For formal vocabularies, the @vocab-identifier attribute value holds a (unique) identifier of the vocabulary, such as (but not limited to) a URI or DOI.
<role vocab="dcmi" vocab-identifier= "http://dublincore.org/documents/dcmi-terms/#terms-DDC">
<role vocab="CRediT" vocab-identifier= "http://dictionary.casrai.org/Contributor_Roles">
<kwd-group vocab="Inspec" vocab-identifier= "http://www.theiet.org/resources/inspec/about/records/ithesaurus.cfm" >