'menu').querySelectorAll('li span');
    var nr_lists = lists.length;

    // register click to eack span-li
    if(nr_lists > 0) {
      for(var i=0; i<nr_lists; i++) {
        lists[i].addEventListener('click', function(e){
          if(e.target.id == current_span) return false;
          else {
            // removes and sets id for current element
            if(document.getElementById(current_li)) document.getElementById(current_li).removeAttribute('id');
            if(document.getElementById(current_