Multiple CNAME RRSets, which is having multiple CNAMEs for the same name, are not as in-demand as apex aliases, but there are use cases for them. To make matters more confusing, these actually used to work back in the BIND4 days, then optionally worked later under BIND8 (with the allow- multiple-cnames option enabled) and were discontinued as of BIND 9.1.
Now most people will simply point at the "CNAME cannot coexist with other data" rule and leave it at that.
The POOL record would then implement multiple CNAMEs, such as:
us.example.com.IN CNAME us1.provider.example.
us.example.com. IN CNAME us2.contributed.dom.
us.example.com. IN CNAME www4.example.net.
The nameserver would be responsible for cycling through the available results, just as in the case of a round-robin of A or AAAA records. However, instead of returning all available...