Blink’s CSS Bucketing and Style Resolution Optimization
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The provided source offers a highly detailed internal technical analysis of CSS "bucketing" within Chrome's Blink engine, which is the mechanism used to optimize CSS style matching by partitioning rules into structured categories. This system organizes CSS rules, sourced from User Agent, User, and Author stylesheets, into a RuleSet data structure based on the rightmost component of the selector (prioritizing IDs, classes, and tag names). The purpose of bucketing is to ensure that when computing an element's style, Blink only examines candidate rules that could possibly match, avoiding a linear scan of all stylesheet rules. Furthermore, the document describes the use of specialized lists for stateful pseudo-classes like :focus and :target, and elements of Shadow DOM like ::part and ::slotted, while rules that lack specific identifiers fall into the catch-all universal bucket. Finally, the analysis explores how this system integrates with style invalidation to efficiently determine which elements need restyling after dynamic changes, such as attribute mutations or state changes like hover or focus.
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