autoScrollEdgeZone property
Height in pixels from each viewport edge within which the pointer triggers autoscroll. Velocity ramps linearly from 0 at the zone's inner edge to autoScrollMaxVelocity at the viewport edge.
Mutable at runtime. Captured once per drag session at startDrag (the same per-session policy as the animation style), so a change never retunes a live drag; the next drag picks it up.
Implementation
double autoScrollEdgeZone;