gnus-sum.el (gnus-summary-hide-all-threads): Add update message every 1000 iterations.

[gnu-emacs] / doc / emacs / custom.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2011
@c   Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Customization, Quitting, Amusements, Top
@chapter Customization
@cindex customization

  This chapter describes some simple methods to customize the behavior
of Emacs.

  Apart from the methods described here, see @ref{X Resources} for
information about using X resources to customize Emacs, and see
@ref{Keyboard Macros} for information about recording and replaying
keyboard macros.  Making more far-reaching and open-ended changes
involves writing Emacs Lisp code; see
@iftex
@cite{The Emacs Lisp Reference Manual}.
@end iftex
@ifnottex
@ref{Top, Emacs Lisp, Emacs Lisp, elisp, The Emacs Lisp
Reference Manual}.
@end ifnottex

@menu
* Minor Modes::         Each minor mode is a 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.  Minor modes are independent of one
another 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.

  Each minor mode is associated with a command, called the @dfn{mode
command}, which turns it on or off.  The name of this command consists
of the name of the minor mode, followed by @samp{-mode}; for instance,
the mode command for Auto Fill mode is @code{auto-fill-mode}.  Calling
the minor mode command with no prefix argument @dfn{toggles} the mode,
turning it on if it was off, and off if it was on.  A positive
argument always turns the mode on, and a zero or negative argument
always turns it off.  Mode commands are usually invoked with
@kbd{M-x}, but you can bind keys to them if you wish (@pxref{Key
Bindings}).

  Most minor modes also have a @dfn{mode variable}, with the same name
as the mode command.  Its value is non-@code{nil} if the mode is
enabled, and @code{nil} if it is disabled.  In some minor modes---but
not all---the value of the variable alone determines whether the mode
is active: the mode command works simply by setting the variable, and
changing the value of the variable has the same effect as calling the
mode command.  Because not all minor modes work this way, we recommend
that you avoid changing the mode variables directly; use the mode
commands instead.

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

  The following is a list of some buffer-local minor modes:

@itemize @bullet
@item
Abbrev mode automatically expands text based on pre-defined
abbreviation definitions.  @xref{Abbrevs}.

@item
Auto Fill mode inserts newlines as you type to prevent lines from
becoming too long.  @xref{Filling}.

@item
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}.

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

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

@item
Font-Lock mode automatically highlights certain textual units found in
programs.  It is enabled globally by default, but you can disable it
in individual buffers.  @xref{Faces}.

@findex linum-mode
@cindex Linum mode
@item
Linum mode displays each line's line number in the window's left
margin.  Its mode command is @code{linum-mode}.

@item
Outline minor mode provides similar facilities to the major mode
called Outline mode.  @xref{Outline Mode}.

@cindex Overwrite mode
@cindex mode, Overwrite
@findex overwrite-mode
@kindex INSERT
@item
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.  The mode command,
@code{overwrite-mode}, is bound to the @key{Insert} key.

@findex binary-overwrite-mode
@item
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.

@item
Visual Line mode performs ``word wrapping'', causing long lines to be
wrapped at word boundaries.  @xref{Visual Line Mode}.
@end itemize

  Here are some useful global minor modes.  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}.

@itemize @bullet
@item
Column Number mode enables display of the current column number in the
mode line.  @xref{Mode Line}.

@item
Delete Selection mode causes text insertion to first delete the text
in the region, if the region is active.  @xref{Using Region}.

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

@item
Line Number mode enables display of the current line number in the
mode line.  It is enabled by default.  @xref{Mode Line}.

@item
Menu Bar mode gives each frame a menu bar.  It is enabled by default.
@xref{Menu Bars}.

@item
Scroll Bar mode gives each window a scroll bar.  It is enabled by
default, but the scroll bar is only displayed on graphical terminals.
@xref{Scroll Bars}.

@item
Tool Bar mode gives each frame a tool bar.  It is enabled by default,
but the tool bar is only displayed on graphical terminals.  @xref{Tool
Bars}.

@item
Transient Mark mode highlights the region, and makes many Emacs
commands operate on the region when the mark is active.  It is enabled
by default.  @xref{Mark}.
@end itemize

@node Easy Customization
@section Easy Customization Interface

@cindex settings
  Emacs has many @dfn{settings} which have values that you can change.
Many are documented in this manual.  Most settings are @dfn{user
options}---that is to say, Lisp variables (@pxref{Variables})---and
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 settings and change them using @kbd{M-x customize}.
This creates a @dfn{customization buffer}, which lets you navigate
through a logically organized list of settings, edit and set their
values, and save them permanently in your initialization file
(@pxref{Init File}).

@menu
* Customization Groups::     How settings are classified in a structure.
* 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: Customization of the One True Editor. -------------\
      [State]: visible group members are all at standard values.
   
   See also [Manual].

[Editing] : Basic text editing facilities.

[External] : 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.  Each group name, such as @samp{[Editing]}, is a hypertext
link to that group; invoking it creates a new customization buffer,
showing the group and its contents.

  The @code{Emacs} group only contains other groups.  These groups, in
turn, can contain settings or still more groups.  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}.  You can thus type @key{RET} when you are finished editing
a field, to move on to the next button or 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

@vindex custom-file
  Saving customizations from the customization buffer works by writing
code to a file.  By reading this code, future sessions can set up the
customizations again.  Normally, the code is saved in your
initialization file (@pxref{Init File}).

  You can choose to save your customizations in a file other than your
initialization file.  To make this work, you must add a couple of
lines of code to your initialization file, to set the variable
@code{custom-file} to the name of the desired file, and to load that
file.  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 22)
       ;; @r{Emacs 21 customization.}
       (setq custom-file "~/.custom-21.el"))
      ((and (= emacs-major-version 22) (< emacs-minor-version 3))
       ;; @r{Emacs 22 customization, before version 22.3.}
       (setq custom-file "~/.custom-22.el"))
      (t
       ;; @r{Emacs version 22.3 or later.}
       (setq custom-file "~/.emacs-custom.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 initialization file.  This is because saving
customizations from such a session would wipe out all the other
customizations you might have on your initialization 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 @dfn{variable name}.  A variable name can
contain any characters that can appear in a file, but most variable
names consist of ordinary words separated by hyphens.

  The name of the variable serves as a compact description of its
role.  Most variables also have a @dfn{documentation string}, which
describes what the variable's purpose is, what kind of value it should
have, and how the value will be used.  You can view this documentation
using the help command @kbd{C-h v} (@code{describe-variable}).
@xref{Examining}.

  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}.  @xref{Easy
Customization}, for information about using the Customize facility to
set user options.  In the following sections, we will describe other
aspects of Emacs variables, such as how to set them outside Customize.

  Emacs Lisp allows any variable (with a few exceptions) to have any
kind of value.  However, many variables are meaningful only if
assigned values of a certain type.  For example, only numbers are
meaningful values for @code{kill-ring-max}, which specifies the
maximum length of the kill ring (@pxref{Earlier Kills}); if you give
@code{kill-ring-max} a string value, commands such as @kbd{C-y}
(@code{yank}) will signal an error.  On the other hand, some variables
don't care about type; for instance, if a variable has one effect for
@code{nil} values and another effect for ``non-@code{nil}'' values,
then any value that is not the symbol @code{nil} induces the second
effect, regardless of its type (by convention, we usually use the
value @code{t}---a symbol which stands for ``true''---to specify a
non-@code{nil} value).  If you set a variable using the customization
buffer, you need not worry about giving it an invalid type: the
customization buffer usually only allows you to enter meaningful
values.  When in doubt, use @kbd{C-h v} (@code{describe-variable}) to
check the variable's documentation string to see kind of value it
expects (@pxref{Examining}).

@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.
* Directory Variables:: How variable values can be specified by directory.
@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.

  Automatically becomes buffer-local when set in any fashion.
  This variable is safe as a file local variable 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.  @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
your initialization 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 customizing 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{kill-emacs-hook} runs just before quitting the Emacs job
(@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 variable/value pairs in this way, each
pair with a colon and semicolon as shown above.  The special
variable/value pair @code{mode: @var{modename};}, if present,
specifies a major mode, and should come first in the line.  The
@var{value}s are used literally, and not evaluated.

