May I ask: 

Roassal and Pharo are really fantastic. I’m trying to get a grip on it and use it. What makes me think:

In the introduction of the superb “Agile Visualization” book it is stated, that the Roassal OO approach allows for visualizations that are “easily extensible”. I guess compared to hand-crafted, imperative visualizations.

Let’s take an example: RTCalendarBuilder

I noticed that present visualization of week days start with Sunday as first day of week. E.g. in Europe/Germany weeks start on Monday (according ISO8601). We are visually so used to it, that other schemes make us think (not intuitive).

How could I modify this?

P.S.: Especially in calendrical visualizations there will be many (local) variations. So maybe it’s a good example to understand how to easily extend Roassal in above and similar topics as an interested user.

BR Mike