How in depth does the new Ruby In Practice book cover JRuby?

I noticed on the website for the book that JRuby is covered in an appendix. If I wanted to use JRuby instead of "pure" Ruby, is this the book for me? Or is this book geared more toward "pure" Ruby?

Thanks!

Most of what we cover in the book applies to both standard Ruby (aka MRI Ruby) and JRuby. You'll be able to use the same code samples and libraries with both.

With JRuby you can also use Java libraries, or run Ruby scripts inside your Java application, so we cover that in a separate appendix. We also deal with deploying Ruby Web applications as WAR files.