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