The currently available Mastering Regular Expressions doesn't cover any of the really cool Perl 5 regex stuff. Jeffrey Friedl is in the process of rewriting the book for a second edition, and has been working with the Perl developers to uncover inconsistencies in the implementation (what normal people would call "bugs" {grin}) and gaps in the documentation.

Don't hold your breath though. I know this effort will probably take one to two years of nights and weekends. "Been there Done that" x $n

-- Randal L. Schwartz, Perl hacker