docs: def register_model(self, model, bundle):
          """
          Registers a bundle as the main bundle for a
          model. Used when we need to lookup urls by
          a model.
          """
          if model in self._model_registry:
              raise AlreadyRegistered('The model %s is already registered' \
                                       % model)
  
          if bundle.url_params:
              raise Exception("A primary model bundle cannot have dynamic \
                              url_parameters")
  
          self._model_registry[model] = bundle