So far this part of the spec was proposed ages ago but is basically unused! So yeah, you can basically write anything in there, yet it will not have an effect yet. Once this stuff is really handled, the version format may just consist of numbers. Things like 1.1.1.1 would be a valid version number, though I don't know what the real thing is ATM. Just look at the examples that sebt3 gave and keep in mind that it has no effect anyway. You can have a look at /etc/op_version or some file similar to this one to get an idea what OS is currently used. Anything else won't work (yet).