I think the point is more that, instead of using X- headers you should just declare your header de-facto standard (because you're using it!) and name it without

I think the point is more that, instead of using X- headers you should just declare your header de-facto standard (because you're using it!) and name it without the "X-". The issue with prefixing headers with "X-" is that, in theory, when people start using it you've got to remove the "X-" at some point -- but that would cause all sorts of compatibility headaches.