docs: function Sequence(iterable) {
      this.sequence = null;
      this._size = 0;
      this.nodeMap = new rMap();
      if (iterable) {
        if (typeof iterable.length === 'number') {
          for (var i = 0; i < iterable.length; i++) {
            this.add.apply(this, iterable[i]);
          }
        } else if (typeof iterable.entries === 'function') {
          var it = iterable.entries();
          while (!it.done) {
            var tmp = it.next();
            this.add.apply(this, tmp);//it.next());
          }
        }
      }
    }