[Fedora-livecd-list] Anyone using the overlay file?

In the iso-to-disk script, one can add an overlay file. However, I don't see that it is being used at all--livesys does not reference it at all. It looks like the XO team passes a kernel parameter, but I haven't seen the code to actually use it. My assumption is that the overlay file would be the backend storage for an LVM snapshot. Has anyone actually used an overlay file? Any ideas on the implementation? Thanks, -- Forrest