I haven't been keeping up, but it certainly used to be the case that domain names can contain digits but have to start with a letter - see https://tools.ietf.or

I haven't been keeping up, but it certainly used to be the case that domain names can contain digits but have to start with a letter - see https://tools.ietf.org/html/rfc1035 https://tools.ietf.org/html/rfc1035 where it mentions "rules for arpanet host names".