The subject of a clinical statement, often called the Patient or the Subject. The SubjectOfRecord typically identifies the clinical record in which this statement is contained. If the statement should be in John Doe's patient record, then John Doe is the subject of record. When there is no patient, the SubjectOfRecord can also be a location, group, or other entity that statement pertains to. For example, observations concerning a hospital ward would have a Location as the SubjectOfRecord.

Note that the word 'Subject' is used here in the sense of a person or entity subjected to observations or actions, not subject as in a conceptual topic, like heart disease.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

Source of the definition for the extension code - a logical name or a URL.

The definition may point directly to a computable or human-readable definition of the extensibility codes, or it may be a logical URI as declared in some other specification. The definition SHALL be a URI for the Structure Definition defining the extension.

Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).