We already knew that there would be three different-sized endos, but Google's also cool with modules that stick out from the bottom or back of the phone, like the pulse oximeter (below) the company's been mentioning for months. It seems a little odd that Google doesn't want manufacturers crafting modules that could stick out of an Ara's phone side, but we're guessing that's a concession made for grippability.

Then there's the little matter of how we the people will actually be able to order our phone parts. Google's guidelines make mention of an online marketplace (somewhere in the Play Store, probably) where we'll be able to pick parts and configure our dream devices. The sales bit of this equation hasn't been totally fleshed out yet, but the folks in Mountain View still have time to iron it out. The full document is 81 pages long and just a little more accessible than you'd think -- you can download the full package here in case you're curious. The first of three Ara developer conferences will kick off next week too, so fear not: the best is surely yet to come.