近些年来，磁盘空间变得异常便宜和丰富，但是网络带宽还没有，因此Subversion工作拷贝为紧缺资源进行了优化。
The .svn administrative directory
serves the same purpose as the CVS
directory, except that it also stores read-only,
“pristine” copies of your files. This allows you
to do much things offline:
显示你所做的本地修改(见“查看你的修改概况”一节)
显示修改的详细信息(见see “检查你的本地修改的详情”一节)
删除你的本地修改(见“取消本地修改”一节)
另外，原始文件的缓存允许Subversion客户端在提交时只提交区别，这是CVS做不到的。
The last subcommand in the list—svn revert—is new. It will not only remove local changes, but it will also unschedule operations such as adds and deletes. While deleting the file and then running svn update will still work, doing so distorts the true purpose of updating. And, while we're on this subject…