The provided text explains the PaintLayer tree, an internal architectural component of Google Chrome’s Blink rendering engine that manages complex visual tasks. PaintLayers are selectively created for layout objects that require specialized handling, such as stacking contexts, transparency, or overflow clipping. This system functions as a parallel hierarchy to the DOM, organizing elements to ensure they follow correct CSS z-index ordering and painting phases. While modern developments like Composite After Paint have moved many responsibilities to property trees, the PaintLayer remains essential for paint invalidation and subsequence caching, which optimize performance by reusing previous drawing results. The documents also describe how these layers facilitate hit testing and coordinate with the compositor to decide which content should be hardware-accelerated. Ultimately, the sources frame the PaintLayer tree as a legacy yet vital bridge that translates layout data into ordered visual commands.

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