public function add_rewrite_slugs( $slugs ) {
		foreach ( self::additional_listings_pages_array() as $additional_listing ) {
			// is this rule valid and active?
			if ( ! self::is_valid_rule( $additional_listing )
				|| ! self::is_active_rule( $additional_listing ) ) {
				continue;
			}
			$slugs[] = $additional_listing['url_path'];
		}
		return $slugs;
	}