localhost vs. localhost6

I'm starting to mess around with IPv6. I've noticed something that may
not be a big deal yet, but still ...

I use F9 for named. In the zone files that install with named,
localhost is 127.0.0.1 and ::1. There is no mention of localhost6 in
named zone files. In /etc/hosts, localhost is 127.0.0.1, and localhost6
is ::1.

The same is true for /etc/hosts in RHEL5. I haven't checked named zones
there.

What's the preference? Is there an RFC for this point? As I dig around
on the web, mostly I only thing I find is "here's my config," which
isn't really authoritative.

Thanks in advance for any info.