Clarify if aria-selected & aria-checked are required on roles 'treeitem' & ('menuitemcheckbox', 'menuitemradio') respectively

[iamrafan]

The ARIA 1.1 treeitem spec mentions that aria-selected is a required attribute but the aria-selected spec mentions that it inherits into role treeitem and need not be explicitly used on this role.

Please clarify if aria-selected is a required or a supported attribute on role treeitem?

aria-checked on roles menuitemcheckbox and menuitemradio also have the same issue

[mcking65]

treeitem is inherriting from option, and option has aria-selected as required, which does not make sense. See #700.

We also have a presentation problem in the spec. If the superclass role of a role requires a property, the subclass role does not have a row in the table for required properties. Instead, the string "(required)" is placed in the list of inherrited states and properties. This makes it very difficult to notice that an inheritted property is required. I think this inconsistency is problematic. It occurs in 3 places:

1. aria-selected on treeitem. This will go away if we do not require aria-selected on option as suggested in Should aria-selected be listed as required for option role?  #700.
2. aria-checked on menuitemcheckbox
3. aria-checked on menuitemradio

I do not think that it is absolutely necessary that aria-checked be a required property on radio, menuitemradio, checkbox, or menuitem checkbox. In all cases, the default value is false for aria-checked. On the other hand, if a validator calls out a missing aria-checked declaration, it is potentially helpful.

I am sure there are "invalid" implementations that rely on the default value to work. So, we would not want to keep it required and remove the default value.

[scottaohara]

also related #1052

[mcking65]

Note to self ... part of the solution here is changing tree item so it does not inherit from option.