code: def _construct_connector(self, pos):
          
          # connector symbol, either L or |- shaped.
          connectorw = None
          connector = None
          if self._tree.next_sibling_position(pos) is not None:  # |- shaped
              if self._arrow_connector_tchar is not None:
                  connectorw = urwid.Text(self._arrow_connector_tchar)
          else:  # L shaped
              if self._arrow_connector_lchar is not None:
                  connectorw = urwid.Text(self._arrow_connector_lchar)
          if connectorw is not None:
              att = self._arrow_connector_att or self._arrow_att
              connector = urwid.AttrMap(connectorw, att)
          return connector
docs: build widget to be used as "connector" bit between the vertical bar
          between siblings and their respective horizontal bars leading to the
          arrow tip