Object-group network can have multiple members, be they hosts, subnets, or nested object-groups. They can even have members from both IPv4 and IPv6 protocols, though I don't recommend that.
Network objects can only have one member, either host or subnet, either IPv4 or IPv6. Optionally network objects can specify a phase II NAT mapping for their subject.
Generally, in twice NAT statements and access-lists entries, you can use either network object-groups or network objects, or a mixture of the two.
-- Jim Leinweber, WI State Lab of Hygiene
