FHIR R4 Current Build
This is the current officially released version of FHIR, which is R4 (v4.0.0). For a full list of all versions, see the Directory of published versions .
FHIR Infrastructure Work Group Maturity Level : Normative Standards Status : Normative
This page has been approved as part of an ANSI standard. See the Infrastructure Package for further details.
Standards Status This element has a standards status of "Normative"

Optional Extension Element - found in all resources.

Cardinality 0..*
Type Element

The ability to add extensions in a structured way is what keeps FHIR resources simple.

Defined on this element
ext-1 Rule Must have either extensions or value[x], not both extension.exists() != value.exists()

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

Cardinality 1..1
Type uri

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).

Cardinality 0..1
Type *
[x] Note See Choice of Data Types for further information about how to use [x]