code: def _register(self, form_class, check_middleware=True):
          
          if not issubclass(form_class, _ConfigFormBase):
              raise ValueError(
                  "The form does not inherit from `forms.ConfigForm`")
  
          self._registry.add(form_class)
  
          if check_middleware:
              _check_backend()
docs: Register a config form into the registry
  
          :param object form_class: The form class to register.\
          Must be an instance of :py:class:`djconfig.forms.ConfigForm`
          :param bool check_middleware: Check\
          :py:class:`djconfig.middleware.DjConfigMiddleware`\
          is registered into ``settings.MIDDLEWARE_CLASSES``. Default True