Function: Add an already registered taxonomy to an object type.

Function: Creates the initial taxonomies.

Function: Retrieves a list of registered taxonomy names or objects.

Function: Return the names or objects of the taxonomies which are registered for the requested object or object type, such as a post object or post type name.

Function: Retrieves the taxonomy object of $taxonomy.

Function: Checks that the taxonomy name exists.

Function: Whether the taxonomy object is hierarchical.