definition and term were added in ARIA 1.1. We do expose these generically through the xml-roles object attribute. However, even though we do have Gecko roles for these, we don't have atoms for them, so they aren't in ARIAMap. This means we can't expose the correct ARIA role token via ComputedARIARole. The platform mappings also need to be updated.

Actually, term is already in ARIAMap, but it doesn't map to an ARIA role in RoleMap. definition needs an atom and ARIA mappings.