Hide/Show Layer
http://developer.apple.com/internet/webcontent/hideshow_layer.html

Apple Inc.
2006

Abstract:

This script uses dynamic HTML (DHTML) to pop open a box with info in it when you click on a link. In my demo I’ve used this to pop up contextual help about filling in a form. It could also be used, for example, to give pop-up definitions for terms in an article. In both cases, it makes sense to give the information in context, modelessly. Likewise, this solution avoids the problems of statelessness and latency.