1. beforeunloadevent api

2. beforeunloadevent api: returnvalue

3. beforeunloadevent api: user interaction required for dialog box

4. performancenavigationtiming api: unloadeventend

5. performancenavigationtiming api: unloadeventstart

6. performancetiming api: unloadeventend

7. performancetiming api: unloadeventstart

8. window api: `beforeunload` event

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

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

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

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

13. window api: `unload` event