Suggested by the spec only "@XmlRootType" JAXB annotated classes should be passed to context creation JAXBContext#newInstance(Class[] classesToBeBound, ..)

For example, given the following Java classes:

@XmlRootElement2 class Foo { Bar b;}
@XmlType class Bar { FooBar fb;}
@XmlType class FooBar { int x; }

The invocation of JAXBContext.newInstance(Foo.class) registers Foo and the statically referenced classes, Bar and FooBar.

If Bar and FooBar are in different package than Foo, than openness is not propagated for them with current implementation.