texinfo/texi2html/test/xemacs_manual/major.texi

@node Major Modes, Indentation, Mule, Top
@chapter Major Modes
@cindex major modes
@kindex TAB
@kindex DEL
@kindex LFD

  Emacs has many different @dfn{major modes}, each of which customizes
Emacs for editing text of a particular sort.  The major modes are mutually
exclusive;  at any time, each buffer has one major mode.  The mode line
normally contains the name of the current major mode in parentheses.
@xref{Mode Line}.

  The least specialized major mode is called @dfn{Fundamental mode}.  This
mode has no mode-specific redefinitions or variable settings.  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.  @key{TAB},
@key{DEL}, and @key{LFD} are changed frequently.  In addition, commands
which handle comments use the mode to determine how to delimit comments.
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, and Muddle mode 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 by Emacs for specific
purposes and include Dired mode for buffers made by Dired (@pxref{Dired}),
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 Choosing Major Modes

  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 some text in the file.

  Use a @kbd{M-x} command to explicitly select a new major mode.  Add
@code{-mode} to the name of a major mode to get the name of a command to
select that mode.  For example, to enter Lisp mode, execute @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
@code{.c} are edited in C mode.  The variable @code{auto-mode-alist}
controls the correspondence between file names and major mode.  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)}. 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 non-blank 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.  Note how the semicolon is used to make Lisp
treat this line as a comment.  Such an explicit specification overrides any
default mode based on the file name.

  Another format of mode specification is:

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

@noindent
which allows other things besides the major mode name to be specified.
However, Emacs does not look for anything except the mode name.

The major mode can also be specified in a local variables list.
@xref{File Variables}.

@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}, Emacs uses the major mode
specified by the variable @code{default-major-mode}.  Normally this
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.