$ perl -E 'my $re = qr{(?d-imnsx:(?u-d:(?x: PAT )))}'
Regexp modifier "d" may not appear after the "-" in regex; ...
$ perl -E 'my $re = qr{(?d-imnsx:(?umsx-d: PAT ))}'
Regexp modifier "d" may not appear after the "-" in regex; ...