基础类型定义所有其他类型从中扩展的核心类型，并提供内容支持的所有通用属性。

Base types define the core types from which all other types extend, and provide all common properties that the content will support.

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增加兼容性：核心的信息类型能够集中维护，用所有专门类型反映到核心类型的变化。

Increases compatibility: the core information types can be centrally maintained, and changes to the core types are reflected in all specializing types.

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第一个插件打包了两个资产——前面章节中提到的概要文件和一个数据类型库——它是一个核心类型的模型，经常在Objective-C编程中被用到。

The first plug-in packages two assets -- the profile introduced in the previous section and a data type library -- and is a model of core types commonly used in Objective-C programming.

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