Since I am writing a hypertext book, let me explain what this genre (or format) is exactly.
In the 1960s, philosopher and sociologist Ted Nelson defined hypertext as "a body of written or pictorial material interconnected in such a complex way that it could not conveniently be presented or represented on paper". More specifically, a hypertext can only exist on an electronic device (e.g., a computer). Its special feature is that it contains links. (It's important to clarify that each link or even each page itself cannot not be called a hypertext.)
In this sense, the World Wide Web is a great example of this modern way of sharing and storing information. Of course, the World Wide Web is not one book. Rather, it's a huge depository - very different from a "traditional" library containing multiple linear narratives. So, what is a hypertext book as opposed to a regular book? How would one recognize a hypertext book when she sees it?
To understand this, let's think about the difference between one print book and the whole library. Although each "traditional" book can contain references to some other volumes stored in the same place, a single book is supposed to be self-sufficient. In other words, you should be able to go through this text and learn some ideas that the author wanted to share without having to constantly take other volumes from the shelves of this collection. That said, some print books display more intertextuality than others, and they can be very difficult to read without understanding all the overt and hidden references. One example would be Ulysses by James Joyce. It must be noted, however, that this novel is hardly a traditional book. So, we can safely assume that regular books are supposed to be mostly self-sufficient after all.
Using the criterion of self-sufficiency, we can say that a hypertext book is a narrative (fictional or nonfictional) that is a part of the giant virtual library of the World Wide Web, but a distinct part that can be read separately from the whole. (That said, we can imagine a hypertext that exists on one computer, not online.) Same as a print book can contain references to other print books, a hypertext book can contain links that lead outside of it. At the same time, most of the links will allow the reader to stay within the same text, confirming its self-sufficiency.
A traditional book contains pages that the reader is supposed to go through in a predetermined order. You start on the first page and finish on the last page (unless there are some boring or scary parts you will decide to skip). The reader does not go through pages randomly. Instead, she trusts page numbers. That is what a linear narrative is. A hypertext book also contains pages combined into one self-sufficient whole. However, there is no path going through the narrative that would be predetermined by page numbers. Each reader can use any path they choose by clicking links that every page contains. Even the same reader may not be able to read a particular hypertext book the same way twice. Thus, we can say that the second criterion of this genre is its nonlinearity.
The third essential feature of this electronic genre is its open-endedness. A traditional print book can be considered complete after it's printed. New editions may be created, but that's an exception rather than a rule. In contrast, a hypertext book will keep changing and growing as much as its author(s) will allow it. That said, such a book does not have to be remain open-ended forever. It can be also completed at any point.
Now, let's move to examples. Do hypertext books actually exist? Wikipedia gets close to being one, although most of the links it contains probably lead the reader outside of it. The self-sufficiency criterion is not really met in this case, which is not surprising: Wikipedia is not meant to be read as one text. Speaking of Wikipedia, it actually contains an entry Hypertext fiction, which provides some interesting examples of this genre. One reason why hypertext fiction has not become popular is that it is hard to use a nonlinear narrative structure for telling a story with characters a developing plot.
In my opinion, the hypertext format is much more appropriate for nonfiction. In fact, I believe that this format offers unique opportunities for nonfiction authors. Human thinking is nonlinear, so expressing ideas about complex issues is actually easier when one does not have to force them into a sequential structure. And yet, proper hypertext nonfiction books are even harder to come by than hypertext fiction. Why? Probably because writing such a book requires some serious commitment and consistency from the author without much hope of being appreciated by readers. A nonlinear book will not receive an endorsement from a traditional publisher. It cannot be promoted like a regular book. And yet, I believe that unique properties of this format must be used to tackle topics that are especially hard to navigate. That is why, having considered the cons, I decided to write the hypertext book presented here.