Ah, ok, it's only a proposal now: http://tools.ietf.org/html/rfc5789

Still, I'd write the comment a little differently since it's definitely going to be standardized and then this line will no longer be true.

Besides, I wouldn't write just `XHR` here; this is a sentence on its own and it's not that `XHR` itself doesn't support `PATCH`, it's IE8 implementation of it. So `s/XHR/IE<9 XHR`.