This is bug 156536 for the subscriptshift and superscriptshift attributes.
These attributes are currently parsed in RenderMathMLScripts.
Created attachment 283902 [details] Patch
Comment on attachment 283902 [details] Patch The constructor of RenderMathMLScripts should also be changed to take MathMLScriptsElement& instead of Element&.
(In reply to comment #3) > The constructor of RenderMathMLScripts should also be changed to take > MathMLScriptsElement& instead of Element&. I can not do that now since this renderer is also used for munder/mover/munderover but will consider it in bug 159625 and keep it in mind for other renderers too.
Committed r203396: <http://trac.webkit.org/changeset/203396>