The Bifrost Music plugin registers a custom taxonomy for categorizing music albums by genre.
Music Genre Taxonomy The Genre taxonomy (music_genre) is a non-hierarchical taxonomy (like tags) used to categorize albums.
Registration Registered in inc/Content/Genre.php:36
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 , // ... additional parameters ] );
Parameters taxonomy
string
default: "music_genre"
The taxonomy identifier
object_type
array
default: "['music_album']"
Post types this taxonomy applies to. Currently only assigned to music_album
Whether the taxonomy is publicly accessible
Display UI for managing terms in the admin
Enables the REST API endpoint at /wp-json/wp/v2/music_genre
Genres behave like tags (non-hierarchical) rather than categories
Display a column for this taxonomy in the album list table
Allow genre tag cloud widget
query_var
string
default: "music_genre"
Query variable for filtering by genre
Capabilities The taxonomy uses custom capabilities for permission management:
'capabilities' => [ 'manage_terms' => 'manage_music_genres' , 'edit_terms' => 'edit_music_genres' , 'delete_terms' => 'delete_music_genres' , 'assign_terms' => 'assign_music_genres' ]
Source: inc/Content/Genre.php:50-55
manage_music_genres Ability to manage the genre taxonomy
edit_music_genres Permission to edit genre terms
delete_music_genres Permission to delete genre terms
assign_music_genres Permission to assign genres to albums
Labels The taxonomy includes comprehensive labels for the admin interface:
'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' ) ]
Source: inc/Content/Genre.php:56-78 URL Rewrite Rules Genre archive pages use custom URL structure:
'rewrite' => [ 'slug' => 'genres' , 'with_front' => false , 'hierarchical' => false , 'ep_mask' => EP_NONE ]
Source: inc/Content/Genre.php:81-86
URL slug for genre archives (/genres/{genre-slug})
Do not prepend the front base to genre permalinks
Non-hierarchical URL structure (flat, not nested)
ep_mask
constant
default: "EP_NONE"
No endpoint mask applied
Usage Examples Query Albums by Genre // Get all albums in the "Rock" genre $args = [ 'post_type' => 'music_album' , 'tax_query' => [ [ 'taxonomy' => 'music_genre' , 'field' => 'slug' , 'terms' => 'rock' , ], ], ]; $query = new WP_Query ( $args );
Get Genres for an Album // Get all genres assigned to an album $genres = get_the_terms ( $album_id , 'music_genre' ); if ( $genres && ! is_wp_error ( $genres )) { foreach ( $genres as $genre ) { echo $genre -> name ; } }
REST API Access # Get all genres GET /wp-json/wp/v2/music_genre # Get a specific genre GET /wp-json/wp/v2/music_genre/{id} # Get albums for a genre GET /wp-json/wp/v2/music_album?music_genre={genre_id}
Admin Interface Update Messages Custom admin messages for genre operations:
private function termUpdatedMessages ( array $messages ) : array { $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 ; }
Source: inc/Content/Genre.php:93-107
Admin Column Since show_admin_column is set to true, a Genres column automatically appears in the Albums admin list table, displaying all genres assigned to each album.
Technical Details
The taxonomy is registered on the init action with priority 9: add_action ( 'init' , $this -> register ( ... ), 9 );
This ensures it’s registered before the default priority of 10, allowing other hooks to properly reference the taxonomy. Source: inc/Content/Genre.php:26
Non-Hierarchical Behavior
By setting hierarchical to false, genres behave like WordPress tags:
Multiple genres can be assigned to a single album
No parent-child relationships between genres
Text input with comma separation in the editor
“Popular Genres” and “Choose from most used” functionality
Tag cloud support for widgets
This design choice reflects how music genres are typically applied, where albums can belong to multiple genres without a strict hierarchy. 