The XLS format is based on the BIFF8 specification. Full support of this format is realized starting with the Excel 9.0 (Excel 2000).
Excel 8.0 (Excel 97):
does not support correct color;
does not fully support the Right to Left mode.
Excel 7.0 (Excel 95) and earlier versions:
does not support vertical alignment in a cell;
does not support integrated cells;
does not support some other parameters.