Oh. When I read the page, I missed this:IIRC, basically it's just the result of "tar cf rootfs.img /"
-RaspberryPI- : using rebuilt kernel from https://github.com/raspberrypi/linux
-Generic- : using rebuilt LTS kernel from https://www.kernel.org
And what about -RootFS- ?
I think it was mentionned on this list some time back.