Ah. Well, they can, but not in a way that would delete other items. In general, I'd suggest a 1:1 ratio between source and destination volumes. You want to dedicate the volume to the purpose of backing up, not mix things up.
Note that you can also use a sparse image to store a volume in a file that can be placed in a folder. The 'guide has info on that, too.
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--Dave Nanian
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