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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  <style>.highlight{background-color: yellow}</style>
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  <script type="text/javascript" src="/js/jquery.js"></script>
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</head>
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​
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<body>
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  <p><span>Look:</span> <span>This is some text in a paragraph.</span> <span>This is a note about it.</span></p>
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  <script>$("p span").first().addClass('highlight');</script>
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</body>
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</html>
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​