The node storage. Type:

protected BookManager::recurseTableOfContents(array $tree, $indent, array

public BookOutlineStorageInterface::loadMultiple($nids

protected BookManager::flatBookTree(array $tree, array &$flat)

public BookManager::addFormElements(array $form, FormStateInterface $form_state

The renderer. Type:

Defines the book navigation cache context service. Cache context ID: 'route.book_navigation'. This allows for

public BookManager::bookTreeCheckAccess(&$tree, $node_links = array())

The book export service. Type:

public BookManagerInterface::deleteFromBook($nid)