Rails allows to extend the class you're including a module in. Basic techniques are described in http://api.rubyonrails.org/classes/ActiveSupport/Concern.html#method-i-included
This allows to "set up" a module, like
module Foo
extend ActiveSupport::Concern
included do
# Within this area "self" now refers to the class in which the module is included
# Every method you now call is called agains the class
# As such you can now write things like
validates_inclusion_of ...
define_method ...
end
end