While the DocReference, Parameter and Binary would cover many of these use-cases. We will update the spec to: Enable implementer-specific extensions in a known and predictable way, e.g.: >The specification is not prescriptive about support for extensions. However, to support extensions, the specification reserves the name  extension  and will never define an element with that name, allowing implementations to use it to provide custom behavior and information. The value of an extension element MUST be a pre-coordinated JSON object. Will also provide example of a FHIRcast event notification, including an extension within the context element, containing the user's timezone.