<html>
<body>
<dialog id="searching">
<p>Searching ...</p>
<button>Cancel</button>
</dialog>
<script>
(function () {
var dialog = document.getElementById('searching');
dialog.show();
})();
</script>
</body>
</html>
The dialog element was originally created to represent spoken conversation.
Experimental
It has been repurposed as a tool for displaying popup windows.
A live example:
N of