In this paper we discuss models for systems that support reading. Our account identifies important models and presents a framework for organizing them. To evaluate this account, we show its ability to suggest a wide range of text presentation systems, many of them novel. This evaluation not only provides interesting ideas for future systems, it also shows the usefulness of the account, and further, exemplifies a general approach to evaluating meta-level discussions such as this, namely,

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... ng by assessing ability to generate interesting implications.