Interface to implement to react to focus enter/exit.
public interface IMixedRealityFocusHandler : IEventSystemHandler
The events on this interface are related to those of IMixedRealityFocusChangedHandler, whose event have a known ordering with this interface:
Because these two interfaces are different, consumers must be wary about having nested hierarchies where some game objects will implement both interfaces, and more deeply nested object within the same parent-child chain that implement a single one of these - such a presence can lead to scenarios where one interface is invoked on the child object, and then the other interface is invoked on the parent object (thus, the parent would "miss" getting the event that the child had already processed).
void OnFocusEnter(FocusEventData eventData)
void OnFocusExit(FocusEventData eventData)