Core Invoice Extension
EN 16931 conformance mechanism for adding new business content beyond the European core.
Definition
A Core Invoice Extension adds business terms or groups that the EN 16931 core does not provide, for a sector or process that needs more data. Where a CIUS may only narrow the core (forbidding, narrowing cardinalities, fixing values), an extension introduces additional content. A compliant instance must still satisfy all core rules.
Origin
Defined in EN 16931-1 (CEN/TC 434), which sets the conformance framework distinguishing CIUS from extensions for the European semantic standard on electronic invoicing.
Example in context
The German XRechnung and the construction-sector extensions layer additional groups on top of EN 16931 while keeping every core business rule (e.g. BR-1, BR-CO-10) satisfied.