book_node_view

book_node_view(array &$build, EntityInterface $node, EntityViewDisplayInterface $display, $view_mode)

function book_node_view(array &$build, EntityInterface $node, EntityViewDisplayInterface $display, $view_mode) {
  if ($view_mode == 'full') {
    if (!empty($node->book['bid']) && empty($node->in_preview)) {
      $book_node = Node::load($node->book['bid']);
      if (!$book_node->access()) {
        return;
      }
      $build['book_navigation'] = array(
        '#theme' => 'book_navigation',
        '#book_link' => $node->book,
        '#weight' => 100,
        // The book navigation is a listing of Node entities, so associate its
        // list cache tag for correct invalidation.
        '#cache' => [
          'tags' => $node->getEntityType()->getListCacheTags(),
        ],
      );
    }
  }
}