Larch/C++ is a model-based interface specification language tailored to the specification of C++ programs. As background, some basics of model-based interface specifications were described. By giving an abstract model of container objects, one can state conditions that require elements to remain in a container after they are inserted. Aspects of specification related to templates, the so-called "required interface" can be precisely described by Larch/C++, as shown by a case study involving the set template of the Standard Template Library (STL). This case study revealed some minor documentation problems in the STL, and pointed out some problems in Larch/C++.