This is probably a nitpick but Instance:FindFirstChildOfClass and Instance:FindFirstAncestorOfClass both show superclasses in the autocomplete when instances of this class cannot exist. This is an issue because people who may not know the immediate difference between FindFirstChild/AncestorOfClass and FindFirstChild/AncestorWhichIsA may use the former to try to find an instance which inherits a class but whose ClassName is not that class.
For example, in this gif observe that both Instance and BasePart are among the first superclasses which will always return nil because an instance cannot have a ClassName Instance, nor can it have a ClassName BasePart.
Expected behavior
Superclasses that cannot be created/assigned to an instance’s ClassName property are omitted from FindFirstChild/AncestorOfClass’s autocomplete.