References a requirement that this element satisfies. This might be referenced at the resource level by a profile, operation definition, etc. However, it could also point from a specific code in a value set, an interaction or search parameter in a CapabilityStatement, an action in a PlanDefinition, etc. to the requirement satisfied by that specific portion of the resource. Note that this extension is only used as part of the IG publication tooling process. Use the Requirements extension extension for use outside the IG publishing framework.