code: protected boolean requestIsEmbedded(HttpServletRequest httpRequest,
  			WaybackRequest wbRequest) {
  		// without a wbRequest, assume it is not embedded: send back HTML
  		if (wbRequest == null) {
  			return false;
  		}
  		String referer = wbRequest.getRefererUrl();
  		return (referer != null && referer.length() > 0);
  	}
docs: /* ERROR HANDLING RESPONSES: