docs: def start(self):
          """Starts the execution of the root state.
          """
          # load default input data for the state
          self._root_state.input_data = self._root_state.get_default_input_values_for_state(self._root_state)
          self._root_state.output_data = self._root_state.create_output_dictionary_for_state(self._root_state)
          new_execution_history = self._add_new_execution_history()
          new_execution_history.push_state_machine_start_history_item(self, run_id_generator())
          self._root_state.start(new_execution_history)