If nobody can assist me directly with this can anybody at least suggest some visual code I can use as a reference point? I used to use the FunnelChart, but gradually even the code for that has shifted to undocumented helper libraries that handle areas such as these, e.g. my issue is obviously something to do with SelectionManager.select(), but the SelectionManager class doesn't even make an appearance in FunnelChart.ts, which I think it used to. I'm left trying to find a needle in a haystack.
Should it really be necessary to understand every line of code in the custom visuals github to have any chance of building a working visual?