MDB Message Receipt Part of Transaction

Hi!
In section 5.4.12 of the EJB 3.1 specification it says:

When a message-driven bean using bean-managed transaction demarcation uses the javax.transaction.UserTransaction interface to demarcate transactions, the message receipt that causes the bean to be invoked is not part of the transaction. If the message receipt is to be part of the transaction, container-managed transaction demarcation with the REQUIRED transaction attribute must be used.

Is it message receipt by the message driven bean that they are talking about?
Does this mean that there are circumstances under which the message delivered to the bean will not be re-delivered?
Thanks in advance!

I think it's the message receipt by the container. This post should bring some light about it. (although it's about EJB2.0)