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The plugin implements a Genre taxonomy for categorizing music albums. It demonstrates WordPress taxonomy registration with custom capabilities and admin messaging.

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Genre Taxonomy

The Genre taxonomy is a non-hierarchical (tag-like) taxonomy applied to Album posts.

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Registration

Location: inc/Content/Genre.php:34 
private function register(): void
{
    register_taxonomy(
        Definitions::TAXONOMY_GENRE,
        [
            Definitions::POST_TYPE_ALBUM
        ],
        [
        'public'            => true,
        'show_ui'           => true,
        'show_in_nav_menus' => true,
        'show_in_rest'      => true,
        'show_tagcloud'     => true,
        'show_admin_column' => true,
        'hierarchical'      => false,
        'query_var'         => Definitions::TAXONOMY_GENRE,
        // ... capabilities and labels
    ]);
}
Definitions::TAXONOMY_GENRE is defined as 'music_genre' in inc/Support/Definitions.php:25

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Key Configuration Options

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Non-Hierarchical Structure

'hierarchical' => false,
This makes the taxonomy behave like tags rather than categories:
  • Uses a text input for adding terms (not a checkbox tree)
  • Terms don’t have parent-child relationships
  • Better suited for genres which typically don’t have hierarchies

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Show in Admin Column

'show_admin_column' => true,
Automatically adds a “Genres” column to the Albums list table in wp-admin.

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REST API Support

'show_in_rest' => true,
Exposes the taxonomy in the WordPress REST API, allowing:
  • Block editor integration
  • Querying via /wp-json/wp/v2/music_genre
  • Filtering albums by genre in REST requests

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Custom Capabilities

Location: inc/Content/Genre.php:50 
'capabilities' => [
    'manage_terms' => 'manage_music_genres',
    'edit_terms'   => 'edit_music_genres',
    'delete_terms' => 'delete_music_genres',
    'assign_terms' => 'assign_music_genres'
],
These capabilities allow granular control over who can:
  • manage_terms: Access the taxonomy management screen
  • edit_terms: Create and edit genre terms
  • delete_terms: Delete genre terms
  • assign_terms: Assign genres to albums
These capabilities are granted to administrators during plugin activation (see inc/Lifecycle.php:48).

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Taxonomy Labels

Location: inc/Content/Genre.php:56 Comprehensive labels improve the admin user experience: 
'labels' => [
    'name'                  => __('Genres',                 'bifrost-music'),
    'singular_name'         => __('Genre',                  'bifrost-music'),
    'menu_name'             => __('Genres',                 'bifrost-music'),
    'name_admin_bar'        => __('Genre',                  'bifrost-music'),
    'search_items'          => __('Search Genres',          'bifrost-music'),
    'popular_items'         => __('Popular Genres',         'bifrost-music'),
    'all_items'             => __('All Genres',             'bifrost-music'),
    'edit_item'             => __('Edit Genre',             'bifrost-music'),
    'view_item'             => __('View Genre',             'bifrost-music'),
    'update_item'           => __('Update Genre',           'bifrost-music'),
    'add_new_item'          => __('Add New Genre',          'bifrost-music'),
    'new_item_name'         => __('New Genre Name',         'bifrost-music'),
    'not_found'             => __('No genres found.',       'bifrost-music'),
    'no_terms'              => __('No genres',              'bifrost-music'),
    'items_list_navigation' => __('Genres list navigation', 'bifrost-music'),
    'items_list'            => __('Genres list',            'bifrost-music'),

    // Non-hierarchical only labels
    'separate_items_with_commas' => __('Separate genres with commas',      'bifrost-music'),
    'add_or_remove_items'        => __('Add or remove genres',             'bifrost-music'),
    'choose_from_most_used'      => __('Choose from the most used genres', 'bifrost-music')
],
The last three labels are specific to non-hierarchical taxonomies and control the tag-like interface.

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URL Structure

Location: inc/Content/Genre.php:81 
'rewrite' => [
    'slug'         => 'genres',
    'with_front'   => false,
    'hierarchical' => false,
    'ep_mask'      => EP_NONE
]
This creates URLs like:
  • Single genre archive: https://example.com/genres/rock/
  • Genre feeds: https://example.com/genres/rock/feed/

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Custom Admin Messages

The Genre class provides custom messages for taxonomy operations. Location: inc/Content/Genre.php:93 
private function termUpdatedMessages(array $messages): array
{
    // Add the music genre messages.
    $messages[Definitions::TAXONOMY_GENRE] = [
        0 => '',
        1 => __('Genre added.',       'bifrost-music'),
        2 => __('Genre deleted.',     'bifrost-music'),
        3 => __('Genre updated.',     'bifrost-music'),
        4 => __('Genre not added.',   'bifrost-music'),
        5 => __('Genre not updated.', 'bifrost-music'),
        6 => __('Genres deleted.',    'bifrost-music'),
    ];

    return $messages;
}
These messages appear when:
  • Adding a new genre (message 1)
  • Deleting a genre (message 2)
  • Updating an existing genre (message 3)
  • Bulk deleting genres (message 6)

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Service Implementation

The Genre class implements the Bootable interface: Location: inc/Content/Genre.php:24 
public function boot(): void
{
    add_action('init', $this->register(...), 9);

    add_filter('term_updated_messages', $this->termUpdatedMessages(...), 5);
}
The taxonomy is registered at priority 9 on the init hook, which is before the default priority of 10. This ensures the taxonomy exists before the Album post type tries to associate with it.

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Querying Albums by Genre

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WP_Query Example

$args = [
    'post_type' => 'music_album',
    'tax_query' => [
        [
            'taxonomy' => 'music_genre',
            'field'    => 'slug',
            'terms'    => 'rock',
        ],
    ],
];

$query = new WP_Query($args);

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REST API Example

GET /wp-json/wp/v2/music_album?music_genre=5
This returns all albums tagged with the genre that has ID 5.

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Capability Management

Like the post types, Genre capabilities are managed during the plugin lifecycle.

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Activation

Location: inc/Lifecycle.php:48 
public static function activate(): void
{
    if ($role = get_role('administrator')) {
        // Taxonomy caps.
        $role->add_cap('manage_music_genres');
        $role->add_cap('edit_music_genres');
        $role->add_cap('delete_music_genres');
        $role->add_cap('assign_music_genres');
    }
}

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Uninstall

Location: inc/Lifecycle.php:107 
public static function uninstall(): void
{
    if ($role = get_role('administrator')) {
        // Genre caps.
        $role->remove_cap('manage_music_genres');
        $role->remove_cap('edit_music_genres');
        $role->remove_cap('delete_music_genres');
        $role->remove_cap('assign_music_genres');
    }
}

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Integration with Albums

The Genre taxonomy is registered for the Album post type: 
register_taxonomy(
    Definitions::TAXONOMY_GENRE,
    [
        Definitions::POST_TYPE_ALBUM  // Applied to albums only
    ],
    // ... configuration
);
This means:
  • Genres appear in the Album editor sidebar
  • Albums can be filtered by genre in wp-admin
  • Genre archives show only albums (not artists)
  • The taxonomy is available in block patterns and queries

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Best Practices Demonstrated

Non-Hierarchical Design

Using hierarchical => false provides a tag-like interface suitable for genres

Custom Capabilities

Separate capabilities allow role-based access control for taxonomy management

Internationalization

All strings use __() for translation support

Clean URLs

Custom rewrite rules create SEO-friendly URLs like /genres/rock/

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Next Steps

Custom Post Types

Learn how the Album post type uses this taxonomy

Block Editor Integration

See how the block editor interacts with genres

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