code: def to_json(self, propval, extraneous=False, to_json_func=None):
          
          if self.json_out:
              return self.json_out(propval)
          else:
              if not to_json_func:
                  from normalize.record.json import to_json
                  to_json_func = to_json
              return to_json_func(propval, extraneous)
docs: This function calls the ``json_out`` function, if it was specified,
          otherwise continues with JSON conversion of the value in the slot by
          calling ``to_json_func`` on it.