In reply to Justin Tadlock.

This raises a few interesting aspects of the proposal that I think are still unsettled:

1) Does there need to be individual margin/padding/gap values or could a single scale of spacing units work?
2) What's the right number of values on a spacing scale(s) that all themes should try to support and how do themes support more than that number?

I think the pros for t-shirt sizing and numeric scales are both very compelling. I'd love to figure out a way to keep the numeric scales in some way but support indefinite ranges while keeping things interoperable/portable.

The most obvious way is to use 0 (zero) as default and then work out in both directions. The downsides to that are that negative positions on the scale wouldn't necessarily correspond to negative values and class naming is weird because CSS classes use so many hyphens (which are also the negative/minus symbol).

I've put together this demo of a way to support a scale of values where only a few are required but themes could offer up to a set maximum. For a spacing scale, I could imagine 5 required values with up to 11 available. I think it's pretty cool and it makes me even more excited about the possibilities!