code: def visit_object(self, node):
          
          if current_app.debug:
              return tags.comment('no implementation in {} to render {}'.format(
                  self.__class__.__name__,
                  node.__class__.__name__, ))
          return ''
docs: Fallback rendering for objects.
  
          If the current application is in debug-mode
          (``flask.current_app.debug`` is ``True``), an ``<!-- HTML comment
          -->`` will be rendered, indicating which class is missing a visitation
          function.
  
          Outside of debug-mode, returns an empty string.