The source documentation provides a detailed analysis of the RenderFrameHost (RFH) and its implementing class, RenderFrameHostImpl, which constitute the essential browser-side representation of every individual web frame or document in Chromium. The RFH acts as the main interface for the browser to interact with the frame, enabling core functions like retrieving the document URL and security origin and executing JavaScript. The specialized RenderFrameHostImpl manages the frame's complex lifecycle, tracks critical security features such as Content Security Policy (CSP), and facilitates communication via Mojo interface endpoints. Each host is tightly bound to a specific SiteInstance and RenderProcessHost, which is fundamental to maintaining isolation and security boundaries across different parts of a web page. Crucially, this system supports advanced architectural features like Back/Forward Cache (BFCache) and prerendering, allowing the frame state to be preserved and reactivated rapidly following certain navigations. Ultimately, the RFH is indispensable for governing the state, policy enforcement, and inter-process coordination required for Chromium's multi-process page architecture.
