The DIGIT transformer is used for selecting components of a domain name or
IP address when constructing auxiliary DNS lookups. However the maximum
practical value is 9 -- any more than that and you will have
interoperability problems because an implementation MAY be unable to deal
with 2 DIGITs in a directive.
This is a problem for IPv6 since a nibble format address has 32
components, and common delegation boundaries occur after 12 or 16
components (/48 and /64 networks in CIDR notation) both of which are
greater than 9.
I note that the maximum number of labels in a domain name is 128. Perhaps
the limit in the spec should be removed and this fact should be noted
instead.
--
Tony Finch <dot(_at_)dotat(_dot_)at> http://dotat.at/