1. beforeunloadevent api

2. beforeunloadevent api: returnvalue

3. beforeunloadevent api: user interaction required for dialog box

4. window api: `beforeunload` event

5. window api: `beforeunload` event: activation by setting `event.returnvalue` to any truthy value

6. window api: `beforeunload` event: dialog displays a generic string, not event handler return value

7. window api: `beforeunload` event: activation using `event.preventdefault()`

8. window api: `beforeunload` event: activation by returning a string