try the case in http://books.zkoss.org/wiki/ZK_Developer's_Reference/Performance_Tips/Specify_Stubonly_for_Client-only_Components#Event_Handling

<textbox stubonly="true" onChange='System.out.println(event.getClass().getName()+":"+event.getName())'/> doesn't work in my 6.0.1

try following in zksandbox, it doesn't work too, but it work in fiddle with 5.0.x
<textbox stubonly="true" onChange='alert(event.getClass().getName()+":"+event.getName())'/>