function initSubMenus(){
  $$("#mainNav li").each(function(node) {
      // if there’s a ul
      var ul = $A(node.getElementsByTagName("ul")).first();
      if (ul != null) {
        var keepCurrentClass = false;
        // toggle it’s visibility on these events
        node.onmouseover = function() {
          if(node.hasClassName('current')) keepCurrentClass = true;
          node.addClassName('current');
          Element.show(ul);
        }
        
        node.onmouseout = function() {
          if(!keepCurrentClass) node.removeClassName('current');
          Element.hide(ul);
        }
      }
  });
}