Unspecified treegrid Shift+Tab behavior if first cell is focused

[tychonievich]

What is the desired behavior of the Shift+Tab key when a cell is focused and there is no previous interactive widget in the current row? The corresponding case is specified for Tab (focus leaves the treegrid) but for Shift+Tab it is ambiguous if focus should leave the treegrid or focus should transfer to the row.

I'd recommend this case be added to the Shift+Tab row in the table at https://www.w3.org/WAI/ARIA/apg/patterns/treegrid/examples/treegrid-1/#kbd_label by changing the entry to say one of the following two options (changes italicized; wording borrowed from elsewhere in the table to hopefully maintain linguistic style):

Shift + Tab

If a cell is focused, moves focus to the previous interactive widget in the current row (if there is one). If a cell is focused and there are no more interactive widgets in the current row, focuses the row. If a row is focused, moves focus out of the treegrid.

or

Shift + Tab

If a cell is focused, moves focus to the previous interactive widget in the current row (if there is one). If a cell is focused and there are no more interactive widgets in the current row, moves focus out of the treegrid. If a row is focused, moves focus out of the treegrid.

depending on which behavior is preferred.

[css-meeting-bot]

The ARIA Authoring Practices (APG) Task Force just discussed Tab and Shift+Tab in treegrid.

The full IRC log of that discussion

<jugglinmike> Topic: Tab and Shift+Tab in treegrid
<jugglinmike> github: https://github.com//issues/2865
<jugglinmike> Matt_King: I'm kind of unclear about the inconsistency that has cropped up in treegrid where tab sometimes stays in the grid and other times it does not
<jamesn> q+
<jugglinmike> Matt_King: I'm not really sure what we should do here because we have inconsistencies in what we do between grid and treegrid
<jugglinmike> Matt_King: I know there have been a variety of approaches in different implementations
<jugglinmike> Matt_King: There's a suggestion in tree grid that tab doesn't have just one tab stop in the grid but stops in every cell in the focused row
<jugglinmike> jamesn: Yes, though sometimes that behavior only occurs following an action on a specific row
<jugglinmike> jamesn: Subtle differences in the way these implementations work can make it tough to specify a single solution here
<jugglinmike> Matt_King: So should the focus go to the row or should it go out of the grid?
<jugglinmike> Jem: I thought that the focus should go out of the row
<jugglinmike> jamesn: I think it should go to the row
<jugglinmike> jamesn: the desired behavior appears to be implemented in the APG's example, so I think this is strictly an editorial problem
<jugglinmike> Matt_King: I'm labeling this as "editorial"
<jugglinmike> jamesn: Focus isn't reversible when you tab out of the treegrid and go back. Focus goes to the row--it doesn't go to the final cell in the row
<jugglinmike> jamesn: I'm actually okay with that non-reversible behavior because (due to the way the web platform works) implementing the reversible behavior would be a significant burden on authors
<jugglinmike> Matt_King: I can see it either way. That said, it's not directly related to the issue we're discussing right now
<jugglinmike> Matt_King: I will fix it