How to determine if "html" or "body" scrolls the window.

Question

The code below is used to find the element that can be scrolled (body or html) via javascript.

    var scrollElement = (function (tags) {
        var el, $el, init;
        // iterate through the tags...
        while (el = tags.pop()) {
            $el = $(el);
            // if the scrollTop value is already > 0 then this element will work
            if ( $el.scrollTop() > 0){
                return $el;
            }
            // if scrollTop is 0 try to scroll.
            else if($el.scrollTop( 1 ).scrollTop() > 0) {
                // if that worked reset the scroll top and return the element
                return $el.scrollTop(0);
            }
        }
        return $();
    } (["html", "body"]));

    // do stuff with scrollElement...like:
    // scrollElement.animate({"scrollTop":target.offset().top},1000);

This code works perfectly when the height of the document is greater than the height of the window. However, when the height of the document is the same or less than the window the method above will not work because scrollTop() will always be equal to 0. This becomes a problem if the DOM is updated and the height of the document grows beyond the height of the window after the code runs.

Also, I generally don't wait until document.ready to set up my javascript handlers (this generally works). I could append a tall div to the body temporarily to force the method above to work BUT that would required the document to be ready in IE (you can't add a node to the body element before the tag is closed). For more on the document.ready "anti-pattern" topic read this.

So, I'd love to find a solution that finds the scrollable element even when the document is short. Any ideas?