code: private function _createDocument ($withUrlSet = true)
  	{
  		// Create the XML Document
  		$document = new \DOMDocument('1.0', 'utf-8');
  
  		// Pretty print for debugging
  		if (\Craft::$app->config->general->devMode)
  			$document->formatOutput = true;
  
  		if ($withUrlSet)
  		{
  			$urlSet = $document->createElement('urlset');
  			$urlSet->setAttribute(
  				'xmlns',
  				'http://www.sitemaps.org/schemas/sitemap/0.9'
  			);
  			$urlSet->setAttribute(
  				'xmlns:xhtml',
  				'http://www.w3.org/1999/xhtml'
  			);
  			$document->appendChild($urlSet);
  			$this->_urlSet = $urlSet;
  		}
  
  		$this->_document = $document;
  	}
docs: Creates the XML document
  
  @param bool $withUrlSet - Will append the URLSet if true