Not sure if my HostRegexp is right

Traefik Traefik v2
1

i would like to make a subdomain [ex.mydomain.xyz] to also be reachable by [ex[0-9].mydomain.xyz] where any number from 0-9 after ex works
would (HostRegexp('ex{num:[0-9]}.mydomain.xyz') work? (backtics replaced with ' for formatting)