[Webkit-unassigned] [Bug 212409] [Web Animations] CSS-originated and JS-originated keyframe animations with implicit values behave differently

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=212409

--- Comment #5 from Antoine Quint <graouts at webkit.org> ---
I think WebKit might actually be correct for its runtime behavior due to this excerpt from section 3 of the CSS Animation 2 spec (https://drafts.csswg.org/css-animations-2/#keyframes):

    6. If there is no keyframe in keyframes with offset 0, or if amongst the keyframes in keyframes
       with offset 0 not all of the properties in animated properties are present,

        1. Let initial keyframe be the keyframe in keyframes with offset 0 and timing function default
           timing function. If there is no such keyframe, let initial keyframe be a new empty keyframe
           with offset 0, and timing function default timing function, and add it to keyframes after
           the last keyframe with offset 0.

        2. For each property in animated properties that is not present in some other keyframe with
           offset 0, add the computed value of that property for element to the keyframe.

This leads me to think that we are correct in specifying the implicit keyframe's values when the animation is created. However, as the newly attached test shows, we are not reflecting this in the getKeyframes() output since there is "left" property for the implicit keyframes, unlike Firefox and Chrome.

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