4.1.1 Parsing (Obsolete and removed)

TL;DR: This criterion was removed in WCAG 2.2, but the underlying idea still matters: write valid, well-formed markup so assistive technologies can reliably interpret the page. Avoid duplicate IDs and broken nesting because they can create unpredictable accessibility trees.

Official description of the success criterion

The criterion is now obsolete. Official note from the WCAG recommendation:

This criterion was originally adopted to address problems that assistive technology had directly parsing HTML. Assistive technology no longer has any need to directly parse HTML. Consequently, these problems either no longer exist or are addressed by other criteria. This criterion no longer has utility and is removed.