This value has no precise programmatic control. Instead it is used as a helper to more easily learn which TARGET this Event is being shot on. Programmatically, the SegmentGroupSegment, in the range script controls the selected TARGET (via its TargetCollectionIndex). The definition's author is responsible for composing values that are consistent.
This value may only be seet on Event with EventType Stage. All children on a Event, of EventType Stage are assumed to use the same TargetCollectionIndex.
Value must be between 0 and n - 1, where n is the number of TargetDefs in the TARGET COLLECTION definition. The special value of -9999 means not to set a value.
public int TargetCollectionIndex { get; set; }