css-animations-1 defines the initial value of animation-duration to be 0s. However, the web-animations specification allows for the 'auto' keyword which is useful for scroll-animations and group animations where the duration should be determined automatically.

Since the computed value of 'auto' for regular animations is 0s, it seems to me that we could safely change the initial value of animation-duration to be 'auto', and this would allow using a scroll-timeline animation or possibly a group effect animation without having to explicitly set the auto duration.

@birtles WDYT?