The provided sources explain that Chromium’s paint system is structured as a flat stream of operations rather than a traditional hierarchical scene graph. While a shallow C++ class hierarchy exists for the code itself, the runtime storage in a PaintOpBuffer functions more like a linear bytecode tape. Specific container-like operations, such as DrawScrollingContentsOp and DrawRecordOp, allow for nesting by referencing separate DisplayItemList or PaintRecord objects. This design enables structural recursion for scrolling and sub-records while maintaining high performance through spatial indexing and linear playback. Ultimately, these nested structures are often flattened during serialization, reinforcing a model centered on efficient, sequential data processing.