A council has to tell a tenant their rent is in arrears. The words that do it are governed by six orthogonal content standards, each composed in by reference — readability, British-English conventions, tone, purpose, audience and medium.

Because the axes are independent, you can hold five of them fixed and swap just one. Only what that axis owns changes; everything else stays put. Below, the very same message is put through two swaps — and each rendering is governed by a real throughline-compose project whose build fails if a requirement drifts.

The requirement graph says how the message must read; the rendered artifact is the writing. throughline doesn't lint prose — so what you see below is the human deliverable each graph governs.

Five axes are held byte-identical — readability, conventions, the formal register, the instruct purpose and a general (lay tenant) reader. Only the medium changes, and it is a one-line edit in the project's config. Watch what the channel — and only the channel — brings with it.

Now hold readability and conventions fixed, keep the channel a page, and move the reader instead — from a lay tenant, to a housing officer, to a housing lawyer. Register and purpose shift to match. The subject is identical rent arrears; the pitch is not.

The renderings above are human deliverables — the graph governs how they must read, but throughline deliberately doesn't lint prose. throughline-content-service is a working prototype that closes that last gap. Give it the one canonical message and a composed profile and it does two things: it projects the message into the profile's medium, and it runs the clause-by-clause conformance pass the graph itself omits — so a deliverable can be checked, not merely asserted.

The service is a consumer of throughline, the way a compiler consumes a language spec. It carries its own throughline graph, and — because it ingests external input and holds a backend secret — it composes the OWASP ASVS security baseline by reference as the standard suitable for its own delivery.

Each example is a public repository you can clone and validate. The requirement graph lives under system-requirements/; the deliverable prose lives under content/; and tl-compose check --strict fetches every pinned source, merges them into one graph and fails the build if anything is ungrounded or has drifted.

The composed standards themselves — plain language, UK conventions, the tone, purpose, audience and medium families — are separate, reusable source repositories under the same organisation.