code: def root_block(template_name=DEFAULT_TEMPLATE_NAME):
      
      def decorator(block_func):
          block = RootBlock(block_func, template_name)
          return block_func
      return decorator
docs: A decorator that is used to define that the decorated block function
      will be at the root of the block template hierarchy.  In the usual case
      this will be the HTML skeleton of the document, unless the template is used
      to serve partial HTML rendering for Ajax.
  
      The :func:`root_block` decorator accepts the following arguments:
  
      :param template_name: The name of the block template hierarchy which is
                            passed to the :func:`render_template` document
                            rendering function.  Different templates are useful
                            for rendering documents with differing layouts
                            (e.g. admin back-end vs. site front-end), or for
                            partial HTML rendering for Ajax.