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In the MSAA + IAccessible2 column, everything with a IA2-specific role should have an MSAA role as well, for backwards compatibility. For example, the WAI-ARIA User Agent Implementation Guide maps menuitemcheckbox to ROLE_SYSTEM_CHECKBUTTON or ROLE_SYSTEM_MENUITEM (admittedly confusing - which one?) but then says it should expose an IA2 role of IA2_ROLE_CHECK_MENU_ITEM - but the HTML AAPI just lists IA2_ROLE_CHECK_MENU_ITEM.