c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"use 5.010;
 ;;
 my $s = 'abc';
 ;;
 my @captures = $s =~ m{ (?| (a)(b)(c) | (w)(x)(y)) (z)? }xms;
 dd \@captures;
"
["a", "b", "c", undef]