The second option— gathering all the notes on a separate, full-sized window or page— is a variation on the endnote idea. The reader must switch back and forth, using either the mouse pressing a graphic button or a keyboard shortcut such as the ALT and arrow keys provided in MS Internet Explorer.
It is not highly satisfactory, but readers familiarize themselves quickly enough with these two pages and do as best they can to find their bearings after each landing. It is less disorienting than jumping around within the same page because readers can count on the browser to restore the former page precisely as it looked when last seen. In this way, shuttling between pages can come close to page-flipping with a book.
Pop-ups, the third option, are definitely a more attractive technology, since they keep the eye focused close to that zone in the page which is the jumping-off point. For some years they had to be created by scripting, and were not in common use. They were though, for example, used to good effect in articles on Nupedia (since superseded by Wikipedia; tooltip script devised by Magnus Manske in mid-2001). A simpler model was demonstrated on Herb Drake's House Church website together with the commendable feature of a separate page of notes for those who need to print the text.
Today, pop-ups can be created with simple CSS. The method will be explained later in this article.