<!DOCTYPE html>
<body>
<a rel="ar"></a>
<script>
window.addEventListener("load", function () {
    const a = document.querySelector("a");

    const elementID = internals.elementIdentifier(a);
    const pageID = internals.pageIdentifier(document);
    const documentID = internals.documentIdentifier(document);

    a.addEventListener("message", function (event) {
        window.webkit.messageHandlers.testSystemPreview.postMessage({ message: "triggered", action: event.data });
    });

    const msg = { message: "loaded", elementID, pageID, documentID };
    window.webkit.messageHandlers.testSystemPreview.postMessage(msg);
});


</script>