use strict;
use warnings;

my $textInner =
  '(outer(inner(most "this (shouldn\'t match)" inner)))';
my $innerRe;
my $idx=0;
my(@match);

$innerRe = qr/
                \(
                (
                   (?:
                      [^()"]+
                   |
                      "[^"]*"
                   |
                      (??{$innerRe})
                   )*
                )
                \)(?{$match[$idx++]=$1;})
             /sx;

$textInner =~ /^$innerRe/g;

print "inner: $match[0]\n";