>perl -wMstrict -MData::Dump -le
"my $s = 'AAA BBB CCC DDD AAA BBB';
 ;;
 my @captures = $s =~ m{ (AAA) | (BBB) | (XXX) | (YYY) }xmsg;
 dd \@captures
 ;;
 my @matches = grep defined, $s =~ m{ (AAA) | (BBB) | (XXX) | (YYY) }xmsg;
 dd \@matches;
"
[
  "AAA",
  undef,
  undef,
  undef,
  undef,
  "BBB",
  undef,
  undef,
  "AAA",
  undef,
  undef,
  undef,
  undef,
  "BBB",
  undef,
  undef,
]

["AAA", "BBB", "AAA", "BBB"]