Comment 2 for bug 235267

As mentioned in email, I think we still want to pass a config name for the pop() method we recommend people use. In the following sequence of events, I want an error at (3):

  1. push overlay1
  2. push overlay2
  3. pop overlay1
  4. pop overlay2

Without the config name, we can't distinguish this kind of error from correct usage of the API.