code: public static function PROPERCASE($mixedCaseString)
      {
          $mixedCaseString = Functions::flattenSingleValue($mixedCaseString);
  
          if (is_bool($mixedCaseString)) {
              $mixedCaseString = ($mixedCaseString) ? Calculation::getTRUE() : Calculation::getFALSE();
          }
  
          return StringHelper::strToTitle($mixedCaseString);
      }
docs: PROPERCASE.
  
  Converts a string value to upper case.
  
  @param string $mixedCaseString
  
  @return string