The need for code documentation is evident to all software developers, but varies in extent from project to project. We consider in this paper the documentation of PSAS software modules -- being developed by by a medium-sized team -- which will then be offered to other programmers as building blocks, i.e., a library.
The reusability of the code calls not only for adequate documentation in the code but also on-line reference documents (e.g., manual or HTML pages) for other programmers to consult. Generally writing such reference material entails an additional documenting effort: if the code documentation can be used at all, it usually must be reformatted.
Subsequently we present several examples of documentation for well-known reusable software libraries, and point out their strengths and weaknesses in order to determine what is important for the PSAS modules.