public function scopeByTagNames($query, $tag_names)
	{
		$normalize_tag_names = [];
		foreach ($tag_names as $tag_name) {
			// mormalize string
			$normalize_tag_names[] = app(TaggingUtility::class)->normalizeTagName(trim($tag_name));
		}
		return $query->whereIn('name', $normalize_tag_names);
	}