diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index e2f571e..e118467 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -5,6 +5,7 @@
  * Allows users to create and organize related content in an outline.
  */
 
+use Drupal\book\BookManagerInterface;
 use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\node\NodeInterface;
@@ -355,7 +356,7 @@ function book_prev($book_link) {
   } while ($key && $key != $book_link['nid']);
 
   if ($key == $book_link['nid']) {
-    /** @var \Drupal\book\BookManager $book_manager */
+    /** @var BookManagerInterface $book_manager */
     $book_manager = \Drupal::service('book.manager');
     // The previous page in the book may be a child of the previous visible link.
     if ($prev['depth'] == $book_link['depth']) {
@@ -517,7 +518,7 @@ function book_node_update(EntityInterface $node) {
  */
 function book_node_predelete(EntityInterface $node) {
   if (!empty($node->book['bid'])) {
-    /** @var \Drupal\book\BookManager $book_manager */
+    /** @var BookManagerInterface $book_manager */
     $book_manager = \Drupal::service('book.manager');
     $book_manager->deleteFromBook($node->book['nid']);
   }
@@ -645,7 +646,7 @@ function template_preprocess_book_navigation(&$variables) {
       $variables['prev_title'] = String::checkPlain($prev['title']);
     }
 
-    /** @var \Drupal\book\BookManager $book_manager */
+    /** @var BookManagerInterface $book_manager */
     $book_manager = \Drupal::service('book.manager');
     if ($book_link['pid'] && $parent = $book_manager->loadBookLink($book_link['pid'])) {
       $parent_href = \Drupal::url('node.view', array('node' => $book_link['pid']));
diff --git a/core/modules/book/lib/Drupal/book/Access/BookNodeIsRemovableAccessCheck.php b/core/modules/book/lib/Drupal/book/Access/BookNodeIsRemovableAccessCheck.php
index 7b12219..9477a76 100644
--- a/core/modules/book/lib/Drupal/book/Access/BookNodeIsRemovableAccessCheck.php
+++ b/core/modules/book/lib/Drupal/book/Access/BookNodeIsRemovableAccessCheck.php
@@ -8,6 +8,7 @@
 namespace Drupal\book\Access;
 
 use Drupal\book\BookManager;
+use Drupal\book\BookManagerInterface;
 use Drupal\Core\Routing\Access\AccessInterface;
 use Drupal\Core\Session\AccountInterface;
 use Symfony\Component\Routing\Route;
@@ -21,17 +22,17 @@ class BookNodeIsRemovableAccessCheck implements AccessInterface {
   /**
    * Book Manager Service.
    *
-   * @var \Drupal\book\BookManager
+   * @var BookManagerInterface
    */
   protected $bookManager;
 
   /**
    * Constructs a BookNodeIsRemovableAccessCheck object.
    *
-   * @param \Drupal\book\BookManager $book_manager
+   * @param BookManagerInterface $book_manager
    *   Book Manager Service.
    */
-  public function __construct(BookManager $book_manager) {
+  public function __construct(BookManagerInterface $book_manager) {
     $this->bookManager = $book_manager;
   }
 
diff --git a/core/modules/book/lib/Drupal/book/BookManager.php b/core/modules/book/lib/Drupal/book/BookManager.php
index f184121..bc246f5 100644
--- a/core/modules/book/lib/Drupal/book/BookManager.php
+++ b/core/modules/book/lib/Drupal/book/BookManager.php
@@ -18,10 +18,7 @@
 use Drupal\Core\Config\ConfigFactory;
 use Drupal\node\NodeInterface;
 
-/**
- * Book Manager Service.
- */
-class BookManager {
+class BookManager implements BookManagerInterface {
 
   /**
    * Defines the maximum supported depth of the book tree.
@@ -74,13 +71,7 @@ public function __construct(Connection $connection, EntityManagerInterface $enti
   }
 
   /**
-   * Returns an array of all books.
-   *
-   * This list may be used for generating a list of all the books, or for building
-   * the options for a form select.
-   *
-   * @return
-   *   An array of all books.
+   * {@inheritdoc}
    */
   public function getAllBooks() {
     if (!isset($this->books)) {
@@ -121,13 +112,7 @@ protected function loadBooks() {
   }
 
