root/trunk/man/custom.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2000, 2001,
@c   2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Customization, Quitting, Amusements, Top
@chapter Customization
@cindex customization

  This chapter talks about various topics relevant to adapting the
behavior of Emacs in ways we have anticipated.
@iftex
See @cite{The Emacs Lisp Reference Manual}
@end iftex
@ifnottex
@xref{Top, Emacs Lisp, Emacs Lisp, elisp, The Emacs Lisp
Reference Manual},
@end ifnottex
for how to make more far-reaching and open-ended changes.  @xref{X
Resources}, for information on using X resources to customize Emacs.

  Customization that you do within Emacs normally affects only the
particular Emacs session that you do it in---it does not persist
between sessions unless you save the customization in a file such as
your init file (@file{.emacs}) that will affect future sessions.
(@xref{Init File}.)  When you tell the customization buffer to save
customizations for future sessions, this actually works by editing
@file{.emacs} for you.

  Another means of customization is the keyboard macro, which is a
sequence of keystrokes to be replayed with a single command.
@xref{Keyboard Macros}, for full instruction how to record, manage, and
replay sequences of keys.

@menu
* Minor Modes::         Each minor mode is one feature you can turn on
                          independently of any others.
* Easy Customization::  Convenient way to browse and change settings.
* Variables::           Many Emacs commands examine Emacs variables
                          to decide what to do; by setting variables,
                          you can control their functioning.
* Key Bindings::        The keymaps say what command each key runs.
                          By changing them, you can "redefine keys".
* Syntax::              The syntax table controls how words and
                          expressions are parsed.
* Init File::           How to write common customizations in the
                          @file{.emacs} file.
@end menu

@node Minor Modes
@section Minor Modes
@cindex minor modes
@cindex mode, minor

  Minor modes are optional features which you can turn on or off.  For
example, Auto Fill mode is a minor mode in which @key{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 enabled; for example, @samp{Fill} in the mode line means
that Auto Fill mode is enabled.

  You should append @code{-mode} to the name of a minor mode to
produce the name of the command that turns the mode on or off.  Thus,
the command to enable or disable Auto Fill mode is called
@code{auto-fill-mode}.  These commands are usually invoked with
@kbd{M-x}, but you can bind keys to them if you wish.

  With no argument, the minor mode function turns the mode on if it
was off, and off if it was on.  This is known as @dfn{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.  The variable's value is non-@code{nil} if the mode is
enabled and @code{nil} if it is disabled.  Some minor-mode commands
work by just setting the variable.  For example, the command
@code{abbrev-mode} works by setting the value of @code{abbrev-mode} as
a variable; it is this variable that directly turns Abbrev mode on and
off.  You can directly set the variable's value instead of calling the
mode function.  For other minor modes, you need to either set the
variable through the Customize interface or call the mode function to
correctly enable or disable the mode.  To check which of these two
possibilities applies to a given minor mode, use @kbd{C-h v} to ask
for documentation on the variable name.

  For minor mode commands that work by just setting the minor mode
variable, that variable provides a good way for Lisp programs to turn
minor modes on and off; it is also useful in a file's local variables
list (@pxref{File Variables}).  But please think twice before setting
minor modes with a local variables list, because most minor modes are
a matter of user preference---other users editing the same file might
not want the same minor modes you prefer.

  The most useful buffer-local minor modes include Abbrev mode, Auto
Fill mode, Auto Save mode, Font-Lock mode, Glasses 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, @samp{amd} might expand to @samp{abbrev
mode}.  @xref{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.  @xref{Filling}.

  Auto Save mode saves the buffer contents periodically to reduce the
amount of work you can lose in case of a crash.  @xref{Auto Save}.

  Enriched mode enables editing and saving of formatted text.
@xref{Formatted Text}.

  Flyspell mode automatically highlights misspelled words.
@xref{Spelling}.

  Font-Lock mode automatically highlights certain textual units found
in programs, such as comments, strings, and function names being
defined.  This requires a display that can show multiple fonts or
colors.  @xref{Faces}.

@ignore
  ISO Accents mode makes the characters @samp{`}, @samp{'}, @samp{"},
@samp{^}, @samp{/} and @samp{~} 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.  @xref{Unibyte Mode}.
@end ignore

  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.  @xref{Outline Mode}.

@cindex Overwrite mode
@cindex mode, Overwrite
  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 @samp{B} in @samp{FOOBAR}, then in Overwrite mode typing a
@kbd{G} changes it to @samp{FOOGAR}, instead of producing @samp{FOOGBAR}
as usual.  In Overwrite mode, the command @kbd{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.

@findex overwrite-mode
@kindex INSERT
  The command @code{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 @key{INSERT} function key.  This is because many other
programs bind @key{INSERT} to similar functions.

@findex binary-overwrite-mode
  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 @kbd{C-q} specify an
octal character code, as usual.

  Here are some useful minor modes that normally apply to all buffers
at once.  Since Line Number mode and Transient Mark mode can be
enabled or disabled just by setting the value of the minor mode
variable, you @emph{can} set them differently for particular buffers,
by explicitly making the corresponding variable local in those
buffers.  @xref{Locals}.

