Many composite workflow services utilize non-imperative XML technologies such as WSDL, XPath, XML schema, and XML messages. Regression testing should assure the services against regression faults that appear in both the workflows and these artifacts. In this paper, we propose a refinement-oriented level-exploration strategy and a multilevel coverage model that captures progressively the coverage of different types of artifacts by the test cases. We show that by using them, the test case prioritization techniques initialized on top of existing greedy-based test case prioritization strategy form a subsumption hierarchy such that a technique can produce more test suite permutations than a technique that subsumes it. Our experimental study of a model instance shows that a technique generally achieves a higher fault detection rate than a subsumed technique, which validates that the proposed hierarchy and model have the potential to improve the cost-effectiveness of test case prioritization techniques.