BC mode allows certain automatic type conversions to occur, as well as automatic selection of the first member of a node-set.

BC模式允许进行某些自动类型转换和自动选择节点集的第一个成员。

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If the BC feature is available, you can set version 1.0 to be in effect for an element with expression evaluation, eliminating worry about type mismatches.

如果支持BC特性，可以设置version 1.0让它在表达式求值的元素中生效，这样就不用担心类型匹配问题了。

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BC mode impacts numeric comparisons in two ways: allowing selection of the first member of a set and obtaining NaN for a non-numeric value, rather than throwing a type error.

BC模式对数字比较的影响有两个方面：允许选择集合的第一个成员，对于非数字值返回NaN而不是抛出类型错误。

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