  Icomplete mode displays an indication of available completions when
you are in the minibuffer and completion is active.  @xref{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.  @xref{Mode Line}.

  Scroll Bar mode gives each window a scroll bar (@pxref{Scroll Bars}).
Menu Bar mode gives each frame a menu bar (@pxref{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.  @xref{Mark}.

@node Easy Customization
@section Easy Customization Interface

@cindex settings
  Emacs has many @dfn{settings} which have values that you can specify
in order to customize various commands.  Many are documented in this
manual.  Most settings are @dfn{user options}---that is to say, Lisp
variables (@pxref{Variables})---so their names appear in the Variable
Index (@pxref{Variable Index}).  The other settings are faces and
their attributes (@pxref{Faces}).

@findex customize
@cindex customization buffer
  You can browse interactively through settings and change them using
@kbd{M-x customize}.  This command creates a @dfn{customization
buffer}, which offers commands to navigate through a logically
organized structure of the Emacs settings; you can also use it to edit
and set their values, and to save settings permanently in your
@file{~/.emacs} file (@pxref{Init File}).

  The appearance of the example buffers in this section is typically
different under a graphical display, since faces are then used to indicate
buttons, links and editable fields.

@menu
* Groups: Customization Groups.   How settings are classified in a structure.
* Browsing: Browsing Custom.   Browsing and searching for settings.
* Changing a Variable::      How to edit an option's value and set the option.
* Saving Customizations::    Specifying the file for saving customizations.
* Face Customization::       How to edit the attributes of a face.
* Specific Customization::   Making a customization buffer for specific
                                variables, faces, or groups.
* Custom Themes::            How to define collections of customized options
                                that can be loaded and unloaded together.
@end menu

@node Customization Groups
@subsection Customization Groups
@cindex customization groups

  For customization purposes, settings are organized into @dfn{groups}
to help you find them.  Groups are collected into bigger groups, all
the way up to a master group called @code{Emacs}.

  @kbd{M-x customize} creates a customization buffer that shows the
top-level @code{Emacs} group and the second-level groups immediately
under it.  It looks like this, in part:

@c we want the buffer example to all be on one page, but unfortunately
@c that's quite a bit of text, so force all space to the bottom.
@page
@smallexample
@group
/- Emacs group: ---------------------------------------------------\
      [State]: visible group members are all at standard values.
   Customization of the One True Editor.
   See also [Manual].

Editing group: [Go to Group]
Basic text editing facilities.

External group: [Go to Group]
Interfacing to external utilities.

@var{more second-level groups}

\- Emacs group end ------------------------------------------------/
@end group
@end smallexample

@noindent
This says that the buffer displays the contents of the @code{Emacs}
group.  The other groups are listed because they are its contents.  But
they are listed differently, without indentation and dashes, because
@emph{their} contents are not included.  Each group has a single-line
documentation string; the @code{Emacs} group also has a @samp{[State]}
line.

@cindex editable fields (customization buffer)
@cindex buttons (customization buffer)
@cindex links (customization buffer)
  Most of the text in the customization buffer is read-only, but it
typically includes some @dfn{editable fields} that you can edit.
There are also @dfn{buttons} and @dfn{links}, which do something when
you @dfn{invoke} them.  To invoke a button or a link, either click on
it with @kbd{Mouse-1}, or move point to it and type @key{RET}.

  For example, the phrase @samp{[State]} that appears in
a second-level group is a button.  It operates on the same
customization buffer.  The phrase @samp{[Go to Group]} is a kind
of hypertext link to another group.  Invoking it creates a new
customization buffer, which shows that group and its contents.

  The @code{Emacs} group includes a few settings, but mainly it
contains other groups, which contain more groups, which contain the
settings.  By browsing the hierarchy of groups, you will eventually
find the feature you are interested in customizing.  Then you can use
the customization buffer to set that feature's settings.  You can also
go straight to a particular group by name, using the command @kbd{M-x
customize-group}.

@node Browsing Custom
@subsection Browsing and Searching for Options and Faces
@findex customize-browse

  @kbd{M-x customize-browse} is another way to browse the available
settings.  This command creates a special customization buffer which
shows only the names of groups and settings, and puts them in a
structure.

  In this buffer, you can show the contents of a group by invoking the
@samp{[+]} button.  When the group contents are visible, this button
changes to @samp{[-]}; invoking that hides the group contents again.

  Each group or setting in this buffer has a link which says
@samp{[Group]}, @samp{[Option]} or @samp{[Face]}.  Invoking this link
creates an ordinary customization buffer showing just that group and
its contents, just that user option, or just that face.  This is the
way to change settings that you find with @kbd{M-x customize-browse}.

  If you can guess part of the name of the settings you are interested
in, @kbd{M-x customize-apropos} is another way to search for settings.
However, unlike @code{customize} and @code{customize-browse},
@code{customize-apropos} can only find groups and settings that are
loaded in the current Emacs session.  @xref{Specific Customization,,
Customizing Specific Items}.

