docs: def append(self, key, value=None, dir=False, ttl=None, timeout=None):
          """Requests to create an ordered node into a node by the given key."""
          url = self.make_key_url(key)
          data = self.build_args({
              'value': (six.text_type, value),
              'dir': (bool, dir or None),
              'ttl': (int, ttl),
          })
          try:
              res = self.session.post(url, data=data, timeout=timeout)
          except:
              self.erred()
          return self.wrap_response(res)