The base type roles are all abstract and should not be used in content.

基本类型角色都是抽象的，并且不应在内容中使用。

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Metadata types are those that specific content types aggregate with the base types to provide specific, well-known properties that are specific to a type of content.

元数据类型是特定内容类型与基础类型聚合的类型，提供特定于某类内容的特定属性。

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If you need to allow more content structures than the base types allow, you can specialize directly from topic, or form your own base type.

如果您需要比基本类型允许还要多的内容结构，可以直接从topic专门化或形成您自己的基类型。

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