template_exempt_from_layout?

# File actionpack/lib/action_controller/base.rb, line 1201
      def template_exempt_from_layout?(template_name = default_template_name)
        extension = @template.pick_template_extension(template_name) rescue nil
        name_with_extension = !template_name.include?('.') && extension ? "#{template_name}.#{extension}" : template_name
        extension == :rjs || @@exempt_from_layout.any? { |ext| name_with_extension =~ ext }
      end