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+Title: Consider switching the CSS parser to flex + bison
+Author: rodarima
+Created: Sun, 01 Dec 2024 15:56:11 +0000
+State: closed
+
+Given that CSS is a context-free grammar, we may be able to switch to flex + bison and create a parser that can easily handle the latest CSS spec. Extending the current parser to add support for variables and functions can be done, but will likely require more effort.
+
+The CSS standard provides some reference grammar that we can use as a starting point, and it would make it much easier to read and be sure we are following the spec correctly.
+
+Notice that a page may cause a DoS by abusing the `calc()` functions. We may want to also consider a CPU budget per page, so we can stop hungry sites from hanging the browser.
+
+We would also need to consider how much the generated parser weights, not to exceed out release tarball size budget, as we are already at 90% of the floppy size. Considering only the `.l` and `.y` sources is not acceptable, as that would add flex and bison as a mandatory build dependency. Preliminary results show at least 50KiB (15KiB compressed) for the scanner and 60KiB+ (17KiB compressed) for the parser.
+
+--%--
+From: rodarima
+Date: Wed, 04 Dec 2024 18:34:29 +0000
+
+While CSS might be a context-free grammar, it has moved away from being easily described by a flex scanner and bison parser. All major rendering engines have moved to a recursive descend, and the whole specification has also moved to a recursive descend approach.
+
+The current CSS parser in dillo is also a recursive descend parser with "only" 1800 lines (56 KiB). LALR parsers have some benefits over RD, but I don't think they are particularly useful for Dillo.
+
+I think it would be better to wait until we see clear drawbacks with the current parser before we implement a new LALR parser. We can improve the current one first, specially the error reporting which is currently missing.
+
+A very different topic is why the CSS WG had decided to implement a painfully complicated language that cannot be easily scanned by ignoring whitespace.
+
+Closing for now.
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