parse_extensions

# File actionpack/lib/action_view/template.rb, line 239
      def parse_extensions(extensions)
        exts = extensions.split(".")

        if extension = valid_extension?(exts.last) && exts.pop || nil
          locale = valid_locale?(exts.first) && exts.shift || nil
          format = exts.join('.') if exts.any? # join('.') is needed for multipart templates
        else # no extension, just format
          format = exts.last
        end

        [locale, format, extension]
      end