private function errorHandler($level, $message)
    {
        Types::assert(
            ['int' => [$level], 'string' => [$message]]
        );

        if (error_reporting() & $level
            and (strtolower(ini_get('display_errors')) === 'on'
            and ini_get('display_errors'))
        ) {
            if ($level === E_USER_NOTICE)
            {
                $error = '<strong>Notice:</strong> ' .$message. "<br><br>\n\n";
            }
            elseif ($level === E_USER_WARNING)
            {
                $error = '<strong>Warning:</strong> ' .$message. "<br><br>\n\n";
            }

            if (isset($error))
            {
                echo $error;
                $this->errorString .= $error;
                return true;
            }
        }
        return false;
    }