/**
  * PROPERCASE
  *
  * Converts a string value to upper case.
  *
  * @param	string		$mixedCaseString
  * @return	string
  */
 public static function PROPERCASE($mixedCaseString)
 {
     $mixedCaseString = PHPExcel_Calculation_Functions::flattenSingleValue($mixedCaseString);
     if (is_bool($mixedCaseString)) {
         $mixedCaseString = $mixedCaseString ? PHPExcel_Calculation::getTRUE() : PHPExcel_Calculation::getFALSE();
     }
     return PHPExcel_Shared_String::StrToTitle($mixedCaseString);
 }