diff --git a/src/EventSubscriber/MigrationSubscriber.php b/src/EventSubscriber/MigrationSubscriber.php
index b65d83c..1c4b84b 100644
--- a/src/EventSubscriber/MigrationSubscriber.php
+++ b/src/EventSubscriber/MigrationSubscriber.php
@@ -9,10 +9,23 @@ use Drupal\migrate\Event\MigrateEvents;
 use Drupal\migrate\Event\MigratePostRowSaveEvent;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 
+/**
+ * Create a simplenews field on relevant content types.
+ *
+ * Since simplenews configuration on a node is stored as a field, it has to
+ * be added explicitly during a migration. This listener checks if the node
+ * type is a simplenews content type and adds the field.
+ */
 class MigrationSubscriber implements EventSubscriberInterface {
 
   protected $entityFieldManager;
 
+  /**
+   * Constructs a new migration subscriber.
+   *
+   * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entityFieldManager
+   *   The entity field manager service.
+   */
   public function __construct(EntityFieldManagerInterface $entityFieldManager) {
     $this->entityFieldManager = $entityFieldManager;
   }