There are all the other vague categories to consider too: Cabin Scooters, Cabin Mopeds, Cycle Cars, Light Cars, Disabled Cars and Mobility Aids, unusual one-offs and home-made vehicles, cargo carriers and light agricultural vehicles, and many of these might also be classed as Micro Cars
Having seen Morgan 3 wheel sports cars and Bond Bugs at RUM Open Days, as well as that large and lovely 1930s Voisin Touring Car I am glad that RUM allows a certain amount of "interlopers" in, as long as the core focus remains on distinctive small vehicles!