docs: function getAllResponseHeaders() {
              if (this.readyState < IsotropyXMLHttpRequest.HEADERS_RECEIVED) {
                  return "";
              }
  
              var headers = "";
  
              for (var header in this.responseHeaders) {
                  if (this.responseHeaders.hasOwnProperty(header) && !/^Set-Cookie2?$/i.test(header)) {
                      headers += header + ": " + this.responseHeaders[header] + "\r\n";
                  }
              }
  
              return headers;
          }