The sources provide an extensive reference guide detailing the key classes and infrastructure involved in handling user interactions—specifically scrolling, gestures, and input—within the Blink and Chromium Compositor (cc) rendering pipeline. The components are separated into sections covering Blink Scrolling and Viewport Infrastructure (e.g., ScrollableArea, ScrollingCoordinator), Blink Main-Thread Input Handling (e.g., EventHandler, ScrollManager), Browser Input Event Routing (e.g., InputRouter, InputHandlerProxy), and the Compositor Property Trees and Layer Systems (e.g., ScrollNode, PropertyTreeManager). A major focus is placed on the coordination between the main thread and the compositor thread, explaining how high-performance features like composited scrolling and animations (ScrollAnimatorCompositorCoordinator) are managed to ensure responsiveness and frame synchronization. These details are presented to aid the Interactions Team in diagnosing issues like scroll jank, input latency, and animation synchronization problems.