[#] CS195 [Section] 5.1.22 [Statement text] 
This optional field contains the data for the event and becomes a REQUIRED field when either the relevant EventDescription or the Event structures specify a value for the type field. One example of when this field might not be included is when the event is simply a signal and the event's name thereby carries all of the semantics of the event. Its contents MUST conform to the schema referenced by the type field.