   /**
-   * Returns an array with default values for a book page's menu link.
-   *
-   * @param string|int $nid
-   *   The ID of the node whose menu link is being created.
-   *
-   * @return array
-   *   The default values for the menu link.
+   * {@inheritdoc}
    */
   public function getLinkDefaults($nid) {
     return array(
@@ -142,13 +127,7 @@ public function getLinkDefaults($nid) {
   }
 
   /**
-   * Finds the depth limit for items in the parent select.
-   *
-   * @param array $book_link
-   *   A fully loaded menu link that is part of the book hierarchy.
-   *
-   * @return int
-   *   The depth limit for items in the parent select.
+   * {@inheritdoc}
    */
   public function getParentDepthLimit(array $book_link) {
     return static::BOOK_MAX_DEPTH - 1 - (($book_link['bid'] && $book_link['has_children']) ? $this->findChildrenRelativeDepth($book_link) : 0);
@@ -177,21 +156,7 @@ protected function findChildrenRelativeDepth(array $entity) {
   }
 
   /**
-   * Builds the common elements of the book form for the node and outline forms.
-   *
-   * @param array $form
-   *   An associative array containing the structure of the form.
-   * @param array $form_state
-   *   An associative array containing the current state of the form.
-   * @param \Drupal\node\NodeInterface $node
-   *   The node whose form is being viewed.
-   * @param \Drupal\Core\Session\AccountInterface $account
-   *   The account viewing the form.
-   * @param bool $collapsed
-   *   If TRUE, the fieldset start out collpased..
-   *
-   * @return array
-   *   The form structure, with the book elements added.
+   * {@inheritdoc}
    */
   public function addFormElements(array $form, array &$form_state, NodeInterface $node, AccountInterface $account, $collapsed = TRUE) {
     // If the form is being processed during the Ajax callback of our book bid
@@ -274,33 +239,14 @@ public function addFormElements(array $form, array &$form_state, NodeInterface $
   }
 
   /**
-   * Determines if a node can be removed from the book.
-   *
-   * A node can be removed from a book if it is actually in a book and it either
-   * is not a top-level page or is a top-level page with no children.
-   *
-   * @param \Drupal\node\NodeInterface $node
-   *   The node to remove from the outline.
-   *
-   * @return bool
-   *   TRUE if a node can be removed from the book, FALSE otherwise.
+   * {@inheritdoc}
    */
   public function checkNodeIsRemovable(NodeInterface $node) {
     return (!empty($node->book['bid']) && (($node->book['bid'] != $node->id()) || !$node->book['has_children']));
   }
 
   /**
-   * Handles additions and updates to the book outline.
-   *
-   * This common helper function performs all additions and updates to the book
-   * outline through node addition, node editing, node deletion, or the outline
-   * tab.
-   *
-   * @param \Drupal\node\NodeInterface $node
-   *   The node that is being saved, added, deleted, or moved.
-   *
-   * @return bool
-   *   TRUE if the book link was saved; FALSE otherwise.
+   * {@inheritdoc}
    */
   public function updateOutline(NodeInterface $node) {
     if (empty($node->book['bid'])) {
@@ -325,6 +271,9 @@ public function updateOutline(NodeInterface $node) {
     return $this->saveBookLink($node->book, $new);
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function getBookParents(array $item, array $parent = array()) {
     $book = array();
     if ($item['pid'] == 0) {
@@ -363,10 +312,7 @@ protected function t($string, array $args = array(), array $options = array()) {
   }
 
   /**
-   * Updates the book ID of a page and its children when it moves to a new book.
-   *
-   * @param array $book_link
-   *   A fully loaded menu link that is part of the book hierarchy.
+   * {@inheritdoc}
    */
   public function updateId($book_link) {
     $query = $this->connection->select('book');
@@ -487,20 +433,7 @@ protected function recurseTableOfContents(array $tree, $indent, array &$toc, arr
   }
 
   /**
-   * Returns an array of book pages in table of contents order.
-   *
-   * @param int $bid
-   *   The ID of the book whose pages are to be listed.
-   * @param int $depth_limit
-   *   Any link deeper than this value will be excluded (along with its children).
-   * @param array $exclude
-   *   (optional) An array of menu link ID values. Any link whose menu link ID is
-   *   in this array will be excluded (along with its children). Defaults to an
-   *   empty array.
-   *
-   * @return array
-   *   An array of (menu link ID, title) pairs for use as options for selecting a
-   *   book page.
+   * {@inheritdoc}
    */
   public function getTableOfContents($bid, $depth_limit, array $exclude = array()) {
     $tree = $this->bookTreeAllData($bid);
@@ -511,10 +444,7 @@ public function getTableOfContents($bid, $depth_limit, array $exclude = array())
   }
 
