[scroll-animations-1] Behavior of a fixedpos view-timeline

[ydaniv]

Currently the behavior of a ViewTimeline on an element in fixedpos isn't specifically defined, though I'd expect one of the following options:

1. The timeline is inactive.
2. The timeline behaves as if the element is in stickypos inside the root CB.

Since the behavior of stickypos is well defined, I'd expect at least option 2 to occur, but according to implementation of Blink and WebKit it's something else: https://jsbin.com/zabahewure/edit?html,css,output, and it isn't quite clear what that is.

If I'm not mistaken, it should either be one of the 2 options above, or something else that is defined by the spec.

/cc @fantasai @flackr @bramus

[ydaniv]

Now that I think of it, I guess what's happening is:

• fixedpos: range is element height + viewport height
• stickypos: range is element height + container height

Now I wonder whether this is expected? Since it was a bit of a surprise to me.
And whether we can/should change anything? (since it might be too late to change?)

I guess this behavior would be expected if it also would be static and not respond to scroll change, which could be considered as option 3.