Developers could add event listeners to a page (org.zkoss.zk.ui.Page) dynamically. Once added, all events of the specified name the are sent to any components of the specified page will be sent to the listener.

All page-level event listeners are non-ASAP. In other words, the isArap method is ignored.

A typical example is to use a page-level event listener to maintain the modification flag as follows.

public class ModificationListener implements EventListener, Deferrable {
    private final Window _owner;    
    private final Page _page;    
    private boolean _modified;    

    public ModificationListener(Window owner) {    
        //Note: we have to remember the page because unregister might        
        //be called after the owner is detached        
        _owner = owner;        
        _page = owner.getPage();        
        _page.addEventListener("onChange", this);        
        _page.addEventListener("onSelect", this);        
        _page.addEventListener("onCheck", this);        
    }    
    /** Called to unregister the event listener.    
     */    
    public void unregister() {    
        _page.removeEventListener("onChange", this);        
        _page.removeEventListener("onSelect", this);        
        _page.removeEventListener("onCheck", this);        
    }    
    /** Returns whether the modified flag is set.    
     */    
    public boolean isModified() {    
        return _modified;        
    }    
    //-- EventListener --//    
    public void onEvent(Event event) throws UiException {    
        _modified = true;        
    }    
    //-- Deferrable --//    
    public boolean isDeferrable() {    
        return true;        
    }    
}

Note: Whether to implement the Deferrable interface is optional in this example, because the page's event listeners are always assumed to be deferrable, no matter Deferrable is implemented or not.