code: public static function checkString($pValue)
      {
          if ($pValue instanceof RichText) {
              // TODO: Sanitize Rich-Text string (max. character count is 32,767)
              return $pValue;
          }
  
          // string must never be longer than 32,767 characters, truncate if necessary
          $pValue = StringHelper::substring($pValue, 0, 32767);
  
          // we require that newline is represented as "\n" in core, not as "\r\n" or "\r"
          $pValue = str_replace(["\r\n", "\r"], "\n", $pValue);
  
          return $pValue;
      }
docs: Check a string that it satisfies Excel requirements.
  
  @param null|RichText|string $pValue Value to sanitize to an Excel string
  
  @return null|RichText|string Sanitized value