Extensibility Implementations can add of the form @namespace.termname or property@namespace.termname to any JSON object, property MAY or MAY NOT match the name of a name/value pair within the JSON object. However, the namespace MUST NOT start with odata and SHOULD NOT be required to be understood by the receiving party in order to correctly interpret the rest of the payload as the receiving party MUST ignore unknown annotations not defined in this version of the OData JSON Specification.
Extensibility Implementations can add of the form @namespace.termname or property@namespace.termname to any JSON object, property MAY or MAY NOT match the name of a name/value pair within the JSON object. However, the namespace MUST NOT start with odata and SHOULD NOT be required to be understood by the receiving party in order to correctly interpret the rest of the payload as the receiving party MUST ignore unknown annotations not defined in this version of the OData JSON Specification.
odata-json-format-v4.01-csprd02.docx