@node Changing a Variable
@subsection Changing a Variable

  Here is an example of what a variable (a user option) looks like in
the customization buffer:

@smallexample
Kill Ring Max: [Hide Value] 60
   [State]: STANDARD.
Maximum length of kill ring before oldest elements are thrown away.
@end smallexample

  The text following @samp{[Hide Value]}, @samp{60} in this case, indicates
the current value of the variable.  If you see @samp{[Show Value]} instead of
@samp{[Hide Value]}, it means that the value is hidden; the customization
buffer initially hides values that take up several lines.  Invoke
@samp{[Show Value]} to show the value.

  The line after the variable name indicates the @dfn{customization
state} of the variable: in the example above, it says you have not
changed the option yet.  The @samp{[State]} button at the beginning of
this line gives you a menu of various operations for customizing the
variable.

  The line after the @samp{[State]} line displays the beginning of the
variable's documentation string.  If there are more lines of
documentation, this line ends with a @samp{[More]} button; invoke that
to show the full documentation string.

  To enter a new value for @samp{Kill Ring Max}, move point to the
value and edit it textually.  For example, you can type @kbd{M-d},
then insert another number.  As you begin to alter the text, you will
see the @samp{[State]} line change to say that you have edited the
value:

@smallexample
[State]: EDITED, shown value does not take effect until you set or @r{@dots{}}
                                                           save it.
@end smallexample

@cindex user options, how to set
@cindex variables, how to set
@cindex settings, how to set
  Editing the value does not actually set the variable.  To do that,
you must @dfn{set} the variable.  To do this, invoke the
@samp{[State]} button and choose @samp{Set for Current Session}.

  The state of the variable changes visibly when you set it:

@smallexample
[State]: SET for current session only.
@end smallexample

   You don't have to worry about specifying a value that is not valid;
the @samp{Set for Current Session} operation checks for validity and
will not install an unacceptable value.

@kindex M-TAB @r{(customization buffer)}
@findex widget-complete
  While editing a field that is a file name, directory name,
command name, or anything else for which completion is defined, you
can type @kbd{M-@key{TAB}} (@code{widget-complete}) to do completion.
(@kbd{@key{ESC} @key{TAB}} and @kbd{C-M-i} do the same thing.)

  Some variables have a small fixed set of possible legitimate values.
These variables don't let you edit the value textually.  Instead, a
@samp{[Value Menu]} button appears before the value; invoke this
button to change the value.  For a boolean ``on or off'' value, the
button says @samp{[Toggle]}, and it changes to the other value.
@samp{[Value Menu]} and @samp{[Toggle]} simply edit the buffer; the
changes take real effect when you use the @samp{Set for Current
Session} operation.

  Some variables have values with complex structure.  For example, the
value of @code{file-coding-system-alist} is an association list.  Here
is how it appears in the customization buffer:

@smallexample
File Coding System Alist: [Hide Value]
[INS] [DEL] File regexp: \.elc\'
            Choice: [Value Menu] Encoding/decoding pair:
            Decoding: emacs-mule
            Encoding: emacs-mule
[INS] [DEL] File regexp: \(\`\|/\)loaddefs.el\'
            Choice: [Value Menu] Encoding/decoding pair:
            Decoding: raw-text
            Encoding: raw-text-unix
[INS] [DEL] File regexp: \.tar\'
            Choice: [Value Menu] Encoding/decoding pair:
            Decoding: no-conversion
            Encoding: no-conversion
[INS] [DEL] File regexp:
            Choice: [Value Menu] Encoding/decoding pair:
            Decoding: undecided
            Encoding: nil
[INS]
   [State]: STANDARD.
Alist to decide a coding system to use for a file I/O @r{@dots{}}
                                operation. [Hide Rest]
The format is ((PATTERN . VAL) ...),
where PATTERN is a regular expression matching a file name,
@r{[@dots{}more lines of documentation@dots{}]}
@end smallexample

@noindent
Each association in the list appears on four lines, with several
editable fields and/or buttons.  You can edit the regexps and coding
systems using ordinary editing commands.  You can also invoke
@samp{[Value Menu]} to switch to a different kind of value---for
instance, to specify a function instead of a pair of coding systems.

To delete an association from the list, invoke the @samp{[DEL]} button
for that item.  To add an association, invoke @samp{[INS]} at the
position where you want to add it.  There is an @samp{[INS]} button
between each pair of associations, another at the beginning and another
at the end, so you can add a new association at any position in the
list.

@kindex TAB @r{(customization buffer)}
@kindex S-TAB @r{(customization buffer)}
@findex widget-forward
@findex widget-backward
  Two special commands, @key{TAB} and @kbd{S-@key{TAB}}, are useful
for moving through the customization buffer.  @key{TAB}
(@code{widget-forward}) moves forward to the next button or editable
field; @kbd{S-@key{TAB}} (@code{widget-backward}) moves backward to
the previous button or editable field.

  Typing @key{RET} on an editable field also moves forward, just like
@key{TAB}.  We set it up this way because people often type @key{RET}
when they are finished editing a field.  To insert a newline within an
editable field, use @kbd{C-o} or @kbd{C-q C-j}.

