public function taxonomy($var = null)
    {
        if ($var !== null) {
            // make sure first level are arrays
            array_walk($var, function(&$value) {
                $value = (array) $value;
            });
            // make sure all values are strings
            array_walk_recursive($var, function(&$value) {
                $value = (string) $value;
            });
            $this->taxonomy = $var;
        }

        return $this->taxonomy;
    }