How configurable behaviour flows through CSS-Bookends - every unit (calipers primitive / bookends book) has a factory config, units of a kind share an IDENTICAL config shape, and a bundle (corpus / compendium) carries a `global` plus per-unit keys that resolve unit-key -> global -> factory default. Use when adding or changing ANY config option, a unit factory, or bundle wiring. Always paired with failing-first tests.
The build order for any non-trivial change in CSS-Bookends — FIRST document the goal/value space, THEN write failing tests, THEN write the code. Includes the config rule (a new/changed config option's shape is discussed and ALWAYS wired into the master/bundle factory with the cascade). Use before implementing any value type, book, feature, or config change.
How a CSS-Bookends book's factory should behave - bound via `publishBook<Name>` with a SMART default config (best out of the box, fully overridable), no pre-made instance, a library-agnostic public surface, and configurable strictness with fail-fast errors. Use when adding or reviewing a book's factory, default config, or error/strictness handling.
How to build or rework a CSS-Bookends book with self-publish, the publishBook engine, the manuscript, and the three steps (input, storage, output). Use whenever adding or changing a book/helper in this repo.
The output contract every CSS-Bookends book follows - a single `.css()` render terminal, typed variant/format objects (never magic strings), output hardened to its variant type, and immutable results. Use when adding or reviewing a book's output step, `.css()`, format/variant selectors, or result type.
How to add a custom colour format to calipers end to end (input parse bridge, output render, registration via `createColor`, the typed named selector, the output priority list). Use when adding, reviewing, or extending a custom `ColorFormatPlugin`, or wiring a new format through the colour factory.
The order to build a new CSS-Bookends book - settle the INPUT first, then the internal STORAGE, then the OUTPUT, with passing unit tests gating each part. Use when starting a new book/helper or porting one in. For the model/contracts see authoring-a-book; for values see using-calipers.
Rules for css-calipers in this repo - every numeric, unit-bearing CSS value is an m() measurement (never a hand-written string), math stays in measurement space, and .css() emits once at the edge. Use when writing or reviewing any CSS value, unit, or measurement, or any helper input that takes a length/angle/time/etc.