code: def build(self) -> type:
          
          def _get_property_mappings(encoder: MappingJSONEncoder) -> List[JsonPropertyMapping]:
              return _get_all_property_mappings(encoder, self.mappings, self.superclasses)
  
          def get_deserializable_cls(decoder: MappingJSONDecoder) -> type:
              return self.target_cls
  
          return type(
              "%sDynamicMappingJSONDecoder" % self.target_cls.__name__,
              self.superclasses,
              {
                  "_get_property_mappings": _get_property_mappings,
                  "_get_deserializable_cls": get_deserializable_cls
              }
          )
docs: Build a subclass of `MappingJSONDecoder`.
          :return: the built subclass