USCDI v3 indicates use of US@ ([| Interoperability Standards Advisory (ISA) (healthit.gov)|https://www.healthit.gov/isa/taxonomy/term/756/uscdi-v3]), yet C-CDA CG 4 does not reference that.  The HTI-1 proposed rule is very clear on USCDI v3 including US@ and furthermore lists the criteria that reference USCDI.  To avoid any confusion whether absence of a reference in C-CDA CG v4 implies that there is no support required for US@, propose that a statement is made that support of US@ is required, or potentially a clearly agreed to subset if appropriate to step into it. 

The resolution must be kept in sync with https://jira.hl7.org/browse/FHIR-43025 , including the need to backport this to CDA C-CDA CG R4 as there must be clarity that it is not necessary to adopt C-CDA R3 in total to satisfy USCDI v3. which  would be inappropriate to encumber implementers.