Cool.

One bit of feedback on the typography: The book uses some characters that are not available in many fonts. For example, the THIN SPACE (U+2009) is used after :: in Perl::Identifiers::Like::This. I suspect your goal was typographic refinement, but the result, at least when the characters are not available, is exacly the opposite: the browser inserts a big, fat I-can't-find-that-character-in-the-font-so-I'll-use-this-boxy-all-purpose-placeholder glyph instead. The result looks pretty bad: Perl::[]Identifiers::[]Like::[]This.