<https://schema.org/unitCode>
<http://www.w3.org/2000/01/rdf-schema#comment>
"The unit of measurement given using the UN/CEFACT Common Code (3 characters) or a URL. Other codes than the UN/CEFACT Common Code may be used with a prefix followed by a colon."
<https://www.schema.org/LocationFeatureSpecification>