39.19.2 Button Types

Every button has a button type, which defines default values for the button’s properties. Button types are arranged in a hierarchy, with specialized types inheriting from more general types, so that it’s easy to define special-purpose types of buttons for specific tasks.

function define-button-type name \&rest properties

Define a button type called name (a symbol). The remaining arguments form a sequence of property value pairs, specifying default property values for buttons with this type (a button’s type may be set by giving it a type property when creating the button, using the :type keyword argument).

In addition, the keyword argument :supertype may be used to specify a button-type from which name inherits its default property values. Note that this inheritance happens only when name is defined; subsequent changes to a supertype are not reflected in its subtypes.

Using define-button-type to define default properties for buttons is not necessary—buttons without any specified type use the built-in button-type button—but it is encouraged, since doing so usually makes the resulting code clearer and more efficient.