docs: def hint_tuples(o):
      """
      Annotates tuples before JSON serialization, so that they can be
      reconstructed during deserialization. Each tuple is converted into a
      dictionary of the form:
  
          {'_type': 'tuple', 'items': (...)}
  
      This function acts recursively on lists, so that tuples nested inside a list
      (or doubly nested, triply nested, etc.) will also be annotated.
      """
      if isinstance(o, tuple):
          return dict(_type='tuple', items=o)
      elif isinstance(o, list):
          return [hint_tuples(el) for el in o]
      else:
          return o