Enhance JAXB to allow validation based on annotations, without requiring a schema.
One of the benefits of JAXB 2 is that a schema is not required; annotating Java
classes alone allows for XML serialization/deserialization. With the deprecation
of the Unmarshaller.setValidating() in favor of the unmarshaller.setSchema()
method, however, validation is only available when an XSD is present. Ideally,
validation can occur during unarshalling (or marshalling) without a physical