public class PresentWhenExtensionAnnotationMatchesExtensionSet
extends Object
implements ImplicitOptionalConverter

We use the annotation Extension to bind a class that implements an extension API to an Extension. Match in the following order: 1. Match by namespace 2. Match by namespace aliases 3. Match by alias 4. Match by name New versions of openstack have no namespaces anymore. Alias is different than a namespace alias - it's an alternative namespace URL to match against.