@findex add-file-local-variable-prop-line
@findex delete-file-local-variable-prop-line
@findex copy-dir-locals-to-file-locals-prop-line
  You can use the command @code{add-file-local-variable-prop-line}
instead of adding entries by hand.  It prompts for a variable
and value, and adds them to the first line in the appropriate way.
The command @code{delete-file-local-variable-prop-line} deletes a
variable from the line.  The command
@code{copy-dir-locals-to-file-locals-prop-line} copies directory-local
variables (@pxref{Directory Variables}) to the first line.

  Here is an example first line that specifies Lisp mode and sets two
variables with numeric values:

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

@noindent
Aside from @code{mode}, other keywords that have special meanings as
file variables are @code{coding}, @code{unibyte}, and @code{eval}.
These are described below.

@cindex shell scripts, and local file variables
@cindex man pages, 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 if the first line specifies an interpreter.  The
same is true for man pages which start with the magic string
@samp{'\"} to specify a list of troff preprocessors (not all do,
however).

  Instead of using a @samp{-*-} line, you can define file local
variables using a @dfn{local variables list} near the end of the file.
The start of the local variables list should be no more than 3000
characters from the end of the file, and must be on the last page if
the file is divided into pages.

  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.

  A 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, like this:

@example
/* Local Variables: */
/* mode:c           */
/* comment-column:0 */
/* End:             */
@end example

@noindent
In this example, each line starts with the prefix @samp{/*} and ends
with the suffix @samp{*/}.  Emacs recognizes the prefix and suffix by
finding them surrounding the magic string @samp{Local Variables:}, on
the first line of the list; it then 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 for.  The
example above is for the C programming language, where comment lines
start with @samp{/*} and end with @samp{*/}.

@findex add-file-local-variable
@findex delete-file-local-variable
@findex copy-dir-locals-to-file-locals
  You can construct the local variables list yourself, or use the
command @code{add-file-local-variable}.  This prompts for a variable
and value, and adds them to the list.  If necessary, it also adds the
start and end markers.  The command @code{delete-file-local-variable}
deletes a variable from the list.  The command
@code{copy-dir-locals-to-file-locals} copies directory-local variables
(@pxref{Directory Variables}) to the list.

  As with the @samp{-*-} line, the variables in a local variables list
are used literally, and are not evaluated first.  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; you
should put the prefix and suffix on each line, even lines that start
or end within the string, as they will be stripped off when processing
the list.  Here is an example:

@example
# Local Variables:
# compile-command: "cc foo.c -Dfoo=bar -Dhack=whatever \
#   -Dmumble=blaah"
# End:
@end example

  Some ``variable names'' have special meanings in a local variables
list:

@itemize
@item
@code{mode} enables the specified major mode.

@item
@code{eval} evaluates the specified Lisp expression (the value
returned by that expression is ignored).

@item
@code{coding} specifies the coding system for character code
conversion of this file.  @xref{Coding Systems}.

@item
@code{unibyte} says to visit the file in a unibyte buffer, if the
value is @code{t}.  @xref{Enabling Multibyte}.
@end itemize

@noindent
These four ``variables'' are not really variables; setting them in any
other context has no special meaning.

  @emph{If @code{mode} is used to set a major mode, it should be the
first ``variable'' in the list.}  Otherwise, the entries that precede
it will usually have no effect, since most major modes kill all local
variables as part of their initialization.

  You can use the @code{mode} ``variable'' to enable minor modes as
well as the major modes; in fact, you can use it more than once, first
to set the major mode and then to enable minor modes which are
specific to particular buffers.  Using @code{mode} for minor modes
is deprecated, though---instead, use @code{eval: (minor-mode)}. 

  Often, however, it is a mistake to enable minor modes in file local
variables.  Most minor modes, like Auto Fill mode, represent individual user
preferences.  If you want to use a minor mode, it is better to set up
major mode hooks with your init file to turn that minor mode on for
yourself alone (@pxref{Init File}), instead of using a local variable
list to impose your taste on everyone.

  Use the command @code{normal-mode} to reset the local variables and
major mode of a buffer according to the file name and contents,
including the local variables list if any.  @xref{Choosing Modes}.

@node Safe File Variables
@subsubsection Safety of File Variables

  File-local variables can be dangerous; when you visit someone else's
file, there's no telling what its local variables list could do to
your Emacs.  Improper values of the @code{eval} ``variable'', and
other variables such as @code{load-path}, could execute Lisp code you
didn't intend to run.

  Therefore, whenever Emacs encounters file local variable values that
are not known to be safe, it displays the file's entire local
variables list, and asks you for confirmation before setting them.
You can type @kbd{y} or @key{SPC} to put the local variables list into
effect, or @kbd{n} to ignore it.  When Emacs is run in batch mode
(@pxref{Initial Options}), it can't really ask you, so it assumes the
answer @kbd{n}.

  Emacs normally recognizes certain variable/value pairs as safe.
For instance, it is safe to give @code{comment-column} or
@code{fill-column} any integer value.  If a file specifies only
known-safe variable/value pairs, Emacs does not ask for confirmation
before setting them.  Otherwise, you can tell Emacs to record all the
variable/value pairs in this file as safe, by typing @kbd{!} at the
confirmation prompt.  When Emacs encounters these variable/value pairs
subsequently, in the same file or others, it will assume they are
safe.

@vindex safe-local-variable-values
@cindex risky variable
  Some variables, such as @code{load-path}, are considered
particularly @dfn{risky}: there is seldom any reason to specify them
as local variables, and changing them can be dangerous.  If a file
contains only risky local variables, Emacs neither offers nor accepts
@kbd{!} as input at the confirmation prompt.  If some of the local
variables in a file are risky, and some are only potentially unsafe, you
can enter @kbd{!} at the prompt.  It applies all the variables, but only
marks the non-risky ones as safe for the future.  If you really want to
record safe values for risky variables, do it directly by customizing
@samp{safe-local-variable-values} (@pxref{Easy Customization}).

@vindex enable-local-variables
  The variable @code{enable-local-variables} allows you to change the
way Emacs processes local variables.  Its default value is @code{t},
which specifies the behavior described above.  If it is @code{nil},
Emacs simply ignores all file local variables.  @code{:safe} means use
only the safe values and ignore the rest.  Any other value says to
query you about each file that has local variables, without trying to
determine whether the values are known to be safe.

@vindex enable-local-eval
@vindex safe-local-eval-forms
  The variable @code{enable-local-eval} controls whether Emacs
processes @code{eval} variables.  The three possibilities for the
variable's value are @code{t}, @code{nil}, and anything else, just as
for @code{enable-local-variables}.  The default is @code{maybe}, which
is neither @code{t} nor @code{nil}, so normally Emacs does ask for
confirmation about processing @code{eval} variables.

  As an exception, Emacs never asks for confirmation to evaluate any
@code{eval} form if that form occurs within the variable
@code{safe-local-eval-forms}.

@node Directory Variables
@subsection Per-Directory Local Variables
@cindex local variables, for all files in a directory
@cindex directory local variables
@cindex per-directory local variables

  A @dfn{project} is a collection of files on which you work together.
Usually, the project's files are kept in one or more directories.
Occasionally, you may wish to define Emacs settings that are common to
all the files that belong to the project.

  Emacs provides two ways to specify settings that are applicable to
files in a specific directory: you can put a special file in that
directory, or you can define a @dfn{project class} for that directory.

@cindex @file{.dir-locals.el} file
  If you put a file with a special name @file{.dir-locals.el}@footnote{
On MS-DOS, the name of this file should be @file{_dir-locals.el}, due
to limitations of the DOS filesystems.  If the filesystem is limited
to 8+3 file names, the name of the file will be truncated by the OS to
@file{_dir-loc.el}.
} in a directory, Emacs will read it when it visits any file in that
directory or any of its subdirectories, and apply the settings it
specifies to the file's buffer.  Emacs searches for
@file{.dir-locals.el} starting in the directory of the visited file,
and moving up the directory tree.  (To avoid slowdown, this search is
skipped for remote files.)

  The @file{.dir-locals.el} file should hold a specially-constructed
list.  This list maps Emacs mode names (symbols) to alists; each alist
specifies values for variables to use when the respective mode is
turned on.  The special mode name @samp{nil} means that its alist
applies to any mode.  Instead of a mode name, you can specify a string
that is a name of a subdirectory of the project's directory; then the
corresponding alist applies to all the files in that subdirectory.

