code: function setAnimationFraction(element, itemIndex, fraction) {
    const animation = getAnimationForItemIndex(element, itemIndex);
    if (animation) {
      const duration = element.selectionAnimationDuration;
      if (duration) {
        animation.currentTime = fraction * duration;
      }
    }
  }
docs: /*
  Pause the indicated animation and have it show the animation at the given
  fraction (between 0 and 1) of the way through the animation.