The system for registering and managing presentation types and generic functions was implemented in about 400 lines of portable Common LISP code. Standard presentation type definitions similar to those in CLIM are supplied, as well as standard presentation methods. Standard methods include those for parsing input, rendering output, handling input errors, and prompting a user for a particular type of data. While this set of methods will be sufficient for most developers, additional functionality can be defined using the interface to the basic system. The W3P system also allows the definition of presentation views that use CLOS class inheritance.
Views facilitate the specialization of presentation methods over different content types or styles.
Consider, for instance, a presentation type describing an item of technical documentation. The developer may wish to specify methods for plain textual output such as electronic mail, for a mark-up language like HTML, or even for a graphical representation. In addition, one may with to define an abbreviated view for technical experts and a detailed view for novice users. W3P condition handling must also be highly modular and configurable. Varying applications will have very different needs when it comes to responding to input errors.