... multiple matches in "re_str" being captured ...

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(pp);
 ;;
 my $re_str1 = '' . qr{ [0-6BS] }xms;
 print 'A: reference: ', ref $re_str1 if ref $re_str1;
 ;;
 my $str = 'ab3c64dSeBf';
 my @captures = $str =~ m{ $re_str1 }xmsg;
 pp @captures;
 ;;
 my $re_str2 = '' . qr{ [a-f] }xms;
 print 'B: reference: ', ref $re_str2 if ref $re_str2;
 ;;
 my ($one, $two, $three) = $str =~ m{ ($re_str1) ($re_str2) ($re_str1)
+ }xms;
 pp $one, $two, $three;
"
(3, 6, 4, "S", "B")

(3, "c", 6)
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Note the  /g modifier in the
    my @captures = $str =~ m{ $re_str1 }xmsg;
statement.