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"

Base definition for all elements in a resource.

Cardinality 0..*
Defined on this element
ele-1 Rule All FHIR elements must have a @value or children hasValue() or (children().count() > id.count())
Affect this element

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

Cardinality 0..1
Type string

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.

Cardinality 0..*
Type Extension
Alternate Names extensions; user content

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.