From the spec: Name: shape-margin Value: <length> | <percentage> Initial: 0 Applies to: floats Inherited: no Media: visual Computed value: the absolute length Animatable: as length, percentage, or calc. The computed value is returned as the original percentage.
Created attachment 230381 [details] Test case for bug
It turns out that this one is not valid. W3C thread: http://lists.w3.org/Archives/Public/www-style/2014Apr/0475.html Altered spec: http://dev.w3.org/csswg/css-shapes/#shape-margin-property