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="ProductionMetric"><xsd:annotation><xsd:documentation>A categorization scheme whose values and use are defined by DDNI-A.</xsd:documentation></xsd:annotation><xsd:complexType><xsd:all minOccurs="1" maxOccurs="1"><xsd:element ref="irm:ProductionMetricSubject" minOccurs="1" maxOccurs="1"/><xsd:element ref="irm:ProductionMetricCoverage" minOccurs="1" maxOccurs="1"/></xsd:all><xsd:attributeGroup ref="ism:SecurityAttributesGroup"/></xsd:complexType></xsd:element>