private function parent($id, $indent, array $children, $level)
    {
        $realChildren = array_filter($children, array(__CLASS__, 'onlyBlockArgs'));

        if (empty($realChildren)) {
            return sprintf($this->prepare(self::PARENT_NO_CONTEXT, $level), var_export($id, true));
        }

        return sprintf(
            $this->prepare(self::PARENT, $level),
            var_export($id, true),
            $this->walk($realChildren, $level + 1)
        );
    }