Lower priority of RUN, so that TMPFS and especially the mount flags given with
`TemporaryFileSystem=` are used.
This allows making `/run` private with drop-ins such as:
```
[Service]
BindReadOnlyPaths=/run/systemd:/run/systemd:norbind
TemporaryFileSystem=/run:nodev,noexec,nosuid,rw,size=32k,nr_inodes=10,mode=0755
```
EMPTY_DIR,
SYSFS,
PROCFS,
- RUN,
READONLY,
READWRITE,
NOEXEC,
EXEC,
TMPFS,
+ RUN,
EXTENSION_IMAGES, /* Mounted outside the root directory, and used by subsequent mounts */
MQUEUEFS,
READWRITE_IMPLICIT, /* Should have the lowest priority. */