human-readable definition of the extensibility codes, or it may be a logical URI as declared in some other specification. The definition SHALL be a URI for the Structure Definition defining the extension.</p>
</td></tr><tr><td style="white-space: nowrap"><a href="http://hl7.org/fhir/R4/conformance-rules.html#conformance">Control</a></td><td>1..1</td></tr><tr><td style="white-space: nowrap"><a href="http://hl7.org/fhir/R4/datatypes.html">Type</a></td><td><a href="http://hl7.org/fhir/R4/datatypes.html#uri">ur