Spec proposal: harmonize compact, compact-n, horizontal, horizontal-compact appearances

Taking a step back, the problems I have with the existing appearances (compact, compact-n, horizontal and horizontal-compact) are:

  • we're missing a way to represent n columns WITH radio buttons/checkboxes
  • it's not clear what the relationship between compact and horizontal-compact is. One doesn't have radio buttons/checkboxes and the other does. That should be clear from the naming
  • it's unclear what horizontal does and what its relationship to the others is.

Given how confused I am trying to explain the suggestion and how the proposed appearances do and don't combine, I don't think we've addressed the second two points.

I have a strong preference to only introduce a modifier if it is used consistently. That is, in the proposal above, compact is a modifier but only in one case AND it can also act alone.

The proposal I've seen so far that most meets my criteria is as described here by @Tino_Kreutzer :
compact
compact-n
compact-auto
with modifier show-buttons or markers that can apply to any of them.

It's really easy to understand, there are no compatibility issues and it adds the missing combination.