# File lib/simple_form/action_view_extensions/builder.rb, line 100
      def simple_fields_for(*args, &block)
        options = args.extract_options!
        if self.class < ActionView::Helpers::FormBuilder
          options[:builder] ||= self.class
        else
          options[:builder] ||= SimpleForm::FormBuilder
        end
        fields_for(*(args << options), &block)
      end