public static function get_attendee_meta_fields_key( $ticket_id, $attendee_id = null ) {
		/**
		 * Allow the modification of the key used to fetch attendee registration fields.
		 *
		 * @since 5.3.0
		 *
		 * @param string     $meta_key    Which key is used to get the meta fields.
		 * @param string|int $ticket_id   Which ticket we are fetching for.
		 * @param string|int $attendee_id Which attendee we are fetching for.
		 */
		return apply_filters( 'tec_tickets_commerce_legacy_attendee_meta_key', static::META_KEY, $ticket_id, $attendee_id );
	}