Overscroll orchestration and animation. This Blink-side controller manages the rubber-banding (elastic stretch and rebound) effect when a scrollable area is overscrolled. It observes gesture scroll events and scroll results, and computes the overscroll stretch and bounce-back animations for the currently scrolling element . In practice, ElasticOverscrollController applies platform-specific physics (e.g. exponential spring on Android/macOS vs. a cubic-bezier curve on Windows) to produce the elastic overscroll visual feedback. It’s the central class coordinating overscroll state and animation timing, making it critical for implementing elastic overscroll on any scroll container (not just the root). (Note: Internally, Blink provides different implementations like ElasticOverscrollControllerExponential and ElasticOverscrollControllerBezier that define the physics for various platforms , but the base controller interface is where the overscroll behavior is orchestrated.)