These sources describe the architectural design of the Chromium Blink layout engine, specifically focusing on how physical fragments serve as durable post-layout output. The documentation explains that fragments store geometric data and state needed for painting and hit-testing, while intentionally excluding parent-relative offsets to facilitate subtree caching and reuse. Instead of a single monolithic structure, the engine utilizes a modular storage approach where inline content is flattened into items, and layout-specific metadata is offloaded to separate result and token objects. By separating physical rendering data from active layout computation and continuation state, the system optimizes both memory efficiency and performance. Ultimately, the fragment tree functions as an immutable physical representation of the page rather than a direct mirror of the CSS box tree.