4.1.1 Parsing
Do you love pedantic nitpickery shoved in under the banner of accessibility? Then you'll love parsing this criterion! All sorts of minor HTML fuckery like duplicate IDs will fail here, even when they have literally zero user impact! As another example, did you ever have the dastardly idea to use the <style> element inside of the <body>? That shit's invalid HTML, so technically that nonsense fails here too! Who cares if it'll pose no real issue to anyone. WCAG!