Secondary Windows in Online Help - What Do Users Really Make of Them?
http://www.stcsig.org/usability/newsletter/0101-secondary-windows.html

Ellison, Matthew
Usability Interface
2001

Abstract:

Digitext, a UK-based consultancy specializing in online information, has recently conducted two different usability tests, each of which sheds new light on the way in which people respond to secondary windows in online Help. The overall conclusions from the two tests were: there is little reason to assign specific types of topic to different secondary windows; it can be helpful to use a secondary window for a link to a sub-procedure or layer of additional detail, as long as the current window remains visible on screen when the new window appears. This article explains how the tests led to these findings.