Chapter 14 of the CSDL specifications Metadata annotations are terms applied to model elements. Behaviors or constraints described by a metadata annotation must be consistent with the annotated model element. Such annotations define additional behaviors or constraints on the model element, such as a service, entity type, property, function, action, or parameter. For example, a metadata annotation may define ranges of valid values for a particular property. An instance annotation is a term applied to a particular instance within an OData payload as described in [OData‑JSON] . An instance annotation can be used to define additional information associated with a particular result, entity, property, or error. For example, whether a property is read-only for a particular instance.