可以通过从现有类型派生新的类型来满足这类需求。
You can meet some of these needs can be met by deriving types from existing ones, but not others.
联合数据类型必须从原子数据类型或列表数据类型派生。
A union data type must be derived from an atomic or list data type.
DITA包括三种从基本主题类型派生的信息类型：任务、概念和参考。
DITA includes three information types derived from the base topic type: task, concept, and reference.
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