(emacs.info) Locals

 
 Local Variables
 ---------------
 
 `M-x make-local-variable <RET> VAR <RET>'
      Make variable VAR have a local value in the current buffer.
 
 `M-x kill-local-variable <RET> VAR <RET>'
      Make variable VAR use its global value in the current buffer.
 
 `M-x make-variable-buffer-local <RET> VAR <RET>'
      Mark variable VAR so that setting it will make it local to the
      buffer that is current at that time.
 
    Almost any variable can be made "local" to a specific Emacs buffer.
 This means that its value in that buffer is independent of its value in
 other buffers.  A few variables are always local in every buffer.
 Every other Emacs variable has a "global" value which is in effect in
 all buffers that have not made the variable local.
 
    `M-x make-local-variable' reads the name of a variable and makes it
 local to the current buffer.  Further changes in this buffer will not
 affect others, and further changes in the global value will not affect
 this buffer.
 
    `M-x make-variable-buffer-local' reads the name of a variable and
 changes the future behavior of the variable so that it will become local
 automatically when it is set.  More precisely, once a variable has been
 marked in this way, the usual ways of setting the variable automatically
 do `make-local-variable' first.  We call such variables "per-buffer"
 variables.
 
    Major modes ( Major Modes) always make variables local to the
 buffer before setting the variables.  This is why changing major modes
 in one buffer has no effect on other buffers.  Minor modes also work by
 setting variables--normally, each minor mode has one controlling
 variable which is non-`nil' when the mode is enabled ( Minor
 Modes).  For most minor modes, the controlling variable is per buffer.
 
    Emacs contains a number of variables that are always per-buffer.
 These include `abbrev-mode', `auto-fill-function', `case-fold-search',
 `comment-column', `ctl-arrow', `fill-column', `fill-prefix',
 `indent-tabs-mode', `left-margin', `mode-line-format', `overwrite-mode',
 `selective-display-ellipses', `selective-display', `tab-width', and
 `truncate-lines'.  Some other variables are always local in every
 buffer, but they are used for internal purposes.
 
    A few variables cannot be local to a buffer because they are always
 local to each display instead ( Multiple Displays).  If you try
 to make one of these variables buffer-local, you'll get an error
 message.
 
    `M-x kill-local-variable' reads the name of a variable and makes it
 cease to be local to the current buffer.  The global value of the
 variable henceforth is in effect in this buffer.  Setting the major mode
 kills all the local variables of the buffer except for a few variables
 specially marked as "permanent locals".
 
    To set the global value of a variable, regardless of whether the
 variable has a local value in the current buffer, you can use the Lisp
 construct `setq-default'.  This construct is used just like `setq', but
 it sets variables' global values instead of their local values (if
 any).  When the current buffer does have a local value, the new global
 value may not be visible until you switch to another buffer.  Here is
 an example:
 
      (setq-default fill-column 75)
 
 `setq-default' is the only way to set the global value of a variable
 that has been marked with `make-variable-buffer-local'.
 
    Lisp programs can use `default-value' to look at a variable's
 default value.  This function takes a symbol as argument and returns its
 default value.  The argument is evaluated; usually you must quote it
 explicitly.  For example, here's how to obtain the default value of
 `fill-column':
 
      (default-value 'fill-column)
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