(lispref.info)Auto Major Mode


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How Emacs Chooses a Major Mode
------------------------------

   Based on information in the file name or in the file itself, Emacs
automatically selects a major mode for the new buffer when a file is
visited.

 - Command: fundamental-mode
     Fundamental mode is a major mode that is not specialized for
     anything in particular.  Other major modes are defined in effect
     by comparison with this one--their definitions say what to change,
     starting from Fundamental mode.  The `fundamental-mode' function
     does *not* run any hooks, so it is not readily customizable.

 - Command: normal-mode &optional FIND-FILE
     This function establishes the proper major mode and local variable
     bindings for the current buffer.  First it calls `set-auto-mode',
     then it runs `hack-local-variables' to parse, and bind or evaluate
     as appropriate, any local variables.

     If the FIND-FILE argument to `normal-mode' is non-`nil',
     `normal-mode' assumes that the `find-file' function is calling it.
     In this case, it may process a local variables list at the end of
     the file.  The variable `enable-local-variables' controls whether
     to do so.

     If you run `normal-mode' yourself, the argument FIND-FILE is
     normally `nil'.  In this case, `normal-mode' unconditionally
     processes any local variables list.  Note: Local Variables in
     Files, for the syntax of the local
     variables section of a file.

     `normal-mode' uses `condition-case' around the call to the major
     mode function, so errors are caught and reported as a `File mode
     specification error',  followed by the original error message.

 - User Option: enable-local-variables
     This variable controls processing of local variables lists in files
     being visited.  A value of `t' means process the local variables
     lists unconditionally; `nil' means ignore them; anything else means
     ask the user what to do for each file.  The default value is `t'.

 - User Option: enable-local-eval
     This variable controls processing of `Eval:' in local variables
     lists in files being visited.  A value of `t' means process them
     unconditionally; `nil' means ignore them; anything else means ask
     the user what to do for each file.  The default value is `maybe'.

 - Function: set-auto-mode
     This function selects the major mode that is appropriate for the
     current buffer.  It may base its decision on the value of the `-*-'
     line, on the visited file name (using `auto-mode-alist'), or on the
     value of a local variable).  However, this function does not look
     for the `mode:' local variable near the end of a file; the
     `hack-local-variables' function does that.  Note: How Major Modes
     are Chosen.

 - User Option: default-major-mode
     This variable holds the default major mode for new buffers.  The
     standard value is `fundamental-mode'.

     If the value of `default-major-mode' is `nil', Emacs uses the
     (previously) current buffer's major mode for the major mode of a
     new buffer.  However, if the major mode symbol has a `mode-class'
     property with value `special', then it is not used for new buffers;
     Fundamental mode is used instead.  The modes that have this
     property are those such as Dired and Rmail that are useful only
     with text that has been specially prepared.

 - Variable: initial-major-mode
     The value of this variable determines the major mode of the initial
     `*scratch*' buffer.  The value should be a symbol that is a major
     mode command name.  The default value is `lisp-interaction-mode'.

 - Variable: auto-mode-alist
     This variable contains an association list of file name patterns
     (regular expressions; Note: Regular Expressions.) and
     corresponding major mode functions.  Usually, the file name
     patterns test for suffixes, such as `.el' and `.c', but this need
     not be the case.  Each element of the alist looks like `(REGEXP .
     mODE-FUNCTION)'.

     For example,

          (("^/tmp/fol/" . text-mode)
           ("\\.texinfo$" . texinfo-mode)
           ("\\.texi$" . texinfo-mode)

          ("\\.el$" . emacs-lisp-mode)
           ("\\.c$" . c-mode)
           ("\\.h$" . c-mode)
           ...)

     When you visit a file whose *expanded* file name (Note: File Name
     Expansion.) matches a REGEXP, `set-auto-mode' calls the
     corresponding MODE-FUNCTION.  This feature enables Emacs to select
     the proper major mode for most files.

     Here is an example of how to prepend several pattern pairs to
     `auto-mode-alist'.  (You might use this sort of expression in your
     `.emacs' file.)

          (setq auto-mode-alist
            (append
             ;; Filename starts with a dot.
             '(("/\\.[^/]*$" . fundamental-mode)
               ;; Filename has no dot.
               ("[^\\./]*$" . fundamental-mode)
               ("\\.C$" . c++-mode))
             auto-mode-alist))

 - Function: hack-local-variables &optional FORCE
     This function parses, and binds or evaluates as appropriate, any
     local variables for the current buffer.

     The handling of `enable-local-variables' documented for
     `normal-mode' actually takes place here.  The argument FORCE
     reflects the argument FIND-FILE given to `normal-mode'.


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