code: def _traverse(self, n=1):
          
          if not self.history:
              raise exceptions.RoboError('Not tracking history')
          cursor = self._cursor + n
          if cursor >= len(self._states) or cursor < 0:
              raise exceptions.RoboError('Index out of range')
          self._cursor = cursor
docs: Traverse state history. Used by `back` and `forward` methods.
  
          :param int n: Cursor increment. Positive values move forward in the
              browser history; negative values move backward.