code: public static function builtInFormatCode($pIndex)
      {
          // Clean parameter
          $pIndex = (int) $pIndex;
  
          // Ensure built-in format codes are available
          self::fillBuiltInFormatCodes();
  
          // Lookup format code
          if (isset(self::$builtInFormats[$pIndex])) {
              return self::$builtInFormats[$pIndex];
          }
  
          return '';
      }
docs: Get built-in format code.
  
  @param int $pIndex
  
  @return string