working but incomplete version with new build.

dist/editor/extensions/ext-php_savefile.js

@@ -0,0 +1,30 @@
+// TODO: Might add support for "exportImage" custom
+//   handler as in "ext-server_opensave.js" (and in savefile.php)
+
+export default {
+  name: 'php_savefile',
+  init ({$}) {
+    const svgEditor = this;
+    const {
+      curConfig: {extPath},
+      canvas: svgCanvas
+    } = svgEditor;
+    /**
+     * Get file name out of SVGEdit document title.
+     * @returns {string}
+     */
+    function getFileNameFromTitle () {
+      const title = svgCanvas.getDocumentTitle();
+      return title.trim();
+    }
+    const saveSvgAction = extPath + 'savefile.php';
+    svgEditor.setCustomHandlers({
+      save (win, data) {
+        const svg = '<?xml version="1.0" encoding="UTF-8"?>\n' + data,
+          filename = getFileNameFromTitle();
+
+        $.post(saveSvgAction, {output_svg: svg, filename});
+      }
+    });
+  }
+};