The self link is especially useful; if you ever end up with an Atom document that you didn't download yourself, this is your trail of breadcrumbs back to the canonical source.
self链接特别有用；如果有一个不是自己下载的Atom文档，那么通过该链接就可以回溯到规范来源。
2
(You can also embed the three final lines of the script in a loop, dynamically change SOURCE, and backup a series of separate directories on the same system.) Here's how the backup works.
(还可以把脚本的最后三行嵌入一个循环，动态地修改SOURCE，从而备份同一系统上的一系列目录)。
3
You should backup any data source before implementation is started.