_From @birtles on June 30, 2015 23:58_ As raised in issue #62 (see https://github.com/w3c/web-animations/issues/62#issuecomment-117357703 and https://github.com/w3c/web-animations/issues/62#issuecomment-117374689) _Copied from original issue: w3c/web-animations#97_