ruby version: ruby 1.9.1p378
I used the commands presented below to install rdoc.
gem install rdoc
gem rdoc --all
However, I was not able to load rdoc/usage
irb(main):001:0> require ‘rdoc/usage’
LoadError: no such file to load – rdoc/usage
require' from (irb):1 from /usr/bin/irb:12:in’
Is there anything else that needs to be installed using gem?