Well, I went truding around and I found these:

This first one was from a client who accidentally did something like: s/\n//g; to a few hundred text files. The files happened to be lists:

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)
[download]

which turned into:

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

Anyways, it was my job to fix them. I was having a difficult time correctly parsing, but ended up solving the problem using your sexeger technique.

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

A few weeks later, for fun, I was able to solve the problem using a forward regex:

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

Which is exponentially uglier, and proves just how useful sexeger really is.

Another possibly useful example is a dealing from irc, where the person needed to perform a crude form escaping that involved stripping all backslashes that were between brackets. This solved his problem:

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

Finally, theres a bunch of stuff at the end of Parsing with Perl 6 you might find useful...

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