Additional accessibility guidance for popover

[scottaohara]

Now that #8221 has been merged, I've drafted the two following notes (edits welcome) that I think need to be included for popover and the popover target attributes sections:

for popover:

The popover attribute is a global attribute to allow authors flexibility in ensuring popover functionality can be applied to the most appropriate semantic element which represents the content of the popover. Authors can use the popover attribute on generic elements, such as div, or author defined custom elements, but it will generally be recommended that authors also ensure proper accessibility semantics are also provided to these generic elements, by also specifying the appropriate ARIA roles and properties.

for the popover target attributes section:

To help ensure a popover will be programmatically exposed in a logical reading order to users of assistive technology, it is strongly recommended for most use cases that authors include their popover following its triggering element in the DOM.

in addition to the above note, I'd also want to adjust the examples to also reflect this guidance. The popover ideally would come after the button element. Additionally, at least one of the examples would also use a non-generic element (a list or an article, for example). Maybe one of the examples could also have an ARIA role to match the guidance of the note. If we want to leave one of the examples as is, I'd be happy to include another to demonstrate this, instead.

I'm happy to make the PR for this, but would just request any preferences as to where these notes (particularly the one i mentioned as being for the popover attribute) would best fit in the flow of each section's content.

cc @mfreed7, @josepharhar, @aleventhal, @domenic

Thanks

[aleventhal]

ecommended that authors also ensure proper accessibility semantics

Should we say where authors can find examples of this? I think we specifically mean setting the role, perhaps we should say that. We could consider listing an incomplete set of commonly used roles in popups, such as diallog, group, listbox, etc.

[josepharhar]

The PR was reverted and reopened, you can see the latest version here: https://whatpr.org/html/8717/popover.html

any preferences as to where these notes (particularly the one i mentioned as being for the popover attribute) would best fit in the flow of each section's content

Domenic knows best but I suppose that putting the "The popover attribute is a global attribute to allow authors flexibility" paragraph after the "All HTML elements may have the popover content attribute set" paragraph sounds good, and the "To help ensure a popover will be programmatically exposed" paragraph could go after the "The popover target attributes allow certain types of buttons" paragraph.

in addition to the above note, I'd also want to adjust the examples to also reflect this guidance

If you could do that in your followup PR that would be awesome!

[scottaohara]

appreciate the responses. will look to do that asap