Conciseness

Mostly efficient, but with noticeable redundancy: the Quick Reference bullets largely restate the Check and Fix sections, WCAG 2.1 SC 3.1.1 is cited twice (Quick Reference and Explain), and the Code Review section's boilerplate about "roles, labels, focus behavior, or keyboard interactions" is irrelevant to language attributes. This is more than the minor trimming of anchor 4, though far from the heavy padding of anchor 2.

Actionability

Concrete, executable audit guidance: inspect the <html> element, verify values are identical including subtags (with the en vs en-US edge case called out), validate the BCP 47 tag with example codes, and document-type-specific fixes (remove xml:lang for text/html, keep both for polyglot). Minor gap: the code examples live only in references/rule.md rather than inline, keeping it just below fully copy-paste-ready.

Workflow Clarity

This is a simple, single-purpose audit skill and the Check → Fix → Explain sequence is unambiguous, including how to verify the fix with accessibility tooling in the Code Review section. No destructive or batch operations, so no validation checkpoint is required.

Progressive Disclosure

The body is a concise overview that clearly signals a single one-level-deep reference ("For full implementation details, code examples, and framework-specific guidance, see references/rule.md"), and that file exists and contains exactly the promised details and examples. Structure is clean and easy to navigate.

Specificity

The description names a concrete domain (lang/xml:lang on XHTML and polyglot HTML documents, with the application/xhtml+xml MIME type) but its only action verbs are "Check when auditing" — the actual capability (verifying the attribute values match, flagging mismatches) is never stated. It sits between anchor 3 and anchor 4: domain plus 1-2 actions, but not several specific actions.

Completeness

Both parts are explicitly present: the 'what' ("Check when auditing documents served as application/xhtml+xml or documents that include both attributes") and the 'when' (two explicit trigger clauses covering XHTML, polyglot documents, and documents with both attributes). Below a 5 because the word "mismatch" never appears — what exactly to check for is implied rather than clearly stated.

Trigger Term Quality

Good keyword coverage: "XHTML documents", "polyglot HTML documents", "HTML5", "XML", "application/xhtml+xml", "lang", "xml:lang" are terms a user auditing this issue would naturally say. Missing common natural variations like "language mismatch", "document language", or "i18n", so it falls short of the comprehensive synonym coverage of the top anchor.

Distinctiveness Conflict Risk

A clear niche (lang/xml:lang agreement in XHTML/polyglot documents) with distinct triggers (application/xhtml+xml serving, presence of both attributes) and minimal risk of firing for an unrelated skill.