@cindex saving a setting
@cindex settings, how to save
  Setting the variable changes its value in the current Emacs session;
@dfn{saving} the value changes it for future sessions as well.  To
save the variable, invoke @samp{[State]} and select the @samp{Save for
Future Sessions} operation.  This works by writing code so as to set
the variable again, each time you start Emacs (@pxref{Saving
Customizations}).

  You can also restore the variable to its standard value by invoking
@samp{[State]} and selecting the @samp{Erase Customization} operation.
There are actually four reset operations:

@table @samp
@item Undo Edits
If you have made some modifications and not yet set the variable,
this restores the text in the customization buffer to match
the actual value.

@item Reset to Saved
This restores the value of the variable to the last saved value,
and updates the text accordingly.

@item Erase Customization
This sets the variable to its standard value, and updates the text
accordingly.  This also eliminates any saved value for the variable,
so that you will get the standard value in future Emacs sessions.

@item Set to Backup Value
This sets the variable to a previous value that was set in the
customization buffer in this session.  If you customize a variable
and then reset it, which discards the customized value,
you can get the discarded value back again with this operation.
@end table

@cindex comments on customized settings
  Sometimes it is useful to record a comment about a specific
customization.  Use the @samp{Add Comment} item from the
@samp{[State]} menu to create a field for entering the comment.  The
comment you enter will be saved, and displayed again if you again view
the same variable in a customization buffer, even in another session.

  The state of a group indicates whether anything in that group has been
edited, set or saved.

  Near the top of the customization buffer there are two lines of buttons:

@smallexample
 [Set for Current Session] [Save for Future Sessions]
 [Undo Edits] [Reset to Saved] [Erase Customization]   [Finish]
@end smallexample

@vindex custom-buffer-done-function
@noindent
Invoking @samp{[Finish]} either buries or kills this customization
buffer according to the setting of the option
@code{custom-buffer-done-kill}; the default is to bury the buffer.
Each of the other buttons performs an operation---set, save or
reset---on each of the settings in the buffer that could meaningfully
be set, saved or reset.  They do not operate on settings whose values
are hidden, nor on subgroups which are hidden or not visible in the buffer.

@node Saving Customizations
@subsection Saving Customizations

  Saving customizations from the customization buffer works by writing
code that future sessions will read, code to set up those
customizations again.

@vindex custom-file
  Normally this saves customizations in your init file,
@file{~/.emacs}.  If you wish, you can save customizations in another
file instead.  To make this work, your @file{~/.emacs} should set
@code{custom-file} to the name of that file.  Then you should load the
file by calling @code{load}.  For example:

@example
(setq custom-file "~/.emacs-custom.el")
(load custom-file)
@end example

  You can use @code{custom-file} to specify different customization
files for different Emacs versions, like this:

@example
(cond ((< emacs-major-version 21)
       ;; @r{Emacs 20 customization.}
       (setq custom-file "~/.custom-20.el"))
      ((and (= emacs-major-version 21) (< emacs-minor-version 4))
       ;; @r{Emacs 21 customization, before version 21.4.}
       (setq custom-file "~/.custom-21.el"))
      ((< emacs-major-version 22)
       ;; @r{Emacs version 21.4 or later.}
       (setq custom-file "~/.custom-21.4.el"))
      (t
       ;; @r{Emacs version 22.1 or later.}
       (setq custom-file "~/.custom-22.el")))

(load custom-file)
@end example

  If Emacs was invoked with the @option{-q} or @option{--no-init-file}
options (@pxref{Initial Options}), it will not let you save your
customizations in your @file{~/.emacs} init file.  This is because
saving customizations from such a session would wipe out all the other
customizations you might have on your init file.

@node Face Customization
@subsection Customizing Faces
@cindex customizing faces
@cindex bold font
@cindex italic font
@cindex fonts and faces

  In addition to variables, some customization groups also include
faces.  When you show the contents of a group, both the variables and
the faces in the group appear in the customization buffer.  Here is an
example of how a face looks:

@smallexample
Custom Changed Face:(sample) [Hide Face]
   [State]: STANDARD.
Face used when the customize item has been changed.
Parent groups: [Custom Magic Faces]
Attributes: [ ] Font Family: *
            [ ] Width: *
            [ ] Height: *
            [ ] Weight: *
            [ ] Slant: *
            [ ] Underline: *
            [ ] Overline: *
            [ ] Strike-through: *
            [ ] Box around text: *
            [ ] Inverse-video: *
            [X] Foreground: white       (sample)
            [X] Background: blue        (sample)
            [ ] Stipple: *
            [ ] Inherit: *
@end smallexample

  Each face attribute has its own line.  The @samp{[@var{x}]} button
before the attribute name indicates whether the attribute is
@dfn{enabled}; @samp{[X]} means that it's enabled, and @samp{[ ]}
means that it's disabled.  You can enable or disable the attribute by
clicking that button.  When the attribute is enabled, you can change
the attribute value in the usual ways.

