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.