Base definition for all elements in a resource. Control 1..1 Invariants Defined on this element ele-1 : All FHIR elements must have a @value or children ( expression : hasValue() | (children().count() > id.count()), xpath: @value|f:*|h:div) Affect this element Element.id Definition Unique id for the element within 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.

May be used to represent additional information that is not part of the basic definition of the element. element and that modifies the understanding of the element in which it is contained. 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).

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.