<!DOCTYPE HTML>
<html>
<head>
  <script>
    function tweak() {
      var oldShadowRoot = document.getElementById('outer').createShadowRoot();
      oldShadowRoot.innerHTML = 'World';

      var youngShadowRoot = document.getElementById('outer').createShadowRoot();
      youngShadowRoot.innerHTML = 'Hello<content></content><shadow></shadow>';
    }
  </script>
</head>
<body onload="tweak()">
<div id="outer"></div>
</body>
</html>