There are no (further) constraints on this element Element idShort description Additional content defined by implementations Alternate names extensions, user content Definition 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.
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.
Extension Sliced: Unordered, Open, by url(Value) Extensions are always sliced by (at least) url Constraints- ele-1: All FHIR elements must have a @value or children
hasValue() or (children().count() > id.count()) - ext-1: Must have either extensions or value[x], not both
extension.exists() != value.exists()
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