docs: function send(data) {
      verifyState(this);
  
      if (!/^(get|head)$/i.test(this.method)) {
        var hasContentTypeHeader = false
  
        Object.keys(this.requestHeaders).forEach(function (key) {
          if (key.toLowerCase() === 'content-type') {
            hasContentTypeHeader = true;
          }
        });
  
        if (!hasContentTypeHeader && !(data || '').toString().match('FormData')) {
          this.requestHeaders["Content-Type"] = "text/plain;charset=UTF-8";
        }
  
        this.requestBody = data;
      }
  
      this.errorFlag = false;
      this.sendFlag = this.async;
      this._readyStateChange(FakeXMLHttpRequest.OPENED);
  
      if (typeof this.onSend == "function") {
        this.onSend(this);
      }
  
      this.dispatchEvent(new _Event("loadstart", false, false, this));
    }