a0d929ca_WSRP_v2_0_Specification__Statement_text
[#] CS010 [Section] 4.1.1 [Statement text] 
It is RECOMMENDED extensions be of type xsd:string (where xsd stands for http://www.w3c.org/2001/XMLSchema), or be of a type from the WSRP-defined "wsrp-extra" namespace (urn:oasis:names:tc:wsrp:extra) or be of a type defined in the Producer's WSDL as this enables Consumers to prepare an appropriate serializer/deserializer.
WSRP v2.0 Specification
Statement text