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="Addressee"><xsd:annotation><xsd:documentation xml:lang="en">Addressee is a wrapper element for child elements identifying an organization or individual to whom this task has been assigned.</xsd:documentation></xsd:annotation><xsd:complexType><xsd:choice minOccurs="1" maxOccurs="1"><xsd:element ref="ddms:Organization" minOccurs="1" maxOccurs="1"/><xsd:element ref="ddms:Person" minOccurs="1" maxOccurs="1"/></xsd:choice><xsd:attributeGroup ref="ism:SecurityAttributesGroup"/></xsd:complexType></xsd:element>