module_scope.rb

module Foo
  class Bar;end
end

module Foo
  class Baz
    # lookup order: Foo::Baz::Bar, Foo::Bar, Bar
    Bar.new # => #<Foo::Bar:...>
  end
end

class Foo::Baz
  # Note that here it skips lookup for Foo::Bar. This is because
  # we are not in the Foo namespace, only in the Foo::Baz namespace

  # lookup order: Foo::Baz::Bar, Bar
  Bar.new # => NameError: uninitialized constant Foo::Baz::Bar
end