This feature is in the spec because OOXML is not a document interchange format; it's a careful, bit-for-bit, replication of Microsoft's historical binary formats, wrapped up in Angle brackets.

这个特性之所以出现在规范中，是因为OOXML并不是一个文档交换格式；而是对Microsoft以前的二进制格式的精确重复，只不过用尖括号括起来而已。

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