public function getCommonMetadata($revision = null)
	{
		// Without revision, use current info
		if (!isset($revision)) {
			return $this->info['commonmetadata'];
		}

		// Obtain the properties of the revision
		if (($info = $this->getRevision($revision)) === null) {
			return null;
		}

		return $info['commonmetadata'];
	}