You can add new and existing taxonomies to a post type by passing the taxonomy name to the taxonomy()
method.
// Create a book post type.$books = new PostType( 'book' );// Add the genre taxonomy to the book post type.$books->taxonomy( 'genre' );// Add the default category taxonomy.$books->taxonomy( 'category' );// Register the post type to WordPress.$books->register();
This method only attaches the taxonomy to the post type, to create a taxonomy see the documentation on creating a new taxonomy.
Taxonomies and post types can be created in any order.