c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $s = 'abcd efgh';
 ;;
 my @caps = $s =~ m{ \w+ }xmsg;
 dd 'non-overlapping captures: ', \@caps;
 ;;
 @caps = $s =~ m{ (?= (\w+)) }xmsg;
 dd 'overlapping captures: ', \@caps;
"
("non-overlapping captures: ", ["abcd", "efgh"])

(
  "overlapping captures: ",
  ["abcd", "bcd", "cd", "d", "efgh", "fgh", "gh", "h"],
)