I think I just found my problem: running the query on a detached node straight from `document.createElement`, which throws syntax errors on IE. It's worth noting because that's _precisely_ what `div` is in the `assert` callbacks, so for this to work you'll want to do something like `docElem.appendChild( div ).innerHTML = …` à la [L526](https://github.com/cmcnulty/sizzle/blob/sizzle-174/src/sizzle.js#L526).