docs: function ReadableParallel(list, iterator, callback)
  {
    if (!(this instanceof ReadableParallel))
    {
      return new ReadableParallel(list, iterator, callback);
    }
  
    // turn on object mode
    ReadableParallel.super_.call(this, {objectMode: true});
  
    this._start(parallel, list, iterator, callback);
  }