既然您已经了解了该模型的基本元素，那么，您还需要了解这些元素在CDT操作时是如何进行交互的。
Now that you know the basic elements of the model, you need to know how they interact during CDT operation.
当在“贡献”模型中被使用的时候，一个元素能够将新的内容添加到一个基本元素之中，而无需直接修改现任何一个已存在的性质。
When used through the "contribution" pattern, an element can add new content to a base element without directly modifying any of the existing properties.
专门化的内容模型必须同基本元素的内容模型一致。
The specialized content model must be consistent with the content model for the base element.
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