Accessibility/TreeGrid

Starting with raw notes here. Help with organization appreciated.

Legend:

• UA = User Agent
• WD = Web developer
• AT = Assistive Technology

I'll try to add these acronyms to the information below to show which audience(s) should care.

[WD,AT] if a cell has aria-expanded then:

• if grid, assume it expands the cell
• if tree grid, assume it expands relative to a row

When should rows get an accessible name? We don't want repetition due to virtual buffers.