若要解决此错误，请在函数或类型定义内声明 CLR 类型的变量。
To resolve this error, declare variables of CLR types inside a function or type definition.
简单性：通过使用单个head元素或类型定义来选择一组元素，使代码更加紧凑高效。
Simplicity: the code is more efficient and compact by using the single head element or type definition to select a group of elements.
简单性：程序可以使用这些节点测试，选择基于共同组head元素或类型定义的一组元素，而不是逐一列举所有具体的元素名。
Simplicity: the program can use these node tests to select a group of elements based on their common group head element or type definition rather than enumerate all concrete element names one by one.
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