Edit SOLVED: Initially I got under the impression that Ace will be completely unusable due to editable code cutting off on 2nd line. So I thought 'let's not even load it in IE'. Turns our the bug was fixed, Ace works just fine in 9 (or close enough, not quite as nice as in FF or Chrome though).
ORIGINAL QUESTION: I find myself having to prevent Ace editor from loading in IE and wonder what specific browser features need detection? Trying to avoid browser sniffing.