Hi,
xmlns定义了应该解析XML元素名称的默认命名空间。你可以尝试参考以下文档：
WPF，Silverlight 中的 xmlns，xmlns:x
c#的xml文件中的 xmlns 和 xmlns:x
What is xmlns in every WPF file?
有关wpf我建议你到以下子论坛提问：
https://social.msdn.microsoft.com/Forums/zh-CN/home?forum=wpfzhchs
Regards,
Kyle
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