code: def do_macro_arg(parser, token):
      
      # macro_arg takes no arguments, so we don't
      # need to split the token/do validation.
      nodelist = parser.parse(('endmacro_arg',))
      parser.delete_first_token()
      # simply save the contents to a MacroArgNode.
      return MacroArgNode(nodelist)
docs: Function taking a parsed template tag
      to a MacroArgNode.