Javadoc for EMF#unwrap:
" <T> T unwrap(Class<T> cls)
Return an object of the specified type to allow access to the provider-specific API. If the provider's EntityManagerFactory implementation does not support the specified class, the PersistenceException is thrown.
Parameters: cls - the class of the object to be returned. This is normally either the underlying EntityManagerFactory implementation class or an interface that it implements. Returns: an instance of the specified class Throws: PersistenceException - if the provider does not support the call Since: Java Persistence 2.1 "
From the above javadoc comment, I think that users can expect access to the EntityManagerFactory implementation class as well as access to other interfaces.
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