# Concepts

> How the burgee family works, on its own terms: the ideas every package shares, the exact rules behind them, and the tests that hold each rule.

Source: https://burgee.interlace.tools/docs/concepts

The package sites say how to use each package, and the comparison pages say how it differs from
what it replaces. These pages say how the family itself works: the ideas the ten packages share,
why each exists, the rule as the code applies it, and the test that fails if the rule stops
being true. Each has an example this site's tests run.

## The shape of the family

- [The family and its layers](/docs/concepts/family) — one job per package, six leaves and three
  packages that compose them, dependencies that point one way, and nothing installed from outside.
- [Drop-in façades and migration](/docs/concepts/drop-ins) — reproduce an incumbent's API and
  behaviour, never its mechanism; how `burgee migrate` decides what it may move.
- [The plugin system](/docs/concepts/plugins) — one plain object, one published schema, one set
  of refusal codes, and a `check` command in every package.

## What every run decides

- [The output policy](/docs/concepts/output-policy) — which mode a run is in, how much colour it
  may use, and whether anybody is there to type.
- [The static projection](/docs/concepts/static-projection) — the plain-text form every live
  widget and terminal capability must have.
- [Agent surfaces](/docs/concepts/agent-surfaces) — one declaration projected into `--json`,
  `--schema`, `--mcp` and completions, and a program that never prompts an agent.
- [Exit codes and errors](/docs/concepts/exit-codes) — seven typed codes, one error envelope, and
  which stream a failure goes to.
- [Configuration and precedence](/docs/concepts/configuration) — one fixed order, a pure resolve,
  and provenance for every value.
- [Shutdown and terminal restore](/docs/concepts/shutdown) — one registry for every way a process
  leaves, a deadline, and the terminal restored last.
- [Width and text correctness](/docs/concepts/text-width) — how many columns a string occupies,
  counted by grapheme cluster and East Asian Width.

## How the claims are kept

- [How we prove claims](/docs/concepts/evidence) — incumbent suites graded against a control,
  baselines that only ratchet, weight bands, capability matrices with evidence in every cell, and
  the locks that fail when prose outruns a measurement.