public function add($data = null) {
		if (is_array($data)) {
			foreach ($data as $elem) {
				$this->add($elem);
			}
		} else {
			$guid = $this->toGUID($data);
			if ($guid) {
				array_push($this->guids, $guid);
				sort($this->guids);
			}
		}
		return $this;
	}