protected function unmarshallChildrenKnown(DOMElement $element, QtiComponentCollection $children)
    {
        if (($figures = $this->getDOMElementAttributeAs($element, 'figures', 'string')) !== null) {

            if (!Format::isVariableRef($figures)) {
                $figures = intval($figures);
            }

            $object = new RoundTo($children, $figures);

            if (($roundingMode = $this->getDOMElementAttributeAs($element, 'roundingMode')) !== null) {
                $object->setRoundingMode(RoundingMode::getConstantByName($roundingMode));
            }

            return $object;
        } else {
            $msg = "The mandatory attribute 'figures' is missing from element '" . $element->localName . "'.";
            throw new UnmarshallingException($msg, $element);
        }
    }