One (out of many!) Possible Way to Do It
Modeled after <xenc:EncryptedKeyType>
<element name="DerivedKeyŌ type="xmlsec:DerivedKeyType"/>
<complexType name="DerivedKeyType">
<sequence>
<element name="KeyDerivationMethod"
type="xmlsec:KeyDerivationMethodType" minOccurs="0"/>
<element ref="xenc:ReferenceList" minOccurs="0"/>
<element name="CarriedKeyName" type="string" minOccurs="0"/>
</sequence>
<attribute name="Id" type="ID" use="optional"/>
<attribute name="Type" type="anyURI" use="optional"/>
</complexType>