I have this friend. He often blogs about RSS and a lot of people consider him really knowledgeable on the subject of RSS. In fact, he's a major participant in the Atom mailing list. Unfortunately, his feed hasn't validated in a few months now. Neither have I been able to retrieve his feed w/ the various RSS readers that I use. I've told him on numerous occasions that his feed doesn't validate and still months later it still doesn't validate. I think there should be a requirement to validate your feed before you blog about RSS or post to an RSS or Atom mailing list. Not that my feed validates 100% of the time. But at least my feeds don't validate 0% of the time. What do you think?