Baum\SetBuilder::scopedKey PHP Method

    protected function scopedKey($node)
    {
        $attributes = $this->scopedAttributes($node);
        $output = [];
        foreach ($attributes as $fld => $value) {
            $output[] = $this->qualify($fld) . '=' . (is_null($value) ? 'NULL' : $value);
        }
        // NOTE: Maybe an md5 or something would be better. Should be unique though.
        return implode(',', $output);
    }