This is wonderful affordance is made possible by having control over the editor environment and not making it a text based language.
I was thinking about this earlier when a typo in C++ resulted in a valid program that did not do what I wanted, where I wrote:
double Fnord = ReturnsDoubleRef();
instead of
double& Fnord = ReturnsDoubleRef();
and how in a sense this is a similar property (though C++ doesn't strive to be error free), and how in this case it is not a positive quality