The document’s frame & viewport; LocalFrameView is the scrollable root that triggers layout/paint when needed.

provided source outlines the fundamental components of the Blink rendering engine, specifically focusing on the specialized roles and constant collaboration of three core classes: blink::Page, blink::LocalFrame, and blink::LocalFrameView. The blink::Page acts as the top-level context, managing global state for an entire tab, such as the frame tree, focus coordination, and visibility status. The blink::LocalFrame handles the logical side of a specific rendered area, owning the DOM document, executing scripts, and triggering layout updates. Finally, the blink::LocalFrameView serves as the visual interface for a frame, responsible for managing the viewport geometry, scrolling, and coordinating painting and compositing with the graphics system, often running on the main thread but synchronizing frequently with the compositor thread for performance. This tiered system is essential for everything from handling input events and animations to managing the complete lifecycle of web content.