We develop a basic form of framework comprehension which is based on simple, reuse-related metrics for the as-implemented design and usage of frameworks. To this end, we provide a framework profile which incorporates potential reuse characteristics (e.g., specializability of types in a framework) as well as actual reuse characteristics (e.g., evidence of specialization of framework types in projects). We apply framework comprehension in an empirical study of the Microsoft .NET Framework. The approach is helpful in several contexts of software reverse and re-engineering.