这个魔法的中心是撤销和重做的能力。

At the heart of this magic is the ability to undo and redo.

youdao

在编辑、撤销和重做的过程中，模型是唯一保持不变的。

During the course of editing, undo, and redo, the model is the only thing that endures.

youdao

命令可用来验证用户的交互，并且提供撤销和重做支持。

Commands can be used to validate the user's interaction, and to provide undo and redo support.

youdao