Google helped me find it:��https://pharoweekly.wordpress.com/2015/03/07/athenssketch-how-to-browse-cool-athens-graphics-example/

I subclassed as suggested and re-typed the drawStepOn: method (I had to do it in a System Browser, as the SketchBrowser gave me troubles to compile, in Pharo 8 at least). It works as shown in the video (more or less). The graphics portal has no window frame, but you can move it around.��

However, making the live changes in Pharo 8 finally leads to a bad state:

When I have more time, I'll try it with Pharo 7. It's a great demo for live programming.

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