(emacs.info) Minor Modes

 
 Minor Modes
 ===========
 
    Minor modes are optional features which you can turn on or off.  For
 example, Auto Fill mode is a minor mode in which <SPC> breaks lines
 between words as you type.  All the minor modes are independent of each
 other and of the selected major mode.  Most minor modes say in the mode
 line when they are on; for example, `Fill' in the mode line means that
 Auto Fill mode is on.
 
    Append `-mode' to the name of a minor mode to get the name of a
 command function that turns the mode on or off.  Thus, the command to
 enable or disable Auto Fill mode is called `M-x auto-fill-mode'.  These
 commands are usually invoked with `M-x', but you can bind keys to them
 if you wish.  With no argument, the function turns the mode on if it was
 off and off if it was on.  This is known as "toggling".  A positive
 argument always turns the mode on, and an explicit zero argument or a
 negative argument always turns it off.
 
    Enabling or disabling some minor modes applies only to the current
 buffer; each buffer is independent of the other buffers.  Therefore, you
 can enable the mode in particular buffers and disable it in others.  The
 per-buffer minor modes include Abbrev mode, Auto Fill mode, Auto Save
 mode, Font-Lock mode, Hscroll mode, ISO Accents mode, Outline minor
 mode, Overwrite mode, and Binary Overwrite mode.
 
    Abbrev mode allows you to define abbreviations that automatically
 expand as you type them.  For example, `amd' might expand to `abbrev
 mode'.   Abbrevs, for full information.
 
    Auto Fill mode allows you to enter filled text without breaking lines
 explicitly.  Emacs inserts newlines as necessary to prevent lines from
 becoming too long.   Filling.
 
    Auto Save mode causes the contents of a buffer to be saved
 periodically to reduce the amount of work you can lose in case of a
 system crash.   Auto Save.
 
    Enriched mode enables editing and saving of formatted text.  
 Formatted Text.
 
    Flyspell mode automatically highlights misspelled words.  
 Spelling.
 
    Font-Lock mode automatically highlights certain textual units found
 in programs, such as comments, strings, and function names being
 defined.  This requires a window system that can display multiple fonts.
  Faces.
 
    Hscroll mode performs horizontal scrolling automatically to keep
 point on the screen.   Horizontal Scrolling.
 
    ISO Accents mode makes the characters ``', `'', `"', `^', `/' and
 `~' combine with the following letter, to produce an accented letter in
 the ISO Latin-1 character set.   Single-Byte European Support.
 
    Outline minor mode provides the same facilities as the major mode
 called Outline mode; but since it is a minor mode instead, you can
 combine it with any major mode.   Outline Mode.
 
    Overwrite mode causes ordinary printing characters to replace
 existing text instead of shoving it to the right.  For example, if
 point is in front of the `B' in `FOOBAR', then in Overwrite mode typing
 a `G' changes it to `FOOGAR', instead of producing `FOOGBAR' as usual.
 In Overwrite mode, the command `C-q' inserts the next character
 whatever it may be, even if it is a digit--this gives you a way to
 insert a character instead of replacing an existing character.
 
    Binary Overwrite mode is a variant of Overwrite mode for editing
 binary files; it treats newlines and tabs like other characters, so that
 they overwrite other characters and can be overwritten by them.
 
    The following minor modes normally apply to all buffers at once.
 Since each is enabled or disabled by the value of a variable, you _can_
 set them differently for particular buffers, by explicitly making the
 corresponding variables local in those buffers.   Locals.
 
    Icomplete mode displays an indication of available completions when
 you are in the minibuffer and completion is active.   Completion
 Options.
 
    Line Number mode enables continuous display in the mode line of the
 line number of point.   Mode Line.
 
    Resize-Minibuffer mode makes the minibuffer expand as necessary to
 hold the text that you put in it.   Minibuffer Edit.
 
    Scroll Bar mode gives each window a scroll bar ( Scroll Bars).
 Menu Bar mode gives each frame a menu bar ( Menu Bars).  Both of
 these modes are enabled by default when you use the X Window System.
 
    In Transient Mark mode, every change in the buffer contents
 "deactivates" the mark, so that commands that operate on the region
 will get an error.  This means you must either set the mark, or
 explicitly "reactivate" it, before each command that uses the region.
 The advantage of Transient Mark mode is that Emacs can display the
 region highlighted (currently only when using X).   Setting Mark.
 
    For most minor modes, the command name is also the name of a variable
 which directly controls the mode.  The mode is enabled whenever this
 variable's value is non-`nil', and the minor-mode command works by
 setting the variable.  For example, the command `outline-minor-mode'
 works by setting the value of `outline-minor-mode' as a variable; it is
 this variable that directly turns Outline minor mode on and off.  To
 check whether a given minor mode works this way, use `C-h v' to ask for
 documentation on the variable name.
 
    These minor-mode variables provide a good way for Lisp programs to
 turn minor modes on and off; they are also useful in a file's local
 variables list.  But please think twice before setting minor modes with
 a local variables list, because most minor modes are matter of user
 preference--other users editing the same file might not want the same
 minor modes you prefer.
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