code: def registration_function_for_optionable(self, optionable_class):
      
      self._assert_not_frozen()
      # TODO(benjy): Make this an instance of a class that implements __call__, so we can
      # docstring it, and so it's less weird than attatching properties to a function.
      def register(*args, **kwargs):
        kwargs['registering_class'] = optionable_class
        self.register(optionable_class.options_scope, *args, **kwargs)
      # Clients can access the bootstrap option values as register.bootstrap.
      register.bootstrap = self.bootstrap_option_values()
      # Clients can access the scope as register.scope.
      register.scope = optionable_class.options_scope
      return register
docs: Returns a function for registering options on the given scope.