  Here's an example of a @file{.dir-locals.el} file:

@example
((nil . ((indent-tabs-mode . t)
         (tab-width . 4)
         (fill-column . 80)))
 (c-mode . ((c-file-style . "BSD")))
 (java-mode . ((c-file-style . "BSD")
               (subdirs . nil)))
 ("src/imported"
  . ((nil . ((change-log-default-name . "ChangeLog.local"))))))
@end example

@noindent
This example shows some settings for a hypothetical project.  It sets
@samp{indent-tabs-mode}, @code{tab-width}, and @code{fill-column} for
any file in the project's directory tree, and it sets the indentation
style for any C or Java source file.  The special @code{subdirs} element
indicates that the Java mode settings are only to be applied in the
current directory, not in any subdirectories.  Finally, it specifies a
different @file{ChangeLog} file name for any file in the @file{src/imported}
subdirectory of the directory where you put the @file{.dir-locals.el}
file.

@findex add-dir-local-variable
@findex delete-dir-local-variable
@findex copy-file-locals-to-dir-locals
  You can edit the @file{.dir-locals.el} file by hand, or use the
command @code{add-dir-local-variable}.  This prompts for a mode (or
subdirectory), variable and value, and adds an entry to the file.
The command @code{delete-dir-local-variable} deletes an entry.  The
command @code{copy-file-locals-to-dir-locals} copies file local
variables (@pxref{File Variables}) to the @file{.dir-locals.el} file.

@findex dir-locals-set-class-variables
@findex dir-locals-set-directory-class
  Another method of specifying directory-local variables is to explicitly
define a project class using @code{dir-locals-set-class-variables}, and
then tell Emacs which directories correspond to that class, using
@code{dir-locals-set-directory-class}.  You can put calls to these functions
in your @file{~/.emacs} init file; this can be useful when you can't put
@file{.dir-locals.el} in the directory for some reason, or if you want
to keep in a single place settings for several directories that don't
have a common parent.  For example, you could apply settings to an
unwritable directory this way:

@example
(dir-locals-set-class-variables 'unwritable-directory
   '((nil . ((some-useful-setting . value)))))

(dir-locals-set-directory-class
   "/usr/include/" 'unwritable-directory)
@end example

  Unsafe directory-local variables are handled in the same way as
unsafe file-local variables (@pxref{Safe File Variables}).

@node Key Bindings
@section Customizing Key Bindings
@cindex key bindings

  This section describes @dfn{key bindings}, which map keys to
commands, and @dfn{keymaps}, which record key bindings.  It also
explains how to customize key bindings, which is done by editing your
init file (@pxref{Init Rebinding}).

@menu
* Keymaps::             Generalities.  The global keymap.
* Prefix Keymaps::      Keymaps for prefix keys.
* Local Keymaps::       Major and minor modes have their own keymaps.
* Minibuffer Maps::     The minibuffer uses its own local keymaps.
* Rebinding::           How to redefine one key's meaning conveniently.
* Init Rebinding::      Rebinding keys with your init file, @file{.emacs}.
* Modifier Keys::       Using modifier keys in key bindings.
* Function Keys::       Rebinding terminal function keys.
* Named ASCII Chars::   Distinguishing @key{TAB} from @kbd{C-i}, and so on.
* Mouse Buttons::       Rebinding mouse buttons in Emacs.
* Disabling::           Disabling a command means confirmation is required
                          before it can be executed.  This is done to protect
                          beginners from surprises.
@end menu

@node Keymaps
@subsection Keymaps
@cindex keymap

  As described in @ref{Commands}, each Emacs command is a Lisp
function whose definition provides for interactive use.  Like every
Lisp function, a command has a function name, which usually consists
of lower-case letters and hyphens.

  A @dfn{key sequence} (@dfn{key}, for short) is a sequence of
@dfn{input events} that have a meaning as a unit.  Input events
include characters, function keys and mouse buttons---all the inputs
that you can send to the computer.  A key sequence gets its meaning
from its @dfn{binding}, which says what command it runs.

  The bindings between key sequences and command functions are
recorded in data structures called @dfn{keymaps}.  Emacs has many of
these, each used on particular occasions.

@cindex global keymap
  The @dfn{global} keymap is the most important keymap because it is
always in effect.  The global keymap defines keys for Fundamental mode
(@pxref{Major Modes}); most of these definitions are common to most or
all major modes.  Each major or minor mode can have its own keymap
which overrides the global definitions of some keys.

  For example, a self-inserting character such as @kbd{g} is
self-inserting because the global keymap binds it to the command
@code{self-insert-command}.  The standard Emacs editing characters
such as @kbd{C-a} also get their standard meanings from the global
keymap.  Commands to rebind keys, such as @kbd{M-x global-set-key},
work by storing the new binding in the proper place in the global map
(@pxref{Rebinding}).

@cindex function key
  Most modern keyboards have function keys as well as character keys.
Function keys send input events just as character keys do, and keymaps
can have bindings for them.  Key sequences can mix function keys and
characters.  For example, if your keyboard has a @key{Home} function
key, Emacs can recognize key sequences like @kbd{C-x @key{Home}}.  You
can even mix mouse events with keyboard events, such as
@kbd{S-down-mouse-1}.

  On text terminals, typing a function key actually sends the computer
a sequence of characters; the precise details of the sequence depends
on the function key and on the terminal type.  (Often the sequence
starts with @kbd{@key{ESC} [}.)  If Emacs understands your terminal
type properly, it automatically handles such sequences as single input
events.

@node Prefix Keymaps
@subsection Prefix Keymaps

  Internally, Emacs records only single events in each keymap.
Interpreting a key sequence of multiple events involves a chain of
keymaps: the first keymap gives a definition for the first event,
which is another keymap, which is used to look up the second event in
the sequence, and so on.  Thus, a prefix key such as @kbd{C-x} or
@key{ESC} has its own keymap, which holds the definition for the event
that immediately follows that prefix.

  The definition of a prefix key is usually the keymap to use for
looking up the following event.  The definition can also be a Lisp
symbol whose function definition is the following keymap; the effect is
the same, but it provides a command name for the prefix key that can be
used as a description of what the prefix key is for.  Thus, the binding
of @kbd{C-x} is the symbol @code{Control-X-prefix}, whose function
definition is the keymap for @kbd{C-x} commands.  The definitions of
@kbd{C-c}, @kbd{C-x}, @kbd{C-h} and @key{ESC} as prefix keys appear in
the global map, so these prefix keys are always available.

  Aside from ordinary prefix keys, there is a fictitious ``prefix key''
which represents the menu bar; see @ref{Menu Bar,,,elisp, The Emacs Lisp
Reference Manual}, for special information about menu bar key bindings.
Mouse button events that invoke pop-up menus are also prefix keys; see
@ref{Menu Keymaps,,,elisp, The Emacs Lisp Reference Manual}, for more
details.

  Some prefix keymaps are stored in variables with names:

@itemize @bullet
@item
@vindex ctl-x-map
@code{ctl-x-map} is the variable name for the map used for characters that
follow @kbd{C-x}.
@item
@vindex help-map
@code{help-map} is for characters that follow @kbd{C-h}.
@item
@vindex esc-map
@code{esc-map} is for characters that follow @key{ESC}.  Thus, all Meta
characters are actually defined by this map.
@item
@vindex ctl-x-4-map
@code{ctl-x-4-map} is for characters that follow @kbd{C-x 4}.
@item
@vindex mode-specific-map
@code{mode-specific-map} is for characters that follow @kbd{C-c}.
@end itemize

@node Local Keymaps
@subsection Local Keymaps

@cindex local keymap
@cindex minor mode keymap
  So far, we have explained the ins and outs of the global map.  Major
modes customize Emacs by providing their own key bindings in
@dfn{local keymaps}.  For example, C mode overrides @key{TAB} to make
it indent the current line for C code.  Minor modes can also have
local keymaps; whenever a minor mode is in effect, the definitions in
its keymap override both the major mode's local keymap and the global
keymap.  In addition, portions of text in the buffer can specify their
own keymaps, which override all other keymaps.

