Tools/TestWebKitAPI/Tests/WebKitCocoa/system-preview-trigger.html

<!DOCTYPE html>
<body>
<a rel="ar"></a>
<script>
function runTest(element, message, loadedMessage) {
    const elementID = internals.elementIdentifier(element);
    const pageID = internals.pageIdentifier(document);
    const documentID = internals.documentIdentifier(document);

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

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

window.addEventListener("load", function () {
    const attachedElement = document.querySelector("a");
    runTest(attachedElement, "triggered", "loaded_triggered");

    const detachedElement = document.createElement("a");
    runTest(detachedElement, "triggered_detached", "loaded_triggered_detached");
});
</script>