> >   | rdoc --main maindocpage rex.rb  |
> Without telling rdoc what files to treat as "main", you may be surprised
> which file it picks if you have more than one.

According to the Pickaxe3, there is a :main: directive that can be
used instead of the command line. IIRC the rdoc that shipped with ruby
1.8.7 didn't support that directive though.