docs: private int getPackedGroupPosition(final int groupIndex) {
          int packedPosition = getHeaderViewsCount();
  
          if (groupIndex > 0) {
              for (int i = groupIndex - 1; i >= 0; i--) {
                  packedPosition += getExpandableListAdapter().getChildrenCount(i) + 1;
              }
          }
  
          return packedPosition;
      }