I think we should abstract out this jQuery quirk inside dom-jquery, here and in slideUp as well.

Aside from this case, it would actually be super helpful to have a little DOM helper to check if an element is in the DOM.

I can't think of a good name, but basically, `dom.isInDOM = function(el) { !!jQuery(el).closest('html').length }`. [This jsperf test](http://jsperf.com/jquery-element-in-dom/2) shows it's a performant way of checking whether a node is in the doc or not, found via [this SO thread](http://stackoverflow.com/questions/3086068/how-do-i-check-whether-a-jquery-element-is-in-the-dom).