* prefixed with a suitable extension receiver type (like in `Foo.bar`, or `foo.Foo.bar`).
     *
     * Relies on the fact that in such references only the last qualifier refers to the
     * actual extension callable, and the part before that refers to the receiver type (either fully
     * or partially qualified).
     *
     * For example, `foo.Foo.bar` may only refer to the extension callable `bar` with