I don't know if this is supported but poorly documented, or not supported; if it's the former it would be nice to have a documented example.

Is it possible to add a dimension other than the ones included in the library already (length, time, information, etc.)? For example, if I want to model economic activity as well, is there a way to let me type:

auto cost_of_gold = 41.63_dollars / 1_g;

(In the real world, of course, money isn't a particularly good fit because exchange rates change all the time; it just works as a good example here.)