High-level architecture:

```mermaid
flowchart TD
    Cellar[Cellar API]
    Frontend

    subgraph backend
        client[Cellar Client]
        conv[Formex -> HTML converter]
        FastAPI
    end

    Cellar --> meta@{ shape: docs, label: "XML/RDF Metadata"}
    Cellar --> docs@{ shape: docs, label: "Formex/XHTML/PDF text"}

    meta --> client
    docs --> client

    client -- Formex --> FastAPI
    client -- Formex --> conv

    conv -- HTML --> FastAPI

    FastAPI -- TOC, HTML article text --> Frontend
```