docs: function flush(done) {
      this.once('done', done);
  
      if (this._res.finished) {
        this.emit('done', new Error('Response was closed, unable to flush content'));
      }
  
      if (!this._queue.length) this.emit('done');
      var data = new Buffer(this.join(), this.charset);
  
      if (data.length) {
        this.debug('Writing %d bytes of %s to response', data.length, this.charset);
        this._res.write(data, this.emits('done'));
      }
  
      //
      // Optional write confirmation, it got added in more recent versions of
      // node, so if it's not supported we're just going to call the callback
      // our selfs.
      //
      if (this._res.write.length !== 3 || !data.length) this.emit('done');
    }