text: let Url = null;
  
  /**
   * Sets the WHATWG URL class for this library
   * @param {class} [cls=URL] the class to use for parsing URLs
   */
  export function setUrl(cls=URL) {
    Url = cls;
  }
  
  try {
    setUrl();
  } catch (err) {
    if (!(err instanceof ReferenceError)) {
      throw err;
    }
  }
  
  let fetcher = null;
  let hdrs = null;
  let req = null;
  let res = null;
  
  /**
   * Sets the WHATWG URL fetch API for this library
   * @param {function} [func=fetch] the global fetch function
   * @param {class} [headers=Headers] a collection of HTTP headers
   * @param {class} [request=Request] a request to the server
   * @param {class} [response=Response] a response from the server
   */
  export function setFetch(func=fetch, headers=Headers, request=Request, response=Response) {
    fetcher = func;
    hdrs = headers;
    req = request;
    res = response;
  }
  
  try {
    setFetch();
  } catch (err) {
    if (!(err instanceof ReferenceError)) {
      throw err;
    }
  }
  
  export {Url as URL, fetcher as fetch, hdrs as Headers, req as Request, res as Response};
  