<!DOCTYPE html>
<title>HTMLUnknownElement</title>
<link rel="author" title="Ms2ger" href="mailto:ms2ger@gmail.com">
<link rel="help" href="https://html.spec.whatwg.org/multipage/#htmlunknownelement">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="log"></div>
<script>
test(function() {
  var elt = document.createElement("xxx");
  assert_true(window.HTMLUnknownElement && elt instanceof HTMLUnknownElement,
              "not an instance of HTMLUnknownElement");
  assert_true(window.HTMLSpanElement && !(elt instanceof HTMLSpanElement),
              "an instance of HTMLSpanElement");
});
</script>