Overprinting versus Knockout
10 Great Examples of Overprint Design (and how to do it).
Use of Overprint
Imagesource, Knockout and Overprint
The Best Method for Setting Up Overprint in Adobe InDesign — Fraga Graphic Solutions, LLC
Over printing problems and solutions in Quark, InDesign and Illustrator
Turn on Overprint Preview Before Printing
How to use overprinting in Illustrator
Composite Overprint - Canon - Setting the Machine (PS/PCL/UFR II Printer) - User's Guide (Product Manual)