This attribute is only a placeholder so that all the ISM attributes are not shown
in the schemaGuide for every element. If you refer to the documentation of the
attribute group it will say what attributes should be here.
Source
<xsd:element name="ProductionMetricCoverage" type="irm:ProductionMetricCoverageType"><xsd:annotation><xsd:documentation>A method of categorizing the coverage of a document in a fashion understandable by DDNI-A</xsd:documentation></xsd:annotation></xsd:element>