code: def update(self, desc=None, **kwds):
          
          sections.update(self._desc, desc, **kwds)
docs: This method updates the description much like dict.update(), *except*:
  
          1. for description which have dictionary values, it uses update
             to alter the existing value and does not replace them.
  
          2. `None` is a special value that means "clear section to default" or
             "delete field".