Non-Public IP addresses - W3C Validator

Ladies/Gentlemen-

Blocking non-public IP addresses is rather mysterious particularly as it
applies to 10.0.0.2.  I can't be the only person who runs Microsoft's IIS
over an internal development network and relies heavily on the validator to
check code compliance.

Thank you very much.

NOTE: Whenever possible, give the address of the document you were checking.