<div></div>
<div id=d1><p id=p1> And</p></div>
<div id=d2><p id=p2> And</p></div>
<div id=d3><p id=p3> And</p></div>

<script src="../testing.js"></script>
<script id=mutationObserver>
  // doesn't crash, yay.
  new MutationObserver(() => {}).observe(document, { childList: true });

  var nb = 0;
  var mrs;
  new MutationObserver((mu) => {
     mrs = mu;
     nb++;
  }).observe(document.firstElementChild, { attributes: true, attributeOldValue: true });
  document.firstElementChild.setAttribute("foo", "bar")