IDNA forms and original-label analysis for an explicit domain check.
unicode and ascii are whole-name U-label and A-label forms, including an
optional final root dot. They are nil after any hostname validity failure,
while labels retains independently safe partial results. mapped? reports
whether the whole Unicode form differs from original input. valid_idna?
includes IDNA rules, DNS lengths, and public hostname restrictions.
uts46_revision identifies the pinned nontransitional processing rules.