[csswg-drafts] [web-animations-2] Iteration duration is never set if specified iteration duration is "auto" in "convert a time based animation to a proportional animation" (#13220)

Calme1709 has just created a new issue for https://github.com/w3c/csswg-drafts:

== [web-animations-2] Iteration duration is never set if specified iteration duration is "auto" in "convert a time based animation to a proportional animation" ==
Within the [convert a time-based animation to a proportional animation](https://drafts.csswg.org/web-animations-2/#time-based-animation-to-a-proportional-animation) algorithm, the steps associated with the case where (specified) iteration duration is "auto" only tell us to set the start delay and end delay, leaving iteration duration untouched:
>Set start delay and end delay to 0, as it is not possible to mix time and proportions.

This doesn't match the behavior of either [Chromium](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/animation/animation_effect.cc;l=168) or [WebKit](https://github.com/WebKit/WebKit/blob/5f19b4bcec9ae2e645504594bae5c15e85b513dd/Source/WebCore/animation/AnimationEffectTiming.cpp#L65) which respectively set the iteration duration to the intrinsic animation duration and `timeline duration / iteration count` (which is functionally equivalent to the intrinsic animation duration).

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13220 using your GitHub account


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Received on Monday, 15 December 2025 06:56:42 UTC