code: public function invalidateSourceCacheTag(Contao\DataContainer $dc, array $tags)
  	{
  		$commentModel = Contao\CommentsModel::findByPk($dc->id);
  
  		if (null !== $commentModel)
  		{
  			$tags[] = sprintf('contao.comments.%s.%s', $commentModel->source, $commentModel->parent);
  		}
  
  		return $tags;
  	}
docs: Adds the cache invalidation tags for the source.
  
  @param Contao\DataContainer $dc
  @param array                $tags
  
  @return array