Consider the specialization hierarchy for a reference topic.

下图是一个引用主题的专门化层次结构。

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Define the specialization hierarchy for the element with class attribute.

为具有class属性的元素定义专门化层次结构。

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Each level of specialization has its own set of class attributes, which in the end provide the full specialization hierarchy for all specialized elements.

每个层次的专门化都有自己的一组class属性，最终提供了所有专门化元素的专门化层次结构。

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