These are instance methods being defined on the Group class, so they're executed in the context of an instance of the Group class.

class Group
  def foo
  end
end

> x = Group.new
> x.foo  # yah!

Class methods would looks something like this

class Group
  def self.bar
  end
end

> Group.bar #yah!


Here's a pretty good article on the matter: http://www.railstips.org/blog/archives/2009/05/11/class-and-instance-methods-in-ruby/