ruby on rails - Same controller name in two different directories

Question

From 'Agile Web Development with Rails 4' pag.272.

If an incoming request has a controller named (say) admin/book, Rails will look for the controller called book_controller in the directory app/controllers/admin. That is, the final part of the controller name will always resolve to a file called name_controller.rb, and any leading path information will be used to navigate through subdirectories, starting in the app/controllers directory.

Imagine that our program has two such groups of controllers (say, admin/xxx and content/xxx) and that both groups define a book controller. There’d be a file called book_controller.rb in both the admin and content subdirectories of app/controllers. Both of these controller files would define a class named BookController. If Rails took no further steps, these two classes would clash. To deal with this, Rails assumes that controllers in subdirectories of the directory app/controllers are in Ruby modules named after the subdirectory.

My question is: how could the two book_controller.rb files clash?
I have two different URLs: ..../admin/book and ..../content/book, how can they clash? In the previous paragraph it explicit says

[..] any leading path information will be used to navigate through subdirectories, starting in the app/controllers directory

Answer 1

The file names do not matter. What matter are the constant names.

It's totally okay to have two files with identical names, like controllers/admin/books_controller.rb, and controllers/books_controller.rb.

However, the class names inside those controller should be different. You can add namespace to differentiate them. For example

class Admin::BooksController

class BooksController