  A local keymap can redefine a key as a prefix key by defining it as
a prefix keymap.  If the key is also defined globally as a prefix, its
local and global definitions (both keymaps) effectively combine: both
definitions are used to look up the event that follows the prefix key.
For example, if a local keymap defines @kbd{C-c} as a prefix keymap,
and that keymap defines @kbd{C-z} as a command, this provides a local
meaning for @kbd{C-c C-z}.  This does not affect other sequences that
start with @kbd{C-c}; if those sequences don't have their own local
bindings, their global bindings remain in effect.

  Another way to think of this is that Emacs handles a multi-event key
sequence by looking in several keymaps, one by one, for a binding of the
whole key sequence.  First it checks the minor mode keymaps for minor
modes that are enabled, then it checks the major mode's keymap, and then
it checks the global keymap.  This is not precisely how key lookup
works, but it's good enough for understanding the results in ordinary
circumstances.

@node Minibuffer Maps
@subsection Minibuffer Keymaps

@cindex minibuffer keymaps
@vindex minibuffer-local-map
@vindex minibuffer-local-ns-map
@vindex minibuffer-local-completion-map
@vindex minibuffer-local-must-match-map
@vindex minibuffer-local-filename-completion-map
@vindex minibuffer-local-must-match-filename-map
  The minibuffer has its own set of local keymaps; they contain various
completion and exit commands.

@itemize @bullet
@item
@code{minibuffer-local-map} is used for ordinary input (no completion).
@item
@code{minibuffer-local-ns-map} is similar, except that @key{SPC} exits
just like @key{RET}.
@item
@code{minibuffer-local-completion-map} is for permissive completion.
@item
@code{minibuffer-local-must-match-map} is for strict completion and
for cautious completion.
@item
Finally, @code{minibuffer-local-filename-completion-map} and
@code{minibuffer-local-must-match-filename-map} are like the two
previous ones, but they are specifically for file name completion.
They do not bind @key{SPC}.
@end itemize

@node Rebinding
@subsection Changing Key Bindings Interactively
@cindex key rebinding, this session
@cindex redefining keys, this session
@cindex binding keys

  The way to redefine an Emacs key is to change its entry in a keymap.
You can change the global keymap, in which case the change is
effective in all major modes (except those that have their own
overriding local bindings for the same key).  Or you can change a
local keymap, which affects all buffers using the same major mode.

  In this section, we describe how to rebind keys for the present
Emacs session.  @xref{Init Rebinding}, for a description of how to
make key rebindings affect future Emacs sessions.

@findex global-set-key
@findex local-set-key
@findex global-unset-key
@findex local-unset-key
@table @kbd
@item M-x global-set-key @key{RET} @var{key} @var{cmd} @key{RET}
Define @var{key} globally to run @var{cmd}.
@item M-x local-set-key @key{RET} @var{key} @var{cmd} @key{RET}
Define @var{key} locally (in the major mode now in effect) to run
@var{cmd}.
@item M-x global-unset-key @key{RET} @var{key}
Make @var{key} undefined in the global map.
@item M-x local-unset-key @key{RET} @var{key}
Make @var{key} undefined locally (in the major mode now in effect).
@end table

  For example, the following binds @kbd{C-z} to the @code{shell}
command (@pxref{Interactive Shell}), replacing the normal global
definition of @kbd{C-z}:

@example
M-x global-set-key @key{RET} C-z shell @key{RET}
@end example

@noindent
The @code{global-set-key} command reads the command name after the
key.  After you press the key, a message like this appears so that you
can confirm that you are binding the key you want:

@example
Set key C-z to command:
@end example

  You can redefine function keys and mouse events in the same way; just
type the function key or click the mouse when it's time to specify the
key to rebind.

  You can rebind a key that contains more than one event in the same
way.  Emacs keeps reading the key to rebind until it is a complete key
(that is, not a prefix key).  Thus, if you type @kbd{C-f} for
@var{key}, that's the end; it enters the minibuffer immediately to
read @var{cmd}.  But if you type @kbd{C-x}, since that's a prefix, it
reads another character; if that is @kbd{4}, another prefix character,
it reads one more character, and so on.  For example,

@example
M-x global-set-key @key{RET} C-x 4 $ spell-other-window @key{RET}
@end example

@noindent
redefines @kbd{C-x 4 $} to run the (fictitious) command
@code{spell-other-window}.

  You can remove the global definition of a key with
@code{global-unset-key}.  This makes the key @dfn{undefined}; if you
type it, Emacs will just beep.  Similarly, @code{local-unset-key} makes
a key undefined in the current major mode keymap, which makes the global
definition (or lack of one) come back into effect in that major mode.

  If you have redefined (or undefined) a key and you subsequently wish
to retract the change, undefining the key will not do the job---you need
to redefine the key with its standard definition.  To find the name of
the standard definition of a key, go to a Fundamental mode buffer in a
fresh Emacs and use @kbd{C-h c}.  The documentation of keys in this
manual also lists their command names.

  If you want to prevent yourself from invoking a command by mistake, it
is better to disable the command than to undefine the key.  A disabled
command is less work to invoke when you really want to.
@xref{Disabling}.

@node Init Rebinding
@subsection Rebinding Keys in Your Init File
@cindex rebinding major mode keys
@c This node is referenced in the tutorial.  When renaming or deleting
@c it, the tutorial needs to be adjusted.  (TUTORIAL.de)

  If you have a set of key bindings that you like to use all the time,
you can specify them in your initialization file by writing Lisp code.
@xref{Init File}, for a description of the initialization file.

@findex kbd
  There are several ways to write a key binding using Lisp.  The
simplest is to use the @code{kbd} macro, which converts a textual
representation of a key sequence---similar to how we have written key
sequences in this manual---into a form that can be passed as an
argument to @code{global-set-key}.  For example, here's how to bind
@kbd{C-z} to the @code{shell} command (@pxref{Interactive Shell}):

@example
(global-set-key (kbd "C-z") 'shell)
@end example

@noindent
The single-quote before the command name, @code{shell}, marks it as a
constant symbol rather than a variable.  If you omit the quote, Emacs
would try to evaluate @code{shell} as a variable.  This probably
causes an error; it certainly isn't what you want.

  Here are some additional examples, including binding function keys
and mouse events:

@example
(global-set-key (kbd "C-c y") 'clipboard-yank)
(global-set-key (kbd "C-M-q") 'query-replace)
(global-set-key (kbd "<f5>") 'flyspell-mode)
(global-set-key (kbd "C-<f5>") 'linum-mode)
(global-set-key (kbd "C-<right>") 'forward-sentence)
(global-set-key (kbd "<mouse-2>") 'mouse-save-then-kill)
(global-set-key (kbd "C-<down-mouse-3>") 'mouse-yank-at-click)
@end example

  Instead of using the @code{kbd} macro, you can use a Lisp string or
vector to specify the key sequence.  Using a string is simpler, but
only works for @acronym{ASCII} characters and Meta-modified
@acronym{ASCII} characters.  For example, here's how to bind @kbd{C-x
M-l} to @code{make-symbolic-link} (@pxref{Misc File Ops}):

@example
(global-set-key "\C-x\M-l" 'make-symbolic-link)
@end example

  To put @key{TAB}, @key{RET}, @key{ESC}, or @key{DEL} in the string,
use the Emacs Lisp escape sequences @samp{\t}, @samp{\r}, @samp{\e},
and @samp{\d} respectively.  Here is an example which binds @kbd{C-x
@key{TAB}} to @code{indent-rigidly} (@pxref{Indentation}):

@example
(global-set-key "\C-x\t" 'indent-rigidly)
@end example

  When the key sequence includes function keys or mouse button events,
or non-@acronym{ASCII} characters such as @code{C-=} or @code{H-a},
you can use a vector to specify the key sequence.  Each element in the
vector stands for an input event; the elements are separated by spaces
and surrounded by a pair of square brackets.  If a vector element is a
character, write it as a Lisp character constant: @samp{?} followed by
the character as it would appear in a string.  Function keys are
represented by symbols (@pxref{Function Keys}); simply write the
symbol's name, with no other delimiters or punctuation.  Here are some
examples:

@example
(global-set-key [?\C-=] 'make-symbolic-link)
(global-set-key [?\M-\C-=] 'make-symbolic-link)
(global-set-key [?\H-a] 'make-symbolic-link)
(global-set-key [f7] 'make-symbolic-link)
(global-set-key [C-mouse-1] 'make-symbolic-link)
@end example

@noindent
You can use a vector for the simple cases too:

@example
(global-set-key [?\C-z ?\M-l] 'make-symbolic-link)
@end example

  Language and coding systems may cause problems with key bindings for
non-@acronym{ASCII} characters.  @xref{Init Non-ASCII}.

