#!/usr/bin/perl -w
use strict;

our $re = qr{
          \(
          (?:
            (?> [^()]+ )
           |
            (??{ $re })
          )*
          \)
        }x;

##</code><code>##

#!/usr/bin/perl -w
use strict;

our $re = qr{
          \(
          (?:
            (?> [^()]+ )
           |
            (??{ $main::re })
          )*
          \)
        }x;

##</code><code>##

$_ = 'aa bb (cc (dd) ee) ff ';
#   wanting ^----------^
print "$1\n" while m/($re)/g ;
__END__
__OUTPUT__
(cc (dd) ee)