How do I create a named set of interfaces by name in nftables?

Using sets in nftables is really cool. I am currently using a lot of statements like these in my nftables.conf rulesets: iifname {clients0, dockernet} oifname wan0 accept \ comment "Allow clients and Docker containers to reach the internet" In the rule above {clients0, dockernet} is an *anonymous* (inline) set of interfaces. Instead of repetition in the rules over and over, I'd like to define a set of interfaces at the top of the file, called a *named set* in nftables. The manpage (Debian Buster) shows how to do that for several types of sets: *ipv4_addr*, *ipv6_addr*, *ether_addr*, *inet_proto*, *inet_service* and *mark*. However, it seems it's not available for interfaces by name or simple primitive type such as strings. I've the approach below, but this does not work with the errors given: 1. Omitting the type:

table inet filter {
      set myset {
        elements = {
          clients0,
          dockernet,           
        }
      }
      [...]
    }

Result: Error: set definition does not specify key. 1. Using the string type:

table inet filter {
      type string;
      set myset {
        elements = {
          clients0,
          dockernet,           
        }
      }
      [...]
    }

Result: Error: unqualified key type string specified in set definition. Is there really no way of naming the anonymous set I've shown on the top?