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chromium/third_party/blink/web_tests/external/wpt/focus/support/activeelement-after-immediately-focusing-different-site-iframe-inner.html 

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Inner document</title>
</head>
<body>
<h1>Inner</h1>
<script>
document.body.onfocus = function() {
    parent.postMessage("innerbodyfocus,", "*");
}
document.body.onblur = function() {
    parent.postMessage("innerbodyblur,", "*");
}
</script>
</body>
</html>