PS: Oh, now I finally understand what you were thinking of. facepalm I never even thought in that direction because it's simply not done. A mesh is a manifold. Period. Most modelers won't accept meshes that aren't, or worse, accept them but do very strange and wrong things with them. The algorithms I use wouldn't work with what you're suggesting. If you paid my wages for a few years, I could go and singlehandedly change that whole paradigm, but I'm not even sure that's so desirable.

-- I'm not mad at you, just Westphalian.