I can do
sudo gem rdoc activerecord --no-ri
and
sudo gem rdoc actionpack --no-ri
both of which give me good docs.
But
sudo gem rdoc rails --no-ri
gives me pretty much nothing, as the Rails gem itself is really just a holder for the others. How can I generate the equivalent of http://api.rubyonrails.org/?
The easiest I found was to just download them from railsapi.com and unpack the file into /Library/Ruby/Gems/1.8/doc/rails-2.3.3/rdoc/