Tri-State Checkbox Example: clarify usage of aria-controls

[jscholes]

In the Tri-State Checkbox Example, aria-controls is applied to the "All condiments" checkbox, with a value referencing all four IDs of the individual condiment two-state checkboxes. This is programmatically correct, but:

• aria-controls usage isn't mentioned anywhere within the Checkbox design pattern; and
• as covered in What to do about aria-controls #995, there is still no consensus about how aria-controls should be surfaced by assistive technology. Indeed, the previous surfacing by JAWS (now silenced by default) didn't take multiple IDREFs into account.

Given the above, should aria-controls usage be added to the "WAI-ARIA Roles, States, and Properties" section of the Checkbox design pattern? And for the purposes of ARIA-AT testing (ref: w3c/aria-at#322), my belief is that no assertions can be included as of the time of filing, because there is no meaningful understanding of how to surface the information.

[jscholes]

Accidentally filed here due to browser autocomplete mistake. Apologies; actual issue is: w3c/aria-practices#1599