docs: function _setResponseBody(body) {
      verifyRequestSent(this);
      verifyHeadersReceived(this);
      verifyResponseBodyType(body);
  
      var chunkSize = this.chunkSize || 10;
      var index = 0;
      this.responseText = "";
  
      do {
        if (this.async) {
          this._readyStateChange(FakeXMLHttpRequest.LOADING);
        }
  
        this.responseText += body.substring(index, index + chunkSize);
        index += chunkSize;
      } while (index < body.length);
  
      var type = this.getResponseHeader("Content-Type");
  
      if (this.responseText && (!type || /(text\/xml)|(application\/xml)|(\+xml)/.test(type))) {
        try {
          this.responseXML = parseXML(this.responseText);
        } catch (e) {
          // Unable to parse XML - no biggie
        }
      }
  
      if (this.async) {
        this._readyStateChange(FakeXMLHttpRequest.DONE);
      } else {
        this.readyState = FakeXMLHttpRequest.DONE;
      }
    }