Out-of-bounds keyframe values

[KevinDoughty]

There is no useful form of additive animation that does not allow out-of-bounds keyframe values. SMIL has a special carve-out to allow out-of-bounds keyframe values for opacity, as per this comment:
w3c/csswg-drafts#3340 (comment)

Firefox behavior has recently changed and broken my preferred usage, for opacity:
https://phabricator.services.mozilla.com/D263038

I am unsure about Safari but Chromium and Firefox behavior now differ. Because of this, Web-Animations and WPT might be under-specified and need clarification or correction.
w3c/csswg-drafts#12648 (comment)

Other properties like lineHeight, width, and height explicitly disallow out-of-bounds keyframe values and console warn, which is a shame. (I’ve made many proposals which permit useful additive animation but also do not require out-of-bounds keyframe values, via behind-the-scenes conversion. Just sayin’)

[KevinDoughty]

Using out-of-bounds keyframe values is a poor dev experience and bad design. I’m aware action taken might result in removal from Chromium, but I am not requesting it