Should user agents calculate aria-posinset and aria-setsize on treegrid row if there is no author-provided value?

[joanmarie]

In ARIA 1.2, aria-posinset and aria-setsize became supported properties of row if that row lives in a treegrid.

I have to confess that I don't understand the difference between aria-posinset and aria-rowindex in the context of a treegrid row. Ditto for aria-setsize versus aria-rowcount.

Assuming the author and user do understand these differences, exposing it to ATs is fine. But the spec also says under aria-posinset:

If all items in a set are present in the document structure, it is not necessary to set this attribute, as the user agent can automatically calculate the set size and position for each item.

For user agents that DO this calculation for other roles, e.g. menuitem, listitem, tab, etc., should they be doing so for row?

Personally that strikes me as leading to potential chattiness. Then again, it might be seen as weird to not calculate on row but calculate it on all the other roles.

Some guidance in the spec would be useful. Also, if the answer is calculate it, how is the calculation different from that of rowindex and rowcount?

[joanmarie]

Just found #1303 and w3c/aria-practices#1442.

In the latter, Matt says:

It does seem like we have made aria-rowindex redundant with aria-posinset in treegrids.

And in the former, he says:

We should consider prohibiting aria-rowcount and aria-rowindex on rows in a treegrid. Using them instead of or in addition to aria-posinset and aria-setsize could create problems.

So silly me has a new question: Why exactly did we add aria-posinset as a supported property on treegrid row in ARIA 1.2 (on 21 Aug 2018, according to the list of Substantive changes) when aria-rowindex was already a supported property on it in ARIA 1.1?

But I'm starting to think that the answer to the question I asked in the opening report is: "Yes, user agents should calculate them using the very same calculation as they would for rowindex and rowcount"

[joanmarie]

Here's the issue where aria-setsize and aria-posinset were added to row descending from treegrid: #558

[jnurthen]

@aleventhal can you please help.

[joanmarie]

Straw poll done during today's ARIA WG meeting:

Yes: 9
No: 0
Abstention: 1

[jnurthen]

discussion at https://www.w3.org/2021/12/09-aria-minutes.html#t05