| event[x] | Yes | Coding, uri | Code for the event this message represents or link to event definition |
| destination | No | MessageHeaderDestination | Message destination application(s) |
| - id | No | string | Unique id for inter-element referencing |
| - extension | No | Extension[] | Additional content defined by implementations |
| - modifierExtension | No | Extension[] | Extensions that cannot be ignored even if unrecognized |
| - name | No | string | Name of system |
| - target | No | Reference<Device> | Particular delivery destination within the destination |
| - endpoint | Yes | url | Actual destination address or id |
| - receiver | No | Reference<Practitioner / PractitionerRole / Organization> | Intended “real-world” recipient for the data |
| sender | No | Reference<Practitioner / PractitionerRole / Organization> | Real world sender of the message |
| enterer | No | Reference<Practitioner / PractitionerRole> | The source of the data entry |
| author | No | Reference<Practitioner / PractitionerRole> | The source of the decision |
| source | Yes | MessageHeaderSource | Message source application |
| - id | No | string | Unique id for inter-element referencing |
| - extension | No | Extension[] | Additional content defined by implementations |
| - modifierExtension | No | Extension[] | Extensions that cannot be ignored even if unrecognized |
| - name | No | string | Name of system |
| - software | No | string | Name of software running the system |
| - version | No | string | Version of software running |
| - contact | No | ContactPoint | Human contact for problems |
| - endpoint | Yes | url | Actual message source address or id |
| responsible | No | Reference<Practitioner / PractitionerRole / Organization> | Final responsibility for event |
| reason | No | CodeableConcept | Cause of event |
| response | No | MessageHeaderResponse | If this is a reply to prior message |
| - id | No | string | Unique id for inter-element referencing |
| - extension | No | Extension[] | Additional content defined by implementations |
| - modifierExtension | No | Extension[] | Extensions that cannot be ignored even if unrecognized |
| - identifier | Yes | id | Id of original message |
| - code | Yes | code | ok / transient-error / fatal-error |
| - details | No | Reference<OperationOutcome> | Specific list of hints/warnings/errors |
| focus | No | Reference<Resource>[] | The actual content of the message |
| definition | No | canonical | Link to the definition for this message |
