In current build of FHIRcast, Section 2.3.1 contains text the following text:

Hubs SHOULD use the FHIR _elements parameter to limit the size of the data being passed while also including additional, local identifiers that are likely already in use in production implementations. Subscribers SHALL accept a full FHIR resource or the _elements-limited resource as defined in the Event Catalog.

In discussion of ticket:

https://jira.hl7.org/browse/FHIR-40570

it was noted that there were conflicting understandings of a Hub's behavior regarding attributes not directly related to establishing context.  As and example:

ImagingStudy-open includes in the Context section (http://build.fhir.org/ig/HL7/fhircast-docs/branches/contentSharingUpdate/3-5-1-imagingstudy-open.html#context), only Patient and ImagingStudy references.  However, there are four additional classes of attributes that should be considered:

1. Attributes that are required by the FHIR specification of the resource being used to establish context.  For example, the status attribute is required by the FHIR specification of the ImagingStudy resource (https://build.fhir.org/imagingstudy.html#resource).

2. Other attributes in the FHIR specification of the resource which are not required; however, may be logical for Subscribers to exchange as part of a context change event.  For example, a description or endpoint attribute may have substantial value for Subscribers to exchange.

3. As a subset of the second type of resource attributes that may often be non-trivial in size.  For example, in an ImagingStudy the note attribute (an attachment) could contain markdown of a substantial size

4. Application specific extensions to FHIR resources

The question is what flexibility the Hub should have in handling these attribute types and the expectation of Subscribers on the Hub's behavior.  Specifically:

1. MAY the Hub filter out all attributes of resources that are not mentioned in the Context section of the FHIRcast event library?

2. Should (SHALL?) all resources be conformant with the minimum FHIR specification of that resource (for example, should (SHALL?) the status attribute be part of the the ImagingStudy resource used in an ImagingStudy-open event)?

3. Should (SHALL?) the Hub pass forward all attributes provided in the context setting request?

4. MAY the Hub removed attributes it believes (or finds) to exceed a certain size threshold?

Is the text in the STU2 specification (http://fhircast.org/specification/STU2/#events) more appropriate than that in the current build of FHIRcast?

It was also noted that the links which are part of Section 2.3.1 are not appropriate to the text.  Such as: https://www.hl7.org/fhir/search.html#elements