Originally, I had these two attributes spec'd for V8, but they have been moved to V9. I just proofed the changes made by this PR, and they look good to me.

However, I seem to recall Bill telling me these should be marked as "conditionally normative." That is, support for them is optional, but if either is included, they must have the syntax/semantics, as specified. Should they be a combined package? That is, if one is implemented then so too should the other?