Writing a book on Modern Perl is nuts.

As the author of this post points out, there have been about twenty releases since Perl 5.6, when the book was published. Features like the "switch" and "state" keywords have been introduced. If you look away too quickly, another database interface crops up, or people are doing objects differently. Perl changes so often that writing about it is like trapping a unicorn.

It's impressive that users of a 25-year-old language are not afraid to improve upon it (with the caveat that it stays backwards compatible). But since I started using $OTHER_LANGUAGE I don't have to worry about keeping up to date because language features change twice a decade.