6.2 register_taxonomy (ok)

function wpdocs_codex_book_init() {
  $labels = array(
    'name'                  => _x('Books', 'Post type general name', 'textdomain'),
    'singular_name'         => _x('Book', 'Post type singular name', 'textdomain'),
    'menu_name'             => _x('Books', 'Admin Menu text', 'textdomain'),
    'name_admin_bar'        => _x('Book', 'Add New on Toolbar', 'textdomain'),
    'add_new'               => __('Add New', 'textdomain'),
    'add_new_item'          => __('Add New Book', 'textdomain'),
    'new_item'              => __('New Book', 'textdomain'),
    'edit_item'             => __('Edit Book', 'textdomain'),
    'view_item'             => __('View Book', 'textdomain'),
    'all_items'             => __('All Books', 'textdomain'),
    'search_items'          => __('Search Books', 'textdomain'),
    'parent_item_colon'     => __('Parent Books:', 'textdomain'),
    'not_found'             => __('No books found.', 'textdomain'),
    'not_found_in_trash'    => __('No books found in Trash.', 'textdomain'),
    'featured_image'        => _x('Book Cover Image', 'Overrides the “Featured Image” phrase for this post type. Added in 4.3', 'textdomain'),
    'set_featured_image'    => _x('Set cover image', 'Overrides the “Set featured image” phrase for this post type. Added in 4.3', 'textdomain'),
    'remove_featured_image' => _x('Remove cover image', 'Overrides the “Remove featured image” phrase for this post type. Added in 4.3', 'textdomain'),
    'use_featured_image'    => _x('Use as cover image', 'Overrides the “Use as featured image” phrase for this post type. Added in 4.3', 'textdomain'),
    'archives'              => _x('Book archives', 'The post type archive label used in nav menus. Default “Post Archives”. Added in 4.4', 'textdomain'),
    'insert_into_item'      => _x('Insert into book', 'Overrides the “Insert into post”/”Insert into page” phrase (used when inserting media into a post). Added in 4.4', 'textdomain'),
    'uploaded_to_this_item' => _x('Uploaded to this book', 'Overrides the “Uploaded to this post”/”Uploaded to this page” phrase (used when viewing media attached to a post). Added in 4.4', 'textdomain'),
    'filter_items_list'     => _x('Filter books list', 'Screen reader text for the filter links heading on the post type listing screen. Default “Filter posts list”/”Filter pages list”. Added in 4.4', 'textdomain'),
    'items_list_navigation' => _x('Books list navigation', 'Screen reader text for the pagination heading on the post type listing screen. Default “Posts list navigation”/”Pages list navigation”. Added in 4.4', 'textdomain'),
    'items_list'            => _x('Books list', 'Screen reader text for the items list heading on the post type listing screen. Default “Posts list”/”Pages list”. Added in 4.4', 'textdomain'),
  );
  $args = array(
    'labels'             => $labels,
    'public'             => true,
    'publicly_queryable' => true,
    'show_ui'            => true,
    'show_in_menu'       => true,
    'query_var'          => true,
    'rewrite'            => array('slug' => 'book'),
    'capability_type'    => 'post',
    'has_archive'        => true,
    'hierarchical'       => false,
    'menu_position'      => null,
    'supports'           => array(
    	'title', 
    	'editor', 
    	'author', 
    	'thumbnail', 
    	'excerpt', 
    	'comments',
    	'tags',
      'page-attributes',
    ),
    'taxonomies' => array(
      'post_tag',
    ),
  );

  register_post_type('book', $args);
}
add_action('init', 'wpdocs_codex_book_init');
function wpdocs_create_book_taxonomies() {
  $labels = array(
    'name'              => _x('Genres', 'taxonomy general name', 'textdomain'),
    'singular_name'     => _x('Genre', 'taxonomy singular name', 'textdomain'),
    'search_items'      => __('Search Genres', 'textdomain'),
    'all_items'         => __('All Genres', 'textdomain'),
    'parent_item'       => __('Parent Genre', 'textdomain'),
    'parent_item_colon' => __('Parent Genre:', 'textdomain'),
    'edit_item'         => __('Edit Genre', 'textdomain'),
    'update_item'       => __('Update Genre', 'textdomain'),
    'add_new_item'      => __('Add New Genre', 'textdomain'),
    'new_item_name'     => __('New Genre Name', 'textdomain'),
    'menu_name'         => __('Genre', 'textdomain'),
  );
  $args = array(
    'hierarchical'      => true,
    'labels'            => $labels,
    'show_ui'           => true,
    'show_admin_column' => true,
    'query_var'         => true,
    'rewrite'           => array('slug' => 'genre'),
  );
  register_taxonomy('genre', array('book'), $args);
  unset($args);
  unset($labels);
  // Add new taxonomy, NOT hierarchical (like tags)
  $labels = array(
    'name'                       => _x('Writers', 'taxonomy general name', 'textdomain'),
    'singular_name'              => _x('Writer', 'taxonomy singular name', 'textdomain'),
    'search_items'               => __('Search Writers', 'textdomain'),
    'popular_items'              => __('Popular Writers', 'textdomain'),
    'all_items'                  => __('All Writers', 'textdomain'),
    'parent_item'                => null,
    'parent_item_colon'          => null,
    'edit_item'                  => __('Edit Writer', 'textdomain'),
    'update_item'                => __('Update Writer', 'textdomain'),
    'add_new_item'               => __('Add New Writer', 'textdomain'),
    'new_item_name'              => __('New Writer Name', 'textdomain'),
    'separate_items_with_commas' => __('Separate writers with commas', 'textdomain'),
    'add_or_remove_items'        => __('Add or remove writers', 'textdomain'),
    'choose_from_most_used'      => __('Choose from the most used writers', 'textdomain'),
    'not_found'                  => __('No writers found.', 'textdomain'),
    'menu_name'                  => __('Writers', 'textdomain'),
  );
  $args = array(
    'hierarchical'          => false,
    'labels'                => $labels,
    'show_ui'               => true,
    'show_admin_column'     => true,
    'update_count_callback' => '_update_post_term_count',
    'query_var'             => true,
    'rewrite'               => array('slug' => 'writer'),
  );
  register_taxonomy('writer', 'book', $args);
}
add_action('init', 'wpdocs_create_book_taxonomies', 0);