diff --git a/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php b/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
index 2e18753..120cad6 100644
--- a/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
+++ b/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
@@ -36,21 +36,21 @@ public function __construct(CacheBackendInterface $cache) {
   }
 
   /**
-   * Implements \Drupal\Core\ControllerInterface::create().
+   * {@inheritdoc}
    */
   public static function create(ContainerInterface $container) {
     return new static($container->get('cache.menu'));
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::getFormID().
+   * {@inheritdoc}
    */
   public function getFormID() {
     return 'book_admin_edit';
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::buildForm().
+   * {@inheritdoc}
    *
    * @param \Drupal\Core\Entity\EntityInterface $node
    *   The node of the top-level page in the book.
@@ -70,7 +70,7 @@ public function buildForm(array $form, array &$form_state, EntityInterface $node
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::validateForm().
+   * {@inheritdoc}
    *
    * Checks that the book has not been changed while using the form.
    */
@@ -81,7 +81,7 @@ public function validateForm(array &$form, array &$form_state) {
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::submitForm().
+   * {@inheritdoc}
    *
    * This function takes care to save parent menu items before their children.
    * Saving menu items in the incorrect order can break the menu tree.
@@ -151,7 +151,8 @@ protected function bookAdminTable(EntityInterface $node, &$form) {
     );
 
     $tree = book_menu_subtree_data($node->book);
-    $tree = array_shift($tree); // Do not include the book item itself.
+    // Do not include the book item itself.
+    $tree = array_shift($tree);
     if ($tree['below']) {
       $hash = drupal_hash_base64(serialize($tree['below']));
       // Store the hash value as a hidden form element so that we can detect