A11Y_AXE_HTML_XML_LANG_MISMATCH
Ensure that HTML elements with both valid lang and xml:lang attributes agree on the base language of the page Evaluated against the live rendered page by a WCAG rule engine, so it only runs on a full scan.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.
Built at scan time by accessibility engine, not from our static registry. That engine evaluates its whole rule set in one pass, so this check cannot be run on its own — it runs as part of a scan.