getScrollingElement.js

/*
 * How to get the scrolling element in charge of scrolling the viewport:
 *
 * - in Quirks mode the scrolling element is the "body"
 * - in Standard mode the scrolling element is the "documentElement"
 *
 * webkit based browsers always use the "body" element disrespectfull of the specifications:
 *    http://dev.w3.org/csswg/cssom-view/#dom-element-scrolltop
 */
function getScrollingElement() {
  var d = document;
  return d.documentElement.scrollHeight > d.body.scrollHeight &&
          d.compatMode.indexOf('CSS1') == 0 ?
          d.documentElement :
          d.body;
}