code: def add_model_string(self, model_str, position=1, file_id=None):
          
          if file_id is None:
              file_id = self.make_unique_id('inlined_input')
          ret_data = self.file_create(File.from_string(model_str, position,
                                                       file_id))
          return ret_data
docs: Add a kappa model given in a string to the project.