Nesting webpages sounds odd and unnatural, but we've been doing it since the very start of the Web. Back then, people were using painfully slow modem connections (56K or even less). To shorten the download time, we broke webpages up into small documents called frames, embedded in a master document called a frameset. Unfortunately, in practice HTML frames created more problems than they solved, and the whole "frames and frameset" idea has gone away now that AJAX has come on the scene.