docs: def catalog(self, table='', column=''):
          """Lookup the values available for querying."""
          lookup_table = self.lookup_table
          if lookup_table is not None:
              if table:
                  if column:
                      column = column.upper()
                      return lookup_table[table][column]
                  return lookup_table[table]
              # Show what methods are available.
              return self.lookup_methods
          return None