working but incomplete version with new build.

dist/editor/extensions/ext-xdomain-messaging.js

@@ -0,0 +1,48 @@
+/**
+* Should not be needed for same domain control (just call via child frame),
+*  but an API common for cross-domain and same domain use can be found
+*  in embedapi.js with a demo at embedapi.html.
+*/
+export default {
+  name: 'xdomain-messaging',
+  init () {
+    const svgEditor = this;
+    const svgCanvas = svgEditor.canvas;
+    try {
+      window.addEventListener('message', function (e) {
+        // We accept and post strings for the sake of IE9 support
+        if (!e.data || !['string', 'object'].includes(typeof e.data) || e.data.charAt() === '|') {
+          return;
+        }
+        const data = typeof e.data === 'object' ? e.data : JSON.parse(e.data);
+        if (!data || typeof data !== 'object' || data.namespace !== 'svgCanvas') {
+          return;
+        }
+        // The default is not to allow any origins, including even the same domain or
+        //  if run on a `file:///` URL. See `svgedit-config-es.js` for an example of how
+        //  to configure
+        const {allowedOrigins} = svgEditor.curConfig;
+        if (!allowedOrigins.includes('*') && !allowedOrigins.includes(e.origin)) {
+          console.log(`Origin ${e.origin} not whitelisted for posting to ${window.origin}`); // eslint-disable-line no-console
+          return;
+        }
+        const cbid = data.id;
+        const {name, args} = data;
+        const message = {
+          namespace: 'svg-edit',
+          id: cbid
+        };
+        try {
+          // Now that we know the origin is trusted, we perform otherwise
+          //   unsafe arbitrary canvas method execution
+          message.result = svgCanvas[name](...args); // lgtm [js/remote-property-injection]
+        } catch (err) {
+          message.error = err.message;
+        }
+        e.source.postMessage(JSON.stringify(message), '*');
+      });
+    } catch (err) {
+      console.log('Error with xdomain message listener: ' + err); // eslint-disable-line no-console
+    }
+  }
+};