WordPress: create custom taxonomy

wp_functions_customTaxonomy.php

// ----------------------------------------------
// ---------- Create custom taxonomies ---------- 
// ----------------------------------------------
<?php
    function custom_taxonomies() {
        register_taxonomy('collection', 'post', array(
            'hierarchical' => true,
            'label'        => 'Collections',
            'query_var'    => true,
            'rewrite'      => true
        ));
    }
    add_action('init', 'custom_taxonomies', 0);
?>