docs: def register_queryset(self, queryset, validator=None, default=False):
          """
          Add a given queryset to the iterator with custom logic for iteration.
  
          :param queryset: List of objects included in the reading list.
          :param validator: Custom logic to determine a queryset's position in a reading_list.
              Validators must accept an index as an argument and return a truthy value.
          :param default: Sets the given queryset as the primary queryset when no validator applies.
          """
          if default or self.default_queryset is None:
              self.default_queryset = queryset
              return
          if validator:
              self.querysets[validator] = queryset
          else:
              raise ValueError(
                  """Querysets require validation logic to integrate with reading lists."""
              )