Add support for ARIA 1.1 attribute 'aria-describedat'. http://www.w3.org/TR/wai-aria-1.1/#aria-describedat Identifies a URI referencing content that describes the object.
<rdar://problem/22613038>
Not to be fixed.
Some history: https://lists.w3.org/Archives/Public/public-html-admin/2014Aug/0028.html