I neither expect this to happen nor think this is a matter for browsers (rather than system name resolvers), but in any case[1] top-level domain names [must]

I neither expect this to happen nor think this is a matter for browsers (rather than system name resolvers), but in any case[1] top-level domain names [must] not be all-numeric so these are simply bad DNS. Browsers, even though they deliberately disregard RFCs on matters of URI syntax, concur on this particular point[2] If asciiDomain [split on periods] ends in a [C-style decimal, octal, or hexadecimal] number, then return the result of IPv4 parsing asciiDomain. [1] https://datatracker.ietf.org/doc/html/rfc3696#section-2 https://datatracker.ietf.org/doc/html/rfc3696#section-2 [2] https://url.spec.whatwg.org/#host-parsing https://url.spec.whatwg.org/#host-parsing