Background The commenter is proposing the minimum cardinality of O bservation.code should be changed from Min = 0 to Min =1   Decision We find this proposal not persuasive because, similar to the base FHIR standard , US Core Profiles are designed to be flexible for reuse by other US Realm profiles.  The proposal has the potential to limit reuse and interoperability.  Therefore, we define most Must Support elements with a minimum cardinality of 0.  Exceptions are rare and include instances where the minimum cardinality is inherited from the base standard.  In addition, US Core documents how to  deal with missing and suppressed data .