The DOCTYPE declaration should always be the first line in an XHTML document.

文档声明必须出现在XHTML文档的首行。

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Your pages must have a DOCTYPE declaration if you want them to validate as correct XHTML.

如果你想使你的页面满足正确的XHTML的有效性你就必须使用DOCTYPE声明。

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Remember, you can use any of the XHTML document types as long as you include the full !DOCTYPE declaration.

请记住，只要包含全部 ! DOCTYPE 声明，就可以使用任何 XHTML 文档类型。

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