一个类别还拥有一个唯一的ID，它被其他类别和规则用来决定控制。

A category also has a unique ID, which is used by other categories and rules to determine containment.

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这个类别有3个属性：owner、document title和case ID。

This class has three properties: owner, document title, and case ID.

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在 updateGUI() 内，"Bookstore_sublink" + index 是此类别链接的 ID。"

Inside updateGUI(), "Bookstore_sublink" + index is the ID of the category link.

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