Constraint
constraints, schema constraint, cross-field constraintDefinitions
A rule in a Component Schema relating two things nothing else connects, usually a prop and a field it restricts, with an authoring-time action (onViolation) and, where needed, a deterministic runtimeFallback
The accordion's single-default-open is the motivating case: when allowMultipleOpen is false, at most one item may set defaultOpen. onViolation: block-publish stops it at authoring time, and runtimeFallback (first true wins) fixes what renders if bad data arrives anyway. The schema's enum allows only block-publish: a constraint states what should happen.
The same record kept as evidence: what the estate actually does when the rule is broken
A cwds Component Contract can record onViolation: none, because the authoring surface it observed enforces nothing. That is a fact about production, not a design choice, and it has no place in the schema's enum. Realizations follow the declared rule, not the observed one.
The rule for a combination no single field can catch on its own. Preferable alternative, where it costs nothing: reshape the data so the bad combination can't be written at all.