I really couldn't follow the use case. it looked like, they have a chain of method calls with some kind of `mark_circle().encode().properties()`, OK, so, if you want to make those methods do something different, you reach into OOP wisdom from the 1980s and write an appropriate "impl" used by whatever `alt.Chart()` is.

Someone explain to me, an old, aging programmer old enough to know UML, why this isn't some we presume very young person who has no idea how to write OOP coming up with some horrible convoluted way to do something routine?