code: def _history_buffer_pos_changed(self, _):
          
          # Only when this buffer has the focus.
          if self.app.current_buffer == self.history_buffer:
              line_no = self.history_buffer.document.cursor_position_row
  
              if line_no in self.history_mapping.selected_lines:
                  default_lineno = sorted(self.history_mapping.selected_lines).index(line_no) + \
                      self.history_mapping.result_line_offset
  
                  self.default_buffer.cursor_position = \
                      self.default_buffer.document.translate_row_col_to_index(default_lineno, 0)
docs: When the cursor changes in the history buffer. Synchronize.