  As described in @ref{Local Keymaps}, major modes and minor modes can
define local keymaps.  These keymaps are constructed when the mode is
used for the first time in a session.  If you wish to change one of
these keymaps, you must use the @dfn{mode hook} (@pxref{Hooks}).

@findex define-key
  For example, Texinfo mode runs the hook @code{texinfo-mode-hook}.
Here's how you can use the hook to add local bindings for @kbd{C-c n}
and @kbd{C-c p} in Texinfo mode:

@example
(add-hook 'texinfo-mode-hook
          '(lambda ()
             (define-key texinfo-mode-map "\C-cp" 'backward-paragraph)
             (define-key texinfo-mode-map "\C-cn" 'forward-paragraph)))
@end example

@node Modifier Keys
@subsection Modifier Keys
@cindex modifier keys

  The default key bindings in Emacs are set up so that modified
alphabetical characters are case-insensitive.  In other words,
@kbd{C-A} does the same thing as @kbd{C-a}, and @kbd{M-A} does the
same thing as @kbd{M-a}.  This concerns only alphabetical characters,
and does not apply to ``shifted'' versions of other keys; for
instance, @kbd{C-@@} is not the same as @kbd{C-2}.

  A @key{Control}-modified alphabetical character is always considered
case-insensitive: Emacs always treats @kbd{C-A} as @kbd{C-a},
@kbd{C-B} as @kbd{C-b}, and so forth.  The reason for this is
historical.

  For all other modifiers, you can make the modified alphabetical
characters case-sensitive when you customize Emacs.  For instance, you
could make @kbd{M-a} and @kbd{M-A} run different commands.

  Although only the @key{Control} and @key{Meta} modifier keys are
commonly used, Emacs supports three other modifier keys.  These are
called @key{Super}, @key{Hyper} and @key{Alt}.  Few terminals provide
ways to use these modifiers; the key labeled @key{Alt} on most
keyboards usually issues the @key{Meta} modifier, not @key{Alt}.  The
standard key bindings in Emacs do not include any characters with
these modifiers.  However, you can customize Emacs to assign meanings
to them.  The modifier bits are labelled as @samp{s-}, @samp{H-} and
@samp{A-} respectively.

  Even if your keyboard lacks these additional modifier keys, you can
enter it using @kbd{C-x @@}: @kbd{C-x @@ h} adds the ``hyper'' flag to
the next character, @kbd{C-x @@ s} adds the ``super'' flag, and
@kbd{C-x @@ a} adds the ``alt'' flag.  For instance, @kbd{C-x @@ h
C-a} is a way to enter @kbd{Hyper-Control-a}.  (Unfortunately, there
is no way to add two modifiers by using @kbd{C-x @@} twice for the
same character, because the first one goes to work on the @kbd{C-x}.)

@node Function Keys
@subsection Rebinding Function Keys

  Key sequences can contain function keys as well as ordinary
characters.  Just as Lisp characters (actually integers) represent
keyboard characters, Lisp symbols represent function keys.  If the
function key has a word as its label, then that word is also the name of
the corresponding Lisp symbol.  Here are the conventional Lisp names for
common function keys:

@table @asis
@item @code{left}, @code{up}, @code{right}, @code{down}
Cursor arrow keys.

@item @code{begin}, @code{end}, @code{home}, @code{next}, @code{prior}
Other cursor repositioning keys.

@item @code{select}, @code{print}, @code{execute}, @code{backtab}
@itemx @code{insert}, @code{undo}, @code{redo}, @code{clearline}
@itemx @code{insertline}, @code{deleteline}, @code{insertchar}, @code{deletechar}
Miscellaneous function keys.

@item @code{f1}, @code{f2}, @dots{} @code{f35}
Numbered function keys (across the top of the keyboard).

@item @code{kp-add}, @code{kp-subtract}, @code{kp-multiply}, @code{kp-divide}
@itemx @code{kp-backtab}, @code{kp-space}, @code{kp-tab}, @code{kp-enter}
@itemx @code{kp-separator}, @code{kp-decimal}, @code{kp-equal}
Keypad keys (to the right of the regular keyboard), with names or punctuation.

@item @code{kp-0}, @code{kp-1}, @dots{} @code{kp-9}
Keypad keys with digits.

@item @code{kp-f1}, @code{kp-f2}, @code{kp-f3}, @code{kp-f4}
Keypad PF keys.
@end table

  These names are conventional, but some systems (especially when using
X) may use different names.  To make certain what symbol is used for a
given function key on your terminal, type @kbd{C-h c} followed by that
key.

  @xref{Init Rebinding}, for examples of binding function keys.

@cindex keypad
  Many keyboards have a ``numeric keypad'' on the right hand side.
The numeric keys in the keypad double up as cursor motion keys,
toggled by a key labeled @samp{Num Lock}.  By default, Emacs
translates these keys to the corresponding keys in the main keyboard.
For example, when @samp{Num Lock} is on, the key labeled @samp{8} on
the numeric keypad produces @code{kp-8}, which is translated to
@kbd{8}; when @samp{Num Lock} is off, the same key produces
@code{kp-up}, which is translated to @key{UP}.  If you rebind a key
such as @kbd{8} or @key{UP}, it affects the equivalent keypad key too.
However, if you rebind a @samp{kp-} key directly, that won't affect
its non-keypad equivalent.  Note that the modified keys are not
translated: for instance, if you hold down the @key{META} key while
pressing the @samp{8} key on the numeric keypad, that generates
@kbd{M-@key{kp-8}}.

  Emacs provides a convenient method for binding the numeric keypad
keys, using the variables @code{keypad-setup},
@code{keypad-numlock-setup}, @code{keypad-shifted-setup}, and
@code{keypad-numlock-shifted-setup}.  These can be found in the
@samp{keyboard} customization group (@pxref{Easy Customization}).  You
can rebind the keys to perform other tasks, such as issuing numeric
prefix arguments.

@node Named ASCII Chars
@subsection Named @acronym{ASCII} Control Characters

  @key{TAB}, @key{RET}, @key{BS}, @key{LFD}, @key{ESC} and @key{DEL}
started out as names for certain @acronym{ASCII} control characters,
used so often that they have special keys of their own.  For instance,
@key{TAB} was another name for @kbd{C-i}.  Later, users found it
convenient to distinguish in Emacs between these keys and the ``same''
control characters typed with the @key{CTRL} key.  Therefore, on most
modern terminals, they are no longer the same: @key{TAB} is different
from @kbd{C-i}.

  Emacs can distinguish these two kinds of input if the keyboard does.
It treats the ``special'' keys as function keys named @code{tab},
@code{return}, @code{backspace}, @code{linefeed}, @code{escape}, and
@code{delete}.  These function keys translate automatically into the
corresponding @acronym{ASCII} characters @emph{if} they have no
bindings of their own.  As a result, neither users nor Lisp programs
need to pay attention to the distinction unless they care to.

  If you do not want to distinguish between (for example) @key{TAB} and
@kbd{C-i}, make just one binding, for the @acronym{ASCII} character @key{TAB}
(octal code 011).  If you do want to distinguish, make one binding for
this @acronym{ASCII} character, and another for the ``function key'' @code{tab}.

  With an ordinary @acronym{ASCII} terminal, there is no way to distinguish
between @key{TAB} and @kbd{C-i} (and likewise for other such pairs),
because the terminal sends the same character in both cases.

@node Mouse Buttons
@subsection Rebinding Mouse Buttons
@cindex mouse button events
@cindex rebinding mouse buttons
@cindex click events
@cindex drag events
@cindex down events
@cindex button down events

  Emacs uses Lisp symbols to designate mouse buttons, too.  The ordinary
mouse events in Emacs are @dfn{click} events; these happen when you
press a button and release it without moving the mouse.  You can also
get @dfn{drag} events, when you move the mouse while holding the button
down.  Drag events happen when you finally let go of the button.

