[web-animations-2] Why are Range Configs Applied to the Animation and not the Timeline?

[nxtexe]

Why are the range configs (rangeStart, rangeEnd, rangeName, offset) for ScrollTimeline and ViewTimeline animations specified on KeyframeAnimationOptions instead of on the timeline themselves? These seem specific to the timeline in use and I'm further confused by the fact that in JavaScript you can only specify these configs using the Animatable.animate() method and not via the Animation constructor.