public static function isValid(string $number) : bool
    {
        if (ctype_digit($number)) {
            return self::checksum($number) === 0;
        }

        return false;
    }
public static function isValid(string $number) : bool
    {
        if (ctype_digit($number)) {
            return self::checksum($number) === 0;
        }

        return false;
    }
public static function isValid ( string $ number ) : bool { if ( ctype_digit ( $ number ) ) { return self :: checksum ( $ number ) === 0 ; } return false ; }
Checks that a number is valid.

@param string $number

@return bool
Checks that a number is valid .