NOTE CLASS OR MODULE? [R4R page 175]

When you see a construct like :
ActionController::Routing::Route
you can’t tell from that construct what’s a class and what’s a module. If there’s a call to new, you can be pretty sure the last element in the chain is a class, but otherwise the last element could be any constant—class, module, or other—and the elements on the left could be either classes or modules. In many cases, the fact that you can’t tell classes from modules in this kind of context doesn’t matter; what matters is the nesting or chaining of names in a way that makes sense. That’s just as well, because
you can’t tell what’s what without looking at the source code or the documentation. This is a consequence of the fact that classes are modules—the class Class is a subclass of the class Module—and in many respects (with the most notable exception being the fact that classes can be instantiated), their behavior is similar.