The maximum string length is 255 due to the Excel 5 format which is
still used. The long_string.pl example coming with
SpreadSheet::WriteExcel does not work for some reason. It must be
figured out why.

Volker Sauer has reported that sheet names in Excel files generated by
php_writeexcel get prepended with ".xls]" when he renames them, but I
can't reproduce it. If you can, please send me the generated file and
the version number of Excel you are using.
