> Ras Bodik’s group at the University of California Berkeley worked on a parallel browsing project (funded in part by Mozilla Research) that focused on improving the parallelism of layout. Instead of our approach to parallel layout, which focuses on multiple parallel tree traversals, they modeled a subset of CSS using attribute grammars. They showed significant speedups with their system over a reimplementation of Safari’s algorithms, but we have not used this approach due to questions of whether it is possible to use attribute grammars to both accurately model the web as it is implemented today and to support new features as they are added. Servo uses a very similar CSS selector matching algorithm to theirs.