docs: def pop(self, key, default=UNSET):
          """Remove the first key-value pair with key *key*.
  
          If a pair was removed, return its value. Otherwise if *default* was
          provided, return *default*. Otherwise a ``KeyError`` is raised.
          """
          self._find_lt(key)
          node = self._path[0][2]
          if node is self._tail or key < node[0]:
              if default is self.UNSET:
                  raise KeyError('key {!r} not in list')
              return default
          self._remove(node)
          return node[1]