Lots of multipkg stuff is magic and undocumented.
Questions I've got or have heard:
I'm happy to write this, but @erikwb - can you throw together a list of anything clever you can think of in multipkg?
Agreed. Wasn't there a multipkg wiki page? Someone should paste it into this project. Though I think it has references to all the other auxiliary build stuff, like the 'ssh to build hosts and actually build it' bits.
I am able to make multipkg work but a lot of things I'm going on from memory. Some documentation of all the features would be nice.