TapTapTaperoo:

Sure ... use a character class (or non-capturing grouping). Something like:

my $string = 'xxxxxxabxxx';
print $1 if $string = /(x*[ab][ab]x*)/;
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should work.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

I want to keep these matches in the context of the larger string, while still being able to distinguish matches. Is there a way to substitute and return the successful event...

If "keep these matches in the context of the larger string" means "don't alter the string", then you wouldn't do a substitution; just do a match (with capturing parens), and assign the return value of the match to an array:

my @strings =
    qw/XXXXXXXXXABXXXXXXX
       XXXXXXXBAXXXBBXXXX
       BBAABAABBXBX/;

for my $string ( @strings ) {
    my @matches = ( $string =~ /([AB]{2})/g );
    printf( "Found %d matches in %s: %s\n",
             scalar @matches, $string, join( ', ', @matches ));
}
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you want this:

$string =~ m/(A|B)(A|B)/;
$match="$1$2";
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or this:

 $string =~ s/(A|B)(A|B)/lc("$1$2")/e;
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or do you need $PREMATCH, $MATCH and $POSTMATCH ?

When I try to substitute it returns indistinguishable for the original hit ie:

Que?

Um. I cannot even guess as to what you mean here?

Why not post your code showing exactly what result you're getting; and what you want to get. Making us guess what you are trying to do is unlikely to encourage us to help you.

use strict;
use warnings;
my $string = 'XXXXXXXXXXABXXXXXXXXX';
my ($match) = $string =~ m/X{10}([AB]{2})X{9}/;
print $match;
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OUTPUT:

UPDATE: Added Output