diff --git a/plugin_type_example/plugin_type_example.module b/plugin_type_example/plugin_type_example.module
index c466283..eea5ec8 100644
--- a/plugin_type_example/plugin_type_example.module
+++ b/plugin_type_example/plugin_type_example.module
@@ -28,8 +28,9 @@
  * Start at the class \Drupal\plugin_type_example\SandwichPluginManager, which
  * defines our plugin manager. Our plugin manager is exposed to Drupal as a
  * service in the plugin_type_example.services.yml file, and is used to glue
- * our Drupal\plugin_type_example\SandwichInterface, and INSERT ANNOTATION CLASSNAME HERE
- * annotation definition together into a new plugin type.
+ * our Drupal\plugin_type_example\SandwichInterface, and
+ * \Drupal\plugin_type_example\Annotation\Sandwich annotation definition
+ * together into a new plugin type.
  *
  * We've also defined two implementations of our plugin type,
  * \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich and
diff --git a/plugin_type_example/src/Controller/PluginTypeExampleController.php b/plugin_type_example/src/Controller/PluginTypeExampleController.php
index 4463596..a22834d 100644
--- a/plugin_type_example/src/Controller/PluginTypeExampleController.php
+++ b/plugin_type_example/src/Controller/PluginTypeExampleController.php
@@ -78,8 +78,9 @@ class PluginTypeExampleController extends ControllerBase {
 
     // If we want just a single plugin definition, we can use getDefinition().
     // This requires us to know the ID of the plugin we want. This is set in the
-    // annotation on the plugin class: see \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich.
-    //$ham_sandwich_plugin_definition = $this->sandwichManager->getDefinition('meatball_sandwich');
+    // annotation on the plugin class: see
+    // \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich.
+    $ham_sandwich_plugin_definition = $this->sandwichManager->getDefinition('meatball_sandwich');
 
     // To get an instance of a plugin, we call createInstance() on the plugin
     // manager, passing the ID of the plugin we want to load. Let's output a
@@ -110,7 +111,10 @@ class PluginTypeExampleController extends ControllerBase {
    * Override the parent method so that we can inject our sandwich plugin
    * manager service into the controller.
    *
-   * For more about how dependency injection works read https://www.drupal.org/node/2133171
+   * For more about how dependency injection works read
+   * https://www.drupal.org/node/2133171
+   *
+   * @see container
    */
   public static function create(ContainerInterface $container) {
     // Inject the plugin.manager.sandwich service that represents our plugin
diff --git a/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php b/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php
index 63f8450..10aa35f 100644
--- a/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php
+++ b/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php
@@ -10,7 +10,8 @@ use Drupal\plugin_type_example\SandwichBase;
  * Because the plugin manager class for our plugins uses annotated class
  * discovery, our meatball sandwich only needs to exist within the
  * Plugin\Sandwich namespace, and provide a Sandwich annotation to be declared
- *  as a plugin. This is defined in
+ * as a plugin. This is defined in
+ * \Drupal\plugin_type_example\SandwichPluginManager::__construct().
  *
  * The following is the plugin annotation. This is parsed by Doctrine to make
  * the plugin definition. Any values defined here will be available in the
diff --git a/plugin_type_example/src/SandwichBase.php b/plugin_type_example/src/SandwichBase.php
index edaf167..4f28909 100644
--- a/plugin_type_example/src/SandwichBase.php
+++ b/plugin_type_example/src/SandwichBase.php
@@ -46,4 +46,10 @@ abstract class SandwichBase extends PluginBase implements SandwichInterface {
   public function calories() {
     return (float) $this->pluginDefinition['calories'];
   }
+
+  /**
+   * {@inheritdoc}
+   */
+  abstract public function order(array $extras);
+
 }
diff --git a/plugin_type_example/src/SandwichInterface.php b/plugin_type_example/src/SandwichInterface.php
index 210f3d9..3413268 100644
--- a/plugin_type_example/src/SandwichInterface.php
+++ b/plugin_type_example/src/SandwichInterface.php
@@ -43,10 +43,13 @@ interface SandwichInterface {
   public function calories();
 
   /**
+   * Place an order for a sandwich.
+   *
    * @param array $extras
    *   An array of extra ingredients to include with this sandwich.
    *
-   * @return mixed
+   * @return string
+   *   Description of the sandwich that was just ordered.
    */
   public function order(array $extras);
 }
diff --git a/plugin_type_example/src/SandwichPluginManager.php b/plugin_type_example/src/SandwichPluginManager.php
index e77fce5..9e68b9a 100644
--- a/plugin_type_example/src/SandwichPluginManager.php
+++ b/plugin_type_example/src/SandwichPluginManager.php
@@ -5,6 +5,8 @@ namespace Drupal\plugin_type_example;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Plugin\DefaultPluginManager;
+use Drupal\plugin_type_example\SandwichInterface;
+use Drupal\plugin_type_example\Annotation\Sandwich;
 
 /**
  * A plugin manager for sandwich plugins.
@@ -45,10 +47,10 @@ class SandwichPluginManager extends DefaultPluginManager {
     // The name of the interface that plugins should adhere to. Drupal will
     // enforce this as a requirement. If a plugin does not implement this
     // interface, than Drupal will throw an error.
-    $plugin_interface = 'Drupal\plugin_type_example\SandwichInterface';
+    $plugin_interface = SandwichInterface::class;
 
     // The name of the annotation class that contains the plugin definition.
-    $plugin_definition_annotation_name = 'Drupal\plugin_type_example\Annotation\Sandwich';
+    $plugin_definition_annotation_name = Sandwich::class;
 
     parent::__construct($subdir, $namespaces, $module_handler, $plugin_interface, $plugin_definition_annotation_name);