[eterps]

So, what would the syntax be in Io? Like this?

  valid := base bottom between(ligature bottom + height, base top / scale factor)

[draegtun]

Yes, unless I've totally misunderstood that Self/Smalltalk code!

Also instead of between method with two args you could also create an and message/method:

  valid := base bottom between(ligature bottom + height) and(base top / scale factor)