  The symbols for basic click events are @code{mouse-1} for the leftmost
button, @code{mouse-2} for the next, and so on.  Here is how you can
redefine the second mouse button to split the current window:

@example
(global-set-key [mouse-2] 'split-window-vertically)
@end example

  The symbols for drag events are similar, but have the prefix
@samp{drag-} before the word @samp{mouse}.  For example, dragging the
first button generates a @code{drag-mouse-1} event.

  You can also define bindings for events that occur when a mouse button
is pressed down.  These events start with @samp{down-} instead of
@samp{drag-}.  Such events are generated only if they have key bindings.
When you get a button-down event, a corresponding click or drag event
will always follow.

@cindex double clicks
@cindex triple clicks
  If you wish, you can distinguish single, double, and triple clicks.  A
double click means clicking a mouse button twice in approximately the
same place.  The first click generates an ordinary click event.  The
second click, if it comes soon enough, generates a double-click event
instead.  The event type for a double-click event starts with
@samp{double-}: for example, @code{double-mouse-3}.

  This means that you can give a special meaning to the second click at
the same place, but it must act on the assumption that the ordinary
single click definition has run when the first click was received.

  This constrains what you can do with double clicks, but user interface
designers say that this constraint ought to be followed in any case.  A
double click should do something similar to the single click, only
``more so.''  The command for the double-click event should perform the
extra work for the double click.

  If a double-click event has no binding, it changes to the
corresponding single-click event.  Thus, if you don't define a
particular double click specially, it executes the single-click command
twice.

  Emacs also supports triple-click events whose names start with
@samp{triple-}.  Emacs does not distinguish quadruple clicks as event
types; clicks beyond the third generate additional triple-click events.
However, the full number of clicks is recorded in the event list, so
if you know Emacs Lisp you can distinguish if you really want to
(@pxref{Click Events,,, elisp, The Emacs Lisp Reference Manual}).
We don't recommend distinct meanings for more than three clicks, but
sometimes it is useful for subsequent clicks to cycle through the same
set of three meanings, so that four clicks are equivalent to one
click, five are equivalent to two, and six are equivalent to three.

  Emacs also records multiple presses in drag and button-down events.
For example, when you press a button twice, then move the mouse while
holding the button, Emacs gets a @samp{double-drag-} event.  And at the
moment when you press it down for the second time, Emacs gets a
@samp{double-down-} event (which is ignored, like all button-down
events, if it has no binding).

@vindex double-click-time
  The variable @code{double-click-time} specifies how much time can
elapse between clicks and still allow them to be grouped as a multiple
click.  Its value is in units of milliseconds.  If the value is
@code{nil}, double clicks are not detected at all.  If the value is
@code{t}, then there is no time limit.  The default is 500.

@vindex double-click-fuzz
  The variable @code{double-click-fuzz} specifies how much the mouse
can move between clicks and still allow them to be grouped as a multiple
click.  Its value is in units of pixels on windowed displays and in
units of 1/8 of a character cell on text-mode terminals; the default is
3.

  The symbols for mouse events also indicate the status of the modifier
keys, with the usual prefixes @samp{C-}, @samp{M-}, @samp{H-},
@samp{s-}, @samp{A-} and @samp{S-}.  These always precede @samp{double-}
or @samp{triple-}, which always precede @samp{drag-} or @samp{down-}.

  A frame includes areas that don't show text from the buffer, such as
the mode line and the scroll bar.  You can tell whether a mouse button
comes from a special area of the screen by means of dummy ``prefix
keys.''  For example, if you click the mouse in the mode line, you get
the prefix key @code{mode-line} before the ordinary mouse-button symbol.
Thus, here is how to define the command for clicking the first button in
a mode line to run @code{scroll-up}:

@example
(global-set-key [mode-line mouse-1] 'scroll-up)
@end example

  Here is the complete list of these dummy prefix keys and their
meanings:

@table @code
@item mode-line
The mouse was in the mode line of a window.
@item vertical-line
The mouse was in the vertical line separating side-by-side windows.  (If
you use scroll bars, they appear in place of these vertical lines.)
@item vertical-scroll-bar
The mouse was in a vertical scroll bar.  (This is the only kind of
scroll bar Emacs currently supports.)
@item menu-bar
The mouse was in the menu bar.
@item header-line
The mouse was in a header line.
@ignore
@item horizontal-scroll-bar
The mouse was in a horizontal scroll bar.  Horizontal scroll bars do
horizontal scrolling, and people don't use them often.
@end ignore
@end table

  You can put more than one mouse button in a key sequence, but it isn't
usual to do so.

@node Disabling
@subsection Disabling Commands
@cindex disabled command

  Disabling a command means that invoking it interactively asks for
confirmation from the user.  The purpose of disabling a command is to
prevent users from executing it by accident; we do this for commands
that might be confusing to the uninitiated.

  Attempting to invoke a disabled command interactively in Emacs
displays a window containing the command's name, its documentation,
and some instructions on what to do immediately; then Emacs asks for
input saying whether to execute the command as requested, enable it
and execute it, or cancel.  If you decide to enable the command, you
must then answer another question---whether to do this permanently, or
just for the current session.  (Enabling permanently works by
automatically editing your @file{.emacs} file.)  You can also type
@kbd{!} to enable @emph{all} commands, for the current session only.

  The direct mechanism for disabling a command is to put a
non-@code{nil} @code{disabled} property on the Lisp symbol for the
command.  Here is the Lisp program to do this:

@example
(put 'delete-region 'disabled t)
@end example

  If the value of the @code{disabled} property is a string, that string
is included in the message displayed when the command is used:

@example
(put 'delete-region 'disabled
     "It's better to use `kill-region' instead.\n")
@end example

@findex disable-command
@findex enable-command
  You can make a command disabled either by editing the @file{.emacs}
file directly, or with the command @kbd{M-x disable-command}, which edits
the @file{.emacs} file for you.  Likewise, @kbd{M-x enable-command}
edits @file{.emacs} to enable a command permanently.  @xref{Init File}.

  If Emacs was invoked with the @option{-q} or @option{--no-init-file}
options (@pxref{Initial Options}), it will not edit your
@file{~/.emacs} init file.  Doing so could lose information
because Emacs has not read your init file.

  Whether a command is disabled is independent of what key is used to
invoke it; disabling also applies if the command is invoked using
@kbd{M-x}.  However, disabling a command has no effect on calling it
as a function from Lisp programs.

@node Syntax
@section The Syntax Table
@cindex syntax table

  All the Emacs commands which parse words or balance parentheses are
controlled by the @dfn{syntax table}.  The syntax table says which
characters are opening delimiters, which are parts of words, which are
string quotes, and so on.  It does this by assigning each character to
one of fifteen-odd @dfn{syntax classes}.  In some cases it specifies
some additional information also.

  Each major mode has its own syntax table (though related major modes
sometimes share one syntax table), which it installs in each buffer
that uses the mode.  The syntax table installed in the current buffer
is the one that all commands use, so we call it ``the'' syntax table.

@kindex C-h s
@findex describe-syntax
  To display a description of the contents of the current syntax
table, type @kbd{C-h s} (@code{describe-syntax}).  The description of
each character includes the string you would have to give to
@code{modify-syntax-entry} to set up that character's current syntax,
starting with the character which designates its syntax class, plus
some English text to explain its meaning.

  A syntax table is actually a Lisp object, a char-table, whose
elements are cons cells.  For full information on the syntax table,
see @ref{Syntax Tables,, Syntax Tables, elisp, The Emacs Lisp
Reference Manual}.

@node Init File
@section The Init File, @file{~/.emacs}
@cindex init file
@cindex .emacs file
@cindex ~/.emacs file
@cindex Emacs initialization file
@cindex key rebinding, permanent
@cindex rebinding keys, permanently
@cindex startup (init file)

  When Emacs is started, it normally tries to load a Lisp program from
an @dfn{initialization file}, or @dfn{init file} for short.  This
file, if it exists, specifies how to initialize Emacs for you.  Emacs
looks for your init file using the filenames @file{~/.emacs},
@file{~/.emacs.el}, or @file{~/.emacs.d/init.el}; you can choose to
use any one of these three names (@pxref{Find Init}).  Here, @file{~/}
stands for your home directory.

