Larry Tesler at PARC devised insights for a modeless word processor from the feedback gathered from a user test with newly-hired Sylvia Adams, where she was asked to ad lib some gestures to correct proofreading marks on the digital text.[5] This test convinced Tesler's manager Bill English of the problems with their previous modal interface... Interface expert Jef Raskin came out strongly against modes, writing, "Modes are a significant source of errors, confusion, unnecessary restrictions, and complexity in interfaces." Later he notes, " 'It is no accident that swearing is denoted by #&%!#$&,' writes my colleague, Dr. James Winter; it is 'what a typewriter used to do when you typed numbers when the Caps Lock was engaged'." Raskin dedicated his book The Humane Interface to describe the principles of a modeless interface for computers. Those principles were implemented in the Canon Cat and Archy systems.

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