$ sudo gem install builder
Bulk updating Gem source index for: http://gems.rubyforge.org
Successfully installed builder-2.0.0
Installing ri documentation for builder-2.0.0...
While generating documentation for builder-2.0.0
... MESSAGE:   Unhandled special: Special: type=17, text="<!-- HI -->"
... RDOC args: --ri --op /usr/local/lib/ruby/gems/1.8/doc/builder-2.0.0/ri --title Builder -- Easy XML Building --main README --line-numbers --quiet lib README Rakefile CHANGES doc/releases/builder-1.2.4.rdoc doc/releases/builder-2.0.0.rdoc
(continuing with the rest of the installation)
Installing RDoc documentation for builder-2.0.0...