  You can use the command line switch @samp{-q} to prevent loading
your init file, and @samp{-u} (or @samp{--user}) to specify a
different user's init file (@pxref{Initial Options}).

@cindex @file{default.el}, the default init file
  There can also be a @dfn{default init file}, which is the library
named @file{default.el}, found via the standard search path for
libraries.  The Emacs distribution contains no such library; your site
may create one for local customizations.  If this library exists, it is
loaded whenever you start Emacs (except when you specify @samp{-q}).
But your init file, if any, is loaded first; if it sets
@code{inhibit-default-init} non-@code{nil}, then @file{default} is not
loaded.

@cindex site init file
@cindex @file{site-start.el}, the site startup file
  Your site may also have a @dfn{site startup file}; this is named
@file{site-start.el}, if it exists.  Like @file{default.el}, Emacs
finds this file via the standard search path for Lisp libraries.
Emacs loads this library before it loads your init file.  To inhibit
loading of this library, use the option @samp{--no-site-file}.
@xref{Initial Options}.  We recommend against using
@file{site-start.el} for changes that some users may not like.  It is
better to put them in @file{default.el}, so that users can more easily
override them.

  You can place @file{default.el} and @file{site-start.el} in any of
the directories which Emacs searches for Lisp libraries.  The variable
@code{load-path} (@pxref{Lisp Libraries}) specifies these directories.
Many sites put these files in the @file{site-lisp} subdirectory of the
Emacs installation directory, typically
@file{/usr/local/share/emacs/site-lisp}.

  Byte-compiling your init file is not recommended (@pxref{Byte
Compilation,, Byte Compilation, elisp, the Emacs Lisp Reference
Manual}).  It generally does not speed up startup very much, and often
leads to problems when you forget to recompile the file.  A better
solution is to use the Emacs server to reduce the number of times you
have to start Emacs (@pxref{Emacs Server}).  If your init file defines
many functions, consider moving them to a separate (byte-compiled)
file that you load in your init file.

  If you are going to write actual Emacs Lisp programs that go beyond
minor customization, you should read the @cite{Emacs Lisp Reference Manual}.
@ifnottex
@xref{Top, Emacs Lisp, Emacs Lisp, elisp, the Emacs Lisp Reference
Manual}.
@end ifnottex

@menu
* Init Syntax::         Syntax of constants in Emacs Lisp.
* Init Examples::       How to do some things with an init file.
* Terminal Init::       Each terminal type can have an init file.
* Find Init::           How Emacs finds the init file.
* Init Non-ASCII::      Using non-@acronym{ASCII} characters in an init file.
@end menu

@node Init Syntax
@subsection Init File Syntax

  The init file contains one or more Lisp expressions.  Each of these
consists of a function name followed by arguments, all surrounded by
parentheses.  For example, @code{(setq fill-column 60)} calls the
function @code{setq} to set the variable @code{fill-column}
(@pxref{Filling}) to 60.

  You can set any Lisp variable with @code{setq}, but with certain
variables @code{setq} won't do what you probably want in the
@file{.emacs} file.  Some variables automatically become buffer-local
when set with @code{setq}; what you want in @file{.emacs} is to set
the default value, using @code{setq-default}.  Some customizable minor
mode variables do special things to enable the mode when you set them
with Customize, but ordinary @code{setq} won't do that; to enable the
mode in your @file{.emacs} file, call the minor mode command.  The
following section has examples of both of these methods.

  The second argument to @code{setq} is an expression for the new
value of the variable.  This can be a constant, a variable, or a
function call expression.  In @file{.emacs}, constants are used most
of the time.  They can be:

@table @asis
@item Numbers:
Numbers are written in decimal, with an optional initial minus sign.

@item Strings:
@cindex Lisp string syntax
@cindex string syntax
Lisp string syntax is the same as C string syntax with a few extra
features.  Use a double-quote character to begin and end a string constant.

In a string, you can include newlines and special characters literally.
But often it is cleaner to use backslash sequences for them: @samp{\n}
for newline, @samp{\b} for backspace, @samp{\r} for carriage return,
@samp{\t} for tab, @samp{\f} for formfeed (control-L), @samp{\e} for
escape, @samp{\\} for a backslash, @samp{\"} for a double-quote, or
@samp{\@var{ooo}} for the character whose octal code is @var{ooo}.
Backslash and double-quote are the only characters for which backslash
sequences are mandatory.

@samp{\C-} can be used as a prefix for a control character, as in
@samp{\C-s} for @acronym{ASCII} control-S, and @samp{\M-} can be used as a prefix for
a Meta character, as in @samp{\M-a} for @kbd{Meta-A} or @samp{\M-\C-a} for
@kbd{Control-Meta-A}.@refill

@xref{Init Non-ASCII}, for information about including
non-@acronym{ASCII} in your init file.

@item Characters:
@cindex Lisp character syntax
@cindex character syntax
Lisp character constant syntax consists of a @samp{?} followed by
either a character or an escape sequence starting with @samp{\}.
Examples: @code{?x}, @code{?\n}, @code{?\"}, @code{?\)}.  Note that
strings and characters are not interchangeable in Lisp; some contexts
require one and some contexts require the other.

@xref{Init Non-ASCII}, for information about binding commands to
keys which send non-@acronym{ASCII} characters.

@item True:
@code{t} stands for `true'.

@item False:
@code{nil} stands for `false'.

@item Other Lisp objects:
@cindex Lisp object syntax
Write a single-quote (@code{'}) followed by the Lisp object you want.
@end table

@node Init Examples
@subsection Init File Examples

  Here are some examples of doing certain commonly desired things with
Lisp expressions:

@itemize @bullet
@item
Add a directory to the variable @code{load-path}.  You can then put
Lisp libraries that are not included with Emacs in this directory, and
load them with @kbd{M-x load-library}.  @xref{Lisp Libraries}.

@example
(add-to-list 'load-path "/path/to/lisp/libraries")
@end example

@item
Make @key{TAB} in C mode just insert a tab if point is in the middle of a
line.

@example
(setq c-tab-always-indent nil)
@end example

Here we have a variable whose value is normally @code{t} for `true'
and the alternative is @code{nil} for `false'.

@item
Make searches case sensitive by default (in all buffers that do not
override this).

@example
(setq-default case-fold-search nil)
@end example

This sets the default value, which is effective in all buffers that do
not have local values for the variable (@pxref{Locals}).  Setting
@code{case-fold-search} with @code{setq} affects only the current
buffer's local value, which is probably not what you want to do in an
init file.

@item
@vindex user-mail-address
Specify your own email address, if Emacs can't figure it out correctly.

@example
(setq user-mail-address "cheney@@torture.gov")
@end example

Various Emacs packages, such as Message mode, consult
@code{user-mail-address} when they need to know your email address.
@xref{Mail Headers}.

@item
Make Text mode the default mode for new buffers.

@example
(setq-default major-mode 'text-mode)
@end example

Note that @code{text-mode} is used because it is the command for
entering Text mode.  The single-quote before it makes the symbol a
constant; otherwise, @code{text-mode} would be treated as a variable
name.

@need 1500
@item
Set up defaults for the Latin-1 character set
which supports most of the languages of Western Europe.

@example
(set-language-environment "Latin-1")
@end example

@need 1500
@item
Turn off Line Number mode, a global minor mode.

@example
(line-number-mode 0)
@end example

@need 1500
@item
Turn on Auto Fill mode automatically in Text mode and related modes.

@example
(add-hook 'text-mode-hook
  '(lambda () (auto-fill-mode 1)))
@end example

This shows how to add a hook function to a normal hook variable
(@pxref{Hooks}).  The function we supply is a list starting with
@code{lambda}, with a single-quote in front of it to make it a list
constant rather than an expression.

It's beyond the scope of this manual to explain Lisp functions, but for
this example it is enough to know that the effect is to execute
@code{(auto-fill-mode 1)} when Text mode is entered.  You can replace
that with any other expression that you like, or with several
expressions in a row.

