Audience element in Literature v3.0 guidelines

[ACz-UniBi]

"audience" [ https://github.com/openaire/guidelines/blob/master/docs/literature/field_audience.rst ] is not an element included in the metadata schema oai_dc (http://www.openarchives.org/OAI/2.0/oai_dc.xsd), it was introduced only later as part of the "DCMI Metadata Terms".