docs: function( xhr, url ) {
  		var lastModified = xhr.getResponseHeader("Last-Modified"),
  			etag = xhr.getResponseHeader("Etag");
  
  		if ( lastModified ) {
  			jQuery.lastModified[url] = lastModified;
  		}
  
  		if ( etag ) {
  			jQuery.etag[url] = etag;
  		}
  
  		// Opera returns 0 when status is 304
  		return xhr.status === 304 || xhr.status === 0;
  	}