/**
* Add `AdSystem` element to `Ad' element
*
* @param string $adSystem
* @return \Sokil\Vast\Ad\InLine|\Sokil\Vast\Ad\Wrapper
*/
public function setAdSystem($adSystem)
{
$adSystemDomElement = $this->domElement->getElementsByTagName('AdSystem')->item(0);
if ($adSystemDomElement) {
$adSystemDomElement->nodeValue = $adSystem;
} else {
$adSystemDomElement = $this->domElement->ownerDocument->createElement('AdSystem', $adSystem);
$this->domElement->firstChild->appendChild($adSystemDomElement);
}
return $this;
}
