案例：html/html5 案例     状态：可编辑再运行    进入竖版
 运行结果　
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<html>
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<body>
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​
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<h3>This is a header</h3>
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<p>This is a paragraph.</p>
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​
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<div style="color:#00FF00">
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  <h3>This is a header</h3>
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  <p>This is a paragraph.</p>
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</div>
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​
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</body>
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</html>
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​