Yes, people. The videos you <embed> from YouTube will produce invalid markup

The W3C has written it clearly on it’s FAQ page here.

This is really stupid. It’s like using an ancient dictionary. The embed tag is so popular, the W3C should have added the tag as part of standard xHTML. Because of that dumb tag, all the pages where I’ve embedded videos return invalid markup errors.

As of now, the W3C recommends using this technique to embed videos. Who’s got the time?