On the virtual disks page: https://www.freebsd.org/doc/handbook/disks-virtual.html
Multiple ways of calling newfs are used, one using the -U (softupdates) flag and one not. Additionally, neither use the -n (no snapshots) flag.
There is also a typo where the copy says "This example creates an empty 5K file named newimage" but then goes on to describe commands to create a 5MB file.
A commit references this bug:
Date: Sun Dec 23 15:31:49 UTC 2018
New revision: 52711
Make the format of memory-backed disks consistent (soft-updates)
Correct size of file-backed disk
Submitted by: Hugh O'Brien
I agree on consistency, but I don't think disabling snapshots is a good thing to recommend on this, because the most common use cases are going to be for much larger memdisks. I've committed two of your suggestions. Thanks!
Thank you, for reference I suggested disabling snaps due to the following man page entry.
-n Do not create a .snap directory on the new file system. The
resulting file system will not support snapshot generation, so
dump(8) in live mode and background fsck(8) will not function
properly. The traditional fsck(8) and offline dump(8) will work
on the file system. This option is intended primarily for memory
or vnode-backed file systems that do not require dump(8) or
*** Bug 223248 has been marked as a duplicate of this bug. ***