) {
    this.step = aStep;
    var old = this.slides[this.idx - 1].$('.incremental > *[aria-selected]');
    if (old) {
      old.removeAttribute('aria-selected');
    }
    var incrementals = $$('.incremental');
    if (this.step <= 0) {
      $$.forEach(incrementals, function(aNode) {
        aNode.removeAttribute('active');
      });
      return;
    }
    var next = this.slides[this.idx - 1].$$('.incremental > *')[this.step - 1];
    if (next) {
      next.setAttribute('aria-selected', true);
      nex