Originally Posted by kiwidude
For an omnibus (bundle), you put all the HTML files and resources from the individual EPUB books together into one combined EPUB. Then at the start of that combined EPUB file add an additional TOC page which points to the individual start of book pages within it.
Edit: Man Eating Duck beat me
As we're in the process of making a series of omnibi (ha! I fear, it is really the mundane "omnibuses," but I prefer omnibi...sounds like a bus full of succubi), I can indeed confirm that this is precisely what they mean--the "future volumes" are the succeeding volumes in the same
omnibus, not some future event. (And, not to get all Doctor Whovian, but, hell, how could you link to "a future volume," any damn way?) I did discuss this with my Tech. Acct. Mgr at Amazon, so, yes, MED and kiwidude are correct.