aria-expanded question/suggestion

Morning! I was recently working on an a11y treegrid with button elements set to control the expansion/collapsing of sub-level rows and ran into a snag with aria-expanded.

The expand/collapse button is controlling any sub-level row below its parent row , so I’ve set ‘aria-controls’ to every row ID that is its child, and then am using the ‘aria-expanded’ state on the button to show whether they are collapsed or not.

The issue however is that those rows have sub-levels that control their sub-levels, etc. so at any given time ‘aria-expanded=true’ at the higher level may not make sense, nor would ‘aria-expanded=false’, as some will be expanded and some may not be.

Would it be worth having a 'mixed’ state similar to ‘aria-pressed’?

Thanks for your consideration.

Feel free to visit this demo as well to see what I’m talking about.<https://dl.dropboxusercontent.com/u/116053/a11y/Treegrid.html>

-Chris LaChance