In the latest revision of the WD, the region-overflow property name was changed to region-fragment. Need to update this in Webkit.
Correction: as of today, this change is only in the Editor's Draft
Spec link: http://dev.w3.org/csswg/css3-regions/#the-region-fragment-property Summary of change: http://dev.w3.org/csswg/css3-regions/#changes_from_Aug_28_2012
*** This bug has been marked as a duplicate of bug 117397 ***