The EventSinkGUIInterface structure is a callback interface for use with UI-side event sinks. The interface is registered with a call to EventRegisterSinkGUI. The framework will call you via this interface when it needs you to perform actions relevant to your event sink.
Queries your event sink to see whether it will allow hooking/unhooking the specified event. See EventSinkGUIHookQuery
Asks your event sink to hook or unhook from the specified event. This is only called if you returned true from EventSinkGUIHookQuery. See EventSinkGUIHookAction
Requests that your event sink presents a user interface to edit the event hook. See EventSinkGUIHookEdit