To what does every extension in a resource apply directly?

To what does every extension in a resource apply directly?

• A. definition
• B. resource
• C. StructureDefinition
• D. element

Answer: (A)

In FHIR, an extension’s meaning and constraints come from its Definition. Each extension attached to a resource carries a URL that points to this Definition, which is described by a StructureDefinition. That Definition formally specifies what the extension means, its data type, cardinality, and any constraints. So the extension is defined by and directly tied to its Definition—the formal description that governs how the extension is interpreted in the resource. The other options don’t capture this direct link; the critical link is to the Definition that describes the extension.

In FHIR, an extension’s meaning and constraints come from its Definition. Each extension attached to a resource carries a URL that points to this Definition, which is described by a StructureDefinition. That Definition formally specifies what the extension means, its data type, cardinality, and any constraints. So the extension is defined by and directly tied to its Definition—the formal description that governs how the extension is interpreted in the resource. The other options don’t capture this direct link; the critical link is to the Definition that describes the extension.