public function untag($tagNames=null)
    {
        if(is_null($tagNames)) {
            $tagNames = $this->tagNames();
        }

        $tagNames = static::$taggingUtility->makeTagArray($tagNames);

        foreach($tagNames as $tagName) {
            $this->removeTag($tagName);
        }

        if(static::shouldDeleteUnused()) {
            static::$taggingUtility->deleteUnusedTags();
        }
    }