code: public void show(int itemIndex, Bounds region) {
        navigator.showLengthRegion(itemIndex, orientation.minY(region), orientation.maxY(region));
        showBreadthRegion(orientation.minX(region), orientation.maxX(region));
      }
docs: Forces the viewport to show the given item by "scrolling" to it and then further "scrolling," so that the
  {@code region} is visible, in one layout call (e.g., this method does not "scroll" twice).