Ugh, again. Releasing an entire distribution of Perl along with the module is not an option for me. I was able to confirm that Leopard is 5.8.8, though. I'm going to make that the minimum requirement, because 5.8.6 had a known bug dealing with using substr on unicode strings
I reserve the right to reclaim 5.10 features once 5.10 is standard both on Debian Stable and MacOSX, however.