TLD registry intelligence and public-suffix analysis. Mode 1 (tld=io): IANA root-zone metadata — type (generic / country-code / sponsored), managing organization, unicode form for IDN TLDs. Mode 2 (domain=shop.example.co.uk): full Public Suffix List algorithm — the effective public suffix (co.uk), the registrable domain (example.co.uk), the subdomain part, the matched PSL rule, and whether the suffix is ICANN (registry) or private (corporate, e.g. github.io / s3.amazonaws.com) — plus the root-zone metadata for its TLD. Correctly handles wildcard and exception rules and IDN/punycode input. Use for cookie scoping, per-registrant rate limiting, URL dedup, and abuse/phishing analysis. Data: IANA root zone + Mozilla PSL, refreshed weekly.