这一节还演示了如何将置换组与抽象元素结合使用，以便构建XML模板。

This section also demonstrates the use of abstract elements with substitution groups to build an XML template.

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置换组是可兼容内容模型交换元素的机制。

Substitution groups are a mechanism for swapping elements of compatible content models with each other.

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也许扩展NIEM最容易的方式是通过使用置换组来做到，置换组允许您声明自己的元素和指定它是NIEM元素的替代。

Perhaps the easiest way to extend NIEM is through the use of substitution groups, which allow you to declare your own element and specify that it is substitutable for a NIEM element.

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