Rules to avoid retain cycles

Please note: this article is part of the older "Objective-C era" on Cocoa with Love. I don't keep these articles up-to-date; please be wary of broken code or potentially out-of-date information. Read "A new era for Cocoa with Love" for more. Normally in Objective-C, if you follow the basic rule of maintaining a positive retain count for everything you need to hold onto and releasing when you're do