  For the colors, you can specify a color name (use @kbd{M-x
list-colors-display} for a list of them) or a hexadecimal color
specification of the form @samp{#@var{rr}@var{gg}@var{bb}}.
(@samp{#000000} is black, @samp{#ff0000} is red, @samp{#00ff00} is
green, @samp{#0000ff} is blue, and @samp{#ffffff} is white.)  On a
black-and-white display, the colors you can use for the background are
@samp{black}, @samp{white}, @samp{gray}, @samp{gray1}, and
@samp{gray3}.  Emacs supports these shades of gray by using background
stipple patterns instead of a color.

  Setting, saving and resetting a face work like the same operations for
variables (@pxref{Changing a Variable}).

  A face can specify different appearances for different types of
display.  For example, a face can make text red on a color display, but
use a bold font on a monochrome display.  To specify multiple
appearances for a face, select @samp{For All Kinds of Displays} in the
menu you get from invoking @samp{[State]}.

@findex modify-face
  Another more basic way to set the attributes of a specific face is
with @kbd{M-x modify-face}.  This command reads the name of a face, then
reads the attributes one by one.  For the color and stipple attributes,
the attribute's current value is the default---type just @key{RET} if
you don't want to change that attribute.  Type @samp{none} if you want
to clear out the attribute.

@node Specific Customization
@subsection Customizing Specific Items

  Instead of finding the setting you want to change by navigating the
structure of groups, here are other ways to specify the settings that
you want to customize.

@table @kbd
@item M-x customize-option @key{RET} @var{option} @key{RET}
Set up a customization buffer with just one user option variable,
@var{option}.
@item M-x customize-face @key{RET} @var{face} @key{RET}
Set up a customization buffer with just one face, @var{face}.
@item M-x customize-group @key{RET} @var{group} @key{RET}
Set up a customization buffer with just one group, @var{group}.
@item M-x customize-apropos @key{RET} @var{regexp} @key{RET}
Set up a customization buffer with all the settings and groups that
match @var{regexp}.
@item M-x customize-changed @key{RET} @var{version} @key{RET}
Set up a customization buffer with all the settings and groups
whose meaning has changed since Emacs version @var{version}.
@item M-x customize-saved
Set up a customization buffer containing all settings that you
have saved with customization buffers.
@item M-x customize-unsaved
Set up a customization buffer containing all settings that you have
set but not saved.
@end table

@findex customize-option
  If you want to alter a particular user option with the customization
buffer, and you know its name, you can use the command @kbd{M-x
customize-option} and specify the user option (variable) name.  This
sets up the customization buffer with just one user option---the one
that you asked for.  Editing, setting and saving the value work as
described above, but only for the specified user option.  Minibuffer
completion is handy if you only know part of the name.  However, this
command can only see options that have been loaded in the current
Emacs session.

@findex customize-face
  Likewise, you can modify a specific face, chosen by name, using
@kbd{M-x customize-face}.  By default it operates on the face used
on the character after point.

@findex customize-group
  You can also set up the customization buffer with a specific group,
using @kbd{M-x customize-group}.  The immediate contents of the chosen
group, including settings (user options and faces), and other groups,
all appear as well (even if not already loaded).  However, the
subgroups' own contents are not included.

@findex customize-apropos
  For a more general way of controlling what to customize, you can use
@kbd{M-x customize-apropos}.  You specify a regular expression as
argument; then all @emph{loaded} settings and groups whose names match
this regular expression are set up in the customization buffer.  If
you specify an empty regular expression, this includes @emph{all}
loaded groups and settings---which takes a long time to set up.

@findex customize-changed
  When you upgrade to a new Emacs version, you might want to consider
customizing new settings, and settings whose meanings or default
values have changed.  To do this, use @kbd{M-x customize-changed} and
specify a previous Emacs version number using the minibuffer.  It
creates a customization buffer which shows all the settings and groups
whose definitions have been changed since the specified version,
loading them if necessary.

@findex customize-saved
@findex customize-unsaved
  If you change settings and then decide the change was a mistake, you
can use two special commands to revisit your previous changes.  Use
@kbd{M-x customize-saved} to look at the settings that you have saved.
Use @kbd{M-x customize-unsaved} to look at the settings that you
have set but not saved.

@node Custom Themes
@subsection Customization Themes
@cindex custom themes

  @dfn{Custom themes} are collections of settings that can be enabled
or disabled as a unit.  You can use Custom themes to switch quickly
and easily between various collections of settings, and to transfer
such collections from one computer to another.

@findex customize-create-theme
  To define a Custom theme, use @kbd{M-x customize-create-theme},
which brings up a buffer named @samp{*New Custom Theme*}.  At the top
of the buffer is an editable field where you can specify the name of
the theme.  Click on the button labelled @samp{Insert Variable} to add
a variable to the theme, and click on @samp{Insert Face} to add a
face.  You can edit these values in the @samp{*New Custom Theme*}
buffer like in an ordinary Customize buffer.  To remove an option from
the theme, click on its @samp{State} button and select @samp{Delete}.

