Message in Chinese (Simplified) (中文(简体))
步骤操作必须包括节点测试，或代数表达式(在是谓词的情况下)，根据此代数表达式，可以计算对前一个节点集所标识的节点集中的每个节点进行的测试。
Unlocalized message
A step operation must involve either a node test or, in the case of a predicate, an algebraic expression against which to test each node in the node set identified by the preceeding node set can be evaluated.
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