How do I create a document using the Varient format? What edition is this available in?

Using one source manual and then using it to make off shoot manuals. So, for example, I have 10 manuals that share a lot of common text, it would be easier to go to the source document and make one change rather than going to all 10 and making the very same change. I've never heard of it either, a branch of my company in Switzerland suggested I use it. I don't think they are referring to "conditional" text because that wouldn't make sense for the amount of complications that would introduce. So I'm wondering myself what it would be?