[Serif height] should derive from [Contrast]

[loicsander]

…to allow variation on [serif height] while keeping contrast consistent over all.

[yannickmathey]

Or keep the possibility to experience new kind of shapes?
Could also be an option: mode [rooky] - [expert] - [fool]

[loicsander]

Thing is, user could still tweak serifs separately, but when moving contrast, serifs’ height would move along. But true, it’s a specific expectation and not an essential one. : )