The reference chapters answer “what can I write” and “what is it telling me”:

• Config overview — every block a config can carry, and where the authoritative field-by-field schema lives.
• Metrics — the zgix_* families rendered on the admin scrape: inventory, RED, per-endpoint, the shed ladder, and pool gauges.

For the reasoning behind each behaviour, read docs/DESIGN.md in the repository — a bare § reference anywhere in the tree points there.