We describe fuzzy sets of type-2 and look at the definition of some of the available operations. With the aid of the extension principle we suggest some operations for implementing the concept of containment between fuzzy sets of type-2. We discuss the idea of specificity of a fuzzy set. We suggest a procedure for calculating the specificity of a interval value type-2 fuzzy subset. We show the uniqueness of this procedure. We then extend our method to the case of a general type-2 fuzzy subset.