[OTVar] Axis Interaction and Literality

In discussing the inter-relation of axes with @Laurence Penney it struck me that there's a conundrum here that might need to be resolved sooner rather than later (although it's possible others have actually already worked through this).

Consider a typeface with weight and width axes. We know that –at least conventionally– adding weight adds set width to a font, arguably to maintain apparent width. The question becomes, should a width axis then be considered "non-literal"? Because the set width would change with weight but without actually changing the position on the width axis... This is probably not intuitive in terms of user expectation, although it seems like a logical compromise for designers who have worked with discrete weights/widths.

I posit that in this new continuous-axis world there's another approach that might be more intuitive for users: the weight axis maintains set width; this would cause a shift in apparent width, but the width axis would become literal (as the weight axis is); any apparent-width compensation would be done manually via the width axis. Of course this gives the user more power, but also arguably a responsibility that might backfire.

So maybe an interface could provide a choice between Set Width and Apparent Width...