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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 `M-x' command.
From the name of a major mode, add `-mode' to get the name of a command
to select that mode. Thus, you can enter Lisp mode by executing `M-x
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 `.c'
are edited in C mode. The correspondence between file names and major
mode is controlled by the variable `auto-mode-alist'. Its value is a
list in which each element has the form
(REGEXP . MODE-FUNCTION)
For example, one element normally found in the list has the form
`("\\.c$" . c-mode)', and it is responsible for selecting C mode for
files whose names end in `.c'. (Note that `\\' is needed in Lisp
syntax to include a `\' in the string, which is needed to suppress the
special meaning of `.' 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
`-*-'. Other text may appear on the line as well. For example,
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
which allows you to specify local variables as well, like this:
-*- mode: MODENAME; VAR: VALUE; ... -*-
Note: File Variables, for more information about this.
When you visit a file that does not specify a major mode to use, or
when you create a new buffer with `C-x b', the variable
`default-major-mode' specifies which major mode to use. Normally its
value is the symbol `fundamental-mode', which specifies Fundamental
mode. If `default-major-mode' is `nil', the major mode is taken from
the previously selected buffer.
If you change the major mode of a buffer, you can go back to the
major mode Emacs would choose automatically: use the command `M-x
normal-mode' to do this. This is the same function that `find-file'
calls to choose the major mode. It also processes the file's local
variables list if any.
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