Mongoid Scope order by syntax please

I'm using the latest mongoid...

How do I do the mongoid equivalent of this active record named_scope:

class Comment
  include Mongoid::Document
  include Mongoid::Timestamps

  embedded_in :post

  field :body, :type => String

  named_scope :recent, :limit => 100, :order => 'created_at DESC'
...
end