The org.zkoss.zk.ui.util.EventInterceptor interface
A listener could implement EventInterceptor to intercept when an event is sent, posted and processed.
Once registered, an instance is created and shared within the whole application. If you want to intercept events only for a particular desktop, use Desktop.addListener(Object).
Instantiation: For better performance, a single instance of the given class is instantiated when registered. It is then shared in the whole application. Thus, the implementation must be thread safe.