ScrollTop in IE

IE6 and DTD 4.01 requires you to use document.documentElement in stead of document.body, so u will need somthing like the below:

if (document.documentElement && !document.documentElement.scrollTop)
// IE6 +4.01 but no scrolling going on
else if (document.documentElement && document.documentElement.scrollTop)
// IE6 +4.01 and user has scrolled
else if (document.body && document.body.scrollTop)
// IE5 or DTD 3.2

Taken from this post

It was used in a very important fix in our code.