@vindex custom-theme-directory
  After adding the desired options, click on @samp{Save Theme} to save
the Custom theme.  This writes the theme definition to a file
@file{@var{foo}-theme.el} (where @var{foo} is the theme name you
supplied), in the directory @file{~/.emacs.d/}.  You can specify the
directory by setting @code{custom-theme-directory}.

  You can view and edit the settings of a previously-defined theme by
clicking on @samp{Visit Theme} and specifying the theme name.  You can
also import the variables and faces that you have set using Customize
by visiting the ``special'' theme named @samp{user}.  This theme, which
records all the options that you set in the ordinary customization
buffer, is always enabled, and always takes precedence over all other
enabled Custom themes.  Additionally, the @samp{user} theme is
recorded with code in your @file{.emacs} file, rather than a
@file{user-theme.el} file.

@vindex custom-enabled-themes
  Once you have defined a Custom theme, you can use it by customizing
the variable @code{custom-enabled-themes}.  This is a list of Custom
themes that are @dfn{enabled}, or put into effect.  If you set
@code{custom-enabled-themes} using the Customize interface, the theme
definitions are automatically loaded from the theme files, if they
aren't already.  If you save the value of @code{custom-enabled-themes}
for future Emacs sessions, those Custom themes will be enabled
whenever Emacs is started up.

  If two enabled themes specify different values for an option, the
theme occurring earlier in @code{custom-enabled-themes} takes effect.

@findex load-theme
@findex enable-theme
@findex disable-theme
  You can temporarily enable a Custom theme with @kbd{M-x
enable-theme}.  This prompts for a theme name in the minibuffer, loads
the theme from the theme file if necessary, and enables the theme.
You can @dfn{disable} any enabled theme with the command @kbd{M-x
disable-theme}; this returns the options specified in the theme to
their original values.  To re-enable the theme, type @kbd{M-x
enable-theme} again.  If a theme file is changed during your Emacs
session, you can reload it by typing @kbd{M-x load-theme}.  (This also
enables the theme.)

@node Variables
@section Variables
@cindex variable
@cindex option, user
@cindex user option

  A @dfn{variable} is a Lisp symbol which has a value.  The symbol's
name is also called the name of the variable.  A variable name can
contain any characters that can appear in a file, but conventionally
variable names consist of words separated by hyphens.  A variable can
have a documentation string which describes what kind of value it should
have and how the value will be used.

  Emacs Lisp allows any variable (with a few exceptions) to have any
kind of value, but most variables that Emacs uses expect a value of a
certain type.  Often the value should always be a string, or should
always be a number.  Sometimes we say that a certain feature is turned
on if a variable is ``non-@code{nil},'' meaning that if the variable's
value is @code{nil}, the feature is off, but the feature is on for
@emph{any} other value.  The conventional value to use to turn on the
feature---since you have to pick one particular value when you set the
variable---is @code{t}.

  Emacs uses many Lisp variables for internal record keeping, but the
most interesting variables for a non-programmer user are those meant
for users to change---these are called @dfn{user options}.

  Each user option that you can set with the customization buffer is
in fact a Lisp variable.  Emacs does not (usually) change the values
of these variables on its own; instead, you set the values in order to
control the behavior of certain Emacs commands.  Use of the
customization buffer is explained above (@pxref{Easy Customization});
here we describe other aspects of Emacs variables.

@menu
* Examining::           Examining or setting one variable's value.
* Hooks::               Hook variables let you specify programs for parts
                          of Emacs to run on particular occasions.
* Locals::              Per-buffer values of variables.
* File Variables::      How files can specify variable values.
@end menu

@node Examining
@subsection Examining and Setting Variables
@cindex setting variables

@table @kbd
@item C-h v @var{var} @key{RET}
Display the value and documentation of variable @var{var}
(@code{describe-variable}).
@item M-x set-variable @key{RET} @var{var} @key{RET} @var{value} @key{RET}
Change the value of variable @var{var} to @var{value}.
@end table

  To examine the value of a single variable, use @kbd{C-h v}
(@code{describe-variable}), which reads a variable name using the
minibuffer, with completion.  It displays both the value and the
documentation of the variable.  For example,

@example
C-h v fill-column @key{RET}
@end example

@noindent
displays something like this:

@smallexample
fill-column is a variable defined in `C source code'.
fill-column's value is 70
Local in buffer custom.texi; global value is 70
Automatically becomes buffer-local when set in any fashion.

This variable is safe to use as a file local variable only if its value
satisfies the predicate `integerp'.

Documentation:
*Column beyond which automatic line-wrapping should happen.
Interactively, you can set the buffer local value using C-x f.

You can customize this variable.
@end smallexample

@noindent
The line that says you can customize the variable indicates that this
variable is a user option.  (The star also indicates this, but it is
an obsolete indicator that may eventually disappear.)  @kbd{C-h v} is
not restricted to user options; it allows any variable name.

