iOS Guidelines for Free vs. Paid apps [closed]

Question

A few months back, I was doing some recreational reading at the iOS Dev Center, and I came across a small list of guidelines for free vs. paid apps. It included guidance along these lines:

• How not to promote a paid version within a free version
• Not displaying "placeholder" buttons in a free version that "work" in a paid version

I can't remember much more than that, and I cannot find it anymore on the iOS Dev Center. It's possible I imagined it entirely, but I doubt it - does anyone have a link to this information, or have a set of guidelines for free vs. paid apps in the App Store?