the xx stuff in overrides

I noticed that the xx stuff in overrides doesn't seem to be documented anywhere in the cust faqs. for example, when it does < xx-body > etc cause you've put bad stuff in. it might be nice to add that into My overrides won't work. What's wrong- cause its something that can cause your overrides to not work and people go "whats this xx stuff i didn't put it there"

...i've edited this twice already >.< should not make suggestions when i'm sleepy