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