/**
* @return string
*/
public function getXmlString()
{
$str = '<items>%s</items>';
$itemsStr = [];
$iterator = $this->items->getIterator();
while ($iterator->valid()) {
$item = $iterator->current();
$itemsStr[] = $this->getItemXmlString($item);
$iterator->next();
}
return sprintf($str, implode('', $itemsStr));
}
