$ cat p5.pl
#!/opt/perl5.16/bin/perl
use strict;
use warnings;
our $paren = qr/                # Need declared variable with use strict.
      \(
        ( 
           [^()]+               # Not parens
         | 
           (??{ our $paren })   # Another balanced group (not interpolated yet)
        )*
      \)
    /x;                         # 'x' means ignore whitespace, comments.
my $stuff = "On the outside now then (we go( in( and in (&stop)(awhile) ( further ))) but still (here) ) and now (for a while) we are out again.";
$stuff =~ /($paren)/;
print "Orig----------\n";
print "|" . $stuff . "|\n";
print '$1------------' . "\n";
print "|" . $1 . "|\n";
print 'Match---------' . "\n";
print "|" . $& . "|\n";
print 'B4------------' . "\n";
print "|" . $` . "|\n";
print 'After---------' . "\n";
print "|" . $' . "|\n";
print "----------\n";

$ ./p5.pl
Orig----------
|On the outside now then (we go( in( and in (&stop)(awhile) ( further ))) but still (here) ) and now (for a while) we are out again.|
$1------------
|(we go( in( and in (&stop)(awhile) ( further ))) but still (here) )|
Match---------
|(we go( in( and in (&stop)(awhile) ( further ))) but still (here) )|
B4------------
|On the outside now then |
After---------
| and now (for a while) we are out again.|
----------
$