Defines an "extension", which is much like a helper bean, but is part of a
library or application specification (and has the same lifecycle as the
Returns an immutable Map of the configuration; keyed on property name,
with values as properties to assign.
Invoked to instantiate an instance of the extension and return it. It
also configures properties of the extension.
Returns true if the extensions should be instantiated immediately after
parsed. Non-immediate extensions are instantiated only as needed.