<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function boom()
{
window.addEventListener("DOMSubtreeModified", function(){});
var span = document.createElement("span");
document.body.appendChild(span);
}
</script>
<style type="text/css">
span:before { content: '0'; }
span:after { content: '1'; }
</style>
</head>
<body onload="boom();"></body>
</html>