code: def addClass(self, cn):
          '''Add the specific class names to the class set and return ``self``.
          '''
          if cn:
              if isinstance(cn, (tuple, list, set, frozenset)):
                  add = self.addClass
                  for c in cn:
                      add(c)
              else:
                  classes = self._classes
                  if classes is None:
                      self._extra['classes'] = classes = set()
                  add = classes.add
                  for cn in cn.split():
                      add(slugify(cn))
          return self addClass(self, cn):
          '''Add the specific class names to the class set and return ``self``.
          '''
          if cn:
              if isinstance(cn, (tuple, list, set, frozenset)):
                  add = self.addClass
                  for c in cn:
                      add(c)
              else:
                  classes = self._classes
                  if classes is None:
                      self._extra['classes'] = classes = set()
                  add = classes.add
                  for cn in cn.split():
                      add(slugify(cn))
          return self
docs: Add the specific class names to the class set and return ``self``.