k done on one copy has
 no effect on the others; acknowledging one does not acknowledge the
 others; one message may be delivered immediately, while another waits
 for its subscriber to process messages ahead of it.

 <P>Regular <code>TopicSubscriber</code> objects are not durable. They 
 receive only messages that are published while they are active.

 <P>Messages filtered out by a subscriber's message selector will never 
 be delivered to the subscriber. From the subscriber's perspective, they 
 do not ex