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
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Extension
Standards Status This element has a standards status of "Normative"
Definition

Optional Extension Element - found in all resources.

Cardinality 0..*
Type Element
Requirements

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

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

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

Cardinality 1..1
Type uri
Comments

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.

Extension.value[x]
Definition

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]