<style>
dfn:focus-within { display: contents }
html { mask-image: url(about:)}
</style>

<script>
if (window.testRunner)
  testRunner.dumpAsText();

function main() {
  input.setCustomValidity("foo");
  input.reportValidity();
}
</script>

</style>
<body onload="main()">
  <dfn>
    <textarea autofocus>
    </textarea>
  </dfn>
  <input id="input">
  <p>This test passes if it doesn't crash.</p>
</body>
