src/third_party/web_platform_tests/custom-elements/creating-and-passing-registries/share-registry-create-document.html

<!DOCTYPE html>
<html>
<head>
<title>Document, created with createHTMLDocument or createDocument with HTML namespace, should share registry with the associated document</title>
<meta name="author" title="Sergey G. Grekhov" href="mailto:sgrekhov@unipro.ru">
<meta name="assert" content="When DOMImplementation's createDocument method is invoked with namespace set to HTML Namespace or when the createHTMLDocument method is invoked, use the registry of the associated document to the new instance.">
<link rel="help" href="http://www.w3.org/TR/custom-elements/#creating-and-passing-registries">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../testcommon.js"></script>
<link rel="stylesheet" href="/resources/testharness.css">
</head>
<body>
<div id="log"></div>
<script>
test(function() {
    var doc = newHTMLDocument();
    var name = 'x-frame';

    var GeneratedConstructor = doc.registerElement(name);
    var doc2 = doc.implementation.createHTMLDocument('Document 2');
    assert_throws(
        'NotSupportedError',
        function() { doc2.registerElement(name); },
        'Registering a custom element type name that is already registered in a shared ' +
            'registry should throw an exception');

    var xframe = doc2.createElement(name);
    assert_true(xframe instanceof GeneratedConstructor,
        'Created element should be x-frame instance');
}, 'Document created by createHTMLDocument should share an existing registry');


test(function() {
    var doc = newHTMLDocument();
    var name = 'x-frame-1';

    var GeneratedConstructor = doc.registerElement(name);
    var doc2 = doc.implementation.createDocument(HTML_NAMESPACE, 'html', null);
    assert_throws(
        'NotSupportedError',
        function() { doc2.registerElement(name); },
        'Exception should be thrown for custom element, ' +
            'which is already registered in shared registry');

    var xframe = doc2.createElement(name);
    assert_true(xframe instanceof GeneratedConstructor,
        'Created element should be x-frame instance');
}, 'Document created by createDocument with HTML namespace should share an existing registry');
</script>
</body>
</html>