Define term, semantics for inserting error information into a (mostly) successful response

Add a term to the Core vocabulary that is shaped similar to the standard OData error response: <Term Name="Messages" Type="Collection(Core.MessageType)"> <Annotation Term="Core.Description" String="Instance annotation for warning and info messages" /> </Term> <ComplexType Name="MessageType"> <Property Name="code" Type="Edm.String" Nullable="false" /> <Property Name="message" Type="Edm.String" Nullable="false"> <Annotation Term="Core.IsLanguageDependent" /> </Property> <Property Name="severity" Type="Core.MessageSeverity" Nullable="false" /> <Property Name="target" Type="Edm.String" Nullable="true"> <Annotation Term="Core.Description" String="A path to the target of the message detail, relative to the annotated instance" /> </Property> <Property Name="details" Type="Collection(Core.MessageType)" Nullable="false" /> </ComplexType> <TypeDefinition Name="MessageSeverity" UnderlyingType="Edm.String"> <Annotation Term="Validation.AllowedValues"> <Collection> <Record> <PropertyValue Property="Value" String="success" /> </Record> <Record> <PropertyValue Property="Value" String="info" /> </Record> <Record> <PropertyValue Property="Value" String="warning" /> </Record> <Record> <PropertyValue Property="Value" String="error" /> </Record> </Collection> </Annotation> </TypeDefinition> Notification details may target properties of the annotated structured type instance, related instances, or their properties