Usage Guide. Tutorial introduction to a library. Focuses on the most common uses in an order reflecting the needs of a first-time user. Most explanation by means of progressively elaborated examples. Serves as a guided tour of major library capabilities. No attempt at reference-style completeness.

Advanced Usage Guide.  Continues overview of all significant capabilities of a library, including those which might be needed by advanced users customizing or extending built-in capability. Provides examples of specialized uses extending beyond normal, basic usage, but still using built-in features of the library framework. Helps to simplify the Usage Guide by providing a location for overflow of more advanced features.

Interface Reference.  Complete, concise summary of all features of a library. Fills the role a Unix "man page" in providing comprehensive definition of library services. Little or no concern to provide path of tutorial introduction. Does not contain extended examples, at most only fragments of examples which serve needs of specification.

Subclassing Reference.  Documents the rules for writing new classes which subclass from classes that implement the library. Because a library might use complex combinations of classes to implement the range of behaviors defined by its types, the classes in a library are not automatically usable as superclasses of user-defined classes. Each library documents which classes are available for use as superclasses, and the specific rules that must be followed when subclassing from these classes.

Implementation Notes.  Explains the structure of classes by which the types of a library are implemented. Summarizes the status of implementation if still incomplete and lists items of possible future work. Provides overview and high-level structure of the implementation in whatever ways would best guide a reader of implementation source code. May also discuss tradeoffs considered along with references to related or supporting work.