public function is_ticket_id_list( $tickets, $sep = ',' ) {
		$sep     = is_string( $sep ) ? $sep : ',';
		$tickets = Tribe__Utils__Array::list_to_array( $tickets, $sep );

		$valid = array_filter( $tickets, array( $this, 'is_ticket_id' ) );

		return ! empty( $valid ) && count( $valid ) === count( $tickets );
	}