nftables : sets or dictionaries for applying one rule to many subnets

What is the most efficient way of applying a single filter rule to a great many diverse subnets in nftables? Would that be sets or dictionaries or something else?

Normally, with PF, I'd use a table, but PF is not available for Linux and nftables seems to be the way to go nowadays.

Also, can I add an AS number directly to nftables to get a whole administrative entity at once?