Answer Re: Does the "GPL version choice" impact GPL-compatibility?
Glenn Maynard asked:
>Is it valid to combine GPL work placed under "GPL version 2" with one
>under "GPL version 2 or any later version"? That is, do versioning
>choices impact compatibility (when the versions overlap)? Are all future
>modifications bound to give the same permission to upgrade the GPL?
Yes, it's valid to combine them. The combined work, however, is effectively
GPL-version-2-only. No, future modifications do not have to give upgrade
permission. Ever -- you can take a "version 2 or later" program and put your
modifications under "version 2 only". (In fact, you can take a "version 1 or
later" program and put your modifications under "version 2 only", or under
"version 1 only".)
This is pretty straightforward; the "version 2 or later" is a form of
dual-licensing (dual-licensed under version 2, version 3, etc.).
You pick which license you want to use. If you combine a work dual-licensed
under version 2 and version 3 with a work licensed only under version 2, you
have to use version 2.