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.
