No universally agreed upon definition exists. Indeed, how can one define an object which may take potentially any form and which may be constructed using nearly any type of material? In the field of artists' books, attempts to define the genre are often viewed as exclusionary and undesirable. It may be more informative to consider what book artists have done: "They have manipulated page, format, and content--sometimes subtly, sometimes turning the book into a reflexive discussion of its own tradition. They have illustrated real time in simple flip books or collaged real time with fictive time into complex layers. They have disguised artists' books as traditional books and made others that are scarcely recognizable. The best of the bookworks are multinotational. Within them, words, images, colors, marks, and silences become plastic organisms that play across the pages in variable linear sequence. Their importance lies in the formulation of a new perceptual literature whose content alters the concept of authorship and challenges the reader to a new discourse with the printed page." (Joan Lyons in her introduction to Artists' Books: A Critical Anthology and Sourcebook. Rochester, N.Y.: The Visual Studies Workshop Press, 1985.)