aria-atomic doesn't say what its missing/invalid value defaults are

[zcorpan]

https://w3c.github.io/aria/#aria-atomic

The algorithm seems to leave undefined what happens when the attribute is present but the value is not one of the keywords "true" or "false".

https://w3c.github.io/aria/#typemapping says true/false ARIA attributes map to HTML enumerated attributes. These can have a defined "missing value default" and "invalid value default". If they are not defined, invalid values end up in no state.

Since ARIA doesn't define its processing in terms of states of an attribute, it's unclear what is intended. Is aria-atomic=foobar equivalent to no attribute? Or equivalent to aria-atomic=false? Something else?

[zcorpan]

cc @spectranaut

[jnurthen]

Deleting as need to rethink :)

[jnurthen]

@joanmarie can you take a look at this....
I thought it should resolve to false for aria-atomic="foobar" but according to the "handling author errors" section it would actually resolve to true.... Is this correct?
My understanding is that:

• aria-atomic would be exposed as a platform Accessibility API boolean state
• It doesn't have the value "", undefined or no attribute present
• so it would be exposed as true

[jnurthen]

related to #777

[jnurthen]

closing as duplicate of #777