docs: def relative_ref(*parts):
      """
      Create a reference builder with specified relative location.
      using getter.relative_ref("some", "submodel") to get a value with key
      "toto" will gives reference.Relative("some", "submodel", "toto")
      """
  
      def relative_ref(_value, context, **_params):
          return reference.Relative(*(parts + (context["key"], )))
  
      return relative_ref