default_layout_with_format

# File actionpack/lib/action_controller/layout.rb, line 209
        def default_layout_with_format(format, layout)
          list = layout_list
          if list.grep(%r{layouts/#{layout}\.#{format}(\.[a-z][0-9a-z]*)+$}).empty?
            (!list.grep(%r{layouts/#{layout}\.([a-z][0-9a-z]*)+$}).empty? && format == :html) ? layout : nil
          else
            layout
          end
        end