The provider theoretiacly can look up a UserTransaction and call begin/commit/rollback on it when the user code calls the corresponding method on the EntityTransaction, allowing to use JTA PUs with application-managed EMFs (i.e. acquired via Persistence api). They can do it for RESOURCE_LOCAL as well, but that would probably be against the spec.
I'm not saying there are providers that do it that way, just that it is possible.
Regards,
-marina
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