@findex set-variable
The most convenient way to set a specific user option variable is with
@kbd{M-x set-variable}.  This reads the variable name with the
minibuffer (with completion), and then reads a Lisp expression for the
new value using the minibuffer a second time (you can insert the old
value into the minibuffer for editing via @kbd{M-n}).  For example,

@example
M-x set-variable @key{RET} fill-column @key{RET} 75 @key{RET}
@end example

@noindent
sets @code{fill-column} to 75.

 @kbd{M-x set-variable} is limited to user option variables, but you can
set any variable with a Lisp expression, using the function @code{setq}.
Here is a @code{setq} expression to set @code{fill-column}:

@example
(setq fill-column 75)
@end example

  To execute an expression like this one, go to the @samp{*scratch*}
buffer, type in the expression, and then type @kbd{C-j}.  @xref{Lisp
Interaction}.

  Setting variables, like all means of customizing Emacs except where
otherwise stated, affects only the current Emacs session.  The only
way to alter the variable in future sessions is to put something in
the @file{~/.emacs} file to set it those sessions (@pxref{Init File}).

@node Hooks
@subsection Hooks
@cindex hook
@cindex running a hook

  @dfn{Hooks} are an important mechanism for customization of Emacs.  A
hook is a Lisp variable which holds a list of functions, to be called on
some well-defined occasion.  (This is called @dfn{running the hook}.)
The individual functions in the list are called the @dfn{hook functions}
of the hook.  With rare exceptions, hooks in Emacs are empty when Emacs
starts up, so the only hook functions in any given hook are the ones you
explicitly put there as customization.

  Most major modes run one or more @dfn{mode hooks} as the last step of
initialization.  This makes it easy for you to customize the behavior of
the mode, by setting up a hook function to override the local variable
assignments already made by the mode.  But hooks are also used in other
contexts.  For example, the hook @code{suspend-hook} runs just before
Emacs suspends itself (@pxref{Exiting}).

@cindex normal hook
  Most Emacs hooks are @dfn{normal hooks}.  This means that running the
hook operates by calling all the hook functions, unconditionally, with
no arguments.  We have made an effort to keep most hooks normal so that
you can use them in a uniform way.  Every variable in Emacs whose name
ends in @samp{-hook} is a normal hook.

@cindex abnormal hook
  There are also a few @dfn{abnormal hooks}.  These variables' names end
in @samp{-hooks} or @samp{-functions}, instead of @samp{-hook}.  What
makes these hooks abnormal is that there is something peculiar about the
way its functions are called---perhaps they are given arguments, or
perhaps the values they return are used in some way.  For example,
@code{find-file-not-found-functions} (@pxref{Visiting}) is abnormal because
as soon as one hook function returns a non-@code{nil} value, the rest
are not called at all.  The documentation of each abnormal hook variable
explains in detail what is peculiar about it.

@findex add-hook
  You can set a hook variable with @code{setq} like any other Lisp
variable, but the recommended way to add a hook function to a hook
(either normal or abnormal) is by calling @code{add-hook}.
@xref{Hooks,,, elisp, The Emacs Lisp Reference Manual}.

  For example, here's how to set up a hook to turn on Auto Fill mode
when entering Text mode and other modes based on Text mode:

@example
(add-hook 'text-mode-hook 'turn-on-auto-fill)
@end example

  The next example shows how to use a hook to customize the indentation
of C code.  (People often have strong personal preferences for one
format compared to another.)  Here the hook function is an anonymous
lambda expression.

@example
@group
(setq my-c-style
  '((c-comment-only-line-offset . 4)
@end group
@group
    (c-cleanup-list . (scope-operator
                       empty-defun-braces
                       defun-close-semi))
@end group
@group
    (c-offsets-alist . ((arglist-close . c-lineup-arglist)
                        (substatement-open . 0)))))
@end group

@group
(add-hook 'c-mode-common-hook
  '(lambda ()
     (c-add-style "my-style" my-c-style t)))
@end group
@end example

  It is best to design your hook functions so that the order in which
they are executed does not matter.  Any dependence on the order is
``asking for trouble.''  However, the order is predictable: the most
recently added hook functions are executed first.

@findex remove-hook
  If you play with adding various different versions of a hook
function by calling @code{add-hook} over and over, remember that all
the versions you added will remain in the hook variable together.  You
can clear out individual functions by calling @code{remove-hook}, or
do @code{(setq @var{hook-variable} nil)} to remove everything.

@node Locals
@subsection Local Variables

@table @kbd
@item M-x make-local-variable @key{RET} @var{var} @key{RET}
Make variable @var{var} have a local value in the current buffer.
@item M-x kill-local-variable @key{RET} @var{var} @key{RET}
Make variable @var{var} use its global value in the current buffer.
@item M-x make-variable-buffer-local @key{RET} @var{var} @key{RET}
Mark variable @var{var} so that setting it will make it local to the
buffer that is current at that time.
@end table

@cindex local variables
  Almost any variable can be made @dfn{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 @dfn{global} value which is in
effect in all buffers that have not made the variable local.

@findex make-local-variable
  @kbd{M-x make-local-variable} reads the name of a variable and makes
it local to the current buffer.  Changing its value subsequently in
this buffer will not affect others, and changes in its global value
will not affect this buffer.

