The value of tVrrpRtUnknEvtPriority specifies the
priority level associated with this event. When the operational
state of the event transitions to one of the 'set' states, this
value will either be subtracted from the in-use priority (if the
event is a 'delta' event) or the in-use priority will be
explicitly overridden by this priority value (if the event is
an 'explicit' event).