I'm in favor of ".Pandora XML-annotated application archive". Yes, with spaces. It's time we finally rid ourselves of the "file extensions with spaces are unintuitive" notion.
I mean, look at it like this: You see the following files in your file manager:
- Quake 5.pnd
- Quake 5.box
- Quake 5.Pandora XML-annotated application archive
Which one makes sure you know what's inside? The first one could contain a Panda. Or a pound of something. The second one could be any kind of box. The third one can only contain an XML-annotated application archive for the Pandora.
".Pandora XML-annotated application archive" is the only logical choice.