You document your source code and applications using the freely available tools KDOC, jade, and the DocBook DTD.
Source-code documentation is written directly into C++ header files as specially marked comments—that is, comments that begin with /**. You use the tool KDOC to process the header files into HTML documentation, that can be referred to by programmers using the documented classes.
Documentation for applications is written in text files formatted using SGML tags according to the DocBook DTD. This documentation should be included with the application so that the user may view it when they need assistance with your application.
Examples of well-written KDE DocBook documentation can be found in the KDE CVS source code repository (see Chapter 17) along with the applications that they document. A fine example of DocBook documentation is the KDevelop documentation by Ralf Nolden and the KDevelop team in the CVS file kdevelop/doc/manual/index.docbook.