@findex make-variable-buffer-local
@cindex per-buffer variables
  @kbd{M-x make-variable-buffer-local} marks a variable so it will
become local automatically whenever it is set.  More precisely, once a
variable has been marked in this way, the usual ways of setting the
variable automatically do @code{make-local-variable} first.  We call
such variables @dfn{per-buffer} variables.  Many variables in Emacs
are normally per-buffer; the variable's document string tells you when
this is so.  A per-buffer variable's global value is normally never
effective in any buffer, but it still has a meaning: it is the initial
value of the variable for each new buffer.

  Major modes (@pxref{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-@code{nil} when the mode is enabled
(@pxref{Minor Modes}).  For many minor modes, the controlling variable
is per buffer, and thus always buffer-local.  Otherwise, you can make
it local in a specific buffer like any other variable.

  A few variables cannot be local to a buffer because they are always
local to each display instead (@pxref{Multiple Displays}).  If you try to
make one of these variables buffer-local, you'll get an error message.

@findex kill-local-variable
  @kbd{M-x kill-local-variable} makes a specified variable 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 @dfn{permanent locals}.

@findex setq-default
  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 @code{setq-default}.  This construct is used just like
@code{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:

@example
(setq-default fill-column 75)
@end example

@noindent
@code{setq-default} is the only way to set the global value of a variable
that has been marked with @code{make-variable-buffer-local}.

@findex default-value
  Lisp programs can use @code{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
@code{fill-column}:

@example
(default-value 'fill-column)
@end example

@node File Variables
@subsection Local Variables in Files
@cindex local variables in files
@cindex file local variables

  A file can specify local variable values for use when you edit the
file with Emacs.  Visiting the file checks for local variable
specifications; it automatically makes these variables local to the
buffer, and sets them to the values specified in the file.

@menu
* Specifying File Variables:: Specifying file local variables.
* Safe File Variables::       Making sure file local variables are safe.
@end menu

@node Specifying File Variables
@subsubsection Specifying File Variables

  There are two ways to specify file local variable values: in the first
line, or with a local variables list.  Here's how to specify them in the
first line:

@example
-*- mode: @var{modename}; @var{var}: @var{value}; @dots{} -*-
@end example

@noindent
You can specify any number of variables/value pairs in this way, each
pair with a colon and semicolon as shown above.  @code{mode:
@var{modename};} specifies the major mode; this should come first in the
line.  The @var{value}s are not evaluated; they are used literally.
Here is an example that specifies Lisp mode and sets two variables with
numeric values:

@smallexample
;; -*- mode: Lisp; fill-column: 75; comment-column: 50; -*-
@end smallexample

  You can also specify the coding system for a file in this way: just
specify a value for the ``variable'' named @code{coding}.  The ``value''
must be a coding system name that Emacs recognizes.  @xref{Coding
Systems}.  @w{@samp{unibyte: t}} specifies unibyte loading for a
particular Lisp file.  @xref{Enabling Multibyte}.

  The @code{eval} pseudo-variable, described below, can be specified in
the first line as well.

@cindex shell scripts, and local file variables
  In shell scripts, the first line is used to identify the script
interpreter, so you cannot put any local variables there.  To
accommodate this, Emacs looks for local variable specifications in the
@emph{second} line when the first line specifies an interpreter.

  A @dfn{local variables list} goes near the end of the file, in the
last page.  (It is often best to put it on a page by itself.)  The local
variables list starts with a line containing the string @samp{Local
Variables:}, and ends with a line containing the string @samp{End:}.  In
between come the variable names and values, one set per line, as
@samp{@var{variable}:@: @var{value}}.  The @var{value}s are not
evaluated; they are used literally.  If a file has both a local
variables list and a @samp{-*-} line, Emacs processes @emph{everything}
in the @samp{-*-} line first, and @emph{everything} in the local
variables list afterward.

  Here is an example of a local variables list:

@example
;; Local Variables: **
;; mode:lisp **
;; comment-column:0 **
;; comment-start: ";; "  **
;; comment-end:"**" **
;; End: **
@end example

  Each line starts with the prefix @samp{;; } and each line ends with
the suffix @samp{ **}.  Emacs recognizes these as the prefix and
suffix based on the first line of the list, by finding them
surrounding the magic string @samp{Local Variables:}; then it
automatically discards them from the other lines of the list.

  The usual reason for using a prefix and/or suffix is to embed the
local variables list in a comment, so it won't confuse other programs
that the file is intended as input for.  The example above is for a
language where comment lines start with @samp{;; } and end with
@samp{**}; the local values for @code{comment-start} and
@code{comment-end} customize the rest of Emacs for this unusual
syntax.  Don't use a prefix (or a suffix) if you don't need one.

  If you write a multi-line string value, you should put the prefix
and suffix on each line, even lines that start or end within the
string.  They will be stripped off for processing the list.  If you
want to split a long string across multiple lines of the file, you can
use backslash-newline, which is ignored in Lisp string constants.
Here's an example of doing this:

@example