When the user is done and closes the document, the application is faced with a decision: whether to replace the original on disk with the changed copy from memory, or to discard the altered copy.

• 当用户完成对文档的修改并且关闭文档时，程序面临两种选择，即是用内存中的复制取代硬盘上的原始复制，还是放弃修改的复制?