HTTP clients and servers should absolutely not emit broken headers, but that's a violation of the robustness principle of itself. The way I think about it is

HTTP clients and servers should absolutely not emit broken headers, but that's a violation of the robustness principle of itself. The way I think about it is imagining how many websites I use daily just wouldn't work if HTML parsing were completely strict. I regularly open up Dev Tools to see which of the websites I visit work without CSS or HTML parsing errors. My primary concern is that there needs to be a way to implement strict parsing that doesn't greatly raise the barrier to entry or make the product unusable. I do think a lot about this but it's nonetheless confounding from both perspectives and I think the usability of strict parsers needs to be addressed, whether that means better error messages or really good linting or whatever.