@JoeLamyman for me the whole discussion from some quarters about 4.1.1 really seems to be missing the fundamental issues behind it: 1) people have long misinterpreted the SC (to fail things that weren't normative failures); 2) yes invalid markup can lead to accessibility issues but browsers already reasonably and consistently error-correct for the most common aspects; 3) where they don't we then fail the actual accessibility effects/issues specifically in their relevant SCs