docs: function Response(req, options) {
    options = options || {};
    this.req = req;
    this.xhr = this.req.xhr;
    // responseText is accessible only if responseType is '' or 'text' and on older browsers
    this.text = ((this.req.method !='HEAD' && (this.xhr.responseType === '' || this.xhr.responseType === 'text')) || typeof this.xhr.responseType === 'undefined')
       ? this.xhr.responseText
       : null;
    this.statusText = this.req.xhr.statusText;
    this._setStatusProperties(this.xhr.status);
    this.header = this.headers = parseHeader(this.xhr.getAllResponseHeaders());
    // getAllResponseHeaders sometimes falsely returns "" for CORS requests, but
    // getResponseHeader still works. so we get content-type even if getting
    // other headers fails.
    this.header['content-type'] = this.xhr.getResponseHeader('content-type');
    this._setHeaderProperties(this.header);
    this.body = this.req.method != 'HEAD'
      ? this._parseBody(this.text ? this.text : this.xhr.response)
      : null;
  }