One specifically for @Fil - Is there a way to detect when brushing has started / finished here? Brushing Plot (#1653) / Observable | Observable through something like on.
Thanks 
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Currently, I don’t think it’s possible, but I’ve added the feature request to the TODO list of brush interaction by Fil · Pull Request #1653 · observablehq/plot · GitHub. Feel free to comment on that PR too. It’s quite possible that this will be rewritten from scratch at some point