The commenter is suggesting that we add Encounter.diagnosis to US Core as a Must Support element. Implementer (EHR) feedback drove the decision to not make Encounter.diagnosis a Must Support element. We document that in the guidance: To search for an encounter diagnosis, query for Condition resources that reference the Encounter of interest and have a category of encounter-diagnosis. An example search is shown in the Condition Quick Start section.   US Core defines the minimal set of constraints and will not add the elements or extensions if the EHR/HIT systems that are a source of patient data don't support them.  However, It is reasonable to add the Encounter.diagnosis element for a particular use case in a dependent guide like the commenter described for QI Core or define