diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb
index d1b10a9281..6302491c2a 100644
--- a/actionpack/lib/action_view/helpers/form_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_helper.rb
@@ -213,12 +213,22 @@ module ActionView
       #     ...
       #   <% end %>
       #
-      # And for namespaced routes, like +admin_post_url+:
+      # For namespaced routes, like +admin_post_url+:
       #
       #   <%= form_for([:admin, @post]) do |f| %>
       #    ...
       #   <% end %>
       #
+      # If your resource has associations defined, for example, you want to add comments 
+      # to the post given that the routes are set correctly:
+      #
+      #   <%= form_for([@document, @comment]) do |f| %>
+      #    ...
+      #   <% end %>
+      #
+      # Where +@document = Document.find(params[:id])+ and
+      # +@comment = Comment.new+.
+      #
       # === Unobtrusive JavaScript
       #
       # Specifying: