/// Used by the `child-index()` mixin in _family.scss. It will return the proper
/// sorted numbers depending on the `$index` value.
///
/// @param {Number} $num - The number of children.
/// @param {Number} $index - The index of the sorting.
///
/// @return {Number} The order index.
///
/// @access public
/// @group Utilities
/// @see {mixin} child-index
@function order-index($num, $index) {
  @return ($index + $num);
}