hierarchy casts a hierarchy into a hierarchy. Used to resolve ambiguity resulting from two or more function signatures with the same name. For example, assume that you have two function signatures. One takes a hierarchy and the other takes a dimension. If the name of the hierarchy and the dimension are the same, then invoking that function in a formula creates ambiguity. By explicitly casting the string with the hierarchy function, the ambiguity is resolved.
hierarchy(Hierarchy h)