docs: public View findTopChildUnder(int x, int y) {
          final int childCount = mParentView.getChildCount();
          for (int i = childCount - 1; i >= 0; i--) {
              final View child = mParentView.getChildAt(mCallback.getOrderedChildIndex(i));
              if (x >= child.getLeft() && x < child.getRight() &&
                      y >= child.getTop() && y < child.getBottom()) {
                  return child;
              }
          }
          return null;
      }