1) foo and his friend bar
2) Stuff and more (stuff)
3) More (and30) more (and) more
4) garbage (8)
5) some other things
6) (7lalala)

##</code><code>##

1) foo and his friend bar2) Stuff and more (stuff)3) More (and30) more (and) more4) garbage (8)5) some other things6) (7lalala)

##</code><code>##

$text = reverse $copy;
$text =~
s/
    (?<= \) )
    (\d+)
    (?= [^()]* \) )
/$1\n/gx;
$text = reverse $text;

##</code><code>##

my $bal = # this is from perlre
qr/
    \(
    (?:
        (?> [^()]+ )
        |
        (??{$bal})
    )*
    \)
/x;
$text =~
s/
    (
        (?:
            (??{$bal})
            [^(\d]*
        )*
    )
    (\d+)
    (?= \) )
/$1\n$2/xg;

##</code><code>##

$text =~
s/
    (?<= \[ )
    ([^\]]*)
    (?= \] )
/ strip_slash($1) /gex;
sub strip_slash { $_=pop; s/\\//g; $_; }