ESB Message Priority

The ESB message holds a Priority field. The documentation doesn't give much information on how to use this field so I am curious to get some information and experience on it.

I have seen Priroty fields in some MOM's like WebSphere MQ and MSMQ. It gives the putting application the ability to signal priority on the message. The retrieving application can get messages using FIFO within priority sequence in contrast to FIFO on the queue itself. Of course one has to be careful about the impact when higher priority messages is retrieved before older messages with lower priority.

Does the ESB message Priority field have a semilar semantic?
Is it set on basis of the priority given on the actual message e.g. when publishing from an MSMQ adapter?
In many cases the message doesn't have a specific field to set priority e.g. when retrieved via file adapter or Client Connector. But then it could be set within a pipelinie.

I imagine the ESB message Priority is used in the Neuron pub/sub engine such that subscribers retrieve the messages in priority order and within same priority with order of arrival. Is it possible for the subscriber to control the order of retrieved messages or will it always adhere to the priority?