public function quoteListOfInt($list, string $delimiter, string $enclosure, string $escape): string
  {
    if ($list===null || $list===false || $list==='' || $list===[])
    {
      return 'null';
    }

    $ret = '';
    if (is_scalar($list))
    {
      $list = str_getcsv($list, $delimiter, $enclosure, $escape);
    }
    elseif (is_array($list))
    {
      // Nothing to do.
      ;
    }
    else
    {
      throw new RuntimeException("Unexpected parameter type '%s'. Array or scalar expected.", gettype($list));
    }

    foreach ($list as $number)
    {
      if ($list===null || $list===false || $list==='')
      {
        throw new RuntimeException('Empty values are not allowed.');
      }
      if (!is_numeric($number))
      {
        throw new RuntimeException("Value '%s' is not a number.", (is_scalar($number)) ? $number : gettype($number));
      }

      if ($ret) $ret .= ',';
      $ret .= $number;
    }

    return $this->quoteString($ret);
  }