They also cause Auto Fill mode to use the definition of
42 @key{TAB} to indent the new lines it creates. This is because most lines
43 in a program are usually indented. @xref{Indentation}.
44
45 @menu
46 * Choosing Modes:: How major modes are specified or chosen.
47 @end menu
48
49 @node Choosing Modes,,Major Modes,Major Modes
50 @section Choosing Major Modes
51
52 You can select a major mode explicitly for the current buffer, but
53 most of the time Emacs determines which mode to use based on the file
54 name or some text in the file.
55
56 Use a @kbd{M-x} command to explicitly select a new major mode. Add
57 @code{-mode} to the name of a major mode to get the name of a command to
58 select that mode. For example, to enter Lisp mode, execute @kbd{M-x
59 lisp-mode}.
60
61 @vindex auto-mode-alist
62 When you visit a file, Emacs usually chooses the right major mode
63 based on the file's name. For example, files whose names end in
64 @code{.c} are edited in C mode. The variable @code{auto-mode-alist}
65 controls the correspondence between file names and major mode. Its value
66 is a list in which each element has the form:
67
68 @example
69 (@var{regexp} . @var{mode-function})
70 @end example
71
72 @noindent
73 For example, one element normally found in the list has the form
74 @code{(@t{"\\.c$"} . c-mode)}. It is responsible for selecting C mode
75 for files whose names end in @file{.c}. (Note that @samp{\\} is needed in
76 Lisp syntax to include a @samp{\} in the string, which is needed to
77 suppress the special meaning of @samp{.} in regexps.) The only practical
78 way to change this variable is with Lisp code.
79
80 You can specify which major mode should be used for editing a certain
81 file by a special sort of text in the first non-blank line of the file.
82 The mode name should appear in this line both preceded and followed by
83 @samp{-*-}. Other text may appear on the line as well. For example,
84
85 @example
86 ;-*-Lisp-*-
87 @end example
88
89 @noindent
90 tells Emacs to use Lisp mode. Note how the semicolon is used to make Lisp
91 treat this line as a comment. Such an explicit specification overrides any
92 default mode based on the file name.
93
94 Another format of mode specification is:
95
96 @example
97 -*-Mode: @var{modename};-*-
98 @end example
99
100 @noindent
101 which allows other things besides the major mode name to be specified.
102 However, Emacs does not look for anything except the mode name.
103
104 The major mode can also be specified in a local variables list.
105 @xref{File Variables}.
106
107 @vindex default-major-mode
108 When you visit a file that does not specify a major mode to use, or
109 when you create a new buffer with @kbd{C-x b}, Emacs uses the major mode
110 specified by the variable @code{default-major-mode}. Normally this
111 value is the symbol @code{fundamental-mode}, which specifies Fundamental
112 mode. If @code{default-major-mode} is @code{nil}, the major mode is
113 taken from the previously selected buffer.