class里包含两个类，用less的嵌套怎么写呢？？

                        <div class="row row-wrap">
                            <div class="col-xs-9 xm-title ">
                                <span>SECRET系列的产品</span>
                            </div>
                            <div class="col-xs-3 xm-state-on">
                                <span>已付款</span>
                            </div>
                        </div>

像上边的row row-wrap怎么接下边的col-xs-9 xm-title呢？真心求教

---

. col-xs-9 {
    &.xm-title {
    }
}