AS I understand it, originally the DNS system interpreted w.x in domain
y.z first as w.x.y.z. then w.x.z. then w.x.. If you wanted to be
absolutely sure you got w.y you had to say w.y..
In interesting aside - many countries (e.g. UK) seem to be using a
domain naming system that ends in .cc (.uk) but kind of echoes what we
have locally in the US (.com, .org, .edu etc), but (maybe) don't go the
next step and allow people to just say something like ibm.com and mean
ibm.com.uk.. I wonder why not - it would make things a lot more relevant
to the local people, and if they really wanted the international .com
they could add the trailing dot. Or does it already work that way?
Simon Josefsson wrote:
one added some text to clarify that it was actually intended to allow
for zero length dnsname's (to denote the DNS root).
This is technically correct, according to RFC 1034, but will be confusing.
"dns:" intuitively looks incomplete. It's more conventional to name
the root domain in absolute form, as ".". An interesting comparison:
the "dig" DNS lookup tool from the BIND folks doesn't accept "" as a
domain name; it insists on the root domain being specified as ".".
So I argue that requiring the root domain to be represented as "." in the
context of the URI, forbidding a zero-length <dnsname>, will make for a
clearer protocol, more likely to be implemented correctly. This isn't
an absolute matter, though; both versions of the protocol are workable.