Add a header that tells Internet Explorer (all versions) to use the best available standards support. This ensures that IE doesn't go into quirks mode because it has been blacklisted by too many users pressing the incompatible button. It also tells IE to use the ChromeFrame renderer, if the user has installed the plugin.

This guarantees that the best available standards support will be used on the client.

Author: wycats

actionpack/lib/action_dispatch.rb

@@ -47,6 +47,7 @@ module ActionDispatch
   end
 
   autoload_under 'middleware' do
+    autoload :BestStandardsSupport
     autoload :Callbacks
     autoload :Cookies
     autoload :Flash

actionpack/lib/action_dispatch/railtie.rb

@@ -7,10 +7,11 @@ class Railtie < Rails::Railtie
     config.action_dispatch.x_sendfile_header = ""
     config.action_dispatch.ip_spoofing_check = true
     config.action_dispatch.show_exceptions = true
+    config.action_dispatch.best_standards_support = true
 
     # Prepare dispatcher callbacks and run 'prepare' callbacks
     initializer "action_dispatch.prepare_dispatcher" do |app|
       ActionDispatch::Callbacks.to_prepare { app.routes_reloader.execute_if_updated }
     end
   end
-end
+end

railties/lib/rails/application.rb

@@ -205,6 +205,7 @@ def default_middleware_stack
         middleware.use ::ActionDispatch::ParamsParser
         middleware.use ::Rack::MethodOverride
         middleware.use ::ActionDispatch::Head
+        middleware.use ::ActionDispatch::BestStandardsSupport if config.action_dispatch.best_standards_support
       end
     end
 

railties/lib/rails/commands.rb

@@ -70,4 +70,4 @@
 
 All commands can be run with -h for more information.
   EOT
-end
+end

railties/lib/rails/engine/configuration.rb

@@ -50,4 +50,4 @@ def autoload_paths
       end
     end
   end
-end
+end

railties/test/application/routing_test.rb

@@ -40,6 +40,7 @@ def index
 
       get '/foo'
       assert_equal 'foo', last_response.body
+      assert_equal "IE=Edge,chrome=1", last_response.headers["X-UA-Compatible"]
     end
 
     test "simple controller with helper" do