Alex,
Thanks for the tip. I've added it to our tracker to investigate for the next release in February.
Honestly, we're always trying very hard to improve our validation wherever we can. It's really not something that search engines or most/any browsers actually care about.. but we know that many users (and their clients) demand validation. If we can update that namespace string, which from a *very* quick investigation, it does seem like your solution is viable and recommended from the few places I've seen. I'm not sure when Facebook updated that syntax, but we'll get on it.
With luck, this update should be in the release in a few weeks.
Thanks,
Alex