code: @Override
  	public void handleRequest(final Request request) {
  		String clientState = request.getParameter(getId());
  
  		if (clientState != null) {
  			setCollapsed(clientState.equalsIgnoreCase("closed"));
  		}
  	}
docs: Override handleRequest to perform processing necessary for this component. This is used to handle the server-side
  collapsible mode and to synchronise with the client-side state for the other modes.
  
  @param request the request being responded to.