Exactly. And prior to Ruby 2.7, even calling a private method with an explicit `self` as the receiver was not allowed, only the implicit `self` from "within" th

Exactly. And prior to Ruby 2.7, even calling a private method with an explicit `self` as the receiver was not allowed, only the implicit `self` from "within" the class body ("within" in quotes because, as the blog post points out, Ruby's concept of being inside a class body is unlike many other languages).