function addClass(id,new_class){
       var i,n=0;
       new_class=new_class.split(",");
       for(i=0;i<new_class.length;i++){
               if((" "+document.getElementById(id).className+" ").indexOf(" "+new_class[i]+" ")==-1){
                       document.getElementById(id).className+=" "+new_class[i];
                       n++;
               }
       }
       return n;
}