<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.dumpChildFramesAsText();
}
</script>
This tests having an input element with autofocus content attribute inside a sandboxed iframe.<br>
The input element should be autofocused since scripts are allowed.
<iframe sandbox="allow-scripts"
    src="data:text/html,<input id=input autofocus onfocus><script>
    if (window.testRunner)
        testRunner.waitUntilDone();
    window.onload = function () {
        requestAnimationFrame(() => {
            document.body.append(document.activeElement == input ? 'PASS' : 'FAIL');
            if (window.testRunner)
                testRunner.notifyDone();
        });
    }</script>"></iframe>