[scroll-animations] Mention design constraint of not blocking scrolling? #819
Description
Depending on exactly how your interpret it, the avoiding cycles section implies that scrolling may need to block on JavaScript / layout.
For blink (and probably also at least Edge) that is a non-starter. Ensuring scrolling never blocks on the main thread has been our #1 scroll performance effort for several years, we're unwilling to allow that without an explicit scary-sounding opt-in API and a mitigation strategy (eg. "intervention" that applies on sites whose performance isn't good enough to permit a reasonable user experience on low end phones).
Is there agreement on this non-blocking design constraint for scroll animations? If so, perhaps it's worth mentioning in the introduction somewhere?