We provide a framework that allows one to study structural properties of hypertext in connection with formal language theory. We model hypertext as a transformation device (an atransducer) that transforms a link-following into a sequence of matched pairs: basic linkable units. Then, we address the following questions: What can hypertext do? What structure is formed when a link-following is done? What structure is built when a virtual document is constructed? We show that the set of all link-followingsin hypertext is a regular set. Then, the set of all possible outputs of link-followings is shown to be context-free, which means that constructing virtual documents is essentially same as generating words of a contextfree language.