No code offered, but the relevant rfc is Domain names - implementation and specification (rfc1035).

Now, this disallows 411.com, as each word in a domain name must start with a letter (not a digit). So what is valid in practice is clearly at variance with the spec.

Also this is a specification in flux at the moment with the introduction of internationalized domain names. (already available on the .jp tld).

In reply to Re: Syntactically check domain name/IP by zeimusu
in thread Syntactically check domain name/IP by johnnywang

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