Few Fedora 20 ProjectAtomic VM questions

Hello all,
    I've been working with the Fedora 20 image from projectatomic.io for
the past few days off and on in preparation for a presentation I'm
giving on Friday and I had a few questions that popped up.

1) For the command 'ostree log REFSPEC', where do I find out what it
wants as a REFSPEC?

I tried a number of combinations of the output from 'ostree admin
status' but nothing I try seems to not error.

2) Does the latest version of the Fedora 20 projectatomic.io VM support
installing packages "on top" (for lack of a better phrasing) using yum?
Or is that still in the pipeline?

3) I'm curious about the output from findmnt, I'm seeing entries where
the source is /dev/vda3[some_stuff_in_brackets], I'm not familiar with
what that is or where it comes from and was hoping someone could provide
clarification.

Example:
-bash-4.2# findmnt
TARGET                           SOURCE     FSTYPE     OPTIONS
/                                /dev/vda3[/ostree/deploy/project-atomic-controller/deploy/6b6b1362241f1c658b54797b51c2215e32b0978f2201eeb7cd2068276adb9015.0]

I'm sure I'll come up with more questions in the future and would like
to apologize if this is line noise, but also offer some preliminary
gratitude to whom ever has answers.

Thanks,
-AdamM