from the default `/usr/etc` (of the same deployment) are retained.
- Files in the currently booted deployment's `/etc` which were not
modified from the default `/usr/etc` (of the same deployment) are
- upgraded to the new defaults from the new deployment's `/etc/etc`.
+ upgraded to the new defaults from the new deployment's `/usr/etc`.
Roughly, this means that as soon as you modify or add a file in `/etc`,
this file will be propagated forever as is (though there is a