* mostly complete

src/App/Plates/StringExtensionFactory.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Plates;
+
+use League\CommonMark\CommonMarkConverter;
+use Psr\Container\ContainerInterface;
+
+class StringExtensionFactory
+{
+    public function __invoke(ContainerInterface $container) : StringExtension
+    {
+        $converter = new CommonMarkConverter();
+        return new StringExtension($converter);
+    }
+}