[Accessibility-ia2] aria-colcount and aria-rowcount mapping, again

[Dominic Mazzoni]

I don't think it's true that tables can currently only have missing cells
at the end of a row. There's nothing preventing an author from marking any
cell as aria-hidden, which removes it from the accessibility tree, but
doesn't affect its row and column index. NVDA gets confused if you do this.
I filed a new issue with an example:

https://github.com/nvaccess/nvda/issues/5655

I think it'd make sense for screen readers to be as robust as possible at
dealing with sparse tables using existing APIs. Then if we also want to add
additional APIs to make this faster and easier, that's great too.

On Tue, Jan 5, 2016 at 2:50 PM James Teh <jamie at nvaccess.org> wrote:

> I suppose we could do that, but it's pretty inelegant. Oh look, we have a
> table interface... but uh, sometimes it's not very useful, so you might
> need to use tree navigation. It's not so bad for columns i guess, but see
> below for rows.
>

As I said, I'm totally happy to implement extensions to the table
interface, I'm just pointing out that there are APIs available as a
fallback in the meantime.

It's up to you. Maybe as a compromise you could look at the aria-hidden
table above and make NVDA slightly more robust in the presence of missing
cells, then when we extend IAccessibleTable2 you could make it handle these
cases well.

Navigating to the next row has two problems:
> 1. It's not a simple navigation, since there might be thead/tbody/rowgroup
> elements to think about. Sure, it's just a depth-first traversal, but now
> we're starting to get fairly complicated for what should be a simple
> operation.
> 2. What if the next row doesn't include that column, but there is a row 3
> rows beyond that that does? Surely we should move to the row with the
> matching column. That's not possible with your algorithm.
>

I'm not sure that's the best behavior, because the user wouldn't realize
they skipped over rows containing content. Think about what happens when
you move the cursor in a text editor: when you press the down arrow, it
tries to move to the same column in the next line. However, if there's no
text at that column position in the next line, it moves the cursor to the
closest character in that line.
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