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(emacs)Minor Modes

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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.

   Some minor modes are global: while enabled, they affect everything
you do in the Emacs session, in all buffers.  Other minor modes are
buffer-local; they apply only to the current buffer, so you can enable
the mode in certain buffers and not others.

   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.

   The buffer-local minor modes include Abbrev mode, Auto Fill mode,
Auto Save mode, Font-Lock mode, Glasses 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'.  Note: 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.  Note: 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.  Note: Auto Save.

   Enriched mode enables editing and saving of formatted text.  Note:
Formatted Text.

   Flyspell mode automatically highlights misspelled words.  Note:
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.
Note: Faces.

   ISO Accents mode makes the characters ``', `'', `"', `^', `/' and
`~' combine with the following letter, to produce an accented letter in
the ISO Latin-1 character set.  The newer and more general feature of
input methods more or less supersedes ISO Accents mode.  Note:
Single-Byte Character 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.  Note: 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.

   The command `overwrite-mode' is an exception to the rule that
commands which toggle minor modes are normally not bound to keys: it is
bound to the <INSERT> function key.  This is because many other
programs bind <INSERT> to similar functions.

   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.  In
Binary Overwrite mode, digits after `C-q' specify an octal character
code, as usual.

   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.  Note: Locals.

   Icomplete mode displays an indication of available completions when
you are in the minibuffer and completion is active.  Note: Completion
Options.

   Line Number mode enables continuous display in the mode line of the
line number of point, and Column Number mode enables display of the
column number.  Note: Mode Line.

   Scroll Bar mode gives each window a scroll bar (Note: Scroll Bars).
Menu Bar mode gives each frame a menu bar (Note: 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).  Note: Mark.