code: @Override
  	public void onBeforeRender()
  	{
  
  
  		addOrReplace(overlayReference = newOverlayReference("overlayReference", getModel()));
  		overlayReference.add(newPopupoverlayBehavior());
  		overlayReference.setOutputMarkupId(true);
  
  		addOrReplace(openButton = newOpenButton("openButton"));
  		// add class attributte with the markup id from the overlay with the
  		// suffix '_open' that indicates that the overlay shell open...
  		openButton.add(new AttributeAppender("class",
  			" " + overlayReference.getMarkupId() + OPEN_OVERLAY_SUFFIX));
  		super.onBeforeRender();
  	}
docs: {@inheritDoc}