>perl -wMstrict -le
"my %xlate = (
   A    => '1',
   AA   => '2',
   AAA  => '3',
   AAAA => '4',
   );
 my $mooch = join '|', keys %xlate;
    $mooch = qr{ (?i) $mooch }xms;
 my $match = join '|', reverse sort keys %xlate;
    $match = qr{ (?i) $match }xms;
 print $mooch;
 print $match;
 ;;
 my $s = 'xAxAAxAAAxAAAAx';
 print qq{'$s'};
 $s =~ s{ ($mooch) }{$xlate{ uc $1 }}xmsg;
 print qq{'$s'};
 ;;
 $s = 'xAxaaxAaAxaAaAx';
 print qq{'$s'};
 $s =~ s{ ($match) }{$xlate{ uc $1 }}xmsg;
 print qq{'$s'};
"
(?msx-i: (?i) A|AA|AAAA|AAA )
(?msx-i: (?i) AAAA|AAA|AA|A )
'xAxAAxAAAxAAAAx'
'x1x11x111x1111x'
'xAxaaxAaAxaAaAx'
'x1x2x3x4x'