YAHOO.util.Event.onDOMReady(function() { 
    // var fader = YAHOO.util.Dom.getElementsByClassName("fader"); 
    // YAHOO.util.Dom.setStyle(fader, "opacity", "0.5");
    var aniObj = new YAHOO.util.Anim(
      'doc',
      { opacity: {from: 0, to: 1 } },
      'duration in second',
      'easing'
    );
}
);