提供者包含类别（规则或者其他类别的松散组织，或者两者皆有）。
Providers contain categories, which are loose organizations of rules or other categories, or both.
以至少与包含类别相同的可视性，将扩充方法实作为静态方法。
Implement the extension method as a static method with at least the same visibility as the containing class.
管理员和编写者创建一个包含类别、术语和已经分类的对象的逻辑结构。
Administrators and authors create a logical structure of categories, terms, and classified objects.
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