We don't have an implementation for CSSNumericValue.parse(). This prevents some Web Animations tests from passing: https://wpt.fyi/results/web-animations/timing-model/animations/setting-the-current-time-of-an-animation.html?label=experimental&label=master&aligned https://wpt.fyi/results/web-animations/timing-model/animations/setting-the-start-time-of-an-animation.html?label=experimental&label=master&aligned
<rdar://problem/89974416>
This has been done as part of the overall effort towards implementing the CSS Typed OM.