def get_cursor_down_position(self, count=1, preferred_column=None):
        """
        Return the relative cursor position (character index) where we would be if the
        user pressed the arrow-down button.

        :param preferred_column: When given, go to this column instead of
                                 staying at the current column.
        """
        assert count >= 1
        column = self.cursor_position_col if preferred_column is None else preferred_column

        return self.translate_row_col_to_index(
            self.cursor_position_row + count, column) - self.cursor_position
Return the relative cursor position (character index) where we would be if the
        user pressed the arrow-down button.

        :param preferred_column: When given, go to this column instead of
                                 staying at the current column.