ddns-rev-domainname

The ISC dhcp server has the "ddns-rev-domainname" keyword which allows one to override the default reverse dns domain.
This could be handy when working with delegations of address spaces below octet boundaries. for example:

20.0.168.192.in-addr.arpa. CNAME 20.0-64.0.168.192.in-addr.arpa.
20.0-64.0.168.192.in-addr.arpa. PTR mypc.example.com.

From a question raised on Kea-users@lists.isc.org mailing list.