类别只提供操作，不提供属性。
当然，在您开始实际使用并操作树时，您可能会发现这些类别的其他许多有趣的组合和扩展。
Of course, you may find many other curious combinations and extensions of these categories as you begin to use and manipulate trees in practice.
还可以使应用程序能够操作与库关联的类别。
It also enables applications to manipulate the categories associated with a library.
应用推荐