protected function marshall(QtiComponent $component)
    {
        $element = self::getDOMCradle()->createElement('colgroup');
        $this->setDOMElementAttribute($element, 'span', $component->getSpan());

        foreach ($component->getContent() as $col) {
            $marshaller = $this->getMarshallerFactory()->createMarshaller($col);
            $element->appendChild($marshaller->marshall($col));
        }

        $this->fillElement($element, $component);

        return $element;
    }