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 that are defined inside a resource - but not those in a data type.

Cardinality 0..*
Type Element

May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. 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. Applications processing a resource are required to check for modifier extensions.

Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

Cardinality 0..*
Type Extension
Is Modifier true (Reason: Modifier extensions are expected to modify the meaning or interpretation of the element that contains them)

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions .

Alternate Names extensions; user content; modifiers
Summary true

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.