Enhancing WordPress functionality often involves creating custom content types. By using register_post_type and register_taxonomy, you can build tailored solutions for your site. Let’s go through the process together.  

Step 1: Define the Post Type "Books"

We'll register a new post type named Books using the function below:

function create_books_post_type() {
    $labels = array(
        'name'               => 'Books',
        'singular_name'      => 'Book',
        'menu_name'          => 'Books',
        'add_new'            => 'Add New',
        'add_new_item'       => 'Add New Book',
        'edit_item'          => 'Edit Book',
        'view_item'          => 'View Book',
        'all_items'          => 'All Books',
        'search_items'       => 'Search Books',
        'not_found'          => 'No Books Found',
        'not_found_in_trash' => 'No Books in Trash',
    );

    $args = array(
        'labels'             => $labels,
        'public'             => true,
        'has_archive'        => true,
        'rewrite'            => array('slug' => 'books'),
        'supports'           => array('title', 'editor', 'thumbnail'),
    );

    register_post_type('book', $args);
}
add_action('init', 'create_books_post_type');

Step 2: Create the "Genres" Taxonomy

Now, let’s define a custom taxonomy called Genres for classifying books.

function register_genres_taxonomy() {
    $labels = array(
        'name'               => 'Genres',
        'singular_name'      => 'Genre',
        'search_items'       => 'Search Genres',
        'all_items'          => 'All Genres',
        'edit_item'          => 'Edit Genre',
        'add_new_item'       => 'Add New Genre',
        'new_item_name'      => 'New Genre Name',
        'menu_name'          => 'Genres',
    );

    $args = array(
        'hierarchical'      => true,
        'labels'            => $labels,
        'show_ui'           => true,
        'show_admin_column' => true,
        'rewrite'           => array('slug' => 'genre'),
    );

    register_taxonomy('genre', 'book', $args);
}
add_action('init', 'register_genres_taxonomy');

  Your WordPress site is now ready to handle "Books" as a content type, and "Genres" as their categories. This adds a whole new level of content organization.

Final Thoughts

WordPress customization using post types and taxonomies is a powerful way to expand your site. These functions open doors to fully structured and manageable content types.

Further Resources

• WordPress Codex: Post Types
• WordPress Codex: Taxonomies
• register_post_type()
• register_taxonomy()