<script>
if (window.testRunner) { testRunner.dumpAsText(); }    
function onBodyLoad() {
    var observer = new MutationObserver(()=>{ container.replaceWith(undefined) });
    observer.observe(selectElement, { attributes: true });
    selectElement.setAttribute("attribute", "observe this attribute change");
    textAreaElement.setSelectionRange(1, 0);
    window.getSelection().modify("extend", "backward", "lineboundary");
    sourceElement.appendChild(document.createElement("frame"));
}
</script>
<body onload=onBodyLoad()>
    <textarea id="textAreaElement" draggable="true"></textarea>
    <div id="container">
        <source id="sourceElement"></source>
        <select id="selectElement"></select>
    </div>
    Test passes if it does not assert.
</body>