docs: def _to_json(self):
          """Save :class:`~nmrstarlib.plsimulator.PeakList` into JSON string.
  
          :return: Peak list representation in JSON format.
          :rtype: :py:class:`str`
          """
          json_list = [{"Assignment": peak.assignments_list, "Dimensions": peak.chemshifts_list} for peak in self]
          return json.dumps(json_list, sort_keys=True, indent=4)