docs: def _clone_node(self) -> 'Tag':
          """Need to copy class, not tag.
  
          So need to re-implement copy.
          """
          clone = type(self)()
          for attr in self.attributes:
              clone.setAttribute(attr, self.getAttribute(attr))
          for c in self.classList:
              clone.addClass(c)
          clone.style.update(self.style)
          # TODO: should clone event listeners???
          return clone