OXIO Headnote: official citation

Capture the Official Citation in the headnote in a metaDescribes element with a predicate of 'official-citation'

If there are multiple official citations listed (separated by a semicolon), capture each in a separate metaDescribes.


      <metaItem about="e">
        <!-- content skipped for brevity -->
        <metaDescribes predicate="product">OXIO</metaDescribes>
        <metaDescribes predicate="publishing-group">Law-UK</metaDescribes>
        <metaDescribes predicate="source-document-date">1973-06-28</metaDescribes>
        <metaDescribes predicate="official-citation">UNJYB, 1973, p171</metaDescribes>
      </metaItem>