Paper books often have an index. The index is a list, near the end of the book, where indexed words are given, often in alphabetical order, and for each indexed word, page numbers where the indexed word can be found are given.
In an electronic book on the web, an alternative is to create an interactive index. This can be done using a search box where the reader can type a word, and if the word is in the index, one or more links to where the word can be found are displayed.
In a Book with Views, one could go a step further, and let the indexed words be view-specific. This can be tried out, in the book Into Programming, for example by first searching for the word computer, which is in all views, and then searching for compiler and interpreter, which are not available in all views.
The search works in any page of the book.