Thank you very much, I appreciate the explanation.
But is it possible to leave the bl.ocks.org vanilla examples up after they are ported to Observable (with the caveat that they are no longer maintained and may even be slightly different from the new sample)? While it is true that there are many other D3 examples on the web, the bl.ocks.org examples that have been removed are the closest thing to the new Observable samples that we can use as a reference for understanding the transition.