Send message to parent frame with document height when embedded

public/index.php

@@ -255,3 +255,16 @@ if (isset($_GET["backgroundcolor"]) && !empty($_GET["backgroundcolor"]) && preg_
         </div>
     </div>
 </div>
+
+<?php
+// Send message to parent frame with our height so they can adjust the iframe
+if (isset($_GET["embed"])) {
+    ?>
+    <script nonce="<?php echo $SECURE_NONCE; ?>">
+        window.addEventListener("load", function () {
+            window.postMessage(document.documentElement.scrollHeight + "px", "*");
+        });
+    </script>
+    <?php
+}
+?>