See Web Animations specification KeyframeEffect/KeyframeEffectReadOnly interfaces: https://w3c.github.io/web-animations/#the-keyframeeffect-interfaces The constructor argument "keyframes" sets the keyframes used for the animation. The "keyframes" argument may be specified in two forms (see https://w3c.github.io/web-animations/#processing-a-keyframes-argument) - this patch addresses specifying the keyframes argument in the array-form (i.e canonical form).
This has been done for quite some time.