1. If CSS Regions is not enabled (it's turned off in about:flags in Chrome) then the following should be true
document.body.style.webkitRegionOverflow == undefined
Currently it'll return an empty string.
2. Additionally, in http://adobe.github.com/web-platform/utilities/css-regions-support-matrix/
One of the assertions ('Initial default value for region-overflow') will pass in Chrome Canary with the flag turned off. Chrome should score a 0 with the feature turned off.
3. With this fixed, feature detects would fail fast:
4. More importantly, this may end up being a false positive in the upcoming @supports functionality (bug 86146)
(Feel free to rename ticket if I've gotten the details wrong)
*** Bug 98884 has been marked as a duplicate of this bug. ***
This seems to be a Chromium bug, closing.
The bug actually has some WebKit ramifications, too.
Keeping it open.
Since Regions are enabled by default in Safari, will close as RESOLVED/INVALID