void Format::setUnderline ( 
      
       integer $underline
      
     )
Sets the underline of the text
        integer $underline -
        The value for underline. Possible values are
                          1 => underline, 2 => double underline.
       
This function can not be called statically.
Using setUnderline()
<?php
require_once 'Spreadsheet/Excel/Writer.php';
  $workbook = new Spreadsheet_Excel_Writer();
  $format_underline =& $workbook->addFormat();
  $format_underline->setUnderline(1);
  $worksheet =& $workbook->addWorksheet();
  $worksheet->write(0, 0, "This is underlined", $format_underline);
  $format_underline->setUnderline(2);
  $worksheet->write(1, 0, "This is twice underlined", $format_underline);
?>