Update the web animations JavaScript API to align with the specifications in https://drafts.csswg.org/web-animations-1/. The Animation interface is extended to include support for promises, replaceable animations, and read-only access to the animation timeline. The Animatable and DocumentOrShadowRoot interfaces are expanded to support getAnimations. The KeyframeEffect interface is expanded to support compositing modes, getKeyframes, setKeyframes, and pseudoElement.
Docs: https://drafts.csswg.org/web-animations-1/
Samples: https://birtles.github.io/mozdev2019/ https://mozdevs.github.io/Animation-examples/
Explainers: Draft of detailed explainer: https://docs.google.com/document/d/1sWAEytrZDxQWnnqozMSzI2lHvIJ0kF3dzgy9Q1PbYjE/edit?usp=sharing https://developer.mozilla.org/en-US/docs/Web/API/Web_Animations_API https://developer.mozilla.org/en-US/docs/Web/API/Animation/timeline https://developer.mozilla.org/en-US/docs/Web/API/EffectTiming/fill https://css-tricks.com/additive-animation-web-animations-api/ https://developer.mozilla.org/en-US/docs/Web/API/Web_Animations_API/Using_the_Web_Animations_API