Events from a GTID-incapable master inherit domain ID of the slave

If I have replication, for example, from 5.5 master to 10.0 slave, then even if I set gtid_domain_id on the slave to a non-default value, events from master and slave still end up in the slave's binlog with the same (slave's) domain ID. I'm not sure whether it's designed to be this way, I'd rather expect master's events to have the default domain ID 0, so that I could still have a choice – either to keep the slave in the same domain or put it into a different one.

But maybe there is a bigger plan behind it, then it should be somehow documented (if it isn't yet).