1. htmlbuttonelement api: popovertargetaction

2. htmlbuttonelement api: popovertargetelement

3. htmlelement api: `beforetoggle` event: `beforetoggle` event fires at popover elements

4. htmlelement api: hidepopover

5. htmlelement api: popover

6. htmlelement api: showpopover

7. htmlelement api: togglepopover

8. htmlelement api: togglepopover: returns `true` or `false`

9. htmlelement api: `toggle` event: `toggle` event fires at popover elements

10. htmlinputelement api: popovertargetaction

11. htmlinputelement api: popovertargetelement

12. css selector: `::backdrop`: support on popovers

13. css selector: `:popover-open`

14. html element: button: popovertarget

15. html element: button: popovertargetaction

16. html element: input: popovertarget

17. html element: input: popovertargetaction

18. html attribute: popover