code: public function custom ()
  	{
  		$this->_createDocument();
  		$sitemapData = $this->getSitemap();
  
  		if (!array_key_exists('customUrls', $sitemapData))
  			return $this->_document->saveXML();
  
  		foreach ($sitemapData['customUrls'] as $custom) if ($custom->enabled)
  		{
  			$url = $this->_document->createElement('url');
  			$loc = $this->_document->createElement(
  				'loc',
  				UrlHelper::url($custom->url)
  			);
  			$frequency = $this->_document->createElement(
  				'changefreq',
  				$custom->frequency
  			);
  			$priority = $this->_document->createElement(
  				'priority',
  				$custom->priority
  			);
  
  			$url->appendChild($loc);
  			$url->appendChild($frequency);
  			$url->appendChild($priority);
  
  			$this->_urlSet->appendChild($url);
  		}
  
  		return $this->_document->saveXML();
  	}
docs: -------------------------------------------------------------------------