(function initializeMenuHoverBehaviour() {
  var menu = document.getElementById('menu');
  var i,li,lis = menu.getElementsByTagName('li');
  
  var msover = function() {
    if (this.className == null) {
      this.className = 'hover';
    } else {
      this.className += ' hover';
    }
  };
  var msout = function() {
    if (this.className != null) {
      this.className = this.className.replace(/ ?hover/gi, '');
    }
  };
  
  for (i=0; (li=lis[i]); i++) {
    li.onmouseover = msover;
    li.onmouseout = msout;
  }
})();