High priority, a #SoupMessage with this priority will be processed before the ones with the default priority.
Use this for low priority messages, a #SoupMessage with the default priority will be processed first.
The default priotity, this is the priority assigned to the #SoupMessage by default.
The highest priority, use this for very urgent #SoupMessage as they will be the first ones to be attended.
The lowest priority, the messages with this priority will be the last ones to be attended.
Priorities that can be set on a #SoupMessage to instruct the message queue to process it before any other message with lower priority.