_callObserver(transaction, parentSubs) {
    if (!transaction.local && this._searchMarker) {
      this._searchMarker.length = 0;
    }
  }
Creates YEvent and calls all type observers.
Must be implemented by each type.

@param {Transaction} transaction
@param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.