   /**
-   * Deletes node's entry from book table.
-   *
-   * @param int $nid
-   *   The nid to delete.
+   * {@inheritdoc}
    */
   public function deleteFromBook($nid) {
     $original = $this->loadBookLink($nid, FALSE);
@@ -536,26 +466,7 @@ public function deleteFromBook($nid) {
   }
 
   /**
-   * Gets the data structure representing a named menu tree.
-   *
-   * Since this can be the full tree including hidden items, the data returned
-   * may be used for generating an an admin interface or a select.
-   *
-   * @param int $bid
-   *   The Book ID to find links for.
-   * @param $link
-   *   A fully loaded menu link, or NULL. If a link is supplied, only the
-   *   path to root will be included in the returned tree - as if this link
-   *   represented the current page in a visible menu.
-   * @param int $max_depth
-   *   Optional maximum depth of links to retrieve. Typically useful if only one
-   *   or two levels of a sub tree are needed in conjunction with a non-NULL
-   *   $link, in which case $max_depth should be greater than $link['depth'].
-   *
-   * @return array
-   *   An tree of menu links in an array, in the order they should be rendered.
-   *
-   * Note: copied from menu_tree_all_data().
+   * {@inheritdoc}
    */
   public function bookTreeAllData($bid, $link = NULL, $max_depth = NULL) {
     $tree = &drupal_static(__FUNCTION__, array());
@@ -607,21 +518,7 @@ public function bookTreeAllData($bid, $link = NULL, $max_depth = NULL) {
   }
 
   /**
-   * Returns a rendered menu tree.
-   *
-   * The menu item's LI element is given one of the following classes:
-   * - expanded: The menu item is showing its submenu.
-   * - collapsed: The menu item has a submenu which is not shown.
-   * - leaf: The menu item has no submenu.
-   *
-   * @param array $tree
-   *   A data structure representing the tree as returned from menu_tree_data.
-   *
-   * @return array
-   *   A structured array to be rendered by drupal_render().
-   *
-   * Note: copied from menu_tree_output() but some hacky code using
-   * menu_get_item() was removed.
+   * {@inheritdoc}
    */
   public function bookTreeOutput(array $tree) {
     $build = array();
@@ -791,12 +688,7 @@ protected function _menu_build_tree($bid, array $parameters = array()) {
   }
 
   /**
-   * Collects node links from a given menu tree recursively.
-   *
-   * @param array $tree
-   *   The menu tree you wish to collect node links from.
-   * @param array $node_links
-   *   An array in which to store the collected node links.
+   * {@inheritdoc}
    */
   public function bookTreeCollectNodeLinks(&$tree, &$node_links) {
     // All book links are nodes.
@@ -814,15 +706,7 @@ public function bookTreeCollectNodeLinks(&$tree, &$node_links) {
   }
 
   /**
-   * Load a single book entry.
-   *
-   * @param int $nid
-   *   The node ID of the book.
-   * @param book $translate
-   *   If TRUE, set access, title, and other elements.
-   *
-   * @return array
-   *   The book data of that node.
+   * {@inheritdoc}
    */
   public function loadBookLink($nid, $translate = TRUE) {
     $link = $this->connection->query("SELECT * FROM {book} WHERE nid = :nid", array(':nid' => $nid))->fetchAssoc();
@@ -833,13 +717,7 @@ public function loadBookLink($nid, $translate = TRUE) {
   }
 
   /**
-   * Save a single book entry.
-   *
-   * @param array $link
-   *   The link data to save.
-   *
-   * @return array
-   *   The book data of that node.
+   * {@inheritdoc}
    */
   public function saveBookLink(array $link, $new) {
     if ($new) {
@@ -928,10 +806,16 @@ protected function moveChildren(array $link, array $original) {
   }
 
   /**
-   * @todo: what happens here?
+   * Updates the has_children flag of the parent of the original book.
+   *
+   * This method is mostly called when a book is moved/created etc. so we want
+   * to update the has_children flag of the parent book.
    *
    * @param array $original
-   * @return type
+   *   The book which parent we want to update.
+   *
+   * @return bool
+   *   TRUE if there was no parent, otherwise TRUE on success, FALSE on failure.
    */
   protected function updateParentalStatus(array $original) {
     if ($original['pid'] == 0) {
@@ -978,13 +862,7 @@ protected function setParents(array &$link, array $parent) {
   }
 
