This is what most programmers mean when using the term software documentation. When creating software, code alone is insufficient. There must be some text along with it to describe various aspects of its intended operation. It is important for the code documents to be thorough, but not so verbose that it becomes difficult to maintain them.

Often, tools such as Doxygen, NDoc, javadoc, SandCastle, ROBODoc, POD , TwinText , or Universal Report can be used to auto-generate the code documentsthat is, they extract the comments from the source code and create reference manuals in such forms as text or HTML files. Code documents are often organized into a reference guide style, allowing a programmer to quickly look up an arbitrary function or class.

Many programmers really like the idea of auto-generating documentation for various reasons. For example, because it is extracted from the source code itself (for example, through comments), the programmer can write it while referring to his code, and can use the same tools he used to create the source code, to make the documentation. This makes it much easier to keep the documentation up-to-date.

Of course, a downside is that only programmers can edit this kind of documentation, and it depends on them to refresh the output (for example, by running a cron job to update the documents nightly). Some would characterize this as a pro rather than a con.

Donald Knuth has insisted on the fact that documentation can be a very difficult afterthought process and has advocated literate programming, writing at the same time and location as the source code and extracted by automatic means.

Elucidative Programming is the result of practical applications of Literate Programming in real programming contexts. The Elucidative paradigm proposes that source code and documentation be stored separately. This paradigm was inspired by the same experimental findings that produced Kelp. Often, software developers need to be able to create and access information that is not going to be part of the source file itself. Such annotations are usually part of several software development activities, such as code walks and porting, where third party source code is an*lysed in a functional way. Annotations can therefore help the developer during any stage of software development where a formal documentation system would hinder progress. Kelp stores annotations in separate files, linking the information to the source code dynamically.