Tree-traversals would be triggered in that language by referencing parent or child data. I'd probably have this language lower arbitrarily-structured trees into binary trees that easier to implement in hardware.
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However CSS layout isn't the only thing I'd want to run on this tree-SIMT, & the nicer language would likely yield code which would heavily benefit from further optimization.
Text layout can be heavily involved. And I'd involve it in rasterizing vector graphics like fonts.
3/4?