Prefixes would be nice, but they appear to be very buggy.
A few examples:
- `udevadm test-builtin net_setup_link /sys<TAB><TAB>`: `/sysblock/`
- `udevadm test-builtin net_setup_link /sys/<TAB><TAB>`: `/sys/bin/`
- `journalctl /dev<TAB>`: `/dev//dev/`
