Cross-browser, mouse leaving the window event

gistfile1.txt

      function addEvent(obj, evt, fn) {
          if (obj.addEventListener) {
              obj.addEventListener(evt, fn, false);
          }
          else if (obj.attachEvent) {
              obj.attachEvent("on" + evt, fn);
          }
      }

      addEvent(document, "mouseout", function(e) {
          e = e ? e : window.event;
          var from = e.relatedTarget || e.toElement;
          if (!from || from.nodeName == "HTML") {
              alert('mouse gone');
          }
      });