Rails 3.0: ActionController::Base render()

Can anyone explain where render() comes from in
I managed to trace it down only that far:
ActionController::Base includes ActionController::Rendering where
render() method is defined. This definition however calls to render of
the superclass. Superclass is ActionController::Metal. Which in its
turn inherits from AbstractController::Base. None of those have render
() either defined or included.

Now, presumably it comes from AbstractController::Rendering, but I’m
really missing how it gets included.