diff --git a/editor/extensions/ext-imagelib.js b/editor/extensions/ext-imagelib.js
index f1f97d58..bfdae794 100644
--- a/editor/extensions/ext-imagelib.js
+++ b/editor/extensions/ext-imagelib.js
@@ -75,8 +75,38 @@ export default {
     let transferStopped = false;
     let preview, submit;
 
-    // Receive `postMessage` data
-    window.addEventListener('message', async function ({origin, data: response}) { // eslint-disable-line no-shadow
+    /**
+    * @typedef {PlainObject} ImageLibMessage
+    * @property {"imagelib"} namespace Required to distinguish from any other messages of app.
+    * @property {string} href Set to same value as previous `ImageLibMetaMessage` `id`.
+    * @property {string} data The response (as an SVG string or URL)
+    */
+
+    /**
+     * @typedef {PlainObject} ImageLibMetaMessage
+     * @property {"imagelib"} namespace Required to distinguish from any other messages of app.
+     * @property {string} name If the subsequent response is an SVG string or if `preview_url`
+     *   is present, will be used as the title for the preview image. When an
+     *   SVG string is present, will default to the first `<title>`'s contents or
+     *   "(SVG #<Length of response>)" if none is present. Otherwise, if `preview_url`
+     *   is present, will default to the empty string.
+     * @property {string} id Identifier (the expected `href` for a subsequent response message);
+     * used for ensuring the subsequent response can be tied to this `ImageLibMetaMessage` object.
+     * @property {string} [preview_url] Used to set an image source along with the
+     * name/title. If the subsequent response is an SVG string and there is no `preview_url`,
+     * the default will just be to show the name/title. If the response is not an SVG
+     * string, the default will be to show that response (i.e., the URL).
+     * @property {string} entry Set automatically with div holding retrieving message (until ready to delete)
+     * @todo Should use a separate Map instead of `entry`
+    */
+
+    /**
+     * @param {PlainObject} cfg
+     * @param {string} cfg.origin
+     * @param {ImageLibMetaMessage|ImageLibMessage|string} cfg.data String is deprecated when parsed to JSON `ImageLibMessage`
+     * @returns {void}
+     */
+    async function onMessage ({origin, data: response}) { // eslint-disable-line no-shadow
       if (!response || !['string', 'object'].includes(typeof response)) {
         // Do nothing
         return;
@@ -283,7 +313,10 @@ export default {
         break;
       }
       }
-    }, true);
+    }
+
+    // Receive `postMessage` data
+    window.addEventListener('message', onMessage, true);
 
     /**
     * @param {boolean} show