Simple operations from the Web Animations API like a composite add do not work as expected in Safari. This simple example: https://codepen.io/benfrain/pen/JjXQqVO Click 'Move Me' to start the box moving, and then click the 'Scale Me' button to add a scale (using composite: add). It in no way renders as expected in Safari! Fine in Firefox/Chrome.
Created attachment 464009 [details] Reduction
Pull request: https://github.com/WebKit/WebKit/pull/7488
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/37456
Committed 257731@main (4374420d956e): <https://commits.webkit.org/257731@main> Reviewed commits have been landed. Closing PR #7488 and removing active labels.
<rdar://problem/103257151>