add_format(%properties)
  The "add_format()" method can be used to create new Format objects which
  are used to apply formatting to a cell. You can either define the
  properties at creation time via a hash of property values or later via
  method calls.

      $format1 = $workbook->add_format(%props); # Set properties at creation
      $format2 = $workbook->add_format();       # Set properties later

  See the "CELL FORMATTING" section for more details about Format
  properties and how to set them.

##</code><code>##

  One problem with the "write()" method is that occasionally data looks
  like a number but you don't want it treated as a number. For example,
  zip codes or ID numbers often start with a leading zero. If you write
  this data as a number then the leading zero(s) will be stripped. You can
  change this default behaviour by using the "keep_leading_zeros()"
  method. While this property is in place any integers with leading zeros
  will be treated as strings and the zeros will be preserved. See the
  "keep_leading_zeros()" section for a full discussion of this issue.
 More  -- ...

##</code><code>##

 See the note about "Cell notation". The $format parameter is optional

 In general it is sufficient to use the "write()" method.

rite_string($row, $column, $string, $format)
 Write a string to the cell specified by $row and $column:

     $worksheet->write_string(0, 0, 'Your text here' );
     $worksheet->write_string('A2', 'or here' );