@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Major Modes, Indentation, Frames, Top
@chapter Major Modes
@cindex major modes
@cindex mode, major
@kindex TAB
@kindex DEL
@kindex LFD

  Emacs provides many alternative @dfn{major modes}, each of which
customizes Emacs for editing text of a particular sort.  The major modes
are mutually exclusive, and each buffer has one major mode at any time.
The mode line normally shows the name of the current major mode, in
parentheses (@pxref{Mode Line}).

  The least specialized major mode is called @dfn{Fundamental mode}.  This
mode has no mode-specific redefinitions or variable settings, so that each
Emacs command behaves in its most general manner, and each option is in its
default state.  For editing any specific type of text, such as Lisp code or
English text, you should switch to the appropriate major mode, such as Lisp
mode or Text mode.

  Selecting a major mode changes the meanings of a few keys to become more
specifically adapted to the language being edited.  The ones which are
changed frequently are @key{TAB}, @key{DEL}, and @key{LFD}.  In addition,
the commands which handle comments use the mode to determine how comments
are to be delimited.  Many major modes redefine the syntactical properties
of characters appearing in the buffer.  @xref{Syntax}.

  The major modes fall into three major groups.  Lisp mode (which has
several variants), C mode, Fortran mode and others are for specific
programming languages.  Text mode, Nroff mode, @TeX{} mode and Outline
mode are for editing English text.  The remaining major modes are not
intended for use on users' files; they are used in buffers created for
specific purposes by Emacs, such as Dired mode for buffers made by Dired
(@pxref{Dired}), and Mail mode for buffers made by @kbd{C-x m}
(@pxref{Sending Mail}), and Shell mode for buffers used for
communicating with an inferior shell process (@pxref{Interactive
Shell}).

  Most programming language major modes specify that only blank lines
separate paragraphs.  This is so that the paragraph commands remain useful.
(@xref{Paragraphs}.)  They also cause Auto Fill mode to use the definition of
@key{TAB} to indent the new lines it creates.  This is because most lines
in a program are usually indented.  (@xref{Indentation}.)

@menu
* Choosing Modes::     How major modes are specified or chosen.
@end menu

@node Choosing Modes,,Major Modes,Major Modes
@section How Major Modes are Chosen

  You can select a major mode explicitly for the current buffer, but
most of the time Emacs determines which mode to use based on the file
name or on special text in the file.

  Explicit selection of a new major mode is done with a @kbd{M-x} command.
From the name of a major mode, add @code{-mode} to get the name of a
command to select that mode.  Thus, you can enter Lisp mode by executing
@kbd{M-x lisp-mode}.

@vindex auto-mode-alist
  When you visit a file, Emacs usually chooses the right major mode based
on the file's name.  For example, files whose names end in @samp{.c} are
edited in C mode.  The correspondence between file names and major mode is
controlled by the variable @code{auto-mode-alist}.  Its value is a list in
which each element has the form

@example
(@var{regexp} . @var{mode-function})
@end example

@noindent
For example, one element normally found in the list has the form
@code{(@t{"\\.c$"} . c-mode)}, and it is responsible for selecting C mode
for files whose names end in @file{.c}.  (Note that @samp{\\} is needed in
Lisp syntax to include a @samp{\} in the string, which is needed to
suppress the special meaning of @samp{.} in regexps.)  The only practical
way to change this variable is with Lisp code.

  You can specify which major mode should be used for editing a certain
file by a special sort of text in the first nonblank line of the file.  The
mode name should appear in this line both preceded and followed by
@samp{-*-}.  Other text may appear on the line as well.  For example,

@example
;-*-Lisp-*-
@end example

@noindent
tells Emacs to use Lisp mode.  Such an explicit specification overrides
any defaulting based on the file name.  Note how the semicolon is used
to make Lisp treat this line as a comment.

  Another format of mode specification is

@example
-*-Mode: @var{modename};-*-
@end example

@noindent
which allows you to specify local variables as well, like this:

@example
-*- mode: @var{modename}; @var{var}: @var{value}; @dots{} -*-
@end example

@noindent
@xref{File Variables}, for more information about this.

@vindex default-major-mode
  When you visit a file that does not specify a major mode to use, or
when you create a new buffer with @kbd{C-x b}, the variable
@code{default-major-mode} specifies which major mode to use.  Normally
its value is the symbol @code{fundamental-mode}, which specifies
Fundamental mode.  If @code{default-major-mode} is @code{nil}, the major
mode is taken from the previously selected buffer.

@findex normal-mode
  If you change the major mode of a buffer, you can go back to the major
mode Emacs would choose automatically: use the command @kbd{M-x
normal-mode} to do this.  This is the same function that
@code{find-file} calls to choose the major mode.  It also processes
the file's local variables list if any.

