* **Callback if script is missing (404) or in error (500)**

This claim is provably unreliable cross-browser (still!), so it's kind of presented in a way that any loader is doing it reliably, when in fact they aren't (because they can't).

Either the item is unfair to list at all, or it should be reworded to something like:

* **(Browser-dependent) Callback if script is missing (404) or in error (500)**