Introduction Hypertext 1 , in its most general sense, allows content to appear in different contexts. The immediate setting in which readers encounter a specific segment of material then changes from reading to reading or from reader to reader. Authors collect and structure materials to reflect their own understanding or in anticipation of readers' possible interests, needs, or ability to comprehend the substrate of interrelated content. This powerful underlying concept is usually realized in

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... th research and practical efforts within a node-link model: nodes are the holders of content, and links are the means by which the content is given context. In this model, links are closely associated with navigation and