code: def model_from_str(self, model_str, debug=None,
                         pre_ref_resolution_callback=None):
          
  
          if type(model_str) is not text:
              raise TextXError("textX accepts only unicode strings.")
  
          model = self._parser_blueprint.clone().get_model_from_str(
              model_str, debug=debug,
              pre_ref_resolution_callback=pre_ref_resolution_callback)
          for p in self._model_processors:
              p(model, self)
          return model
docs: Instantiates model from the given string.
          :param pre_ref_resolution_callback: called before references are
                 resolved. This can be useful to manage models distributed
                 across files (scoping)