lib/action_controller.rb

ああ、つまり、

37 require 'action_controller/base'
38 require 'action_controller/deprecated_redirects'
39 require 'action_controller/rescue'
40 require 'action_controller/benchmarking'
41 require 'action_controller/filters'
42 require 'action_controller/layout'
43 require 'action_controller/flash'
44 require 'action_controller/dependencies'
45 require 'action_controller/pagination'
46 require 'action_controller/scaffolding'
47 require 'action_controller/helpers'
48 require 'action_controller/cookies'
49 require 'action_controller/cgi_process'
50 require 'action_controller/caching'
51 require 'action_controller/components'
52 require 'action_controller/verification'
53 require 'action_controller/streaming'
54 require 'action_controller/session_management'
55 require 'action_controller/macros/auto_complete'
56 require 'action_controller/macros/in_place_editing'
57
58 require 'action_view'
59 ActionController::Base.template_class = ActionView::Base
60
61 ActionController::Base.class_eval do
62 include ActionController::Filters
63 include ActionController::Layout
64 include ActionController::Flash
65 include ActionController::Benchmarking
66 include ActionController::Rescue
67 include ActionController::Dependencies
68 include ActionController::Pagination
69 include ActionController::Scaffolding
70 include ActionController::Helpers
71 include ActionController::Cookies
72 include ActionController::Caching
73 include ActionController::Components
74 include ActionController::Verification
75 include ActionController::Streaming
76 include ActionController::SessionManagement
77 include ActionController::Macros::AutoComplete
78 include ActionController::Macros::InPlaceEditing
79 end

ということで、

1 module ActionController
2 # These methods are available in both the production and test Request objects.
3 class AbstractRequest
4 cattr_accessor :relative_url_root

なわけだ。（すいません、独り言です。）