Rail's App structure in Gem?

I have been looking at the source of some Gems... Within some, I see
an App structure that emulates part of Rail's App structure, i.e,
Controller, Helpers, Models, Views etc....

How do Gem centric paths work when a Rails style App dir is part of a
Gem's design? Do paths to contollers and views created in the Gem
defer to it's App dir instead of the rails_root/app?

Any thoughts or links to useful resources are appreciated.

Thanks, Elliott