Yeah there is a case: Chrome, Firefox & Opera all seem to agree that e.g. `CSS.supports('width', 0)` should be `true`.

If we think `Modernizr.testProp()` should match `CSS.supports()` as closely as possible, we should use `!is(value, 'undefined')` here to ensure we match this result, although [the spec](http://www.w3.org/TR/css3-conditional/#CSS-interface) *does* say that `CSS.supports()` only needs to accept DOMStrings.

This also has me wondering if we should add a build option to *actually* polyfill the `CSS.supports()` API as an alias to `testProp()` if it isn't present...

What do you think?

The other corner case might have been empty strings, although interestingly they all agree that e.g. `CSS.supports('display', '')` should return `false`.