<window hflex="1" vflex="1"
		apply="org.zkoss.zss.essential.EventsComposer">
			<spreadsheet id="ss" hflex="1" vflex="1"
			 maxVisibleRows="100" maxVisibleColumns="40"
			ctrlKeys="^a"/>
</window>

public class EventsComposer extends SelectorComposer<Component>{

	@Listen("onCtrlKey = spreadsheet")
	public void onCtrlKey(KeyEvent event){
		
		System.out.println(event.getKeyCode());
	}
}

	private void reloadUserActionEventRegisteration() {
		...
			String ctrlKeys = ua.getCtrlKeys();
			if(ctrlKeys!=null){//null, don't set, keep the original
				this.setCtrlKeys(ctrlKeys);
			}
		...
	}