This matches the specification as well as Gecko and Chromium.
Created attachment 320629 [details] Patch
Comment on attachment 320629 [details] Patch r=me
Comment on attachment 320629 [details] Patch Clearing flags on attachment: 320629 Committed r221967: <http://trac.webkit.org/changeset/221967>
All reviewed patches have been landed. Closing bug.
<rdar://problem/34694471>