RE: Proposal for "overflow:clip" for stronger painting isolation

> I would be more comfortable with this if it could be turned into an
> independent property that was orthogonal to overflow:hidden

Why not "paint-limit: [ [ content-box | border-box | margin-box ] <paint-limit-padding>? ] | none"? 

That would allow "overflow: visible; paint-limit: margin-box". The optional padding values (paint-limit-padding) would help extend the margin box or the border box by a few pixels if necessary, and would have the same syntax as a normal padding.

This can also serve as an hint for the browser to extend the layer size in case it does gpu compositing for the element (for example, when we expect to animate box-shadow...)