Rails put validation in a module mixin?

module Validations
  extend ActiveSupport::Concern

  included do
    validates :name, :length => { :minimum => 2 }, :presence => true, :uniqueness => true
    validates :name_seo, :length => { :minimum => 2 }, :presence => true, :uniqueness => true
  end
end

The validates macro must be evaluated in the context of the includer, not of the module (like you probably were doing).