Rails / Ruby documentation

Hi all !
As I’m new to Ruby and Rails, I often take a look at the Rails/Ruby
API. I don’t work with “plain” Ruby code and so I can’t distinguish
between methods provided by Ruby and those provided by Rails. I use
two API documentations: http://corelib.rubyonrails.org/ and
Create A Perfect Resume In 5 Minutes! | Online Resume Builder. My question is, if there is
some kind of merged documentation, which covers plain Ruby methods as
well as Rails. It’s very annoying to search a method in the Rails API,
not to find it and than search in the Ruby API.

Thank you very much in advance