案例：jQuery案例     状态：可编辑再运行    进入竖版
 运行结果　
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<!DOCTYPE html>
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<html>
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<head>
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<script type="text/javascript" src="/js/jquery.js"></script>
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</head>
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<body>
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<ul class="level-1">
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  <li class="item-i">I</li>
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  <li class="item-ii">II
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    <ul class="level-2">
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      <li class="item-a">A</li>
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      <li class="item-b">B
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        <ul class="level-3">
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          <li class="item-1">1</li>
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          <li class="item-2">2</li>
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          <li class="item-3">3</li>
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        </ul>
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      </li>
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      <li class="item-c">C</li>
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    </ul>
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  </li>
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  <li class="item-iii">III</li>
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</ul>
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<script>$('ul.level-2').children().css('background-color', 'red');</script>
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</body>
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</html>
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​