[css-regions] Region.flowFrom throwing exception

Hello Alan!

The CSS Regions spec mentions that an exception is thrown when accessing the properties of a Region that's no longer one ( http://dev.w3.org/csswg/css3-regions/#the-region-interface ). However the flowFrom property looks to be more special to me because with it throwing an exception it is difficult (getComputedStyle?) to determine if an Element is region or not.
If flowFrom throws exceptions developers would often need to use try/catch blocks which I don't think is recommended for an API (exceptions hell…). However, it would be much more nice to be able to wrap flowFrom in an IF statement and then use the Region API without worrying about the object not being a region.

Thoughts?
Andrei.