https://youtube.com/rikuslategan guilty on my landing page even I use Circle extends Form or something, I cant even remember. Twas a decade ago though (recorded not uploaded), and who wasn't ever shamefully noobish.
Its amazing how many people are fixated on titles or labels, like the name of a lake or gulf or wearing a hat. It doesnt matter. Food doesnt become tastier because you pretend its healthy. The example of Dog extends Animal is just a few labels it was never perfect.
I wish someone had taught MutableList extends List, and the parent collections were immutable in the API.