AspectJ: A crucial distinction between execution and call join points

Given the following code:

  class Super {
    protected void m() {}
  }
  class Sub extends Super {}

A call( * Sub+.m( .. ) ) join point will match any call to m made on an instance statically known to be a Sub (in particular, ( ( Super )s ).m() will not only not match, but will cause a compiler warning); an execution( * Sub+.m() ) join point will not match s.m(), even if s is Sub, because there's no m() code to execute in Sub!