code: def _connect_begin_to(self, shape, cxn_pt_idx):
          
          cNvCxnSpPr = self._element.nvCxnSpPr.cNvCxnSpPr
          stCxn = cNvCxnSpPr.get_or_add_stCxn()
          stCxn.id = shape.shape_id
          stCxn.idx = cxn_pt_idx
docs: Add or update a stCxn element for this connector that connects its
          begin point to the connection point of *shape* specified by
          *cxn_pt_idx*.