Incomplete Library Class
Reuse is often touted as the purpose of objects. We think reuse is overrated (we just use). However, we can't deny that much of our programming skill is based on library classes so that nobody can tell whether we've forgotten our sort algorithms.
Builders of library classes are rarely omniscient. We don't blame them for that; after all, we can rarely figure out a design until we've mostly built it, so library builders have a really tough job. The trouble is that it is often bad form, and usually impossible, to modify a library class to do something you'd like it to do. This means that tried-and-true tactics such as Move Method lie useless.
We have a couple of special-purpose tools for this job. If there are just a couple of methods that you wish the library class had, use Introduce Foreign Method. If there is a whole load of extra behavior, you need Introduce Local Extension.