@Retention(value=CLASS) public static interface RegionEvent.RegionState extends Annotation
ProximityRegion. Either RegionEvent.UNKNOWN, RegionEvent.INSIDE or
 RegionEvent.OUTSIDE.
 
 Provided as an enumerated annotation for primitive int values representing state.
 This helps IDEs and lint ensure that parameters, return values, or field references use
 the defined constant set. It also allows for code completion within Android Studio.