<!DOCTYPE html>
<html>
<head>
<script>
if (window.testRunner)
    testRunner.dumpAsText();
</script>
</head>
<body onload="document.body.removeChild(document.getElementById('x'));">
<p>PASS did not cause an assertion failure.</p>
<div id="x">
    <form id="a"></form>
    <form id="a">
        <select form="a"></select>
    </form>
</div>
<script>
document.getElementById("a").setAttribute("id", "y");
</script>
</body>
</html>