Great, thanks everyone for the explanation. Having said that, there's still something I don't get.
If a group is a possible configuration to load packages, then it seems that the "reasonable" possible configurations would be: 1 - Core 2 - Tests + Core (explicitly stated) 3 - Default (Tests + Core, implicit when not specified) but NOT Tests (without the Core) Because you wouldn't want to load the tests of a package without the Core. So, why would you define the Tests as a possible configuration for a Version?
