<!DOCTYPE html>
<html>

<script>
var runcount = {'runTest':0}

function runTest() {
    if (window.testRunner)
    {
        testRunner.dumpAsText();
        testRunner.waitUntilDone();
    }
    runcount["runTest"]++; if(runcount["runTest"] > 2) { return; }
    element = document.createElement("command"); //HTMLUnknownElement
    x.addEventListener("DOMSubtreeModified", runTest);
    z.childNodes;
    x.before(progress);
    progress.appendChild(element)
    window.requestAnimationFrame(runTest1);
    iframe = document.createElement("iframe");
    y.appendChild(iframe);
}

function runTest1() {
    win = window; 
    win0 = win[0];
    win0.focus();
    y.slot = "y";
    if (window.testRunner)
        testRunner.notifyDone();
}
</script>

<body>
<p>The test passes if there is no crash.</p>
<details id="x" open="true">
<summary id="y"></summary>
<details id="z" open="true" ontoggle="runTest()">a</details>
</details>
<audio cite="">
<source slot="slot2">
<progress id="progress" ></progress>

</body>
</html>