protected function getOpf() {

		$container_xml = $this->getZipContent( 'META-INF/container.xml' );
		$content_path = $container_xml->rootfiles->rootfile['full-path'];

		$base = dirname( $content_path );
		if ( '.' !== $base ) {
			$this->basedir = "$base/";
		}

		return $this->getZipContent( $content_path );
	}