# Reference

Standards the site interprets, and adjacent work worth knowing about.

## Internet standards

- [RFC 9110 §12.5.1 — Proactive Negotiation](https://www.rfc-editor.org/rfc/rfc9110#name-proactive-negotiation) — how a server uses `Accept` to select a representation.
- [RFC 9110 §12.5.5 — Vary](https://www.rfc-editor.org/rfc/rfc9110#name-vary) — required for correct downstream caching of negotiated responses.
- [RFC 9110 §15.5.7 — 406 Not Acceptable](https://www.rfc-editor.org/rfc/rfc9110#name-406-not-acceptable) — the right response when Accept can't be satisfied.
- [RFC 7763](https://www.rfc-editor.org/rfc/rfc7763) — the `text/markdown` media type registration.
- [RFC 7764](https://www.rfc-editor.org/rfc/rfc7764) — companion RFC, Markdown variants and the `variant` parameter.
- [RFC 8288](https://www.rfc-editor.org/rfc/rfc8288) — Web Linking. Defines the `Link` HTTP header and the `rel` attribute registry; useful for advertising an alternate `.md` representation via `rel="alternate"; type="text/markdown"`.
- [IANA media type registry — text/markdown](https://www.iana.org/assignments/media-types/text/markdown) — the authoritative record.

## Developer docs

- [MDN — Content negotiation](https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Content_negotiation) — approachable overview with examples.
- [MDN — `Accept` header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Accept) — syntax, q-values, and directives for the request header clients use to advertise preferred media types.
- [MDN — `Vary` header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Vary) — the response header that tells caches which request headers (like `Accept`) affect the selected representation.
- [Cloudflare — Markdown for Agents](https://developers.cloudflare.com/fundamentals/reference/markdown-for-agents/) — managed feature that negotiates Markdown at the edge.