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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<iframe src="/example/html/frame_a.html" name="iframe_a">
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  <p>Your browser does not support iframes.</p>
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</iframe>
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<a href="//www.w3xue.com" target="iframe_a">W3xue.com</a>
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</body>
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</html>