private function findAttrParams(Sco $sco, \DOMNode $item, \DOMNodeList $resources)
    {
        $identifier = $item->attributes->getNamedItem('identifier');
        $isVisible = $item->attributes->getNamedItem('isvisible');
        $identifierRef = $item->attributes->getNamedItem('identifierref');
        $parameters = $item->attributes->getNamedItem('parameters');

        // throws an Exception if identifier is undefined
        if (is_null($identifier)) {
            throw new InvalidScormArchiveException('sco_with_no_identifier_message');
        }
        $sco->setIdentifier($identifier->nodeValue);

        // visible is true by default
        if (!is_null($isVisible) && 'false' === $isVisible) {
            $sco->setVisible(false);
        } else {
            $sco->setVisible(true);
        }

        // set parameters for SCO entry resource
        if (!is_null($parameters)) {
            $sco->setParameters($parameters->nodeValue);
        }

        // check if item is a block or a SCO. A block doesn't define identifierref
        if (is_null($identifierRef)) {
            $sco->setBlock(true);
        } else {
            $sco->setBlock(false);
            // retrieve entry URL
            $sco->setEntryUrl($this->findEntryUrl($identifierRef->nodeValue, $resources));
        }
    }