Hmm.

• 411.com - should pass
• penny-arcade.com - should pass
• bad-.com - should fail
• -bad.com - should fail
• 6-7.m-w.com - should pass
• 9999999999999999999999999.z.no - should pass
• 200.100.50.1.uk - should fail
• 1.com should fail
• 1.hostile.com should pass
• 256.com should pass

The original rule was: [a-zA-Z]([a-zA-Z0-9-]*[a-zA-Z0-9])?

for each label between dots since that way a program that discriminated between network addresses and host names could simply sniff the first char. That has since be "warped" in the root tables to allow the much more complex well if it doesn't start with a number between 0-255 without any a-zA-Z- or it has only three labels we'll just assume...

basically, FQDN is just a theory to verify without asking a DNS server. But you SURELY need '-' hyphens in there. and should 1.co.uk match or how about 1.com or 256.com?

Sorry 'bout this but domain name vs. hostname madness is a particular bone in my throat. Just when I think I've swallowed it, it's choking me again.

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