The org.zkoss.zk.ui.util.ExecutionCleanup interface
From Documentation
Listener:
org.zkoss.zk.ui.util.ExecutionCleanup interface
A listener could implement ExecutionCleanup to cleanup an execution that is being destroyed.
When ZK Loader is going to destroy an execution, it invokes the cleanup method of this interface such that developers could plug the application-specific codes to cleanup an execution.