   /**
-   * Checks access and performs dynamic operations for each link in the tree.
-   *
-   * @param array $tree
-   *   The menu tree you wish to operate on.
-   * @param array $node_links
-   *   A collection of node link references generated from $tree by
-   *   menu_tree_collect_node_links().
+   * {@inheritdoc}
    */
   public function bookTreeCheckAccess(&$tree, $node_links = array()) {
     if ($node_links) {
@@ -1031,16 +909,7 @@ protected function _menu_tree_check_access(&$tree) {
   }
 
   /**
-   * Provides menu link access control, translation, and argument handling.
-   *
-   * This function is similar to _menu_translate(), but it also does
-   * link-specific preparation (such as always calling to_arg() functions).
-   *
-   * @param array $link
-   *   A book link.
-   *
-   * Note: copied from _menu_link_translate() in menu.inc, but reduced to the
-   * minimal code that's used.
+   * {@inheritdoc}
    */
   public function bookLinkTranslate(&$link) {
     $node = NULL;
@@ -1120,7 +989,7 @@ protected function _menu_tree_data(&$links, $parents, $depth) {
         // Fetch next link after filling the sub-tree.
         $next = end($links);
       }
-      // Determine if we should exit the loop and return.
+      // Determine if we should exit the loop and $request = return.
       if (!$next || $next['depth'] < $depth) {
         break;
       }
@@ -1129,17 +998,7 @@ protected function _menu_tree_data(&$links, $parents, $depth) {
   }
 
   /**
-   * Gets the data representing a subtree of the book hierarchy.
-   *
-   * The root of the subtree will be the link passed as a parameter, so the
-   * returned tree will contain this item and all its descendents in the menu
-   * tree.
-   *
-   * @param $link
-   *   A fully loaded menu link.
-   *
-   * @return
-   *   A subtree of menu links in an array, in the order they should be rendered.
+   * {@inheritdoc}
    */
   public function bookMenuSubtreeData($link) {
     $tree = &drupal_static(__FUNCTION__, array());
diff --git a/core/modules/book/lib/Drupal/book/BookManagerInterface.php b/core/modules/book/lib/Drupal/book/BookManagerInterface.php
index c32190e..76e24ae 100644
--- a/core/modules/book/lib/Drupal/book/BookManagerInterface.php
+++ b/core/modules/book/lib/Drupal/book/BookManagerInterface.php
@@ -15,6 +15,7 @@
  * Book Manager Service.
  */
 interface BookManagerInterface {
+
   /**
    * Gets the data structure representing a named menu tree.
    *
@@ -44,7 +45,7 @@ public function bookTreeAllData($bid, $link = NULL, $max_depth = NULL);
    *
    * @param int $nid
    *   The node ID of the book.
-   * @param book $translate
+   * @param bool $translate
    *   If TRUE, set access, title, and other elements.
    *
    * @return array
@@ -136,6 +137,8 @@ public function updateOutline(NodeInterface $node);
    *
    * @param array $link
    *   The link data to save.
+   * @param bool $new
+   *   Is this a new book.
    *
    * @return array
    *   The book data of that node.
diff --git a/core/modules/book/lib/Drupal/book/Controller/BookController.php b/core/modules/book/lib/Drupal/book/Controller/BookController.php
index bf6277e..4067a74 100644
--- a/core/modules/book/lib/Drupal/book/Controller/BookController.php
+++ b/core/modules/book/lib/Drupal/book/Controller/BookController.php
@@ -9,6 +9,7 @@
 
 use Drupal\book\BookManager;
 use Drupal\book\BookExport;
+use Drupal\book\BookManagerInterface;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\node\NodeInterface;
 use Symfony\Component\DependencyInjection\Container;
@@ -24,7 +25,7 @@ class BookController implements ContainerInjectionInterface {
   /**
    * The book manager.
    *
-   * @var \Drupal\book\BookManager
+   * @var BookManagerInterface
    */
   protected $bookManager;
 
