docs: def cardinality_class(self):
          """ Group the cardinality of the dimension into one of four buckets,
          from very small (less than 5) to very large (more than 1000). """
          if self.cardinality:
              if self.cardinality > 1000:
                  return 'high'
              if self.cardinality > 50:
                  return 'medium'
              if self.cardinality > 7:
                  return 'low'
              return 'tiny'