The gml:domainOfValidity property implements an association role to an EX_Extent object as encoded in ISO/TS 19139, either referencing or containing the definition of that extent.
<element name="domainOfValidity"><annotation><documentation>The gml:domainOfValidity property implements an association role to an EX_Extent object as encoded in ISO/TS 19139, either referencing or containing the definition of that extent.</documentation></annotation><complexType><sequence minOccurs="0"><element ref="gmd:EX_Extent"/></sequence><attributeGroup ref="gml:AssociationAttributeGroup"/></complexType></element>