IPv6 PTR format -- decimal or hex?

[Dan Foster]

For IPv6 DNS PTR records:

Let's say, it's 3ffe::1, expanded as: 3ffe:0000:0000:0000:0000:0000:0000:0001

With the nibble format for the inverse mapping, the zone name would be:

0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.e.f.f.3.ip6.arpa

...and the PTR record within that zone file would be:

1	IN	PTR	ipv6.example.com.

My question is, is the range for the name of the PTR records: 0-9,a-f
and a single digit as opposed to 0-255?

It's just not clear to me if it's expressed in hexadecimal or decimal.

-Dan