In the previous section, you learned how to provide solutions for the identified feature gaps by using ISV solutions or utilizing some of the common features and tools available. The next step is to start the design process for the requirement gaps that still do not have a home in the overall solution. The functional design documentation (FDD) describes the features of the desired customizations. The document can include things such as flowcharts, screenshots, wire frames, and so on. At a minimum, an FDD will contain an organized list of requirements that can be used for development, testing, and client sign off. Before going further with the details of why functional design is important, what it should cover, and best practices, let's first learn about the process of the fit-gap review session, which is critical before moving forward with writing an FDD.