Input techniques should maximise richness and variation in marking. The reader might want to write on one document while writing on another. Two handed input can aid navigation, e.g., one thumb holds the current position in the document, the other scrolls through it. Feedback should be designed to aid 'navigation' within a document. The need to support more flexibility and control in spatial layout.
Electronic displays have limited dimensions.
Modelling for mode awareness. Again, the question is what type of modelling is best suited for this design problem. The incident occurred while the second author was driving on a highway during a rainy night. The cruise control engaged, and the car cruised at 40 mph. He drove in this configuration for some 10 miles until coming to his planned exit from the highway.