I found your post while trying to solve one of my own problems at (??{ code }) versus (?PARNO) for recursive regular expressions. Anyway, in that process, I solved your original problem using both (??{ code }) and (?PARNO) which had not been introduced at the time of your question. I'm therefore just sharing them here in case anyone else happens by this thread.

#!/usr/bin/perl

use strict;
use warnings;

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

our $parno_re = qr{
    (
    \(
    (?: (?>[^()]+) | (?-1) )*
    \)
    )
}x;

while (<DATA>) {
    chomp;
    print /^(?:(?>[^()]+)|$code_re)*$/  ?  'PASS' :  '    ';
    print /^(?:(?>[^()]+)|$parno_re)*$/ ? ' PASS' : '     ';
    print " $_\n";
}

__DATA__
+ Cont(ains balanced( nested Br(ack)ets )in t)he text
- Con(tains i(mbalan(ced Br(ack)ets, )one c)lose missing
- Contains i(mbalan(ced Br(ack)ets, )one op)en m)missing
+ No brackets in this string
- Won)ky br(ackets in) this s(tring
- More wonky br(ackets in) th)is s(tring
- Just the one( leading bracket
- And just th)e one trailing bracket
+ So(me m(ultip)le n(est(s in) thi)s o)ne
+ Ther(e is( mo(re) de(e)p )nes(ti(n(g i)n (mul)ti)p(l)es) he)re
+ Some d((oub)le b)rackets
+ ab(())cde
+ ab()()cde
- ab(c(d)e
- ab(c)d)e
[download]

Output

PASS PASS + Cont(ains balanced( nested Br(ack)ets )in t)he text
          - Con(tains i(mbalan(ced Br(ack)ets, )one c)lose missing
          - Contains i(mbalan(ced Br(ack)ets, )one op)en m)missing
PASS PASS + No brackets in this string
          - Won)ky br(ackets in) this s(tring
          - More wonky br(ackets in) th)is s(tring
          - Just the one( leading bracket
          - And just th)e one trailing bracket
PASS PASS + So(me m(ultip)le n(est(s in) thi)s o)ne
PASS PASS + Ther(e is( mo(re) de(e)p )nes(ti(n(g i)n (mul)ti)p(l)es) h
+e)re
PASS PASS + Some d((oub)le b)rackets
PASS PASS + ab(())cde
PASS PASS + ab()()cde
          - ab(c(d)e
          - ab(c)d)e
[download]

I also attempted to get the tracking of captured groups working like ikegami and others demonstrated. I can't think of a way to get it to work with (?PARNO). However, I did get a working solution using (??{ code }). The biggest problem I noticed with your doubling of results was that you didn't have enough (?> ) sections to avoid backtracking.

our @matches;

our $code_re;
$code_re = qr{
    (
    \(
    (?: (?>[^()]+) | (??{$code_re}) )*
    \)
    )
    (?{ push @matches, $1 })
}x;


while (<DATA>) {
    chomp;
    @matches = ();
    print /^(?:(?>[^()]+)|$code_re)*$/  ?  'PASS' : (@matches = (), ' 
+   ');
    print " $_\n";
    print "       $_\n" foreach @matches;
}
[download]

It might be an interesting challenge to get the results to print out aligned with where they're captured. But this was the limit of the goofing off I'm going to do for now :).

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