Bug 80533

The handbook tells, for mounted filesystem snapshots, that
"Everything will be in the same state it was during the snapshot
creation time."

This is misleading. While the original snapshot will indeed have
the creation time contents, this may change after mounting it.
Users have the same permissions in the mounted snapshot filesystem
as they have in the "real" filesystem. Unless the snapshot is mounted
readonly, they can easily modify, delete or create files there. The
snapshot is in no way a "frozen" image of the snapshot creation time.

Fix: 

Change the "will be in the same state" sentence from the handbook to
"will initially be in the same state".
How-To-Repeat: I create a file as user "bernd", then take a snapshot as root, then
modify the snapshot's file as user.

$ cd /home/bernd
$ mkdir test
$ echo hello > test/file
$ cat test/file
hello
$ su -m
Password:
# mksnap_ffs /home /home/snap
# mdconfig -a -t vnode -f /home/snap
md12
# mount /dev/md12 /mnt
# cat /mnt/bernd/test/file
hello
# exit
$ echo world > /mnt/bernd/test/file
$ cat /mnt/bernd/test/file
world