Emacs comes with a function named @code{turn-on-auto-fill} whose
definition is @code{(lambda () (auto-fill-mode 1))}.  Thus, a simpler
way to write the above example is as follows:

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

@item
Load the installed Lisp library named @file{foo} (actually a file
@file{foo.elc} or @file{foo.el} in a standard Emacs directory).

@example
(load "foo")
@end example

When the argument to @code{load} is a relative file name, not starting
with @samp{/} or @samp{~}, @code{load} searches the directories in
@code{load-path} (@pxref{Lisp Libraries}).

@item
Load the compiled Lisp file @file{foo.elc} from your home directory.

@example
(load "~/foo.elc")
@end example

Here an absolute file name is used, so no searching is done.

@item
@cindex loading Lisp libraries automatically
@cindex autoload Lisp libraries
Tell Emacs to find the definition for the function @code{myfunction}
by loading a Lisp library named @file{mypackage} (i.e.@: a file
@file{mypackage.elc} or @file{mypackage.el}):

@example
(autoload 'myfunction "mypackage" "Do what I say." t)
@end example

@noindent
Here the string @code{"Do what I say."} is the function's
documentation string.  You specify it in the @code{autoload}
definition so it will be available for help commands even when the
package is not loaded.  The last argument, @code{t}, indicates that
this function is interactive; that is, it can be invoked interactively
by typing @kbd{M-x myfunction @key{RET}} or by binding it to a key.
If the function is not interactive, omit the @code{t} or use
@code{nil}.

@item
Rebind the key @kbd{C-x l} to run the function @code{make-symbolic-link}
(@pxref{Init Rebinding}).

@example
(global-set-key "\C-xl" 'make-symbolic-link)
@end example

or

@example
(define-key global-map "\C-xl" 'make-symbolic-link)
@end example

Note once again the single-quote used to refer to the symbol
@code{make-symbolic-link} instead of its value as a variable.

@item
Do the same thing for Lisp mode only.

@example
(define-key lisp-mode-map "\C-xl" 'make-symbolic-link)
@end example

@item
Redefine all keys which now run @code{next-line} in Fundamental mode
so that they run @code{forward-line} instead.

@findex substitute-key-definition
@example
(substitute-key-definition 'next-line 'forward-line
                           global-map)
@end example

@item
Make @kbd{C-x C-v} undefined.

@example
(global-unset-key "\C-x\C-v")
@end example

One reason to undefine a key is so that you can make it a prefix.
Simply defining @kbd{C-x C-v @var{anything}} will make @kbd{C-x C-v} a
prefix, but @kbd{C-x C-v} must first be freed of its usual non-prefix
definition.

@item
Make @samp{$} have the syntax of punctuation in Text mode.
Note the use of a character constant for @samp{$}.

@example
(modify-syntax-entry ?\$ "." text-mode-syntax-table)
@end example

@item
Enable the use of the command @code{narrow-to-region} without confirmation.

@example
(put 'narrow-to-region 'disabled nil)
@end example

@item
Adjusting the configuration to various platforms and Emacs versions.

Users typically want Emacs to behave the same on all systems, so the
same init file is right for all platforms.  However, sometimes it
happens that a function you use for customizing Emacs is not available
on some platforms or in older Emacs versions.  To deal with that
situation, put the customization inside a conditional that tests whether
the function or facility is available, like this:

@example
(if (fboundp 'blink-cursor-mode)
    (blink-cursor-mode 0))

(if (boundp 'coding-category-utf-8)
    (set-coding-priority '(coding-category-utf-8)))
@end example

@noindent
You can also simply disregard the errors that occur if the
function is not defined.

@example
(condition case ()
    (set-face-background 'region "grey75")
  (error nil))
@end example

A @code{setq} on a variable which does not exist is generally
harmless, so those do not need a conditional.
@end itemize

@node Terminal Init
@subsection Terminal-specific Initialization

  Each terminal type can have a Lisp library to be loaded into Emacs when
it is run on that type of terminal.  For a terminal type named
@var{termtype}, the library is called @file{term/@var{termtype}} and it is
found by searching the directories @code{load-path} as usual and trying the
suffixes @samp{.elc} and @samp{.el}.  Normally it appears in the
subdirectory @file{term} of the directory where most Emacs libraries are
kept.@refill

  The usual purpose of the terminal-specific library is to map the
escape sequences used by the terminal's function keys onto more
meaningful names, using @code{input-decode-map} (or
@code{function-key-map} before it).  See the file
@file{term/lk201.el} for an example of how this is done.  Many function
keys are mapped automatically according to the information in the
Termcap data base; the terminal-specific library needs to map only the
function keys that Termcap does not specify.

  When the terminal type contains a hyphen, only the part of the name
before the first hyphen is significant in choosing the library name.
Thus, terminal types @samp{aaa-48} and @samp{aaa-30-rv} both use
the library @file{term/aaa}.  The code in the library can use
@code{(getenv "TERM")} to find the full terminal type name.@refill

@vindex term-file-prefix
  The library's name is constructed by concatenating the value of the
variable @code{term-file-prefix} and the terminal type.  Your @file{.emacs}
file can prevent the loading of the terminal-specific library by setting
@code{term-file-prefix} to @code{nil}.

@vindex term-setup-hook
  Emacs runs the hook @code{term-setup-hook} at the end of
initialization, after both your @file{.emacs} file and any
terminal-specific library have been read in.  Add hook functions to this
hook if you wish to override part of any of the terminal-specific
libraries and to define initializations for terminals that do not have a
library.  @xref{Hooks}.

@node Find Init
@subsection How Emacs Finds Your Init File

  Normally Emacs uses the environment variable @env{HOME}
(@pxref{General Variables, HOME}) to find @file{.emacs}; that's what
@samp{~} means in a file name.  If @file{.emacs} is not found inside
@file{~/} (nor @file{.emacs.el}), Emacs looks for
@file{~/.emacs.d/init.el} (which, like @file{~/.emacs.el}, can be
byte-compiled).

  However, if you run Emacs from a shell started by @code{su}, Emacs
tries to find your own @file{.emacs}, not that of the user you are
currently pretending to be.  The idea is that you should get your own
editor customizations even if you are running as the super user.

  More precisely, Emacs first determines which user's init file to use.
It gets your user name from the environment variables @env{LOGNAME} and
@env{USER}; if neither of those exists, it uses effective user-ID.
If that user name matches the real user-ID, then Emacs uses @env{HOME};
otherwise, it looks up the home directory corresponding to that user
name in the system's data base of users.
@c  LocalWords:  backtab

@node Init Non-ASCII
@subsection Non-@acronym{ASCII} Characters in Init Files
@cindex international characters in @file{.emacs}
@cindex non-@acronym{ASCII} characters in @file{.emacs}
@cindex non-@acronym{ASCII} keys, binding
@cindex rebinding non-@acronym{ASCII} keys

  Language and coding systems may cause problems if your init file
contains non-@acronym{ASCII} characters, such as accented letters, in
strings or key bindings.

  If you want to use non-@acronym{ASCII} characters in your init file,
you should put a @w{@samp{-*-coding: @var{coding-system}-*-}} tag on
the first line of the init file, and specify a coding system that
supports the character(s) in question.  @xref{Recognize Coding}.  This
is because the defaults for decoding non-@acronym{ASCII} text might
not yet be set up by the time Emacs reads those parts of your init
file which use such strings, possibly leading Emacs to decode those
strings incorrectly.  You should then avoid adding Emacs Lisp code
that modifies the coding system in other ways, such as calls to
@code{set-language-environment}.

  To bind non-@acronym{ASCII} keys, you must use a vector (@pxref{Init
Rebinding}).  The string syntax cannot be used, since the
non-@acronym{ASCII} characters will be interpreted as meta keys.  For
instance:

@example
(global-set-key [?@var{char}] 'some-function)
@end example

@noindent
Type @kbd{C-q}, followed by the key you want to bind, to insert @var{char}.

  @strong{Warning:} if you change the keyboard encoding, or change
between multibyte and unibyte mode, or anything that would alter which
code @kbd{C-q} would insert for that character, this key binding may
stop working.  It is therefore advisable to use one and only one
coding system, for your init file as well as the files you edit.  For
example, don't mix the @samp{latin-1} and @samp{latin-9} coding
systems.