The autobackup property can have 3 values - child option?

[ozgurerdogan]

Dataset contains children dataset only? What else? So what is this option for?
child: Only backup the children off the dataset, not the dataset itself.

Is it to exclude if dataset has any mount points?

[psy0rz]

That was a typo in the documentation, should read 'only backup the childeren of the dataset, not the dataset itself'

So if you:
zfs set autobackup:test=child somepool/test

it will only backup somepool/test/* and not somepool/test

if you
zfs set autobackup:test=true somepool/test

then it will backup somepool/test as well as somepool/*

[ozgurerdogan]

Ok. Sometime I may need to create mountpoints like:
zfs create rpool/data/backups -o mountpoint=/P1BACKUP
To store iso files. So is this setting has anything to backup these iso file when using "true" ?