qr/ (?(DEFINE)
          ( 00 (?1) | 11 (?2) | )               # group 1:  carry = 0
          ( 01 (?1) | 10 (?3) )                 # group 2:  carry = 1
          ( 00 (?2) | 11 (?3) )                 # group 3:  carry = 2
        )

        \A(?1)\Z /x;

##</code><code>##

    qr/ (?(DEFINE)
          ( 00 (?1) | 11 01 (?1) | 11 10 (?3) | )
          ( )
          ( 00 01 (?1) | 00 10 (?3) | 11 (?3) )
        )

        \A(?1)\Z /x;

##</code><code>##

my $Regex_Pattern =

    qr/ \A ( 00 | 11 01 | 11 10 ( 00 10 | 11 )* 00 01 )* \Z /x;