Empty attribute. Useful for building up queries. Returns other attribute when ORed or ANDed. It can be considered an empty query that you can use as an initial value if you want to build up your query in a loop.
So, if we wanted an attr matching all the time intervals between the times stored as (from, to) tuples in a list, we could do.
attr = DummyAttr() for from, to in times: attr |= Time(from, to)