2 @node Major Modes, Indentation, Mule, Top
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.
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
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}.
29 The major modes fall into three major groups. Programming modes
30 (@pxref{Programs}) are for specific programming languages. Text modes
31 (like Nroff mode, @TeX{} mode, Outline mode, XML mode, etc.@:) are for
32 editing human readable text. The remaining major modes are not intended
33 for direct use in editing user files; they are used in buffers created
34 by Emacs for specific purposes. Examples of such modes include Dired
35 mode which is used for buffers made by Dired (@pxref{Dired}), Mail mode
36 for buffers made by @kbd{C-x m} (@pxref{Sending Mail}), and Shell mode
37 for buffers used for communicating with an inferior shell process
38 (@pxref{Interactive Shell}).
40 Most programming language major modes specify that only blank lines
41 separate paragraphs. This is so that the paragraph commands remain useful.
42 @xref{Paragraphs}. They also cause Auto Fill mode to use the definition of
43 @key{TAB} to indent the new lines it creates. This is because most lines
44 in a program are usually indented. @xref{Indentation}.
47 * Choosing Modes:: How major modes are specified or chosen.
48 * Mode Hooks:: Customizing a major mode
51 @node Choosing Modes, Mode Hooks, Major Modes, Major Modes
52 @section Choosing Major Modes
54 You can select a major mode explicitly for the current buffer, but
55 most of the time Emacs determines which mode to use based on the file
56 name or some text in the file.
58 Use a @kbd{M-x} command to explicitly select a new major mode. Add
59 @code{-mode} to the name of a major mode to get the name of a command to
60 select that mode. For example, to enter Lisp mode, execute @kbd{M-x
63 @vindex auto-mode-alist
64 When you visit a file, Emacs usually chooses the right major mode
65 based on the file's name. For example, files whose names end in
66 @code{.c} are edited in C mode. The variable @code{auto-mode-alist}
67 controls the correspondence between file names and major mode. Its value
68 is a list in which each element has the form:
71 (@var{regexp} . @var{mode-function})
75 For example, one element normally found in the list has the form
76 @code{(@t{"\\.c$"} . c-mode)}. It is responsible for selecting C mode
77 for files whose names end in @file{.c}. (Note that @samp{\\} is needed in
78 Lisp syntax to include a @samp{\} in the string, which is needed to
79 suppress the special meaning of @samp{.} in regexps.) The only practical
80 way to change this variable is with Lisp code.
82 You can specify which major mode should be used for editing a certain
83 file by a special sort of text in the first non-blank line of the file.
84 The mode name should appear in this line both preceded and followed by
85 @samp{-*-}. Other text may appear on the line as well. For example,
92 tells Emacs to use Lisp mode. Note how the semicolon is used to make Lisp
93 treat this line as a comment. Such an explicit specification overrides any
94 default mode based on the file name.
96 Another format of mode specification is:
99 -*-Mode: @var{modename};-*-
103 which allows other things besides the major mode name to be specified.
104 However, Emacs does not look for anything except the mode name.
106 The major mode can also be specified in a local variables list.
107 @xref{File Variables}.
109 @vindex default-major-mode
110 When you visit a file that does not specify a major mode to use, or
111 when you create a new buffer with @kbd{C-x b}, Emacs uses the major mode
112 specified by the variable @code{default-major-mode}. Normally this
113 value is the symbol @code{fundamental-mode}, which specifies Fundamental
114 mode. If @code{default-major-mode} is @code{nil}, the major mode is
115 taken from the previously selected buffer.
117 @node Mode Hooks, , Choosing Modes, Major Modes
118 @section Mode Hook Variables
120 @cindex Hook variables
124 @vindex lisp-mode-hook
125 @vindex emacs-lisp-mode-hook
126 @vindex lisp-interaction-mode-hook
127 @vindex scheme-mode-hook
129 The last step taken by a major mode, by convention, is to invoke a
130 list of user supplied functions that are stored in a ``hook'' variable.
131 This allows a user to further customize the major mode, and is
132 particularly convenient for setting up buffer local variables
135 The name of the hook variable is created by appending the string
136 @code{-hook} to the name of the major mode. For example, the hook
137 variable used by @code{text-mode} would be named @code{text-mode-hook}.
138 By convention the mode hook function receives no arguments. If a hook
139 variable does not exist, or it has the value @code{nil}, the major mode
142 The recommended way to add functions to a hook variable is with the
143 @code{add-hook} function. For example, to automatically turn on the
144 Auto Fill mode when Text mode is invoked the following code can be used in
145 the initialization file (@pxref{Init File})
148 (add-hook 'text-mode-hook 'turn-on-auto-fill)
151 The @code{add-hook} function will check that the function is not already
152 listed in the hook variable before adding it. It will also create a hook
153 variable with the value @code{nil} if one does not exist before adding
154 the function. @code{add-hook} adds functions to the front of the hook
155 variable list. This means that the last hook added is run first by the
156 major mode. It is considered very poor style to write hook functions
157 that depend on the order that hooks are executed.
159 Hooks can be removed from hook variables with @code{remove-hook}.