public function getCollections($urnOrSuffix = null)
    {
        $knownUrns = [
            'contributor' => self::URN_CONTRIBUTOR,
            'property' => self::URN_PROPERTY,
            'series' => self::URN_SERIES,
            'topic' => self::URN_TOPIC,
        ];
        $urnOrSuffix = isset($knownUrns[$urnOrSuffix]) ? $knownUrns[$urnOrSuffix] : $urnOrSuffix;
        return $this->links('collection', $urnOrSuffix);
    }