I was looking in the Rails source code, and during the call to form_for, it creates a new instance of FormBuilder and during the initialization, it checks if the options hash contains an index: @default_options = @options ? @options.slice(:index, :namespace) : {} When will the options hash to form_for ever contain an index? I''m not sure why the options hash would ever contain an index (all the options hash contains up to this point in the form_for call are the :html options and :url option). If you look at line 1196 of form_helper.rb from latest rails release on github, you''ll see that exact line a paste above: https://github.com/rails/rails/blob/master/actionpack/lib/action_view/helpers/form_helper.rb -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out.