FHIR Release 3 (STU) Current Build
FHIR Infrastructure Work Group Maturity Level : 5 Normative Ballot Standards Status : Trial Use Normative
null Definition Base definition for all elements in a resource.
Element BackboneElement
Control Standards Status 1..1 Invariants Defined on this This element ele-1 : All FHIR elements must have has a @value or children ( expression : hasValue() | (children().count() > id.count()), xpath: @value|f:*|h:div) Affect this element Element.id standards status of "Normative"
Definition

unique id Base definition for the element within all elements that are defined inside a resource (for internal references). This may be any string value that does - but not contain spaces. those in a data type.

Control Cardinality 0..1 0..*
Type string Element
Element.extension BackboneElement.modifierExtension
Definition

May be used to represent additional information that is not part of the basic definition of the element. In order to 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 is allowed to 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).

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

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 content; modifiers
Summary true
Comments

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.