I agree the two sentences should say the same thing. Don't feel
strongly about the wording since the way UTF->punycode works is the
same for all domain names everywhere.
My point is that the citation is essentially specifying a functional
interface and, therefore, needs to be a highly precise reference into the
specific function(s) to be incorporated into DKIM.
It wouldn't hurt, but since there is exactly one (1) standard specified
way to encode IDNs in the DNS, there'd be no ambiguity even if the DKIM
spec had said nothing at all about IDNs.
Encoding IDNs as punycode is like encoding text domains in ASCII.
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