SubEtha persistence - default hibernate detection

Hello to all developers.

I have started to study SubEtha code to find out more about
persistence in EJB3. However I can not find out where hibernate is
specified in either JBoss as default persistence provider or in
SubEtha explicitly.

This article http://www.ociweb.com/jnb/jnbApr2006.html contains a note
that provider class must be specified in persistence.xml, but
persistence.xml contains only hibernate properties and there is no
mention of any hibernate classes.

Does anybody know where Hibernate persistence provider is chosen for SubEtha?

-- 
--t.