y>
<div id="log"></div>
<my-custom-element id="instance1"></my-custom-element>
<script>

class MyCustomElement extends HTMLElement { };

test(function () {
    var customElement = document.getElementById('instance1');

    assert_true(customElement instanceof HTMLElement, 'An unresolved custom element must be an instance of HTMLElement');
    assert_false(customElement instanceof MyCustomElement, 'An unresolved custom element must NOT be an instance of that custom element');
    assert_equals(customElement.