// Cross-browser addEventListener()/attachEvent() replacement.
function addEvent(elt, name, handler, atEnd) {
  name = name.replace(/^(on)?/, 'on'); 
  var prev = elt[name];
  var tmp = '__tmp';
  elt[name] = function(e) {
    if (!e) e = window.event;
    var result;
    if (!atEnd) {
      elt[tmp] = handler; result = elt[tmp](e); elt[tmp] = null; // delete() does not work in IE 5.0 (???!!!)
      if (result === false) return result;
    }
    if (prev) {
      elt[tmp] = prev; result = elt[tmp](e); elt[tmp] = null;
    }
    if (atEnd && result !== false) {
      elt[tmp] = handler; result = elt[tmp](e); elt[tmp] = null;
    }
    return result;
  }
  return handler;
}