code: def _sanitize_position(self, pos, tree=None):
          
          if pos is not None:
              tree = tree or self._tree
              entry = self._lookup_entry(tree, pos)
              if isinstance(entry, Tree):
                  pos = pos + self._sanitize_position((entry.root,), tree=entry)
          return pos
docs: Ensure a position tuple until the result does not
          point to a :class:`Tree` any more.