Info Catalog elisp: Variable Definitions elisp: Customization elisp: Applying Customizations

elisp: Customization Types

 
 14.4 Customization Types
 ========================
 
 When you define a user option with ‘defcustom’, you must specify its
 “customization type”.  That is a Lisp object which describes (1) which
 values are legitimate and (2) how to display the value in the
 customization buffer for editing.
 
    You specify the customization type in ‘defcustom’ with the ‘:type’
 keyword.  The argument of ‘:type’ is evaluated, but only once when the
 ‘defcustom’ is executed, so it isn’t useful for the value to vary.
 Normally we use a quoted constant.  For example:
 
      (defcustom diff-command "diff"
        "The command to use to run diff."
        :type '(string)
        :group 'diff)
 
    In general, a customization type is a list whose first element is a
 symbol, one of the customization type names defined in the following
 sections.  After this symbol come a number of arguments, depending on
 the symbol.  Between the type symbol and its arguments, you can
 optionally write keyword-value pairs (Type Keywords).
 
    Some type symbols do not use any arguments; those are called “simple
 types”.  For a simple type, if you do not use any keyword-value pairs,
 you can omit the parentheses around the type symbol.  For example just
 ‘string’ as a customization type is equivalent to ‘(string)’.
 
    All customization types are implemented as widgets; see 
 Introduction (widget)Top, for details.
 

Menu

 
· Simple Types            Simple customization types: sexp, integer, etc.
· Composite Types         Build new types from other types or data.
· Splicing into Lists     Splice elements into list with ‘:inline’.
· Type Keywords           Keyword-argument pairs in a customization type.
· Defining New Types      Give your type a name.
 

Info Catalog elisp: Variable Definitions elisp: Customization elisp: Applying Customizations