public B on(EventType type,EventListener listener){
  assertCurrent();
  Element element=elements.peek().element;
  type.register(element,listener);
  return that();
}

public B on ( EventType type , EventListener listener ) { assertCurrent ( ) ; Element element = elements . peek ( ) . element ; type . register ( element , listener ) ; return that ( ) ; }
adds the given event listener to the the last added element .
