Hi,

In message "[ruby-talk:7604] Any corrections for Programming Ruby"
    on 00/12/19, Dave Thomas <Dave / PragmaticProgrammer.com> writes:
>We just heard that there's going to be a second printing of
>Programming Ruby, and AWL need all corrections by Wednesday (thanks
>for the notice, guys ;-)
>
>So, apart from the errata at
>
>  http://www.pragmaticprogrammer.com/ruby/errata.html

I found another one.

on P.520-521

  ((:index term:))
is not a target of cross reference. It is a term for `Index' which your
book have at the end of it. (i.e. something like \index{...} of LaTeX.)

The reason why RD have such a feature is mostly historical one.
I think, you can omit its explanation.

---
Tosh
Toshiro Kuwabara