code: def values(self):
          
          return [self.policy.header_fetch_parse(k, v)
                  for k, v in self._headers]
docs: Return a list of all the message's header values.
  
          These will be sorted in the order they appeared in the original
          message, or were added to the message, and may contain duplicates.
          Any fields deleted and re-inserted are always appended to the header
          list.