http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-rendering-criticalExtension|4.0.0-ballot

Indicates an extension that must be supported by the system presenting the instance for data capture or end-user consumption. If a system does not recognize the extension or cannot implement the functionality defined by the extension, it should display an error message or warning and refrain from presenting the instance to the user or using it when capturing data.