As code below, click 'test two' then you will see JS Error
<zk> <tabbox width="400px" id="tbx"> <tabs> <tab label="Tab 1" /> <tab label="Tab 2" /> </tabs> <tabpanels> <tabpanel id="tp"> This is panel 1 <button id="btnOne" visible="false"> <attribute name="onLater"><![CDATA[ System.out.println("button one on later"); ]]></attribute> </button> </tabpanel> <tabpanel id="tp2"> <button id="btnTwo"> <attribute name="onLater"><![CDATA[ System.out.println("button two on later"); ]]></attribute> </button> </tabpanel> </tabpanels> </tabbox> <button label="test one"> <attribute name="onClick"><![CDATA[ Events.echoEvent("onLater", btnOne, null); //echo an event back ]]></attribute> </button> <button label="test two"> <attribute name="onClick"><![CDATA[ Events.echoEvent("onLater", btnTwo, null); //echo an event back ]]></attribute> </button> </zk>