docs: def _GetCallingPrototypeAsString(self, flow_cls):
      """Get a description of the calling prototype for this flow class."""
      output = []
      output.append("flow.StartAFF4Flow(client_id=client_id, ")
      output.append("flow_name=\"%s\", " % flow_cls.__name__)
      prototypes = []
      if flow_cls.args_type:
        for type_descriptor in flow_cls.args_type.type_infos:
          if not type_descriptor.hidden:
            prototypes.append("%s=%s" %
                              (type_descriptor.name, type_descriptor.name))
      output.append(", ".join(prototypes))
      output.append(")")
      return "".join(output)