The implementation of scroll anchoring will notify scroll anchor containers to apply any adjustments when it's possible an anchor node may have been moved.

This is usually done after reflow, but there's also a fast path for directly changing the position of a frame during restyling. The initial implementation will notify the applicable scroll anchor container immediately after each positioned item is moved. We should coalesce these notifications to once per restyle flush.

This was filed from this comment from David Baron.