"Focus+Context Displays of Web Pages: Implementation Alternatives"
Marc H. Brown, Hannes Marais, Marc A. Najork, William E. Weihl
Note #1997-010, May, 1997.

This paper describes an outline processor display of Web pages. We
attach icons, called zippers, to the  HTML heading tags (H1, H2, ...),
and the user can dynamically include or elide the body of each section
by clicking on the zipper. We have implemented zippers in three
different ways: zippers that are inserted by a custom-built Web browser
and that control the browser's display engine; zippers that are inserted
into the HTML document by a Web proxy and that use the proxy to generate
modified HTML reflecting the changed state of the zipper; and zippers
that trigger a JavaScript program which redisplays an appropriately
modified version of the page.