Add description of flash.now

railties/doc/guides/actioncontroller/session.txt

@@ -162,3 +162,24 @@ class MainController < ApplicationController
 
 end
 ------------------------------------------
+
+==== flash.now ====
+
+By default, adding values to the flash will make them available to the next request, but sometimes you may want to access those values in the same request. For example, if the `create` action fails to save a resource and you render the `new` template directly, that's not going to result in a new request, but you may still want to display a message using the flash. To do this, you can use `flash.now` in the same way you use the normal `flash`:
+
+[source, ruby]
+------------------------------------------
+class ClientsController < ApplicationController
+
+  def create
+    @client = Client.new(params[:client])
+    if @client.save
+      # ...
+    else
+      flash.now[:error] = "Could not save client"
+      render :action => "new"
+    end
+  end
+
+end
+------------------------------------------