diff --git a/core/modules/book/book.admin.css b/core/modules/book/book.admin.css
index 08e1cb1..1059aad 100644
--- a/core/modules/book/book.admin.css
+++ b/core/modules/book/book.admin.css
@@ -1,6 +1,6 @@
 /**
  * @file
- * Administration styles for Book module.
+ * Administration styles for the Book module.
  */
 
 /**
diff --git a/core/modules/book/book.admin.inc b/core/modules/book/book.admin.inc
index c8f4096..d112180 100644
--- a/core/modules/book/book.admin.inc
+++ b/core/modules/book/book.admin.inc
@@ -185,7 +185,7 @@ function book_admin_edit_submit($form, &$form_state) {
  * @param Drupal\node\Node $node
  *   The node of the top-level page in the book.
  * @param $form
- *   The form that is being modified, passed by reference
+ *   The form that is being modified, passed by reference.
  *
  * @see book_admin_edit()
  */
diff --git a/core/modules/book/book.install b/core/modules/book/book.install
index e9abf1d..797902a 100644
--- a/core/modules/book/book.install
+++ b/core/modules/book/book.install
@@ -88,7 +88,7 @@ function book_schema() {
 }
 
 /**
- * Move Book settings from variables to config.
+ * Move the Book module settings from variables to config.
  *
  * @ingroup config_upgrade
  */
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 090ccaf..a521893 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -204,9 +204,6 @@ function book_menu() {
  * @param Drupal\node\Node $node
  *   The node whose outline tab is to be viewed.
  *
- * @return
- *   A Boolean TRUE if the current user has the requested permission.
- *
  * @see book_menu()
  */
 function _book_outline_access(Node $node) {
@@ -219,9 +216,6 @@ function _book_outline_access(Node $node) {
  * @param Drupal\node\Node $node
  *   The node to remove from the outline.
  *
- * @return
- *   A Boolean TRUE if the current user has the requested permission.
- *
  * @see book_menu()
  */
 function _book_outline_remove_access(Node $node) {
@@ -236,9 +230,6 @@ function _book_outline_remove_access(Node $node) {
  *
  * @param Drupal\node\Node $node
  *   The node to remove from the outline.
- *
- * @return bool
- *   A Boolean indicating whether the node can be removed from the book.
  */
 function _book_node_is_removable($node) {
   return (!empty($node->book['bid']) && (($node->book['bid'] != $node->nid) || !$node->book['has_children']));
@@ -1303,6 +1294,7 @@ function book_node_export(Node $node, $children = '') {
  * @param array $variables
  *   An associative array containing the following keys:
  *   - node
+ *   - children
  *
  * @see book-node-export-html.tpl.php
  */
diff --git a/core/modules/book/lib/Drupal/book/Tests/BookTest.php b/core/modules/book/lib/Drupal/book/Tests/BookTest.php
index a91a322..7a20d73 100644
--- a/core/modules/book/lib/Drupal/book/Tests/BookTest.php
+++ b/core/modules/book/lib/Drupal/book/Tests/BookTest.php
@@ -102,7 +102,7 @@ function createBook() {
   }
 
   /**
-   * Tests Book functionality through node interfaces.
+   * Tests book functionality through node interfaces.
    */
   function testBook() {
     // Create new book.
@@ -141,7 +141,9 @@ function testBook() {
   }
 
   /**
-   * Checks the outline of sub-pages; previous, up, and next; and printer friendly version.
+   * Checks the outline of sub-pages; previous, up, and next.
+   *
+   * Also checks the printer friendly version of the outline.
    *
    * @param Drupal\node\Node $node
    *   Node to check.
@@ -212,10 +214,10 @@ function checkBookNode(Node $node, $nodes, $previous = FALSE, $up = FALSE, $next
    * Creates a regular expression to check for the sub-nodes in the outline.
    *
    * @param array $nodes
-   *   An array of Nodes to check in outline.
+   *   An array of nodes to check in outline.
    *
    * @return string
-   *   A customized regular expression as a string.
+   *   A regular expression that locates sub-nodes of the outline.
    */
   function generateOutlinePattern($nodes) {
     $outline = '';
@@ -230,9 +232,9 @@ function generateOutlinePattern($nodes) {
    * Creates a book node.
    *
    * @param int|string $book_nid
-   *   Book node ID or set to 'new' to create new book.
+   *   A book node ID or set to 'new' to create a new book.
    * @param int|null $parent
-   *   (optional) Parent book reference id. Defaults to NULL.
+   *   (optional) Parent book reference ID. Defaults to NULL.
    */
   function createBookNode($book_nid, $parent = NULL) {
     // $number does not use drupal_static as it should not be reset