I assume that edge guides have edgeguides in the domain name (for example http://edgeguides.rubyonrails.org/getting_started.html), and that guides for older versions of Rails have the version in the path (for example http://guides.rubyonrails.org/v3.2/getting_started.html).
But when googling I came across http://guides.rubyonrails.org/migrations.html, which I assumed would be for the latest released version of Rails. But it redirected me to http://edgeguides.rubyonrails.org/active_record_migrations.html (the migrations page for the current version of Rails is http://guides.rubyonrails.org/active_record_migrations.html).
How does Rails Guides work with versions of Rails, and how do I correctly get the Rails Guides for the version of Rails I'm using?
Use the Rails Github.
You can view the Rails Guides for whichever branch you'd like from there.
Also - when you go to the Rails Guide website there are links to various versions of the Rails Guides including: