<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1800543">
<script>
document.addEventListener('DOMContentLoaded', () => {
  b.setCustomValidity("x")
  a.reportValidity()
  c.appendChild(a)
  document.adoptNode(d)
  document.documentElement.style.display = 'none'
})
</script>
<form id="a">
<textarea id="b">a</textarea>
</form>
<dl id="d">
<canvas id="c"></canvas>
</dl>
<input form="a">
