HTML also defines extremely flexible error recovery that is de-facto required. There's no way a browser's getting away without it when the competition allows such documents, and there's so much legacy content around.
I wouldn't expect huge perf increases, but there are a few minor non-local effects such as self-closing tags that imply more branches than strictly necessary. It's not going to add up to much of anything, that's for sure. A simpler spec might, however, leave more complexity-budget for clever optimizations, but that's pretty speculative. The kind of thing I'm thinking about here is that when the language is fairly restrictive, you can consider using SIMD operations to match content cleverly; e.g. you might find the closing quote of an attribute four-chars at a time. Those kind of tricks require interplay decoding and parsing and are typically way to complicated in all but the simplest of cases.
In any case, this is drifting off topic: perf is not a primary reason to aim for simplicity, it's just a possible windfall.
People have definitely done work on using SIMD for HTML parsing, FWIW. There's plenty of places where you can easily do it, especially in what tends to be the most expensive tokeniser states.
I wouldn't expect huge perf increases, but there are a few minor non-local effects such as self-closing tags that imply more branches than strictly necessary. It's not going to add up to much of anything, that's for sure. A simpler spec might, however, leave more complexity-budget for clever optimizations, but that's pretty speculative. The kind of thing I'm thinking about here is that when the language is fairly restrictive, you can consider using SIMD operations to match content cleverly; e.g. you might find the closing quote of an attribute four-chars at a time. Those kind of tricks require interplay decoding and parsing and are typically way to complicated in all but the simplest of cases.
In any case, this is drifting off topic: perf is not a primary reason to aim for simplicity, it's just a possible windfall.