code: function(elem, interval) {
        if (+elem.style.opacity < 1) {
          interval = interval || 16;
          elem.style.opacity = 0;
          elem.style.display = 'block';
          var last = +new Date();
          var tick = function() {
            elem.style.opacity = +elem.style.opacity + (new Date() - last) / 100;
            last = +new Date();
  
            if (+elem.style.opacity < 1) {
              setTimeout(tick, interval);
            }
          };
          tick();
        }
        elem.style.display = 'block'; //fallback IE8
      }
docs: /*
  Manipulate DOM