The interactive sketching notation is an emerging visual language which affords the representation of interface states and event-based user actions. Through a few simple and standardized rules, what the user sees (drawn in greys and blacks) and does (drawn in red) are unified into a coherent sketching system. This unification of both interface and use, intends to enable designers to tell more powerful stories of interaction.

The original Page Description Diagram article.

Page description diagrams are a text-only alternative to wireframes.