What is the dot (.) in an Nftables rule

In many nftables examples, I sometimes see statement like this:

map nat-udp-services {
        type ipv4_addr . inet_service : verdict
    }

and this:

ip daddr . udp dport vmap @nat-udp-services

What does the dot (.) mean in these cases?

Concatenation

There's some more details about it in the wiki