See [AGENTS.md](AGENTS.md) — that file holds the canonical agent
instructions for this crate. Keeping the guidance in one file avoids
the two drifting apart.
The behavior itself is specified in `hl7-2`'s
[spec/index.md](../hl7-2/spec/index.md) (single source of truth for
`hl7::v2`); [README.md](README.md) is the user-facing summary.