These are equiv.

  class Base
    def self.ameth
      # ...
    end
  end


  class Base
    class << self
      def ameth
        # ...
      end
    end
  end


  class Base; end
  class << Base
    def ameth
      # ...
    end
  end

  class Base; end
  def Base.ameth
    # ...
  end

They are all our ways to get into the
singletonclass/metaclass/ownclass/
eigenclass/whatever-you-want-to-call-it-class. For a class that's quite
useful b/c its were class methods reside, essentially the object that
*is* the class itself rather then its "instance level".

If that seems confusing, don't worry, it is ;-)

T.