关于jquery $(':last－child')匹配问题

Question

<ul class="u">
<li> <span>1</span></li>
<li> <span>2</span></li>
<li> <span>3</span></li>
</ul>

$('ul li:last-child') 能匹配到
$('ul span:last-child') 匹配不到

why?

Answer 1

span不在同一个li里，彼此不是同级