code: def _highlight_digraph(self, cli, new_screen):
          
          digraph_char = self._get_digraph_char(cli)
          if digraph_char:
              cpos = new_screen.cursor_position
              new_screen.data_buffer[cpos.y][cpos.x] = \
                  _CHAR_CACHE[digraph_char, Token.Digraph]
docs: When we are in Vi digraph mode, put a question mark underneath the
          cursor.