### 返回值:Array<Element(s)>:first-child
### *V1.1.4*概述
匹配第一个子元素
':first' 只匹配一个元素，而此选择符将为每个父元素匹配一个子元素
### 示例
#### 描述:
在每个 ul 中查找第一个 li
##### HTML 代码:
~~~
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
<ul>
<li>Glen</li>
<li>Tane</li>
<li>Ralph</li>
</ul>
~~~
##### jQuery 代码:
~~~
$("ul li:first-child")
~~~
##### 结果:
~~~
[ <li>John</li>, <li>Glen</li> ]
~~~
- 速查表
- 核心
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