code: function updateScroll () {
      if (!elements.li[0]) return;
      var height = elements.li[0].offsetHeight,
          top = height * ctrl.index,
          bot = top + height,
          hgt = elements.scroller.clientHeight,
          scrollTop = elements.scroller.scrollTop;
      if (top < scrollTop) {
        scrollTo(top);
      } else if (bot > scrollTop + hgt) {
        scrollTo(bot - hgt);
      }
    }
docs: Makes sure that the focused element is within view.