@@ -38,12 +39,12 @@ class BookController implements ContainerInjectionInterface {
   /**
    * Constructs a BookController object.
    *
-   * @param \Drupal\book\BookManager $bookManager
+   * @param BookManagerInterface $bookManager
    *   The book manager.
    * @param \Drupal\book\BookExport $bookExport
    *   The book export service.
    */
-  public function __construct(BookManager $bookManager, BookExport $bookExport) {
+  public function __construct(BookManagerInterface $bookManager, BookExport $bookExport) {
     $this->bookManager = $bookManager;
     $this->bookExport = $bookExport;
   }
diff --git a/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php b/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
index de57b07..d1db3c9 100644
--- a/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
+++ b/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
@@ -8,6 +8,7 @@
 namespace Drupal\book\Form;
 
 use \Drupal\book\BookManager;
+use Drupal\book\BookManagerInterface;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
@@ -38,7 +39,7 @@ class BookAdminEditForm extends FormBase {
   /**
    * The book manager.
    *
-   * @var \Drupal\book\BookManager
+   * @var BookManagerInterface
    */
   protected $bookManager;
 
@@ -49,10 +50,10 @@ class BookAdminEditForm extends FormBase {
    *   The menu cache object to be used by this controller.
    * @param \Drupal\Core\Entity\EntityStorageControllerInterface $node_storage
    *   The custom block storage controller.
-   * @param \Drupal\book\BookManager $book_manager
+   * @param BookManagerInterface $book_manager
    *   The book manager.
    */
-  public function __construct(CacheBackendInterface $cache, EntityStorageControllerInterface $node_storage, BookManager $book_manager) {
+  public function __construct(CacheBackendInterface $cache, EntityStorageControllerInterface $node_storage, BookManagerInterface $book_manager) {
     $this->cache = $cache;
     $this->nodeStorage = $node_storage;
     $this->bookManager = $book_manager;
diff --git a/core/modules/book/lib/Drupal/book/Form/BookOutlineForm.php b/core/modules/book/lib/Drupal/book/Form/BookOutlineForm.php
index 28aa7eb..78a5d28 100644
--- a/core/modules/book/lib/Drupal/book/Form/BookOutlineForm.php
+++ b/core/modules/book/lib/Drupal/book/Form/BookOutlineForm.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\book\Form;
 
+use Drupal\book\BookManagerInterface;
 use Drupal\Core\Entity\ContentEntityFormController;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\book\BookManager;
@@ -27,7 +28,7 @@ class BookOutlineForm extends ContentEntityFormController {
   /**
    * BookManager service.
    *
-   * @var \Drupal\book\BookManager
+   * @var BookManagerInterface
    */
   protected $bookManager;
 
@@ -36,10 +37,10 @@ class BookOutlineForm extends ContentEntityFormController {
    *
    * @param \Drupal\Core\Entity\EntityManagerInterface $entity_manager
    *   The entity manager.
-   * @param \Drupal\book\BookManager $book_manager
+   * @param BookManagerInterface $book_manager
    *   The BookManager service.
    */
-  public function __construct(EntityManagerInterface $entity_manager, BookManager $book_manager) {
+  public function __construct(EntityManagerInterface $entity_manager, BookManagerInterface $book_manager) {
     parent::__construct($entity_manager);
     $this->bookManager = $book_manager;
   }
diff --git a/core/modules/book/lib/Drupal/book/Form/BookRemoveForm.php b/core/modules/book/lib/Drupal/book/Form/BookRemoveForm.php
index 2038d83..d370d7e 100644
--- a/core/modules/book/lib/Drupal/book/Form/BookRemoveForm.php
+++ b/core/modules/book/lib/Drupal/book/Form/BookRemoveForm.php
@@ -8,6 +8,7 @@
 namespace Drupal\book\Form;
 
 use Drupal\book\BookManager;
+use Drupal\book\BookManagerInterface;
 use Drupal\Core\Form\ConfirmFormBase;
 use Drupal\node\NodeInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -20,7 +21,7 @@ class BookRemoveForm extends ConfirmFormBase {
   /**
    * The book manager.
    *
-   * @var \Drupal\book\BookManager
+   * @var BookManagerInterface
    */
   protected $bookManager;
 
@@ -34,10 +35,10 @@ class BookRemoveForm extends ConfirmFormBase {
   /**
    * Constructs a BookRemoveForm object.
    *
-   * @param \Drupal\book\BookManager $book_manager
+   * @param BookManagerInterface $book_manager
    *   The book manager.
    */
-  public function __construct(BookManager $book_manager) {
+  public function __construct(BookManagerInterface $book_manager) {
     $this->bookManager = $book_manager;
   }