W3C's HTML validator doesn't just validate HTML as I found out
Just as a test, I decided to see if the validator had a static list to choose from when validating against dtd's, or if it actually went out to the internet and checked against the dtd's.
I put the URI of my RSS feed, and found that it actually came back with some errors. I checked the dtd, and lo and behold, the errors where correct.
I ended up making some changes to the layout of the rss feed to make it validate against the dtd, and I gotta say that I'm glad I did so. From now on, I will always validate any designs I do. It will ensure that the HTML will be valid for versions to come