TFA wasn't "shocked" (I suspect he was being slightly hyperbolic) at the sole invalidity-through-broken-namespacing, broken templating also had a hand in it: simply exporting a post and proof-reading the output is sufficient to catch the latter.
Then again, you just have to put the output through any XML parser (it's not hard to find) to realize the document is completely broken, but...
Then again, you just have to put the output through any XML parser (it's not hard to find) to realize the document is completely broken, but...