(http://www.ruby-lang.org/en/news/2013/02/24/ruby-2-0-0-p0-is-released/)
Documentation
We have also made documentation improvements which many rubyists have requested. We have added a huge amount of rdoc for modules and methods. 2.0.0 will be around 75% documented while 1.9.3 was about 60%. Also, we have added a description of Ruby's syntax. You can see:
ri ruby:syntax