docs: def register(cls, range_mixin):
          """
          Decorator for registering range set mixins for global use. This works
          the same as :meth:`~spans.settypes.MetaRangeSet.add`
  
          :param range_mixin: A :class:`~spans.types.Range` mixin class to
                              to register a decorated range set mixin class for
          :return: A decorator to use on a range set mixin class
          """
  
          def decorator(range_set_mixin):
              cls.add(range_mixin, range_set_mixin)
              return range_set_mixin
          return decorator