When APIs are developed, documentation often comes last. It is squeezed in when the deadline is near or in jeopardy. And quite often, the software developer, already working overtime, fixing bugs, making last-minute changes, is asked to write it.
There are developers who can both: code and write. But most likely the developer is much better at coding than at writing. And honestly – many developers do not enjoy writing documentation.
I have found little information on the Internet on how to write good API documentation. When I finally came across this excellent MSDN article by Peter Gruenbaum, I was delighted.
We also started to write down our own thoughts and concepts. See Ulrike Parson's article Documentation for Software Engineers.