Harnessing the Power of Annotations -- An Interview with Dan Brown
http://www.uie.com/articles/brown_interview/

Spool, Jared M.
User Interface Engineering
2009

Abstract:

Annotations come in all shapes and sizes depending on the artifact and the intent of the document. People are probably most familiar with wireframe annotations, where the author calls out areas of the screen to describe functionality not immediately discernible from the picture alone.