whole_func_string: function jump(history, n) {
      if (n > 0) return jumpToFuture(history, n - 1);
      if (n < 0) return jumpToPast(history, history.past.length + n);
      return history;
  }
func_code_string: function jump(history, n) {
      if (n > 0) return jumpToFuture(history, n - 1);
      if (n < 0) return jumpToPast(history, history.past.length + n);
      return history;
  }
func_documentation_string: jump: jump n steps in the past or forward