docs: def _append_callback_id(ids, obj, callback_id):
      '''
      Helper function adding a callback ID to the IDs dict.
      The callback ids dict maps an object to event callback ids.
  
      :param ids: dict of callback IDs to update
      :param obj: one of the keys of REGISTER_FUNCTIONS
      :param callback_id: the result of _register_callback
      '''
      if obj not in ids:
          ids[obj] = []
      ids[obj].append(callback_id)