types of use flags

Ok so I have yet another idea for portage and other portage like package managers. actually this is probably more aimed at EAPI. Different types of USE flags. The 2 I'm thinking of off the top of my head could be described as volatile and non-volatile. Basically a use flag marked volatile means a package needs to be recompiled if it gets changed one marked non-volatile most likely just pulls in another dependency or copies files such as documentation. I'm sure this feature could have lots of uses I'm not thinking of.