Create or modify a taxonomy object. Do not use before init.

A simple function for creating or modifying a taxonomy object based on the parameters given. The function will accept an array (third optional parameter), along with strings for the taxonomy name and another string for the object type.

Nothing is returned, so expect error maybe or use taxonomy_exists() to check whether taxonomy exists.

Optional $args contents:

*- label – Name of the taxonomy shown in the menu. Usually plural. If not set, labels['name'] will be used.
*- labels – An array of labels for this taxonomy. By default tag labels are used for non-hierarchical types and category labels for hierarchical ones. You can see accepted values in {@link get_taxonomy_labels()}.
*- description – A short descriptive summary of what the taxonomy is for. Defaults to blank.
*- public – If the taxonomy should be publicly queryable; //@TODO not implemented. Defaults to true.
*- hierarchical – Whether the taxonomy is hierarchical (e.g. category). Defaults to false.
*- show_ui – Whether to generate a default UI for managing this taxonomy in the admin. If not set, the default is inherited from public.
*- show_in_menu – Whether to show the taxonomy in the admin menu. If true, the taxonomy is shown as a submenu of the object type menu. If false, no menu is shown. show_ui must be true. If not set, the default is inherited from show_ui.
*- show_in_nav_menus – Makes this taxonomy available for selection in navigation menus. If not set, the default is inherited from public.
*- show_tagcloud – Whether to list the taxonomy in the Tag Cloud Widget. If not set, the default is inherited from show_ui.
*- show_admin_column – Whether to display a column for the taxonomy on its post type listing screens. Defaults to false.
*- meta_box_cb – Provide a callback function for the meta box display. If not set, defaults to post_categories_meta_box for hierarchical taxonomies and post_tags_meta_box for non-hierarchical. If false, no meta box is shown.
*- capabilities – Array of capabilities for this taxonomy. You can see accepted values in this function.
*- rewrite – Triggers the handling of rewrites for this taxonomy. Defaults to true, using $taxonomy as slug. To prevent rewrite, set to false. To specify rewrite rules, an array can be passed with any of these keys ‘slug’ => string Customize the permastruct slug. Defaults to $taxonomy key ‘with_front’ => bool Should the permastruct be prepended with WP_Rewrite::$front. Defaults to true. ‘hierarchical’ => bool Either hierarchical rewrite tag or not. Defaults to false. ‘ep_mask’ => const Assign an endpoint mask. If not specified, defaults to EP_NONE.
*- query_var – Sets the query_var key for this taxonomy. Defaults to $taxonomy key If false, a taxonomy cannot be loaded at ?{query_var}={term_slug If specified as a string, the query ?{query_var_string}={term_slug} will be valid.
*- update_count_callback – Works much like a hook, in that it will be called when the count is updated. Defaults to _update_post_term_count() for taxonomies attached to post types, which then confirms that the objects are published before counting them. Defaults to _update_generic_term_count() for taxonomies attached to other object types, such as links.
*- _builtin – true if this taxonomy is a native or “built-in” taxonomy. THIS IS FOR INTERNAL USE ONLY!

Signature

register_taxonomy( $taxonomy, $object_type, $args = array() )
taxonomy
 (string) Taxonomy key, must not exceed 32 characters.
object_type
 (array|string) Name of the object type for the taxonomy object.
args
 (array|string) See optional args description above.
Default: array()

Return

(null|WP_Error) WP_Error if errors, otherwise null.

Source

function register_taxonomy( $taxonomy, $object_type, $args = array() ) {
	global $wp_taxonomies, $wp;

	if ( ! is_array( $wp_taxonomies ) )
		$wp_taxonomies = array();

	$defaults = array(
		'labels'                => array(),
		'description'           => '',
		'public'                => true,
		'hierarchical'          => false,
		'show_ui'               => null,
		'show_in_menu'          => null,
		'show_in_nav_menus'     => null,
		'show_tagcloud'         => null,
		'show_admin_column'     => false,
		'meta_box_cb'           => null,
		'capabilities'          => array(),
		'rewrite'               => true,
		'query_var'             => $taxonomy,
92 more lines...
WP Trac GitHub

Link here