The secret Documentation needs to include and be structured around its four different functions: tutorials, how-to guides, explanation and technical reference.

The secret Documentation needs to include and be structured around its four different functions: tutorials, how-to guides, explanation and technical reference. Each of them requires a distinct mode of writing. People working with software need these four different kinds of documentation at different times, in different circumstances - so software usually needs them all. And documentation needs to be explicitly structured around them, and they all must be kept separate and distinct from each other.