So now, looking at the internal/external aspects, I am wondering whether you can distinguish design from potential use (i.e. the intentions of the maker vs. the intentions of the user). The Internal AND External type seems pretty clearcut (needs two distinct thingies*), and the External only, I'm relatively convinced due to their smaller size (presumably?). But Internal, and Internal OR External, seem to me to raise the issue of design vs. use ... or perhaps you would care to expand?

*Note: 'Thingy' is a technical term. I have defined it in my own mind.