c:\@Work\Perl\monks>perl -wMstrict -le
"my %rx = ( 2 => 'Oops...' );
 my $rx = qr{ \b foo \b }xms;
 ;;
 my $n = 2;
 my $ry = qr{ $rx{2} X $rx{$n} Y (?:$rx){$n} }xms;
 print $ry;
"
(?msx-i: (?msx-i: \b foo \b ){2} X Oops... Y (?:(?msx-i: \b foo \b )){2} )