module MyExtension

def registered(app, options={})
  # Setup extension-specific config
  app.set :config_variable, false
  
  # Include class methods
  # app.extend ClassMethods
  
  # Include instance methods
  # app.send :include, InstanceMethods
  
  app.after_configuration do
    # Do something
    
    # config_variable is now either the default or the user's 
    # setting from config.rb
  end
end