The value of the test attribute of the xs: assertionelement facet is an XPath 2.0 expression or XPath 2.0 subset as defined by the XML Schema 1.1 specification that evaluates to either true or false.
Role assignments are made at the configuration unit scope, and the policy that it inherits from its ancestor element and will apply if there is no explicit policy assertion attached to the element.
角色分配在配置单元范围内进行，如果没有附加到元素的显式策略断言，则将应用从其祖先元素继承的策略。
3
If the element namespace is recognized as a policy-extension namespace, unmarshal as an empty marker assertion.