Illegal XPath expression?

[sunspider]

when suppling XPath expressions to subscription filter, following
org.jboss.test.ws.jaxws.wseventing.EventingSupport sample code, some legal expressions are not allowed? I don't understand.

FilterType filter = new FilterType();
filter.setDialect(EventingConstants.getDialectXPath().toString());
filter.getContent().add("/ns3:ticketsOperationResponse/ns2:ticketsOut/totalPrice>0");
filter.getContent().add("string-length(/ns3:orderOperationResponse/ns2:orderOut/clientID)>0");
return filter;

[sunspider]

after checking source code, org.jboss.ws.extensions.eventing.mgmt.SubscriptionManager supports one single expression. so I combined them into one using "or".

filter.getContent().add("/ns3:ticketsOperationResponse/ns2:ticketsOut/totalPrice>0 or string-length(/ns3:orderOperationResponse/ns2:orderOut/clientID/text())>0");