A list of named managed persistence classes may be specified instead of or in addition to the JAR files and mapping files. Any mapping metadata annotation found on these classes will be processed, or they will be mapped using the mapping annotation defaults. The class element is used to list a managed persistence class.
With JPA 2.0, we can use @Entity to specify managed persistence class or by using <Entity> in orm.xml
Is this <class> element of <persistence-unit> necessary?