@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1997, 1998, 1999, 2000, 2002, 2003 Free Software Foundation, Inc.
+@c Copyright (C) 1997, 1998, 1999, 2000, 2002, 2003, 2004,
+@c 2005 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/customize
@node Customization, Loading, Macros, Top
definitions---as well as face definitions (@pxref{Defining Faces}).
@menu
-* Common Keywords::
-* Group Definitions::
-* Variable Definitions::
-* Customization Types::
+* Common Keywords:: Common keyword arguments for all kinds of
+ customization declarations.
+* Group Definitions:: Writing customization group definitions.
+* Variable Definitions:: Declaring user options.
+* Customization Types:: Specifying the type of a user option.
@end menu
@node Common Keywords
Use the @code{:set} function to initialize the variable, if it is
already set or has been customized; otherwise, just use
@code{set-default}.
+
+@item custom-initialize-safe-set
+@itemx custom-initialize-safe-default
+These functions behave like @code{custom-initialize-set}
+(@code{custom-initialize-default}, respectively), but catch errors.
+If an error occurs during initialization, they set the variable to
+@code{nil} using @code{set-default}, and throw no error.
+
+These two functions are only meant for options defined in pre-loaded
+files, where some variables or functions used to compute the option's
+value may not yet be defined. The option normally gets updated in
+@file{startup.el}, ignoring the previously computed value. Because of
+this typical usage, the value which these two functions compute
+normally only matters when, after startup, one unsets the option's
+value and then reevaluates the defcustom. By that time, the necessary
+variables and functions will be defined, so there will not be an error.
@end table
@item :set-after @var{variables}
operation of a certain feature. Assuming that the package is coded to
check the value of the option, you still need to arrange for the package
to be loaded. You can do that with @code{:require}. @xref{Common
-Keywords}. Here is an example, from the library @file{tooltip.el}:
+Keywords}. Here is an example, from the library @file{saveplace.el}:
@example
-(defcustom tooltip-mode nil
- "Non-nil if Tooltip mode is enabled..."
- :set (lambda (symbol value)
- (tooltip-mode (or value 0)))
- :initialize 'custom-initialize-default
+(defcustom save-place nil
+ "*Non-nil means automatically save place in each file..."
:type 'boolean
- :require 'tooltip
- :group 'tooltip)
+ :require 'saveplace
+ :group 'save-place)
@end example
If a customization item has a type such as @code{hook} or @code{alist},
Internally, @code{defcustom} uses the symbol property
@code{standard-value} to record the expression for the default value,
and @code{saved-value} to record the value saved by the user with the
-customization buffer. The @code{saved-value} property is actually a
-list whose car is an expression which evaluates to the value.
+customization buffer. Both properties are actually lists whose car is
+an expression which evaluates to the value.
@node Customization Types
@section Customization Types
most general last. Here's an example of proper usage:
@example
-(choice (const :tag "Off" nil) symbol (sexp :tag "Other"))
+(choice (const :tag "Off" nil)
+ symbol (sexp :tag "Other"))
@end example
@noindent
argument with the same syntax as the keyword argument to
@code{defcustom} with the same name. The third argument is a
documentation string for the new widget. You will be able to see that
-string with the @kbd{M-x widget-browse @key{ret} binary-tree-of-string
-@key{ret}} command.
+string with the @kbd{M-x widget-browse @key{RET} binary-tree-of-string
+@key{RET}} command.
After these mandatory arguments follow the keyword arguments. The most
important is @code{:type}, which describes the data type we want to match